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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 } | |
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