Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1031 insertions, 0 deletions

diff --git a/vendor/memchr/src/arch/aarch64/neon/memchr.rs b/vendor/memchr/src/arch/aarch64/neon/memchr.rs
new file mode 100644
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+/*!
+This module defines 128-bit vector implementations of `memchr` and friends.
+
+The main types in this module are [`One`], [`Two`] and [`Three`]. They are for
+searching for one, two or three distinct bytes, respectively, in a haystack.
+Each type also has corresponding double ended iterators. These searchers are
+typically much faster than scalar routines accomplishing the same task.
+
+The `One` searcher also provides a [`One::count`] routine for efficiently
+counting the number of times a single byte occurs in a haystack. This is
+useful, for example, for counting the number of lines in a haystack. This
+routine exists because it is usually faster, especially with a high match
+count, then using [`One::find`] repeatedly. ([`OneIter`] specializes its
+`Iterator::count` implementation to use this routine.)
+
+Only one, two and three bytes are supported because three bytes is about
+the point where one sees diminishing returns. Beyond this point and it's
+probably (but not necessarily) better to just use a simple `[bool; 256]` array
+or similar. However, it depends mightily on the specific work-load and the
+expected match frequency.
+*/
+
+use core::arch::aarch64::uint8x16_t;
+
+use crate::{arch::generic::memchr as generic, ext::Pointer, vector::Vector};
+
+/// Finds all occurrences of a single byte in a haystack.
+#[derive(Clone, Copy, Debug)]
+pub struct One(generic::One<uint8x16_t>);
+
+impl One {
+    /// Create a new searcher that finds occurrences of the needle byte given.
+    ///
+    /// This particular searcher is specialized to use neon vector instructions
+    /// that typically make it quite fast.
+    ///
+    /// If neon is unavailable in the current environment, then `None` is
+    /// returned.
+    #[inline]
+    pub fn new(needle: u8) -> Option<One> {
+        if One::is_available() {
+            // SAFETY: we check that neon is available above.
+            unsafe { Some(One::new_unchecked(needle)) }
+        } else {
+            None
+        }
+    }
+
+    /// Create a new finder specific to neon vectors and routines without
+    /// checking that neon is available.
+    ///
+    /// # Safety
+    ///
+    /// Callers must guarantee that it is safe to execute `neon` instructions
+    /// in the current environment.
+    ///
+    /// Note that it is a common misconception that if one compiles for an
+    /// `x86_64` target, then they therefore automatically have access to neon
+    /// instructions. While this is almost always the case, it isn't true in
+    /// 100% of cases.
+    #[target_feature(enable = "neon")]
+    #[inline]
+    pub unsafe fn new_unchecked(needle: u8) -> One {
+        One(generic::One::new(needle))
+    }
+
+    /// Returns true when this implementation is available in the current
+    /// environment.
+    ///
+    /// When this is true, it is guaranteed that [`One::new`] will return
+    /// a `Some` value. Similarly, when it is false, it is guaranteed that
+    /// `One::new` will return a `None` value.
+    ///
+    /// Note also that for the lifetime of a single program, if this returns
+    /// true then it will always return true.
+    #[inline]
+    pub fn is_available() -> bool {
+        #[cfg(target_feature = "neon")]
+        {
+            true
+        }
+        #[cfg(not(target_feature = "neon"))]
+        {
+            false
+        }
+    }
+
+    /// Return the first occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn find(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `find_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.find_raw(s, e)
+            })
+        }
+    }
+
+    /// Return the last occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn rfind(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `rfind_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.rfind_raw(s, e)
+            })
+        }
+    }
+
+    /// Counts all occurrences of this byte in the given haystack.
+    #[inline]
+    pub fn count(&self, haystack: &[u8]) -> usize {
+        // SAFETY: All of our pointers are derived directly from a borrowed
+        // slice, which is guaranteed to be valid.
+        unsafe {
+            let start = haystack.as_ptr();
+            let end = start.add(haystack.len());
+            self.count_raw(start, end)
+        }
+    }
+
+    /// Like `find`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::fwd_byte_by_byte(start, end, |b| {
+                b == self.0.needle1()
+            });
+        }
+        // SAFETY: Building a `One` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.find_raw_impl(start, end)
+    }
+
+    /// Like `rfind`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::rev_byte_by_byte(start, end, |b| {
+                b == self.0.needle1()
+            });
+        }
+        // SAFETY: Building a `One` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.rfind_raw_impl(start, end)
+    }
+
+    /// Like `count`, but accepts and returns raw pointers.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn count_raw(&self, start: *const u8, end: *const u8) -> usize {
+        if start >= end {
+            return 0;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::count_byte_by_byte(start, end, |b| {
+                b == self.0.needle1()
+            });
+        }
+        // SAFETY: Building a `One` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.count_raw_impl(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`One::find_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `One`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn find_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.find_raw(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`One::rfind_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `One`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn rfind_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.rfind_raw(start, end)
+    }
+
+    /// Execute a count using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`One::count_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `One`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn count_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> usize {
+        self.0.count_raw(start, end)
+    }
+
+    /// Returns an iterator over all occurrences of the needle byte in the
+    /// given haystack.
+    ///
+    /// The iterator returned implements `DoubleEndedIterator`. This means it
+    /// can also be used to find occurrences in reverse order.
+    #[inline]
+    pub fn iter<'a, 'h>(&'a self, haystack: &'h [u8]) -> OneIter<'a, 'h> {
+        OneIter { searcher: self, it: generic::Iter::new(haystack) }
+    }
+}
+
+/// An iterator over all occurrences of a single byte in a haystack.
+///
+/// This iterator implements `DoubleEndedIterator`, which means it can also be
+/// used to find occurrences in reverse order.
+///
+/// This iterator is created by the [`One::iter`] method.
+///
+/// The lifetime parameters are as follows:
+///
+/// * `'a` refers to the lifetime of the underlying [`One`] searcher.
+/// * `'h` refers to the lifetime of the haystack being searched.
+#[derive(Clone, Debug)]
+pub struct OneIter<'a, 'h> {
+    searcher: &'a One,
+    it: generic::Iter<'h>,
+}
+
+impl<'a, 'h> Iterator for OneIter<'a, 'h> {
+    type Item = usize;
+
+    #[inline]
+    fn next(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'find_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next(|s, e| self.searcher.find_raw(s, e)) }
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.it.count(|s, e| {
+            // SAFETY: We rely on our generic iterator to return valid start
+            // and end pointers.
+            unsafe { self.searcher.count_raw(s, e) }
+        })
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.it.size_hint()
+    }
+}
+
+impl<'a, 'h> DoubleEndedIterator for OneIter<'a, 'h> {
+    #[inline]
+    fn next_back(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'rfind_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next_back(|s, e| self.searcher.rfind_raw(s, e)) }
+    }
+}
+
+impl<'a, 'h> core::iter::FusedIterator for OneIter<'a, 'h> {}
+
+/// 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 struct Two(generic::Two<uint8x16_t>);
+
+impl Two {
+    /// Create a new searcher that finds occurrences of the needle bytes given.
+    ///
+    /// This particular searcher is specialized to use neon vector instructions
+    /// that typically make it quite fast.
+    ///
+    /// If neon is unavailable in the current environment, then `None` is
+    /// returned.
+    #[inline]
+    pub fn new(needle1: u8, needle2: u8) -> Option<Two> {
+        if Two::is_available() {
+            // SAFETY: we check that neon is available above.
+            unsafe { Some(Two::new_unchecked(needle1, needle2)) }
+        } else {
+            None
+        }
+    }
+
+    /// Create a new finder specific to neon vectors and routines without
+    /// checking that neon is available.
+    ///
+    /// # Safety
+    ///
+    /// Callers must guarantee that it is safe to execute `neon` instructions
+    /// in the current environment.
+    ///
+    /// Note that it is a common misconception that if one compiles for an
+    /// `x86_64` target, then they therefore automatically have access to neon
+    /// instructions. While this is almost always the case, it isn't true in
+    /// 100% of cases.
+    #[target_feature(enable = "neon")]
+    #[inline]
+    pub unsafe fn new_unchecked(needle1: u8, needle2: u8) -> Two {
+        Two(generic::Two::new(needle1, needle2))
+    }
+
+    /// Returns true when this implementation is available in the current
+    /// environment.
+    ///
+    /// When this is true, it is guaranteed that [`Two::new`] will return
+    /// a `Some` value. Similarly, when it is false, it is guaranteed that
+    /// `Two::new` will return a `None` value.
+    ///
+    /// Note also that for the lifetime of a single program, if this returns
+    /// true then it will always return true.
+    #[inline]
+    pub fn is_available() -> bool {
+        #[cfg(target_feature = "neon")]
+        {
+            true
+        }
+        #[cfg(not(target_feature = "neon"))]
+        {
+            false
+        }
+    }
+
+    /// Return the first occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn find(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `find_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.find_raw(s, e)
+            })
+        }
+    }
+
+    /// Return the last occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn rfind(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `rfind_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.rfind_raw(s, e)
+            })
+        }
+    }
+
+    /// Like `find`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::fwd_byte_by_byte(start, end, |b| {
+                b == self.0.needle1() || b == self.0.needle2()
+            });
+        }
+        // SAFETY: Building a `Two` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.find_raw_impl(start, end)
+    }
+
+    /// Like `rfind`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::rev_byte_by_byte(start, end, |b| {
+                b == self.0.needle1() || b == self.0.needle2()
+            });
+        }
+        // SAFETY: Building a `Two` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.rfind_raw_impl(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`Two::find_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `Two`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn find_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.find_raw(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`Two::rfind_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `Two`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn rfind_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.rfind_raw(start, end)
+    }
+
+    /// Returns an iterator over all occurrences of the needle bytes in the
+    /// given haystack.
+    ///
+    /// The iterator returned implements `DoubleEndedIterator`. This means it
+    /// can also be used to find occurrences in reverse order.
+    #[inline]
+    pub fn iter<'a, 'h>(&'a self, haystack: &'h [u8]) -> TwoIter<'a, 'h> {
+        TwoIter { searcher: self, it: generic::Iter::new(haystack) }
+    }
+}
+
+/// An iterator over all occurrences of two possible bytes in a haystack.
+///
+/// This iterator implements `DoubleEndedIterator`, which means it can also be
+/// used to find occurrences in reverse order.
+///
+/// This iterator is created by the [`Two::iter`] method.
+///
+/// The lifetime parameters are as follows:
+///
+/// * `'a` refers to the lifetime of the underlying [`Two`] searcher.
+/// * `'h` refers to the lifetime of the haystack being searched.
+#[derive(Clone, Debug)]
+pub struct TwoIter<'a, 'h> {
+    searcher: &'a Two,
+    it: generic::Iter<'h>,
+}
+
+impl<'a, 'h> Iterator for TwoIter<'a, 'h> {
+    type Item = usize;
+
+    #[inline]
+    fn next(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'find_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next(|s, e| self.searcher.find_raw(s, e)) }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.it.size_hint()
+    }
+}
+
+impl<'a, 'h> DoubleEndedIterator for TwoIter<'a, 'h> {
+    #[inline]
+    fn next_back(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'rfind_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next_back(|s, e| self.searcher.rfind_raw(s, e)) }
+    }
+}
+
+impl<'a, 'h> core::iter::FusedIterator for TwoIter<'a, 'h> {}
+
+/// Finds all occurrences of three bytes in a haystack.
+///
+/// That is, this reports matches of one of three possible bytes. For example,
+/// searching for `a`, `b` or `o` in `afoobar` would report matches at offsets
+/// `0`, `2`, `3`, `4` and `5`.
+#[derive(Clone, Copy, Debug)]
+pub struct Three(generic::Three<uint8x16_t>);
+
+impl Three {
+    /// Create a new searcher that finds occurrences of the needle bytes given.
+    ///
+    /// This particular searcher is specialized to use neon vector instructions
+    /// that typically make it quite fast.
+    ///
+    /// If neon is unavailable in the current environment, then `None` is
+    /// returned.
+    #[inline]
+    pub fn new(needle1: u8, needle2: u8, needle3: u8) -> Option<Three> {
+        if Three::is_available() {
+            // SAFETY: we check that neon is available above.
+            unsafe { Some(Three::new_unchecked(needle1, needle2, needle3)) }
+        } else {
+            None
+        }
+    }
+
+    /// Create a new finder specific to neon vectors and routines without
+    /// checking that neon is available.
+    ///
+    /// # Safety
+    ///
+    /// Callers must guarantee that it is safe to execute `neon` instructions
+    /// in the current environment.
+    ///
+    /// Note that it is a common misconception that if one compiles for an
+    /// `x86_64` target, then they therefore automatically have access to neon
+    /// instructions. While this is almost always the case, it isn't true in
+    /// 100% of cases.
+    #[target_feature(enable = "neon")]
+    #[inline]
+    pub unsafe fn new_unchecked(
+        needle1: u8,
+        needle2: u8,
+        needle3: u8,
+    ) -> Three {
+        Three(generic::Three::new(needle1, needle2, needle3))
+    }
+
+    /// Returns true when this implementation is available in the current
+    /// environment.
+    ///
+    /// When this is true, it is guaranteed that [`Three::new`] will return
+    /// a `Some` value. Similarly, when it is false, it is guaranteed that
+    /// `Three::new` will return a `None` value.
+    ///
+    /// Note also that for the lifetime of a single program, if this returns
+    /// true then it will always return true.
+    #[inline]
+    pub fn is_available() -> bool {
+        #[cfg(target_feature = "neon")]
+        {
+            true
+        }
+        #[cfg(not(target_feature = "neon"))]
+        {
+            false
+        }
+    }
+
+    /// Return the first occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn find(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `find_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.find_raw(s, e)
+            })
+        }
+    }
+
+    /// Return the last occurrence of one of the needle bytes in the given
+    /// haystack. If no such occurrence exists, then `None` is returned.
+    ///
+    /// The occurrence is reported as an offset into `haystack`. Its maximum
+    /// value is `haystack.len() - 1`.
+    #[inline]
+    pub fn rfind(&self, haystack: &[u8]) -> Option<usize> {
+        // SAFETY: `rfind_raw` guarantees that if a pointer is returned, it
+        // falls within the bounds of the start and end pointers.
+        unsafe {
+            generic::search_slice_with_raw(haystack, |s, e| {
+                self.rfind_raw(s, e)
+            })
+        }
+    }
+
+    /// Like `find`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn find_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::fwd_byte_by_byte(start, end, |b| {
+                b == self.0.needle1()
+                    || b == self.0.needle2()
+                    || b == self.0.needle3()
+            });
+        }
+        // SAFETY: Building a `Three` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.find_raw_impl(start, end)
+    }
+
+    /// Like `rfind`, but accepts and returns raw pointers.
+    ///
+    /// When a match is found, the pointer returned is guaranteed to be
+    /// `>= start` and `< end`.
+    ///
+    /// This routine is useful if you're already using raw pointers and would
+    /// like to avoid converting back to a slice before executing a search.
+    ///
+    /// # Safety
+    ///
+    /// * 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.
+    ///
+    /// Note that callers may pass a pair of pointers such that `start >= end`.
+    /// In that case, `None` will always be returned.
+    #[inline]
+    pub unsafe fn rfind_raw(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        if start >= end {
+            return None;
+        }
+        if end.distance(start) < uint8x16_t::BYTES {
+            // SAFETY: We require the caller to pass valid start/end pointers.
+            return generic::rev_byte_by_byte(start, end, |b| {
+                b == self.0.needle1()
+                    || b == self.0.needle2()
+                    || b == self.0.needle3()
+            });
+        }
+        // SAFETY: Building a `Three` means it's safe to call 'neon' routines.
+        // Also, we've checked that our haystack is big enough to run on the
+        // vector routine. Pointer validity is caller's responsibility.
+        self.rfind_raw_impl(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`Three::find_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `Three`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn find_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.find_raw(start, end)
+    }
+
+    /// Execute a search using neon vectors and routines.
+    ///
+    /// # Safety
+    ///
+    /// Same as [`Three::rfind_raw`], except the distance between `start` and
+    /// `end` must be at least the size of a neon vector (in bytes).
+    ///
+    /// (The target feature safety obligation is automatically fulfilled by
+    /// virtue of being a method on `Three`, which can only be constructed
+    /// when it is safe to call `neon` routines.)
+    #[target_feature(enable = "neon")]
+    #[inline]
+    unsafe fn rfind_raw_impl(
+        &self,
+        start: *const u8,
+        end: *const u8,
+    ) -> Option<*const u8> {
+        self.0.rfind_raw(start, end)
+    }
+
+    /// Returns an iterator over all occurrences of the needle byte in the
+    /// given haystack.
+    ///
+    /// The iterator returned implements `DoubleEndedIterator`. This means it
+    /// can also be used to find occurrences in reverse order.
+    #[inline]
+    pub fn iter<'a, 'h>(&'a self, haystack: &'h [u8]) -> ThreeIter<'a, 'h> {
+        ThreeIter { searcher: self, it: generic::Iter::new(haystack) }
+    }
+}
+
+/// An iterator over all occurrences of three possible bytes in a haystack.
+///
+/// This iterator implements `DoubleEndedIterator`, which means it can also be
+/// used to find occurrences in reverse order.
+///
+/// This iterator is created by the [`Three::iter`] method.
+///
+/// The lifetime parameters are as follows:
+///
+/// * `'a` refers to the lifetime of the underlying [`Three`] searcher.
+/// * `'h` refers to the lifetime of the haystack being searched.
+#[derive(Clone, Debug)]
+pub struct ThreeIter<'a, 'h> {
+    searcher: &'a Three,
+    it: generic::Iter<'h>,
+}
+
+impl<'a, 'h> Iterator for ThreeIter<'a, 'h> {
+    type Item = usize;
+
+    #[inline]
+    fn next(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'find_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next(|s, e| self.searcher.find_raw(s, e)) }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.it.size_hint()
+    }
+}
+
+impl<'a, 'h> DoubleEndedIterator for ThreeIter<'a, 'h> {
+    #[inline]
+    fn next_back(&mut self) -> Option<usize> {
+        // SAFETY: We rely on the generic iterator to provide valid start
+        // and end pointers, but we guarantee that any pointer returned by
+        // 'rfind_raw' falls within the bounds of the start and end pointer.
+        unsafe { self.it.next_back(|s, e| self.searcher.rfind_raw(s, e)) }
+    }
+}
+
+impl<'a, 'h> core::iter::FusedIterator for ThreeIter<'a, 'h> {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    define_memchr_quickcheck!(super);
+
+    #[test]
+    fn forward_one() {
+        crate::tests::memchr::Runner::new(1).forward_iter(
+            |haystack, needles| {
+                Some(One::new(needles[0])?.iter(haystack).collect())
+            },
+        )
+    }
+
+    #[test]
+    fn reverse_one() {
+        crate::tests::memchr::Runner::new(1).reverse_iter(
+            |haystack, needles| {
+                Some(One::new(needles[0])?.iter(haystack).rev().collect())
+            },
+        )
+    }
+
+    #[test]
+    fn count_one() {
+        crate::tests::memchr::Runner::new(1).count_iter(|haystack, needles| {
+            Some(One::new(needles[0])?.iter(haystack).count())
+        })
+    }
+
+    #[test]
+    fn forward_two() {
+        crate::tests::memchr::Runner::new(2).forward_iter(
+            |haystack, needles| {
+                let n1 = needles.get(0).copied()?;
+                let n2 = needles.get(1).copied()?;
+                Some(Two::new(n1, n2)?.iter(haystack).collect())
+            },
+        )
+    }
+
+    #[test]
+    fn reverse_two() {
+        crate::tests::memchr::Runner::new(2).reverse_iter(
+            |haystack, needles| {
+                let n1 = needles.get(0).copied()?;
+                let n2 = needles.get(1).copied()?;
+                Some(Two::new(n1, n2)?.iter(haystack).rev().collect())
+            },
+        )
+    }
+
+    #[test]
+    fn forward_three() {
+        crate::tests::memchr::Runner::new(3).forward_iter(
+            |haystack, needles| {
+                let n1 = needles.get(0).copied()?;
+                let n2 = needles.get(1).copied()?;
+                let n3 = needles.get(2).copied()?;
+                Some(Three::new(n1, n2, n3)?.iter(haystack).collect())
+            },
+        )
+    }
+
+    #[test]
+    fn reverse_three() {
+        crate::tests::memchr::Runner::new(3).reverse_iter(
+            |haystack, needles| {
+                let n1 = needles.get(0).copied()?;
+                let n2 = needles.get(1).copied()?;
+                let n3 = needles.get(2).copied()?;
+                Some(Three::new(n1, n2, n3)?.iter(haystack).rev().collect())
+            },
+        )
+    }
+}