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1 /* | 1 /* |
2 * Copyright 2012 Google Inc. | 2 * Copyright 2012 Google Inc. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license that can be | 4 * Use of this source code is governed by a BSD-style license that can be |
5 * found in the LICENSE file. | 5 * found in the LICENSE file. |
6 */ | 6 */ |
7 | 7 |
8 #ifndef SkChecksum_DEFINED | 8 #ifndef SkChecksum_DEFINED |
9 #define SkChecksum_DEFINED | 9 #define SkChecksum_DEFINED |
10 | 10 |
11 #include "SkString.h" | 11 #include "SkString.h" |
12 #include "SkTLogic.h" | 12 #include "SkTLogic.h" |
13 #include "SkTypes.h" | 13 #include "SkTypes.h" |
14 | 14 |
| 15 // #include "SkOpts.h" |
| 16 // It's sort of pesky to be able to include SkOpts.h here, so we'll just re-decl
are what we need. |
| 17 namespace SkOpts { |
| 18 extern uint32_t (*hash_fn)(const void*, size_t, uint32_t); |
| 19 } |
| 20 |
15 class SkChecksum : SkNoncopyable { | 21 class SkChecksum : SkNoncopyable { |
16 public: | 22 public: |
17 /** | 23 /** |
18 * uint32_t -> uint32_t hash, useful for when you're about to trucate this h
ash but you | 24 * uint32_t -> uint32_t hash, useful for when you're about to trucate this h
ash but you |
19 * suspect its low bits aren't well mixed. | 25 * suspect its low bits aren't well mixed. |
20 * | 26 * |
21 * This is the Murmur3 finalizer. | 27 * This is the Murmur3 finalizer. |
22 */ | 28 */ |
23 static uint32_t Mix(uint32_t hash) { | 29 static uint32_t Mix(uint32_t hash) { |
24 hash ^= hash >> 16; | 30 hash ^= hash >> 16; |
25 hash *= 0x85ebca6b; | 31 hash *= 0x85ebca6b; |
26 hash ^= hash >> 13; | 32 hash ^= hash >> 13; |
27 hash *= 0xc2b2ae35; | 33 hash *= 0xc2b2ae35; |
28 hash ^= hash >> 16; | 34 hash ^= hash >> 16; |
29 return hash; | 35 return hash; |
30 } | 36 } |
31 | 37 |
32 /** | 38 /** |
33 * uint32_t -> uint32_t hash, useful for when you're about to trucate this h
ash but you | 39 * uint32_t -> uint32_t hash, useful for when you're about to trucate this h
ash but you |
34 * suspect its low bits aren't well mixed. | 40 * suspect its low bits aren't well mixed. |
35 * | 41 * |
36 * This version is 2-lines cheaper than Mix, but seems to be sufficient for
the font cache. | 42 * This version is 2-lines cheaper than Mix, but seems to be sufficient for
the font cache. |
37 */ | 43 */ |
38 static uint32_t CheapMix(uint32_t hash) { | 44 static uint32_t CheapMix(uint32_t hash) { |
39 hash ^= hash >> 16; | 45 hash ^= hash >> 16; |
40 hash *= 0x85ebca6b; | 46 hash *= 0x85ebca6b; |
41 hash ^= hash >> 16; | 47 hash ^= hash >> 16; |
42 return hash; | 48 return hash; |
43 } | 49 } |
44 | |
45 /** | |
46 * Calculate 32-bit Murmur hash (murmur3). | |
47 * See en.wikipedia.org/wiki/MurmurHash. | |
48 * | |
49 * @param data Memory address of the data block to be processed. | |
50 * @param size Size of the data block in bytes. | |
51 * @param seed Initial hash seed. (optional) | |
52 * @return hash result | |
53 */ | |
54 static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0); | |
55 }; | 50 }; |
56 | 51 |
57 // SkGoodHash should usually be your first choice in hashing data. | 52 // SkGoodHash should usually be your first choice in hashing data. |
58 // It should be both reasonably fast and high quality. | 53 // It should be both reasonably fast and high quality. |
59 struct SkGoodHash { | 54 struct SkGoodHash { |
60 template <typename K> | 55 template <typename K> |
61 SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const { | 56 SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const { |
62 return SkChecksum::Mix(*(const uint32_t*)&k); | 57 return SkChecksum::Mix(*(const uint32_t*)&k); |
63 } | 58 } |
64 | 59 |
65 template <typename K> | 60 template <typename K> |
66 SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const { | 61 SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const { |
67 return SkChecksum::Murmur3(&k, sizeof(K)); | 62 return SkOpts::hash_fn(&k, sizeof(K), 0); |
68 } | 63 } |
69 | 64 |
70 uint32_t operator()(const SkString& k) const { | 65 uint32_t operator()(const SkString& k) const { |
71 return SkChecksum::Murmur3(k.c_str(), k.size()); | 66 return SkOpts::hash_fn(k.c_str(), k.size(), 0); |
72 } | 67 } |
73 }; | 68 }; |
74 | 69 |
75 #endif | 70 #endif |
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