Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

1 files changed, 136 insertions, 0 deletions

diff --git a/third_party/rust/memchr/src/memmem/rarebytes.rs b/third_party/rust/memchr/src/memmem/rarebytes.rs
new file mode 100644
index 0000000000..fb33f68945
--- /dev/null
+++ b/third_party/rust/memchr/src/memmem/rarebytes.rs
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+/// 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
+}