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 "include/core/SkString.h"
12#include "include/core/SkTypes.h"
13#include "include/private/SkNoncopyable.h"
14#include "include/private/SkTLogic.h"
15
16// #include "src/core/SkOpts.h"
17// It's sort of pesky to be able to include SkOpts.h here, so we'll just re-declare what we need.
18namespace SkOpts {
19 extern uint32_t (*hash_fn)(const void*, size_t, uint32_t);
20}
21
22class SkChecksum : SkNoncopyable {
23public:
24 /**
25 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
26 * suspect its low bits aren't well mixed.
27 *
28 * This is the Murmur3 finalizer.
29 */
30 static uint32_t Mix(uint32_t hash) {
31 hash ^= hash >> 16;
32 hash *= 0x85ebca6b;
33 hash ^= hash >> 13;
34 hash *= 0xc2b2ae35;
35 hash ^= hash >> 16;
36 return hash;
37 }
38
39 /**
40 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
41 * suspect its low bits aren't well mixed.
42 *
43 * This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache.
44 */
45 static uint32_t CheapMix(uint32_t hash) {
46 hash ^= hash >> 16;
47 hash *= 0x85ebca6b;
48 hash ^= hash >> 16;
49 return hash;
50 }
51};
52
53// SkGoodHash should usually be your first choice in hashing data.
54// It should be both reasonably fast and high quality.
55struct SkGoodHash {
56 template <typename K>
57 SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const {
58 return SkChecksum::Mix(*(const uint32_t*)&k);
59 }
60
61 template <typename K>
62 SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const {
63 return SkOpts::hash_fn(&k, sizeof(K), 0);
64 }
65
66 uint32_t operator()(const SkString& k) const {
67 return SkOpts::hash_fn(k.c_str(), k.size(), 0);
68 }
69};
70
71#endif
72