| /* |
| * 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); |
| } |