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- /*
- * Copyright 2012 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
- #ifndef SkChecksum_DEFINED
- #define SkChecksum_DEFINED
- #include "include/core/SkString.h"
- #include "include/core/SkTypes.h"
- #include "include/private/SkNoncopyable.h"
- #include "include/private/SkTLogic.h"
- // #include "src/core/SkOpts.h"
- // It's sort of pesky to be able to include SkOpts.h here, so we'll just re-declare what we need.
- namespace SkOpts {
- extern uint32_t (*hash_fn)(const void*, size_t, uint32_t);
- }
- class SkChecksum : SkNoncopyable {
- public:
- /**
- * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
- * suspect its low bits aren't well mixed.
- *
- * This is the Murmur3 finalizer.
- */
- static uint32_t Mix(uint32_t hash) {
- hash ^= hash >> 16;
- hash *= 0x85ebca6b;
- hash ^= hash >> 13;
- hash *= 0xc2b2ae35;
- hash ^= hash >> 16;
- return hash;
- }
- /**
- * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
- * suspect its low bits aren't well mixed.
- *
- * This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache.
- */
- static uint32_t CheapMix(uint32_t hash) {
- hash ^= hash >> 16;
- hash *= 0x85ebca6b;
- hash ^= hash >> 16;
- return hash;
- }
- };
- // SkGoodHash should usually be your first choice in hashing data.
- // It should be both reasonably fast and high quality.
- struct SkGoodHash {
- template <typename K>
- SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const {
- return SkChecksum::Mix(*(const uint32_t*)&k);
- }
- template <typename K>
- SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const {
- return SkOpts::hash_fn(&k, sizeof(K), 0);
- }
- uint32_t operator()(const SkString& k) const {
- return SkOpts::hash_fn(k.c_str(), k.size(), 0);
- }
- };
- #endif
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