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Diffstat (limited to 'vendor/memchr/src/memmem/rarebytes.rs')
| -rw-r--r-- | vendor/memchr/src/memmem/rarebytes.rs | 136 |
1 files changed, 0 insertions, 136 deletions
diff --git a/vendor/memchr/src/memmem/rarebytes.rs b/vendor/memchr/src/memmem/rarebytes.rs deleted file mode 100644 index fb33f6894..000000000 --- a/vendor/memchr/src/memmem/rarebytes.rs +++ /dev/null @@ -1,136 +0,0 @@ -/// A heuristic frequency based detection of rare bytes for substring search. -/// -/// This detector attempts to pick out two bytes in a needle that are predicted -/// to occur least frequently. The purpose is to use these bytes to implement -/// fast candidate search using vectorized code. -/// -/// A set of offsets is only computed for needles of length 2 or greater. -/// Smaller needles should be special cased by the substring search algorithm -/// in use. (e.g., Use memchr for single byte needles.) -/// -/// Note that we use `u8` to represent the offsets of the rare bytes in a -/// needle to reduce space usage. This means that rare byte occurring after the -/// first 255 bytes in a needle will never be used. -#[derive(Clone, Copy, Debug, Default)] -pub(crate) struct RareNeedleBytes { - /// The leftmost offset of the rarest byte in the needle, according to - /// pre-computed frequency analysis. The "leftmost offset" means that - /// rare1i <= i for all i where needle[i] == needle[rare1i]. - rare1i: u8, - /// The leftmost offset of the second rarest byte in the needle, according - /// to pre-computed frequency analysis. The "leftmost offset" means that - /// rare2i <= i for all i where needle[i] == needle[rare2i]. - /// - /// The second rarest byte is used as a type of guard for quickly detecting - /// a mismatch if the first byte matches. This is a hedge against - /// pathological cases where the pre-computed frequency analysis may be - /// off. (But of course, does not prevent *all* pathological cases.) - /// - /// In general, rare1i != rare2i by construction, although there is no hard - /// requirement that they be different. However, since the case of a single - /// byte needle is handled specially by memchr itself, rare2i generally - /// always should be different from rare1i since it would otherwise be - /// ineffective as a guard. - rare2i: u8, -} - -impl RareNeedleBytes { - /// Create a new pair of rare needle bytes with the given offsets. This is - /// only used in tests for generating input data. - #[cfg(all(test, feature = "std"))] - pub(crate) fn new(rare1i: u8, rare2i: u8) -> RareNeedleBytes { - RareNeedleBytes { rare1i, rare2i } - } - - /// Detect the leftmost offsets of the two rarest bytes in the given - /// needle. - pub(crate) fn forward(needle: &[u8]) -> RareNeedleBytes { - if needle.len() <= 1 || needle.len() > core::u8::MAX as usize { - // For needles bigger than u8::MAX, our offsets aren't big enough. - // (We make our offsets small to reduce stack copying.) - // If you have a use case for it, please file an issue. In that - // case, we should probably just adjust the routine below to pick - // some rare bytes from the first 255 bytes of the needle. - // - // Also note that for needles of size 0 or 1, they are special - // cased in Two-Way. - // - // TODO: Benchmar this. - return RareNeedleBytes { rare1i: 0, rare2i: 0 }; - } - - // Find the rarest two bytes. We make them distinct by construction. - let (mut rare1, mut rare1i) = (needle[0], 0); - let (mut rare2, mut rare2i) = (needle[1], 1); - if rank(rare2) < rank(rare1) { - core::mem::swap(&mut rare1, &mut rare2); - core::mem::swap(&mut rare1i, &mut rare2i); - } - for (i, &b) in needle.iter().enumerate().skip(2) { - if rank(b) < rank(rare1) { - rare2 = rare1; - rare2i = rare1i; - rare1 = b; - rare1i = i as u8; - } else if b != rare1 && rank(b) < rank(rare2) { - rare2 = b; - rare2i = i as u8; - } - } - // While not strictly required, we really don't want these to be - // equivalent. If they were, it would reduce the effectiveness of - // candidate searching using these rare bytes by increasing the rate of - // false positives. - assert_ne!(rare1i, rare2i); - RareNeedleBytes { rare1i, rare2i } - } - - /// Return the rare bytes in the given needle in the forward direction. - /// The needle given must be the same one given to the RareNeedleBytes - /// constructor. - pub(crate) fn as_rare_bytes(&self, needle: &[u8]) -> (u8, u8) { - (needle[self.rare1i as usize], needle[self.rare2i as usize]) - } - - /// Return the rare offsets such that the first offset is always <= to the - /// second offset. This is useful when the caller doesn't care whether - /// rare1 is rarer than rare2, but just wants to ensure that they are - /// ordered with respect to one another. - #[cfg(memchr_runtime_simd)] - pub(crate) fn as_rare_ordered_usize(&self) -> (usize, usize) { - let (rare1i, rare2i) = self.as_rare_ordered_u8(); - (rare1i as usize, rare2i as usize) - } - - /// Like as_rare_ordered_usize, but returns the offsets as their native - /// u8 values. - #[cfg(memchr_runtime_simd)] - pub(crate) fn as_rare_ordered_u8(&self) -> (u8, u8) { - if self.rare1i <= self.rare2i { - (self.rare1i, self.rare2i) - } else { - (self.rare2i, self.rare1i) - } - } - - /// Return the rare offsets as usize values in the order in which they were - /// constructed. rare1, for example, is constructed as the "rarer" byte, - /// and thus, callers may want to treat it differently from rare2. - pub(crate) fn as_rare_usize(&self) -> (usize, usize) { - (self.rare1i as usize, self.rare2i as usize) - } - - /// Return the byte frequency rank of each byte. The higher the rank, the - /// more frequency the byte is predicted to be. The needle given must be - /// the same one given to the RareNeedleBytes constructor. - pub(crate) fn as_ranks(&self, needle: &[u8]) -> (usize, usize) { - let (b1, b2) = self.as_rare_bytes(needle); - (rank(b1), rank(b2)) - } -} - -/// Return the heuristical frequency rank of the given byte. A lower rank -/// means the byte is believed to occur less frequently. -fn rank(b: u8) -> usize { - crate::memmem::byte_frequencies::BYTE_FREQUENCIES[b as usize] as usize -} |