diff options
Diffstat (limited to 'library')
| -rw-r--r-- | library/alloc/benches/str.rs | 65 | ||||
| -rw-r--r-- | library/alloc/tests/str.rs | 26 | ||||
| -rw-r--r-- | library/core/src/str/pattern.rs | 232 |
3 files changed, 311 insertions, 12 deletions
diff --git a/library/alloc/benches/str.rs b/library/alloc/benches/str.rs index 391475bc0c7..54af389dedc 100644 --- a/library/alloc/benches/str.rs +++ b/library/alloc/benches/str.rs @@ -1,3 +1,4 @@ +use core::iter::Iterator; use test::{black_box, Bencher}; #[bench] @@ -122,14 +123,13 @@ fn bench_contains_short_short(b: &mut Bencher) { let haystack = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."; let needle = "sit"; + b.bytes = haystack.len() as u64; b.iter(|| { - assert!(haystack.contains(needle)); + assert!(black_box(haystack).contains(black_box(needle))); }) } -#[bench] -fn bench_contains_short_long(b: &mut Bencher) { - let haystack = "\ +static LONG_HAYSTACK: &str = "\ Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse quis lorem sit amet dolor \ ultricies condimentum. Praesent iaculis purus elit, ac malesuada quam malesuada in. Duis sed orci \ eros. Suspendisse sit amet magna mollis, mollis nunc luctus, imperdiet mi. Integer fringilla non \ @@ -164,10 +164,48 @@ feugiat. Etiam quis mauris vel risus luctus mattis a a nunc. Nullam orci quam, i vehicula in, porttitor ut nibh. Duis sagittis adipiscing nisl vitae congue. Donec mollis risus eu \ leo suscipit, varius porttitor nulla porta. Pellentesque ut sem nec nisi euismod vehicula. Nulla \ malesuada sollicitudin quam eu fermentum."; + +#[bench] +fn bench_contains_2b_repeated_long(b: &mut Bencher) { + let haystack = LONG_HAYSTACK; + let needle = "::"; + + b.bytes = haystack.len() as u64; + b.iter(|| { + assert!(!black_box(haystack).contains(black_box(needle))); + }) +} + +#[bench] +fn bench_contains_short_long(b: &mut Bencher) { + let haystack = LONG_HAYSTACK; let needle = "english"; + b.bytes = haystack.len() as u64; + b.iter(|| { + assert!(!black_box(haystack).contains(black_box(needle))); + }) +} + +#[bench] +fn bench_contains_16b_in_long(b: &mut Bencher) { + let haystack = LONG_HAYSTACK; + let needle = "english language"; + + b.bytes = haystack.len() as u64; + b.iter(|| { + assert!(!black_box(haystack).contains(black_box(needle))); + }) +} + +#[bench] +fn bench_contains_32b_in_long(b: &mut Bencher) { + let haystack = LONG_HAYSTACK; + let needle = "the english language sample text"; + + b.bytes = haystack.len() as u64; b.iter(|| { - assert!(!haystack.contains(needle)); + assert!(!black_box(haystack).contains(black_box(needle))); }) } @@ -176,8 +214,20 @@ fn bench_contains_bad_naive(b: &mut Bencher) { let haystack = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; let needle = "aaaaaaaab"; + b.bytes = haystack.len() as u64; + b.iter(|| { + assert!(!black_box(haystack).contains(black_box(needle))); + }) +} + +#[bench] +fn bench_contains_bad_simd(b: &mut Bencher) { + let haystack = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"; + let needle = "aaabaaaa"; + + b.bytes = haystack.len() as u64; b.iter(|| { - assert!(!haystack.contains(needle)); + assert!(!black_box(haystack).contains(black_box(needle))); }) } @@ -186,8 +236,9 @@ fn bench_contains_equal(b: &mut Bencher) { let haystack = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."; let needle = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."; + b.bytes = haystack.len() as u64; b.iter(|| { - assert!(haystack.contains(needle)); + assert!(black_box(haystack).contains(black_box(needle))); }) } diff --git a/library/alloc/tests/str.rs b/library/alloc/tests/str.rs index e30329aa1cb..9689196ef21 100644 --- a/library/alloc/tests/str.rs +++ b/library/alloc/tests/str.rs @@ -1590,11 +1590,27 @@ fn test_bool_from_str() { assert_eq!("not even a boolean".parse::<bool>().ok(), None); } -fn check_contains_all_substrings(s: &str) { - assert!(s.contains("")); - for i in 0..s.len() { - for j in i + 1..=s.len() { - assert!(s.contains(&s[i..j])); +fn check_contains_all_substrings(haystack: &str) { + let mut modified_needle = String::new(); + + for i in 0..haystack.len() { + // check different haystack lengths since we special-case short haystacks. + let haystack = &haystack[0..i]; + assert!(haystack.contains("")); + for j in 0..haystack.len() { + for k in j + 1..=haystack.len() { + let needle = &haystack[j..k]; + assert!(haystack.contains(needle)); + modified_needle.clear(); + modified_needle.push_str(needle); + modified_needle.replace_range(0..1, "\0"); + assert!(!haystack.contains(&modified_needle)); + + modified_needle.clear(); + modified_needle.push_str(needle); + modified_needle.replace_range(needle.len() - 1..needle.len(), "\0"); + assert!(!haystack.contains(&modified_needle)); + } } } } diff --git a/library/core/src/str/pattern.rs b/library/core/src/str/pattern.rs index ec2cb429e67..c5be32861f9 100644 --- a/library/core/src/str/pattern.rs +++ b/library/core/src/str/pattern.rs @@ -39,6 +39,7 @@ )] use crate::cmp; +use crate::cmp::Ordering; use crate::fmt; use crate::slice::memchr; @@ -946,6 +947,32 @@ impl<'a, 'b> Pattern<'a> for &'b str { haystack.as_bytes().starts_with(self.as_bytes()) } + /// Checks whether the pattern matches anywhere in the haystack + #[inline] + fn is_contained_in(self, haystack: &'a str) -> bool { + if self.len() == 0 { + return true; + } + + match self.len().cmp(&haystack.len()) { + Ordering::Less => { + if self.len() == 1 { + return haystack.as_bytes().contains(&self.as_bytes()[0]); + } + + #[cfg(all(target_arch = "x86_64", target_feature = "sse2"))] + if self.len() <= 32 { + if let Some(result) = simd_contains(self, haystack) { + return result; + } + } + + self.into_searcher(haystack).next_match().is_some() + } + _ => self == haystack, + } + } + /// Removes the pattern from the front of haystack, if it matches. #[inline] fn strip_prefix_of(self, haystack: &'a str) -> Option<&'a str> { @@ -1684,3 +1711,208 @@ impl TwoWayStrategy for RejectAndMatch { SearchStep::Match(a, b) } } + +/// SIMD search for short needles based on +/// Wojciech Muła's "SIMD-friendly algorithms for substring searching"[0] +/// +/// It skips ahead by the vector width on each iteration (rather than the needle length as two-way +/// does) by probing the first and last byte of the needle for the whole vector width +/// and only doing full needle comparisons when the vectorized probe indicated potential matches. +/// +/// Since the x86_64 baseline only offers SSE2 we only use u8x16 here. +/// If we ever ship std with for x86-64-v3 or adapt this for other platforms then wider vectors +/// should be evaluated. +/// +/// For haystacks smaller than vector-size + needle length it falls back to +/// a naive O(n*m) search so this implementation should not be called on larger needles. +/// +/// [0]: http://0x80.pl/articles/simd-strfind.html#sse-avx2 +#[cfg(all(target_arch = "x86_64", target_feature = "sse2"))] +#[inline] +fn simd_contains(needle: &str, haystack: &str) -> Option<bool> { + let needle = needle.as_bytes(); + let haystack = haystack.as_bytes(); + + debug_assert!(needle.len() > 1); + + use crate::ops::BitAnd; + use crate::simd::mask8x16 as Mask; + use crate::simd::u8x16 as Block; + use crate::simd::{SimdPartialEq, ToBitMask}; + + let first_probe = needle[0]; + + // the offset used for the 2nd vector + let second_probe_offset = if needle.len() == 2 { + // never bail out on len=2 needles because the probes will fully cover them and have + // no degenerate cases. + 1 + } else { + // try a few bytes in case first and last byte of the needle are the same + let Some(second_probe_offset) = (needle.len().saturating_sub(4)..needle.len()).rfind(|&idx| needle[idx] != first_probe) else { + // fall back to other search methods if we can't find any different bytes + // since we could otherwise hit some degenerate cases + return None; + }; + second_probe_offset + }; + + // do a naive search if the haystack is too small to fit + if haystack.len() < Block::LANES + second_probe_offset { + return Some(haystack.windows(needle.len()).any(|c| c == needle)); + } + + let first_probe: Block = Block::splat(first_probe); + let second_probe: Block = Block::splat(needle[second_probe_offset]); + // first byte are already checked by the outer loop. to verify a match only the + // remainder has to be compared. + let trimmed_needle = &needle[1..]; + + // this #[cold] is load-bearing, benchmark before removing it... + let check_mask = #[cold] + |idx, mask: u16, skip: bool| -> bool { + if skip { + return false; + } + + // and so is this. optimizations are weird. + let mut mask = mask; + + while mask != 0 { + let trailing = mask.trailing_zeros(); + let offset = idx + trailing as usize + 1; + // SAFETY: mask is between 0 and 15 trailing zeroes, we skip one additional byte that was already compared + // and then take trimmed_needle.len() bytes. This is within the bounds defined by the outer loop + unsafe { + let sub = haystack.get_unchecked(offset..).get_unchecked(..trimmed_needle.len()); + if small_slice_eq(sub, trimmed_needle) { + return true; + } + } + mask &= !(1 << trailing); + } + return false; + }; + + let test_chunk = |idx| -> u16 { + // SAFETY: this requires at least LANES bytes being readable at idx + // that is ensured by the loop ranges (see comments below) + let a: Block = unsafe { haystack.as_ptr().add(idx).cast::<Block>().read_unaligned() }; + // SAFETY: this requires LANES + block_offset bytes being readable at idx + let b: Block = unsafe { + haystack.as_ptr().add(idx).add(second_probe_offset).cast::<Block>().read_unaligned() + }; + let eq_first: Mask = a.simd_eq(first_probe); + let eq_last: Mask = b.simd_eq(second_probe); + let both = eq_first.bitand(eq_last); + let mask = both.to_bitmask(); + + return mask; + }; + + let mut i = 0; + let mut result = false; + // The loop condition must ensure that there's enough headroom to read LANE bytes, + // and not only at the current index but also at the index shifted by block_offset + const UNROLL: usize = 4; + while i + second_probe_offset + UNROLL * Block::LANES < haystack.len() && !result { + let mut masks = [0u16; UNROLL]; + for j in 0..UNROLL { + masks[j] = test_chunk(i + j * Block::LANES); + } + for j in 0..UNROLL { + let mask = masks[j]; + if mask != 0 { + result |= check_mask(i + j * Block::LANES, mask, result); + } + } + i += UNROLL * Block::LANES; + } + while i + second_probe_offset + Block::LANES < haystack.len() && !result { + let mask = test_chunk(i); + if mask != 0 { + result |= check_mask(i, mask, result); + } + i += Block::LANES; + } + + // Process the tail that didn't fit into LANES-sized steps. + // This simply repeats the same procedure but as right-aligned chunk instead + // of a left-aligned one. The last byte must be exactly flush with the string end so + // we don't miss a single byte or read out of bounds. + let i = haystack.len() - second_probe_offset - Block::LANES; + let mask = test_chunk(i); + if mask != 0 { + result |= check_mask(i, mask, result); + } + + Some(result) +} + +/// Compares short slices for equality. +/// +/// It avoids a call to libc's memcmp which is faster on long slices +/// due to SIMD optimizations but it incurs a function call overhead. +/// +/// # Safety +/// +/// Both slices must have the same length. +#[cfg(all(target_arch = "x86_64", target_feature = "sse2"))] // only called on x86 +#[inline] +unsafe fn small_slice_eq(x: &[u8], y: &[u8]) -> bool { + // This function is adapted from + // https://github.com/BurntSushi/memchr/blob/8037d11b4357b0f07be2bb66dc2659d9cf28ad32/src/memmem/util.rs#L32 + + // If we don't have enough bytes to do 4-byte at a time loads, then + // fall back to the naive slow version. + // + // Potential alternative: We could do a copy_nonoverlapping combined with a mask instead + // of a loop. Benchmark it. + if x.len() < 4 { + for (&b1, &b2) in x.iter().zip(y) { + if b1 != b2 { + return false; + } + } + return true; + } + // When we have 4 or more bytes to compare, then proceed in chunks of 4 at + // a time using unaligned loads. + // + // Also, why do 4 byte loads instead of, say, 8 byte loads? The reason is + // that this particular version of memcmp is likely to be called with tiny + // needles. That means that if we do 8 byte loads, then a higher proportion + // of memcmp calls will use the slower variant above. With that said, this + // is a hypothesis and is only loosely supported by benchmarks. There's + // likely some improvement that could be made here. The main thing here + // though is to optimize for latency, not throughput. + + // SAFETY: Via the conditional above, we know that both `px` and `py` + // have the same length, so `px < pxend` implies that `py < pyend`. + // Thus, derefencing both `px` and `py` in the loop below is safe. + // + // Moreover, we set `pxend` and `pyend` to be 4 bytes before the actual + // end of of `px` and `py`. Thus, the final dereference outside of the + // loop is guaranteed to be valid. (The final comparison will overlap with + // the last comparison done in the loop for lengths that aren't multiples + // of four.) + // + // Finally, we needn't worry about alignment here, since we do unaligned + // loads. + unsafe { + let (mut px, mut py) = (x.as_ptr(), y.as_ptr()); + let (pxend, pyend) = (px.add(x.len() - 4), py.add(y.len() - 4)); + while px < pxend { + let vx = (px as *const u32).read_unaligned(); + let vy = (py as *const u32).read_unaligned(); + if vx != vy { + return false; + } + px = px.add(4); + py = py.add(4); + } + let vx = (pxend as *const u32).read_unaligned(); + let vy = (pyend as *const u32).read_unaligned(); + vx == vy + } +} |