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Side by Side Diff: src/core/SkChecksum.cpp

Issue 1415133003: Move SkChecksum::Murmur3 out of the header. (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: fix Created 5 years, 2 months ago
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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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