56da025020
SkChecksum::Compute is a very, very poorly distributed hash function. This replaces all remaining uses with Murmur3. The only interesting stuff is in src/gpu. BUG=skia: Committed: https://skia.googlesource.com/skia/+/1d024a3c909ae5cefa5e8b339e2b52dc73ee85ac Committed: https://skia.googlesource.com/skia/+/540e95483d285b555e9b1a73d18c16e7d7c0deba Review URL: https://codereview.chromium.org/1436973003
76 lines
2.1 KiB
C++
76 lines
2.1 KiB
C++
/*
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* Copyright 2012 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkChecksum_DEFINED
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#define SkChecksum_DEFINED
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#include "SkString.h"
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#include "SkTLogic.h"
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#include "SkTypes.h"
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class SkChecksum : SkNoncopyable {
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public:
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/**
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* uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
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* suspect its low bits aren't well mixed.
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*
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* This is the Murmur3 finalizer.
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*/
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static uint32_t Mix(uint32_t hash) {
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hash ^= hash >> 16;
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hash *= 0x85ebca6b;
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hash ^= hash >> 13;
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hash *= 0xc2b2ae35;
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hash ^= hash >> 16;
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return hash;
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}
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/**
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* uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
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* suspect its low bits aren't well mixed.
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*
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* This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache.
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*/
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static uint32_t CheapMix(uint32_t hash) {
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hash ^= hash >> 16;
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hash *= 0x85ebca6b;
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hash ^= hash >> 16;
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return hash;
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}
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/**
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* Calculate 32-bit Murmur hash (murmur3).
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* See en.wikipedia.org/wiki/MurmurHash.
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*
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* @param data Memory address of the data block to be processed.
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* @param size Size of the data block in bytes.
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* @param seed Initial hash seed. (optional)
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* @return hash result
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*/
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static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0);
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};
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// SkGoodHash should usually be your first choice in hashing data.
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// It should be both reasonably fast and high quality.
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struct SkGoodHash {
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template <typename K>
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SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const {
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return SkChecksum::Mix(*(const uint32_t*)&k);
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}
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template <typename K>
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SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const {
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return SkChecksum::Murmur3(&k, sizeof(K));
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}
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uint32_t operator()(const SkString& k) const {
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return SkChecksum::Murmur3(k.c_str(), k.size());
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}
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};
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#endif
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