Use sse4.2 CRC32 instructions to hash when available.

src/core/SkChecksum.cpp

-/*
- * Copyright 2015 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkChecksum.h"
-
-uint32_t SkChecksum::Murmur3(const void* data, size_t bytes, uint32_t seed) {
-    // Use may_alias to remind the compiler we're intentionally violating strict aliasing,
-    // and so not to apply strict-aliasing-based optimizations.
-    typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t;
-    typedef uint8_t SK_ATTRIBUTE(may_alias) aliased_uint8_t;
-
-    // Handle 4 bytes at a time while possible.
-    const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data;
-    const size_t words = bytes/4;
-    uint32_t hash = seed;
-    for (size_t i = 0; i < words; i++) {
-        uint32_t k = safe_data[i];
-        k *= 0xcc9e2d51;
-        k = (k << 15) | (k >> 17);
-        k *= 0x1b873593;
-
-        hash ^= k;
-        hash = (hash << 13) | (hash >> 19);
-        hash *= 5;
-        hash += 0xe6546b64;
-    }
-
-    // Handle last 0-3 bytes.
-    const aliased_uint8_t* safe_tail = (const uint8_t*)(safe_data + words);
-    uint32_t k = 0;
-    switch (bytes & 3) {
-        case 3: k ^= safe_tail[2] << 16;
-        case 2: k ^= safe_tail[1] <<  8;
-        case 1: k ^= safe_tail[0] <<  0;
-                k *= 0xcc9e2d51;
-                k = (k << 15) | (k >> 17);
-                k *= 0x1b873593;
-                hash ^= k;
-    }
-
-    hash ^= bytes;
-    return SkChecksum::Mix(hash);
-}