Merging upstream version 1.74.1+dfsg1.

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

1 files changed, 1214 insertions, 0 deletions

diff --git a/vendor/memchr/src/arch/generic/memchr.rs b/vendor/memchr/src/arch/generic/memchr.rs
new file mode 100644
index 000000000..580b3cc1a
--- /dev/null
+++ b/vendor/memchr/src/arch/generic/memchr.rs
@@ -0,0 +1,1214 @@
+/*!
+Generic crate-internal routines for the `memchr` family of functions.
+*/
+
+// What follows is a vector algorithm generic over the specific vector
+// type to detect the position of one, two or three needles in a haystack.
+// From what I know, this is a "classic" algorithm, although I don't
+// believe it has been published in any peer reviewed journal. I believe
+// it can be found in places like glibc and Go's standard library. It
+// appears to be well known and is elaborated on in more detail here:
+// https://gms.tf/stdfind-and-memchr-optimizations.html
+//
+// While the routine below is fairly long and perhaps intimidating, the basic
+// idea is actually very simple and can be expressed straight-forwardly in
+// pseudo code. The psuedo code below is written for 128 bit vectors, but the
+// actual code below works for anything that implements the Vector trait.
+//
+//     needle = (n1 << 15) | (n1 << 14) | ... | (n1 << 1) | n1
+//     // Note: shift amount is in bytes
+//
+//     while i <= haystack.len() - 16:
+//       // A 16 byte vector. Each byte in chunk corresponds to a byte in
+//       // the haystack.
+//       chunk = haystack[i:i+16]
+//       // Compare bytes in needle with bytes in chunk. The result is a 16
+//       // byte chunk where each byte is 0xFF if the corresponding bytes
+//       // in needle and chunk were equal, or 0x00 otherwise.
+//       eqs = cmpeq(needle, chunk)
+//       // Return a 32 bit integer where the most significant 16 bits
+//       // are always 0 and the lower 16 bits correspond to whether the
+//       // most significant bit in the correspond byte in `eqs` is set.
+//       // In other words, `mask as u16` has bit i set if and only if
+//       // needle[i] == chunk[i].
+//       mask = movemask(eqs)
+//
+//       // Mask is 0 if there is no match, and non-zero otherwise.
+//       if mask != 0:
+//         // trailing_zeros tells us the position of the least significant
+//         // bit that is set.
+//         return i + trailing_zeros(mask)
+//
+//     // haystack length may not be a multiple of 16, so search the rest.
+//     while i < haystack.len():
+//       if haystack[i] == n1:
+//         return i
+//
+//     // No match found.
+//     return NULL
+//
+// In fact, we could loosely translate the above code to Rust line-for-line
+// and it would be a pretty fast algorithm. But, we pull out all the stops
+// to go as fast as possible:
+//
+// 1. We use aligned loads. That is, we do some finagling to make sure our
+//    primary loop not only proceeds in increments of 16 bytes, but that
+//    the address of haystack's pointer that we dereference is aligned to
+//    16 bytes. 16 is a magic number here because it is the size of SSE2
+//    128-bit vector. (For the AVX2 algorithm, 32 is the magic number.)
+//    Therefore, to get aligned loads, our pointer's address must be evenly
+//    divisible by 16.
+// 2. Our primary loop proceeds 64 bytes at a time instead of 16. It's
+//    kind of like loop unrolling, but we combine the equality comparisons
+//    using a vector OR such that we only need to extract a single mask to
+//    determine whether a match exists or not. If so, then we do some
+//    book-keeping to determine the precise location but otherwise mush on.
+// 3. We use our "chunk" comparison routine in as many places as possible,
+//    even if it means using unaligned loads. In particular, if haystack
+//    starts with an unaligned address, then we do an unaligned load to
+//    search the first 16 bytes. We then start our primary loop at the
+//    smallest subsequent aligned address, which will actually overlap with
+//    previously searched bytes. But we're OK with that. We do a similar
+//    dance at the end of our primary loop. Finally, to avoid a
+//    byte-at-a-time loop at the end, we do a final 16 byte unaligned load
+//    that may overlap with a previous load. This is OK because it converts
+//    a loop into a small number of very fast vector instructions. The overlap
+//    is OK because we know the place where the overlap occurs does not
+//    contain a match.
+//
+// And that's pretty all there is to it. Note that since the below is
+// generic and since it's meant to be inlined into routines with a
+// `#[target_feature(enable = "...")]` annotation, we must mark all routines as
+// both unsafe and `#[inline(always)]`.
+//
+// The fact that the code below is generic does somewhat inhibit us. For
+// example, I've noticed that introducing an unlineable `#[cold]` function to
+// handle the match case in the loop generates tighter assembly, but there is
+// no way to do this in the generic code below because the generic code doesn't
+// know what `target_feature` annotation to apply to the unlineable function.
+// We could make such functions part of the `Vector` trait, but we instead live
+// with the slightly sub-optimal codegen for now since it doesn't seem to have
+// a noticeable perf difference.
+
+use crate::{
+    ext::Pointer,
+    vector::{MoveMask, Vector},
+};
+
+/// Finds all occurrences of a single byte in a haystack.
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct One<V> {
+    s1: u8,
+    v1: V,
+}
+
+impl<V: Vector> One<V> {
+    /// The number of bytes we examine per each iteration of our search loop.
+    const LOOP_SIZE: usize = 4 * V::BYTES;
+
+    /// Create a new searcher that finds occurrences of the byte given.
+    #[inline(always)]
+    pub(crate) unsafe fn new(needle: u8) -> One<V> {
+        One { s1: needle, v1: V::splat(needle) }
+    }
+
+    /// Returns the needle given to `One::new`.
+    #[inline(always)]
+    pub(crate) fn needle1(&self) -> u8 {
+        self.s1
+    }
+
+    /// Return a pointer to the first occurrence of the needle in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::first_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        // Search a possibly unaligned chunk at `start`. This covers any part
+        // of the haystack prior to where aligned loads can start.
+        if let Some(cur) = self.search_chunk(start, topos) {
+            return Some(cur);
+        }
+        // Set `cur` to the first V-aligned pointer greater than `start`.
+        let mut cur = start.add(V::BYTES - (start.as_usize() & V::ALIGN));
+        debug_assert!(cur > start && end.sub(V::BYTES) >= start);
+        if len >= Self::LOOP_SIZE {
+            while cur <= end.sub(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(1 * V::BYTES));
+                let c = V::load_aligned(cur.add(2 * V::BYTES));
+                let d = V::load_aligned(cur.add(3 * V::BYTES));
+                let eqa = self.v1.cmpeq(a);
+                let eqb = self.v1.cmpeq(b);
+                let eqc = self.v1.cmpeq(c);
+                let eqd = self.v1.cmpeq(d);
+                let or1 = eqa.or(eqb);
+                let or2 = eqc.or(eqd);
+                let or3 = or1.or(or2);
+                if or3.movemask_will_have_non_zero() {
+                    let mask = eqa.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(topos(mask)));
+                    }
+
+                    let mask = eqb.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(1 * V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqc.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(2 * V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqd.movemask();
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(3 * V::BYTES).add(topos(mask)));
+                }
+                cur = cur.add(Self::LOOP_SIZE);
+            }
+        }
+        // Handle any leftovers after the aligned loop above. We use unaligned
+        // loads here, but I believe we are guaranteed that they are aligned
+        // since `cur` is aligned.
+        while cur <= end.sub(V::BYTES) {
+            debug_assert!(end.distance(cur) >= V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+            cur = cur.add(V::BYTES);
+        }
+        // Finally handle any remaining bytes less than the size of V. In this
+        // case, our pointer may indeed be unaligned and the load may overlap
+        // with the previous one. But that's okay since we know the previous
+        // load didn't lead to a match (otherwise we wouldn't be here).
+        if cur < end {
+            debug_assert!(end.distance(cur) < V::BYTES);
+            cur = cur.sub(V::BYTES - end.distance(cur));
+            debug_assert_eq!(end.distance(cur), V::BYTES);
+            return self.search_chunk(cur, topos);
+        }
+        None
+    }
+
+    /// Return a pointer to the last occurrence of the needle in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::last_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        if let Some(cur) = self.search_chunk(end.sub(V::BYTES), topos) {
+            return Some(cur);
+        }
+        let mut cur = end.sub(end.as_usize() & V::ALIGN);
+        debug_assert!(start <= cur && cur <= end);
+        if len >= Self::LOOP_SIZE {
+            while cur >= start.add(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                cur = cur.sub(Self::LOOP_SIZE);
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(1 * V::BYTES));
+                let c = V::load_aligned(cur.add(2 * V::BYTES));
+                let d = V::load_aligned(cur.add(3 * V::BYTES));
+                let eqa = self.v1.cmpeq(a);
+                let eqb = self.v1.cmpeq(b);
+                let eqc = self.v1.cmpeq(c);
+                let eqd = self.v1.cmpeq(d);
+                let or1 = eqa.or(eqb);
+                let or2 = eqc.or(eqd);
+                let or3 = or1.or(or2);
+                if or3.movemask_will_have_non_zero() {
+                    let mask = eqd.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(3 * V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqc.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(2 * V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqb.movemask();
+                    if mask.has_non_zero() {
+                        return Some(cur.add(1 * V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqa.movemask();
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(topos(mask)));
+                }
+            }
+        }
+        while cur >= start.add(V::BYTES) {
+            debug_assert!(cur.distance(start) >= V::BYTES);
+            cur = cur.sub(V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+        }
+        if cur > start {
+            debug_assert!(cur.distance(start) < V::BYTES);
+            return self.search_chunk(start, topos);
+        }
+        None
+    }
+
+    /// Return a count of all matching bytes in the given haystack.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn count_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> usize {
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let confirm = |b| b == self.needle1();
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        // Set `cur` to the first V-aligned pointer greater than `start`.
+        let mut cur = start.add(V::BYTES - (start.as_usize() & V::ALIGN));
+        // Count any matching bytes before we start our aligned loop.
+        let mut count = count_byte_by_byte(start, cur, confirm);
+        debug_assert!(cur > start && end.sub(V::BYTES) >= start);
+        if len >= Self::LOOP_SIZE {
+            while cur <= end.sub(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(1 * V::BYTES));
+                let c = V::load_aligned(cur.add(2 * V::BYTES));
+                let d = V::load_aligned(cur.add(3 * V::BYTES));
+                let eqa = self.v1.cmpeq(a);
+                let eqb = self.v1.cmpeq(b);
+                let eqc = self.v1.cmpeq(c);
+                let eqd = self.v1.cmpeq(d);
+                count += eqa.movemask().count_ones();
+                count += eqb.movemask().count_ones();
+                count += eqc.movemask().count_ones();
+                count += eqd.movemask().count_ones();
+                cur = cur.add(Self::LOOP_SIZE);
+            }
+        }
+        // Handle any leftovers after the aligned loop above. We use unaligned
+        // loads here, but I believe we are guaranteed that they are aligned
+        // since `cur` is aligned.
+        while cur <= end.sub(V::BYTES) {
+            debug_assert!(end.distance(cur) >= V::BYTES);
+            let chunk = V::load_unaligned(cur);
+            count += self.v1.cmpeq(chunk).movemask().count_ones();
+            cur = cur.add(V::BYTES);
+        }
+        // And finally count any leftovers that weren't caught above.
+        count += count_byte_by_byte(cur, end, confirm);
+        count
+    }
+
+    /// Search `V::BYTES` starting at `cur` via an unaligned load.
+    ///
+    /// `mask_to_offset` should be a function that converts a `movemask` to
+    /// an offset such that `cur.add(offset)` corresponds to a pointer to the
+    /// match location if one is found. Generally it is expected to use either
+    /// `mask_to_first_offset` or `mask_to_last_offset`, depending on whether
+    /// one is implementing a forward or reverse search, respectively.
+    ///
+    /// # Safety
+    ///
+    /// `cur` must be a valid pointer and it must be valid to do an unaligned
+    /// load of size `V::BYTES` at `cur`.
+    #[inline(always)]
+    unsafe fn search_chunk(
+        &self,
+        cur: *const u8,
+        mask_to_offset: impl Fn(V::Mask) -> usize,
+    ) -> Option<*const u8> {
+        let chunk = V::load_unaligned(cur);
+        let mask = self.v1.cmpeq(chunk).movemask();
+        if mask.has_non_zero() {
+            Some(cur.add(mask_to_offset(mask)))
+        } else {
+            None
+        }
+    }
+}
+
+/// Finds all occurrences of two bytes in a haystack.
+///
+/// That is, this reports matches of one of two possible bytes. For example,
+/// searching for `a` or `b` in `afoobar` would report matches at offsets `0`,
+/// `4` and `5`.
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct Two<V> {
+    s1: u8,
+    s2: u8,
+    v1: V,
+    v2: V,
+}
+
+impl<V: Vector> Two<V> {
+    /// The number of bytes we examine per each iteration of our search loop.
+    const LOOP_SIZE: usize = 2 * V::BYTES;
+
+    /// Create a new searcher that finds occurrences of the byte given.
+    #[inline(always)]
+    pub(crate) unsafe fn new(needle1: u8, needle2: u8) -> Two<V> {
+        Two {
+            s1: needle1,
+            s2: needle2,
+            v1: V::splat(needle1),
+            v2: V::splat(needle2),
+        }
+    }
+
+    /// Returns the first needle given to `Two::new`.
+    #[inline(always)]
+    pub(crate) fn needle1(&self) -> u8 {
+        self.s1
+    }
+
+    /// Returns the second needle given to `Two::new`.
+    #[inline(always)]
+    pub(crate) fn needle2(&self) -> u8 {
+        self.s2
+    }
+
+    /// Return a pointer to the first occurrence of one of the needles in the
+    /// given haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::first_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        // Search a possibly unaligned chunk at `start`. This covers any part
+        // of the haystack prior to where aligned loads can start.
+        if let Some(cur) = self.search_chunk(start, topos) {
+            return Some(cur);
+        }
+        // Set `cur` to the first V-aligned pointer greater than `start`.
+        let mut cur = start.add(V::BYTES - (start.as_usize() & V::ALIGN));
+        debug_assert!(cur > start && end.sub(V::BYTES) >= start);
+        if len >= Self::LOOP_SIZE {
+            while cur <= end.sub(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(V::BYTES));
+                let eqa1 = self.v1.cmpeq(a);
+                let eqb1 = self.v1.cmpeq(b);
+                let eqa2 = self.v2.cmpeq(a);
+                let eqb2 = self.v2.cmpeq(b);
+                let or1 = eqa1.or(eqb1);
+                let or2 = eqa2.or(eqb2);
+                let or3 = or1.or(or2);
+                if or3.movemask_will_have_non_zero() {
+                    let mask = eqa1.movemask().or(eqa2.movemask());
+                    if mask.has_non_zero() {
+                        return Some(cur.add(topos(mask)));
+                    }
+
+                    let mask = eqb1.movemask().or(eqb2.movemask());
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(V::BYTES).add(topos(mask)));
+                }
+                cur = cur.add(Self::LOOP_SIZE);
+            }
+        }
+        // Handle any leftovers after the aligned loop above. We use unaligned
+        // loads here, but I believe we are guaranteed that they are aligned
+        // since `cur` is aligned.
+        while cur <= end.sub(V::BYTES) {
+            debug_assert!(end.distance(cur) >= V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+            cur = cur.add(V::BYTES);
+        }
+        // Finally handle any remaining bytes less than the size of V. In this
+        // case, our pointer may indeed be unaligned and the load may overlap
+        // with the previous one. But that's okay since we know the previous
+        // load didn't lead to a match (otherwise we wouldn't be here).
+        if cur < end {
+            debug_assert!(end.distance(cur) < V::BYTES);
+            cur = cur.sub(V::BYTES - end.distance(cur));
+            debug_assert_eq!(end.distance(cur), V::BYTES);
+            return self.search_chunk(cur, topos);
+        }
+        None
+    }
+
+    /// Return a pointer to the last occurrence of the needle in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::last_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        if let Some(cur) = self.search_chunk(end.sub(V::BYTES), topos) {
+            return Some(cur);
+        }
+        let mut cur = end.sub(end.as_usize() & V::ALIGN);
+        debug_assert!(start <= cur && cur <= end);
+        if len >= Self::LOOP_SIZE {
+            while cur >= start.add(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                cur = cur.sub(Self::LOOP_SIZE);
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(V::BYTES));
+                let eqa1 = self.v1.cmpeq(a);
+                let eqb1 = self.v1.cmpeq(b);
+                let eqa2 = self.v2.cmpeq(a);
+                let eqb2 = self.v2.cmpeq(b);
+                let or1 = eqa1.or(eqb1);
+                let or2 = eqa2.or(eqb2);
+                let or3 = or1.or(or2);
+                if or3.movemask_will_have_non_zero() {
+                    let mask = eqb1.movemask().or(eqb2.movemask());
+                    if mask.has_non_zero() {
+                        return Some(cur.add(V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqa1.movemask().or(eqa2.movemask());
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(topos(mask)));
+                }
+            }
+        }
+        while cur >= start.add(V::BYTES) {
+            debug_assert!(cur.distance(start) >= V::BYTES);
+            cur = cur.sub(V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+        }
+        if cur > start {
+            debug_assert!(cur.distance(start) < V::BYTES);
+            return self.search_chunk(start, topos);
+        }
+        None
+    }
+
+    /// Search `V::BYTES` starting at `cur` via an unaligned load.
+    ///
+    /// `mask_to_offset` should be a function that converts a `movemask` to
+    /// an offset such that `cur.add(offset)` corresponds to a pointer to the
+    /// match location if one is found. Generally it is expected to use either
+    /// `mask_to_first_offset` or `mask_to_last_offset`, depending on whether
+    /// one is implementing a forward or reverse search, respectively.
+    ///
+    /// # Safety
+    ///
+    /// `cur` must be a valid pointer and it must be valid to do an unaligned
+    /// load of size `V::BYTES` at `cur`.
+    #[inline(always)]
+    unsafe fn search_chunk(
+        &self,
+        cur: *const u8,
+        mask_to_offset: impl Fn(V::Mask) -> usize,
+    ) -> Option<*const u8> {
+        let chunk = V::load_unaligned(cur);
+        let eq1 = self.v1.cmpeq(chunk);
+        let eq2 = self.v2.cmpeq(chunk);
+        let mask = eq1.or(eq2).movemask();
+        if mask.has_non_zero() {
+            let mask1 = eq1.movemask();
+            let mask2 = eq2.movemask();
+            Some(cur.add(mask_to_offset(mask1.or(mask2))))
+        } else {
+            None
+        }
+    }
+}
+
+/// Finds all occurrences of two bytes in a haystack.
+///
+/// That is, this reports matches of one of two possible bytes. For example,
+/// searching for `a` or `b` in `afoobar` would report matches at offsets `0`,
+/// `4` and `5`.
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct Three<V> {
+    s1: u8,
+    s2: u8,
+    s3: u8,
+    v1: V,
+    v2: V,
+    v3: V,
+}
+
+impl<V: Vector> Three<V> {
+    /// The number of bytes we examine per each iteration of our search loop.
+    const LOOP_SIZE: usize = 2 * V::BYTES;
+
+    /// Create a new searcher that finds occurrences of the byte given.
+    #[inline(always)]
+    pub(crate) unsafe fn new(
+        needle1: u8,
+        needle2: u8,
+        needle3: u8,
+    ) -> Three<V> {
+        Three {
+            s1: needle1,
+            s2: needle2,
+            s3: needle3,
+            v1: V::splat(needle1),
+            v2: V::splat(needle2),
+            v3: V::splat(needle3),
+        }
+    }
+
+    /// Returns the first needle given to `Three::new`.
+    #[inline(always)]
+    pub(crate) fn needle1(&self) -> u8 {
+        self.s1
+    }
+
+    /// Returns the second needle given to `Three::new`.
+    #[inline(always)]
+    pub(crate) fn needle2(&self) -> u8 {
+        self.s2
+    }
+
+    /// Returns the third needle given to `Three::new`.
+    #[inline(always)]
+    pub(crate) fn needle3(&self) -> u8 {
+        self.s3
+    }
+
+    /// Return a pointer to the first occurrence of one of the needles in the
+    /// given haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::first_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        // Search a possibly unaligned chunk at `start`. This covers any part
+        // of the haystack prior to where aligned loads can start.
+        if let Some(cur) = self.search_chunk(start, topos) {
+            return Some(cur);
+        }
+        // Set `cur` to the first V-aligned pointer greater than `start`.
+        let mut cur = start.add(V::BYTES - (start.as_usize() & V::ALIGN));
+        debug_assert!(cur > start && end.sub(V::BYTES) >= start);
+        if len >= Self::LOOP_SIZE {
+            while cur <= end.sub(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(V::BYTES));
+                let eqa1 = self.v1.cmpeq(a);
+                let eqb1 = self.v1.cmpeq(b);
+                let eqa2 = self.v2.cmpeq(a);
+                let eqb2 = self.v2.cmpeq(b);
+                let eqa3 = self.v3.cmpeq(a);
+                let eqb3 = self.v3.cmpeq(b);
+                let or1 = eqa1.or(eqb1);
+                let or2 = eqa2.or(eqb2);
+                let or3 = eqa3.or(eqb3);
+                let or4 = or1.or(or2);
+                let or5 = or3.or(or4);
+                if or5.movemask_will_have_non_zero() {
+                    let mask = eqa1
+                        .movemask()
+                        .or(eqa2.movemask())
+                        .or(eqa3.movemask());
+                    if mask.has_non_zero() {
+                        return Some(cur.add(topos(mask)));
+                    }
+
+                    let mask = eqb1
+                        .movemask()
+                        .or(eqb2.movemask())
+                        .or(eqb3.movemask());
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(V::BYTES).add(topos(mask)));
+                }
+                cur = cur.add(Self::LOOP_SIZE);
+            }
+        }
+        // Handle any leftovers after the aligned loop above. We use unaligned
+        // loads here, but I believe we are guaranteed that they are aligned
+        // since `cur` is aligned.
+        while cur <= end.sub(V::BYTES) {
+            debug_assert!(end.distance(cur) >= V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+            cur = cur.add(V::BYTES);
+        }
+        // Finally handle any remaining bytes less than the size of V. In this
+        // case, our pointer may indeed be unaligned and the load may overlap
+        // with the previous one. But that's okay since we know the previous
+        // load didn't lead to a match (otherwise we wouldn't be here).
+        if cur < end {
+            debug_assert!(end.distance(cur) < V::BYTES);
+            cur = cur.sub(V::BYTES - end.distance(cur));
+            debug_assert_eq!(end.distance(cur), V::BYTES);
+            return self.search_chunk(cur, topos);
+        }
+        None
+    }
+
+    /// Return a pointer to the last occurrence of the needle in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// # Safety
+    ///
+    /// * It must be the case that `start < end` and that the distance between
+    /// them is at least equal to `V::BYTES`. That is, it must always be valid
+    /// to do at least an unaligned load of `V` at `start`.
+    /// * Both `start` and `end` must be valid for reads.
+    /// * Both `start` and `end` must point to an initialized value.
+    /// * Both `start` and `end` must point to the same allocated object and
+    /// must either be in bounds or at most one byte past the end of the
+    /// allocated object.
+    /// * Both `start` and `end` must be _derived from_ a pointer to the same
+    /// object.
+    /// * The distance between `start` and `end` must not overflow `isize`.
+    /// * The distance being in bounds must not rely on "wrapping around" the
+    /// address space.
+    #[inline(always)]
+    pub(crate) unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        // If we want to support vectors bigger than 256 bits, we probably
+        // need to move up to using a u64 for the masks used below. Currently
+        // they are 32 bits, which means we're SOL for vectors that need masks
+        // bigger than 32 bits. Overall unclear until there's a use case.
+        debug_assert!(V::BYTES <= 32, "vector cannot be bigger than 32 bytes");
+
+        let topos = V::Mask::last_offset;
+        let len = end.distance(start);
+        debug_assert!(
+            len >= V::BYTES,
+            "haystack has length {}, but must be at least {}",
+            len,
+            V::BYTES
+        );
+
+        if let Some(cur) = self.search_chunk(end.sub(V::BYTES), topos) {
+            return Some(cur);
+        }
+        let mut cur = end.sub(end.as_usize() & V::ALIGN);
+        debug_assert!(start <= cur && cur <= end);
+        if len >= Self::LOOP_SIZE {
+            while cur >= start.add(Self::LOOP_SIZE) {
+                debug_assert_eq!(0, cur.as_usize() % V::BYTES);
+
+                cur = cur.sub(Self::LOOP_SIZE);
+                let a = V::load_aligned(cur);
+                let b = V::load_aligned(cur.add(V::BYTES));
+                let eqa1 = self.v1.cmpeq(a);
+                let eqb1 = self.v1.cmpeq(b);
+                let eqa2 = self.v2.cmpeq(a);
+                let eqb2 = self.v2.cmpeq(b);
+                let eqa3 = self.v3.cmpeq(a);
+                let eqb3 = self.v3.cmpeq(b);
+                let or1 = eqa1.or(eqb1);
+                let or2 = eqa2.or(eqb2);
+                let or3 = eqa3.or(eqb3);
+                let or4 = or1.or(or2);
+                let or5 = or3.or(or4);
+                if or5.movemask_will_have_non_zero() {
+                    let mask = eqb1
+                        .movemask()
+                        .or(eqb2.movemask())
+                        .or(eqb3.movemask());
+                    if mask.has_non_zero() {
+                        return Some(cur.add(V::BYTES).add(topos(mask)));
+                    }
+
+                    let mask = eqa1
+                        .movemask()
+                        .or(eqa2.movemask())
+                        .or(eqa3.movemask());
+                    debug_assert!(mask.has_non_zero());
+                    return Some(cur.add(topos(mask)));
+                }
+            }
+        }
+        while cur >= start.add(V::BYTES) {
+            debug_assert!(cur.distance(start) >= V::BYTES);
+            cur = cur.sub(V::BYTES);
+            if let Some(cur) = self.search_chunk(cur, topos) {
+                return Some(cur);
+            }
+        }
+        if cur > start {
+            debug_assert!(cur.distance(start) < V::BYTES);
+            return self.search_chunk(start, topos);
+        }
+        None
+    }
+
+    /// Search `V::BYTES` starting at `cur` via an unaligned load.
+    ///
+    /// `mask_to_offset` should be a function that converts a `movemask` to
+    /// an offset such that `cur.add(offset)` corresponds to a pointer to the
+    /// match location if one is found. Generally it is expected to use either
+    /// `mask_to_first_offset` or `mask_to_last_offset`, depending on whether
+    /// one is implementing a forward or reverse search, respectively.
+    ///
+    /// # Safety
+    ///
+    /// `cur` must be a valid pointer and it must be valid to do an unaligned
+    /// load of size `V::BYTES` at `cur`.
+    #[inline(always)]
+    unsafe fn search_chunk(
+        &self,
+        cur: *const u8,
+        mask_to_offset: impl Fn(V::Mask) -> usize,
+    ) -> Option<*const u8> {
+        let chunk = V::load_unaligned(cur);
+        let eq1 = self.v1.cmpeq(chunk);
+        let eq2 = self.v2.cmpeq(chunk);
+        let eq3 = self.v3.cmpeq(chunk);
+        let mask = eq1.or(eq2).or(eq3).movemask();
+        if mask.has_non_zero() {
+            let mask1 = eq1.movemask();
+            let mask2 = eq2.movemask();
+            let mask3 = eq3.movemask();
+            Some(cur.add(mask_to_offset(mask1.or(mask2).or(mask3))))
+        } else {
+            None
+        }
+    }
+}
+
+/// An iterator over all occurrences of a set of bytes in a haystack.
+///
+/// This iterator implements the routines necessary to provide a
+/// `DoubleEndedIterator` impl, which means it can also be used to find
+/// occurrences in reverse order.
+///
+/// The lifetime parameters are as follows:
+///
+/// * `'h` refers to the lifetime of the haystack being searched.
+///
+/// This type is intended to be used to implement all iterators for the
+/// `memchr` family of functions. It handles a tiny bit of marginally tricky
+/// raw pointer math, but otherwise expects the caller to provide `find_raw`
+/// and `rfind_raw` routines for each call of `next` and `next_back`,
+/// respectively.
+#[derive(Clone, Debug)]
+pub(crate) struct Iter<'h> {
+    /// The original starting point into the haystack. We use this to convert
+    /// pointers to offsets.
+    original_start: *const u8,
+    /// The current starting point into the haystack. That is, where the next
+    /// search will begin.
+    start: *const u8,
+    /// The current ending point into the haystack. That is, where the next
+    /// reverse search will begin.
+    end: *const u8,
+    /// A marker for tracking the lifetime of the start/cur_start/cur_end
+    /// pointers above, which all point into the haystack.
+    haystack: core::marker::PhantomData<&'h [u8]>,
+}
+
+// SAFETY: Iter contains no shared references to anything that performs any
+// interior mutations. Also, the lifetime guarantees that Iter will not outlive
+// the haystack.
+unsafe impl<'h> Send for Iter<'h> {}
+
+// SAFETY: Iter perform no interior mutations, therefore no explicit
+// synchronization is necessary. Also, the lifetime guarantees that Iter will
+// not outlive the haystack.
+unsafe impl<'h> Sync for Iter<'h> {}
+
+impl<'h> Iter<'h> {
+    /// Create a new generic memchr iterator.
+    #[inline(always)]
+    pub(crate) fn new(haystack: &'h [u8]) -> Iter<'h> {
+        Iter {
+            original_start: haystack.as_ptr(),
+            start: haystack.as_ptr(),
+            end: haystack.as_ptr().wrapping_add(haystack.len()),
+            haystack: core::marker::PhantomData,
+        }
+    }
+
+    /// Returns the next occurrence in the forward direction.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that if a pointer is returned from the closure
+    /// provided, then it must be greater than or equal to the start pointer
+    /// and less than the end pointer.
+    #[inline(always)]
+    pub(crate) unsafe fn next(
+        &mut self,
+        mut find_raw: impl FnMut(*const u8, *const u8) -> Option<*const u8>,
+    ) -> Option<usize> {
+        // SAFETY: Pointers are derived directly from the same &[u8] haystack.
+        // We only ever modify start/end corresponding to a matching offset
+        // found between start and end. Thus all changes to start/end maintain
+        // our safety requirements.
+        //
+        // The only other assumption we rely on is that the pointer returned
+        // by `find_raw` satisfies `self.start <= found < self.end`, and that
+        // safety contract is forwarded to the caller.
+        let found = find_raw(self.start, self.end)?;
+        let result = found.distance(self.original_start);
+        self.start = found.add(1);
+        Some(result)
+    }
+
+    /// Returns the number of remaining elements in this iterator.
+    #[inline(always)]
+    pub(crate) fn count(
+        self,
+        mut count_raw: impl FnMut(*const u8, *const u8) -> usize,
+    ) -> usize {
+        // SAFETY: Pointers are derived directly from the same &[u8] haystack.
+        // We only ever modify start/end corresponding to a matching offset
+        // found between start and end. Thus all changes to start/end maintain
+        // our safety requirements.
+        count_raw(self.start, self.end)
+    }
+
+    /// Returns the next occurrence in reverse.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that if a pointer is returned from the closure
+    /// provided, then it must be greater than or equal to the start pointer
+    /// and less than the end pointer.
+    #[inline(always)]
+    pub(crate) unsafe fn next_back(
+        &mut self,
+        mut rfind_raw: impl FnMut(*const u8, *const u8) -> Option<*const u8>,
+    ) -> Option<usize> {
+        // SAFETY: Pointers are derived directly from the same &[u8] haystack.
+        // We only ever modify start/end corresponding to a matching offset
+        // found between start and end. Thus all changes to start/end maintain
+        // our safety requirements.
+        //
+        // The only other assumption we rely on is that the pointer returned
+        // by `rfind_raw` satisfies `self.start <= found < self.end`, and that
+        // safety contract is forwarded to the caller.
+        let found = rfind_raw(self.start, self.end)?;
+        let result = found.distance(self.original_start);
+        self.end = found;
+        Some(result)
+    }
+
+    /// Provides an implementation of `Iterator::size_hint`.
+    #[inline(always)]
+    pub(crate) fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, Some(self.end.as_usize().saturating_sub(self.start.as_usize())))
+    }
+}
+
+/// Search a slice using a function that operates on raw pointers.
+///
+/// Given a function to search a contiguous sequence of memory for the location
+/// of a non-empty set of bytes, this will execute that search on a slice of
+/// bytes. The pointer returned by the given function will be converted to an
+/// offset relative to the starting point of the given slice. That is, if a
+/// match is found, the offset returned by this routine is guaranteed to be a
+/// valid index into `haystack`.
+///
+/// Callers may use this for a forward or reverse search.
+///
+/// # Safety
+///
+/// Callers must ensure that if a pointer is returned by `find_raw`, then the
+/// pointer must be greater than or equal to the starting pointer and less than
+/// the end pointer.
+#[inline(always)]
+pub(crate) unsafe fn search_slice_with_raw(
+    haystack: &[u8],
+    mut find_raw: impl FnMut(*const u8, *const u8) -> Option<*const u8>,
+) -> Option<usize> {
+    // SAFETY: We rely on `find_raw` to return a correct and valid pointer, but
+    // otherwise, `start` and `end` are valid due to the guarantees provided by
+    // a &[u8].
+    let start = haystack.as_ptr();
+    let end = start.add(haystack.len());
+    let found = find_raw(start, end)?;
+    Some(found.distance(start))
+}
+
+/// Performs a forward byte-at-a-time loop until either `ptr >= end_ptr` or
+/// until `confirm(*ptr)` returns `true`. If the former occurs, then `None` is
+/// returned. If the latter occurs, then the pointer at which `confirm` returns
+/// `true` is returned.
+///
+/// # Safety
+///
+/// Callers must provide valid pointers and they must satisfy `start_ptr <=
+/// ptr` and `ptr <= end_ptr`.
+#[inline(always)]
+pub(crate) unsafe fn fwd_byte_by_byte<F: Fn(u8) -> bool>(
+    start: *const u8,
+    end: *const u8,
+    confirm: F,
+) -> Option<*const u8> {
+    debug_assert!(start <= end);
+    let mut ptr = start;
+    while ptr < end {
+        if confirm(*ptr) {
+            return Some(ptr);
+        }
+        ptr = ptr.offset(1);
+    }
+    None
+}
+
+/// Performs a reverse byte-at-a-time loop until either `ptr < start_ptr` or
+/// until `confirm(*ptr)` returns `true`. If the former occurs, then `None` is
+/// returned. If the latter occurs, then the pointer at which `confirm` returns
+/// `true` is returned.
+///
+/// # Safety
+///
+/// Callers must provide valid pointers and they must satisfy `start_ptr <=
+/// ptr` and `ptr <= end_ptr`.
+#[inline(always)]
+pub(crate) unsafe fn rev_byte_by_byte<F: Fn(u8) -> bool>(
+    start: *const u8,
+    end: *const u8,
+    confirm: F,
+) -> Option<*const u8> {
+    debug_assert!(start <= end);
+
+    let mut ptr = end;
+    while ptr > start {
+        ptr = ptr.offset(-1);
+        if confirm(*ptr) {
+            return Some(ptr);
+        }
+    }
+    None
+}
+
+/// Performs a forward byte-at-a-time loop until `ptr >= end_ptr` and returns
+/// the number of times `confirm(*ptr)` returns `true`.
+///
+/// # Safety
+///
+/// Callers must provide valid pointers and they must satisfy `start_ptr <=
+/// ptr` and `ptr <= end_ptr`.
+#[inline(always)]
+pub(crate) unsafe fn count_byte_by_byte<F: Fn(u8) -> bool>(
+    start: *const u8,
+    end: *const u8,
+    confirm: F,
+) -> usize {
+    debug_assert!(start <= end);
+    let mut ptr = start;
+    let mut count = 0;
+    while ptr < end {
+        if confirm(*ptr) {
+            count += 1;
+        }
+        ptr = ptr.offset(1);
+    }
+    count
+}