Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

11 files changed, 10974 insertions, 0 deletions

diff --git a/library/core/src/slice/ascii.rs b/library/core/src/slice/ascii.rs
new file mode 100644
index 000000000..63715a6b8
--- /dev/null
+++ b/library/core/src/slice/ascii.rs
@@ -0,0 +1,330 @@
+//! Operations on ASCII `[u8]`.
+
+use crate::ascii;
+use crate::fmt::{self, Write};
+use crate::iter;
+use crate::mem;
+use crate::ops;
+
+#[cfg(not(test))]
+impl [u8] {
+    /// Checks if all bytes in this slice are within the ASCII range.
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[must_use]
+    #[inline]
+    pub fn is_ascii(&self) -> bool {
+        is_ascii(self)
+    }
+
+    /// Checks that two slices are an ASCII case-insensitive match.
+    ///
+    /// Same as `to_ascii_lowercase(a) == to_ascii_lowercase(b)`,
+    /// but without allocating and copying temporaries.
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[must_use]
+    #[inline]
+    pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool {
+        self.len() == other.len() && iter::zip(self, other).all(|(a, b)| a.eq_ignore_ascii_case(b))
+    }
+
+    /// Converts this slice to its ASCII upper case equivalent in-place.
+    ///
+    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To return a new uppercased value without modifying the existing one, use
+    /// [`to_ascii_uppercase`].
+    ///
+    /// [`to_ascii_uppercase`]: #method.to_ascii_uppercase
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn make_ascii_uppercase(&mut self) {
+        for byte in self {
+            byte.make_ascii_uppercase();
+        }
+    }
+
+    /// Converts this slice to its ASCII lower case equivalent in-place.
+    ///
+    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To return a new lowercased value without modifying the existing one, use
+    /// [`to_ascii_lowercase`].
+    ///
+    /// [`to_ascii_lowercase`]: #method.to_ascii_lowercase
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn make_ascii_lowercase(&mut self) {
+        for byte in self {
+            byte.make_ascii_lowercase();
+        }
+    }
+
+    /// Returns an iterator that produces an escaped version of this slice,
+    /// treating it as an ASCII string.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///
+    /// let s = b"0\t\r\n'\"\\\x9d";
+    /// let escaped = s.escape_ascii().to_string();
+    /// assert_eq!(escaped, "0\\t\\r\\n\\'\\\"\\\\\\x9d");
+    /// ```
+    #[must_use = "this returns the escaped bytes as an iterator, \
+                  without modifying the original"]
+    #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+    pub fn escape_ascii(&self) -> EscapeAscii<'_> {
+        EscapeAscii { inner: self.iter().flat_map(EscapeByte) }
+    }
+
+    /// Returns a byte slice with leading ASCII whitespace bytes removed.
+    ///
+    /// 'Whitespace' refers to the definition used by
+    /// `u8::is_ascii_whitespace`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(byte_slice_trim_ascii)]
+    ///
+    /// assert_eq!(b" \t hello world\n".trim_ascii_start(), b"hello world\n");
+    /// assert_eq!(b"  ".trim_ascii_start(), b"");
+    /// assert_eq!(b"".trim_ascii_start(), b"");
+    /// ```
+    #[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
+    pub const fn trim_ascii_start(&self) -> &[u8] {
+        let mut bytes = self;
+        // Note: A pattern matching based approach (instead of indexing) allows
+        // making the function const.
+        while let [first, rest @ ..] = bytes {
+            if first.is_ascii_whitespace() {
+                bytes = rest;
+            } else {
+                break;
+            }
+        }
+        bytes
+    }
+
+    /// Returns a byte slice with trailing ASCII whitespace bytes removed.
+    ///
+    /// 'Whitespace' refers to the definition used by
+    /// `u8::is_ascii_whitespace`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(byte_slice_trim_ascii)]
+    ///
+    /// assert_eq!(b"\r hello world\n ".trim_ascii_end(), b"\r hello world");
+    /// assert_eq!(b"  ".trim_ascii_end(), b"");
+    /// assert_eq!(b"".trim_ascii_end(), b"");
+    /// ```
+    #[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
+    pub const fn trim_ascii_end(&self) -> &[u8] {
+        let mut bytes = self;
+        // Note: A pattern matching based approach (instead of indexing) allows
+        // making the function const.
+        while let [rest @ .., last] = bytes {
+            if last.is_ascii_whitespace() {
+                bytes = rest;
+            } else {
+                break;
+            }
+        }
+        bytes
+    }
+
+    /// Returns a byte slice with leading and trailing ASCII whitespace bytes
+    /// removed.
+    ///
+    /// 'Whitespace' refers to the definition used by
+    /// `u8::is_ascii_whitespace`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(byte_slice_trim_ascii)]
+    ///
+    /// assert_eq!(b"\r hello world\n ".trim_ascii(), b"hello world");
+    /// assert_eq!(b"  ".trim_ascii(), b"");
+    /// assert_eq!(b"".trim_ascii(), b"");
+    /// ```
+    #[unstable(feature = "byte_slice_trim_ascii", issue = "94035")]
+    pub const fn trim_ascii(&self) -> &[u8] {
+        self.trim_ascii_start().trim_ascii_end()
+    }
+}
+
+impl_fn_for_zst! {
+    #[derive(Clone)]
+    struct EscapeByte impl Fn = |byte: &u8| -> ascii::EscapeDefault {
+        ascii::escape_default(*byte)
+    };
+}
+
+/// An iterator over the escaped version of a byte slice.
+///
+/// This `struct` is created by the [`slice::escape_ascii`] method. See its
+/// documentation for more information.
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+#[derive(Clone)]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct EscapeAscii<'a> {
+    inner: iter::FlatMap<super::Iter<'a, u8>, ascii::EscapeDefault, EscapeByte>,
+}
+
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> iter::Iterator for EscapeAscii<'a> {
+    type Item = u8;
+    #[inline]
+    fn next(&mut self) -> Option<u8> {
+        self.inner.next()
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+    #[inline]
+    fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R
+    where
+        Fold: FnMut(Acc, Self::Item) -> R,
+        R: ops::Try<Output = Acc>,
+    {
+        self.inner.try_fold(init, fold)
+    }
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+    where
+        Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.inner.fold(init, fold)
+    }
+    #[inline]
+    fn last(mut self) -> Option<u8> {
+        self.next_back()
+    }
+}
+
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> iter::DoubleEndedIterator for EscapeAscii<'a> {
+    fn next_back(&mut self) -> Option<u8> {
+        self.inner.next_back()
+    }
+}
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> iter::ExactSizeIterator for EscapeAscii<'a> {}
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> iter::FusedIterator for EscapeAscii<'a> {}
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> fmt::Display for EscapeAscii<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.clone().try_for_each(|b| f.write_char(b as char))
+    }
+}
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+impl<'a> fmt::Debug for EscapeAscii<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("EscapeAscii").finish_non_exhaustive()
+    }
+}
+
+/// Returns `true` if any byte in the word `v` is nonascii (>= 128). Snarfed
+/// from `../str/mod.rs`, which does something similar for utf8 validation.
+#[inline]
+fn contains_nonascii(v: usize) -> bool {
+    const NONASCII_MASK: usize = usize::repeat_u8(0x80);
+    (NONASCII_MASK & v) != 0
+}
+
+/// Optimized ASCII test that will use usize-at-a-time operations instead of
+/// byte-at-a-time operations (when possible).
+///
+/// The algorithm we use here is pretty simple. If `s` is too short, we just
+/// check each byte and be done with it. Otherwise:
+///
+/// - Read the first word with an unaligned load.
+/// - Align the pointer, read subsequent words until end with aligned loads.
+/// - Read the last `usize` from `s` with an unaligned load.
+///
+/// If any of these loads produces something for which `contains_nonascii`
+/// (above) returns true, then we know the answer is false.
+#[inline]
+fn is_ascii(s: &[u8]) -> bool {
+    const USIZE_SIZE: usize = mem::size_of::<usize>();
+
+    let len = s.len();
+    let align_offset = s.as_ptr().align_offset(USIZE_SIZE);
+
+    // If we wouldn't gain anything from the word-at-a-time implementation, fall
+    // back to a scalar loop.
+    //
+    // We also do this for architectures where `size_of::<usize>()` isn't
+    // sufficient alignment for `usize`, because it's a weird edge case.
+    if len < USIZE_SIZE || len < align_offset || USIZE_SIZE < mem::align_of::<usize>() {
+        return s.iter().all(|b| b.is_ascii());
+    }
+
+    // We always read the first word unaligned, which means `align_offset` is
+    // 0, we'd read the same value again for the aligned read.
+    let offset_to_aligned = if align_offset == 0 { USIZE_SIZE } else { align_offset };
+
+    let start = s.as_ptr();
+    // SAFETY: We verify `len < USIZE_SIZE` above.
+    let first_word = unsafe { (start as *const usize).read_unaligned() };
+
+    if contains_nonascii(first_word) {
+        return false;
+    }
+    // We checked this above, somewhat implicitly. Note that `offset_to_aligned`
+    // is either `align_offset` or `USIZE_SIZE`, both of are explicitly checked
+    // above.
+    debug_assert!(offset_to_aligned <= len);
+
+    // SAFETY: word_ptr is the (properly aligned) usize ptr we use to read the
+    // middle chunk of the slice.
+    let mut word_ptr = unsafe { start.add(offset_to_aligned) as *const usize };
+
+    // `byte_pos` is the byte index of `word_ptr`, used for loop end checks.
+    let mut byte_pos = offset_to_aligned;
+
+    // Paranoia check about alignment, since we're about to do a bunch of
+    // unaligned loads. In practice this should be impossible barring a bug in
+    // `align_offset` though.
+    debug_assert_eq!(word_ptr.addr() % mem::align_of::<usize>(), 0);
+
+    // Read subsequent words until the last aligned word, excluding the last
+    // aligned word by itself to be done in tail check later, to ensure that
+    // tail is always one `usize` at most to extra branch `byte_pos == len`.
+    while byte_pos < len - USIZE_SIZE {
+        debug_assert!(
+            // Sanity check that the read is in bounds
+            (word_ptr.addr() + USIZE_SIZE) <= start.addr().wrapping_add(len) &&
+            // And that our assumptions about `byte_pos` hold.
+            (word_ptr.addr() - start.addr()) == byte_pos
+        );
+
+        // SAFETY: We know `word_ptr` is properly aligned (because of
+        // `align_offset`), and we know that we have enough bytes between `word_ptr` and the end
+        let word = unsafe { word_ptr.read() };
+        if contains_nonascii(word) {
+            return false;
+        }
+
+        byte_pos += USIZE_SIZE;
+        // SAFETY: We know that `byte_pos <= len - USIZE_SIZE`, which means that
+        // after this `add`, `word_ptr` will be at most one-past-the-end.
+        word_ptr = unsafe { word_ptr.add(1) };
+    }
+
+    // Sanity check to ensure there really is only one `usize` left. This should
+    // be guaranteed by our loop condition.
+    debug_assert!(byte_pos <= len && len - byte_pos <= USIZE_SIZE);
+
+    // SAFETY: This relies on `len >= USIZE_SIZE`, which we check at the start.
+    let last_word = unsafe { (start.add(len - USIZE_SIZE) as *const usize).read_unaligned() };
+
+    !contains_nonascii(last_word)
+}
diff --git a/library/core/src/slice/cmp.rs b/library/core/src/slice/cmp.rs
new file mode 100644
index 000000000..5e1b218e5
--- /dev/null
+++ b/library/core/src/slice/cmp.rs
@@ -0,0 +1,260 @@
+//! Comparison traits for `[T]`.
+
+use crate::cmp::{self, Ordering};
+use crate::ffi;
+use crate::mem;
+
+use super::from_raw_parts;
+use super::memchr;
+
+extern "C" {
+    /// Calls implementation provided memcmp.
+    ///
+    /// Interprets the data as u8.
+    ///
+    /// Returns 0 for equal, < 0 for less than and > 0 for greater
+    /// than.
+    fn memcmp(s1: *const u8, s2: *const u8, n: usize) -> ffi::c_int;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<A, B> PartialEq<[B]> for [A]
+where
+    A: PartialEq<B>,
+{
+    fn eq(&self, other: &[B]) -> bool {
+        SlicePartialEq::equal(self, other)
+    }
+
+    fn ne(&self, other: &[B]) -> bool {
+        SlicePartialEq::not_equal(self, other)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Eq> Eq for [T] {}
+
+/// Implements comparison of vectors [lexicographically](Ord#lexicographical-comparison).
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> Ord for [T] {
+    fn cmp(&self, other: &[T]) -> Ordering {
+        SliceOrd::compare(self, other)
+    }
+}
+
+/// Implements comparison of vectors [lexicographically](Ord#lexicographical-comparison).
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: PartialOrd> PartialOrd for [T] {
+    fn partial_cmp(&self, other: &[T]) -> Option<Ordering> {
+        SlicePartialOrd::partial_compare(self, other)
+    }
+}
+
+#[doc(hidden)]
+// intermediate trait for specialization of slice's PartialEq
+trait SlicePartialEq<B> {
+    fn equal(&self, other: &[B]) -> bool;
+
+    fn not_equal(&self, other: &[B]) -> bool {
+        !self.equal(other)
+    }
+}
+
+// Generic slice equality
+impl<A, B> SlicePartialEq<B> for [A]
+where
+    A: PartialEq<B>,
+{
+    default fn equal(&self, other: &[B]) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter().zip(other.iter()).all(|(x, y)| x == y)
+    }
+}
+
+// Use memcmp for bytewise equality when the types allow
+impl<A, B> SlicePartialEq<B> for [A]
+where
+    A: BytewiseEquality<B>,
+{
+    fn equal(&self, other: &[B]) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        // SAFETY: `self` and `other` are references and are thus guaranteed to be valid.
+        // The two slices have been checked to have the same size above.
+        unsafe {
+            let size = mem::size_of_val(self);
+            memcmp(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
+        }
+    }
+}
+
+#[doc(hidden)]
+// intermediate trait for specialization of slice's PartialOrd
+trait SlicePartialOrd: Sized {
+    fn partial_compare(left: &[Self], right: &[Self]) -> Option<Ordering>;
+}
+
+impl<A: PartialOrd> SlicePartialOrd for A {
+    default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        let l = cmp::min(left.len(), right.len());
+
+        // Slice to the loop iteration range to enable bound check
+        // elimination in the compiler
+        let lhs = &left[..l];
+        let rhs = &right[..l];
+
+        for i in 0..l {
+            match lhs[i].partial_cmp(&rhs[i]) {
+                Some(Ordering::Equal) => (),
+                non_eq => return non_eq,
+            }
+        }
+
+        left.len().partial_cmp(&right.len())
+    }
+}
+
+// This is the impl that we would like to have. Unfortunately it's not sound.
+// See `partial_ord_slice.rs`.
+/*
+impl<A> SlicePartialOrd for A
+where
+    A: Ord,
+{
+    default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        Some(SliceOrd::compare(left, right))
+    }
+}
+*/
+
+impl<A: AlwaysApplicableOrd> SlicePartialOrd for A {
+    fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        Some(SliceOrd::compare(left, right))
+    }
+}
+
+#[rustc_specialization_trait]
+trait AlwaysApplicableOrd: SliceOrd + Ord {}
+
+macro_rules! always_applicable_ord {
+    ($([$($p:tt)*] $t:ty,)*) => {
+        $(impl<$($p)*> AlwaysApplicableOrd for $t {})*
+    }
+}
+
+always_applicable_ord! {
+    [] u8, [] u16, [] u32, [] u64, [] u128, [] usize,
+    [] i8, [] i16, [] i32, [] i64, [] i128, [] isize,
+    [] bool, [] char,
+    [T: ?Sized] *const T, [T: ?Sized] *mut T,
+    [T: AlwaysApplicableOrd] &T,
+    [T: AlwaysApplicableOrd] &mut T,
+    [T: AlwaysApplicableOrd] Option<T>,
+}
+
+#[doc(hidden)]
+// intermediate trait for specialization of slice's Ord
+trait SliceOrd: Sized {
+    fn compare(left: &[Self], right: &[Self]) -> Ordering;
+}
+
+impl<A: Ord> SliceOrd for A {
+    default fn compare(left: &[Self], right: &[Self]) -> Ordering {
+        let l = cmp::min(left.len(), right.len());
+
+        // Slice to the loop iteration range to enable bound check
+        // elimination in the compiler
+        let lhs = &left[..l];
+        let rhs = &right[..l];
+
+        for i in 0..l {
+            match lhs[i].cmp(&rhs[i]) {
+                Ordering::Equal => (),
+                non_eq => return non_eq,
+            }
+        }
+
+        left.len().cmp(&right.len())
+    }
+}
+
+// memcmp compares a sequence of unsigned bytes lexicographically.
+// this matches the order we want for [u8], but no others (not even [i8]).
+impl SliceOrd for u8 {
+    #[inline]
+    fn compare(left: &[Self], right: &[Self]) -> Ordering {
+        // Since the length of a slice is always less than or equal to isize::MAX, this never underflows.
+        let diff = left.len() as isize - right.len() as isize;
+        // This comparison gets optimized away (on x86_64 and ARM) because the subtraction updates flags.
+        let len = if left.len() < right.len() { left.len() } else { right.len() };
+        // SAFETY: `left` and `right` are references and are thus guaranteed to be valid.
+        // We use the minimum of both lengths which guarantees that both regions are
+        // valid for reads in that interval.
+        let mut order = unsafe { memcmp(left.as_ptr(), right.as_ptr(), len) as isize };
+        if order == 0 {
+            order = diff;
+        }
+        order.cmp(&0)
+    }
+}
+
+// Hack to allow specializing on `Eq` even though `Eq` has a method.
+#[rustc_unsafe_specialization_marker]
+trait MarkerEq<T>: PartialEq<T> {}
+
+impl<T: Eq> MarkerEq<T> for T {}
+
+#[doc(hidden)]
+/// Trait implemented for types that can be compared for equality using
+/// their bytewise representation
+#[rustc_specialization_trait]
+trait BytewiseEquality<T>: MarkerEq<T> + Copy {}
+
+macro_rules! impl_marker_for {
+    ($traitname:ident, $($ty:ty)*) => {
+        $(
+            impl $traitname<$ty> for $ty { }
+        )*
+    }
+}
+
+impl_marker_for!(BytewiseEquality,
+                 u8 i8 u16 i16 u32 i32 u64 i64 u128 i128 usize isize char bool);
+
+pub(super) trait SliceContains: Sized {
+    fn slice_contains(&self, x: &[Self]) -> bool;
+}
+
+impl<T> SliceContains for T
+where
+    T: PartialEq,
+{
+    default fn slice_contains(&self, x: &[Self]) -> bool {
+        x.iter().any(|y| *y == *self)
+    }
+}
+
+impl SliceContains for u8 {
+    #[inline]
+    fn slice_contains(&self, x: &[Self]) -> bool {
+        memchr::memchr(*self, x).is_some()
+    }
+}
+
+impl SliceContains for i8 {
+    #[inline]
+    fn slice_contains(&self, x: &[Self]) -> bool {
+        let byte = *self as u8;
+        // SAFETY: `i8` and `u8` have the same memory layout, thus casting `x.as_ptr()`
+        // as `*const u8` is safe. The `x.as_ptr()` comes from a reference and is thus guaranteed
+        // to be valid for reads for the length of the slice `x.len()`, which cannot be larger
+        // than `isize::MAX`. The returned slice is never mutated.
+        let bytes: &[u8] = unsafe { from_raw_parts(x.as_ptr() as *const u8, x.len()) };
+        memchr::memchr(byte, bytes).is_some()
+    }
+}
diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
new file mode 100644
index 000000000..fd7ecf3da
--- /dev/null
+++ b/library/core/src/slice/index.rs
@@ -0,0 +1,730 @@
+//! Indexing implementations for `[T]`.
+
+use crate::intrinsics::assert_unsafe_precondition;
+use crate::intrinsics::const_eval_select;
+use crate::ops;
+use crate::ptr;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+impl<T, I> const ops::Index<I> for [T]
+where
+    I: ~const SliceIndex<[T]>,
+{
+    type Output = I::Output;
+
+    #[inline]
+    fn index(&self, index: I) -> &I::Output {
+        index.index(self)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+impl<T, I> const ops::IndexMut<I> for [T]
+where
+    I: ~const SliceIndex<[T]>,
+{
+    #[inline]
+    fn index_mut(&mut self, index: I) -> &mut I::Output {
+        index.index_mut(self)
+    }
+}
+
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cold]
+#[track_caller]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+const fn slice_start_index_len_fail(index: usize, len: usize) -> ! {
+    // SAFETY: we are just panicking here
+    unsafe {
+        const_eval_select(
+            (index, len),
+            slice_start_index_len_fail_ct,
+            slice_start_index_len_fail_rt,
+        )
+    }
+}
+
+// FIXME const-hack
+fn slice_start_index_len_fail_rt(index: usize, len: usize) -> ! {
+    panic!("range start index {index} out of range for slice of length {len}");
+}
+
+const fn slice_start_index_len_fail_ct(_: usize, _: usize) -> ! {
+    panic!("slice start index is out of range for slice");
+}
+
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cold]
+#[track_caller]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+const fn slice_end_index_len_fail(index: usize, len: usize) -> ! {
+    // SAFETY: we are just panicking here
+    unsafe {
+        const_eval_select((index, len), slice_end_index_len_fail_ct, slice_end_index_len_fail_rt)
+    }
+}
+
+// FIXME const-hack
+fn slice_end_index_len_fail_rt(index: usize, len: usize) -> ! {
+    panic!("range end index {index} out of range for slice of length {len}");
+}
+
+const fn slice_end_index_len_fail_ct(_: usize, _: usize) -> ! {
+    panic!("slice end index is out of range for slice");
+}
+
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cold]
+#[track_caller]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+const fn slice_index_order_fail(index: usize, end: usize) -> ! {
+    // SAFETY: we are just panicking here
+    unsafe { const_eval_select((index, end), slice_index_order_fail_ct, slice_index_order_fail_rt) }
+}
+
+// FIXME const-hack
+fn slice_index_order_fail_rt(index: usize, end: usize) -> ! {
+    panic!("slice index starts at {index} but ends at {end}");
+}
+
+const fn slice_index_order_fail_ct(_: usize, _: usize) -> ! {
+    panic!("slice index start is larger than end");
+}
+
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cold]
+#[track_caller]
+const fn slice_start_index_overflow_fail() -> ! {
+    panic!("attempted to index slice from after maximum usize");
+}
+
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cold]
+#[track_caller]
+const fn slice_end_index_overflow_fail() -> ! {
+    panic!("attempted to index slice up to maximum usize");
+}
+
+mod private_slice_index {
+    use super::ops;
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    pub trait Sealed {}
+
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for usize {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::Range<usize> {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::RangeTo<usize> {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::RangeFrom<usize> {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::RangeFull {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::RangeInclusive<usize> {}
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    impl Sealed for ops::RangeToInclusive<usize> {}
+    #[stable(feature = "slice_index_with_ops_bound_pair", since = "1.53.0")]
+    impl Sealed for (ops::Bound<usize>, ops::Bound<usize>) {}
+}
+
+/// A helper trait used for indexing operations.
+///
+/// Implementations of this trait have to promise that if the argument
+/// to `get_unchecked(_mut)` is a safe reference, then so is the result.
+#[stable(feature = "slice_get_slice", since = "1.28.0")]
+#[rustc_diagnostic_item = "SliceIndex"]
+#[rustc_on_unimplemented(
+    on(T = "str", label = "string indices are ranges of `usize`",),
+    on(
+        all(any(T = "str", T = "&str", T = "std::string::String"), _Self = "{integer}"),
+        note = "you can use `.chars().nth()` or `.bytes().nth()`\n\
+                for more information, see chapter 8 in The Book: \
+                <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
+    ),
+    message = "the type `{T}` cannot be indexed by `{Self}`",
+    label = "slice indices are of type `usize` or ranges of `usize`"
+)]
+pub unsafe trait SliceIndex<T: ?Sized>: private_slice_index::Sealed {
+    /// The output type returned by methods.
+    #[stable(feature = "slice_get_slice", since = "1.28.0")]
+    type Output: ?Sized;
+
+    /// Returns a shared reference to the output at this location, if in
+    /// bounds.
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    fn get(self, slice: &T) -> Option<&Self::Output>;
+
+    /// Returns a mutable reference to the output at this location, if in
+    /// bounds.
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    fn get_mut(self, slice: &mut T) -> Option<&mut Self::Output>;
+
+    /// Returns a shared reference to the output at this location, without
+    /// performing any bounds checking.
+    /// Calling this method with an out-of-bounds index or a dangling `slice` pointer
+    /// is *[undefined behavior]* even if the resulting reference is not used.
+    ///
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    unsafe fn get_unchecked(self, slice: *const T) -> *const Self::Output;
+
+    /// Returns a mutable reference to the output at this location, without
+    /// performing any bounds checking.
+    /// Calling this method with an out-of-bounds index or a dangling `slice` pointer
+    /// is *[undefined behavior]* even if the resulting reference is not used.
+    ///
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    unsafe fn get_unchecked_mut(self, slice: *mut T) -> *mut Self::Output;
+
+    /// Returns a shared reference to the output at this location, panicking
+    /// if out of bounds.
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    #[track_caller]
+    fn index(self, slice: &T) -> &Self::Output;
+
+    /// Returns a mutable reference to the output at this location, panicking
+    /// if out of bounds.
+    #[unstable(feature = "slice_index_methods", issue = "none")]
+    #[track_caller]
+    fn index_mut(self, slice: &mut T) -> &mut Self::Output;
+}
+
+#[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for usize {
+    type Output = T;
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&T> {
+        // SAFETY: `self` is checked to be in bounds.
+        if self < slice.len() { unsafe { Some(&*self.get_unchecked(slice)) } } else { None }
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut T> {
+        // SAFETY: `self` is checked to be in bounds.
+        if self < slice.len() { unsafe { Some(&mut *self.get_unchecked_mut(slice)) } } else { None }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const T {
+        // SAFETY: the caller guarantees that `slice` is not dangling, so it
+        // cannot be longer than `isize::MAX`. They also guarantee that
+        // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
+        // so the call to `add` is safe.
+        unsafe {
+            assert_unsafe_precondition!(self < slice.len());
+            slice.as_ptr().add(self)
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut T {
+        // SAFETY: see comments for `get_unchecked` above.
+        unsafe {
+            assert_unsafe_precondition!(self < slice.len());
+            slice.as_mut_ptr().add(self)
+        }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &T {
+        // N.B., use intrinsic indexing
+        &(*slice)[self]
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut T {
+        // N.B., use intrinsic indexing
+        &mut (*slice)[self]
+    }
+}
+
+#[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        if self.start > self.end || self.end > slice.len() {
+            None
+        } else {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&*self.get_unchecked(slice)) }
+        }
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        if self.start > self.end || self.end > slice.len() {
+            None
+        } else {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&mut *self.get_unchecked_mut(slice)) }
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        // SAFETY: the caller guarantees that `slice` is not dangling, so it
+        // cannot be longer than `isize::MAX`. They also guarantee that
+        // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
+        // so the call to `add` is safe.
+
+        unsafe {
+            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            ptr::slice_from_raw_parts(slice.as_ptr().add(self.start), self.end - self.start)
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        // SAFETY: see comments for `get_unchecked` above.
+        unsafe {
+            assert_unsafe_precondition!(self.end >= self.start && self.end <= slice.len());
+            ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start), self.end - self.start)
+        }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        if self.start > self.end {
+            slice_index_order_fail(self.start, self.end);
+        } else if self.end > slice.len() {
+            slice_end_index_len_fail(self.end, slice.len());
+        }
+        // SAFETY: `self` is checked to be valid and in bounds above.
+        unsafe { &*self.get_unchecked(slice) }
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        if self.start > self.end {
+            slice_index_order_fail(self.start, self.end);
+        } else if self.end > slice.len() {
+            slice_end_index_len_fail(self.end, slice.len());
+        }
+        // SAFETY: `self` is checked to be valid and in bounds above.
+        unsafe { &mut *self.get_unchecked_mut(slice) }
+    }
+}
+
+#[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::RangeTo<usize> {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        (0..self.end).get(slice)
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        (0..self.end).get_mut(slice)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked`.
+        unsafe { (0..self.end).get_unchecked(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked_mut`.
+        unsafe { (0..self.end).get_unchecked_mut(slice) }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        (0..self.end).index(slice)
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        (0..self.end).index_mut(slice)
+    }
+}
+
+#[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::RangeFrom<usize> {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        (self.start..slice.len()).get(slice)
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        (self.start..slice.len()).get_mut(slice)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked`.
+        unsafe { (self.start..slice.len()).get_unchecked(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked_mut`.
+        unsafe { (self.start..slice.len()).get_unchecked_mut(slice) }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        if self.start > slice.len() {
+            slice_start_index_len_fail(self.start, slice.len());
+        }
+        // SAFETY: `self` is checked to be valid and in bounds above.
+        unsafe { &*self.get_unchecked(slice) }
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        if self.start > slice.len() {
+            slice_start_index_len_fail(self.start, slice.len());
+        }
+        // SAFETY: `self` is checked to be valid and in bounds above.
+        unsafe { &mut *self.get_unchecked_mut(slice) }
+    }
+}
+
+#[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::RangeFull {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        Some(slice)
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        Some(slice)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        slice
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        slice
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        slice
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        slice
+    }
+}
+
+#[stable(feature = "inclusive_range", since = "1.26.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::RangeInclusive<usize> {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        if *self.end() == usize::MAX { None } else { self.into_slice_range().get(slice) }
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        if *self.end() == usize::MAX { None } else { self.into_slice_range().get_mut(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked`.
+        unsafe { self.into_slice_range().get_unchecked(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked_mut`.
+        unsafe { self.into_slice_range().get_unchecked_mut(slice) }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        if *self.end() == usize::MAX {
+            slice_end_index_overflow_fail();
+        }
+        self.into_slice_range().index(slice)
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        if *self.end() == usize::MAX {
+            slice_end_index_overflow_fail();
+        }
+        self.into_slice_range().index_mut(slice)
+    }
+}
+
+#[stable(feature = "inclusive_range", since = "1.26.0")]
+#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::RangeToInclusive<usize> {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        (0..=self.end).get(slice)
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        (0..=self.end).get_mut(slice)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked`.
+        unsafe { (0..=self.end).get_unchecked(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked_mut`.
+        unsafe { (0..=self.end).get_unchecked_mut(slice) }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        (0..=self.end).index(slice)
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        (0..=self.end).index_mut(slice)
+    }
+}
+
+/// Performs bounds-checking of a range.
+///
+/// This method is similar to [`Index::index`] for slices, but it returns a
+/// [`Range`] equivalent to `range`. You can use this method to turn any range
+/// into `start` and `end` values.
+///
+/// `bounds` is the range of the slice to use for bounds-checking. It should
+/// be a [`RangeTo`] range that ends at the length of the slice.
+///
+/// The returned [`Range`] is safe to pass to [`slice::get_unchecked`] and
+/// [`slice::get_unchecked_mut`] for slices with the given range.
+///
+/// [`Range`]: ops::Range
+/// [`RangeTo`]: ops::RangeTo
+/// [`slice::get_unchecked`]: slice::get_unchecked
+/// [`slice::get_unchecked_mut`]: slice::get_unchecked_mut
+///
+/// # Panics
+///
+/// Panics if `range` would be out of bounds.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(slice_range)]
+///
+/// use std::slice;
+///
+/// let v = [10, 40, 30];
+/// assert_eq!(1..2, slice::range(1..2, ..v.len()));
+/// assert_eq!(0..2, slice::range(..2, ..v.len()));
+/// assert_eq!(1..3, slice::range(1.., ..v.len()));
+/// ```
+///
+/// Panics when [`Index::index`] would panic:
+///
+/// ```should_panic
+/// #![feature(slice_range)]
+///
+/// use std::slice;
+///
+/// let _ = slice::range(2..1, ..3);
+/// ```
+///
+/// ```should_panic
+/// #![feature(slice_range)]
+///
+/// use std::slice;
+///
+/// let _ = slice::range(1..4, ..3);
+/// ```
+///
+/// ```should_panic
+/// #![feature(slice_range)]
+///
+/// use std::slice;
+///
+/// let _ = slice::range(1..=usize::MAX, ..3);
+/// ```
+///
+/// [`Index::index`]: ops::Index::index
+#[track_caller]
+#[unstable(feature = "slice_range", issue = "76393")]
+#[must_use]
+pub fn range<R>(range: R, bounds: ops::RangeTo<usize>) -> ops::Range<usize>
+where
+    R: ops::RangeBounds<usize>,
+{
+    let len = bounds.end;
+
+    let start: ops::Bound<&usize> = range.start_bound();
+    let start = match start {
+        ops::Bound::Included(&start) => start,
+        ops::Bound::Excluded(start) => {
+            start.checked_add(1).unwrap_or_else(|| slice_start_index_overflow_fail())
+        }
+        ops::Bound::Unbounded => 0,
+    };
+
+    let end: ops::Bound<&usize> = range.end_bound();
+    let end = match end {
+        ops::Bound::Included(end) => {
+            end.checked_add(1).unwrap_or_else(|| slice_end_index_overflow_fail())
+        }
+        ops::Bound::Excluded(&end) => end,
+        ops::Bound::Unbounded => len,
+    };
+
+    if start > end {
+        slice_index_order_fail(start, end);
+    }
+    if end > len {
+        slice_end_index_len_fail(end, len);
+    }
+
+    ops::Range { start, end }
+}
+
+/// Convert pair of `ops::Bound`s into `ops::Range` without performing any bounds checking and (in debug) overflow checking
+fn into_range_unchecked(
+    len: usize,
+    (start, end): (ops::Bound<usize>, ops::Bound<usize>),
+) -> ops::Range<usize> {
+    use ops::Bound;
+    let start = match start {
+        Bound::Included(i) => i,
+        Bound::Excluded(i) => i + 1,
+        Bound::Unbounded => 0,
+    };
+    let end = match end {
+        Bound::Included(i) => i + 1,
+        Bound::Excluded(i) => i,
+        Bound::Unbounded => len,
+    };
+    start..end
+}
+
+/// Convert pair of `ops::Bound`s into `ops::Range`.
+/// Returns `None` on overflowing indices.
+fn into_range(
+    len: usize,
+    (start, end): (ops::Bound<usize>, ops::Bound<usize>),
+) -> Option<ops::Range<usize>> {
+    use ops::Bound;
+    let start = match start {
+        Bound::Included(start) => start,
+        Bound::Excluded(start) => start.checked_add(1)?,
+        Bound::Unbounded => 0,
+    };
+
+    let end = match end {
+        Bound::Included(end) => end.checked_add(1)?,
+        Bound::Excluded(end) => end,
+        Bound::Unbounded => len,
+    };
+
+    // Don't bother with checking `start < end` and `end <= len`
+    // since these checks are handled by `Range` impls
+
+    Some(start..end)
+}
+
+/// Convert pair of `ops::Bound`s into `ops::Range`.
+/// Panics on overflowing indices.
+fn into_slice_range(
+    len: usize,
+    (start, end): (ops::Bound<usize>, ops::Bound<usize>),
+) -> ops::Range<usize> {
+    use ops::Bound;
+    let start = match start {
+        Bound::Included(start) => start,
+        Bound::Excluded(start) => {
+            start.checked_add(1).unwrap_or_else(|| slice_start_index_overflow_fail())
+        }
+        Bound::Unbounded => 0,
+    };
+
+    let end = match end {
+        Bound::Included(end) => {
+            end.checked_add(1).unwrap_or_else(|| slice_end_index_overflow_fail())
+        }
+        Bound::Excluded(end) => end,
+        Bound::Unbounded => len,
+    };
+
+    // Don't bother with checking `start < end` and `end <= len`
+    // since these checks are handled by `Range` impls
+
+    start..end
+}
+
+#[stable(feature = "slice_index_with_ops_bound_pair", since = "1.53.0")]
+unsafe impl<T> SliceIndex<[T]> for (ops::Bound<usize>, ops::Bound<usize>) {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&Self::Output> {
+        into_range(slice.len(), self)?.get(slice)
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut Self::Output> {
+        into_range(slice.len(), self)?.get_mut(slice)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const Self::Output {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked`.
+        unsafe { into_range_unchecked(slice.len(), self).get_unchecked(slice) }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut Self::Output {
+        // SAFETY: the caller has to uphold the safety contract for `get_unchecked_mut`.
+        unsafe { into_range_unchecked(slice.len(), self).get_unchecked_mut(slice) }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &Self::Output {
+        into_slice_range(slice.len(), self).index(slice)
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut Self::Output {
+        into_slice_range(slice.len(), self).index_mut(slice)
+    }
+}
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
new file mode 100644
index 000000000..f1e659309
--- /dev/null
+++ b/library/core/src/slice/iter.rs
@@ -0,0 +1,3388 @@
+//! Definitions of a bunch of iterators for `[T]`.
+
+#[macro_use] // import iterator! and forward_iterator!
+mod macros;
+
+use crate::cmp;
+use crate::cmp::Ordering;
+use crate::fmt;
+use crate::intrinsics::{assume, exact_div, unchecked_sub};
+use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use crate::marker::{PhantomData, Send, Sized, Sync};
+use crate::mem;
+use crate::num::NonZeroUsize;
+use crate::ptr::NonNull;
+
+use super::{from_raw_parts, from_raw_parts_mut};
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> IntoIterator for &'a [T] {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> IntoIterator for &'a mut [T] {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(self) -> IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
+// Macro helper functions
+#[inline(always)]
+fn size_from_ptr<T>(_: *const T) -> usize {
+    mem::size_of::<T>()
+}
+
+/// Immutable slice iterator
+///
+/// This struct is created by the [`iter`] method on [slices].
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// // First, we declare a type which has `iter` method to get the `Iter` struct (`&[usize]` here):
+/// let slice = &[1, 2, 3];
+///
+/// // Then, we iterate over it:
+/// for element in slice.iter() {
+///     println!("{element}");
+/// }
+/// ```
+///
+/// [`iter`]: slice::iter
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct Iter<'a, T: 'a> {
+    ptr: NonNull<T>,
+    end: *const T, // If T is a ZST, this is actually ptr+len.  This encoding is picked so that
+    // ptr == end is a quick test for the Iterator being empty, that works
+    // for both ZST and non-ZST.
+    _marker: PhantomData<&'a T>,
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Iter").field(&self.as_slice()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for Iter<'_, T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Send for Iter<'_, T> {}
+
+impl<'a, T> Iter<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T]) -> Self {
+        let ptr = slice.as_ptr();
+        // SAFETY: Similar to `IterMut::new`.
+        unsafe {
+            assume(!ptr.is_null());
+
+            let end = if mem::size_of::<T>() == 0 {
+                (ptr as *const u8).wrapping_add(slice.len()) as *const T
+            } else {
+                ptr.add(slice.len())
+            };
+
+            Self { ptr: NonNull::new_unchecked(ptr as *mut T), end, _marker: PhantomData }
+        }
+    }
+
+    /// Views the underlying data as a subslice of the original data.
+    ///
+    /// This has the same lifetime as the original slice, and so the
+    /// iterator can continue to be used while this exists.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// // First, we declare a type which has the `iter` method to get the `Iter`
+    /// // struct (`&[usize]` here):
+    /// let slice = &[1, 2, 3];
+    ///
+    /// // Then, we get the iterator:
+    /// let mut iter = slice.iter();
+    /// // So if we print what `as_slice` method returns here, we have "[1, 2, 3]":
+    /// println!("{:?}", iter.as_slice());
+    ///
+    /// // Next, we move to the second element of the slice:
+    /// iter.next();
+    /// // Now `as_slice` returns "[2, 3]":
+    /// println!("{:?}", iter.as_slice());
+    /// ```
+    #[must_use]
+    #[stable(feature = "iter_to_slice", since = "1.4.0")]
+    pub fn as_slice(&self) -> &'a [T] {
+        self.make_slice()
+    }
+}
+
+iterator! {struct Iter -> *const T, &'a T, const, {/* no mut */}, {
+    fn is_sorted_by<F>(self, mut compare: F) -> bool
+    where
+        Self: Sized,
+        F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>,
+    {
+        self.as_slice().windows(2).all(|w| {
+            compare(&&w[0], &&w[1]).map(|o| o != Ordering::Greater).unwrap_or(false)
+        })
+    }
+}}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Clone for Iter<'_, T> {
+    fn clone(&self) -> Self {
+        Iter { ptr: self.ptr, end: self.end, _marker: self._marker }
+    }
+}
+
+#[stable(feature = "slice_iter_as_ref", since = "1.13.0")]
+impl<T> AsRef<[T]> for Iter<'_, T> {
+    fn as_ref(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+/// Mutable slice iterator.
+///
+/// This struct is created by the [`iter_mut`] method on [slices].
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// // First, we declare a type which has `iter_mut` method to get the `IterMut`
+/// // struct (`&[usize]` here):
+/// let mut slice = &mut [1, 2, 3];
+///
+/// // Then, we iterate over it and increment each element value:
+/// for element in slice.iter_mut() {
+///     *element += 1;
+/// }
+///
+/// // We now have "[2, 3, 4]":
+/// println!("{slice:?}");
+/// ```
+///
+/// [`iter_mut`]: slice::iter_mut
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct IterMut<'a, T: 'a> {
+    ptr: NonNull<T>,
+    end: *mut T, // If T is a ZST, this is actually ptr+len.  This encoding is picked so that
+    // ptr == end is a quick test for the Iterator being empty, that works
+    // for both ZST and non-ZST.
+    _marker: PhantomData<&'a mut T>,
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("IterMut").field(&self.make_slice()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for IterMut<'_, T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for IterMut<'_, T> {}
+
+impl<'a, T> IterMut<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T]) -> Self {
+        let ptr = slice.as_mut_ptr();
+        // SAFETY: There are several things here:
+        //
+        // `ptr` has been obtained by `slice.as_ptr()` where `slice` is a valid
+        // reference thus it is non-NUL and safe to use and pass to
+        // `NonNull::new_unchecked` .
+        //
+        // Adding `slice.len()` to the starting pointer gives a pointer
+        // at the end of `slice`. `end` will never be dereferenced, only checked
+        // for direct pointer equality with `ptr` to check if the iterator is
+        // done.
+        //
+        // In the case of a ZST, the end pointer is just the start pointer plus
+        // the length, to also allows for the fast `ptr == end` check.
+        //
+        // See the `next_unchecked!` and `is_empty!` macros as well as the
+        // `post_inc_start` method for more information.
+        unsafe {
+            assume(!ptr.is_null());
+
+            let end = if mem::size_of::<T>() == 0 {
+                (ptr as *mut u8).wrapping_add(slice.len()) as *mut T
+            } else {
+                ptr.add(slice.len())
+            };
+
+            Self { ptr: NonNull::new_unchecked(ptr), end, _marker: PhantomData }
+        }
+    }
+
+    /// Views the underlying data as a subslice of the original data.
+    ///
+    /// To avoid creating `&mut` references that alias, this is forced
+    /// to consume the iterator.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// // First, we declare a type which has `iter_mut` method to get the `IterMut`
+    /// // struct (`&[usize]` here):
+    /// let mut slice = &mut [1, 2, 3];
+    ///
+    /// {
+    ///     // Then, we get the iterator:
+    ///     let mut iter = slice.iter_mut();
+    ///     // We move to next element:
+    ///     iter.next();
+    ///     // So if we print what `into_slice` method returns here, we have "[2, 3]":
+    ///     println!("{:?}", iter.into_slice());
+    /// }
+    ///
+    /// // Now let's modify a value of the slice:
+    /// {
+    ///     // First we get back the iterator:
+    ///     let mut iter = slice.iter_mut();
+    ///     // We change the value of the first element of the slice returned by the `next` method:
+    ///     *iter.next().unwrap() += 1;
+    /// }
+    /// // Now slice is "[2, 2, 3]":
+    /// println!("{slice:?}");
+    /// ```
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[stable(feature = "iter_to_slice", since = "1.4.0")]
+    pub fn into_slice(self) -> &'a mut [T] {
+        // SAFETY: the iterator was created from a mutable slice with pointer
+        // `self.ptr` and length `len!(self)`. This guarantees that all the prerequisites
+        // for `from_raw_parts_mut` are fulfilled.
+        unsafe { from_raw_parts_mut(self.ptr.as_ptr(), len!(self)) }
+    }
+
+    /// Views the underlying data as a subslice of the original data.
+    ///
+    /// To avoid creating `&mut [T]` references that alias, the returned slice
+    /// borrows its lifetime from the iterator the method is applied on.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let mut slice: &mut [usize] = &mut [1, 2, 3];
+    ///
+    /// // First, we get the iterator:
+    /// let mut iter = slice.iter_mut();
+    /// // So if we check what the `as_slice` method returns here, we have "[1, 2, 3]":
+    /// assert_eq!(iter.as_slice(), &[1, 2, 3]);
+    ///
+    /// // Next, we move to the second element of the slice:
+    /// iter.next();
+    /// // Now `as_slice` returns "[2, 3]":
+    /// assert_eq!(iter.as_slice(), &[2, 3]);
+    /// ```
+    #[must_use]
+    #[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
+    pub fn as_slice(&self) -> &[T] {
+        self.make_slice()
+    }
+
+    /// Views the underlying data as a mutable subslice of the original data.
+    ///
+    /// To avoid creating `&mut [T]` references that alias, the returned slice
+    /// borrows its lifetime from the iterator the method is applied on.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(slice_iter_mut_as_mut_slice)]
+    ///
+    /// let mut slice: &mut [usize] = &mut [1, 2, 3];
+    ///
+    /// // First, we get the iterator:
+    /// let mut iter = slice.iter_mut();
+    /// // Then, we get a mutable slice from it:
+    /// let mut_slice = iter.as_mut_slice();
+    /// // So if we check what the `as_mut_slice` method returned, we have "[1, 2, 3]":
+    /// assert_eq!(mut_slice, &mut [1, 2, 3]);
+    ///
+    /// // We can use it to mutate the slice:
+    /// mut_slice[0] = 4;
+    /// mut_slice[2] = 5;
+    ///
+    /// // Next, we can move to the second element of the slice, checking that
+    /// // it yields the value we just wrote:
+    /// assert_eq!(iter.next(), Some(&mut 4));
+    /// // Now `as_mut_slice` returns "[2, 5]":
+    /// assert_eq!(iter.as_mut_slice(), &mut [2, 5]);
+    /// ```
+    #[must_use]
+    // FIXME: Uncomment the `AsMut<[T]>` impl when this gets stabilized.
+    #[unstable(feature = "slice_iter_mut_as_mut_slice", issue = "93079")]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        // SAFETY: the iterator was created from a mutable slice with pointer
+        // `self.ptr` and length `len!(self)`. This guarantees that all the prerequisites
+        // for `from_raw_parts_mut` are fulfilled.
+        unsafe { from_raw_parts_mut(self.ptr.as_ptr(), len!(self)) }
+    }
+}
+
+#[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
+impl<T> AsRef<[T]> for IterMut<'_, T> {
+    fn as_ref(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+// #[stable(feature = "slice_iter_mut_as_mut_slice", since = "FIXME")]
+// impl<T> AsMut<[T]> for IterMut<'_, T> {
+//     fn as_mut(&mut self) -> &mut [T] {
+//         self.as_mut_slice()
+//     }
+// }
+
+iterator! {struct IterMut -> *mut T, &'a mut T, mut, {mut}, {}}
+
+/// An internal abstraction over the splitting iterators, so that
+/// splitn, splitn_mut etc can be implemented once.
+#[doc(hidden)]
+pub(super) trait SplitIter: DoubleEndedIterator {
+    /// Marks the underlying iterator as complete, extracting the remaining
+    /// portion of the slice.
+    fn finish(&mut self) -> Option<Self::Item>;
+}
+
+/// An iterator over subslices separated by elements that match a predicate
+/// function.
+///
+/// This struct is created by the [`split`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = [10, 40, 33, 20];
+/// let mut iter = slice.split(|num| num % 3 == 0);
+/// ```
+///
+/// [`split`]: slice::split
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct Split<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    // Used for `SplitWhitespace` and `SplitAsciiWhitespace` `as_str` methods
+    pub(crate) v: &'a [T],
+    pred: P,
+    // Used for `SplitAsciiWhitespace` `as_str` method
+    pub(crate) finished: bool,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> Split<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], pred: P) -> Self {
+        Self { v: slice, pred, finished: false }
+    }
+    /// Returns a slice which contains items not yet handled by split.
+    /// # Example
+    ///
+    /// ```
+    /// #![feature(split_as_slice)]
+    /// let slice = [1,2,3,4,5];
+    /// let mut split = slice.split(|v| v % 2 == 0);
+    /// assert!(split.next().is_some());
+    /// assert_eq!(split.as_slice(), &[3,4,5]);
+    /// ```
+    #[unstable(feature = "split_as_slice", issue = "96137")]
+    pub fn as_slice(&self) -> &'a [T] {
+        if self.finished { &[] } else { &self.v }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for Split<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Split").field("v", &self.v).field("finished", &self.finished).finish()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, P> Clone for Split<'_, T, P>
+where
+    P: Clone + FnMut(&T) -> bool,
+{
+    fn clone(&self) -> Self {
+        Split { v: self.v, pred: self.pred.clone(), finished: self.finished }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, P> Iterator for Split<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.finished {
+            return None;
+        }
+
+        match self.v.iter().position(|x| (self.pred)(x)) {
+            None => self.finish(),
+            Some(idx) => {
+                let ret = Some(&self.v[..idx]);
+                self.v = &self.v[idx + 1..];
+                ret
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            // If the predicate doesn't match anything, we yield one slice.
+            // If it matches every element, we yield `len() + 1` empty slices.
+            (1, Some(self.v.len() + 1))
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, P> DoubleEndedIterator for Split<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.finished {
+            return None;
+        }
+
+        match self.v.iter().rposition(|x| (self.pred)(x)) {
+            None => self.finish(),
+            Some(idx) => {
+                let ret = Some(&self.v[idx + 1..]);
+                self.v = &self.v[..idx];
+                ret
+            }
+        }
+    }
+}
+
+impl<'a, T, P> SplitIter for Split<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn finish(&mut self) -> Option<&'a [T]> {
+        if self.finished {
+            None
+        } else {
+            self.finished = true;
+            Some(self.v)
+        }
+    }
+}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T, P> FusedIterator for Split<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over subslices separated by elements that match a predicate
+/// function. Unlike `Split`, it contains the matched part as a terminator
+/// of the subslice.
+///
+/// This struct is created by the [`split_inclusive`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = [10, 40, 33, 20];
+/// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
+/// ```
+///
+/// [`split_inclusive`]: slice::split_inclusive
+/// [slices]: slice
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct SplitInclusive<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    v: &'a [T],
+    pred: P,
+    finished: bool,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusive<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], pred: P) -> Self {
+        let finished = slice.is_empty();
+        Self { v: slice, pred, finished }
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitInclusive<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitInclusive")
+            .field("v", &self.v)
+            .field("finished", &self.finished)
+            .finish()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<T, P> Clone for SplitInclusive<'_, T, P>
+where
+    P: Clone + FnMut(&T) -> bool,
+{
+    fn clone(&self) -> Self {
+        SplitInclusive { v: self.v, pred: self.pred.clone(), finished: self.finished }
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<'a, T, P> Iterator for SplitInclusive<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.finished {
+            return None;
+        }
+
+        let idx =
+            self.v.iter().position(|x| (self.pred)(x)).map(|idx| idx + 1).unwrap_or(self.v.len());
+        if idx == self.v.len() {
+            self.finished = true;
+        }
+        let ret = Some(&self.v[..idx]);
+        self.v = &self.v[idx..];
+        ret
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            // If the predicate doesn't match anything, we yield one slice.
+            // If it matches every element, we yield `len()` one-element slices,
+            // or a single empty slice.
+            (1, Some(cmp::max(1, self.v.len())))
+        }
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<'a, T, P> DoubleEndedIterator for SplitInclusive<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.finished {
+            return None;
+        }
+
+        // The last index of self.v is already checked and found to match
+        // by the last iteration, so we start searching a new match
+        // one index to the left.
+        let remainder = if self.v.is_empty() { &[] } else { &self.v[..(self.v.len() - 1)] };
+        let idx = remainder.iter().rposition(|x| (self.pred)(x)).map(|idx| idx + 1).unwrap_or(0);
+        if idx == 0 {
+            self.finished = true;
+        }
+        let ret = Some(&self.v[idx..]);
+        self.v = &self.v[..idx];
+        ret
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<T, P> FusedIterator for SplitInclusive<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over the mutable subslices of the vector which are separated
+/// by elements that match `pred`.
+///
+/// This struct is created by the [`split_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut v = [10, 40, 30, 20, 60, 50];
+/// let iter = v.split_mut(|num| *num % 3 == 0);
+/// ```
+///
+/// [`split_mut`]: slice::split_mut
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct SplitMut<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    v: &'a mut [T],
+    pred: P,
+    finished: bool,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitMut<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], pred: P) -> Self {
+        Self { v: slice, pred, finished: false }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitMut<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitMut").field("v", &self.v).field("finished", &self.finished).finish()
+    }
+}
+
+impl<'a, T, P> SplitIter for SplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn finish(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            None
+        } else {
+            self.finished = true;
+            Some(mem::replace(&mut self.v, &mut []))
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, P> Iterator for SplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            return None;
+        }
+
+        match self.v.iter().position(|x| (self.pred)(x)) {
+            None => self.finish(),
+            Some(idx) => {
+                let tmp = mem::take(&mut self.v);
+                // idx is the index of the element we are splitting on. We want to set self to the
+                // region after idx, and return the subslice before and not including idx.
+                // So first we split after idx
+                let (head, tail) = tmp.split_at_mut(idx + 1);
+                self.v = tail;
+                // Then return the subslice up to but not including the found element
+                Some(&mut head[..idx])
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            // If the predicate doesn't match anything, we yield one slice.
+            // If it matches every element, we yield `len() + 1` empty slices.
+            (1, Some(self.v.len() + 1))
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, P> DoubleEndedIterator for SplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            return None;
+        }
+
+        let idx_opt = {
+            // work around borrowck limitations
+            let pred = &mut self.pred;
+            self.v.iter().rposition(|x| (*pred)(x))
+        };
+        match idx_opt {
+            None => self.finish(),
+            Some(idx) => {
+                let tmp = mem::replace(&mut self.v, &mut []);
+                let (head, tail) = tmp.split_at_mut(idx);
+                self.v = head;
+                Some(&mut tail[1..])
+            }
+        }
+    }
+}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T, P> FusedIterator for SplitMut<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over the mutable subslices of the vector which are separated
+/// by elements that match `pred`. Unlike `SplitMut`, it contains the matched
+/// parts in the ends of the subslices.
+///
+/// This struct is created by the [`split_inclusive_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut v = [10, 40, 30, 20, 60, 50];
+/// let iter = v.split_inclusive_mut(|num| *num % 3 == 0);
+/// ```
+///
+/// [`split_inclusive_mut`]: slice::split_inclusive_mut
+/// [slices]: slice
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct SplitInclusiveMut<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    v: &'a mut [T],
+    pred: P,
+    finished: bool,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitInclusiveMut<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], pred: P) -> Self {
+        let finished = slice.is_empty();
+        Self { v: slice, pred, finished }
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitInclusiveMut<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitInclusiveMut")
+            .field("v", &self.v)
+            .field("finished", &self.finished)
+            .finish()
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<'a, T, P> Iterator for SplitInclusiveMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            return None;
+        }
+
+        let idx_opt = {
+            // work around borrowck limitations
+            let pred = &mut self.pred;
+            self.v.iter().position(|x| (*pred)(x))
+        };
+        let idx = idx_opt.map(|idx| idx + 1).unwrap_or(self.v.len());
+        if idx == self.v.len() {
+            self.finished = true;
+        }
+        let tmp = mem::replace(&mut self.v, &mut []);
+        let (head, tail) = tmp.split_at_mut(idx);
+        self.v = tail;
+        Some(head)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.finished {
+            (0, Some(0))
+        } else {
+            // If the predicate doesn't match anything, we yield one slice.
+            // If it matches every element, we yield `len()` one-element slices,
+            // or a single empty slice.
+            (1, Some(cmp::max(1, self.v.len())))
+        }
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<'a, T, P> DoubleEndedIterator for SplitInclusiveMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.finished {
+            return None;
+        }
+
+        let idx_opt = if self.v.is_empty() {
+            None
+        } else {
+            // work around borrowck limitations
+            let pred = &mut self.pred;
+
+            // The last index of self.v is already checked and found to match
+            // by the last iteration, so we start searching a new match
+            // one index to the left.
+            let remainder = &self.v[..(self.v.len() - 1)];
+            remainder.iter().rposition(|x| (*pred)(x))
+        };
+        let idx = idx_opt.map(|idx| idx + 1).unwrap_or(0);
+        if idx == 0 {
+            self.finished = true;
+        }
+        let tmp = mem::replace(&mut self.v, &mut []);
+        let (head, tail) = tmp.split_at_mut(idx);
+        self.v = head;
+        Some(tail)
+    }
+}
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+impl<T, P> FusedIterator for SplitInclusiveMut<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over subslices separated by elements that match a predicate
+/// function, starting from the end of the slice.
+///
+/// This struct is created by the [`rsplit`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = [11, 22, 33, 0, 44, 55];
+/// let iter = slice.rsplit(|num| *num == 0);
+/// ```
+///
+/// [`rsplit`]: slice::rsplit
+/// [slices]: slice
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RSplit<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: Split<'a, T, P>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> RSplit<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], pred: P) -> Self {
+        Self { inner: Split::new(slice, pred) }
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<T: fmt::Debug, P> fmt::Debug for RSplit<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RSplit")
+            .field("v", &self.inner.v)
+            .field("finished", &self.inner.finished)
+            .finish()
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<T, P> Clone for RSplit<'_, T, P>
+where
+    P: Clone + FnMut(&T) -> bool,
+{
+    fn clone(&self) -> Self {
+        RSplit { inner: self.inner.clone() }
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> Iterator for RSplit<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        self.inner.next_back()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> DoubleEndedIterator for RSplit<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        self.inner.next()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> SplitIter for RSplit<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn finish(&mut self) -> Option<&'a [T]> {
+        self.inner.finish()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<T, P> FusedIterator for RSplit<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An iterator over the subslices of the vector which are separated
+/// by elements that match `pred`, starting from the end of the slice.
+///
+/// This struct is created by the [`rsplit_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = [11, 22, 33, 0, 44, 55];
+/// let iter = slice.rsplit_mut(|num| *num == 0);
+/// ```
+///
+/// [`rsplit_mut`]: slice::rsplit_mut
+/// [slices]: slice
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RSplitMut<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: SplitMut<'a, T, P>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> RSplitMut<'a, T, P> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], pred: P) -> Self {
+        Self { inner: SplitMut::new(slice, pred) }
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<T: fmt::Debug, P> fmt::Debug for RSplitMut<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RSplitMut")
+            .field("v", &self.inner.v)
+            .field("finished", &self.inner.finished)
+            .finish()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> SplitIter for RSplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn finish(&mut self) -> Option<&'a mut [T]> {
+        self.inner.finish()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> Iterator for RSplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        self.inner.next_back()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<'a, T, P> DoubleEndedIterator for RSplitMut<'a, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        self.inner.next()
+    }
+}
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+impl<T, P> FusedIterator for RSplitMut<'_, T, P> where P: FnMut(&T) -> bool {}
+
+/// An private iterator over subslices separated by elements that
+/// match a predicate function, splitting at most a fixed number of
+/// times.
+#[derive(Debug)]
+struct GenericSplitN<I> {
+    iter: I,
+    count: usize,
+}
+
+impl<T, I: SplitIter<Item = T>> Iterator for GenericSplitN<I> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        match self.count {
+            0 => None,
+            1 => {
+                self.count -= 1;
+                self.iter.finish()
+            }
+            _ => {
+                self.count -= 1;
+                self.iter.next()
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (lower, upper_opt) = self.iter.size_hint();
+        (
+            cmp::min(self.count, lower),
+            Some(upper_opt.map_or(self.count, |upper| cmp::min(self.count, upper))),
+        )
+    }
+}
+
+/// An iterator over subslices separated by elements that match a predicate
+/// function, limited to a given number of splits.
+///
+/// This struct is created by the [`splitn`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = [10, 40, 30, 20, 60, 50];
+/// let iter = slice.splitn(2, |num| *num % 3 == 0);
+/// ```
+///
+/// [`splitn`]: slice::splitn
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct SplitN<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: GenericSplitN<Split<'a, T, P>>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitN<'a, T, P> {
+    #[inline]
+    pub(super) fn new(s: Split<'a, T, P>, n: usize) -> Self {
+        Self { inner: GenericSplitN { iter: s, count: n } }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitN<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitN").field("inner", &self.inner).finish()
+    }
+}
+
+/// An iterator over subslices separated by elements that match a
+/// predicate function, limited to a given number of splits, starting
+/// from the end of the slice.
+///
+/// This struct is created by the [`rsplitn`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = [10, 40, 30, 20, 60, 50];
+/// let iter = slice.rsplitn(2, |num| *num % 3 == 0);
+/// ```
+///
+/// [`rsplitn`]: slice::rsplitn
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RSplitN<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: GenericSplitN<RSplit<'a, T, P>>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> RSplitN<'a, T, P> {
+    #[inline]
+    pub(super) fn new(s: RSplit<'a, T, P>, n: usize) -> Self {
+        Self { inner: GenericSplitN { iter: s, count: n } }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for RSplitN<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RSplitN").field("inner", &self.inner).finish()
+    }
+}
+
+/// An iterator over subslices separated by elements that match a predicate
+/// function, limited to a given number of splits.
+///
+/// This struct is created by the [`splitn_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = [10, 40, 30, 20, 60, 50];
+/// let iter = slice.splitn_mut(2, |num| *num % 3 == 0);
+/// ```
+///
+/// [`splitn_mut`]: slice::splitn_mut
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct SplitNMut<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: GenericSplitN<SplitMut<'a, T, P>>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> SplitNMut<'a, T, P> {
+    #[inline]
+    pub(super) fn new(s: SplitMut<'a, T, P>, n: usize) -> Self {
+        Self { inner: GenericSplitN { iter: s, count: n } }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for SplitNMut<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SplitNMut").field("inner", &self.inner).finish()
+    }
+}
+
+/// An iterator over subslices separated by elements that match a
+/// predicate function, limited to a given number of splits, starting
+/// from the end of the slice.
+///
+/// This struct is created by the [`rsplitn_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = [10, 40, 30, 20, 60, 50];
+/// let iter = slice.rsplitn_mut(2, |num| *num % 3 == 0);
+/// ```
+///
+/// [`rsplitn_mut`]: slice::rsplitn_mut
+/// [slices]: slice
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RSplitNMut<'a, T: 'a, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    inner: GenericSplitN<RSplitMut<'a, T, P>>,
+}
+
+impl<'a, T: 'a, P: FnMut(&T) -> bool> RSplitNMut<'a, T, P> {
+    #[inline]
+    pub(super) fn new(s: RSplitMut<'a, T, P>, n: usize) -> Self {
+        Self { inner: GenericSplitN { iter: s, count: n } }
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: fmt::Debug, P> fmt::Debug for RSplitNMut<'_, T, P>
+where
+    P: FnMut(&T) -> bool,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RSplitNMut").field("inner", &self.inner).finish()
+    }
+}
+
+forward_iterator! { SplitN: T, &'a [T] }
+forward_iterator! { RSplitN: T, &'a [T] }
+forward_iterator! { SplitNMut: T, &'a mut [T] }
+forward_iterator! { RSplitNMut: T, &'a mut [T] }
+
+/// An iterator over overlapping subslices of length `size`.
+///
+/// This struct is created by the [`windows`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = ['r', 'u', 's', 't'];
+/// let iter = slice.windows(2);
+/// ```
+///
+/// [`windows`]: slice::windows
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct Windows<'a, T: 'a> {
+    v: &'a [T],
+    size: NonZeroUsize,
+}
+
+impl<'a, T: 'a> Windows<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], size: NonZeroUsize) -> Self {
+        Self { v: slice, size }
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Clone for Windows<'_, T> {
+    fn clone(&self) -> Self {
+        Windows { v: self.v, size: self.size }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for Windows<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.size.get() > self.v.len() {
+            None
+        } else {
+            let ret = Some(&self.v[..self.size.get()]);
+            self.v = &self.v[1..];
+            ret
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.size.get() > self.v.len() {
+            (0, Some(0))
+        } else {
+            let size = self.v.len() - self.size.get() + 1;
+            (size, Some(size))
+        }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.size.get().overflowing_add(n);
+        if end > self.v.len() || overflow {
+            self.v = &[];
+            None
+        } else {
+            let nth = &self.v[n..end];
+            self.v = &self.v[n + 1..];
+            Some(nth)
+        }
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        if self.size.get() > self.v.len() {
+            None
+        } else {
+            let start = self.v.len() - self.size.get();
+            Some(&self.v[start..])
+        }
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        // SAFETY: since the caller guarantees that `i` is in bounds,
+        // which means that `i` cannot overflow an `isize`, and the
+        // slice created by `from_raw_parts` is a subslice of `self.v`
+        // thus is guaranteed to be valid for the lifetime `'a` of `self.v`.
+        unsafe { from_raw_parts(self.v.as_ptr().add(idx), self.size.get()) }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for Windows<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.size.get() > self.v.len() {
+            None
+        } else {
+            let ret = Some(&self.v[self.v.len() - self.size.get()..]);
+            self.v = &self.v[..self.v.len() - 1];
+            ret
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.v.len().overflowing_sub(n);
+        if end < self.size.get() || overflow {
+            self.v = &[];
+            None
+        } else {
+            let ret = &self.v[end - self.size.get()..end];
+            self.v = &self.v[..end - 1];
+            Some(ret)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for Windows<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for Windows<'_, T> {}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T> FusedIterator for Windows<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for Windows<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for Windows<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
+/// time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last slice
+/// of the iteration will be the remainder.
+///
+/// This struct is created by the [`chunks`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.chunks(2);
+/// ```
+///
+/// [`chunks`]: slice::chunks
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct Chunks<'a, T: 'a> {
+    v: &'a [T],
+    chunk_size: usize,
+}
+
+impl<'a, T: 'a> Chunks<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], size: usize) -> Self {
+        Self { v: slice, chunk_size: size }
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Clone for Chunks<'_, T> {
+    fn clone(&self) -> Self {
+        Chunks { v: self.v, chunk_size: self.chunk_size }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for Chunks<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let chunksz = cmp::min(self.v.len(), self.chunk_size);
+            let (fst, snd) = self.v.split_at(chunksz);
+            self.v = snd;
+            Some(fst)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.v.is_empty() {
+            (0, Some(0))
+        } else {
+            let n = self.v.len() / self.chunk_size;
+            let rem = self.v.len() % self.chunk_size;
+            let n = if rem > 0 { n + 1 } else { n };
+            (n, Some(n))
+        }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (start, overflow) = n.overflowing_mul(self.chunk_size);
+        if start >= self.v.len() || overflow {
+            self.v = &[];
+            None
+        } else {
+            let end = match start.checked_add(self.chunk_size) {
+                Some(sum) => cmp::min(self.v.len(), sum),
+                None => self.v.len(),
+            };
+            let nth = &self.v[start..end];
+            self.v = &self.v[end..];
+            Some(nth)
+        }
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let start = (self.v.len() - 1) / self.chunk_size * self.chunk_size;
+            Some(&self.v[start..])
+        }
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let start = idx * self.chunk_size;
+        // SAFETY: the caller guarantees that `i` is in bounds,
+        // which means that `start` must be in bounds of the
+        // underlying `self.v` slice, and we made sure that `len`
+        // is also in bounds of `self.v`. Thus, `start` cannot overflow
+        // an `isize`, and the slice constructed by `from_raw_parts`
+        // is a subslice of `self.v` which is guaranteed to be valid
+        // for the lifetime `'a` of `self.v`.
+        unsafe {
+            let len = cmp::min(self.v.len().unchecked_sub(start), self.chunk_size);
+            from_raw_parts(self.v.as_ptr().add(start), len)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for Chunks<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let remainder = self.v.len() % self.chunk_size;
+            let chunksz = if remainder != 0 { remainder } else { self.chunk_size };
+            // SAFETY: split_at_unchecked requires the argument be less than or
+            // equal to the length. This is guaranteed, but subtle: `chunksz`
+            // will always either be `self.v.len() % self.chunk_size`, which
+            // will always evaluate to strictly less than `self.v.len()` (or
+            // panic, in the case that `self.chunk_size` is zero), or it can be
+            // `self.chunk_size`, in the case that the length is exactly
+            // divisible by the chunk size.
+            //
+            // While it seems like using `self.chunk_size` in this case could
+            // lead to a value greater than `self.v.len()`, it cannot: if
+            // `self.chunk_size` were greater than `self.v.len()`, then
+            // `self.v.len() % self.chunk_size` would return nonzero (note that
+            // in this branch of the `if`, we already know that `self.v` is
+            // non-empty).
+            let (fst, snd) = unsafe { self.v.split_at_unchecked(self.v.len() - chunksz) };
+            self.v = fst;
+            Some(snd)
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &[];
+            None
+        } else {
+            let start = (len - 1 - n) * self.chunk_size;
+            let end = match start.checked_add(self.chunk_size) {
+                Some(res) => cmp::min(self.v.len(), res),
+                None => self.v.len(),
+            };
+            let nth_back = &self.v[start..end];
+            self.v = &self.v[..start];
+            Some(nth_back)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for Chunks<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for Chunks<'_, T> {}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T> FusedIterator for Chunks<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for Chunks<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for Chunks<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) mutable chunks (`chunk_size`
+/// elements at a time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last slice
+/// of the iteration will be the remainder.
+///
+/// This struct is created by the [`chunks_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.chunks_mut(2);
+/// ```
+///
+/// [`chunks_mut`]: slice::chunks_mut
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ChunksMut<'a, T: 'a> {
+    /// # Safety
+    /// This slice pointer must point at a valid region of `T` with at least length `v.len()`. Normally,
+    /// those requirements would mean that we could instead use a `&mut [T]` here, but we cannot
+    /// because `__iterator_get_unchecked` needs to return `&mut [T]`, which guarantees certain aliasing
+    /// properties that we cannot uphold if we hold on to the full original `&mut [T]`. Wrapping a raw
+    /// slice instead lets us hand out non-overlapping `&mut [T]` subslices of the slice we wrap.
+    v: *mut [T],
+    chunk_size: usize,
+    _marker: PhantomData<&'a mut T>,
+}
+
+impl<'a, T: 'a> ChunksMut<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], size: usize) -> Self {
+        Self { v: slice, chunk_size: size, _marker: PhantomData }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for ChunksMut<'a, T> {
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let sz = cmp::min(self.v.len(), self.chunk_size);
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, tail) = unsafe { self.v.split_at_mut(sz) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *head })
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.v.is_empty() {
+            (0, Some(0))
+        } else {
+            let n = self.v.len() / self.chunk_size;
+            let rem = self.v.len() % self.chunk_size;
+            let n = if rem > 0 { n + 1 } else { n };
+            (n, Some(n))
+        }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<&'a mut [T]> {
+        let (start, overflow) = n.overflowing_mul(self.chunk_size);
+        if start >= self.v.len() || overflow {
+            self.v = &mut [];
+            None
+        } else {
+            let end = match start.checked_add(self.chunk_size) {
+                Some(sum) => cmp::min(self.v.len(), sum),
+                None => self.v.len(),
+            };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, tail) = unsafe { self.v.split_at_mut(end) };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (_, nth) = unsafe { head.split_at_mut(start) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth })
+        }
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let start = (self.v.len() - 1) / self.chunk_size * self.chunk_size;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *self.v.get_unchecked_mut(start..) })
+        }
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let start = idx * self.chunk_size;
+        // SAFETY: see comments for `Chunks::__iterator_get_unchecked` and `self.v`.
+        //
+        // Also note that the caller also guarantees that we're never called
+        // with the same index again, and that no other methods that will
+        // access this subslice are called, so it is valid for the returned
+        // slice to be mutable.
+        unsafe {
+            let len = cmp::min(self.v.len().unchecked_sub(start), self.chunk_size);
+            from_raw_parts_mut(self.v.as_mut_ptr().add(start), len)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for ChunksMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let remainder = self.v.len() % self.chunk_size;
+            let sz = if remainder != 0 { remainder } else { self.chunk_size };
+            let len = self.v.len();
+            // SAFETY: Similar to `Chunks::next_back`
+            let (head, tail) = unsafe { self.v.split_at_mut_unchecked(len - sz) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *tail })
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &mut [];
+            None
+        } else {
+            let start = (len - 1 - n) * self.chunk_size;
+            let end = match start.checked_add(self.chunk_size) {
+                Some(res) => cmp::min(self.v.len(), res),
+                None => self.v.len(),
+            };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (temp, _tail) = unsafe { self.v.split_at_mut(end) };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, nth_back) = unsafe { temp.split_at_mut(start) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth_back })
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for ChunksMut<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for ChunksMut<'_, T> {}
+
+#[stable(feature = "fused", since = "1.26.0")]
+impl<T> FusedIterator for ChunksMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for ChunksMut<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for ChunksMut<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T> Send for ChunksMut<'_, T> where T: Send {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T> Sync for ChunksMut<'_, T> where T: Sync {}
+
+/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
+/// time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last
+/// up to `chunk_size-1` elements will be omitted but can be retrieved from
+/// the [`remainder`] function from the iterator.
+///
+/// This struct is created by the [`chunks_exact`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.chunks_exact(2);
+/// ```
+///
+/// [`chunks_exact`]: slice::chunks_exact
+/// [`remainder`]: ChunksExact::remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ChunksExact<'a, T: 'a> {
+    v: &'a [T],
+    rem: &'a [T],
+    chunk_size: usize,
+}
+
+impl<'a, T> ChunksExact<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], chunk_size: usize) -> Self {
+        let rem = slice.len() % chunk_size;
+        let fst_len = slice.len() - rem;
+        // SAFETY: 0 <= fst_len <= slice.len() by construction above
+        let (fst, snd) = unsafe { slice.split_at_unchecked(fst_len) };
+        Self { v: fst, rem: snd, chunk_size }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `chunk_size-1`
+    /// elements.
+    #[must_use]
+    #[stable(feature = "chunks_exact", since = "1.31.0")]
+    pub fn remainder(&self) -> &'a [T] {
+        self.rem
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<T> Clone for ChunksExact<'_, T> {
+    fn clone(&self) -> Self {
+        ChunksExact { v: self.v, rem: self.rem, chunk_size: self.chunk_size }
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<'a, T> Iterator for ChunksExact<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            let (fst, snd) = self.v.split_at(self.chunk_size);
+            self.v = snd;
+            Some(fst)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = self.v.len() / self.chunk_size;
+        (n, Some(n))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (start, overflow) = n.overflowing_mul(self.chunk_size);
+        if start >= self.v.len() || overflow {
+            self.v = &[];
+            None
+        } else {
+            let (_, snd) = self.v.split_at(start);
+            self.v = snd;
+            self.next()
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let start = idx * self.chunk_size;
+        // SAFETY: mostly identical to `Chunks::__iterator_get_unchecked`.
+        unsafe { from_raw_parts(self.v.as_ptr().add(start), self.chunk_size) }
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for ChunksExact<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            let (fst, snd) = self.v.split_at(self.v.len() - self.chunk_size);
+            self.v = fst;
+            Some(snd)
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &[];
+            None
+        } else {
+            let start = (len - 1 - n) * self.chunk_size;
+            let end = start + self.chunk_size;
+            let nth_back = &self.v[start..end];
+            self.v = &self.v[..start];
+            Some(nth_back)
+        }
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<T> ExactSizeIterator for ChunksExact<'_, T> {
+    fn is_empty(&self) -> bool {
+        self.v.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for ChunksExact<'_, T> {}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<T> FusedIterator for ChunksExact<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for ChunksExact<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for ChunksExact<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) mutable chunks (`chunk_size`
+/// elements at a time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last up to
+/// `chunk_size-1` elements will be omitted but can be retrieved from the
+/// [`into_remainder`] function from the iterator.
+///
+/// This struct is created by the [`chunks_exact_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.chunks_exact_mut(2);
+/// ```
+///
+/// [`chunks_exact_mut`]: slice::chunks_exact_mut
+/// [`into_remainder`]: ChunksExactMut::into_remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ChunksExactMut<'a, T: 'a> {
+    /// # Safety
+    /// This slice pointer must point at a valid region of `T` with at least length `v.len()`. Normally,
+    /// those requirements would mean that we could instead use a `&mut [T]` here, but we cannot
+    /// because `__iterator_get_unchecked` needs to return `&mut [T]`, which guarantees certain aliasing
+    /// properties that we cannot uphold if we hold on to the full original `&mut [T]`. Wrapping a raw
+    /// slice instead lets us hand out non-overlapping `&mut [T]` subslices of the slice we wrap.
+    v: *mut [T],
+    rem: &'a mut [T], // The iterator never yields from here, so this can be unique
+    chunk_size: usize,
+    _marker: PhantomData<&'a mut T>,
+}
+
+impl<'a, T> ChunksExactMut<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], chunk_size: usize) -> Self {
+        let rem = slice.len() % chunk_size;
+        let fst_len = slice.len() - rem;
+        // SAFETY: 0 <= fst_len <= slice.len() by construction above
+        let (fst, snd) = unsafe { slice.split_at_mut_unchecked(fst_len) };
+        Self { v: fst, rem: snd, chunk_size, _marker: PhantomData }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `chunk_size-1`
+    /// elements.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[stable(feature = "chunks_exact", since = "1.31.0")]
+    pub fn into_remainder(self) -> &'a mut [T] {
+        self.rem
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<'a, T> Iterator for ChunksExactMut<'a, T> {
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            // SAFETY: self.chunk_size is inbounds because we compared above against self.v.len()
+            let (head, tail) = unsafe { self.v.split_at_mut(self.chunk_size) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *head })
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = self.v.len() / self.chunk_size;
+        (n, Some(n))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<&'a mut [T]> {
+        let (start, overflow) = n.overflowing_mul(self.chunk_size);
+        if start >= self.v.len() || overflow {
+            self.v = &mut [];
+            None
+        } else {
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (_, snd) = unsafe { self.v.split_at_mut(start) };
+            self.v = snd;
+            self.next()
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let start = idx * self.chunk_size;
+        // SAFETY: see comments for `Chunks::__iterator_get_unchecked` and `self.v`.
+        unsafe { from_raw_parts_mut(self.v.as_mut_ptr().add(start), self.chunk_size) }
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for ChunksExactMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            // SAFETY: This subtraction is inbounds because of the check above
+            let (head, tail) = unsafe { self.v.split_at_mut(self.v.len() - self.chunk_size) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *tail })
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &mut [];
+            None
+        } else {
+            let start = (len - 1 - n) * self.chunk_size;
+            let end = start + self.chunk_size;
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (temp, _tail) = unsafe { mem::replace(&mut self.v, &mut []).split_at_mut(end) };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, nth_back) = unsafe { temp.split_at_mut(start) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth_back })
+        }
+    }
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<T> ExactSizeIterator for ChunksExactMut<'_, T> {
+    fn is_empty(&self) -> bool {
+        self.v.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for ChunksExactMut<'_, T> {}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+impl<T> FusedIterator for ChunksExactMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for ChunksExactMut<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for ChunksExactMut<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+unsafe impl<T> Send for ChunksExactMut<'_, T> where T: Send {}
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+unsafe impl<T> Sync for ChunksExactMut<'_, T> where T: Sync {}
+
+/// A windowed iterator over a slice in overlapping chunks (`N` elements at a
+/// time), starting at the beginning of the slice
+///
+/// This struct is created by the [`array_windows`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// #![feature(array_windows)]
+///
+/// let slice = [0, 1, 2, 3];
+/// let iter = slice.array_windows::<2>();
+/// ```
+///
+/// [`array_windows`]: slice::array_windows
+/// [slices]: slice
+#[derive(Debug, Clone, Copy)]
+#[unstable(feature = "array_windows", issue = "75027")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ArrayWindows<'a, T: 'a, const N: usize> {
+    slice_head: *const T,
+    num: usize,
+    marker: PhantomData<&'a [T; N]>,
+}
+
+impl<'a, T: 'a, const N: usize> ArrayWindows<'a, T, N> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T]) -> Self {
+        let num_windows = slice.len().saturating_sub(N - 1);
+        Self { slice_head: slice.as_ptr(), num: num_windows, marker: PhantomData }
+    }
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<'a, T, const N: usize> Iterator for ArrayWindows<'a, T, N> {
+    type Item = &'a [T; N];
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.num == 0 {
+            return None;
+        }
+        // SAFETY:
+        // This is safe because it's indexing into a slice guaranteed to be length > N.
+        let ret = unsafe { &*self.slice_head.cast::<[T; N]>() };
+        // SAFETY: Guaranteed that there are at least 1 item remaining otherwise
+        // earlier branch would've been hit
+        self.slice_head = unsafe { self.slice_head.add(1) };
+
+        self.num -= 1;
+        Some(ret)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.num, Some(self.num))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.num
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        if self.num <= n {
+            self.num = 0;
+            return None;
+        }
+        // SAFETY:
+        // This is safe because it's indexing into a slice guaranteed to be length > N.
+        let ret = unsafe { &*self.slice_head.add(n).cast::<[T; N]>() };
+        // SAFETY: Guaranteed that there are at least n items remaining
+        self.slice_head = unsafe { self.slice_head.add(n + 1) };
+
+        self.num -= n + 1;
+        Some(ret)
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.nth(self.num.checked_sub(1)?)
+    }
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<'a, T, const N: usize> DoubleEndedIterator for ArrayWindows<'a, T, N> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T; N]> {
+        if self.num == 0 {
+            return None;
+        }
+        // SAFETY: Guaranteed that there are n items remaining, n-1 for 0-indexing.
+        let ret = unsafe { &*self.slice_head.add(self.num - 1).cast::<[T; N]>() };
+        self.num -= 1;
+        Some(ret)
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<&'a [T; N]> {
+        if self.num <= n {
+            self.num = 0;
+            return None;
+        }
+        // SAFETY: Guaranteed that there are n items remaining, n-1 for 0-indexing.
+        let ret = unsafe { &*self.slice_head.add(self.num - (n + 1)).cast::<[T; N]>() };
+        self.num -= n + 1;
+        Some(ret)
+    }
+}
+
+#[unstable(feature = "array_windows", issue = "75027")]
+impl<T, const N: usize> ExactSizeIterator for ArrayWindows<'_, T, N> {
+    fn is_empty(&self) -> bool {
+        self.num == 0
+    }
+}
+
+/// An iterator over a slice in (non-overlapping) chunks (`N` elements at a
+/// time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last
+/// up to `N-1` elements will be omitted but can be retrieved from
+/// the [`remainder`] function from the iterator.
+///
+/// This struct is created by the [`array_chunks`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// #![feature(array_chunks)]
+///
+/// let slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.array_chunks::<2>();
+/// ```
+///
+/// [`array_chunks`]: slice::array_chunks
+/// [`remainder`]: ArrayChunks::remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ArrayChunks<'a, T: 'a, const N: usize> {
+    iter: Iter<'a, [T; N]>,
+    rem: &'a [T],
+}
+
+impl<'a, T, const N: usize> ArrayChunks<'a, T, N> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T]) -> Self {
+        let (array_slice, rem) = slice.as_chunks();
+        Self { iter: array_slice.iter(), rem }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `N-1`
+    /// elements.
+    #[must_use]
+    #[unstable(feature = "array_chunks", issue = "74985")]
+    pub fn remainder(&self) -> &'a [T] {
+        self.rem
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<T, const N: usize> Clone for ArrayChunks<'_, T, N> {
+    fn clone(&self) -> Self {
+        ArrayChunks { iter: self.iter.clone(), rem: self.rem }
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<'a, T, const N: usize> Iterator for ArrayChunks<'a, T, N> {
+    type Item = &'a [T; N];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T; N]> {
+        self.iter.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.iter.count()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.iter.nth(n)
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        self.iter.last()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> &'a [T; N] {
+        // SAFETY: The safety guarantees of `__iterator_get_unchecked` are
+        // transferred to the caller.
+        unsafe { self.iter.__iterator_get_unchecked(i) }
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<'a, T, const N: usize> DoubleEndedIterator for ArrayChunks<'a, T, N> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T; N]> {
+        self.iter.next_back()
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        self.iter.nth_back(n)
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<T, const N: usize> ExactSizeIterator for ArrayChunks<'_, T, N> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T, const N: usize> TrustedLen for ArrayChunks<'_, T, N> {}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<T, const N: usize> FusedIterator for ArrayChunks<'_, T, N> {}
+
+#[doc(hidden)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+unsafe impl<'a, T, const N: usize> TrustedRandomAccess for ArrayChunks<'a, T, N> {}
+
+#[doc(hidden)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+unsafe impl<'a, T, const N: usize> TrustedRandomAccessNoCoerce for ArrayChunks<'a, T, N> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) mutable chunks (`N` elements
+/// at a time), starting at the beginning of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last
+/// up to `N-1` elements will be omitted but can be retrieved from
+/// the [`into_remainder`] function from the iterator.
+///
+/// This struct is created by the [`array_chunks_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// #![feature(array_chunks)]
+///
+/// let mut slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.array_chunks_mut::<2>();
+/// ```
+///
+/// [`array_chunks_mut`]: slice::array_chunks_mut
+/// [`into_remainder`]: ../../std/slice/struct.ArrayChunksMut.html#method.into_remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ArrayChunksMut<'a, T: 'a, const N: usize> {
+    iter: IterMut<'a, [T; N]>,
+    rem: &'a mut [T],
+}
+
+impl<'a, T, const N: usize> ArrayChunksMut<'a, T, N> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T]) -> Self {
+        let (array_slice, rem) = slice.as_chunks_mut();
+        Self { iter: array_slice.iter_mut(), rem }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `N-1`
+    /// elements.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[unstable(feature = "array_chunks", issue = "74985")]
+    pub fn into_remainder(self) -> &'a mut [T] {
+        self.rem
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<'a, T, const N: usize> Iterator for ArrayChunksMut<'a, T, N> {
+    type Item = &'a mut [T; N];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T; N]> {
+        self.iter.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.iter.count()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.iter.nth(n)
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        self.iter.last()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> &'a mut [T; N] {
+        // SAFETY: The safety guarantees of `__iterator_get_unchecked` are transferred to
+        // the caller.
+        unsafe { self.iter.__iterator_get_unchecked(i) }
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<'a, T, const N: usize> DoubleEndedIterator for ArrayChunksMut<'a, T, N> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T; N]> {
+        self.iter.next_back()
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        self.iter.nth_back(n)
+    }
+}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<T, const N: usize> ExactSizeIterator for ArrayChunksMut<'_, T, N> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T, const N: usize> TrustedLen for ArrayChunksMut<'_, T, N> {}
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+impl<T, const N: usize> FusedIterator for ArrayChunksMut<'_, T, N> {}
+
+#[doc(hidden)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+unsafe impl<'a, T, const N: usize> TrustedRandomAccess for ArrayChunksMut<'a, T, N> {}
+
+#[doc(hidden)]
+#[unstable(feature = "array_chunks", issue = "74985")]
+unsafe impl<'a, T, const N: usize> TrustedRandomAccessNoCoerce for ArrayChunksMut<'a, T, N> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
+/// time), starting at the end of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last slice
+/// of the iteration will be the remainder.
+///
+/// This struct is created by the [`rchunks`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.rchunks(2);
+/// ```
+///
+/// [`rchunks`]: slice::rchunks
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rchunks", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RChunks<'a, T: 'a> {
+    v: &'a [T],
+    chunk_size: usize,
+}
+
+impl<'a, T: 'a> RChunks<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], size: usize) -> Self {
+        Self { v: slice, chunk_size: size }
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> Clone for RChunks<'_, T> {
+    fn clone(&self) -> Self {
+        RChunks { v: self.v, chunk_size: self.chunk_size }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> Iterator for RChunks<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let len = self.v.len();
+            let chunksz = cmp::min(len, self.chunk_size);
+            // SAFETY: split_at_unchecked just requires the argument be less
+            // than the length. This could only happen if the expression `len -
+            // chunksz` overflows. This could only happen if `chunksz > len`,
+            // which is impossible as we initialize it as the `min` of `len` and
+            // `self.chunk_size`.
+            let (fst, snd) = unsafe { self.v.split_at_unchecked(len - chunksz) };
+            self.v = fst;
+            Some(snd)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.v.is_empty() {
+            (0, Some(0))
+        } else {
+            let n = self.v.len() / self.chunk_size;
+            let rem = self.v.len() % self.chunk_size;
+            let n = if rem > 0 { n + 1 } else { n };
+            (n, Some(n))
+        }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = n.overflowing_mul(self.chunk_size);
+        if end >= self.v.len() || overflow {
+            self.v = &[];
+            None
+        } else {
+            // Can't underflow because of the check above
+            let end = self.v.len() - end;
+            let start = match end.checked_sub(self.chunk_size) {
+                Some(sum) => sum,
+                None => 0,
+            };
+            let nth = &self.v[start..end];
+            self.v = &self.v[0..start];
+            Some(nth)
+        }
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let rem = self.v.len() % self.chunk_size;
+            let end = if rem == 0 { self.chunk_size } else { rem };
+            Some(&self.v[0..end])
+        }
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let end = self.v.len() - idx * self.chunk_size;
+        let start = match end.checked_sub(self.chunk_size) {
+            None => 0,
+            Some(start) => start,
+        };
+        // SAFETY: mostly identical to `Chunks::__iterator_get_unchecked`.
+        unsafe { from_raw_parts(self.v.as_ptr().add(start), end - start) }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for RChunks<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let remainder = self.v.len() % self.chunk_size;
+            let chunksz = if remainder != 0 { remainder } else { self.chunk_size };
+            // SAFETY: similar to Chunks::next_back
+            let (fst, snd) = unsafe { self.v.split_at_unchecked(chunksz) };
+            self.v = snd;
+            Some(fst)
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &[];
+            None
+        } else {
+            // can't underflow because `n < len`
+            let offset_from_end = (len - 1 - n) * self.chunk_size;
+            let end = self.v.len() - offset_from_end;
+            let start = end.saturating_sub(self.chunk_size);
+            let nth_back = &self.v[start..end];
+            self.v = &self.v[end..];
+            Some(nth_back)
+        }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> ExactSizeIterator for RChunks<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for RChunks<'_, T> {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> FusedIterator for RChunks<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for RChunks<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunks<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) mutable chunks (`chunk_size`
+/// elements at a time), starting at the end of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last slice
+/// of the iteration will be the remainder.
+///
+/// This struct is created by the [`rchunks_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.rchunks_mut(2);
+/// ```
+///
+/// [`rchunks_mut`]: slice::rchunks_mut
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rchunks", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RChunksMut<'a, T: 'a> {
+    /// # Safety
+    /// This slice pointer must point at a valid region of `T` with at least length `v.len()`. Normally,
+    /// those requirements would mean that we could instead use a `&mut [T]` here, but we cannot
+    /// because `__iterator_get_unchecked` needs to return `&mut [T]`, which guarantees certain aliasing
+    /// properties that we cannot uphold if we hold on to the full original `&mut [T]`. Wrapping a raw
+    /// slice instead lets us hand out non-overlapping `&mut [T]` subslices of the slice we wrap.
+    v: *mut [T],
+    chunk_size: usize,
+    _marker: PhantomData<&'a mut T>,
+}
+
+impl<'a, T: 'a> RChunksMut<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], size: usize) -> Self {
+        Self { v: slice, chunk_size: size, _marker: PhantomData }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> Iterator for RChunksMut<'a, T> {
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let sz = cmp::min(self.v.len(), self.chunk_size);
+            let len = self.v.len();
+            // SAFETY: split_at_mut_unchecked just requires the argument be less
+            // than the length. This could only happen if the expression
+            // `len - sz` overflows. This could only happen if `sz >
+            // len`, which is impossible as we initialize it as the `min` of
+            // `self.v.len()` (e.g. `len`) and `self.chunk_size`.
+            let (head, tail) = unsafe { self.v.split_at_mut_unchecked(len - sz) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *tail })
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.v.is_empty() {
+            (0, Some(0))
+        } else {
+            let n = self.v.len() / self.chunk_size;
+            let rem = self.v.len() % self.chunk_size;
+            let n = if rem > 0 { n + 1 } else { n };
+            (n, Some(n))
+        }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<&'a mut [T]> {
+        let (end, overflow) = n.overflowing_mul(self.chunk_size);
+        if end >= self.v.len() || overflow {
+            self.v = &mut [];
+            None
+        } else {
+            // Can't underflow because of the check above
+            let end = self.v.len() - end;
+            let start = match end.checked_sub(self.chunk_size) {
+                Some(sum) => sum,
+                None => 0,
+            };
+            // SAFETY: This type ensures that self.v is a valid pointer with a correct len.
+            // Therefore the bounds check in split_at_mut guarantess the split point is inbounds.
+            let (head, tail) = unsafe { self.v.split_at_mut(start) };
+            // SAFETY: This type ensures that self.v is a valid pointer with a correct len.
+            // Therefore the bounds check in split_at_mut guarantess the split point is inbounds.
+            let (nth, _) = unsafe { tail.split_at_mut(end - start) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth })
+        }
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let rem = self.v.len() % self.chunk_size;
+            let end = if rem == 0 { self.chunk_size } else { rem };
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *self.v.get_unchecked_mut(0..end) })
+        }
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let end = self.v.len() - idx * self.chunk_size;
+        let start = match end.checked_sub(self.chunk_size) {
+            None => 0,
+            Some(start) => start,
+        };
+        // SAFETY: see comments for `RChunks::__iterator_get_unchecked` and
+        // `ChunksMut::__iterator_get_unchecked`, `self.v`.
+        unsafe { from_raw_parts_mut(self.v.as_mut_ptr().add(start), end - start) }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for RChunksMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.v.is_empty() {
+            None
+        } else {
+            let remainder = self.v.len() % self.chunk_size;
+            let sz = if remainder != 0 { remainder } else { self.chunk_size };
+            // SAFETY: Similar to `Chunks::next_back`
+            let (head, tail) = unsafe { self.v.split_at_mut_unchecked(sz) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *head })
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &mut [];
+            None
+        } else {
+            // can't underflow because `n < len`
+            let offset_from_end = (len - 1 - n) * self.chunk_size;
+            let end = self.v.len() - offset_from_end;
+            let start = end.saturating_sub(self.chunk_size);
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (tmp, tail) = unsafe { self.v.split_at_mut(end) };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (_, nth_back) = unsafe { tmp.split_at_mut(start) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth_back })
+        }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> ExactSizeIterator for RChunksMut<'_, T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for RChunksMut<'_, T> {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> FusedIterator for RChunksMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for RChunksMut<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunksMut<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+unsafe impl<T> Send for RChunksMut<'_, T> where T: Send {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+unsafe impl<T> Sync for RChunksMut<'_, T> where T: Sync {}
+
+/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
+/// time), starting at the end of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last
+/// up to `chunk_size-1` elements will be omitted but can be retrieved from
+/// the [`remainder`] function from the iterator.
+///
+/// This struct is created by the [`rchunks_exact`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.rchunks_exact(2);
+/// ```
+///
+/// [`rchunks_exact`]: slice::rchunks_exact
+/// [`remainder`]: ChunksExact::remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rchunks", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RChunksExact<'a, T: 'a> {
+    v: &'a [T],
+    rem: &'a [T],
+    chunk_size: usize,
+}
+
+impl<'a, T> RChunksExact<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a [T], chunk_size: usize) -> Self {
+        let rem = slice.len() % chunk_size;
+        // SAFETY: 0 <= rem <= slice.len() by construction above
+        let (fst, snd) = unsafe { slice.split_at_unchecked(rem) };
+        Self { v: snd, rem: fst, chunk_size }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `chunk_size-1`
+    /// elements.
+    #[must_use]
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    pub fn remainder(&self) -> &'a [T] {
+        self.rem
+    }
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> Clone for RChunksExact<'a, T> {
+    fn clone(&self) -> RChunksExact<'a, T> {
+        RChunksExact { v: self.v, rem: self.rem, chunk_size: self.chunk_size }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> Iterator for RChunksExact<'a, T> {
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            let (fst, snd) = self.v.split_at(self.v.len() - self.chunk_size);
+            self.v = fst;
+            Some(snd)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = self.v.len() / self.chunk_size;
+        (n, Some(n))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = n.overflowing_mul(self.chunk_size);
+        if end >= self.v.len() || overflow {
+            self.v = &[];
+            None
+        } else {
+            let (fst, _) = self.v.split_at(self.v.len() - end);
+            self.v = fst;
+            self.next()
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let end = self.v.len() - idx * self.chunk_size;
+        let start = end - self.chunk_size;
+        // SAFETY: mostly identical to `Chunks::__iterator_get_unchecked`.
+        unsafe { from_raw_parts(self.v.as_ptr().add(start), self.chunk_size) }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for RChunksExact<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            let (fst, snd) = self.v.split_at(self.chunk_size);
+            self.v = snd;
+            Some(fst)
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &[];
+            None
+        } else {
+            // now that we know that `n` corresponds to a chunk,
+            // none of these operations can underflow/overflow
+            let offset = (len - n) * self.chunk_size;
+            let start = self.v.len() - offset;
+            let end = start + self.chunk_size;
+            let nth_back = &self.v[start..end];
+            self.v = &self.v[end..];
+            Some(nth_back)
+        }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> ExactSizeIterator for RChunksExact<'a, T> {
+    fn is_empty(&self) -> bool {
+        self.v.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for RChunksExact<'_, T> {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> FusedIterator for RChunksExact<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for RChunksExact<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunksExact<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over a slice in (non-overlapping) mutable chunks (`chunk_size`
+/// elements at a time), starting at the end of the slice.
+///
+/// When the slice len is not evenly divided by the chunk size, the last up to
+/// `chunk_size-1` elements will be omitted but can be retrieved from the
+/// [`into_remainder`] function from the iterator.
+///
+/// This struct is created by the [`rchunks_exact_mut`] method on [slices].
+///
+/// # Example
+///
+/// ```
+/// let mut slice = ['l', 'o', 'r', 'e', 'm'];
+/// let iter = slice.rchunks_exact_mut(2);
+/// ```
+///
+/// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
+/// [`into_remainder`]: ChunksExactMut::into_remainder
+/// [slices]: slice
+#[derive(Debug)]
+#[stable(feature = "rchunks", since = "1.31.0")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct RChunksExactMut<'a, T: 'a> {
+    /// # Safety
+    /// This slice pointer must point at a valid region of `T` with at least length `v.len()`. Normally,
+    /// those requirements would mean that we could instead use a `&mut [T]` here, but we cannot
+    /// because `__iterator_get_unchecked` needs to return `&mut [T]`, which guarantees certain aliasing
+    /// properties that we cannot uphold if we hold on to the full original `&mut [T]`. Wrapping a raw
+    /// slice instead lets us hand out non-overlapping `&mut [T]` subslices of the slice we wrap.
+    v: *mut [T],
+    rem: &'a mut [T],
+    chunk_size: usize,
+}
+
+impl<'a, T> RChunksExactMut<'a, T> {
+    #[inline]
+    pub(super) fn new(slice: &'a mut [T], chunk_size: usize) -> Self {
+        let rem = slice.len() % chunk_size;
+        // SAFETY: 0 <= rem <= slice.len() by construction above
+        let (fst, snd) = unsafe { slice.split_at_mut_unchecked(rem) };
+        Self { v: snd, rem: fst, chunk_size }
+    }
+
+    /// Returns the remainder of the original slice that is not going to be
+    /// returned by the iterator. The returned slice has at most `chunk_size-1`
+    /// elements.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    pub fn into_remainder(self) -> &'a mut [T] {
+        self.rem
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> Iterator for RChunksExactMut<'a, T> {
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            let len = self.v.len();
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, tail) = unsafe { self.v.split_at_mut(len - self.chunk_size) };
+            self.v = head;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *tail })
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = self.v.len() / self.chunk_size;
+        (n, Some(n))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<&'a mut [T]> {
+        let (end, overflow) = n.overflowing_mul(self.chunk_size);
+        if end >= self.v.len() || overflow {
+            self.v = &mut [];
+            None
+        } else {
+            let len = self.v.len();
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (fst, _) = unsafe { self.v.split_at_mut(len - end) };
+            self.v = fst;
+            self.next()
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        let end = self.v.len() - idx * self.chunk_size;
+        let start = end - self.chunk_size;
+        // SAFETY: see comments for `RChunksMut::__iterator_get_unchecked` and `self.v`.
+        unsafe { from_raw_parts_mut(self.v.as_mut_ptr().add(start), self.chunk_size) }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<'a, T> DoubleEndedIterator for RChunksExactMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut [T]> {
+        if self.v.len() < self.chunk_size {
+            None
+        } else {
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (head, tail) = unsafe { self.v.split_at_mut(self.chunk_size) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *head })
+        }
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let len = self.len();
+        if n >= len {
+            self.v = &mut [];
+            None
+        } else {
+            // now that we know that `n` corresponds to a chunk,
+            // none of these operations can underflow/overflow
+            let offset = (len - n) * self.chunk_size;
+            let start = self.v.len() - offset;
+            let end = start + self.chunk_size;
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (tmp, tail) = unsafe { self.v.split_at_mut(end) };
+            // SAFETY: The self.v contract ensures that any split_at_mut is valid.
+            let (_, nth_back) = unsafe { tmp.split_at_mut(start) };
+            self.v = tail;
+            // SAFETY: Nothing else points to or will point to the contents of this slice.
+            Some(unsafe { &mut *nth_back })
+        }
+    }
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> ExactSizeIterator for RChunksExactMut<'_, T> {
+    fn is_empty(&self) -> bool {
+        self.v.is_empty()
+    }
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for RChunksExactMut<'_, T> {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+impl<T> FusedIterator for RChunksExactMut<'_, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for RChunksExactMut<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunksExactMut<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+unsafe impl<T> Send for RChunksExactMut<'_, T> where T: Send {}
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+unsafe impl<T> Sync for RChunksExactMut<'_, T> where T: Sync {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for Iter<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for Iter<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccess for IterMut<'a, T> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<'a, T> TrustedRandomAccessNoCoerce for IterMut<'a, T> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+/// An iterator over slice in (non-overlapping) chunks separated by a predicate.
+///
+/// This struct is created by the [`group_by`] method on [slices].
+///
+/// [`group_by`]: slice::group_by
+/// [slices]: slice
+#[unstable(feature = "slice_group_by", issue = "80552")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct GroupBy<'a, T: 'a, P> {
+    slice: &'a [T],
+    predicate: P,
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> GroupBy<'a, T, P> {
+    pub(super) fn new(slice: &'a [T], predicate: P) -> Self {
+        GroupBy { slice, predicate }
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> Iterator for GroupBy<'a, T, P>
+where
+    P: FnMut(&T, &T) -> bool,
+{
+    type Item = &'a [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.slice.is_empty() {
+            None
+        } else {
+            let mut len = 1;
+            let mut iter = self.slice.windows(2);
+            while let Some([l, r]) = iter.next() {
+                if (self.predicate)(l, r) { len += 1 } else { break }
+            }
+            let (head, tail) = self.slice.split_at(len);
+            self.slice = tail;
+            Some(head)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.slice.is_empty() { (0, Some(0)) } else { (1, Some(self.slice.len())) }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> DoubleEndedIterator for GroupBy<'a, T, P>
+where
+    P: FnMut(&T, &T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.slice.is_empty() {
+            None
+        } else {
+            let mut len = 1;
+            let mut iter = self.slice.windows(2);
+            while let Some([l, r]) = iter.next_back() {
+                if (self.predicate)(l, r) { len += 1 } else { break }
+            }
+            let (head, tail) = self.slice.split_at(self.slice.len() - len);
+            self.slice = head;
+            Some(tail)
+        }
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> FusedIterator for GroupBy<'a, T, P> where P: FnMut(&T, &T) -> bool {}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a + fmt::Debug, P> fmt::Debug for GroupBy<'a, T, P> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("GroupBy").field("slice", &self.slice).finish()
+    }
+}
+
+/// An iterator over slice in (non-overlapping) mutable chunks separated
+/// by a predicate.
+///
+/// This struct is created by the [`group_by_mut`] method on [slices].
+///
+/// [`group_by_mut`]: slice::group_by_mut
+/// [slices]: slice
+#[unstable(feature = "slice_group_by", issue = "80552")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct GroupByMut<'a, T: 'a, P> {
+    slice: &'a mut [T],
+    predicate: P,
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> GroupByMut<'a, T, P> {
+    pub(super) fn new(slice: &'a mut [T], predicate: P) -> Self {
+        GroupByMut { slice, predicate }
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> Iterator for GroupByMut<'a, T, P>
+where
+    P: FnMut(&T, &T) -> bool,
+{
+    type Item = &'a mut [T];
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.slice.is_empty() {
+            None
+        } else {
+            let mut len = 1;
+            let mut iter = self.slice.windows(2);
+            while let Some([l, r]) = iter.next() {
+                if (self.predicate)(l, r) { len += 1 } else { break }
+            }
+            let slice = mem::take(&mut self.slice);
+            let (head, tail) = slice.split_at_mut(len);
+            self.slice = tail;
+            Some(head)
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.slice.is_empty() { (0, Some(0)) } else { (1, Some(self.slice.len())) }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<Self::Item> {
+        self.next_back()
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> DoubleEndedIterator for GroupByMut<'a, T, P>
+where
+    P: FnMut(&T, &T) -> bool,
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.slice.is_empty() {
+            None
+        } else {
+            let mut len = 1;
+            let mut iter = self.slice.windows(2);
+            while let Some([l, r]) = iter.next_back() {
+                if (self.predicate)(l, r) { len += 1 } else { break }
+            }
+            let slice = mem::take(&mut self.slice);
+            let (head, tail) = slice.split_at_mut(slice.len() - len);
+            self.slice = head;
+            Some(tail)
+        }
+    }
+}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a, P> FusedIterator for GroupByMut<'a, T, P> where P: FnMut(&T, &T) -> bool {}
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+impl<'a, T: 'a + fmt::Debug, P> fmt::Debug for GroupByMut<'a, T, P> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("GroupByMut").field("slice", &self.slice).finish()
+    }
+}
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
new file mode 100644
index 000000000..c05242222
--- /dev/null
+++ b/library/core/src/slice/iter/macros.rs
@@ -0,0 +1,423 @@
+//! Macros used by iterators of slice.
+
+// Inlining is_empty and len makes a huge performance difference
+macro_rules! is_empty {
+    // The way we encode the length of a ZST iterator, this works both for ZST
+    // and non-ZST.
+    ($self: ident) => {
+        $self.ptr.as_ptr() as *const T == $self.end
+    };
+}
+
+// To get rid of some bounds checks (see `position`), we compute the length in a somewhat
+// unexpected way. (Tested by `codegen/slice-position-bounds-check`.)
+macro_rules! len {
+    ($self: ident) => {{
+        #![allow(unused_unsafe)] // we're sometimes used within an unsafe block
+
+        let start = $self.ptr;
+        let size = size_from_ptr(start.as_ptr());
+        if size == 0 {
+            // This _cannot_ use `unchecked_sub` because we depend on wrapping
+            // to represent the length of long ZST slice iterators.
+            $self.end.addr().wrapping_sub(start.as_ptr().addr())
+        } else {
+            // We know that `start <= end`, so can do better than `offset_from`,
+            // which needs to deal in signed.  By setting appropriate flags here
+            // we can tell LLVM this, which helps it remove bounds checks.
+            // SAFETY: By the type invariant, `start <= end`
+            let diff = unsafe { unchecked_sub($self.end.addr(), start.as_ptr().addr()) };
+            // By also telling LLVM that the pointers are apart by an exact
+            // multiple of the type size, it can optimize `len() == 0` down to
+            // `start == end` instead of `(end - start) < size`.
+            // SAFETY: By the type invariant, the pointers are aligned so the
+            //         distance between them must be a multiple of pointee size
+            unsafe { exact_div(diff, size) }
+        }
+    }};
+}
+
+// The shared definition of the `Iter` and `IterMut` iterators
+macro_rules! iterator {
+    (
+        struct $name:ident -> $ptr:ty,
+        $elem:ty,
+        $raw_mut:tt,
+        {$( $mut_:tt )?},
+        {$($extra:tt)*}
+    ) => {
+        // Returns the first element and moves the start of the iterator forwards by 1.
+        // Greatly improves performance compared to an inlined function. The iterator
+        // must not be empty.
+        macro_rules! next_unchecked {
+            ($self: ident) => {& $( $mut_ )? *$self.post_inc_start(1)}
+        }
+
+        // Returns the last element and moves the end of the iterator backwards by 1.
+        // Greatly improves performance compared to an inlined function. The iterator
+        // must not be empty.
+        macro_rules! next_back_unchecked {
+            ($self: ident) => {& $( $mut_ )? *$self.pre_dec_end(1)}
+        }
+
+        // Shrinks the iterator when T is a ZST, by moving the end of the iterator
+        // backwards by `n`. `n` must not exceed `self.len()`.
+        macro_rules! zst_shrink {
+            ($self: ident, $n: ident) => {
+                $self.end = ($self.end as * $raw_mut u8).wrapping_offset(-$n) as * $raw_mut T;
+            }
+        }
+
+        impl<'a, T> $name<'a, T> {
+            // Helper function for creating a slice from the iterator.
+            #[inline(always)]
+            fn make_slice(&self) -> &'a [T] {
+                // SAFETY: the iterator was created from a slice with pointer
+                // `self.ptr` and length `len!(self)`. This guarantees that all
+                // the prerequisites for `from_raw_parts` are fulfilled.
+                unsafe { from_raw_parts(self.ptr.as_ptr(), len!(self)) }
+            }
+
+            // Helper function for moving the start of the iterator forwards by `offset` elements,
+            // returning the old start.
+            // Unsafe because the offset must not exceed `self.len()`.
+            #[inline(always)]
+            unsafe fn post_inc_start(&mut self, offset: isize) -> * $raw_mut T {
+                if mem::size_of::<T>() == 0 {
+                    zst_shrink!(self, offset);
+                    self.ptr.as_ptr()
+                } else {
+                    let old = self.ptr.as_ptr();
+                    // SAFETY: the caller guarantees that `offset` doesn't exceed `self.len()`,
+                    // so this new pointer is inside `self` and thus guaranteed to be non-null.
+                    self.ptr = unsafe { NonNull::new_unchecked(self.ptr.as_ptr().offset(offset)) };
+                    old
+                }
+            }
+
+            // Helper function for moving the end of the iterator backwards by `offset` elements,
+            // returning the new end.
+            // Unsafe because the offset must not exceed `self.len()`.
+            #[inline(always)]
+            unsafe fn pre_dec_end(&mut self, offset: isize) -> * $raw_mut T {
+                if mem::size_of::<T>() == 0 {
+                    zst_shrink!(self, offset);
+                    self.ptr.as_ptr()
+                } else {
+                    // SAFETY: the caller guarantees that `offset` doesn't exceed `self.len()`,
+                    // which is guaranteed to not overflow an `isize`. Also, the resulting pointer
+                    // is in bounds of `slice`, which fulfills the other requirements for `offset`.
+                    self.end = unsafe { self.end.offset(-offset) };
+                    self.end
+                }
+            }
+        }
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<T> ExactSizeIterator for $name<'_, T> {
+            #[inline(always)]
+            fn len(&self) -> usize {
+                len!(self)
+            }
+
+            #[inline(always)]
+            fn is_empty(&self) -> bool {
+                is_empty!(self)
+            }
+        }
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, T> Iterator for $name<'a, T> {
+            type Item = $elem;
+
+            #[inline]
+            fn next(&mut self) -> Option<$elem> {
+                // could be implemented with slices, but this avoids bounds checks
+
+                // SAFETY: `assume` calls are safe since a slice's start pointer
+                // must be non-null, and slices over non-ZSTs must also have a
+                // non-null end pointer. The call to `next_unchecked!` is safe
+                // since we check if the iterator is empty first.
+                unsafe {
+                    assume(!self.ptr.as_ptr().is_null());
+                    if mem::size_of::<T>() != 0 {
+                        assume(!self.end.is_null());
+                    }
+                    if is_empty!(self) {
+                        None
+                    } else {
+                        Some(next_unchecked!(self))
+                    }
+                }
+            }
+
+            #[inline]
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                let exact = len!(self);
+                (exact, Some(exact))
+            }
+
+            #[inline]
+            fn count(self) -> usize {
+                len!(self)
+            }
+
+            #[inline]
+            fn nth(&mut self, n: usize) -> Option<$elem> {
+                if n >= len!(self) {
+                    // This iterator is now empty.
+                    if mem::size_of::<T>() == 0 {
+                        // We have to do it this way as `ptr` may never be 0, but `end`
+                        // could be (due to wrapping).
+                        self.end = self.ptr.as_ptr();
+                    } else {
+                        // SAFETY: end can't be 0 if T isn't ZST because ptr isn't 0 and end >= ptr
+                        unsafe {
+                            self.ptr = NonNull::new_unchecked(self.end as *mut T);
+                        }
+                    }
+                    return None;
+                }
+                // SAFETY: We are in bounds. `post_inc_start` does the right thing even for ZSTs.
+                unsafe {
+                    self.post_inc_start(n as isize);
+                    Some(next_unchecked!(self))
+                }
+            }
+
+            #[inline]
+            fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+                let advance = cmp::min(len!(self), n);
+                // SAFETY: By construction, `advance` does not exceed `self.len()`.
+                unsafe { self.post_inc_start(advance as isize) };
+                if advance == n { Ok(()) } else { Err(advance) }
+            }
+
+            #[inline]
+            fn last(mut self) -> Option<$elem> {
+                self.next_back()
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile.
+            #[inline]
+            fn for_each<F>(mut self, mut f: F)
+            where
+                Self: Sized,
+                F: FnMut(Self::Item),
+            {
+                while let Some(x) = self.next() {
+                    f(x);
+                }
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile.
+            #[inline]
+            fn all<F>(&mut self, mut f: F) -> bool
+            where
+                Self: Sized,
+                F: FnMut(Self::Item) -> bool,
+            {
+                while let Some(x) = self.next() {
+                    if !f(x) {
+                        return false;
+                    }
+                }
+                true
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile.
+            #[inline]
+            fn any<F>(&mut self, mut f: F) -> bool
+            where
+                Self: Sized,
+                F: FnMut(Self::Item) -> bool,
+            {
+                while let Some(x) = self.next() {
+                    if f(x) {
+                        return true;
+                    }
+                }
+                false
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile.
+            #[inline]
+            fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item>
+            where
+                Self: Sized,
+                P: FnMut(&Self::Item) -> bool,
+            {
+                while let Some(x) = self.next() {
+                    if predicate(&x) {
+                        return Some(x);
+                    }
+                }
+                None
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile.
+            #[inline]
+            fn find_map<B, F>(&mut self, mut f: F) -> Option<B>
+            where
+                Self: Sized,
+                F: FnMut(Self::Item) -> Option<B>,
+            {
+                while let Some(x) = self.next() {
+                    if let Some(y) = f(x) {
+                        return Some(y);
+                    }
+                }
+                None
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile. Also, the `assume` avoids a bounds check.
+            #[inline]
+            #[rustc_inherit_overflow_checks]
+            fn position<P>(&mut self, mut predicate: P) -> Option<usize> where
+                Self: Sized,
+                P: FnMut(Self::Item) -> bool,
+            {
+                let n = len!(self);
+                let mut i = 0;
+                while let Some(x) = self.next() {
+                    if predicate(x) {
+                        // SAFETY: we are guaranteed to be in bounds by the loop invariant:
+                        // when `i >= n`, `self.next()` returns `None` and the loop breaks.
+                        unsafe { assume(i < n) };
+                        return Some(i);
+                    }
+                    i += 1;
+                }
+                None
+            }
+
+            // We override the default implementation, which uses `try_fold`,
+            // because this simple implementation generates less LLVM IR and is
+            // faster to compile. Also, the `assume` avoids a bounds check.
+            #[inline]
+            fn rposition<P>(&mut self, mut predicate: P) -> Option<usize> where
+                P: FnMut(Self::Item) -> bool,
+                Self: Sized + ExactSizeIterator + DoubleEndedIterator
+            {
+                let n = len!(self);
+                let mut i = n;
+                while let Some(x) = self.next_back() {
+                    i -= 1;
+                    if predicate(x) {
+                        // SAFETY: `i` must be lower than `n` since it starts at `n`
+                        // and is only decreasing.
+                        unsafe { assume(i < n) };
+                        return Some(i);
+                    }
+                }
+                None
+            }
+
+            #[inline]
+            unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+                // SAFETY: the caller must guarantee that `i` is in bounds of
+                // the underlying slice, so `i` cannot overflow an `isize`, and
+                // the returned references is guaranteed to refer to an element
+                // of the slice and thus guaranteed to be valid.
+                //
+                // Also note that the caller also guarantees that we're never
+                // called with the same index again, and that no other methods
+                // that will access this subslice are called, so it is valid
+                // for the returned reference to be mutable in the case of
+                // `IterMut`
+                unsafe { & $( $mut_ )? * self.ptr.as_ptr().add(idx) }
+            }
+
+            $($extra)*
+        }
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, T> DoubleEndedIterator for $name<'a, T> {
+            #[inline]
+            fn next_back(&mut self) -> Option<$elem> {
+                // could be implemented with slices, but this avoids bounds checks
+
+                // SAFETY: `assume` calls are safe since a slice's start pointer must be non-null,
+                // and slices over non-ZSTs must also have a non-null end pointer.
+                // The call to `next_back_unchecked!` is safe since we check if the iterator is
+                // empty first.
+                unsafe {
+                    assume(!self.ptr.as_ptr().is_null());
+                    if mem::size_of::<T>() != 0 {
+                        assume(!self.end.is_null());
+                    }
+                    if is_empty!(self) {
+                        None
+                    } else {
+                        Some(next_back_unchecked!(self))
+                    }
+                }
+            }
+
+            #[inline]
+            fn nth_back(&mut self, n: usize) -> Option<$elem> {
+                if n >= len!(self) {
+                    // This iterator is now empty.
+                    self.end = self.ptr.as_ptr();
+                    return None;
+                }
+                // SAFETY: We are in bounds. `pre_dec_end` does the right thing even for ZSTs.
+                unsafe {
+                    self.pre_dec_end(n as isize);
+                    Some(next_back_unchecked!(self))
+                }
+            }
+
+            #[inline]
+            fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+                let advance = cmp::min(len!(self), n);
+                // SAFETY: By construction, `advance` does not exceed `self.len()`.
+                unsafe { self.pre_dec_end(advance as isize) };
+                if advance == n { Ok(()) } else { Err(advance) }
+            }
+        }
+
+        #[stable(feature = "fused", since = "1.26.0")]
+        impl<T> FusedIterator for $name<'_, T> {}
+
+        #[unstable(feature = "trusted_len", issue = "37572")]
+        unsafe impl<T> TrustedLen for $name<'_, T> {}
+    }
+}
+
+macro_rules! forward_iterator {
+    ($name:ident: $elem:ident, $iter_of:ty) => {
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, $elem, P> Iterator for $name<'a, $elem, P>
+        where
+            P: FnMut(&T) -> bool,
+        {
+            type Item = $iter_of;
+
+            #[inline]
+            fn next(&mut self) -> Option<$iter_of> {
+                self.inner.next()
+            }
+
+            #[inline]
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                self.inner.size_hint()
+            }
+        }
+
+        #[stable(feature = "fused", since = "1.26.0")]
+        impl<'a, $elem, P> FusedIterator for $name<'a, $elem, P> where P: FnMut(&T) -> bool {}
+    };
+}
diff --git a/library/core/src/slice/memchr.rs b/library/core/src/slice/memchr.rs
new file mode 100644
index 000000000..dffeaf6a8
--- /dev/null
+++ b/library/core/src/slice/memchr.rs
@@ -0,0 +1,142 @@
+// Original implementation taken from rust-memchr.
+// Copyright 2015 Andrew Gallant, bluss and Nicolas Koch
+
+use crate::cmp;
+use crate::mem;
+
+const LO_USIZE: usize = usize::repeat_u8(0x01);
+const HI_USIZE: usize = usize::repeat_u8(0x80);
+const USIZE_BYTES: usize = mem::size_of::<usize>();
+
+/// Returns `true` if `x` contains any zero byte.
+///
+/// From *Matters Computational*, J. Arndt:
+///
+/// "The idea is to subtract one from each of the bytes and then look for
+/// bytes where the borrow propagated all the way to the most significant
+/// bit."
+#[inline]
+fn contains_zero_byte(x: usize) -> bool {
+    x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
+}
+
+#[cfg(target_pointer_width = "16")]
+#[inline]
+fn repeat_byte(b: u8) -> usize {
+    (b as usize) << 8 | b as usize
+}
+
+#[cfg(not(target_pointer_width = "16"))]
+#[inline]
+fn repeat_byte(b: u8) -> usize {
+    (b as usize) * (usize::MAX / 255)
+}
+
+/// Returns the first index matching the byte `x` in `text`.
+#[must_use]
+#[inline]
+pub fn memchr(x: u8, text: &[u8]) -> Option<usize> {
+    // Fast path for small slices
+    if text.len() < 2 * USIZE_BYTES {
+        return text.iter().position(|elt| *elt == x);
+    }
+
+    memchr_general_case(x, text)
+}
+
+fn memchr_general_case(x: u8, text: &[u8]) -> Option<usize> {
+    // Scan for a single byte value by reading two `usize` words at a time.
+    //
+    // Split `text` in three parts
+    // - unaligned initial part, before the first word aligned address in text
+    // - body, scan by 2 words at a time
+    // - the last remaining part, < 2 word size
+
+    // search up to an aligned boundary
+    let len = text.len();
+    let ptr = text.as_ptr();
+    let mut offset = ptr.align_offset(USIZE_BYTES);
+
+    if offset > 0 {
+        offset = cmp::min(offset, len);
+        if let Some(index) = text[..offset].iter().position(|elt| *elt == x) {
+            return Some(index);
+        }
+    }
+
+    // search the body of the text
+    let repeated_x = repeat_byte(x);
+    while offset <= len - 2 * USIZE_BYTES {
+        // SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes
+        // between the offset and the end of the slice.
+        unsafe {
+            let u = *(ptr.add(offset) as *const usize);
+            let v = *(ptr.add(offset + USIZE_BYTES) as *const usize);
+
+            // break if there is a matching byte
+            let zu = contains_zero_byte(u ^ repeated_x);
+            let zv = contains_zero_byte(v ^ repeated_x);
+            if zu || zv {
+                break;
+            }
+        }
+        offset += USIZE_BYTES * 2;
+    }
+
+    // Find the byte after the point the body loop stopped.
+    text[offset..].iter().position(|elt| *elt == x).map(|i| offset + i)
+}
+
+/// Returns the last index matching the byte `x` in `text`.
+#[must_use]
+pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
+    // Scan for a single byte value by reading two `usize` words at a time.
+    //
+    // Split `text` in three parts:
+    // - unaligned tail, after the last word aligned address in text,
+    // - body, scanned by 2 words at a time,
+    // - the first remaining bytes, < 2 word size.
+    let len = text.len();
+    let ptr = text.as_ptr();
+    type Chunk = usize;
+
+    let (min_aligned_offset, max_aligned_offset) = {
+        // We call this just to obtain the length of the prefix and suffix.
+        // In the middle we always process two chunks at once.
+        // SAFETY: transmuting `[u8]` to `[usize]` is safe except for size differences
+        // which are handled by `align_to`.
+        let (prefix, _, suffix) = unsafe { text.align_to::<(Chunk, Chunk)>() };
+        (prefix.len(), len - suffix.len())
+    };
+
+    let mut offset = max_aligned_offset;
+    if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
+        return Some(offset + index);
+    }
+
+    // Search the body of the text, make sure we don't cross min_aligned_offset.
+    // offset is always aligned, so just testing `>` is sufficient and avoids possible
+    // overflow.
+    let repeated_x = repeat_byte(x);
+    let chunk_bytes = mem::size_of::<Chunk>();
+
+    while offset > min_aligned_offset {
+        // SAFETY: offset starts at len - suffix.len(), as long as it is greater than
+        // min_aligned_offset (prefix.len()) the remaining distance is at least 2 * chunk_bytes.
+        unsafe {
+            let u = *(ptr.offset(offset as isize - 2 * chunk_bytes as isize) as *const Chunk);
+            let v = *(ptr.offset(offset as isize - chunk_bytes as isize) as *const Chunk);
+
+            // Break if there is a matching byte.
+            let zu = contains_zero_byte(u ^ repeated_x);
+            let zv = contains_zero_byte(v ^ repeated_x);
+            if zu || zv {
+                break;
+            }
+        }
+        offset -= 2 * chunk_bytes;
+    }
+
+    // Find the byte before the point the body loop stopped.
+    text[..offset].iter().rposition(|elt| *elt == x)
+}
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
new file mode 100644
index 000000000..e6ca6ef82
--- /dev/null
+++ b/library/core/src/slice/mod.rs
@@ -0,0 +1,4244 @@
+//! Slice management and manipulation.
+//!
+//! For more details see [`std::slice`].
+//!
+//! [`std::slice`]: ../../std/slice/index.html
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use crate::cmp::Ordering::{self, Greater, Less};
+use crate::intrinsics::{assert_unsafe_precondition, exact_div};
+use crate::marker::Copy;
+use crate::mem;
+use crate::num::NonZeroUsize;
+use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
+use crate::option::Option;
+use crate::option::Option::{None, Some};
+use crate::ptr;
+use crate::result::Result;
+use crate::result::Result::{Err, Ok};
+use crate::simd::{self, Simd};
+use crate::slice;
+
+#[unstable(
+    feature = "slice_internals",
+    issue = "none",
+    reason = "exposed from core to be reused in std; use the memchr crate"
+)]
+/// Pure rust memchr implementation, taken from rust-memchr
+pub mod memchr;
+
+mod ascii;
+mod cmp;
+mod index;
+mod iter;
+mod raw;
+mod rotate;
+mod sort;
+mod specialize;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use iter::{Chunks, ChunksMut, Windows};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use iter::{Iter, IterMut};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use iter::{RSplitN, RSplitNMut, Split, SplitMut, SplitN, SplitNMut};
+
+#[stable(feature = "slice_rsplit", since = "1.27.0")]
+pub use iter::{RSplit, RSplitMut};
+
+#[stable(feature = "chunks_exact", since = "1.31.0")]
+pub use iter::{ChunksExact, ChunksExactMut};
+
+#[stable(feature = "rchunks", since = "1.31.0")]
+pub use iter::{RChunks, RChunksExact, RChunksExactMut, RChunksMut};
+
+#[unstable(feature = "array_chunks", issue = "74985")]
+pub use iter::{ArrayChunks, ArrayChunksMut};
+
+#[unstable(feature = "array_windows", issue = "75027")]
+pub use iter::ArrayWindows;
+
+#[unstable(feature = "slice_group_by", issue = "80552")]
+pub use iter::{GroupBy, GroupByMut};
+
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+pub use iter::{SplitInclusive, SplitInclusiveMut};
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use raw::{from_raw_parts, from_raw_parts_mut};
+
+#[stable(feature = "from_ref", since = "1.28.0")]
+pub use raw::{from_mut, from_ref};
+
+#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
+pub use raw::{from_mut_ptr_range, from_ptr_range};
+
+// This function is public only because there is no other way to unit test heapsort.
+#[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
+pub use sort::heapsort;
+
+#[stable(feature = "slice_get_slice", since = "1.28.0")]
+pub use index::SliceIndex;
+
+#[unstable(feature = "slice_range", issue = "76393")]
+pub use index::range;
+
+#[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
+pub use ascii::EscapeAscii;
+
+/// Calculates the direction and split point of a one-sided range.
+///
+/// This is a helper function for `take` and `take_mut` that returns
+/// the direction of the split (front or back) as well as the index at
+/// which to split. Returns `None` if the split index would overflow.
+#[inline]
+fn split_point_of(range: impl OneSidedRange<usize>) -> Option<(Direction, usize)> {
+    use Bound::*;
+
+    Some(match (range.start_bound(), range.end_bound()) {
+        (Unbounded, Excluded(i)) => (Direction::Front, *i),
+        (Unbounded, Included(i)) => (Direction::Front, i.checked_add(1)?),
+        (Excluded(i), Unbounded) => (Direction::Back, i.checked_add(1)?),
+        (Included(i), Unbounded) => (Direction::Back, *i),
+        _ => unreachable!(),
+    })
+}
+
+enum Direction {
+    Front,
+    Back,
+}
+
+#[cfg(not(test))]
+impl<T> [T] {
+    /// Returns the number of elements in the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.len(), 3);
+    /// ```
+    #[lang = "slice_len_fn"]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+    #[inline]
+    #[must_use]
+    // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
+    pub const fn len(&self) -> usize {
+        // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
+        // As of this writing this causes a "Const-stable functions can only call other
+        // const-stable functions" error.
+
+        // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
+        // and PtrComponents<T> have the same memory layouts. Only std can make this
+        // guarantee.
+        unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
+    }
+
+    /// Returns `true` if the slice has a length of 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert!(!a.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
+    #[inline]
+    #[must_use]
+    pub const fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Returns the first element of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert_eq!(Some(&10), v.first());
+    ///
+    /// let w: &[i32] = &[];
+    /// assert_eq!(None, w.first());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
+    #[inline]
+    #[must_use]
+    pub const fn first(&self) -> Option<&T> {
+        if let [first, ..] = self { Some(first) } else { None }
+    }
+
+    /// Returns a mutable pointer to the first element of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some(first) = x.first_mut() {
+    ///     *first = 5;
+    /// }
+    /// assert_eq!(x, &[5, 1, 2]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
+    #[inline]
+    #[must_use]
+    pub const fn first_mut(&mut self) -> Option<&mut T> {
+        if let [first, ..] = self { Some(first) } else { None }
+    }
+
+    /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &[0, 1, 2];
+    ///
+    /// if let Some((first, elements)) = x.split_first() {
+    ///     assert_eq!(first, &0);
+    ///     assert_eq!(elements, &[1, 2]);
+    /// }
+    /// ```
+    #[stable(feature = "slice_splits", since = "1.5.0")]
+    #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
+    #[inline]
+    #[must_use]
+    pub const fn split_first(&self) -> Option<(&T, &[T])> {
+        if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
+    }
+
+    /// Returns the first and all the rest of the elements of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some((first, elements)) = x.split_first_mut() {
+    ///     *first = 3;
+    ///     elements[0] = 4;
+    ///     elements[1] = 5;
+    /// }
+    /// assert_eq!(x, &[3, 4, 5]);
+    /// ```
+    #[stable(feature = "slice_splits", since = "1.5.0")]
+    #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
+    #[inline]
+    #[must_use]
+    pub const fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
+        if let [first, tail @ ..] = self { Some((first, tail)) } else { None }
+    }
+
+    /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &[0, 1, 2];
+    ///
+    /// if let Some((last, elements)) = x.split_last() {
+    ///     assert_eq!(last, &2);
+    ///     assert_eq!(elements, &[0, 1]);
+    /// }
+    /// ```
+    #[stable(feature = "slice_splits", since = "1.5.0")]
+    #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
+    #[inline]
+    #[must_use]
+    pub const fn split_last(&self) -> Option<(&T, &[T])> {
+        if let [init @ .., last] = self { Some((last, init)) } else { None }
+    }
+
+    /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some((last, elements)) = x.split_last_mut() {
+    ///     *last = 3;
+    ///     elements[0] = 4;
+    ///     elements[1] = 5;
+    /// }
+    /// assert_eq!(x, &[4, 5, 3]);
+    /// ```
+    #[stable(feature = "slice_splits", since = "1.5.0")]
+    #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
+    #[inline]
+    #[must_use]
+    pub const fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
+        if let [init @ .., last] = self { Some((last, init)) } else { None }
+    }
+
+    /// Returns the last element of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert_eq!(Some(&30), v.last());
+    ///
+    /// let w: &[i32] = &[];
+    /// assert_eq!(None, w.last());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_slice_first_last_not_mut", since = "1.56.0")]
+    #[inline]
+    #[must_use]
+    pub const fn last(&self) -> Option<&T> {
+        if let [.., last] = self { Some(last) } else { None }
+    }
+
+    /// Returns a mutable pointer to the last item in the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some(last) = x.last_mut() {
+    ///     *last = 10;
+    /// }
+    /// assert_eq!(x, &[0, 1, 10]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_first_last", issue = "83570")]
+    #[inline]
+    #[must_use]
+    pub const fn last_mut(&mut self) -> Option<&mut T> {
+        if let [.., last] = self { Some(last) } else { None }
+    }
+
+    /// Returns a reference to an element or subslice depending on the type of
+    /// index.
+    ///
+    /// - If given a position, returns a reference to the element at that
+    ///   position or `None` if out of bounds.
+    /// - If given a range, returns the subslice corresponding to that range,
+    ///   or `None` if out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert_eq!(Some(&40), v.get(1));
+    /// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
+    /// assert_eq!(None, v.get(3));
+    /// assert_eq!(None, v.get(0..4));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+    #[inline]
+    #[must_use]
+    pub const fn get<I>(&self, index: I) -> Option<&I::Output>
+    where
+        I: ~const SliceIndex<Self>,
+    {
+        index.get(self)
+    }
+
+    /// Returns a mutable reference to an element or subslice depending on the
+    /// type of index (see [`get`]) or `None` if the index is out of bounds.
+    ///
+    /// [`get`]: slice::get
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some(elem) = x.get_mut(1) {
+    ///     *elem = 42;
+    /// }
+    /// assert_eq!(x, &[0, 42, 2]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+    #[inline]
+    #[must_use]
+    pub const fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
+    where
+        I: ~const SliceIndex<Self>,
+    {
+        index.get_mut(self)
+    }
+
+    /// Returns a reference to an element or subslice, without doing bounds
+    /// checking.
+    ///
+    /// For a safe alternative see [`get`].
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with an out-of-bounds index is *[undefined behavior]*
+    /// even if the resulting reference is not used.
+    ///
+    /// [`get`]: slice::get
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &[1, 2, 4];
+    ///
+    /// unsafe {
+    ///     assert_eq!(x.get_unchecked(1), &2);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+    #[inline]
+    #[must_use]
+    pub const unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
+    where
+        I: ~const SliceIndex<Self>,
+    {
+        // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
+        // the slice is dereferenceable because `self` is a safe reference.
+        // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
+        unsafe { &*index.get_unchecked(self) }
+    }
+
+    /// Returns a mutable reference to an element or subslice, without doing
+    /// bounds checking.
+    ///
+    /// For a safe alternative see [`get_mut`].
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with an out-of-bounds index is *[undefined behavior]*
+    /// even if the resulting reference is not used.
+    ///
+    /// [`get_mut`]: slice::get_mut
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [1, 2, 4];
+    ///
+    /// unsafe {
+    ///     let elem = x.get_unchecked_mut(1);
+    ///     *elem = 13;
+    /// }
+    /// assert_eq!(x, &[1, 13, 4]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
+    #[inline]
+    #[must_use]
+    pub const unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
+    where
+        I: ~const SliceIndex<Self>,
+    {
+        // SAFETY: the caller must uphold the safety requirements for `get_unchecked_mut`;
+        // the slice is dereferenceable because `self` is a safe reference.
+        // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
+        unsafe { &mut *index.get_unchecked_mut(self) }
+    }
+
+    /// Returns a raw pointer to the slice's buffer.
+    ///
+    /// The caller must ensure that the slice outlives the pointer this
+    /// function returns, or else it will end up pointing to garbage.
+    ///
+    /// The caller must also ensure that the memory the pointer (non-transitively) points to
+    /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
+    /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
+    ///
+    /// Modifying the container referenced by this slice may cause its buffer
+    /// to be reallocated, which would also make any pointers to it invalid.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &[1, 2, 4];
+    /// let x_ptr = x.as_ptr();
+    ///
+    /// unsafe {
+    ///     for i in 0..x.len() {
+    ///         assert_eq!(x.get_unchecked(i), &*x_ptr.add(i));
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`as_mut_ptr`]: slice::as_mut_ptr
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_slice_as_ptr", since = "1.32.0")]
+    #[inline]
+    #[must_use]
+    pub const fn as_ptr(&self) -> *const T {
+        self as *const [T] as *const T
+    }
+
+    /// Returns an unsafe mutable pointer to the slice's buffer.
+    ///
+    /// The caller must ensure that the slice outlives the pointer this
+    /// function returns, or else it will end up pointing to garbage.
+    ///
+    /// Modifying the container referenced by this slice may cause its buffer
+    /// to be reallocated, which would also make any pointers to it invalid.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [1, 2, 4];
+    /// let x_ptr = x.as_mut_ptr();
+    ///
+    /// unsafe {
+    ///     for i in 0..x.len() {
+    ///         *x_ptr.add(i) += 2;
+    ///     }
+    /// }
+    /// assert_eq!(x, &[3, 4, 6]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
+    #[rustc_allow_const_fn_unstable(const_mut_refs)]
+    #[inline]
+    #[must_use]
+    pub const fn as_mut_ptr(&mut self) -> *mut T {
+        self as *mut [T] as *mut T
+    }
+
+    /// Returns the two raw pointers spanning the slice.
+    ///
+    /// The returned range is half-open, which means that the end pointer
+    /// points *one past* the last element of the slice. This way, an empty
+    /// slice is represented by two equal pointers, and the difference between
+    /// the two pointers represents the size of the slice.
+    ///
+    /// See [`as_ptr`] for warnings on using these pointers. The end pointer
+    /// requires extra caution, as it does not point to a valid element in the
+    /// slice.
+    ///
+    /// This function is useful for interacting with foreign interfaces which
+    /// use two pointers to refer to a range of elements in memory, as is
+    /// common in C++.
+    ///
+    /// It can also be useful to check if a pointer to an element refers to an
+    /// element of this slice:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// let x = &a[1] as *const _;
+    /// let y = &5 as *const _;
+    ///
+    /// assert!(a.as_ptr_range().contains(&x));
+    /// assert!(!a.as_ptr_range().contains(&y));
+    /// ```
+    ///
+    /// [`as_ptr`]: slice::as_ptr
+    #[stable(feature = "slice_ptr_range", since = "1.48.0")]
+    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
+    #[inline]
+    #[must_use]
+    pub const fn as_ptr_range(&self) -> Range<*const T> {
+        let start = self.as_ptr();
+        // SAFETY: The `add` here is safe, because:
+        //
+        //   - Both pointers are part of the same object, as pointing directly
+        //     past the object also counts.
+        //
+        //   - The size of the slice is never larger than isize::MAX bytes, as
+        //     noted here:
+        //       - https://github.com/rust-lang/unsafe-code-guidelines/issues/102#issuecomment-473340447
+        //       - https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+        //       - https://doc.rust-lang.org/core/slice/fn.from_raw_parts.html#safety
+        //     (This doesn't seem normative yet, but the very same assumption is
+        //     made in many places, including the Index implementation of slices.)
+        //
+        //   - There is no wrapping around involved, as slices do not wrap past
+        //     the end of the address space.
+        //
+        // See the documentation of pointer::add.
+        let end = unsafe { start.add(self.len()) };
+        start..end
+    }
+
+    /// Returns the two unsafe mutable pointers spanning the slice.
+    ///
+    /// The returned range is half-open, which means that the end pointer
+    /// points *one past* the last element of the slice. This way, an empty
+    /// slice is represented by two equal pointers, and the difference between
+    /// the two pointers represents the size of the slice.
+    ///
+    /// See [`as_mut_ptr`] for warnings on using these pointers. The end
+    /// pointer requires extra caution, as it does not point to a valid element
+    /// in the slice.
+    ///
+    /// This function is useful for interacting with foreign interfaces which
+    /// use two pointers to refer to a range of elements in memory, as is
+    /// common in C++.
+    ///
+    /// [`as_mut_ptr`]: slice::as_mut_ptr
+    #[stable(feature = "slice_ptr_range", since = "1.48.0")]
+    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
+    #[rustc_allow_const_fn_unstable(const_mut_refs)]
+    #[inline]
+    #[must_use]
+    pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {
+        let start = self.as_mut_ptr();
+        // SAFETY: See as_ptr_range() above for why `add` here is safe.
+        let end = unsafe { start.add(self.len()) };
+        start..end
+    }
+
+    /// Swaps two elements in the slice.
+    ///
+    /// # Arguments
+    ///
+    /// * a - The index of the first element
+    /// * b - The index of the second element
+    ///
+    /// # Panics
+    ///
+    /// Panics if `a` or `b` are out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = ["a", "b", "c", "d", "e"];
+    /// v.swap(2, 4);
+    /// assert!(v == ["a", "b", "e", "d", "c"]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
+    #[inline]
+    #[track_caller]
+    pub const fn swap(&mut self, a: usize, b: usize) {
+        // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
+        // Can't take two mutable loans from one vector, so instead use raw pointers.
+        let pa = ptr::addr_of_mut!(self[a]);
+        let pb = ptr::addr_of_mut!(self[b]);
+        // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
+        // to elements in the slice and therefore are guaranteed to be valid and aligned.
+        // Note that accessing the elements behind `a` and `b` is checked and will
+        // panic when out of bounds.
+        unsafe {
+            ptr::swap(pa, pb);
+        }
+    }
+
+    /// Swaps two elements in the slice, without doing bounds checking.
+    ///
+    /// For a safe alternative see [`swap`].
+    ///
+    /// # Arguments
+    ///
+    /// * a - The index of the first element
+    /// * b - The index of the second element
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with an out-of-bounds index is *[undefined behavior]*.
+    /// The caller has to ensure that `a < self.len()` and `b < self.len()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_swap_unchecked)]
+    ///
+    /// let mut v = ["a", "b", "c", "d"];
+    /// // SAFETY: we know that 1 and 3 are both indices of the slice
+    /// unsafe { v.swap_unchecked(1, 3) };
+    /// assert!(v == ["a", "d", "c", "b"]);
+    /// ```
+    ///
+    /// [`swap`]: slice::swap
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    #[unstable(feature = "slice_swap_unchecked", issue = "88539")]
+    #[rustc_const_unstable(feature = "const_swap", issue = "83163")]
+    pub const unsafe fn swap_unchecked(&mut self, a: usize, b: usize) {
+        let ptr = self.as_mut_ptr();
+        // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
+        unsafe {
+            assert_unsafe_precondition!(a < self.len() && b < self.len());
+            ptr::swap(ptr.add(a), ptr.add(b));
+        }
+    }
+
+    /// Reverses the order of elements in the slice, in place.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [1, 2, 3];
+    /// v.reverse();
+    /// assert!(v == [3, 2, 1]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn reverse(&mut self) {
+        let half_len = self.len() / 2;
+        let Range { start, end } = self.as_mut_ptr_range();
+
+        // These slices will skip the middle item for an odd length,
+        // since that one doesn't need to move.
+        let (front_half, back_half) =
+            // SAFETY: Both are subparts of the original slice, so the memory
+            // range is valid, and they don't overlap because they're each only
+            // half (or less) of the original slice.
+            unsafe {
+                (
+                    slice::from_raw_parts_mut(start, half_len),
+                    slice::from_raw_parts_mut(end.sub(half_len), half_len),
+                )
+            };
+
+        // Introducing a function boundary here means that the two halves
+        // get `noalias` markers, allowing better optimization as LLVM
+        // knows that they're disjoint, unlike in the original slice.
+        revswap(front_half, back_half, half_len);
+
+        #[inline]
+        fn revswap<T>(a: &mut [T], b: &mut [T], n: usize) {
+            debug_assert_eq!(a.len(), n);
+            debug_assert_eq!(b.len(), n);
+
+            // Because this function is first compiled in isolation,
+            // this check tells LLVM that the indexing below is
+            // in-bounds.  Then after inlining -- once the actual
+            // lengths of the slices are known -- it's removed.
+            let (a, b) = (&mut a[..n], &mut b[..n]);
+
+            for i in 0..n {
+                mem::swap(&mut a[i], &mut b[n - 1 - i]);
+            }
+        }
+    }
+
+    /// Returns an iterator over the slice.
+    ///
+    /// The iterator yields all items from start to end.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &[1, 2, 4];
+    /// let mut iterator = x.iter();
+    ///
+    /// assert_eq!(iterator.next(), Some(&1));
+    /// assert_eq!(iterator.next(), Some(&2));
+    /// assert_eq!(iterator.next(), Some(&4));
+    /// assert_eq!(iterator.next(), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn iter(&self) -> Iter<'_, T> {
+        Iter::new(self)
+    }
+
+    /// Returns an iterator that allows modifying each value.
+    ///
+    /// The iterator yields all items from start to end.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = &mut [1, 2, 4];
+    /// for elem in x.iter_mut() {
+    ///     *elem += 2;
+    /// }
+    /// assert_eq!(x, &[3, 4, 6]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn iter_mut(&mut self) -> IterMut<'_, T> {
+        IterMut::new(self)
+    }
+
+    /// Returns an iterator over all contiguous windows of length
+    /// `size`. The windows overlap. If the slice is shorter than
+    /// `size`, the iterator returns no values.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = ['r', 'u', 's', 't'];
+    /// let mut iter = slice.windows(2);
+    /// assert_eq!(iter.next().unwrap(), &['r', 'u']);
+    /// assert_eq!(iter.next().unwrap(), &['u', 's']);
+    /// assert_eq!(iter.next().unwrap(), &['s', 't']);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// If the slice is shorter than `size`:
+    ///
+    /// ```
+    /// let slice = ['f', 'o', 'o'];
+    /// let mut iter = slice.windows(4);
+    /// assert!(iter.next().is_none());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn windows(&self, size: usize) -> Windows<'_, T> {
+        let size = NonZeroUsize::new(size).expect("size is zero");
+        Windows::new(self, size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
+    /// slice, then the last chunk will not have length `chunk_size`.
+    ///
+    /// See [`chunks_exact`] for a variant of this iterator that returns chunks of always exactly
+    /// `chunk_size` elements, and [`rchunks`] for the same iterator but starting at the end of the
+    /// slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let mut iter = slice.chunks(2);
+    /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
+    /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
+    /// assert_eq!(iter.next().unwrap(), &['m']);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// [`chunks_exact`]: slice::chunks_exact
+    /// [`rchunks`]: slice::rchunks
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
+        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        Chunks::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
+    /// length of the slice, then the last chunk will not have length `chunk_size`.
+    ///
+    /// See [`chunks_exact_mut`] for a variant of this iterator that returns chunks of always
+    /// exactly `chunk_size` elements, and [`rchunks_mut`] for the same iterator but starting at
+    /// the end of the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// for chunk in v.chunks_mut(2) {
+    ///     for elem in chunk.iter_mut() {
+    ///         *elem += count;
+    ///     }
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[1, 1, 2, 2, 3]);
+    /// ```
+    ///
+    /// [`chunks_exact_mut`]: slice::chunks_exact_mut
+    /// [`rchunks_mut`]: slice::rchunks_mut
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
+        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        ChunksMut::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
+    /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
+    /// from the `remainder` function of the iterator.
+    ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
+    /// resulting code better than in the case of [`chunks`].
+    ///
+    /// See [`chunks`] for a variant of this iterator that also returns the remainder as a smaller
+    /// chunk, and [`rchunks_exact`] for the same iterator but starting at the end of the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let mut iter = slice.chunks_exact(2);
+    /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
+    /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
+    /// assert!(iter.next().is_none());
+    /// assert_eq!(iter.remainder(), &['m']);
+    /// ```
+    ///
+    /// [`chunks`]: slice::chunks
+    /// [`rchunks_exact`]: slice::rchunks_exact
+    #[stable(feature = "chunks_exact", since = "1.31.0")]
+    #[inline]
+    pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
+        assert_ne!(chunk_size, 0);
+        ChunksExact::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
+    /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
+    /// retrieved from the `into_remainder` function of the iterator.
+    ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
+    /// resulting code better than in the case of [`chunks_mut`].
+    ///
+    /// See [`chunks_mut`] for a variant of this iterator that also returns the remainder as a
+    /// smaller chunk, and [`rchunks_exact_mut`] for the same iterator but starting at the end of
+    /// the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// for chunk in v.chunks_exact_mut(2) {
+    ///     for elem in chunk.iter_mut() {
+    ///         *elem += count;
+    ///     }
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[1, 1, 2, 2, 0]);
+    /// ```
+    ///
+    /// [`chunks_mut`]: slice::chunks_mut
+    /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
+    #[stable(feature = "chunks_exact", since = "1.31.0")]
+    #[inline]
+    pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
+        assert_ne!(chunk_size, 0);
+        ChunksExactMut::new(self, chunk_size)
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// assuming that there's no remainder.
+    ///
+    /// # Safety
+    ///
+    /// This may only be called when
+    /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
+    /// - `N != 0`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
+    /// let chunks: &[[char; 1]] =
+    ///     // SAFETY: 1-element chunks never have remainder
+    ///     unsafe { slice.as_chunks_unchecked() };
+    /// assert_eq!(chunks, &[['l'], ['o'], ['r'], ['e'], ['m'], ['!']]);
+    /// let chunks: &[[char; 3]] =
+    ///     // SAFETY: The slice length (6) is a multiple of 3
+    ///     unsafe { slice.as_chunks_unchecked() };
+    /// assert_eq!(chunks, &[['l', 'o', 'r'], ['e', 'm', '!']]);
+    ///
+    /// // These would be unsound:
+    /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
+    /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
+        // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
+        let new_len = unsafe {
+            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
+            exact_div(self.len(), N)
+        };
+        // SAFETY: We cast a slice of `new_len * N` elements into
+        // a slice of `new_len` many `N` elements chunks.
+        unsafe { from_raw_parts(self.as_ptr().cast(), new_len) }
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// starting at the beginning of the slice,
+    /// and a remainder slice with length strictly less than `N`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let (chunks, remainder) = slice.as_chunks();
+    /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
+    /// assert_eq!(remainder, &['m']);
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
+        assert_ne!(N, 0);
+        let len = self.len() / N;
+        let (multiple_of_n, remainder) = self.split_at(len * N);
+        // SAFETY: We already panicked for zero, and ensured by construction
+        // that the length of the subslice is a multiple of N.
+        let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
+        (array_slice, remainder)
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// starting at the end of the slice,
+    /// and a remainder slice with length strictly less than `N`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let (remainder, chunks) = slice.as_rchunks();
+    /// assert_eq!(remainder, &['l']);
+    /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
+        assert_ne!(N, 0);
+        let len = self.len() / N;
+        let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
+        // SAFETY: We already panicked for zero, and ensured by construction
+        // that the length of the subslice is a multiple of N.
+        let array_slice = unsafe { multiple_of_n.as_chunks_unchecked() };
+        (remainder, array_slice)
+    }
+
+    /// Returns an iterator over `N` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are array references and do not overlap. If `N` does not divide the
+    /// length of the slice, then the last up to `N-1` elements will be omitted and can be
+    /// retrieved from the `remainder` function of the iterator.
+    ///
+    /// This method is the const generic equivalent of [`chunks_exact`].
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_chunks)]
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let mut iter = slice.array_chunks();
+    /// assert_eq!(iter.next().unwrap(), &['l', 'o']);
+    /// assert_eq!(iter.next().unwrap(), &['r', 'e']);
+    /// assert!(iter.next().is_none());
+    /// assert_eq!(iter.remainder(), &['m']);
+    /// ```
+    ///
+    /// [`chunks_exact`]: slice::chunks_exact
+    #[unstable(feature = "array_chunks", issue = "74985")]
+    #[inline]
+    pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
+        assert_ne!(N, 0);
+        ArrayChunks::new(self)
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// assuming that there's no remainder.
+    ///
+    /// # Safety
+    ///
+    /// This may only be called when
+    /// - The slice splits exactly into `N`-element chunks (aka `self.len() % N == 0`).
+    /// - `N != 0`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
+    /// let chunks: &mut [[char; 1]] =
+    ///     // SAFETY: 1-element chunks never have remainder
+    ///     unsafe { slice.as_chunks_unchecked_mut() };
+    /// chunks[0] = ['L'];
+    /// assert_eq!(chunks, &[['L'], ['o'], ['r'], ['e'], ['m'], ['!']]);
+    /// let chunks: &mut [[char; 3]] =
+    ///     // SAFETY: The slice length (6) is a multiple of 3
+    ///     unsafe { slice.as_chunks_unchecked_mut() };
+    /// chunks[1] = ['a', 'x', '?'];
+    /// assert_eq!(slice, &['L', 'o', 'r', 'a', 'x', '?']);
+    ///
+    /// // These would be unsound:
+    /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
+    /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
+        // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
+        let new_len = unsafe {
+            assert_unsafe_precondition!(N != 0 && self.len() % N == 0);
+            exact_div(self.len(), N)
+        };
+        // SAFETY: We cast a slice of `new_len * N` elements into
+        // a slice of `new_len` many `N` elements chunks.
+        unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), new_len) }
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// starting at the beginning of the slice,
+    /// and a remainder slice with length strictly less than `N`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// let (chunks, remainder) = v.as_chunks_mut();
+    /// remainder[0] = 9;
+    /// for chunk in chunks {
+    ///     *chunk = [count; 2];
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[1, 1, 2, 2, 9]);
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
+        assert_ne!(N, 0);
+        let len = self.len() / N;
+        let (multiple_of_n, remainder) = self.split_at_mut(len * N);
+        // SAFETY: We already panicked for zero, and ensured by construction
+        // that the length of the subslice is a multiple of N.
+        let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
+        (array_slice, remainder)
+    }
+
+    /// Splits the slice into a slice of `N`-element arrays,
+    /// starting at the end of the slice,
+    /// and a remainder slice with length strictly less than `N`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_as_chunks)]
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// let (remainder, chunks) = v.as_rchunks_mut();
+    /// remainder[0] = 9;
+    /// for chunk in chunks {
+    ///     *chunk = [count; 2];
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[9, 1, 1, 2, 2]);
+    /// ```
+    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[inline]
+    #[must_use]
+    pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
+        assert_ne!(N, 0);
+        let len = self.len() / N;
+        let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
+        // SAFETY: We already panicked for zero, and ensured by construction
+        // that the length of the subslice is a multiple of N.
+        let array_slice = unsafe { multiple_of_n.as_chunks_unchecked_mut() };
+        (remainder, array_slice)
+    }
+
+    /// Returns an iterator over `N` elements of the slice at a time, starting at the
+    /// beginning of the slice.
+    ///
+    /// The chunks are mutable array references and do not overlap. If `N` does not divide
+    /// the length of the slice, then the last up to `N-1` elements will be omitted and
+    /// can be retrieved from the `into_remainder` function of the iterator.
+    ///
+    /// This method is the const generic equivalent of [`chunks_exact_mut`].
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_chunks)]
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// for chunk in v.array_chunks_mut() {
+    ///     *chunk = [count; 2];
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[1, 1, 2, 2, 0]);
+    /// ```
+    ///
+    /// [`chunks_exact_mut`]: slice::chunks_exact_mut
+    #[unstable(feature = "array_chunks", issue = "74985")]
+    #[inline]
+    pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
+        assert_ne!(N, 0);
+        ArrayChunksMut::new(self)
+    }
+
+    /// Returns an iterator over overlapping windows of `N` elements of  a slice,
+    /// starting at the beginning of the slice.
+    ///
+    /// This is the const generic equivalent of [`windows`].
+    ///
+    /// If `N` is greater than the size of the slice, it will return no windows.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N` is 0. This check will most probably get changed to a compile time
+    /// error before this method gets stabilized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_windows)]
+    /// let slice = [0, 1, 2, 3];
+    /// let mut iter = slice.array_windows();
+    /// assert_eq!(iter.next().unwrap(), &[0, 1]);
+    /// assert_eq!(iter.next().unwrap(), &[1, 2]);
+    /// assert_eq!(iter.next().unwrap(), &[2, 3]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// [`windows`]: slice::windows
+    #[unstable(feature = "array_windows", issue = "75027")]
+    #[inline]
+    pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
+        assert_ne!(N, 0);
+        ArrayWindows::new(self)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
+    /// of the slice.
+    ///
+    /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
+    /// slice, then the last chunk will not have length `chunk_size`.
+    ///
+    /// See [`rchunks_exact`] for a variant of this iterator that returns chunks of always exactly
+    /// `chunk_size` elements, and [`chunks`] for the same iterator but starting at the beginning
+    /// of the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let mut iter = slice.rchunks(2);
+    /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
+    /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
+    /// assert_eq!(iter.next().unwrap(), &['l']);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// [`rchunks_exact`]: slice::rchunks_exact
+    /// [`chunks`]: slice::chunks
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    #[inline]
+    pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
+        assert!(chunk_size != 0);
+        RChunks::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
+    /// of the slice.
+    ///
+    /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
+    /// length of the slice, then the last chunk will not have length `chunk_size`.
+    ///
+    /// See [`rchunks_exact_mut`] for a variant of this iterator that returns chunks of always
+    /// exactly `chunk_size` elements, and [`chunks_mut`] for the same iterator but starting at the
+    /// beginning of the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// for chunk in v.rchunks_mut(2) {
+    ///     for elem in chunk.iter_mut() {
+    ///         *elem += count;
+    ///     }
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[3, 2, 2, 1, 1]);
+    /// ```
+    ///
+    /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
+    /// [`chunks_mut`]: slice::chunks_mut
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    #[inline]
+    pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
+        assert!(chunk_size != 0);
+        RChunksMut::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the
+    /// end of the slice.
+    ///
+    /// The chunks are slices and do not overlap. If `chunk_size` does not divide the length of the
+    /// slice, then the last up to `chunk_size-1` elements will be omitted and can be retrieved
+    /// from the `remainder` function of the iterator.
+    ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
+    /// resulting code better than in the case of [`rchunks`].
+    ///
+    /// See [`rchunks`] for a variant of this iterator that also returns the remainder as a smaller
+    /// chunk, and [`chunks_exact`] for the same iterator but starting at the beginning of the
+    /// slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = ['l', 'o', 'r', 'e', 'm'];
+    /// let mut iter = slice.rchunks_exact(2);
+    /// assert_eq!(iter.next().unwrap(), &['e', 'm']);
+    /// assert_eq!(iter.next().unwrap(), &['o', 'r']);
+    /// assert!(iter.next().is_none());
+    /// assert_eq!(iter.remainder(), &['l']);
+    /// ```
+    ///
+    /// [`chunks`]: slice::chunks
+    /// [`rchunks`]: slice::rchunks
+    /// [`chunks_exact`]: slice::chunks_exact
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    #[inline]
+    pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
+        assert!(chunk_size != 0);
+        RChunksExact::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over `chunk_size` elements of the slice at a time, starting at the end
+    /// of the slice.
+    ///
+    /// The chunks are mutable slices, and do not overlap. If `chunk_size` does not divide the
+    /// length of the slice, then the last up to `chunk_size-1` elements will be omitted and can be
+    /// retrieved from the `into_remainder` function of the iterator.
+    ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler can often optimize the
+    /// resulting code better than in the case of [`chunks_mut`].
+    ///
+    /// See [`rchunks_mut`] for a variant of this iterator that also returns the remainder as a
+    /// smaller chunk, and [`chunks_exact_mut`] for the same iterator but starting at the beginning
+    /// of the slice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `chunk_size` is 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &mut [0, 0, 0, 0, 0];
+    /// let mut count = 1;
+    ///
+    /// for chunk in v.rchunks_exact_mut(2) {
+    ///     for elem in chunk.iter_mut() {
+    ///         *elem += count;
+    ///     }
+    ///     count += 1;
+    /// }
+    /// assert_eq!(v, &[0, 2, 2, 1, 1]);
+    /// ```
+    ///
+    /// [`chunks_mut`]: slice::chunks_mut
+    /// [`rchunks_mut`]: slice::rchunks_mut
+    /// [`chunks_exact_mut`]: slice::chunks_exact_mut
+    #[stable(feature = "rchunks", since = "1.31.0")]
+    #[inline]
+    pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
+        assert!(chunk_size != 0);
+        RChunksExactMut::new(self, chunk_size)
+    }
+
+    /// Returns an iterator over the slice producing non-overlapping runs
+    /// of elements using the predicate to separate them.
+    ///
+    /// The predicate is called on two elements following themselves,
+    /// it means the predicate is called on `slice[0]` and `slice[1]`
+    /// then on `slice[1]` and `slice[2]` and so on.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_group_by)]
+    ///
+    /// let slice = &[1, 1, 1, 3, 3, 2, 2, 2];
+    ///
+    /// let mut iter = slice.group_by(|a, b| a == b);
+    ///
+    /// assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
+    /// assert_eq!(iter.next(), Some(&[3, 3][..]));
+    /// assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// This method can be used to extract the sorted subslices:
+    ///
+    /// ```
+    /// #![feature(slice_group_by)]
+    ///
+    /// let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];
+    ///
+    /// let mut iter = slice.group_by(|a, b| a <= b);
+    ///
+    /// assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
+    /// assert_eq!(iter.next(), Some(&[2, 3][..]));
+    /// assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[unstable(feature = "slice_group_by", issue = "80552")]
+    #[inline]
+    pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
+    where
+        F: FnMut(&T, &T) -> bool,
+    {
+        GroupBy::new(self, pred)
+    }
+
+    /// Returns an iterator over the slice producing non-overlapping mutable
+    /// runs of elements using the predicate to separate them.
+    ///
+    /// The predicate is called on two elements following themselves,
+    /// it means the predicate is called on `slice[0]` and `slice[1]`
+    /// then on `slice[1]` and `slice[2]` and so on.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_group_by)]
+    ///
+    /// let slice = &mut [1, 1, 1, 3, 3, 2, 2, 2];
+    ///
+    /// let mut iter = slice.group_by_mut(|a, b| a == b);
+    ///
+    /// assert_eq!(iter.next(), Some(&mut [1, 1, 1][..]));
+    /// assert_eq!(iter.next(), Some(&mut [3, 3][..]));
+    /// assert_eq!(iter.next(), Some(&mut [2, 2, 2][..]));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// This method can be used to extract the sorted subslices:
+    ///
+    /// ```
+    /// #![feature(slice_group_by)]
+    ///
+    /// let slice = &mut [1, 1, 2, 3, 2, 3, 2, 3, 4];
+    ///
+    /// let mut iter = slice.group_by_mut(|a, b| a <= b);
+    ///
+    /// assert_eq!(iter.next(), Some(&mut [1, 1, 2, 3][..]));
+    /// assert_eq!(iter.next(), Some(&mut [2, 3][..]));
+    /// assert_eq!(iter.next(), Some(&mut [2, 3, 4][..]));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[unstable(feature = "slice_group_by", issue = "80552")]
+    #[inline]
+    pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
+    where
+        F: FnMut(&T, &T) -> bool,
+    {
+        GroupByMut::new(self, pred)
+    }
+
+    /// Divides one slice into two at an index.
+    ///
+    /// The first will contain all indices from `[0, mid)` (excluding
+    /// the index `mid` itself) and the second will contain all
+    /// indices from `[mid, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `mid > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [1, 2, 3, 4, 5, 6];
+    ///
+    /// {
+    ///    let (left, right) = v.split_at(0);
+    ///    assert_eq!(left, []);
+    ///    assert_eq!(right, [1, 2, 3, 4, 5, 6]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.split_at(2);
+    ///     assert_eq!(left, [1, 2]);
+    ///     assert_eq!(right, [3, 4, 5, 6]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.split_at(6);
+    ///     assert_eq!(left, [1, 2, 3, 4, 5, 6]);
+    ///     assert_eq!(right, []);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    #[track_caller]
+    #[must_use]
+    pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
+        assert!(mid <= self.len());
+        // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
+        // fulfills the requirements of `from_raw_parts_mut`.
+        unsafe { self.split_at_unchecked(mid) }
+    }
+
+    /// Divides one mutable slice into two at an index.
+    ///
+    /// The first will contain all indices from `[0, mid)` (excluding
+    /// the index `mid` itself) and the second will contain all
+    /// indices from `[mid, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `mid > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [1, 0, 3, 0, 5, 6];
+    /// let (left, right) = v.split_at_mut(2);
+    /// assert_eq!(left, [1, 0]);
+    /// assert_eq!(right, [3, 0, 5, 6]);
+    /// left[1] = 2;
+    /// right[1] = 4;
+    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    #[track_caller]
+    #[must_use]
+    pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+        assert!(mid <= self.len());
+        // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
+        // fulfills the requirements of `from_raw_parts_mut`.
+        unsafe { self.split_at_mut_unchecked(mid) }
+    }
+
+    /// Divides one slice into two at an index, without doing bounds checking.
+    ///
+    /// The first will contain all indices from `[0, mid)` (excluding
+    /// the index `mid` itself) and the second will contain all
+    /// indices from `[mid, len)` (excluding the index `len` itself).
+    ///
+    /// For a safe alternative see [`split_at`].
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with an out-of-bounds index is *[undefined behavior]*
+    /// even if the resulting reference is not used. The caller has to ensure that
+    /// `0 <= mid <= self.len()`.
+    ///
+    /// [`split_at`]: slice::split_at
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_split_at_unchecked)]
+    ///
+    /// let v = [1, 2, 3, 4, 5, 6];
+    ///
+    /// unsafe {
+    ///    let (left, right) = v.split_at_unchecked(0);
+    ///    assert_eq!(left, []);
+    ///    assert_eq!(right, [1, 2, 3, 4, 5, 6]);
+    /// }
+    ///
+    /// unsafe {
+    ///     let (left, right) = v.split_at_unchecked(2);
+    ///     assert_eq!(left, [1, 2]);
+    ///     assert_eq!(right, [3, 4, 5, 6]);
+    /// }
+    ///
+    /// unsafe {
+    ///     let (left, right) = v.split_at_unchecked(6);
+    ///     assert_eq!(left, [1, 2, 3, 4, 5, 6]);
+    ///     assert_eq!(right, []);
+    /// }
+    /// ```
+    #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
+    #[inline]
+    #[must_use]
+    pub unsafe fn split_at_unchecked(&self, mid: usize) -> (&[T], &[T]) {
+        // SAFETY: Caller has to check that `0 <= mid <= self.len()`
+        unsafe { (self.get_unchecked(..mid), self.get_unchecked(mid..)) }
+    }
+
+    /// Divides one mutable slice into two at an index, without doing bounds checking.
+    ///
+    /// The first will contain all indices from `[0, mid)` (excluding
+    /// the index `mid` itself) and the second will contain all
+    /// indices from `[mid, len)` (excluding the index `len` itself).
+    ///
+    /// For a safe alternative see [`split_at_mut`].
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with an out-of-bounds index is *[undefined behavior]*
+    /// even if the resulting reference is not used. The caller has to ensure that
+    /// `0 <= mid <= self.len()`.
+    ///
+    /// [`split_at_mut`]: slice::split_at_mut
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_split_at_unchecked)]
+    ///
+    /// let mut v = [1, 0, 3, 0, 5, 6];
+    /// // scoped to restrict the lifetime of the borrows
+    /// unsafe {
+    ///     let (left, right) = v.split_at_mut_unchecked(2);
+    ///     assert_eq!(left, [1, 0]);
+    ///     assert_eq!(right, [3, 0, 5, 6]);
+    ///     left[1] = 2;
+    ///     right[1] = 4;
+    /// }
+    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
+    /// ```
+    #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
+    #[inline]
+    #[must_use]
+    pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+        let len = self.len();
+        let ptr = self.as_mut_ptr();
+
+        // SAFETY: Caller has to check that `0 <= mid <= self.len()`.
+        //
+        // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
+        // is fine.
+        unsafe {
+            assert_unsafe_precondition!(mid <= len);
+            (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
+        }
+    }
+
+    /// Divides one slice into an array and a remainder slice at an index.
+    ///
+    /// The array will contain all indices from `[0, N)` (excluding
+    /// the index `N` itself) and the slice will contain all
+    /// indices from `[N, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_array)]
+    ///
+    /// let v = &[1, 2, 3, 4, 5, 6][..];
+    ///
+    /// {
+    ///    let (left, right) = v.split_array_ref::<0>();
+    ///    assert_eq!(left, &[]);
+    ///    assert_eq!(right, [1, 2, 3, 4, 5, 6]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.split_array_ref::<2>();
+    ///     assert_eq!(left, &[1, 2]);
+    ///     assert_eq!(right, [3, 4, 5, 6]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.split_array_ref::<6>();
+    ///     assert_eq!(left, &[1, 2, 3, 4, 5, 6]);
+    ///     assert_eq!(right, []);
+    /// }
+    /// ```
+    #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
+    #[inline]
+    #[track_caller]
+    #[must_use]
+    pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]) {
+        let (a, b) = self.split_at(N);
+        // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at)
+        unsafe { (&*(a.as_ptr() as *const [T; N]), b) }
+    }
+
+    /// Divides one mutable slice into an array and a remainder slice at an index.
+    ///
+    /// The array will contain all indices from `[0, N)` (excluding
+    /// the index `N` itself) and the slice will contain all
+    /// indices from `[N, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_array)]
+    ///
+    /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
+    /// let (left, right) = v.split_array_mut::<2>();
+    /// assert_eq!(left, &mut [1, 0]);
+    /// assert_eq!(right, [3, 0, 5, 6]);
+    /// left[1] = 2;
+    /// right[1] = 4;
+    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
+    /// ```
+    #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
+    #[inline]
+    #[track_caller]
+    #[must_use]
+    pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]) {
+        let (a, b) = self.split_at_mut(N);
+        // SAFETY: a points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
+        unsafe { (&mut *(a.as_mut_ptr() as *mut [T; N]), b) }
+    }
+
+    /// Divides one slice into an array and a remainder slice at an index from
+    /// the end.
+    ///
+    /// The slice will contain all indices from `[0, len - N)` (excluding
+    /// the index `len - N` itself) and the array will contain all
+    /// indices from `[len - N, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_array)]
+    ///
+    /// let v = &[1, 2, 3, 4, 5, 6][..];
+    ///
+    /// {
+    ///    let (left, right) = v.rsplit_array_ref::<0>();
+    ///    assert_eq!(left, [1, 2, 3, 4, 5, 6]);
+    ///    assert_eq!(right, &[]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.rsplit_array_ref::<2>();
+    ///     assert_eq!(left, [1, 2, 3, 4]);
+    ///     assert_eq!(right, &[5, 6]);
+    /// }
+    ///
+    /// {
+    ///     let (left, right) = v.rsplit_array_ref::<6>();
+    ///     assert_eq!(left, []);
+    ///     assert_eq!(right, &[1, 2, 3, 4, 5, 6]);
+    /// }
+    /// ```
+    #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
+    #[inline]
+    #[must_use]
+    pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]) {
+        assert!(N <= self.len());
+        let (a, b) = self.split_at(self.len() - N);
+        // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at)
+        unsafe { (a, &*(b.as_ptr() as *const [T; N])) }
+    }
+
+    /// Divides one mutable slice into an array and a remainder slice at an
+    /// index from the end.
+    ///
+    /// The slice will contain all indices from `[0, len - N)` (excluding
+    /// the index `N` itself) and the array will contain all
+    /// indices from `[len - N, len)` (excluding the index `len` itself).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `N > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(split_array)]
+    ///
+    /// let mut v = &mut [1, 0, 3, 0, 5, 6][..];
+    /// let (left, right) = v.rsplit_array_mut::<4>();
+    /// assert_eq!(left, [1, 0]);
+    /// assert_eq!(right, &mut [3, 0, 5, 6]);
+    /// left[1] = 2;
+    /// right[1] = 4;
+    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
+    /// ```
+    #[unstable(feature = "split_array", reason = "new API", issue = "90091")]
+    #[inline]
+    #[must_use]
+    pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]) {
+        assert!(N <= self.len());
+        let (a, b) = self.split_at_mut(self.len() - N);
+        // SAFETY: b points to [T; N]? Yes it's [T] of length N (checked by split_at_mut)
+        unsafe { (a, &mut *(b.as_mut_ptr() as *mut [T; N])) }
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`. The matched element is not contained in the subslices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = [10, 40, 33, 20];
+    /// let mut iter = slice.split(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10, 40]);
+    /// assert_eq!(iter.next().unwrap(), &[20]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// If the first element is matched, an empty slice will be the first item
+    /// returned by the iterator. Similarly, if the last element in the slice
+    /// is matched, an empty slice will be the last item returned by the
+    /// iterator:
+    ///
+    /// ```
+    /// let slice = [10, 40, 33];
+    /// let mut iter = slice.split(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10, 40]);
+    /// assert_eq!(iter.next().unwrap(), &[]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// If two matched elements are directly adjacent, an empty slice will be
+    /// present between them:
+    ///
+    /// ```
+    /// let slice = [10, 6, 33, 20];
+    /// let mut iter = slice.split(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10]);
+    /// assert_eq!(iter.next().unwrap(), &[]);
+    /// assert_eq!(iter.next().unwrap(), &[20]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn split<F>(&self, pred: F) -> Split<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        Split::new(self, pred)
+    }
+
+    /// Returns an iterator over mutable subslices separated by elements that
+    /// match `pred`. The matched element is not contained in the subslices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.split_mut(|num| *num % 3 == 0) {
+    ///     group[0] = 1;
+    /// }
+    /// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        SplitMut::new(self, pred)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`. The matched element is contained in the end of the previous
+    /// subslice as a terminator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = [10, 40, 33, 20];
+    /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
+    /// assert_eq!(iter.next().unwrap(), &[20]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    ///
+    /// If the last element of the slice is matched,
+    /// that element will be considered the terminator of the preceding slice.
+    /// That slice will be the last item returned by the iterator.
+    ///
+    /// ```
+    /// let slice = [3, 10, 40, 33];
+    /// let mut iter = slice.split_inclusive(|num| num % 3 == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[3]);
+    /// assert_eq!(iter.next().unwrap(), &[10, 40, 33]);
+    /// assert!(iter.next().is_none());
+    /// ```
+    #[stable(feature = "split_inclusive", since = "1.51.0")]
+    #[inline]
+    pub fn split_inclusive<F>(&self, pred: F) -> SplitInclusive<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        SplitInclusive::new(self, pred)
+    }
+
+    /// Returns an iterator over mutable subslices separated by elements that
+    /// match `pred`. The matched element is contained in the previous
+    /// subslice as a terminator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.split_inclusive_mut(|num| *num % 3 == 0) {
+    ///     let terminator_idx = group.len()-1;
+    ///     group[terminator_idx] = 1;
+    /// }
+    /// assert_eq!(v, [10, 40, 1, 20, 1, 1]);
+    /// ```
+    #[stable(feature = "split_inclusive", since = "1.51.0")]
+    #[inline]
+    pub fn split_inclusive_mut<F>(&mut self, pred: F) -> SplitInclusiveMut<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        SplitInclusiveMut::new(self, pred)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`, starting at the end of the slice and working backwards.
+    /// The matched element is not contained in the subslices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let slice = [11, 22, 33, 0, 44, 55];
+    /// let mut iter = slice.rsplit(|num| *num == 0);
+    ///
+    /// assert_eq!(iter.next().unwrap(), &[44, 55]);
+    /// assert_eq!(iter.next().unwrap(), &[11, 22, 33]);
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// As with `split()`, if the first or last element is matched, an empty
+    /// slice will be the first (or last) item returned by the iterator.
+    ///
+    /// ```
+    /// let v = &[0, 1, 1, 2, 3, 5, 8];
+    /// let mut it = v.rsplit(|n| *n % 2 == 0);
+    /// assert_eq!(it.next().unwrap(), &[]);
+    /// assert_eq!(it.next().unwrap(), &[3, 5]);
+    /// assert_eq!(it.next().unwrap(), &[1, 1]);
+    /// assert_eq!(it.next().unwrap(), &[]);
+    /// assert_eq!(it.next(), None);
+    /// ```
+    #[stable(feature = "slice_rsplit", since = "1.27.0")]
+    #[inline]
+    pub fn rsplit<F>(&self, pred: F) -> RSplit<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        RSplit::new(self, pred)
+    }
+
+    /// Returns an iterator over mutable subslices separated by elements that
+    /// match `pred`, starting at the end of the slice and working
+    /// backwards. The matched element is not contained in the subslices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [100, 400, 300, 200, 600, 500];
+    ///
+    /// let mut count = 0;
+    /// for group in v.rsplit_mut(|num| *num % 3 == 0) {
+    ///     count += 1;
+    ///     group[0] = count;
+    /// }
+    /// assert_eq!(v, [3, 400, 300, 2, 600, 1]);
+    /// ```
+    ///
+    #[stable(feature = "slice_rsplit", since = "1.27.0")]
+    #[inline]
+    pub fn rsplit_mut<F>(&mut self, pred: F) -> RSplitMut<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        RSplitMut::new(self, pred)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`, limited to returning at most `n` items. The matched element is
+    /// not contained in the subslices.
+    ///
+    /// The last element returned, if any, will contain the remainder of the
+    /// slice.
+    ///
+    /// # Examples
+    ///
+    /// Print the slice split once by numbers divisible by 3 (i.e., `[10, 40]`,
+    /// `[20, 60, 50]`):
+    ///
+    /// ```
+    /// let v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.splitn(2, |num| *num % 3 == 0) {
+    ///     println!("{group:?}");
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        SplitN::new(self.split(pred), n)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred`, limited to returning at most `n` items. The matched element is
+    /// not contained in the subslices.
+    ///
+    /// The last element returned, if any, will contain the remainder of the
+    /// slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
+    ///     group[0] = 1;
+    /// }
+    /// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        SplitNMut::new(self.split_mut(pred), n)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred` limited to returning at most `n` items. This starts at the end of
+    /// the slice and works backwards. The matched element is not contained in
+    /// the subslices.
+    ///
+    /// The last element returned, if any, will contain the remainder of the
+    /// slice.
+    ///
+    /// # Examples
+    ///
+    /// Print the slice split once, starting from the end, by numbers divisible
+    /// by 3 (i.e., `[50]`, `[10, 40, 30, 20]`):
+    ///
+    /// ```
+    /// let v = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
+    ///     println!("{group:?}");
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        RSplitN::new(self.rsplit(pred), n)
+    }
+
+    /// Returns an iterator over subslices separated by elements that match
+    /// `pred` limited to returning at most `n` items. This starts at the end of
+    /// the slice and works backwards. The matched element is not contained in
+    /// the subslices.
+    ///
+    /// The last element returned, if any, will contain the remainder of the
+    /// slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut s = [10, 40, 30, 20, 60, 50];
+    ///
+    /// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
+    ///     group[0] = 1;
+    /// }
+    /// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<'_, T, F>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        RSplitNMut::new(self.rsplit_mut(pred), n)
+    }
+
+    /// Returns `true` if the slice contains an element with the given value.
+    ///
+    /// This operation is *O*(*n*).
+    ///
+    /// Note that if you have a sorted slice, [`binary_search`] may be faster.
+    ///
+    /// [`binary_search`]: slice::binary_search
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert!(v.contains(&30));
+    /// assert!(!v.contains(&50));
+    /// ```
+    ///
+    /// If you do not have a `&T`, but some other value that you can compare
+    /// with one (for example, `String` implements `PartialEq<str>`), you can
+    /// use `iter().any`:
+    ///
+    /// ```
+    /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
+    /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
+    /// assert!(!v.iter().any(|e| e == "hi"));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    #[must_use]
+    pub fn contains(&self, x: &T) -> bool
+    where
+        T: PartialEq,
+    {
+        cmp::SliceContains::slice_contains(x, self)
+    }
+
+    /// Returns `true` if `needle` is a prefix of the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert!(v.starts_with(&[10]));
+    /// assert!(v.starts_with(&[10, 40]));
+    /// assert!(!v.starts_with(&[50]));
+    /// assert!(!v.starts_with(&[10, 50]));
+    /// ```
+    ///
+    /// Always returns `true` if `needle` is an empty slice:
+    ///
+    /// ```
+    /// let v = &[10, 40, 30];
+    /// assert!(v.starts_with(&[]));
+    /// let v: &[u8] = &[];
+    /// assert!(v.starts_with(&[]));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    pub fn starts_with(&self, needle: &[T]) -> bool
+    where
+        T: PartialEq,
+    {
+        let n = needle.len();
+        self.len() >= n && needle == &self[..n]
+    }
+
+    /// Returns `true` if `needle` is a suffix of the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [10, 40, 30];
+    /// assert!(v.ends_with(&[30]));
+    /// assert!(v.ends_with(&[40, 30]));
+    /// assert!(!v.ends_with(&[50]));
+    /// assert!(!v.ends_with(&[50, 30]));
+    /// ```
+    ///
+    /// Always returns `true` if `needle` is an empty slice:
+    ///
+    /// ```
+    /// let v = &[10, 40, 30];
+    /// assert!(v.ends_with(&[]));
+    /// let v: &[u8] = &[];
+    /// assert!(v.ends_with(&[]));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    pub fn ends_with(&self, needle: &[T]) -> bool
+    where
+        T: PartialEq,
+    {
+        let (m, n) = (self.len(), needle.len());
+        m >= n && needle == &self[m - n..]
+    }
+
+    /// Returns a subslice with the prefix removed.
+    ///
+    /// If the slice starts with `prefix`, returns the subslice after the prefix, wrapped in `Some`.
+    /// If `prefix` is empty, simply returns the original slice.
+    ///
+    /// If the slice does not start with `prefix`, returns `None`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &[10, 40, 30];
+    /// assert_eq!(v.strip_prefix(&[10]), Some(&[40, 30][..]));
+    /// assert_eq!(v.strip_prefix(&[10, 40]), Some(&[30][..]));
+    /// assert_eq!(v.strip_prefix(&[50]), None);
+    /// assert_eq!(v.strip_prefix(&[10, 50]), None);
+    ///
+    /// let prefix : &str = "he";
+    /// assert_eq!(b"hello".strip_prefix(prefix.as_bytes()),
+    ///            Some(b"llo".as_ref()));
+    /// ```
+    #[must_use = "returns the subslice without modifying the original"]
+    #[stable(feature = "slice_strip", since = "1.51.0")]
+    pub fn strip_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> Option<&[T]>
+    where
+        T: PartialEq,
+    {
+        // This function will need rewriting if and when SlicePattern becomes more sophisticated.
+        let prefix = prefix.as_slice();
+        let n = prefix.len();
+        if n <= self.len() {
+            let (head, tail) = self.split_at(n);
+            if head == prefix {
+                return Some(tail);
+            }
+        }
+        None
+    }
+
+    /// Returns a subslice with the suffix removed.
+    ///
+    /// If the slice ends with `suffix`, returns the subslice before the suffix, wrapped in `Some`.
+    /// If `suffix` is empty, simply returns the original slice.
+    ///
+    /// If the slice does not end with `suffix`, returns `None`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = &[10, 40, 30];
+    /// assert_eq!(v.strip_suffix(&[30]), Some(&[10, 40][..]));
+    /// assert_eq!(v.strip_suffix(&[40, 30]), Some(&[10][..]));
+    /// assert_eq!(v.strip_suffix(&[50]), None);
+    /// assert_eq!(v.strip_suffix(&[50, 30]), None);
+    /// ```
+    #[must_use = "returns the subslice without modifying the original"]
+    #[stable(feature = "slice_strip", since = "1.51.0")]
+    pub fn strip_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> Option<&[T]>
+    where
+        T: PartialEq,
+    {
+        // This function will need rewriting if and when SlicePattern becomes more sophisticated.
+        let suffix = suffix.as_slice();
+        let (len, n) = (self.len(), suffix.len());
+        if n <= len {
+            let (head, tail) = self.split_at(len - n);
+            if tail == suffix {
+                return Some(head);
+            }
+        }
+        None
+    }
+
+    /// Binary searches this slice for a given element.
+    /// This behaves similary to [`contains`] if this slice is sorted.
+    ///
+    /// If the value is found then [`Result::Ok`] is returned, containing the
+    /// index of the matching element. If there are multiple matches, then any
+    /// one of the matches could be returned. The index is chosen
+    /// deterministically, but is subject to change in future versions of Rust.
+    /// If the value is not found then [`Result::Err`] is returned, containing
+    /// the index where a matching element could be inserted while maintaining
+    /// sorted order.
+    ///
+    /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
+    ///
+    /// [`contains`]: slice::contains
+    /// [`binary_search_by`]: slice::binary_search_by
+    /// [`binary_search_by_key`]: slice::binary_search_by_key
+    /// [`partition_point`]: slice::partition_point
+    ///
+    /// # Examples
+    ///
+    /// Looks up a series of four elements. The first is found, with a
+    /// uniquely determined position; the second and third are not
+    /// found; the fourth could match any position in `[1, 4]`.
+    ///
+    /// ```
+    /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    ///
+    /// assert_eq!(s.binary_search(&13),  Ok(9));
+    /// assert_eq!(s.binary_search(&4),   Err(7));
+    /// assert_eq!(s.binary_search(&100), Err(13));
+    /// let r = s.binary_search(&1);
+    /// assert!(match r { Ok(1..=4) => true, _ => false, });
+    /// ```
+    ///
+    /// If you want to insert an item to a sorted vector, while maintaining
+    /// sort order, consider using [`partition_point`]:
+    ///
+    /// ```
+    /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    /// let num = 42;
+    /// let idx = s.partition_point(|&x| x < num);
+    /// // The above is equivalent to `let idx = s.binary_search(&num).unwrap_or_else(|x| x);`
+    /// s.insert(idx, num);
+    /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn binary_search(&self, x: &T) -> Result<usize, usize>
+    where
+        T: Ord,
+    {
+        self.binary_search_by(|p| p.cmp(x))
+    }
+
+    /// Binary searches this slice with a comparator function.
+    /// This behaves similarly to [`contains`] if this slice is sorted.
+    ///
+    /// The comparator function should implement an order consistent
+    /// with the sort order of the underlying slice, returning an
+    /// order code that indicates whether its argument is `Less`,
+    /// `Equal` or `Greater` the desired target.
+    ///
+    /// If the value is found then [`Result::Ok`] is returned, containing the
+    /// index of the matching element. If there are multiple matches, then any
+    /// one of the matches could be returned. The index is chosen
+    /// deterministically, but is subject to change in future versions of Rust.
+    /// If the value is not found then [`Result::Err`] is returned, containing
+    /// the index where a matching element could be inserted while maintaining
+    /// sorted order.
+    ///
+    /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
+    ///
+    /// [`contains`]: slice::contains
+    /// [`binary_search`]: slice::binary_search
+    /// [`binary_search_by_key`]: slice::binary_search_by_key
+    /// [`partition_point`]: slice::partition_point
+    ///
+    /// # Examples
+    ///
+    /// Looks up a series of four elements. The first is found, with a
+    /// uniquely determined position; the second and third are not
+    /// found; the fourth could match any position in `[1, 4]`.
+    ///
+    /// ```
+    /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    ///
+    /// let seek = 13;
+    /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
+    /// let seek = 4;
+    /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
+    /// let seek = 100;
+    /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
+    /// let seek = 1;
+    /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
+    /// assert!(match r { Ok(1..=4) => true, _ => false, });
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
+    where
+        F: FnMut(&'a T) -> Ordering,
+    {
+        let mut size = self.len();
+        let mut left = 0;
+        let mut right = size;
+        while left < right {
+            let mid = left + size / 2;
+
+            // SAFETY: the call is made safe by the following invariants:
+            // - `mid >= 0`
+            // - `mid < size`: `mid` is limited by `[left; right)` bound.
+            let cmp = f(unsafe { self.get_unchecked(mid) });
+
+            // The reason why we use if/else control flow rather than match
+            // is because match reorders comparison operations, which is perf sensitive.
+            // This is x86 asm for u8: https://rust.godbolt.org/z/8Y8Pra.
+            if cmp == Less {
+                left = mid + 1;
+            } else if cmp == Greater {
+                right = mid;
+            } else {
+                // SAFETY: same as the `get_unchecked` above
+                unsafe { crate::intrinsics::assume(mid < self.len()) };
+                return Ok(mid);
+            }
+
+            size = right - left;
+        }
+        Err(left)
+    }
+
+    /// Binary searches this slice with a key extraction function.
+    /// This behaves similarly to [`contains`] if this slice is sorted.
+    ///
+    /// Assumes that the slice is sorted by the key, for instance with
+    /// [`sort_by_key`] using the same key extraction function.
+    ///
+    /// If the value is found then [`Result::Ok`] is returned, containing the
+    /// index of the matching element. If there are multiple matches, then any
+    /// one of the matches could be returned. The index is chosen
+    /// deterministically, but is subject to change in future versions of Rust.
+    /// If the value is not found then [`Result::Err`] is returned, containing
+    /// the index where a matching element could be inserted while maintaining
+    /// sorted order.
+    ///
+    /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
+    ///
+    /// [`contains`]: slice::contains
+    /// [`sort_by_key`]: slice::sort_by_key
+    /// [`binary_search`]: slice::binary_search
+    /// [`binary_search_by`]: slice::binary_search_by
+    /// [`partition_point`]: slice::partition_point
+    ///
+    /// # Examples
+    ///
+    /// Looks up a series of four elements in a slice of pairs sorted by
+    /// their second elements. The first is found, with a uniquely
+    /// determined position; the second and third are not found; the
+    /// fourth could match any position in `[1, 4]`.
+    ///
+    /// ```
+    /// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
+    ///          (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
+    ///          (1, 21), (2, 34), (4, 55)];
+    ///
+    /// assert_eq!(s.binary_search_by_key(&13, |&(a, b)| b),  Ok(9));
+    /// assert_eq!(s.binary_search_by_key(&4, |&(a, b)| b),   Err(7));
+    /// assert_eq!(s.binary_search_by_key(&100, |&(a, b)| b), Err(13));
+    /// let r = s.binary_search_by_key(&1, |&(a, b)| b);
+    /// assert!(match r { Ok(1..=4) => true, _ => false, });
+    /// ```
+    // Lint rustdoc::broken_intra_doc_links is allowed as `slice::sort_by_key` is
+    // in crate `alloc`, and as such doesn't exists yet when building `core`: #74481.
+    // This breaks links when slice is displayed in core, but changing it to use relative links
+    // would break when the item is re-exported. So allow the core links to be broken for now.
+    #[allow(rustdoc::broken_intra_doc_links)]
+    #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
+    #[inline]
+    pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
+    where
+        F: FnMut(&'a T) -> B,
+        B: Ord,
+    {
+        self.binary_search_by(|k| f(k).cmp(b))
+    }
+
+    /// Sorts the slice, but might not preserve the order of equal elements.
+    ///
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
+    /// which combines the fast average case of randomized quicksort with the fast worst case of
+    /// heapsort, while achieving linear time on slices with certain patterns. It uses some
+    /// randomization to avoid degenerate cases, but with a fixed seed to always provide
+    /// deterministic behavior.
+    ///
+    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
+    /// slice consists of several concatenated sorted sequences.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [-5, 4, 1, -3, 2];
+    ///
+    /// v.sort_unstable();
+    /// assert!(v == [-5, -3, 1, 2, 4]);
+    /// ```
+    ///
+    /// [pdqsort]: https://github.com/orlp/pdqsort
+    #[stable(feature = "sort_unstable", since = "1.20.0")]
+    #[inline]
+    pub fn sort_unstable(&mut self)
+    where
+        T: Ord,
+    {
+        sort::quicksort(self, |a, b| a.lt(b));
+    }
+
+    /// Sorts the slice with a comparator function, but might not preserve the order of equal
+    /// elements.
+    ///
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and *O*(*n* \* log(*n*)) worst-case.
+    ///
+    /// The comparator function must define a total ordering for the elements in the slice. If
+    /// the ordering is not total, the order of the elements is unspecified. An order is a
+    /// total order if it is (for all `a`, `b` and `c`):
+    ///
+    /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and
+    /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
+    ///
+    /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use
+    /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`.
+    ///
+    /// ```
+    /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0];
+    /// floats.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
+    /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]);
+    /// ```
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
+    /// which combines the fast average case of randomized quicksort with the fast worst case of
+    /// heapsort, while achieving linear time on slices with certain patterns. It uses some
+    /// randomization to avoid degenerate cases, but with a fixed seed to always provide
+    /// deterministic behavior.
+    ///
+    /// It is typically faster than stable sorting, except in a few special cases, e.g., when the
+    /// slice consists of several concatenated sorted sequences.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [5, 4, 1, 3, 2];
+    /// v.sort_unstable_by(|a, b| a.cmp(b));
+    /// assert!(v == [1, 2, 3, 4, 5]);
+    ///
+    /// // reverse sorting
+    /// v.sort_unstable_by(|a, b| b.cmp(a));
+    /// assert!(v == [5, 4, 3, 2, 1]);
+    /// ```
+    ///
+    /// [pdqsort]: https://github.com/orlp/pdqsort
+    #[stable(feature = "sort_unstable", since = "1.20.0")]
+    #[inline]
+    pub fn sort_unstable_by<F>(&mut self, mut compare: F)
+    where
+        F: FnMut(&T, &T) -> Ordering,
+    {
+        sort::quicksort(self, |a, b| compare(a, b) == Ordering::Less);
+    }
+
+    /// Sorts the slice with a key extraction function, but might not preserve the order of equal
+    /// elements.
+    ///
+    /// This sort is unstable (i.e., may reorder equal elements), in-place
+    /// (i.e., does not allocate), and *O*(m \* *n* \* log(*n*)) worst-case, where the key function is
+    /// *O*(*m*).
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters,
+    /// which combines the fast average case of randomized quicksort with the fast worst case of
+    /// heapsort, while achieving linear time on slices with certain patterns. It uses some
+    /// randomization to avoid degenerate cases, but with a fixed seed to always provide
+    /// deterministic behavior.
+    ///
+    /// Due to its key calling strategy, [`sort_unstable_by_key`](#method.sort_unstable_by_key)
+    /// is likely to be slower than [`sort_by_cached_key`](#method.sort_by_cached_key) in
+    /// cases where the key function is expensive.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [-5i32, 4, 1, -3, 2];
+    ///
+    /// v.sort_unstable_by_key(|k| k.abs());
+    /// assert!(v == [1, 2, -3, 4, -5]);
+    /// ```
+    ///
+    /// [pdqsort]: https://github.com/orlp/pdqsort
+    #[stable(feature = "sort_unstable", since = "1.20.0")]
+    #[inline]
+    pub fn sort_unstable_by_key<K, F>(&mut self, mut f: F)
+    where
+        F: FnMut(&T) -> K,
+        K: Ord,
+    {
+        sort::quicksort(self, |a, b| f(a).lt(&f(b)));
+    }
+
+    /// Reorder the slice such that the element at `index` is at its final sorted position.
+    ///
+    /// This reordering has the additional property that any value at position `i < index` will be
+    /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
+    /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
+    /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
+    /// element" in other libraries. It returns a triplet of the following values: all elements less
+    /// than the one at the given index, the value at the given index, and all elements greater than
+    /// the one at the given index.
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
+    /// used for [`sort_unstable`].
+    ///
+    /// [`sort_unstable`]: slice::sort_unstable
+    ///
+    /// # Panics
+    ///
+    /// Panics when `index >= len()`, meaning it always panics on empty slices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [-5i32, 4, 1, -3, 2];
+    ///
+    /// // Find the median
+    /// v.select_nth_unstable(2);
+    ///
+    /// // We are only guaranteed the slice will be one of the following, based on the way we sort
+    /// // about the specified index.
+    /// assert!(v == [-3, -5, 1, 2, 4] ||
+    ///         v == [-5, -3, 1, 2, 4] ||
+    ///         v == [-3, -5, 1, 4, 2] ||
+    ///         v == [-5, -3, 1, 4, 2]);
+    /// ```
+    #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
+    #[inline]
+    pub fn select_nth_unstable(&mut self, index: usize) -> (&mut [T], &mut T, &mut [T])
+    where
+        T: Ord,
+    {
+        let mut f = |a: &T, b: &T| a.lt(b);
+        sort::partition_at_index(self, index, &mut f)
+    }
+
+    /// Reorder the slice with a comparator function such that the element at `index` is at its
+    /// final sorted position.
+    ///
+    /// This reordering has the additional property that any value at position `i < index` will be
+    /// less than or equal to any value at a position `j > index` using the comparator function.
+    /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
+    /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following
+    /// values: all elements less than the one at the given index, the value at the given index,
+    /// and all elements greater than the one at the given index, using the provided comparator
+    /// function.
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
+    /// used for [`sort_unstable`].
+    ///
+    /// [`sort_unstable`]: slice::sort_unstable
+    ///
+    /// # Panics
+    ///
+    /// Panics when `index >= len()`, meaning it always panics on empty slices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [-5i32, 4, 1, -3, 2];
+    ///
+    /// // Find the median as if the slice were sorted in descending order.
+    /// v.select_nth_unstable_by(2, |a, b| b.cmp(a));
+    ///
+    /// // We are only guaranteed the slice will be one of the following, based on the way we sort
+    /// // about the specified index.
+    /// assert!(v == [2, 4, 1, -5, -3] ||
+    ///         v == [2, 4, 1, -3, -5] ||
+    ///         v == [4, 2, 1, -5, -3] ||
+    ///         v == [4, 2, 1, -3, -5]);
+    /// ```
+    #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
+    #[inline]
+    pub fn select_nth_unstable_by<F>(
+        &mut self,
+        index: usize,
+        mut compare: F,
+    ) -> (&mut [T], &mut T, &mut [T])
+    where
+        F: FnMut(&T, &T) -> Ordering,
+    {
+        let mut f = |a: &T, b: &T| compare(a, b) == Less;
+        sort::partition_at_index(self, index, &mut f)
+    }
+
+    /// Reorder the slice with a key extraction function such that the element at `index` is at its
+    /// final sorted position.
+    ///
+    /// This reordering has the additional property that any value at position `i < index` will be
+    /// less than or equal to any value at a position `j > index` using the key extraction function.
+    /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
+    /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following
+    /// values: all elements less than the one at the given index, the value at the given index, and
+    /// all elements greater than the one at the given index, using the provided key extraction
+    /// function.
+    ///
+    /// # Current implementation
+    ///
+    /// The current algorithm is based on the quickselect portion of the same quicksort algorithm
+    /// used for [`sort_unstable`].
+    ///
+    /// [`sort_unstable`]: slice::sort_unstable
+    ///
+    /// # Panics
+    ///
+    /// Panics when `index >= len()`, meaning it always panics on empty slices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = [-5i32, 4, 1, -3, 2];
+    ///
+    /// // Return the median as if the array were sorted according to absolute value.
+    /// v.select_nth_unstable_by_key(2, |a| a.abs());
+    ///
+    /// // We are only guaranteed the slice will be one of the following, based on the way we sort
+    /// // about the specified index.
+    /// assert!(v == [1, 2, -3, 4, -5] ||
+    ///         v == [1, 2, -3, -5, 4] ||
+    ///         v == [2, 1, -3, 4, -5] ||
+    ///         v == [2, 1, -3, -5, 4]);
+    /// ```
+    #[stable(feature = "slice_select_nth_unstable", since = "1.49.0")]
+    #[inline]
+    pub fn select_nth_unstable_by_key<K, F>(
+        &mut self,
+        index: usize,
+        mut f: F,
+    ) -> (&mut [T], &mut T, &mut [T])
+    where
+        F: FnMut(&T) -> K,
+        K: Ord,
+    {
+        let mut g = |a: &T, b: &T| f(a).lt(&f(b));
+        sort::partition_at_index(self, index, &mut g)
+    }
+
+    /// Moves all consecutive repeated elements to the end of the slice according to the
+    /// [`PartialEq`] trait implementation.
+    ///
+    /// Returns two slices. The first contains no consecutive repeated elements.
+    /// The second contains all the duplicates in no specified order.
+    ///
+    /// If the slice is sorted, the first returned slice contains no duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_partition_dedup)]
+    ///
+    /// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
+    ///
+    /// let (dedup, duplicates) = slice.partition_dedup();
+    ///
+    /// assert_eq!(dedup, [1, 2, 3, 2, 1]);
+    /// assert_eq!(duplicates, [2, 3, 1]);
+    /// ```
+    #[unstable(feature = "slice_partition_dedup", issue = "54279")]
+    #[inline]
+    pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
+    where
+        T: PartialEq,
+    {
+        self.partition_dedup_by(|a, b| a == b)
+    }
+
+    /// Moves all but the first of consecutive elements to the end of the slice satisfying
+    /// a given equality relation.
+    ///
+    /// Returns two slices. The first contains no consecutive repeated elements.
+    /// The second contains all the duplicates in no specified order.
+    ///
+    /// The `same_bucket` function is passed references to two elements from the slice and
+    /// must determine if the elements compare equal. The elements are passed in opposite order
+    /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
+    /// at the end of the slice.
+    ///
+    /// If the slice is sorted, the first returned slice contains no duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_partition_dedup)]
+    ///
+    /// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
+    ///
+    /// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+    ///
+    /// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
+    /// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
+    /// ```
+    #[unstable(feature = "slice_partition_dedup", issue = "54279")]
+    #[inline]
+    pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
+    where
+        F: FnMut(&mut T, &mut T) -> bool,
+    {
+        // Although we have a mutable reference to `self`, we cannot make
+        // *arbitrary* changes. The `same_bucket` calls could panic, so we
+        // must ensure that the slice is in a valid state at all times.
+        //
+        // The way that we handle this is by using swaps; we iterate
+        // over all the elements, swapping as we go so that at the end
+        // the elements we wish to keep are in the front, and those we
+        // wish to reject are at the back. We can then split the slice.
+        // This operation is still `O(n)`.
+        //
+        // Example: We start in this state, where `r` represents "next
+        // read" and `w` represents "next_write`.
+        //
+        //           r
+        //     +---+---+---+---+---+---+
+        //     | 0 | 1 | 1 | 2 | 3 | 3 |
+        //     +---+---+---+---+---+---+
+        //           w
+        //
+        // Comparing self[r] against self[w-1], this is not a duplicate, so
+        // we swap self[r] and self[w] (no effect as r==w) and then increment both
+        // r and w, leaving us with:
+        //
+        //               r
+        //     +---+---+---+---+---+---+
+        //     | 0 | 1 | 1 | 2 | 3 | 3 |
+        //     +---+---+---+---+---+---+
+        //               w
+        //
+        // Comparing self[r] against self[w-1], this value is a duplicate,
+        // so we increment `r` but leave everything else unchanged:
+        //
+        //                   r
+        //     +---+---+---+---+---+---+
+        //     | 0 | 1 | 1 | 2 | 3 | 3 |
+        //     +---+---+---+---+---+---+
+        //               w
+        //
+        // Comparing self[r] against self[w-1], this is not a duplicate,
+        // so swap self[r] and self[w] and advance r and w:
+        //
+        //                       r
+        //     +---+---+---+---+---+---+
+        //     | 0 | 1 | 2 | 1 | 3 | 3 |
+        //     +---+---+---+---+---+---+
+        //                   w
+        //
+        // Not a duplicate, repeat:
+        //
+        //                           r
+        //     +---+---+---+---+---+---+
+        //     | 0 | 1 | 2 | 3 | 1 | 3 |
+        //     +---+---+---+---+---+---+
+        //                       w
+        //
+        // Duplicate, advance r. End of slice. Split at w.
+
+        let len = self.len();
+        if len <= 1 {
+            return (self, &mut []);
+        }
+
+        let ptr = self.as_mut_ptr();
+        let mut next_read: usize = 1;
+        let mut next_write: usize = 1;
+
+        // SAFETY: the `while` condition guarantees `next_read` and `next_write`
+        // are less than `len`, thus are inside `self`. `prev_ptr_write` points to
+        // one element before `ptr_write`, but `next_write` starts at 1, so
+        // `prev_ptr_write` is never less than 0 and is inside the slice.
+        // This fulfils the requirements for dereferencing `ptr_read`, `prev_ptr_write`
+        // and `ptr_write`, and for using `ptr.add(next_read)`, `ptr.add(next_write - 1)`
+        // and `prev_ptr_write.offset(1)`.
+        //
+        // `next_write` is also incremented at most once per loop at most meaning
+        // no element is skipped when it may need to be swapped.
+        //
+        // `ptr_read` and `prev_ptr_write` never point to the same element. This
+        // is required for `&mut *ptr_read`, `&mut *prev_ptr_write` to be safe.
+        // The explanation is simply that `next_read >= next_write` is always true,
+        // thus `next_read > next_write - 1` is too.
+        unsafe {
+            // Avoid bounds checks by using raw pointers.
+            while next_read < len {
+                let ptr_read = ptr.add(next_read);
+                let prev_ptr_write = ptr.add(next_write - 1);
+                if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
+                    if next_read != next_write {
+                        let ptr_write = prev_ptr_write.offset(1);
+                        mem::swap(&mut *ptr_read, &mut *ptr_write);
+                    }
+                    next_write += 1;
+                }
+                next_read += 1;
+            }
+        }
+
+        self.split_at_mut(next_write)
+    }
+
+    /// Moves all but the first of consecutive elements to the end of the slice that resolve
+    /// to the same key.
+    ///
+    /// Returns two slices. The first contains no consecutive repeated elements.
+    /// The second contains all the duplicates in no specified order.
+    ///
+    /// If the slice is sorted, the first returned slice contains no duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_partition_dedup)]
+    ///
+    /// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
+    ///
+    /// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
+    ///
+    /// assert_eq!(dedup, [10, 20, 30, 20, 11]);
+    /// assert_eq!(duplicates, [21, 30, 13]);
+    /// ```
+    #[unstable(feature = "slice_partition_dedup", issue = "54279")]
+    #[inline]
+    pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
+    where
+        F: FnMut(&mut T) -> K,
+        K: PartialEq,
+    {
+        self.partition_dedup_by(|a, b| key(a) == key(b))
+    }
+
+    /// Rotates the slice in-place such that the first `mid` elements of the
+    /// slice move to the end while the last `self.len() - mid` elements move to
+    /// the front. After calling `rotate_left`, the element previously at index
+    /// `mid` will become the first element in the slice.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if `mid` is greater than the length of the
+    /// slice. Note that `mid == self.len()` does _not_ panic and is a no-op
+    /// rotation.
+    ///
+    /// # Complexity
+    ///
+    /// Takes linear (in `self.len()`) time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
+    /// a.rotate_left(2);
+    /// assert_eq!(a, ['c', 'd', 'e', 'f', 'a', 'b']);
+    /// ```
+    ///
+    /// Rotating a subslice:
+    ///
+    /// ```
+    /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
+    /// a[1..5].rotate_left(1);
+    /// assert_eq!(a, ['a', 'c', 'd', 'e', 'b', 'f']);
+    /// ```
+    #[stable(feature = "slice_rotate", since = "1.26.0")]
+    pub fn rotate_left(&mut self, mid: usize) {
+        assert!(mid <= self.len());
+        let k = self.len() - mid;
+        let p = self.as_mut_ptr();
+
+        // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
+        // valid for reading and writing, as required by `ptr_rotate`.
+        unsafe {
+            rotate::ptr_rotate(mid, p.add(mid), k);
+        }
+    }
+
+    /// Rotates the slice in-place such that the first `self.len() - k`
+    /// elements of the slice move to the end while the last `k` elements move
+    /// to the front. After calling `rotate_right`, the element previously at
+    /// index `self.len() - k` will become the first element in the slice.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if `k` is greater than the length of the
+    /// slice. Note that `k == self.len()` does _not_ panic and is a no-op
+    /// rotation.
+    ///
+    /// # Complexity
+    ///
+    /// Takes linear (in `self.len()`) time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
+    /// a.rotate_right(2);
+    /// assert_eq!(a, ['e', 'f', 'a', 'b', 'c', 'd']);
+    /// ```
+    ///
+    /// Rotate a subslice:
+    ///
+    /// ```
+    /// let mut a = ['a', 'b', 'c', 'd', 'e', 'f'];
+    /// a[1..5].rotate_right(1);
+    /// assert_eq!(a, ['a', 'e', 'b', 'c', 'd', 'f']);
+    /// ```
+    #[stable(feature = "slice_rotate", since = "1.26.0")]
+    pub fn rotate_right(&mut self, k: usize) {
+        assert!(k <= self.len());
+        let mid = self.len() - k;
+        let p = self.as_mut_ptr();
+
+        // SAFETY: The range `[p.add(mid) - mid, p.add(mid) + k)` is trivially
+        // valid for reading and writing, as required by `ptr_rotate`.
+        unsafe {
+            rotate::ptr_rotate(mid, p.add(mid), k);
+        }
+    }
+
+    /// Fills `self` with elements by cloning `value`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut buf = vec![0; 10];
+    /// buf.fill(1);
+    /// assert_eq!(buf, vec![1; 10]);
+    /// ```
+    #[doc(alias = "memset")]
+    #[stable(feature = "slice_fill", since = "1.50.0")]
+    pub fn fill(&mut self, value: T)
+    where
+        T: Clone,
+    {
+        specialize::SpecFill::spec_fill(self, value);
+    }
+
+    /// Fills `self` with elements returned by calling a closure repeatedly.
+    ///
+    /// This method uses a closure to create new values. If you'd rather
+    /// [`Clone`] a given value, use [`fill`]. If you want to use the [`Default`]
+    /// trait to generate values, you can pass [`Default::default`] as the
+    /// argument.
+    ///
+    /// [`fill`]: slice::fill
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut buf = vec![1; 10];
+    /// buf.fill_with(Default::default);
+    /// assert_eq!(buf, vec![0; 10]);
+    /// ```
+    #[stable(feature = "slice_fill_with", since = "1.51.0")]
+    pub fn fill_with<F>(&mut self, mut f: F)
+    where
+        F: FnMut() -> T,
+    {
+        for el in self {
+            *el = f();
+        }
+    }
+
+    /// Copies the elements from `src` into `self`.
+    ///
+    /// The length of `src` must be the same as `self`.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the two slices have different lengths.
+    ///
+    /// # Examples
+    ///
+    /// Cloning two elements from a slice into another:
+    ///
+    /// ```
+    /// let src = [1, 2, 3, 4];
+    /// let mut dst = [0, 0];
+    ///
+    /// // Because the slices have to be the same length,
+    /// // we slice the source slice from four elements
+    /// // to two. It will panic if we don't do this.
+    /// dst.clone_from_slice(&src[2..]);
+    ///
+    /// assert_eq!(src, [1, 2, 3, 4]);
+    /// assert_eq!(dst, [3, 4]);
+    /// ```
+    ///
+    /// Rust enforces that there can only be one mutable reference with no
+    /// immutable references to a particular piece of data in a particular
+    /// scope. Because of this, attempting to use `clone_from_slice` on a
+    /// single slice will result in a compile failure:
+    ///
+    /// ```compile_fail
+    /// let mut slice = [1, 2, 3, 4, 5];
+    ///
+    /// slice[..2].clone_from_slice(&slice[3..]); // compile fail!
+    /// ```
+    ///
+    /// To work around this, we can use [`split_at_mut`] to create two distinct
+    /// sub-slices from a slice:
+    ///
+    /// ```
+    /// let mut slice = [1, 2, 3, 4, 5];
+    ///
+    /// {
+    ///     let (left, right) = slice.split_at_mut(2);
+    ///     left.clone_from_slice(&right[1..]);
+    /// }
+    ///
+    /// assert_eq!(slice, [4, 5, 3, 4, 5]);
+    /// ```
+    ///
+    /// [`copy_from_slice`]: slice::copy_from_slice
+    /// [`split_at_mut`]: slice::split_at_mut
+    #[stable(feature = "clone_from_slice", since = "1.7.0")]
+    #[track_caller]
+    pub fn clone_from_slice(&mut self, src: &[T])
+    where
+        T: Clone,
+    {
+        self.spec_clone_from(src);
+    }
+
+    /// Copies all elements from `src` into `self`, using a memcpy.
+    ///
+    /// The length of `src` must be the same as `self`.
+    ///
+    /// If `T` does not implement `Copy`, use [`clone_from_slice`].
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the two slices have different lengths.
+    ///
+    /// # Examples
+    ///
+    /// Copying two elements from a slice into another:
+    ///
+    /// ```
+    /// let src = [1, 2, 3, 4];
+    /// let mut dst = [0, 0];
+    ///
+    /// // Because the slices have to be the same length,
+    /// // we slice the source slice from four elements
+    /// // to two. It will panic if we don't do this.
+    /// dst.copy_from_slice(&src[2..]);
+    ///
+    /// assert_eq!(src, [1, 2, 3, 4]);
+    /// assert_eq!(dst, [3, 4]);
+    /// ```
+    ///
+    /// Rust enforces that there can only be one mutable reference with no
+    /// immutable references to a particular piece of data in a particular
+    /// scope. Because of this, attempting to use `copy_from_slice` on a
+    /// single slice will result in a compile failure:
+    ///
+    /// ```compile_fail
+    /// let mut slice = [1, 2, 3, 4, 5];
+    ///
+    /// slice[..2].copy_from_slice(&slice[3..]); // compile fail!
+    /// ```
+    ///
+    /// To work around this, we can use [`split_at_mut`] to create two distinct
+    /// sub-slices from a slice:
+    ///
+    /// ```
+    /// let mut slice = [1, 2, 3, 4, 5];
+    ///
+    /// {
+    ///     let (left, right) = slice.split_at_mut(2);
+    ///     left.copy_from_slice(&right[1..]);
+    /// }
+    ///
+    /// assert_eq!(slice, [4, 5, 3, 4, 5]);
+    /// ```
+    ///
+    /// [`clone_from_slice`]: slice::clone_from_slice
+    /// [`split_at_mut`]: slice::split_at_mut
+    #[doc(alias = "memcpy")]
+    #[stable(feature = "copy_from_slice", since = "1.9.0")]
+    #[track_caller]
+    pub fn copy_from_slice(&mut self, src: &[T])
+    where
+        T: Copy,
+    {
+        // The panic code path was put into a cold function to not bloat the
+        // call site.
+        #[inline(never)]
+        #[cold]
+        #[track_caller]
+        fn len_mismatch_fail(dst_len: usize, src_len: usize) -> ! {
+            panic!(
+                "source slice length ({}) does not match destination slice length ({})",
+                src_len, dst_len,
+            );
+        }
+
+        if self.len() != src.len() {
+            len_mismatch_fail(self.len(), src.len());
+        }
+
+        // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
+        // checked to have the same length. The slices cannot overlap because
+        // mutable references are exclusive.
+        unsafe {
+            ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
+        }
+    }
+
+    /// Copies elements from one part of the slice to another part of itself,
+    /// using a memmove.
+    ///
+    /// `src` is the range within `self` to copy from. `dest` is the starting
+    /// index of the range within `self` to copy to, which will have the same
+    /// length as `src`. The two ranges may overlap. The ends of the two ranges
+    /// must be less than or equal to `self.len()`.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if either range exceeds the end of the slice,
+    /// or if the end of `src` is before the start.
+    ///
+    /// # Examples
+    ///
+    /// Copying four bytes within a slice:
+    ///
+    /// ```
+    /// let mut bytes = *b"Hello, World!";
+    ///
+    /// bytes.copy_within(1..5, 8);
+    ///
+    /// assert_eq!(&bytes, b"Hello, Wello!");
+    /// ```
+    #[stable(feature = "copy_within", since = "1.37.0")]
+    #[track_caller]
+    pub fn copy_within<R: RangeBounds<usize>>(&mut self, src: R, dest: usize)
+    where
+        T: Copy,
+    {
+        let Range { start: src_start, end: src_end } = slice::range(src, ..self.len());
+        let count = src_end - src_start;
+        assert!(dest <= self.len() - count, "dest is out of bounds");
+        // SAFETY: the conditions for `ptr::copy` have all been checked above,
+        // as have those for `ptr::add`.
+        unsafe {
+            // Derive both `src_ptr` and `dest_ptr` from the same loan
+            let ptr = self.as_mut_ptr();
+            let src_ptr = ptr.add(src_start);
+            let dest_ptr = ptr.add(dest);
+            ptr::copy(src_ptr, dest_ptr, count);
+        }
+    }
+
+    /// Swaps all elements in `self` with those in `other`.
+    ///
+    /// The length of `other` must be the same as `self`.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the two slices have different lengths.
+    ///
+    /// # Example
+    ///
+    /// Swapping two elements across slices:
+    ///
+    /// ```
+    /// let mut slice1 = [0, 0];
+    /// let mut slice2 = [1, 2, 3, 4];
+    ///
+    /// slice1.swap_with_slice(&mut slice2[2..]);
+    ///
+    /// assert_eq!(slice1, [3, 4]);
+    /// assert_eq!(slice2, [1, 2, 0, 0]);
+    /// ```
+    ///
+    /// Rust enforces that there can only be one mutable reference to a
+    /// particular piece of data in a particular scope. Because of this,
+    /// attempting to use `swap_with_slice` on a single slice will result in
+    /// a compile failure:
+    ///
+    /// ```compile_fail
+    /// let mut slice = [1, 2, 3, 4, 5];
+    /// slice[..2].swap_with_slice(&mut slice[3..]); // compile fail!
+    /// ```
+    ///
+    /// To work around this, we can use [`split_at_mut`] to create two distinct
+    /// mutable sub-slices from a slice:
+    ///
+    /// ```
+    /// let mut slice = [1, 2, 3, 4, 5];
+    ///
+    /// {
+    ///     let (left, right) = slice.split_at_mut(2);
+    ///     left.swap_with_slice(&mut right[1..]);
+    /// }
+    ///
+    /// assert_eq!(slice, [4, 5, 3, 1, 2]);
+    /// ```
+    ///
+    /// [`split_at_mut`]: slice::split_at_mut
+    #[stable(feature = "swap_with_slice", since = "1.27.0")]
+    #[track_caller]
+    pub fn swap_with_slice(&mut self, other: &mut [T]) {
+        assert!(self.len() == other.len(), "destination and source slices have different lengths");
+        // SAFETY: `self` is valid for `self.len()` elements by definition, and `src` was
+        // checked to have the same length. The slices cannot overlap because
+        // mutable references are exclusive.
+        unsafe {
+            ptr::swap_nonoverlapping(self.as_mut_ptr(), other.as_mut_ptr(), self.len());
+        }
+    }
+
+    /// Function to calculate lengths of the middle and trailing slice for `align_to{,_mut}`.
+    fn align_to_offsets<U>(&self) -> (usize, usize) {
+        // What we gonna do about `rest` is figure out what multiple of `U`s we can put in a
+        // lowest number of `T`s. And how many `T`s we need for each such "multiple".
+        //
+        // Consider for example T=u8 U=u16. Then we can put 1 U in 2 Ts. Simple. Now, consider
+        // for example a case where size_of::<T> = 16, size_of::<U> = 24. We can put 2 Us in
+        // place of every 3 Ts in the `rest` slice. A bit more complicated.
+        //
+        // Formula to calculate this is:
+        //
+        // Us = lcm(size_of::<T>, size_of::<U>) / size_of::<U>
+        // Ts = lcm(size_of::<T>, size_of::<U>) / size_of::<T>
+        //
+        // Expanded and simplified:
+        //
+        // Us = size_of::<T> / gcd(size_of::<T>, size_of::<U>)
+        // Ts = size_of::<U> / gcd(size_of::<T>, size_of::<U>)
+        //
+        // Luckily since all this is constant-evaluated... performance here matters not!
+        #[inline]
+        fn gcd(a: usize, b: usize) -> usize {
+            use crate::intrinsics;
+            // iterative stein’s algorithm
+            // We should still make this `const fn` (and revert to recursive algorithm if we do)
+            // because relying on llvm to consteval all this is… well, it makes me uncomfortable.
+
+            // SAFETY: `a` and `b` are checked to be non-zero values.
+            let (ctz_a, mut ctz_b) = unsafe {
+                if a == 0 {
+                    return b;
+                }
+                if b == 0 {
+                    return a;
+                }
+                (intrinsics::cttz_nonzero(a), intrinsics::cttz_nonzero(b))
+            };
+            let k = ctz_a.min(ctz_b);
+            let mut a = a >> ctz_a;
+            let mut b = b;
+            loop {
+                // remove all factors of 2 from b
+                b >>= ctz_b;
+                if a > b {
+                    mem::swap(&mut a, &mut b);
+                }
+                b = b - a;
+                // SAFETY: `b` is checked to be non-zero.
+                unsafe {
+                    if b == 0 {
+                        break;
+                    }
+                    ctz_b = intrinsics::cttz_nonzero(b);
+                }
+            }
+            a << k
+        }
+        let gcd: usize = gcd(mem::size_of::<T>(), mem::size_of::<U>());
+        let ts: usize = mem::size_of::<U>() / gcd;
+        let us: usize = mem::size_of::<T>() / gcd;
+
+        // Armed with this knowledge, we can find how many `U`s we can fit!
+        let us_len = self.len() / ts * us;
+        // And how many `T`s will be in the trailing slice!
+        let ts_len = self.len() % ts;
+        (us_len, ts_len)
+    }
+
+    /// Transmute the slice to a slice of another type, ensuring alignment of the types is
+    /// maintained.
+    ///
+    /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
+    /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
+    /// length possible for a given type and input slice, but only your algorithm's performance
+    /// should depend on that, not its correctness. It is permissible for all of the input data to
+    /// be returned as the prefix or suffix slice.
+    ///
+    /// This method has no purpose when either input element `T` or output element `U` are
+    /// zero-sized and will return the original slice without splitting anything.
+    ///
+    /// # Safety
+    ///
+    /// This method is essentially a `transmute` with respect to the elements in the returned
+    /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// unsafe {
+    ///     let bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
+    ///     let (prefix, shorts, suffix) = bytes.align_to::<u16>();
+    ///     // less_efficient_algorithm_for_bytes(prefix);
+    ///     // more_efficient_algorithm_for_aligned_shorts(shorts);
+    ///     // less_efficient_algorithm_for_bytes(suffix);
+    /// }
+    /// ```
+    #[stable(feature = "slice_align_to", since = "1.30.0")]
+    #[must_use]
+    pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
+        // Note that most of this function will be constant-evaluated,
+        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+            // handle ZSTs specially, which is – don't handle them at all.
+            return (self, &[], &[]);
+        }
+
+        // First, find at what point do we split between the first and 2nd slice. Easy with
+        // ptr.align_offset.
+        let ptr = self.as_ptr();
+        // SAFETY: See the `align_to_mut` method for the detailed safety comment.
+        let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
+        if offset > self.len() {
+            (self, &[], &[])
+        } else {
+            let (left, rest) = self.split_at(offset);
+            let (us_len, ts_len) = rest.align_to_offsets::<U>();
+            // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
+            // since the caller guarantees that we can transmute `T` to `U` safely.
+            unsafe {
+                (
+                    left,
+                    from_raw_parts(rest.as_ptr() as *const U, us_len),
+                    from_raw_parts(rest.as_ptr().add(rest.len() - ts_len), ts_len),
+                )
+            }
+        }
+    }
+
+    /// Transmute the slice to a slice of another type, ensuring alignment of the types is
+    /// maintained.
+    ///
+    /// This method splits the slice into three distinct slices: prefix, correctly aligned middle
+    /// slice of a new type, and the suffix slice. The method may make the middle slice the greatest
+    /// length possible for a given type and input slice, but only your algorithm's performance
+    /// should depend on that, not its correctness. It is permissible for all of the input data to
+    /// be returned as the prefix or suffix slice.
+    ///
+    /// This method has no purpose when either input element `T` or output element `U` are
+    /// zero-sized and will return the original slice without splitting anything.
+    ///
+    /// # Safety
+    ///
+    /// This method is essentially a `transmute` with respect to the elements in the returned
+    /// middle slice, so all the usual caveats pertaining to `transmute::<T, U>` also apply here.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// unsafe {
+    ///     let mut bytes: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
+    ///     let (prefix, shorts, suffix) = bytes.align_to_mut::<u16>();
+    ///     // less_efficient_algorithm_for_bytes(prefix);
+    ///     // more_efficient_algorithm_for_aligned_shorts(shorts);
+    ///     // less_efficient_algorithm_for_bytes(suffix);
+    /// }
+    /// ```
+    #[stable(feature = "slice_align_to", since = "1.30.0")]
+    #[must_use]
+    pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
+        // Note that most of this function will be constant-evaluated,
+        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+            // handle ZSTs specially, which is – don't handle them at all.
+            return (self, &mut [], &mut []);
+        }
+
+        // First, find at what point do we split between the first and 2nd slice. Easy with
+        // ptr.align_offset.
+        let ptr = self.as_ptr();
+        // SAFETY: Here we are ensuring we will use aligned pointers for U for the
+        // rest of the method. This is done by passing a pointer to &[T] with an
+        // alignment targeted for U.
+        // `crate::ptr::align_offset` is called with a correctly aligned and
+        // valid pointer `ptr` (it comes from a reference to `self`) and with
+        // a size that is a power of two (since it comes from the alignement for U),
+        // satisfying its safety constraints.
+        let offset = unsafe { crate::ptr::align_offset(ptr, mem::align_of::<U>()) };
+        if offset > self.len() {
+            (self, &mut [], &mut [])
+        } else {
+            let (left, rest) = self.split_at_mut(offset);
+            let (us_len, ts_len) = rest.align_to_offsets::<U>();
+            let rest_len = rest.len();
+            let mut_ptr = rest.as_mut_ptr();
+            // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
+            // SAFETY: see comments for `align_to`.
+            unsafe {
+                (
+                    left,
+                    from_raw_parts_mut(mut_ptr as *mut U, us_len),
+                    from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
+                )
+            }
+        }
+    }
+
+    /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
+    ///
+    /// This is a safe wrapper around [`slice::align_to`], so has the same weak
+    /// postconditions as that method.  You're only assured that
+    /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
+    ///
+    /// Notably, all of the following are possible:
+    /// - `prefix.len() >= LANES`.
+    /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
+    /// - `suffix.len() >= LANES`.
+    ///
+    /// That said, this is a safe method, so if you're only writing safe code,
+    /// then this can at most cause incorrect logic, not unsoundness.
+    ///
+    /// # Panics
+    ///
+    /// This will panic if the size of the SIMD type is different from
+    /// `LANES` times that of the scalar.
+    ///
+    /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
+    /// that from ever happening, as only power-of-two numbers of lanes are
+    /// supported.  It's possible that, in the future, those restrictions might
+    /// be lifted in a way that would make it possible to see panics from this
+    /// method for something like `LANES == 3`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(portable_simd)]
+    /// use core::simd::SimdFloat;
+    ///
+    /// let short = &[1, 2, 3];
+    /// let (prefix, middle, suffix) = short.as_simd::<4>();
+    /// assert_eq!(middle, []); // Not enough elements for anything in the middle
+    ///
+    /// // They might be split in any possible way between prefix and suffix
+    /// let it = prefix.iter().chain(suffix).copied();
+    /// assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
+    ///
+    /// fn basic_simd_sum(x: &[f32]) -> f32 {
+    ///     use std::ops::Add;
+    ///     use std::simd::f32x4;
+    ///     let (prefix, middle, suffix) = x.as_simd();
+    ///     let sums = f32x4::from_array([
+    ///         prefix.iter().copied().sum(),
+    ///         0.0,
+    ///         0.0,
+    ///         suffix.iter().copied().sum(),
+    ///     ]);
+    ///     let sums = middle.iter().copied().fold(sums, f32x4::add);
+    ///     sums.reduce_sum()
+    /// }
+    ///
+    /// let numbers: Vec<f32> = (1..101).map(|x| x as _).collect();
+    /// assert_eq!(basic_simd_sum(&numbers[1..99]), 4949.0);
+    /// ```
+    #[unstable(feature = "portable_simd", issue = "86656")]
+    #[must_use]
+    pub fn as_simd<const LANES: usize>(&self) -> (&[T], &[Simd<T, LANES>], &[T])
+    where
+        Simd<T, LANES>: AsRef<[T; LANES]>,
+        T: simd::SimdElement,
+        simd::LaneCount<LANES>: simd::SupportedLaneCount,
+    {
+        // These are expected to always match, as vector types are laid out like
+        // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
+        // might as well double-check since it'll optimize away anyhow.
+        assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
+
+        // SAFETY: The simd types have the same layout as arrays, just with
+        // potentially-higher alignment, so the de-facto transmutes are sound.
+        unsafe { self.align_to() }
+    }
+
+    /// Split a slice into a prefix, a middle of aligned SIMD types, and a suffix.
+    ///
+    /// This is a safe wrapper around [`slice::align_to_mut`], so has the same weak
+    /// postconditions as that method.  You're only assured that
+    /// `self.len() == prefix.len() + middle.len() * LANES + suffix.len()`.
+    ///
+    /// Notably, all of the following are possible:
+    /// - `prefix.len() >= LANES`.
+    /// - `middle.is_empty()` despite `self.len() >= 3 * LANES`.
+    /// - `suffix.len() >= LANES`.
+    ///
+    /// That said, this is a safe method, so if you're only writing safe code,
+    /// then this can at most cause incorrect logic, not unsoundness.
+    ///
+    /// This is the mutable version of [`slice::as_simd`]; see that for examples.
+    ///
+    /// # Panics
+    ///
+    /// This will panic if the size of the SIMD type is different from
+    /// `LANES` times that of the scalar.
+    ///
+    /// At the time of writing, the trait restrictions on `Simd<T, LANES>` keeps
+    /// that from ever happening, as only power-of-two numbers of lanes are
+    /// supported.  It's possible that, in the future, those restrictions might
+    /// be lifted in a way that would make it possible to see panics from this
+    /// method for something like `LANES == 3`.
+    #[unstable(feature = "portable_simd", issue = "86656")]
+    #[must_use]
+    pub fn as_simd_mut<const LANES: usize>(&mut self) -> (&mut [T], &mut [Simd<T, LANES>], &mut [T])
+    where
+        Simd<T, LANES>: AsMut<[T; LANES]>,
+        T: simd::SimdElement,
+        simd::LaneCount<LANES>: simd::SupportedLaneCount,
+    {
+        // These are expected to always match, as vector types are laid out like
+        // arrays per <https://llvm.org/docs/LangRef.html#vector-type>, but we
+        // might as well double-check since it'll optimize away anyhow.
+        assert_eq!(mem::size_of::<Simd<T, LANES>>(), mem::size_of::<[T; LANES]>());
+
+        // SAFETY: The simd types have the same layout as arrays, just with
+        // potentially-higher alignment, so the de-facto transmutes are sound.
+        unsafe { self.align_to_mut() }
+    }
+
+    /// Checks if the elements of this slice are sorted.
+    ///
+    /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
+    /// slice yields exactly zero or one element, `true` is returned.
+    ///
+    /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
+    /// implies that this function returns `false` if any two consecutive items are not
+    /// comparable.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_sorted)]
+    /// let empty: [i32; 0] = [];
+    ///
+    /// assert!([1, 2, 2, 9].is_sorted());
+    /// assert!(![1, 3, 2, 4].is_sorted());
+    /// assert!([0].is_sorted());
+    /// assert!(empty.is_sorted());
+    /// assert!(![0.0, 1.0, f32::NAN].is_sorted());
+    /// ```
+    #[inline]
+    #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[must_use]
+    pub fn is_sorted(&self) -> bool
+    where
+        T: PartialOrd,
+    {
+        self.is_sorted_by(|a, b| a.partial_cmp(b))
+    }
+
+    /// Checks if the elements of this slice are sorted using the given comparator function.
+    ///
+    /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
+    /// function to determine the ordering of two elements. Apart from that, it's equivalent to
+    /// [`is_sorted`]; see its documentation for more information.
+    ///
+    /// [`is_sorted`]: slice::is_sorted
+    #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[must_use]
+    pub fn is_sorted_by<F>(&self, mut compare: F) -> bool
+    where
+        F: FnMut(&T, &T) -> Option<Ordering>,
+    {
+        self.iter().is_sorted_by(|a, b| compare(*a, *b))
+    }
+
+    /// Checks if the elements of this slice are sorted using the given key extraction function.
+    ///
+    /// Instead of comparing the slice's elements directly, this function compares the keys of the
+    /// elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see its
+    /// documentation for more information.
+    ///
+    /// [`is_sorted`]: slice::is_sorted
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_sorted)]
+    ///
+    /// assert!(["c", "bb", "aaa"].is_sorted_by_key(|s| s.len()));
+    /// assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
+    /// ```
+    #[inline]
+    #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[must_use]
+    pub fn is_sorted_by_key<F, K>(&self, f: F) -> bool
+    where
+        F: FnMut(&T) -> K,
+        K: PartialOrd,
+    {
+        self.iter().is_sorted_by_key(f)
+    }
+
+    /// Returns the index of the partition point according to the given predicate
+    /// (the index of the first element of the second partition).
+    ///
+    /// The slice is assumed to be partitioned according to the given predicate.
+    /// This means that all elements for which the predicate returns true are at the start of the slice
+    /// and all elements for which the predicate returns false are at the end.
+    /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
+    /// (all odd numbers are at the start, all even at the end).
+    ///
+    /// If this slice is not partitioned, the returned result is unspecified and meaningless,
+    /// as this method performs a kind of binary search.
+    ///
+    /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
+    ///
+    /// [`binary_search`]: slice::binary_search
+    /// [`binary_search_by`]: slice::binary_search_by
+    /// [`binary_search_by_key`]: slice::binary_search_by_key
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = [1, 2, 3, 3, 5, 6, 7];
+    /// let i = v.partition_point(|&x| x < 5);
+    ///
+    /// assert_eq!(i, 4);
+    /// assert!(v[..i].iter().all(|&x| x < 5));
+    /// assert!(v[i..].iter().all(|&x| !(x < 5)));
+    /// ```
+    ///
+    /// If you want to insert an item to a sorted vector, while maintaining
+    /// sort order:
+    ///
+    /// ```
+    /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    /// let num = 42;
+    /// let idx = s.partition_point(|&x| x < num);
+    /// s.insert(idx, num);
+    /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
+    /// ```
+    #[stable(feature = "partition_point", since = "1.52.0")]
+    #[must_use]
+    pub fn partition_point<P>(&self, mut pred: P) -> usize
+    where
+        P: FnMut(&T) -> bool,
+    {
+        self.binary_search_by(|x| if pred(x) { Less } else { Greater }).unwrap_or_else(|i| i)
+    }
+
+    /// Removes the subslice corresponding to the given range
+    /// and returns a reference to it.
+    ///
+    /// Returns `None` and does not modify the slice if the given
+    /// range is out of bounds.
+    ///
+    /// Note that this method only accepts one-sided ranges such as
+    /// `2..` or `..6`, but not `2..6`.
+    ///
+    /// # Examples
+    ///
+    /// Taking the first three elements of a slice:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
+    /// let mut first_three = slice.take(..3).unwrap();
+    ///
+    /// assert_eq!(slice, &['d']);
+    /// assert_eq!(first_three, &['a', 'b', 'c']);
+    /// ```
+    ///
+    /// Taking the last two elements of a slice:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
+    /// let mut tail = slice.take(2..).unwrap();
+    ///
+    /// assert_eq!(slice, &['a', 'b']);
+    /// assert_eq!(tail, &['c', 'd']);
+    /// ```
+    ///
+    /// Getting `None` when `range` is out of bounds:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &[_] = &['a', 'b', 'c', 'd'];
+    ///
+    /// assert_eq!(None, slice.take(5..));
+    /// assert_eq!(None, slice.take(..5));
+    /// assert_eq!(None, slice.take(..=4));
+    /// let expected: &[char] = &['a', 'b', 'c', 'd'];
+    /// assert_eq!(Some(expected), slice.take(..4));
+    /// ```
+    #[inline]
+    #[must_use = "method does not modify the slice if the range is out of bounds"]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take<'a, R: OneSidedRange<usize>>(self: &mut &'a Self, range: R) -> Option<&'a Self> {
+        let (direction, split_index) = split_point_of(range)?;
+        if split_index > self.len() {
+            return None;
+        }
+        let (front, back) = self.split_at(split_index);
+        match direction {
+            Direction::Front => {
+                *self = back;
+                Some(front)
+            }
+            Direction::Back => {
+                *self = front;
+                Some(back)
+            }
+        }
+    }
+
+    /// Removes the subslice corresponding to the given range
+    /// and returns a mutable reference to it.
+    ///
+    /// Returns `None` and does not modify the slice if the given
+    /// range is out of bounds.
+    ///
+    /// Note that this method only accepts one-sided ranges such as
+    /// `2..` or `..6`, but not `2..6`.
+    ///
+    /// # Examples
+    ///
+    /// Taking the first three elements of a slice:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
+    /// let mut first_three = slice.take_mut(..3).unwrap();
+    ///
+    /// assert_eq!(slice, &mut ['d']);
+    /// assert_eq!(first_three, &mut ['a', 'b', 'c']);
+    /// ```
+    ///
+    /// Taking the last two elements of a slice:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
+    /// let mut tail = slice.take_mut(2..).unwrap();
+    ///
+    /// assert_eq!(slice, &mut ['a', 'b']);
+    /// assert_eq!(tail, &mut ['c', 'd']);
+    /// ```
+    ///
+    /// Getting `None` when `range` is out of bounds:
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &mut [_] = &mut ['a', 'b', 'c', 'd'];
+    ///
+    /// assert_eq!(None, slice.take_mut(5..));
+    /// assert_eq!(None, slice.take_mut(..5));
+    /// assert_eq!(None, slice.take_mut(..=4));
+    /// let expected: &mut [_] = &mut ['a', 'b', 'c', 'd'];
+    /// assert_eq!(Some(expected), slice.take_mut(..4));
+    /// ```
+    #[inline]
+    #[must_use = "method does not modify the slice if the range is out of bounds"]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take_mut<'a, R: OneSidedRange<usize>>(
+        self: &mut &'a mut Self,
+        range: R,
+    ) -> Option<&'a mut Self> {
+        let (direction, split_index) = split_point_of(range)?;
+        if split_index > self.len() {
+            return None;
+        }
+        let (front, back) = mem::take(self).split_at_mut(split_index);
+        match direction {
+            Direction::Front => {
+                *self = back;
+                Some(front)
+            }
+            Direction::Back => {
+                *self = front;
+                Some(back)
+            }
+        }
+    }
+
+    /// Removes the first element of the slice and returns a reference
+    /// to it.
+    ///
+    /// Returns `None` if the slice is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &[_] = &['a', 'b', 'c'];
+    /// let first = slice.take_first().unwrap();
+    ///
+    /// assert_eq!(slice, &['b', 'c']);
+    /// assert_eq!(first, &'a');
+    /// ```
+    #[inline]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take_first<'a>(self: &mut &'a Self) -> Option<&'a T> {
+        let (first, rem) = self.split_first()?;
+        *self = rem;
+        Some(first)
+    }
+
+    /// Removes the first element of the slice and returns a mutable
+    /// reference to it.
+    ///
+    /// Returns `None` if the slice is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
+    /// let first = slice.take_first_mut().unwrap();
+    /// *first = 'd';
+    ///
+    /// assert_eq!(slice, &['b', 'c']);
+    /// assert_eq!(first, &'d');
+    /// ```
+    #[inline]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take_first_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
+        let (first, rem) = mem::take(self).split_first_mut()?;
+        *self = rem;
+        Some(first)
+    }
+
+    /// Removes the last element of the slice and returns a reference
+    /// to it.
+    ///
+    /// Returns `None` if the slice is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &[_] = &['a', 'b', 'c'];
+    /// let last = slice.take_last().unwrap();
+    ///
+    /// assert_eq!(slice, &['a', 'b']);
+    /// assert_eq!(last, &'c');
+    /// ```
+    #[inline]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take_last<'a>(self: &mut &'a Self) -> Option<&'a T> {
+        let (last, rem) = self.split_last()?;
+        *self = rem;
+        Some(last)
+    }
+
+    /// Removes the last element of the slice and returns a mutable
+    /// reference to it.
+    ///
+    /// Returns `None` if the slice is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_take)]
+    ///
+    /// let mut slice: &mut [_] = &mut ['a', 'b', 'c'];
+    /// let last = slice.take_last_mut().unwrap();
+    /// *last = 'd';
+    ///
+    /// assert_eq!(slice, &['a', 'b']);
+    /// assert_eq!(last, &'d');
+    /// ```
+    #[inline]
+    #[unstable(feature = "slice_take", issue = "62280")]
+    pub fn take_last_mut<'a>(self: &mut &'a mut Self) -> Option<&'a mut T> {
+        let (last, rem) = mem::take(self).split_last_mut()?;
+        *self = rem;
+        Some(last)
+    }
+}
+
+impl<T, const N: usize> [[T; N]] {
+    /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
+    ///
+    /// # Panics
+    ///
+    /// This panics if the length of the resulting slice would overflow a `usize`.
+    ///
+    /// This is only possible when flattening a slice of arrays of zero-sized
+    /// types, and thus tends to be irrelevant in practice. If
+    /// `size_of::<T>() > 0`, this will never panic.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_flatten)]
+    ///
+    /// assert_eq!([[1, 2, 3], [4, 5, 6]].flatten(), &[1, 2, 3, 4, 5, 6]);
+    ///
+    /// assert_eq!(
+    ///     [[1, 2, 3], [4, 5, 6]].flatten(),
+    ///     [[1, 2], [3, 4], [5, 6]].flatten(),
+    /// );
+    ///
+    /// let slice_of_empty_arrays: &[[i32; 0]] = &[[], [], [], [], []];
+    /// assert!(slice_of_empty_arrays.flatten().is_empty());
+    ///
+    /// let empty_slice_of_arrays: &[[u32; 10]] = &[];
+    /// assert!(empty_slice_of_arrays.flatten().is_empty());
+    /// ```
+    #[unstable(feature = "slice_flatten", issue = "95629")]
+    pub fn flatten(&self) -> &[T] {
+        let len = if crate::mem::size_of::<T>() == 0 {
+            self.len().checked_mul(N).expect("slice len overflow")
+        } else {
+            // SAFETY: `self.len() * N` cannot overflow because `self` is
+            // already in the address space.
+            unsafe { self.len().unchecked_mul(N) }
+        };
+        // SAFETY: `[T]` is layout-identical to `[T; N]`
+        unsafe { from_raw_parts(self.as_ptr().cast(), len) }
+    }
+
+    /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
+    ///
+    /// # Panics
+    ///
+    /// This panics if the length of the resulting slice would overflow a `usize`.
+    ///
+    /// This is only possible when flattening a slice of arrays of zero-sized
+    /// types, and thus tends to be irrelevant in practice. If
+    /// `size_of::<T>() > 0`, this will never panic.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_flatten)]
+    ///
+    /// fn add_5_to_all(slice: &mut [i32]) {
+    ///     for i in slice {
+    ///         *i += 5;
+    ///     }
+    /// }
+    ///
+    /// let mut array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
+    /// add_5_to_all(array.flatten_mut());
+    /// assert_eq!(array, [[6, 7, 8], [9, 10, 11], [12, 13, 14]]);
+    /// ```
+    #[unstable(feature = "slice_flatten", issue = "95629")]
+    pub fn flatten_mut(&mut self) -> &mut [T] {
+        let len = if crate::mem::size_of::<T>() == 0 {
+            self.len().checked_mul(N).expect("slice len overflow")
+        } else {
+            // SAFETY: `self.len() * N` cannot overflow because `self` is
+            // already in the address space.
+            unsafe { self.len().unchecked_mul(N) }
+        };
+        // SAFETY: `[T]` is layout-identical to `[T; N]`
+        unsafe { from_raw_parts_mut(self.as_mut_ptr().cast(), len) }
+    }
+}
+
+#[cfg(not(bootstrap))]
+#[cfg(not(test))]
+impl [f32] {
+    /// Sorts the slice of floats.
+    ///
+    /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
+    /// the ordering defined by [`f32::total_cmp`].
+    ///
+    /// # Current implementation
+    ///
+    /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(sort_floats)]
+    /// let mut v = [2.6, -5e-8, f32::NAN, 8.29, f32::INFINITY, -1.0, 0.0, -f32::INFINITY, -0.0];
+    ///
+    /// v.sort_floats();
+    /// let sorted = [-f32::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f32::INFINITY, f32::NAN];
+    /// assert_eq!(&v[..8], &sorted[..8]);
+    /// assert!(v[8].is_nan());
+    /// ```
+    #[unstable(feature = "sort_floats", issue = "93396")]
+    #[inline]
+    pub fn sort_floats(&mut self) {
+        self.sort_unstable_by(f32::total_cmp);
+    }
+}
+
+#[cfg(not(bootstrap))]
+#[cfg(not(test))]
+impl [f64] {
+    /// Sorts the slice of floats.
+    ///
+    /// This sort is in-place (i.e. does not allocate), *O*(*n* \* log(*n*)) worst-case, and uses
+    /// the ordering defined by [`f64::total_cmp`].
+    ///
+    /// # Current implementation
+    ///
+    /// This uses the same sorting algorithm as [`sort_unstable_by`](slice::sort_unstable_by).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(sort_floats)]
+    /// let mut v = [2.6, -5e-8, f64::NAN, 8.29, f64::INFINITY, -1.0, 0.0, -f64::INFINITY, -0.0];
+    ///
+    /// v.sort_floats();
+    /// let sorted = [-f64::INFINITY, -1.0, -5e-8, -0.0, 0.0, 2.6, 8.29, f64::INFINITY, f64::NAN];
+    /// assert_eq!(&v[..8], &sorted[..8]);
+    /// assert!(v[8].is_nan());
+    /// ```
+    #[unstable(feature = "sort_floats", issue = "93396")]
+    #[inline]
+    pub fn sort_floats(&mut self) {
+        self.sort_unstable_by(f64::total_cmp);
+    }
+}
+
+trait CloneFromSpec<T> {
+    fn spec_clone_from(&mut self, src: &[T]);
+}
+
+impl<T> CloneFromSpec<T> for [T]
+where
+    T: Clone,
+{
+    #[track_caller]
+    default fn spec_clone_from(&mut self, src: &[T]) {
+        assert!(self.len() == src.len(), "destination and source slices have different lengths");
+        // NOTE: We need to explicitly slice them to the same length
+        // to make it easier for the optimizer to elide bounds checking.
+        // But since it can't be relied on we also have an explicit specialization for T: Copy.
+        let len = self.len();
+        let src = &src[..len];
+        for i in 0..len {
+            self[i].clone_from(&src[i]);
+        }
+    }
+}
+
+impl<T> CloneFromSpec<T> for [T]
+where
+    T: Copy,
+{
+    #[track_caller]
+    fn spec_clone_from(&mut self, src: &[T]) {
+        self.copy_from_slice(src);
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for &[T] {
+    /// Creates an empty slice.
+    fn default() -> Self {
+        &[]
+    }
+}
+
+#[stable(feature = "mut_slice_default", since = "1.5.0")]
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for &mut [T] {
+    /// Creates a mutable empty slice.
+    fn default() -> Self {
+        &mut []
+    }
+}
+
+#[unstable(feature = "slice_pattern", reason = "stopgap trait for slice patterns", issue = "56345")]
+/// Patterns in slices - currently, only used by `strip_prefix` and `strip_suffix`.  At a future
+/// point, we hope to generalise `core::str::Pattern` (which at the time of writing is limited to
+/// `str`) to slices, and then this trait will be replaced or abolished.
+pub trait SlicePattern {
+    /// The element type of the slice being matched on.
+    type Item;
+
+    /// Currently, the consumers of `SlicePattern` need a slice.
+    fn as_slice(&self) -> &[Self::Item];
+}
+
+#[stable(feature = "slice_strip", since = "1.51.0")]
+impl<T> SlicePattern for [T] {
+    type Item = T;
+
+    #[inline]
+    fn as_slice(&self) -> &[Self::Item] {
+        self
+    }
+}
+
+#[stable(feature = "slice_strip", since = "1.51.0")]
+impl<T, const N: usize> SlicePattern for [T; N] {
+    type Item = T;
+
+    #[inline]
+    fn as_slice(&self) -> &[Self::Item] {
+        self
+    }
+}
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
new file mode 100644
index 000000000..107e71ab6
--- /dev/null
+++ b/library/core/src/slice/raw.rs
@@ -0,0 +1,271 @@
+//! Free functions to create `&[T]` and `&mut [T]`.
+
+use crate::array;
+use crate::intrinsics::{assert_unsafe_precondition, is_aligned_and_not_null};
+use crate::ops::Range;
+use crate::ptr;
+
+/// Forms a slice from a pointer and a length.
+///
+/// The `len` argument is the number of **elements**, not the number of bytes.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `data` must be [valid] for reads for `len * mem::size_of::<T>()` many bytes,
+///   and it must be properly aligned. This means in particular:
+///
+///     * The entire memory range of this slice must be contained within a single allocated object!
+///       Slices can never span across multiple allocated objects. See [below](#incorrect-usage)
+///       for an example incorrectly not taking this into account.
+///     * `data` must be non-null and aligned even for zero-length slices. One
+///       reason for this is that enum layout optimizations may rely on references
+///       (including slices of any length) being aligned and non-null to distinguish
+///       them from other data. You can obtain a pointer that is usable as `data`
+///       for zero-length slices using [`NonNull::dangling()`].
+///
+/// * `data` must point to `len` consecutive properly initialized values of type `T`.
+///
+/// * The memory referenced by the returned slice must not be mutated for the duration
+///   of lifetime `'a`, except inside an `UnsafeCell`.
+///
+/// * The total size `len * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
+///   See the safety documentation of [`pointer::offset`].
+///
+/// # Caveat
+///
+/// The lifetime for the returned slice is inferred from its usage. To
+/// prevent accidental misuse, it's suggested to tie the lifetime to whichever
+/// source lifetime is safe in the context, such as by providing a helper
+/// function taking the lifetime of a host value for the slice, or by explicit
+/// annotation.
+///
+/// # Examples
+///
+/// ```
+/// use std::slice;
+///
+/// // manifest a slice for a single element
+/// let x = 42;
+/// let ptr = &x as *const _;
+/// let slice = unsafe { slice::from_raw_parts(ptr, 1) };
+/// assert_eq!(slice[0], 42);
+/// ```
+///
+/// ### Incorrect usage
+///
+/// The following `join_slices` function is **unsound** ⚠️
+///
+/// ```rust,no_run
+/// use std::slice;
+///
+/// fn join_slices<'a, T>(fst: &'a [T], snd: &'a [T]) -> &'a [T] {
+///     let fst_end = fst.as_ptr().wrapping_add(fst.len());
+///     let snd_start = snd.as_ptr();
+///     assert_eq!(fst_end, snd_start, "Slices must be contiguous!");
+///     unsafe {
+///         // The assertion above ensures `fst` and `snd` are contiguous, but they might
+///         // still be contained within _different allocated objects_, in which case
+///         // creating this slice is undefined behavior.
+///         slice::from_raw_parts(fst.as_ptr(), fst.len() + snd.len())
+///     }
+/// }
+///
+/// fn main() {
+///     // `a` and `b` are different allocated objects...
+///     let a = 42;
+///     let b = 27;
+///     // ... which may nevertheless be laid out contiguously in memory: | a | b |
+///     let _ = join_slices(slice::from_ref(&a), slice::from_ref(&b)); // UB
+/// }
+/// ```
+///
+/// [valid]: ptr#safety
+/// [`NonNull::dangling()`]: ptr::NonNull::dangling
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_stable(feature = "const_slice_from_raw_parts", since = "1.64.0")]
+#[must_use]
+pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
+    // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
+    unsafe {
+        assert_unsafe_precondition!(
+            is_aligned_and_not_null(data)
+                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        );
+        &*ptr::slice_from_raw_parts(data, len)
+    }
+}
+
+/// Performs the same functionality as [`from_raw_parts`], except that a
+/// mutable slice is returned.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `data` must be [valid] for both reads and writes for `len * mem::size_of::<T>()` many bytes,
+///   and it must be properly aligned. This means in particular:
+///
+///     * The entire memory range of this slice must be contained within a single allocated object!
+///       Slices can never span across multiple allocated objects.
+///     * `data` must be non-null and aligned even for zero-length slices. One
+///       reason for this is that enum layout optimizations may rely on references
+///       (including slices of any length) being aligned and non-null to distinguish
+///       them from other data. You can obtain a pointer that is usable as `data`
+///       for zero-length slices using [`NonNull::dangling()`].
+///
+/// * `data` must point to `len` consecutive properly initialized values of type `T`.
+///
+/// * The memory referenced by the returned slice must not be accessed through any other pointer
+///   (not derived from the return value) for the duration of lifetime `'a`.
+///   Both read and write accesses are forbidden.
+///
+/// * The total size `len * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
+///   See the safety documentation of [`pointer::offset`].
+///
+/// [valid]: ptr#safety
+/// [`NonNull::dangling()`]: ptr::NonNull::dangling
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_slice_from_raw_parts_mut", issue = "67456")]
+#[must_use]
+pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
+    // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
+    unsafe {
+        assert_unsafe_precondition!(
+            is_aligned_and_not_null(data)
+                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        );
+        &mut *ptr::slice_from_raw_parts_mut(data, len)
+    }
+}
+
+/// Converts a reference to T into a slice of length 1 (without copying).
+#[stable(feature = "from_ref", since = "1.28.0")]
+#[rustc_const_stable(feature = "const_slice_from_ref_shared", since = "1.63.0")]
+#[must_use]
+pub const fn from_ref<T>(s: &T) -> &[T] {
+    array::from_ref(s)
+}
+
+/// Converts a reference to T into a slice of length 1 (without copying).
+#[stable(feature = "from_ref", since = "1.28.0")]
+#[rustc_const_unstable(feature = "const_slice_from_ref", issue = "90206")]
+#[must_use]
+pub const fn from_mut<T>(s: &mut T) -> &mut [T] {
+    array::from_mut(s)
+}
+
+/// Forms a slice from a pointer range.
+///
+/// This function is useful for interacting with foreign interfaces which
+/// use two pointers to refer to a range of elements in memory, as is
+/// common in C++.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * The `start` pointer of the range must be a [valid] and properly aligned pointer
+///   to the first element of a slice.
+///
+/// * The `end` pointer must be a [valid] and properly aligned pointer to *one past*
+///   the last element, such that the offset from the end to the start pointer is
+///   the length of the slice.
+///
+/// * The range must contain `N` consecutive properly initialized values of type `T`:
+///
+///     * The entire memory range of this slice must be contained within a single allocated object!
+///       Slices can never span across multiple allocated objects.
+///
+/// * The memory referenced by the returned slice must not be mutated for the duration
+///   of lifetime `'a`, except inside an `UnsafeCell`.
+///
+/// * The total length of the range must be no larger than `isize::MAX`.
+///   See the safety documentation of [`pointer::offset`].
+///
+/// Note that a range created from [`slice::as_ptr_range`] fulfills these requirements.
+///
+/// # Caveat
+///
+/// The lifetime for the returned slice is inferred from its usage. To
+/// prevent accidental misuse, it's suggested to tie the lifetime to whichever
+/// source lifetime is safe in the context, such as by providing a helper
+/// function taking the lifetime of a host value for the slice, or by explicit
+/// annotation.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(slice_from_ptr_range)]
+///
+/// use core::slice;
+///
+/// let x = [1, 2, 3];
+/// let range = x.as_ptr_range();
+///
+/// unsafe {
+///     assert_eq!(slice::from_ptr_range(range), &x);
+/// }
+/// ```
+///
+/// [valid]: ptr#safety
+#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
+#[rustc_const_unstable(feature = "const_slice_from_ptr_range", issue = "89792")]
+pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
+    // SAFETY: the caller must uphold the safety contract for `from_ptr_range`.
+    unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
+}
+
+/// Performs the same functionality as [`from_ptr_range`], except that a
+/// mutable slice is returned.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * The `start` pointer of the range must be a [valid] and properly aligned pointer
+///   to the first element of a slice.
+///
+/// * The `end` pointer must be a [valid] and properly aligned pointer to *one past*
+///   the last element, such that the offset from the end to the start pointer is
+///   the length of the slice.
+///
+/// * The range must contain `N` consecutive properly initialized values of type `T`:
+///
+///     * The entire memory range of this slice must be contained within a single allocated object!
+///       Slices can never span across multiple allocated objects.
+///
+/// * The memory referenced by the returned slice must not be accessed through any other pointer
+///   (not derived from the return value) for the duration of lifetime `'a`.
+///   Both read and write accesses are forbidden.
+///
+/// * The total length of the range must be no larger than `isize::MAX`.
+///   See the safety documentation of [`pointer::offset`].
+///
+/// Note that a range created from [`slice::as_mut_ptr_range`] fulfills these requirements.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(slice_from_ptr_range)]
+///
+/// use core::slice;
+///
+/// let mut x = [1, 2, 3];
+/// let range = x.as_mut_ptr_range();
+///
+/// unsafe {
+///     assert_eq!(slice::from_mut_ptr_range(range), &mut [1, 2, 3]);
+/// }
+/// ```
+///
+/// [valid]: ptr#safety
+#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
+#[rustc_const_unstable(feature = "const_slice_from_mut_ptr_range", issue = "89792")]
+pub const unsafe fn from_mut_ptr_range<'a, T>(range: Range<*mut T>) -> &'a mut [T] {
+    // SAFETY: the caller must uphold the safety contract for `from_mut_ptr_range`.
+    unsafe { from_raw_parts_mut(range.start, range.end.sub_ptr(range.start)) }
+}
diff --git a/library/core/src/slice/rotate.rs b/library/core/src/slice/rotate.rs
new file mode 100644
index 000000000..4589c6c0f
--- /dev/null
+++ b/library/core/src/slice/rotate.rs
@@ -0,0 +1,234 @@
+use crate::cmp;
+use crate::mem::{self, MaybeUninit};
+use crate::ptr;
+
+/// Rotates the range `[mid-left, mid+right)` such that the element at `mid` becomes the first
+/// element. Equivalently, rotates the range `left` elements to the left or `right` elements to the
+/// right.
+///
+/// # Safety
+///
+/// The specified range must be valid for reading and writing.
+///
+/// # Algorithm
+///
+/// Algorithm 1 is used for small values of `left + right` or for large `T`. The elements are moved
+/// into their final positions one at a time starting at `mid - left` and advancing by `right` steps
+/// modulo `left + right`, such that only one temporary is needed. Eventually, we arrive back at
+/// `mid - left`. However, if `gcd(left + right, right)` is not 1, the above steps skipped over
+/// elements. For example:
+/// ```text
+/// left = 10, right = 6
+/// the `^` indicates an element in its final place
+/// 6 7 8 9 10 11 12 13 14 15 . 0 1 2 3 4 5
+/// after using one step of the above algorithm (The X will be overwritten at the end of the round,
+/// and 12 is stored in a temporary):
+/// X 7 8 9 10 11 6 13 14 15 . 0 1 2 3 4 5
+///               ^
+/// after using another step (now 2 is in the temporary):
+/// X 7 8 9 10 11 6 13 14 15 . 0 1 12 3 4 5
+///               ^                 ^
+/// after the third step (the steps wrap around, and 8 is in the temporary):
+/// X 7 2 9 10 11 6 13 14 15 . 0 1 12 3 4 5
+///     ^         ^                 ^
+/// after 7 more steps, the round ends with the temporary 0 getting put in the X:
+/// 0 7 2 9 4 11 6 13 8 15 . 10 1 12 3 14 5
+/// ^   ^   ^    ^    ^       ^    ^    ^
+/// ```
+/// Fortunately, the number of skipped over elements between finalized elements is always equal, so
+/// we can just offset our starting position and do more rounds (the total number of rounds is the
+/// `gcd(left + right, right)` value). The end result is that all elements are finalized once and
+/// only once.
+///
+/// Algorithm 2 is used if `left + right` is large but `min(left, right)` is small enough to
+/// fit onto a stack buffer. The `min(left, right)` elements are copied onto the buffer, `memmove`
+/// is applied to the others, and the ones on the buffer are moved back into the hole on the
+/// opposite side of where they originated.
+///
+/// Algorithms that can be vectorized outperform the above once `left + right` becomes large enough.
+/// Algorithm 1 can be vectorized by chunking and performing many rounds at once, but there are too
+/// few rounds on average until `left + right` is enormous, and the worst case of a single
+/// round is always there. Instead, algorithm 3 utilizes repeated swapping of
+/// `min(left, right)` elements until a smaller rotate problem is left.
+///
+/// ```text
+/// left = 11, right = 4
+/// [4 5 6 7 8 9 10 11 12 13 14 . 0 1 2 3]
+///                  ^  ^  ^  ^   ^ ^ ^ ^ swapping the right most elements with elements to the left
+/// [4 5 6 7 8 9 10 . 0 1 2 3] 11 12 13 14
+///        ^ ^ ^  ^   ^ ^ ^ ^ swapping these
+/// [4 5 6 . 0 1 2 3] 7 8 9 10 11 12 13 14
+/// we cannot swap any more, but a smaller rotation problem is left to solve
+/// ```
+/// when `left < right` the swapping happens from the left instead.
+pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize) {
+    type BufType = [usize; 32];
+    if mem::size_of::<T>() == 0 {
+        return;
+    }
+    loop {
+        // N.B. the below algorithms can fail if these cases are not checked
+        if (right == 0) || (left == 0) {
+            return;
+        }
+        if (left + right < 24) || (mem::size_of::<T>() > mem::size_of::<[usize; 4]>()) {
+            // Algorithm 1
+            // Microbenchmarks indicate that the average performance for random shifts is better all
+            // the way until about `left + right == 32`, but the worst case performance breaks even
+            // around 16. 24 was chosen as middle ground. If the size of `T` is larger than 4
+            // `usize`s, this algorithm also outperforms other algorithms.
+            // SAFETY: callers must ensure `mid - left` is valid for reading and writing.
+            let x = unsafe { mid.sub(left) };
+            // beginning of first round
+            // SAFETY: see previous comment.
+            let mut tmp: T = unsafe { x.read() };
+            let mut i = right;
+            // `gcd` can be found before hand by calculating `gcd(left + right, right)`,
+            // but it is faster to do one loop which calculates the gcd as a side effect, then
+            // doing the rest of the chunk
+            let mut gcd = right;
+            // benchmarks reveal that it is faster to swap temporaries all the way through instead
+            // of reading one temporary once, copying backwards, and then writing that temporary at
+            // the very end. This is possibly due to the fact that swapping or replacing temporaries
+            // uses only one memory address in the loop instead of needing to manage two.
+            loop {
+                // [long-safety-expl]
+                // SAFETY: callers must ensure `[left, left+mid+right)` are all valid for reading and
+                // writing.
+                //
+                // - `i` start with `right` so `mid-left <= x+i = x+right = mid-left+right < mid+right`
+                // - `i <= left+right-1` is always true
+                //   - if `i < left`, `right` is added so `i < left+right` and on the next
+                //     iteration `left` is removed from `i` so it doesn't go further
+                //   - if `i >= left`, `left` is removed immediately and so it doesn't go further.
+                // - overflows cannot happen for `i` since the function's safety contract ask for
+                //   `mid+right-1 = x+left+right` to be valid for writing
+                // - underflows cannot happen because `i` must be bigger or equal to `left` for
+                //   a subtraction of `left` to happen.
+                //
+                // So `x+i` is valid for reading and writing if the caller respected the contract
+                tmp = unsafe { x.add(i).replace(tmp) };
+                // instead of incrementing `i` and then checking if it is outside the bounds, we
+                // check if `i` will go outside the bounds on the next increment. This prevents
+                // any wrapping of pointers or `usize`.
+                if i >= left {
+                    i -= left;
+                    if i == 0 {
+                        // end of first round
+                        // SAFETY: tmp has been read from a valid source and x is valid for writing
+                        // according to the caller.
+                        unsafe { x.write(tmp) };
+                        break;
+                    }
+                    // this conditional must be here if `left + right >= 15`
+                    if i < gcd {
+                        gcd = i;
+                    }
+                } else {
+                    i += right;
+                }
+            }
+            // finish the chunk with more rounds
+            for start in 1..gcd {
+                // SAFETY: `gcd` is at most equal to `right` so all values in `1..gcd` are valid for
+                // reading and writing as per the function's safety contract, see [long-safety-expl]
+                // above
+                tmp = unsafe { x.add(start).read() };
+                // [safety-expl-addition]
+                //
+                // Here `start < gcd` so `start < right` so `i < right+right`: `right` being the
+                // greatest common divisor of `(left+right, right)` means that `left = right` so
+                // `i < left+right` so `x+i = mid-left+i` is always valid for reading and writing
+                // according to the function's safety contract.
+                i = start + right;
+                loop {
+                    // SAFETY: see [long-safety-expl] and [safety-expl-addition]
+                    tmp = unsafe { x.add(i).replace(tmp) };
+                    if i >= left {
+                        i -= left;
+                        if i == start {
+                            // SAFETY: see [long-safety-expl] and [safety-expl-addition]
+                            unsafe { x.add(start).write(tmp) };
+                            break;
+                        }
+                    } else {
+                        i += right;
+                    }
+                }
+            }
+            return;
+        // `T` is not a zero-sized type, so it's okay to divide by its size.
+        } else if cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>() {
+            // Algorithm 2
+            // The `[T; 0]` here is to ensure this is appropriately aligned for T
+            let mut rawarray = MaybeUninit::<(BufType, [T; 0])>::uninit();
+            let buf = rawarray.as_mut_ptr() as *mut T;
+            // SAFETY: `mid-left <= mid-left+right < mid+right`
+            let dim = unsafe { mid.sub(left).add(right) };
+            if left <= right {
+                // SAFETY:
+                //
+                // 1) The `else if` condition about the sizes ensures `[mid-left; left]` will fit in
+                //    `buf` without overflow and `buf` was created just above and so cannot be
+                //    overlapped with any value of `[mid-left; left]`
+                // 2) [mid-left, mid+right) are all valid for reading and writing and we don't care
+                //    about overlaps here.
+                // 3) The `if` condition about `left <= right` ensures writing `left` elements to
+                //    `dim = mid-left+right` is valid because:
+                //    - `buf` is valid and `left` elements were written in it in 1)
+                //    - `dim+left = mid-left+right+left = mid+right` and we write `[dim, dim+left)`
+                unsafe {
+                    // 1)
+                    ptr::copy_nonoverlapping(mid.sub(left), buf, left);
+                    // 2)
+                    ptr::copy(mid, mid.sub(left), right);
+                    // 3)
+                    ptr::copy_nonoverlapping(buf, dim, left);
+                }
+            } else {
+                // SAFETY: same reasoning as above but with `left` and `right` reversed
+                unsafe {
+                    ptr::copy_nonoverlapping(mid, buf, right);
+                    ptr::copy(mid.sub(left), dim, left);
+                    ptr::copy_nonoverlapping(buf, mid.sub(left), right);
+                }
+            }
+            return;
+        } else if left >= right {
+            // Algorithm 3
+            // There is an alternate way of swapping that involves finding where the last swap
+            // of this algorithm would be, and swapping using that last chunk instead of swapping
+            // adjacent chunks like this algorithm is doing, but this way is still faster.
+            loop {
+                // SAFETY:
+                // `left >= right` so `[mid-right, mid+right)` is valid for reading and writing
+                // Subtracting `right` from `mid` each turn is counterbalanced by the addition and
+                // check after it.
+                unsafe {
+                    ptr::swap_nonoverlapping(mid.sub(right), mid, right);
+                    mid = mid.sub(right);
+                }
+                left -= right;
+                if left < right {
+                    break;
+                }
+            }
+        } else {
+            // Algorithm 3, `left < right`
+            loop {
+                // SAFETY: `[mid-left, mid+left)` is valid for reading and writing because
+                // `left < right` so `mid+left < mid+right`.
+                // Adding `left` to `mid` each turn is counterbalanced by the subtraction and check
+                // after it.
+                unsafe {
+                    ptr::swap_nonoverlapping(mid.sub(left), mid, left);
+                    mid = mid.add(left);
+                }
+                right -= left;
+                if right < left {
+                    break;
+                }
+            }
+        }
+    }
+}
diff --git a/library/core/src/slice/sort.rs b/library/core/src/slice/sort.rs
new file mode 100644
index 000000000..6a201834b
--- /dev/null
+++ b/library/core/src/slice/sort.rs
@@ -0,0 +1,929 @@
+//! Slice sorting
+//!
+//! This module contains a sorting algorithm based on Orson Peters' pattern-defeating quicksort,
+//! published at: <https://github.com/orlp/pdqsort>
+//!
+//! Unstable sorting is compatible with libcore because it doesn't allocate memory, unlike our
+//! stable sorting implementation.
+
+use crate::cmp;
+use crate::mem::{self, MaybeUninit};
+use crate::ptr;
+
+/// When dropped, copies from `src` into `dest`.
+struct CopyOnDrop<T> {
+    src: *const T,
+    dest: *mut T,
+}
+
+impl<T> Drop for CopyOnDrop<T> {
+    fn drop(&mut self) {
+        // SAFETY:  This is a helper class.
+        //          Please refer to its usage for correctness.
+        //          Namely, one must be sure that `src` and `dst` does not overlap as required by `ptr::copy_nonoverlapping`.
+        unsafe {
+            ptr::copy_nonoverlapping(self.src, self.dest, 1);
+        }
+    }
+}
+
+/// Shifts the first element to the right until it encounters a greater or equal element.
+fn shift_head<T, F>(v: &mut [T], is_less: &mut F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+    // SAFETY: The unsafe operations below involves indexing without a bounds check (by offsetting a
+    // pointer) and copying memory (`ptr::copy_nonoverlapping`).
+    //
+    // a. Indexing:
+    //  1. We checked the size of the array to >=2.
+    //  2. All the indexing that we will do is always between {0 <= index < len} at most.
+    //
+    // b. Memory copying
+    //  1. We are obtaining pointers to references which are guaranteed to be valid.
+    //  2. They cannot overlap because we obtain pointers to difference indices of the slice.
+    //     Namely, `i` and `i-1`.
+    //  3. If the slice is properly aligned, the elements are properly aligned.
+    //     It is the caller's responsibility to make sure the slice is properly aligned.
+    //
+    // See comments below for further detail.
+    unsafe {
+        // If the first two elements are out-of-order...
+        if len >= 2 && is_less(v.get_unchecked(1), v.get_unchecked(0)) {
+            // Read the first element into a stack-allocated variable. If a following comparison
+            // operation panics, `hole` will get dropped and automatically write the element back
+            // into the slice.
+            let tmp = mem::ManuallyDrop::new(ptr::read(v.get_unchecked(0)));
+            let v = v.as_mut_ptr();
+            let mut hole = CopyOnDrop { src: &*tmp, dest: v.add(1) };
+            ptr::copy_nonoverlapping(v.add(1), v.add(0), 1);
+
+            for i in 2..len {
+                if !is_less(&*v.add(i), &*tmp) {
+                    break;
+                }
+
+                // Move `i`-th element one place to the left, thus shifting the hole to the right.
+                ptr::copy_nonoverlapping(v.add(i), v.add(i - 1), 1);
+                hole.dest = v.add(i);
+            }
+            // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
+        }
+    }
+}
+
+/// Shifts the last element to the left until it encounters a smaller or equal element.
+fn shift_tail<T, F>(v: &mut [T], is_less: &mut F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+    // SAFETY: The unsafe operations below involves indexing without a bound check (by offsetting a
+    // pointer) and copying memory (`ptr::copy_nonoverlapping`).
+    //
+    // a. Indexing:
+    //  1. We checked the size of the array to >= 2.
+    //  2. All the indexing that we will do is always between `0 <= index < len-1` at most.
+    //
+    // b. Memory copying
+    //  1. We are obtaining pointers to references which are guaranteed to be valid.
+    //  2. They cannot overlap because we obtain pointers to difference indices of the slice.
+    //     Namely, `i` and `i+1`.
+    //  3. If the slice is properly aligned, the elements are properly aligned.
+    //     It is the caller's responsibility to make sure the slice is properly aligned.
+    //
+    // See comments below for further detail.
+    unsafe {
+        // If the last two elements are out-of-order...
+        if len >= 2 && is_less(v.get_unchecked(len - 1), v.get_unchecked(len - 2)) {
+            // Read the last element into a stack-allocated variable. If a following comparison
+            // operation panics, `hole` will get dropped and automatically write the element back
+            // into the slice.
+            let tmp = mem::ManuallyDrop::new(ptr::read(v.get_unchecked(len - 1)));
+            let v = v.as_mut_ptr();
+            let mut hole = CopyOnDrop { src: &*tmp, dest: v.add(len - 2) };
+            ptr::copy_nonoverlapping(v.add(len - 2), v.add(len - 1), 1);
+
+            for i in (0..len - 2).rev() {
+                if !is_less(&*tmp, &*v.add(i)) {
+                    break;
+                }
+
+                // Move `i`-th element one place to the right, thus shifting the hole to the left.
+                ptr::copy_nonoverlapping(v.add(i), v.add(i + 1), 1);
+                hole.dest = v.add(i);
+            }
+            // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
+        }
+    }
+}
+
+/// Partially sorts a slice by shifting several out-of-order elements around.
+///
+/// Returns `true` if the slice is sorted at the end. This function is *O*(*n*) worst-case.
+#[cold]
+fn partial_insertion_sort<T, F>(v: &mut [T], is_less: &mut F) -> bool
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Maximum number of adjacent out-of-order pairs that will get shifted.
+    const MAX_STEPS: usize = 5;
+    // If the slice is shorter than this, don't shift any elements.
+    const SHORTEST_SHIFTING: usize = 50;
+
+    let len = v.len();
+    let mut i = 1;
+
+    for _ in 0..MAX_STEPS {
+        // SAFETY: We already explicitly did the bound checking with `i < len`.
+        // All our subsequent indexing is only in the range `0 <= index < len`
+        unsafe {
+            // Find the next pair of adjacent out-of-order elements.
+            while i < len && !is_less(v.get_unchecked(i), v.get_unchecked(i - 1)) {
+                i += 1;
+            }
+        }
+
+        // Are we done?
+        if i == len {
+            return true;
+        }
+
+        // Don't shift elements on short arrays, that has a performance cost.
+        if len < SHORTEST_SHIFTING {
+            return false;
+        }
+
+        // Swap the found pair of elements. This puts them in correct order.
+        v.swap(i - 1, i);
+
+        // Shift the smaller element to the left.
+        shift_tail(&mut v[..i], is_less);
+        // Shift the greater element to the right.
+        shift_head(&mut v[i..], is_less);
+    }
+
+    // Didn't manage to sort the slice in the limited number of steps.
+    false
+}
+
+/// Sorts a slice using insertion sort, which is *O*(*n*^2) worst-case.
+fn insertion_sort<T, F>(v: &mut [T], is_less: &mut F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    for i in 1..v.len() {
+        shift_tail(&mut v[..i + 1], is_less);
+    }
+}
+
+/// Sorts `v` using heapsort, which guarantees *O*(*n* \* log(*n*)) worst-case.
+#[cold]
+#[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
+pub fn heapsort<T, F>(v: &mut [T], mut is_less: F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // This binary heap respects the invariant `parent >= child`.
+    let mut sift_down = |v: &mut [T], mut node| {
+        loop {
+            // Children of `node`.
+            let mut child = 2 * node + 1;
+            if child >= v.len() {
+                break;
+            }
+
+            // Choose the greater child.
+            if child + 1 < v.len() && is_less(&v[child], &v[child + 1]) {
+                child += 1;
+            }
+
+            // Stop if the invariant holds at `node`.
+            if !is_less(&v[node], &v[child]) {
+                break;
+            }
+
+            // Swap `node` with the greater child, move one step down, and continue sifting.
+            v.swap(node, child);
+            node = child;
+        }
+    };
+
+    // Build the heap in linear time.
+    for i in (0..v.len() / 2).rev() {
+        sift_down(v, i);
+    }
+
+    // Pop maximal elements from the heap.
+    for i in (1..v.len()).rev() {
+        v.swap(0, i);
+        sift_down(&mut v[..i], 0);
+    }
+}
+
+/// Partitions `v` into elements smaller than `pivot`, followed by elements greater than or equal
+/// to `pivot`.
+///
+/// Returns the number of elements smaller than `pivot`.
+///
+/// Partitioning is performed block-by-block in order to minimize the cost of branching operations.
+/// This idea is presented in the [BlockQuicksort][pdf] paper.
+///
+/// [pdf]: https://drops.dagstuhl.de/opus/volltexte/2016/6389/pdf/LIPIcs-ESA-2016-38.pdf
+fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Number of elements in a typical block.
+    const BLOCK: usize = 128;
+
+    // The partitioning algorithm repeats the following steps until completion:
+    //
+    // 1. Trace a block from the left side to identify elements greater than or equal to the pivot.
+    // 2. Trace a block from the right side to identify elements smaller than the pivot.
+    // 3. Exchange the identified elements between the left and right side.
+    //
+    // We keep the following variables for a block of elements:
+    //
+    // 1. `block` - Number of elements in the block.
+    // 2. `start` - Start pointer into the `offsets` array.
+    // 3. `end` - End pointer into the `offsets` array.
+    // 4. `offsets - Indices of out-of-order elements within the block.
+
+    // The current block on the left side (from `l` to `l.add(block_l)`).
+    let mut l = v.as_mut_ptr();
+    let mut block_l = BLOCK;
+    let mut start_l = ptr::null_mut();
+    let mut end_l = ptr::null_mut();
+    let mut offsets_l = [MaybeUninit::<u8>::uninit(); BLOCK];
+
+    // The current block on the right side (from `r.sub(block_r)` to `r`).
+    // SAFETY: The documentation for .add() specifically mention that `vec.as_ptr().add(vec.len())` is always safe`
+    let mut r = unsafe { l.add(v.len()) };
+    let mut block_r = BLOCK;
+    let mut start_r = ptr::null_mut();
+    let mut end_r = ptr::null_mut();
+    let mut offsets_r = [MaybeUninit::<u8>::uninit(); BLOCK];
+
+    // FIXME: When we get VLAs, try creating one array of length `min(v.len(), 2 * BLOCK)` rather
+    // than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.
+
+    // Returns the number of elements between pointers `l` (inclusive) and `r` (exclusive).
+    fn width<T>(l: *mut T, r: *mut T) -> usize {
+        assert!(mem::size_of::<T>() > 0);
+        // FIXME: this should *likely* use `offset_from`, but more
+        // investigation is needed (including running tests in miri).
+        (r.addr() - l.addr()) / mem::size_of::<T>()
+    }
+
+    loop {
+        // We are done with partitioning block-by-block when `l` and `r` get very close. Then we do
+        // some patch-up work in order to partition the remaining elements in between.
+        let is_done = width(l, r) <= 2 * BLOCK;
+
+        if is_done {
+            // Number of remaining elements (still not compared to the pivot).
+            let mut rem = width(l, r);
+            if start_l < end_l || start_r < end_r {
+                rem -= BLOCK;
+            }
+
+            // Adjust block sizes so that the left and right block don't overlap, but get perfectly
+            // aligned to cover the whole remaining gap.
+            if start_l < end_l {
+                block_r = rem;
+            } else if start_r < end_r {
+                block_l = rem;
+            } else {
+                // There were the same number of elements to switch on both blocks during the last
+                // iteration, so there are no remaining elements on either block. Cover the remaining
+                // items with roughly equally-sized blocks.
+                block_l = rem / 2;
+                block_r = rem - block_l;
+            }
+            debug_assert!(block_l <= BLOCK && block_r <= BLOCK);
+            debug_assert!(width(l, r) == block_l + block_r);
+        }
+
+        if start_l == end_l {
+            // Trace `block_l` elements from the left side.
+            start_l = MaybeUninit::slice_as_mut_ptr(&mut offsets_l);
+            end_l = start_l;
+            let mut elem = l;
+
+            for i in 0..block_l {
+                // SAFETY: The unsafety operations below involve the usage of the `offset`.
+                //         According to the conditions required by the function, we satisfy them because:
+                //         1. `offsets_l` is stack-allocated, and thus considered separate allocated object.
+                //         2. The function `is_less` returns a `bool`.
+                //            Casting a `bool` will never overflow `isize`.
+                //         3. We have guaranteed that `block_l` will be `<= BLOCK`.
+                //            Plus, `end_l` was initially set to the begin pointer of `offsets_` which was declared on the stack.
+                //            Thus, we know that even in the worst case (all invocations of `is_less` returns false) we will only be at most 1 byte pass the end.
+                //        Another unsafety operation here is dereferencing `elem`.
+                //        However, `elem` was initially the begin pointer to the slice which is always valid.
+                unsafe {
+                    // Branchless comparison.
+                    *end_l = i as u8;
+                    end_l = end_l.offset(!is_less(&*elem, pivot) as isize);
+                    elem = elem.offset(1);
+                }
+            }
+        }
+
+        if start_r == end_r {
+            // Trace `block_r` elements from the right side.
+            start_r = MaybeUninit::slice_as_mut_ptr(&mut offsets_r);
+            end_r = start_r;
+            let mut elem = r;
+
+            for i in 0..block_r {
+                // SAFETY: The unsafety operations below involve the usage of the `offset`.
+                //         According to the conditions required by the function, we satisfy them because:
+                //         1. `offsets_r` is stack-allocated, and thus considered separate allocated object.
+                //         2. The function `is_less` returns a `bool`.
+                //            Casting a `bool` will never overflow `isize`.
+                //         3. We have guaranteed that `block_r` will be `<= BLOCK`.
+                //            Plus, `end_r` was initially set to the begin pointer of `offsets_` which was declared on the stack.
+                //            Thus, we know that even in the worst case (all invocations of `is_less` returns true) we will only be at most 1 byte pass the end.
+                //        Another unsafety operation here is dereferencing `elem`.
+                //        However, `elem` was initially `1 * sizeof(T)` past the end and we decrement it by `1 * sizeof(T)` before accessing it.
+                //        Plus, `block_r` was asserted to be less than `BLOCK` and `elem` will therefore at most be pointing to the beginning of the slice.
+                unsafe {
+                    // Branchless comparison.
+                    elem = elem.offset(-1);
+                    *end_r = i as u8;
+                    end_r = end_r.offset(is_less(&*elem, pivot) as isize);
+                }
+            }
+        }
+
+        // Number of out-of-order elements to swap between the left and right side.
+        let count = cmp::min(width(start_l, end_l), width(start_r, end_r));
+
+        if count > 0 {
+            macro_rules! left {
+                () => {
+                    l.offset(*start_l as isize)
+                };
+            }
+            macro_rules! right {
+                () => {
+                    r.offset(-(*start_r as isize) - 1)
+                };
+            }
+
+            // Instead of swapping one pair at the time, it is more efficient to perform a cyclic
+            // permutation. This is not strictly equivalent to swapping, but produces a similar
+            // result using fewer memory operations.
+
+            // SAFETY: The use of `ptr::read` is valid because there is at least one element in
+            // both `offsets_l` and `offsets_r`, so `left!` is a valid pointer to read from.
+            //
+            // The uses of `left!` involve calls to `offset` on `l`, which points to the
+            // beginning of `v`. All the offsets pointed-to by `start_l` are at most `block_l`, so
+            // these `offset` calls are safe as all reads are within the block. The same argument
+            // applies for the uses of `right!`.
+            //
+            // The calls to `start_l.offset` are valid because there are at most `count-1` of them,
+            // plus the final one at the end of the unsafe block, where `count` is the minimum number
+            // of collected offsets in `offsets_l` and `offsets_r`, so there is no risk of there not
+            // being enough elements. The same reasoning applies to the calls to `start_r.offset`.
+            //
+            // The calls to `copy_nonoverlapping` are safe because `left!` and `right!` are guaranteed
+            // not to overlap, and are valid because of the reasoning above.
+            unsafe {
+                let tmp = ptr::read(left!());
+                ptr::copy_nonoverlapping(right!(), left!(), 1);
+
+                for _ in 1..count {
+                    start_l = start_l.offset(1);
+                    ptr::copy_nonoverlapping(left!(), right!(), 1);
+                    start_r = start_r.offset(1);
+                    ptr::copy_nonoverlapping(right!(), left!(), 1);
+                }
+
+                ptr::copy_nonoverlapping(&tmp, right!(), 1);
+                mem::forget(tmp);
+                start_l = start_l.offset(1);
+                start_r = start_r.offset(1);
+            }
+        }
+
+        if start_l == end_l {
+            // All out-of-order elements in the left block were moved. Move to the next block.
+
+            // block-width-guarantee
+            // SAFETY: if `!is_done` then the slice width is guaranteed to be at least `2*BLOCK` wide. There
+            // are at most `BLOCK` elements in `offsets_l` because of its size, so the `offset` operation is
+            // safe. Otherwise, the debug assertions in the `is_done` case guarantee that
+            // `width(l, r) == block_l + block_r`, namely, that the block sizes have been adjusted to account
+            // for the smaller number of remaining elements.
+            l = unsafe { l.offset(block_l as isize) };
+        }
+
+        if start_r == end_r {
+            // All out-of-order elements in the right block were moved. Move to the previous block.
+
+            // SAFETY: Same argument as [block-width-guarantee]. Either this is a full block `2*BLOCK`-wide,
+            // or `block_r` has been adjusted for the last handful of elements.
+            r = unsafe { r.offset(-(block_r as isize)) };
+        }
+
+        if is_done {
+            break;
+        }
+    }
+
+    // All that remains now is at most one block (either the left or the right) with out-of-order
+    // elements that need to be moved. Such remaining elements can be simply shifted to the end
+    // within their block.
+
+    if start_l < end_l {
+        // The left block remains.
+        // Move its remaining out-of-order elements to the far right.
+        debug_assert_eq!(width(l, r), block_l);
+        while start_l < end_l {
+            // remaining-elements-safety
+            // SAFETY: while the loop condition holds there are still elements in `offsets_l`, so it
+            // is safe to point `end_l` to the previous element.
+            //
+            // The `ptr::swap` is safe if both its arguments are valid for reads and writes:
+            //  - Per the debug assert above, the distance between `l` and `r` is `block_l`
+            //    elements, so there can be at most `block_l` remaining offsets between `start_l`
+            //    and `end_l`. This means `r` will be moved at most `block_l` steps back, which
+            //    makes the `r.offset` calls valid (at that point `l == r`).
+            //  - `offsets_l` contains valid offsets into `v` collected during the partitioning of
+            //    the last block, so the `l.offset` calls are valid.
+            unsafe {
+                end_l = end_l.offset(-1);
+                ptr::swap(l.offset(*end_l as isize), r.offset(-1));
+                r = r.offset(-1);
+            }
+        }
+        width(v.as_mut_ptr(), r)
+    } else if start_r < end_r {
+        // The right block remains.
+        // Move its remaining out-of-order elements to the far left.
+        debug_assert_eq!(width(l, r), block_r);
+        while start_r < end_r {
+            // SAFETY: See the reasoning in [remaining-elements-safety].
+            unsafe {
+                end_r = end_r.offset(-1);
+                ptr::swap(l, r.offset(-(*end_r as isize) - 1));
+                l = l.offset(1);
+            }
+        }
+        width(v.as_mut_ptr(), l)
+    } else {
+        // Nothing else to do, we're done.
+        width(v.as_mut_ptr(), l)
+    }
+}
+
+/// Partitions `v` into elements smaller than `v[pivot]`, followed by elements greater than or
+/// equal to `v[pivot]`.
+///
+/// Returns a tuple of:
+///
+/// 1. Number of elements smaller than `v[pivot]`.
+/// 2. True if `v` was already partitioned.
+fn partition<T, F>(v: &mut [T], pivot: usize, is_less: &mut F) -> (usize, bool)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let (mid, was_partitioned) = {
+        // Place the pivot at the beginning of slice.
+        v.swap(0, pivot);
+        let (pivot, v) = v.split_at_mut(1);
+        let pivot = &mut pivot[0];
+
+        // Read the pivot into a stack-allocated variable for efficiency. If a following comparison
+        // operation panics, the pivot will be automatically written back into the slice.
+
+        // SAFETY: `pivot` is a reference to the first element of `v`, so `ptr::read` is safe.
+        let tmp = mem::ManuallyDrop::new(unsafe { ptr::read(pivot) });
+        let _pivot_guard = CopyOnDrop { src: &*tmp, dest: pivot };
+        let pivot = &*tmp;
+
+        // Find the first pair of out-of-order elements.
+        let mut l = 0;
+        let mut r = v.len();
+
+        // SAFETY: The unsafety below involves indexing an array.
+        // For the first one: We already do the bounds checking here with `l < r`.
+        // For the second one: We initially have `l == 0` and `r == v.len()` and we checked that `l < r` at every indexing operation.
+        //                     From here we know that `r` must be at least `r == l` which was shown to be valid from the first one.
+        unsafe {
+            // Find the first element greater than or equal to the pivot.
+            while l < r && is_less(v.get_unchecked(l), pivot) {
+                l += 1;
+            }
+
+            // Find the last element smaller that the pivot.
+            while l < r && !is_less(v.get_unchecked(r - 1), pivot) {
+                r -= 1;
+            }
+        }
+
+        (l + partition_in_blocks(&mut v[l..r], pivot, is_less), l >= r)
+
+        // `_pivot_guard` goes out of scope and writes the pivot (which is a stack-allocated
+        // variable) back into the slice where it originally was. This step is critical in ensuring
+        // safety!
+    };
+
+    // Place the pivot between the two partitions.
+    v.swap(0, mid);
+
+    (mid, was_partitioned)
+}
+
+/// Partitions `v` into elements equal to `v[pivot]` followed by elements greater than `v[pivot]`.
+///
+/// Returns the number of elements equal to the pivot. It is assumed that `v` does not contain
+/// elements smaller than the pivot.
+fn partition_equal<T, F>(v: &mut [T], pivot: usize, is_less: &mut F) -> usize
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Place the pivot at the beginning of slice.
+    v.swap(0, pivot);
+    let (pivot, v) = v.split_at_mut(1);
+    let pivot = &mut pivot[0];
+
+    // Read the pivot into a stack-allocated variable for efficiency. If a following comparison
+    // operation panics, the pivot will be automatically written back into the slice.
+    // SAFETY: The pointer here is valid because it is obtained from a reference to a slice.
+    let tmp = mem::ManuallyDrop::new(unsafe { ptr::read(pivot) });
+    let _pivot_guard = CopyOnDrop { src: &*tmp, dest: pivot };
+    let pivot = &*tmp;
+
+    // Now partition the slice.
+    let mut l = 0;
+    let mut r = v.len();
+    loop {
+        // SAFETY: The unsafety below involves indexing an array.
+        // For the first one: We already do the bounds checking here with `l < r`.
+        // For the second one: We initially have `l == 0` and `r == v.len()` and we checked that `l < r` at every indexing operation.
+        //                     From here we know that `r` must be at least `r == l` which was shown to be valid from the first one.
+        unsafe {
+            // Find the first element greater than the pivot.
+            while l < r && !is_less(pivot, v.get_unchecked(l)) {
+                l += 1;
+            }
+
+            // Find the last element equal to the pivot.
+            while l < r && is_less(pivot, v.get_unchecked(r - 1)) {
+                r -= 1;
+            }
+
+            // Are we done?
+            if l >= r {
+                break;
+            }
+
+            // Swap the found pair of out-of-order elements.
+            r -= 1;
+            let ptr = v.as_mut_ptr();
+            ptr::swap(ptr.add(l), ptr.add(r));
+            l += 1;
+        }
+    }
+
+    // We found `l` elements equal to the pivot. Add 1 to account for the pivot itself.
+    l + 1
+
+    // `_pivot_guard` goes out of scope and writes the pivot (which is a stack-allocated variable)
+    // back into the slice where it originally was. This step is critical in ensuring safety!
+}
+
+/// Scatters some elements around in an attempt to break patterns that might cause imbalanced
+/// partitions in quicksort.
+#[cold]
+fn break_patterns<T>(v: &mut [T]) {
+    let len = v.len();
+    if len >= 8 {
+        // Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
+        let mut random = len as u32;
+        let mut gen_u32 = || {
+            random ^= random << 13;
+            random ^= random >> 17;
+            random ^= random << 5;
+            random
+        };
+        let mut gen_usize = || {
+            if usize::BITS <= 32 {
+                gen_u32() as usize
+            } else {
+                (((gen_u32() as u64) << 32) | (gen_u32() as u64)) as usize
+            }
+        };
+
+        // Take random numbers modulo this number.
+        // The number fits into `usize` because `len` is not greater than `isize::MAX`.
+        let modulus = len.next_power_of_two();
+
+        // Some pivot candidates will be in the nearby of this index. Let's randomize them.
+        let pos = len / 4 * 2;
+
+        for i in 0..3 {
+            // Generate a random number modulo `len`. However, in order to avoid costly operations
+            // we first take it modulo a power of two, and then decrease by `len` until it fits
+            // into the range `[0, len - 1]`.
+            let mut other = gen_usize() & (modulus - 1);
+
+            // `other` is guaranteed to be less than `2 * len`.
+            if other >= len {
+                other -= len;
+            }
+
+            v.swap(pos - 1 + i, other);
+        }
+    }
+}
+
+/// Chooses a pivot in `v` and returns the index and `true` if the slice is likely already sorted.
+///
+/// Elements in `v` might be reordered in the process.
+fn choose_pivot<T, F>(v: &mut [T], is_less: &mut F) -> (usize, bool)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Minimum length to choose the median-of-medians method.
+    // Shorter slices use the simple median-of-three method.
+    const SHORTEST_MEDIAN_OF_MEDIANS: usize = 50;
+    // Maximum number of swaps that can be performed in this function.
+    const MAX_SWAPS: usize = 4 * 3;
+
+    let len = v.len();
+
+    // Three indices near which we are going to choose a pivot.
+    let mut a = len / 4 * 1;
+    let mut b = len / 4 * 2;
+    let mut c = len / 4 * 3;
+
+    // Counts the total number of swaps we are about to perform while sorting indices.
+    let mut swaps = 0;
+
+    if len >= 8 {
+        // Swaps indices so that `v[a] <= v[b]`.
+        // SAFETY: `len >= 8` so there are at least two elements in the neighborhoods of
+        // `a`, `b` and `c`. This means the three calls to `sort_adjacent` result in
+        // corresponding calls to `sort3` with valid 3-item neighborhoods around each
+        // pointer, which in turn means the calls to `sort2` are done with valid
+        // references. Thus the `v.get_unchecked` calls are safe, as is the `ptr::swap`
+        // call.
+        let mut sort2 = |a: &mut usize, b: &mut usize| unsafe {
+            if is_less(v.get_unchecked(*b), v.get_unchecked(*a)) {
+                ptr::swap(a, b);
+                swaps += 1;
+            }
+        };
+
+        // Swaps indices so that `v[a] <= v[b] <= v[c]`.
+        let mut sort3 = |a: &mut usize, b: &mut usize, c: &mut usize| {
+            sort2(a, b);
+            sort2(b, c);
+            sort2(a, b);
+        };
+
+        if len >= SHORTEST_MEDIAN_OF_MEDIANS {
+            // Finds the median of `v[a - 1], v[a], v[a + 1]` and stores the index into `a`.
+            let mut sort_adjacent = |a: &mut usize| {
+                let tmp = *a;
+                sort3(&mut (tmp - 1), a, &mut (tmp + 1));
+            };
+
+            // Find medians in the neighborhoods of `a`, `b`, and `c`.
+            sort_adjacent(&mut a);
+            sort_adjacent(&mut b);
+            sort_adjacent(&mut c);
+        }
+
+        // Find the median among `a`, `b`, and `c`.
+        sort3(&mut a, &mut b, &mut c);
+    }
+
+    if swaps < MAX_SWAPS {
+        (b, swaps == 0)
+    } else {
+        // The maximum number of swaps was performed. Chances are the slice is descending or mostly
+        // descending, so reversing will probably help sort it faster.
+        v.reverse();
+        (len - 1 - b, true)
+    }
+}
+
+/// Sorts `v` recursively.
+///
+/// If the slice had a predecessor in the original array, it is specified as `pred`.
+///
+/// `limit` is the number of allowed imbalanced partitions before switching to `heapsort`. If zero,
+/// this function will immediately switch to heapsort.
+fn recurse<'a, T, F>(mut v: &'a mut [T], is_less: &mut F, mut pred: Option<&'a T>, mut limit: u32)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Slices of up to this length get sorted using insertion sort.
+    const MAX_INSERTION: usize = 20;
+
+    // True if the last partitioning was reasonably balanced.
+    let mut was_balanced = true;
+    // True if the last partitioning didn't shuffle elements (the slice was already partitioned).
+    let mut was_partitioned = true;
+
+    loop {
+        let len = v.len();
+
+        // Very short slices get sorted using insertion sort.
+        if len <= MAX_INSERTION {
+            insertion_sort(v, is_less);
+            return;
+        }
+
+        // If too many bad pivot choices were made, simply fall back to heapsort in order to
+        // guarantee `O(n * log(n))` worst-case.
+        if limit == 0 {
+            heapsort(v, is_less);
+            return;
+        }
+
+        // If the last partitioning was imbalanced, try breaking patterns in the slice by shuffling
+        // some elements around. Hopefully we'll choose a better pivot this time.
+        if !was_balanced {
+            break_patterns(v);
+            limit -= 1;
+        }
+
+        // Choose a pivot and try guessing whether the slice is already sorted.
+        let (pivot, likely_sorted) = choose_pivot(v, is_less);
+
+        // If the last partitioning was decently balanced and didn't shuffle elements, and if pivot
+        // selection predicts the slice is likely already sorted...
+        if was_balanced && was_partitioned && likely_sorted {
+            // Try identifying several out-of-order elements and shifting them to correct
+            // positions. If the slice ends up being completely sorted, we're done.
+            if partial_insertion_sort(v, is_less) {
+                return;
+            }
+        }
+
+        // If the chosen pivot is equal to the predecessor, then it's the smallest element in the
+        // slice. Partition the slice into elements equal to and elements greater than the pivot.
+        // This case is usually hit when the slice contains many duplicate elements.
+        if let Some(p) = pred {
+            if !is_less(p, &v[pivot]) {
+                let mid = partition_equal(v, pivot, is_less);
+
+                // Continue sorting elements greater than the pivot.
+                v = &mut v[mid..];
+                continue;
+            }
+        }
+
+        // Partition the slice.
+        let (mid, was_p) = partition(v, pivot, is_less);
+        was_balanced = cmp::min(mid, len - mid) >= len / 8;
+        was_partitioned = was_p;
+
+        // Split the slice into `left`, `pivot`, and `right`.
+        let (left, right) = v.split_at_mut(mid);
+        let (pivot, right) = right.split_at_mut(1);
+        let pivot = &pivot[0];
+
+        // Recurse into the shorter side only in order to minimize the total number of recursive
+        // calls and consume less stack space. Then just continue with the longer side (this is
+        // akin to tail recursion).
+        if left.len() < right.len() {
+            recurse(left, is_less, pred, limit);
+            v = right;
+            pred = Some(pivot);
+        } else {
+            recurse(right, is_less, Some(pivot), limit);
+            v = left;
+        }
+    }
+}
+
+/// Sorts `v` using pattern-defeating quicksort, which is *O*(*n* \* log(*n*)) worst-case.
+pub fn quicksort<T, F>(v: &mut [T], mut is_less: F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    // Sorting has no meaningful behavior on zero-sized types.
+    if mem::size_of::<T>() == 0 {
+        return;
+    }
+
+    // Limit the number of imbalanced partitions to `floor(log2(len)) + 1`.
+    let limit = usize::BITS - v.len().leading_zeros();
+
+    recurse(v, &mut is_less, None, limit);
+}
+
+fn partition_at_index_loop<'a, T, F>(
+    mut v: &'a mut [T],
+    mut index: usize,
+    is_less: &mut F,
+    mut pred: Option<&'a T>,
+) where
+    F: FnMut(&T, &T) -> bool,
+{
+    loop {
+        // For slices of up to this length it's probably faster to simply sort them.
+        const MAX_INSERTION: usize = 10;
+        if v.len() <= MAX_INSERTION {
+            insertion_sort(v, is_less);
+            return;
+        }
+
+        // Choose a pivot
+        let (pivot, _) = choose_pivot(v, is_less);
+
+        // If the chosen pivot is equal to the predecessor, then it's the smallest element in the
+        // slice. Partition the slice into elements equal to and elements greater than the pivot.
+        // This case is usually hit when the slice contains many duplicate elements.
+        if let Some(p) = pred {
+            if !is_less(p, &v[pivot]) {
+                let mid = partition_equal(v, pivot, is_less);
+
+                // If we've passed our index, then we're good.
+                if mid > index {
+                    return;
+                }
+
+                // Otherwise, continue sorting elements greater than the pivot.
+                v = &mut v[mid..];
+                index = index - mid;
+                pred = None;
+                continue;
+            }
+        }
+
+        let (mid, _) = partition(v, pivot, is_less);
+
+        // Split the slice into `left`, `pivot`, and `right`.
+        let (left, right) = v.split_at_mut(mid);
+        let (pivot, right) = right.split_at_mut(1);
+        let pivot = &pivot[0];
+
+        if mid < index {
+            v = right;
+            index = index - mid - 1;
+            pred = Some(pivot);
+        } else if mid > index {
+            v = left;
+        } else {
+            // If mid == index, then we're done, since partition() guaranteed that all elements
+            // after mid are greater than or equal to mid.
+            return;
+        }
+    }
+}
+
+pub fn partition_at_index<T, F>(
+    v: &mut [T],
+    index: usize,
+    mut is_less: F,
+) -> (&mut [T], &mut T, &mut [T])
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    use cmp::Ordering::Greater;
+    use cmp::Ordering::Less;
+
+    if index >= v.len() {
+        panic!("partition_at_index index {} greater than length of slice {}", index, v.len());
+    }
+
+    if mem::size_of::<T>() == 0 {
+        // Sorting has no meaningful behavior on zero-sized types. Do nothing.
+    } else if index == v.len() - 1 {
+        // Find max element and place it in the last position of the array. We're free to use
+        // `unwrap()` here because we know v must not be empty.
+        let (max_index, _) = v
+            .iter()
+            .enumerate()
+            .max_by(|&(_, x), &(_, y)| if is_less(x, y) { Less } else { Greater })
+            .unwrap();
+        v.swap(max_index, index);
+    } else if index == 0 {
+        // Find min element and place it in the first position of the array. We're free to use
+        // `unwrap()` here because we know v must not be empty.
+        let (min_index, _) = v
+            .iter()
+            .enumerate()
+            .min_by(|&(_, x), &(_, y)| if is_less(x, y) { Less } else { Greater })
+            .unwrap();
+        v.swap(min_index, index);
+    } else {
+        partition_at_index_loop(v, index, &mut is_less, None);
+    }
+
+    let (left, right) = v.split_at_mut(index);
+    let (pivot, right) = right.split_at_mut(1);
+    let pivot = &mut pivot[0];
+    (left, pivot, right)
+}
diff --git a/library/core/src/slice/specialize.rs b/library/core/src/slice/specialize.rs
new file mode 100644
index 000000000..80eb59058
--- /dev/null
+++ b/library/core/src/slice/specialize.rs
@@ -0,0 +1,23 @@
+pub(super) trait SpecFill<T> {
+    fn spec_fill(&mut self, value: T);
+}
+
+impl<T: Clone> SpecFill<T> for [T] {
+    default fn spec_fill(&mut self, value: T) {
+        if let Some((last, elems)) = self.split_last_mut() {
+            for el in elems {
+                el.clone_from(&value);
+            }
+
+            *last = value
+        }
+    }
+}
+
+impl<T: Copy> SpecFill<T> for [T] {
+    fn spec_fill(&mut self, value: T) {
+        for item in self.iter_mut() {
+            *item = value;
+        }
+    }
+}