1 files changed, 111 insertions, 0 deletions
diff --git a/vendor/snap/src/crc32.rs b/vendor/snap/src/crc32.rs
new file mode 100644
index 000000000..1298ef04a
--- /dev/null
+++ b/vendor/snap/src/crc32.rs
@@ -0,0 +1,111 @@
+use crate::bytes;
+use crate::crc32_table::{TABLE, TABLE16};
+
+/// Provides a simple API to generate "masked" CRC32C checksums specifically
+/// for use in Snappy. When available, this will make use of SSE 4.2 to compute
+/// checksums. Otherwise, it falls back to only-marginally-slower "slicing by
+/// 16" technique.
+///
+/// The main purpose of this type is to cache the CPU feature check and expose
+/// a safe API.
+#[derive(Clone, Copy, Debug)]
+pub struct CheckSummer {
+    sse42: bool,
+}
+
+impl CheckSummer {
+    /// Create a new checksummer that can compute CRC32C checksums on arbitrary
+    /// bytes.
+    #[cfg(not(target_arch = "x86_64"))]
+    pub fn new() -> CheckSummer {
+        CheckSummer { sse42: false }
+    }
+
+    /// Create a new checksummer that can compute CRC32C checksums on arbitrary
+    /// bytes.
+    #[cfg(target_arch = "x86_64")]
+    pub fn new() -> CheckSummer {
+        CheckSummer { sse42: is_x86_feature_detected!("sse4.2") }
+    }
+
+    /// Returns the "masked" CRC32 checksum of `buf` using the Castagnoli
+    /// polynomial. This "masked" checksum is defined by the Snappy frame
+    /// format. Masking is supposed to make the checksum robust with respect to
+    /// the data that contains the checksum itself.
+    pub fn crc32c_masked(&self, buf: &[u8]) -> u32 {
+        let sum = self.crc32c(buf);
+        (sum.wrapping_shr(15) | sum.wrapping_shl(17)).wrapping_add(0xA282EAD8)
+    }
+
+    /// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial.
+    #[cfg(not(target_arch = "x86_64"))]
+    fn crc32c(&self, buf: &[u8]) -> u32 {
+        crc32c_slice16(buf)
+    }
+
+    /// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial.
+    #[cfg(target_arch = "x86_64")]
+    fn crc32c(&self, buf: &[u8]) -> u32 {
+        if self.sse42 {
+            // SAFETY: When sse42 is true, we are guaranteed to be running on
+            // a CPU that supports SSE 4.2.
+            unsafe { crc32c_sse(buf) }
+        } else {
+            crc32c_slice16(buf)
+        }
+    }
+}
+
+#[cfg(target_arch = "x86_64")]
+#[target_feature(enable = "sse4.2")]
+unsafe fn crc32c_sse(buf: &[u8]) -> u32 {
+    use std::arch::x86_64::*;
+
+    let mut crc = !0u32;
+    // SAFETY: This is safe since alignment is handled by align_to (oh how I
+    // love you) and since 8 adjacent u8's are guaranteed to have the same
+    // in-memory representation as u64 for all possible values.
+    let (prefix, u64s, suffix) = buf.align_to::<u64>();
+    for &b in prefix {
+        // SAFETY: Safe since we have sse4.2 enabled.
+        crc = _mm_crc32_u8(crc, b);
+    }
+    for &n in u64s {
+        // SAFETY: Safe since we have sse4.2 enabled.
+        crc = _mm_crc32_u64(crc as u64, n) as u32;
+    }
+    for &b in suffix {
+        // SAFETY: Safe since we have sse4.2 enabled.
+        crc = _mm_crc32_u8(crc, b);
+    }
+    !crc
+}
+
+/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial.
+fn crc32c_slice16(mut buf: &[u8]) -> u32 {
+    let mut crc: u32 = !0;
+    while buf.len() >= 16 {
+        crc ^= bytes::read_u32_le(buf);
+        crc = TABLE16[0][buf[15] as usize]
+            ^ TABLE16[1][buf[14] as usize]
+            ^ TABLE16[2][buf[13] as usize]
+            ^ TABLE16[3][buf[12] as usize]
+            ^ TABLE16[4][buf[11] as usize]
+            ^ TABLE16[5][buf[10] as usize]
+            ^ TABLE16[6][buf[9] as usize]
+            ^ TABLE16[7][buf[8] as usize]
+            ^ TABLE16[8][buf[7] as usize]
+            ^ TABLE16[9][buf[6] as usize]
+            ^ TABLE16[10][buf[5] as usize]
+            ^ TABLE16[11][buf[4] as usize]
+            ^ TABLE16[12][(crc >> 24) as u8 as usize]
+            ^ TABLE16[13][(crc >> 16) as u8 as usize]
+            ^ TABLE16[14][(crc >> 8) as u8 as usize]
+            ^ TABLE16[15][(crc) as u8 as usize];
+        buf = &buf[16..];
+    }
+    for &b in buf {
+        crc = TABLE[((crc as u8) ^ b) as usize] ^ (crc >> 8);
+    }
+    !crc
+}