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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 "../private/SkNoncopyable.h"
#include "SkString.h"
#include "SkTLogic.h"
#include "SkTypes.h"
// #include "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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