diff options
Diffstat (limited to 'vendor/memchr/src/arch/generic/memchr.rs')
| -rw-r--r-- | vendor/memchr/src/arch/generic/memchr.rs | 1214 |
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 +} |