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/SkOpts_spi.h" 15 #include "include/private/SkTLogic.h" 16 17 class SkChecksum : SkNoncopyable { 18 public: 19 /** 20 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you 21 * suspect its low bits aren't well mixed. 22 * 23 * This is the Murmur3 finalizer. 24 */ Mix(uint32_t hash)25 static uint32_t Mix(uint32_t hash) { 26 hash ^= hash >> 16; 27 hash *= 0x85ebca6b; 28 hash ^= hash >> 13; 29 hash *= 0xc2b2ae35; 30 hash ^= hash >> 16; 31 return hash; 32 } 33 34 /** 35 * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you 36 * suspect its low bits aren't well mixed. 37 * 38 * This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache. 39 */ CheapMix(uint32_t hash)40 static uint32_t CheapMix(uint32_t hash) { 41 hash ^= hash >> 16; 42 hash *= 0x85ebca6b; 43 hash ^= hash >> 16; 44 return hash; 45 } 46 }; 47 48 // SkGoodHash should usually be your first choice in hashing data. 49 // It should be both reasonably fast and high quality. 50 struct SkGoodHash { 51 template <typename K> operatorSkGoodHash52 std::enable_if_t<sizeof(K) == 4, uint32_t> operator()(const K& k) const { 53 return SkChecksum::Mix(*(const uint32_t*)&k); 54 } 55 56 template <typename K> operatorSkGoodHash57 std::enable_if_t<sizeof(K) != 4, uint32_t> operator()(const K& k) const { 58 return SkOpts::hash_fn(&k, sizeof(K), 0); 59 } 60 operatorSkGoodHash61 uint32_t operator()(const SkString& k) const { 62 return SkOpts::hash_fn(k.c_str(), k.size(), 0); 63 } 64 }; 65 66 #endif 67