d5148e3314
Change-Id: I62f60ea52faeebddecacf03d9429ac3f7c516b8e Reviewed-on: https://skia-review.googlesource.com/141823 Commit-Queue: Ben Wagner <bungeman@google.com> Reviewed-by: Ben Wagner <bungeman@google.com>
72 lines
1.9 KiB
C++
72 lines
1.9 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 "../private/SkNoncopyable.h"
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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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// #include "SkOpts.h"
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// It's sort of pesky to be able to include SkOpts.h here, so we'll just re-declare what we need.
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namespace SkOpts {
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extern uint32_t (*hash_fn)(const void*, size_t, uint32_t);
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}
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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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// 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 SkOpts::hash_fn(&k, sizeof(K), 0);
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}
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uint32_t operator()(const SkString& k) const {
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return SkOpts::hash_fn(k.c_str(), k.size(), 0);
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}
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};
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#endif
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