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

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

1 files changed, 686 insertions, 0 deletions

diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
new file mode 100644
index 000000000..d5ed2c4ad
--- /dev/null
+++ b/library/alloc/src/str.rs
@@ -0,0 +1,686 @@
+//! Unicode string slices.
+//!
+//! *[See also the `str` primitive type](str).*
+//!
+//! The `&str` type is one of the two main string types, the other being `String`.
+//! Unlike its `String` counterpart, its contents are borrowed.
+//!
+//! # Basic Usage
+//!
+//! A basic string declaration of `&str` type:
+//!
+//! ```
+//! let hello_world = "Hello, World!";
+//! ```
+//!
+//! Here we have declared a string literal, also known as a string slice.
+//! String literals have a static lifetime, which means the string `hello_world`
+//! is guaranteed to be valid for the duration of the entire program.
+//! We can explicitly specify `hello_world`'s lifetime as well:
+//!
+//! ```
+//! let hello_world: &'static str = "Hello, world!";
+//! ```
+
+#![stable(feature = "rust1", since = "1.0.0")]
+// Many of the usings in this module are only used in the test configuration.
+// It's cleaner to just turn off the unused_imports warning than to fix them.
+#![allow(unused_imports)]
+
+use core::borrow::{Borrow, BorrowMut};
+use core::iter::FusedIterator;
+use core::mem;
+use core::ptr;
+use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
+use core::unicode::conversions;
+
+use crate::borrow::ToOwned;
+use crate::boxed::Box;
+use crate::slice::{Concat, Join, SliceIndex};
+use crate::string::String;
+use crate::vec::Vec;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::pattern;
+#[stable(feature = "encode_utf16", since = "1.8.0")]
+pub use core::str::EncodeUtf16;
+#[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
+pub use core::str::SplitAsciiWhitespace;
+#[stable(feature = "split_inclusive", since = "1.51.0")]
+pub use core::str::SplitInclusive;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::SplitWhitespace;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
+#[stable(feature = "str_escape", since = "1.34.0")]
+pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{FromStr, Utf8Error};
+#[allow(deprecated)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{Lines, LinesAny};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{MatchIndices, RMatchIndices};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{Matches, RMatches};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplit, Split};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplitN, SplitN};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplitTerminator, SplitTerminator};
+
+/// Note: `str` in `Concat<str>` is not meaningful here.
+/// This type parameter of the trait only exists to enable another impl.
+#[cfg(not(no_global_oom_handling))]
+#[unstable(feature = "slice_concat_ext", issue = "27747")]
+impl<S: Borrow<str>> Concat<str> for [S] {
+    type Output = String;
+
+    fn concat(slice: &Self) -> String {
+        Join::join(slice, "")
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[unstable(feature = "slice_concat_ext", issue = "27747")]
+impl<S: Borrow<str>> Join<&str> for [S] {
+    type Output = String;
+
+    fn join(slice: &Self, sep: &str) -> String {
+        unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+macro_rules! specialize_for_lengths {
+    ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {{
+        let mut target = $target;
+        let iter = $iter;
+        let sep_bytes = $separator;
+        match $separator.len() {
+            $(
+                // loops with hardcoded sizes run much faster
+                // specialize the cases with small separator lengths
+                $num => {
+                    for s in iter {
+                        copy_slice_and_advance!(target, sep_bytes);
+                        let content_bytes = s.borrow().as_ref();
+                        copy_slice_and_advance!(target, content_bytes);
+                    }
+                },
+            )*
+            _ => {
+                // arbitrary non-zero size fallback
+                for s in iter {
+                    copy_slice_and_advance!(target, sep_bytes);
+                    let content_bytes = s.borrow().as_ref();
+                    copy_slice_and_advance!(target, content_bytes);
+                }
+            }
+        }
+        target
+    }}
+}
+
+#[cfg(not(no_global_oom_handling))]
+macro_rules! copy_slice_and_advance {
+    ($target:expr, $bytes:expr) => {
+        let len = $bytes.len();
+        let (head, tail) = { $target }.split_at_mut(len);
+        head.copy_from_slice($bytes);
+        $target = tail;
+    };
+}
+
+// Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
+// Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
+// For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
+// only user of this function. It is left in place for the time when that is fixed.
+//
+// the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
+// [T] and str both impl AsRef<[T]> for some T
+// => s.borrow().as_ref() and we always have slices
+#[cfg(not(no_global_oom_handling))]
+fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+where
+    T: Copy,
+    B: AsRef<[T]> + ?Sized,
+    S: Borrow<B>,
+{
+    let sep_len = sep.len();
+    let mut iter = slice.iter();
+
+    // the first slice is the only one without a separator preceding it
+    let first = match iter.next() {
+        Some(first) => first,
+        None => return vec![],
+    };
+
+    // compute the exact total length of the joined Vec
+    // if the `len` calculation overflows, we'll panic
+    // we would have run out of memory anyway and the rest of the function requires
+    // the entire Vec pre-allocated for safety
+    let reserved_len = sep_len
+        .checked_mul(iter.len())
+        .and_then(|n| {
+            slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
+        })
+        .expect("attempt to join into collection with len > usize::MAX");
+
+    // prepare an uninitialized buffer
+    let mut result = Vec::with_capacity(reserved_len);
+    debug_assert!(result.capacity() >= reserved_len);
+
+    result.extend_from_slice(first.borrow().as_ref());
+
+    unsafe {
+        let pos = result.len();
+        let target = result.spare_capacity_mut().get_unchecked_mut(..reserved_len - pos);
+
+        // Convert the separator and slices to slices of MaybeUninit
+        // to simplify implementation in specialize_for_lengths
+        let sep_uninit = core::slice::from_raw_parts(sep.as_ptr().cast(), sep.len());
+        let iter_uninit = iter.map(|it| {
+            let it = it.borrow().as_ref();
+            core::slice::from_raw_parts(it.as_ptr().cast(), it.len())
+        });
+
+        // copy separator and slices over without bounds checks
+        // generate loops with hardcoded offsets for small separators
+        // massive improvements possible (~ x2)
+        let remain = specialize_for_lengths!(sep_uninit, target, iter_uninit; 0, 1, 2, 3, 4);
+
+        // A weird borrow implementation may return different
+        // slices for the length calculation and the actual copy.
+        // Make sure we don't expose uninitialized bytes to the caller.
+        let result_len = reserved_len - remain.len();
+        result.set_len(result_len);
+    }
+    result
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Borrow<str> for String {
+    #[inline]
+    fn borrow(&self) -> &str {
+        &self[..]
+    }
+}
+
+#[stable(feature = "string_borrow_mut", since = "1.36.0")]
+impl BorrowMut<str> for String {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut str {
+        &mut self[..]
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl ToOwned for str {
+    type Owned = String;
+    #[inline]
+    fn to_owned(&self) -> String {
+        unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
+    }
+
+    fn clone_into(&self, target: &mut String) {
+        let mut b = mem::take(target).into_bytes();
+        self.as_bytes().clone_into(&mut b);
+        *target = unsafe { String::from_utf8_unchecked(b) }
+    }
+}
+
+/// Methods for string slices.
+#[cfg(not(test))]
+impl str {
+    /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "this is a string";
+    /// let boxed_str = s.to_owned().into_boxed_str();
+    /// let boxed_bytes = boxed_str.into_boxed_bytes();
+    /// assert_eq!(*boxed_bytes, *s.as_bytes());
+    /// ```
+    #[rustc_allow_incoherent_impl]
+    #[stable(feature = "str_box_extras", since = "1.20.0")]
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[inline]
+    pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
+        self.into()
+    }
+
+    /// Replaces all matches of a pattern with another string.
+    ///
+    /// `replace` creates a new [`String`], and copies the data from this string slice into it.
+    /// While doing so, it attempts to find matches of a pattern. If it finds any, it
+    /// replaces them with the replacement string slice.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "this is old";
+    ///
+    /// assert_eq!("this is new", s.replace("old", "new"));
+    /// assert_eq!("than an old", s.replace("is", "an"));
+    /// ```
+    ///
+    /// When the pattern doesn't match:
+    ///
+    /// ```
+    /// let s = "this is old";
+    /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
+    /// ```
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "this returns the replaced string as a new allocation, \
+                  without modifying the original"]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
+        let mut result = String::new();
+        let mut last_end = 0;
+        for (start, part) in self.match_indices(from) {
+            result.push_str(unsafe { self.get_unchecked(last_end..start) });
+            result.push_str(to);
+            last_end = start + part.len();
+        }
+        result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
+        result
+    }
+
+    /// Replaces first N matches of a pattern with another string.
+    ///
+    /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
+    /// While doing so, it attempts to find matches of a pattern. If it finds any, it
+    /// replaces them with the replacement string slice at most `count` times.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "foo foo 123 foo";
+    /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
+    /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
+    /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
+    /// ```
+    ///
+    /// When the pattern doesn't match:
+    ///
+    /// ```
+    /// let s = "this is old";
+    /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
+    /// ```
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "this returns the replaced string as a new allocation, \
+                  without modifying the original"]
+    #[stable(feature = "str_replacen", since = "1.16.0")]
+    pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
+        // Hope to reduce the times of re-allocation
+        let mut result = String::with_capacity(32);
+        let mut last_end = 0;
+        for (start, part) in self.match_indices(pat).take(count) {
+            result.push_str(unsafe { self.get_unchecked(last_end..start) });
+            result.push_str(to);
+            last_end = start + part.len();
+        }
+        result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
+        result
+    }
+
+    /// Returns the lowercase equivalent of this string slice, as a new [`String`].
+    ///
+    /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
+    /// `Lowercase`.
+    ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "HELLO";
+    ///
+    /// assert_eq!("hello", s.to_lowercase());
+    /// ```
+    ///
+    /// A tricky example, with sigma:
+    ///
+    /// ```
+    /// let sigma = "Σ";
+    ///
+    /// assert_eq!("σ", sigma.to_lowercase());
+    ///
+    /// // but at the end of a word, it's ς, not σ:
+    /// let odysseus = "ὈΔΥΣΣΕΎΣ";
+    ///
+    /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
+    /// ```
+    ///
+    /// Languages without case are not changed:
+    ///
+    /// ```
+    /// let new_year = "农历新年";
+    ///
+    /// assert_eq!(new_year, new_year.to_lowercase());
+    /// ```
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "this returns the lowercase string as a new String, \
+                  without modifying the original"]
+    #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
+    pub fn to_lowercase(&self) -> String {
+        let out = convert_while_ascii(self.as_bytes(), u8::to_ascii_lowercase);
+
+        // Safety: we know this is a valid char boundary since
+        // out.len() is only progressed if ascii bytes are found
+        let rest = unsafe { self.get_unchecked(out.len()..) };
+
+        // Safety: We have written only valid ASCII to our vec
+        let mut s = unsafe { String::from_utf8_unchecked(out) };
+
+        for (i, c) in rest[..].char_indices() {
+            if c == 'Σ' {
+                // Σ maps to σ, except at the end of a word where it maps to ς.
+                // This is the only conditional (contextual) but language-independent mapping
+                // in `SpecialCasing.txt`,
+                // so hard-code it rather than have a generic "condition" mechanism.
+                // See https://github.com/rust-lang/rust/issues/26035
+                map_uppercase_sigma(rest, i, &mut s)
+            } else {
+                match conversions::to_lower(c) {
+                    [a, '\0', _] => s.push(a),
+                    [a, b, '\0'] => {
+                        s.push(a);
+                        s.push(b);
+                    }
+                    [a, b, c] => {
+                        s.push(a);
+                        s.push(b);
+                        s.push(c);
+                    }
+                }
+            }
+        }
+        return s;
+
+        fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
+            // See https://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
+            // for the definition of `Final_Sigma`.
+            debug_assert!('Σ'.len_utf8() == 2);
+            let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
+                && !case_ignoreable_then_cased(from[i + 2..].chars());
+            to.push_str(if is_word_final { "ς" } else { "σ" });
+        }
+
+        fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
+            use core::unicode::{Case_Ignorable, Cased};
+            match iter.skip_while(|&c| Case_Ignorable(c)).next() {
+                Some(c) => Cased(c),
+                None => false,
+            }
+        }
+    }
+
+    /// Returns the uppercase equivalent of this string slice, as a new [`String`].
+    ///
+    /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
+    /// `Uppercase`.
+    ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "hello";
+    ///
+    /// assert_eq!("HELLO", s.to_uppercase());
+    /// ```
+    ///
+    /// Scripts without case are not changed:
+    ///
+    /// ```
+    /// let new_year = "农历新年";
+    ///
+    /// assert_eq!(new_year, new_year.to_uppercase());
+    /// ```
+    ///
+    /// One character can become multiple:
+    /// ```
+    /// let s = "tschüß";
+    ///
+    /// assert_eq!("TSCHÜSS", s.to_uppercase());
+    /// ```
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "this returns the uppercase string as a new String, \
+                  without modifying the original"]
+    #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
+    pub fn to_uppercase(&self) -> String {
+        let out = convert_while_ascii(self.as_bytes(), u8::to_ascii_uppercase);
+
+        // Safety: we know this is a valid char boundary since
+        // out.len() is only progressed if ascii bytes are found
+        let rest = unsafe { self.get_unchecked(out.len()..) };
+
+        // Safety: We have written only valid ASCII to our vec
+        let mut s = unsafe { String::from_utf8_unchecked(out) };
+
+        for c in rest.chars() {
+            match conversions::to_upper(c) {
+                [a, '\0', _] => s.push(a),
+                [a, b, '\0'] => {
+                    s.push(a);
+                    s.push(b);
+                }
+                [a, b, c] => {
+                    s.push(a);
+                    s.push(b);
+                    s.push(c);
+                }
+            }
+        }
+        s
+    }
+
+    /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let string = String::from("birthday gift");
+    /// let boxed_str = string.clone().into_boxed_str();
+    ///
+    /// assert_eq!(boxed_str.into_string(), string);
+    /// ```
+    #[stable(feature = "box_str", since = "1.4.0")]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[inline]
+    pub fn into_string(self: Box<str>) -> String {
+        let slice = Box::<[u8]>::from(self);
+        unsafe { String::from_utf8_unchecked(slice.into_vec()) }
+    }
+
+    /// Creates a new [`String`] by repeating a string `n` times.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the capacity would overflow.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
+    /// ```
+    ///
+    /// A panic upon overflow:
+    ///
+    /// ```should_panic
+    /// // this will panic at runtime
+    /// let huge = "0123456789abcdef".repeat(usize::MAX);
+    /// ```
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use]
+    #[stable(feature = "repeat_str", since = "1.16.0")]
+    pub fn repeat(&self, n: usize) -> String {
+        unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
+    }
+
+    /// Returns a copy of this string where each character is mapped to its
+    /// ASCII upper case equivalent.
+    ///
+    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To uppercase the value in-place, use [`make_ascii_uppercase`].
+    ///
+    /// To uppercase ASCII characters in addition to non-ASCII characters, use
+    /// [`to_uppercase`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let s = "Grüße, Jürgen ❤";
+    ///
+    /// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
+    /// ```
+    ///
+    /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
+    /// [`to_uppercase`]: #method.to_uppercase
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn to_ascii_uppercase(&self) -> String {
+        let mut bytes = self.as_bytes().to_vec();
+        bytes.make_ascii_uppercase();
+        // make_ascii_uppercase() preserves the UTF-8 invariant.
+        unsafe { String::from_utf8_unchecked(bytes) }
+    }
+
+    /// Returns a copy of this string where each character is mapped to its
+    /// ASCII lower case equivalent.
+    ///
+    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To lowercase the value in-place, use [`make_ascii_lowercase`].
+    ///
+    /// To lowercase ASCII characters in addition to non-ASCII characters, use
+    /// [`to_lowercase`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let s = "Grüße, Jürgen ❤";
+    ///
+    /// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
+    /// ```
+    ///
+    /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
+    /// [`to_lowercase`]: #method.to_lowercase
+    #[cfg(not(no_global_oom_handling))]
+    #[rustc_allow_incoherent_impl]
+    #[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn to_ascii_lowercase(&self) -> String {
+        let mut bytes = self.as_bytes().to_vec();
+        bytes.make_ascii_lowercase();
+        // make_ascii_lowercase() preserves the UTF-8 invariant.
+        unsafe { String::from_utf8_unchecked(bytes) }
+    }
+}
+
+/// Converts a boxed slice of bytes to a boxed string slice without checking
+/// that the string contains valid UTF-8.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let smile_utf8 = Box::new([226, 152, 186]);
+/// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
+///
+/// assert_eq!("☺", &*smile);
+/// ```
+#[stable(feature = "str_box_extras", since = "1.20.0")]
+#[must_use]
+#[inline]
+pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
+    unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
+}
+
+/// Converts the bytes while the bytes are still ascii.
+/// For better average performance, this is happens in chunks of `2*size_of::<usize>()`.
+/// Returns a vec with the converted bytes.
+#[inline]
+#[cfg(not(test))]
+#[cfg(not(no_global_oom_handling))]
+fn convert_while_ascii(b: &[u8], convert: fn(&u8) -> u8) -> Vec<u8> {
+    let mut out = Vec::with_capacity(b.len());
+
+    const USIZE_SIZE: usize = mem::size_of::<usize>();
+    const MAGIC_UNROLL: usize = 2;
+    const N: usize = USIZE_SIZE * MAGIC_UNROLL;
+    const NONASCII_MASK: usize = usize::from_ne_bytes([0x80; USIZE_SIZE]);
+
+    let mut i = 0;
+    unsafe {
+        while i + N <= b.len() {
+            // Safety: we have checks the sizes `b` and `out` to know that our
+            let in_chunk = b.get_unchecked(i..i + N);
+            let out_chunk = out.spare_capacity_mut().get_unchecked_mut(i..i + N);
+
+            let mut bits = 0;
+            for j in 0..MAGIC_UNROLL {
+                // read the bytes 1 usize at a time (unaligned since we haven't checked the alignment)
+                // safety: in_chunk is valid bytes in the range
+                bits |= in_chunk.as_ptr().cast::<usize>().add(j).read_unaligned();
+            }
+            // if our chunks aren't ascii, then return only the prior bytes as init
+            if bits & NONASCII_MASK != 0 {
+                break;
+            }
+
+            // perform the case conversions on N bytes (gets heavily autovec'd)
+            for j in 0..N {
+                // safety: in_chunk and out_chunk is valid bytes in the range
+                let out = out_chunk.get_unchecked_mut(j);
+                out.write(convert(in_chunk.get_unchecked(j)));
+            }
+
+            // mark these bytes as initialised
+            i += N;
+        }
+        out.set_len(i);
+    }
+
+    out
+}