1 /* 2 * Copyright 2015 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8 #include "SkChecksum.h" 9 10 uint32_t SkChecksum::Murmur3(const void* data, size_t bytes, uint32_t seed) { 11 // Use may_alias to remind the compiler we're intentionally violating strict aliasing, 12 // and so not to apply strict-aliasing-based optimizations. 13 typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t; 14 typedef uint8_t SK_ATTRIBUTE(may_alias) aliased_uint8_t; 15 16 // Handle 4 bytes at a time while possible. 17 const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data; 18 const size_t words = bytes/4; 19 uint32_t hash = seed; 20 for (size_t i = 0; i < words; i++) { 21 uint32_t k = safe_data[i]; 22 k *= 0xcc9e2d51; 23 k = (k << 15) | (k >> 17); 24 k *= 0x1b873593; 25 26 hash ^= k; 27 hash = (hash << 13) | (hash >> 19); 28 hash *= 5; 29 hash += 0xe6546b64; 30 } 31 32 // Handle last 0-3 bytes. 33 const aliased_uint8_t* safe_tail = (const uint8_t*)(safe_data + words); 34 uint32_t k = 0; 35 switch (bytes & 3) { 36 case 3: k ^= safe_tail[2] << 16; 37 case 2: k ^= safe_tail[1] << 8; 38 case 1: k ^= safe_tail[0] << 0; 39 k *= 0xcc9e2d51; 40 k = (k << 15) | (k >> 17); 41 k *= 0x1b873593; 42 hash ^= k; 43 } 44 45 hash ^= bytes; 46 return SkChecksum::Mix(hash); 47 } 48
