1 /*
2 * Copyright 2012 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 #ifndef SkChecksum_DEFINED
9 #define SkChecksum_DEFINED
10
11 #include "SkString.h"
12 #include "SkTLogic.h"
13 #include "SkTypes.h"
14
15 // #include "SkOpts.h"
16 // It's sort of pesky to be able to include SkOpts.h here, so we'll just re-declare what we need.
17 namespace SkOpts {
18 extern uint32_t (*hash_fn)(const void*, size_t, uint32_t);
19 }
20
21 class SkChecksum : SkNoncopyable {
BehaviourMaterialProperty(const std::string & t,const std::string & n,const std::string & v,const unsigned short a,const SupportedTypes::TypeSize o,const bool d)22 public:
23 /**
24 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
25 * suspect its low bits aren't well mixed.
26 *
27 * This is the Murmur3 finalizer.
28 */
29 static uint32_t Mix(uint32_t hash) {
30 hash ^= hash >> 16;
31 hash *= 0x85ebca6b;
32 hash ^= hash >> 13;
33 hash *= 0xc2b2ae35;
34 hash ^= hash >> 16;
35 return hash;
36 }
37
38 /**
findBehaviourMaterialProperty(const std::vector<BehaviourMaterialProperty> & mprops,const std::string & n)39 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
40 * suspect its low bits aren't well mixed.
41 *
42 * This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache.
43 */
44 static uint32_t CheapMix(uint32_t hash) {
45 hash ^= hash >> 16;
46 hash *= 0x85ebca6b;
47 hash ^= hash >> 16;
48 return hash;
49 }
50 };
51
52 // SkGoodHash should usually be your first choice in hashing data.
53 // It should be both reasonably fast and high quality.
54 struct SkGoodHash {
buildMaterialPropertiesList(const BehaviourDescription & bd,const std::set<tfel::material::ModellingHypothesis::Hypothesis> & mh)55 template <typename K>
56 SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const {
57 return SkChecksum::Mix(*(const uint32_t*)&k);
58 }
59
60 template <typename K>
61 SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const {
62 return SkOpts::hash_fn(&k, sizeof(K), 0);
63 }
64
65 uint32_t operator()(const SkString& k) const {
66 return SkOpts::hash_fn(k.c_str(), k.size(), 0);
67 }
68 };
69
70 #endif
71