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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 "SkString.h"
#include "SkTLogic.h"
#include "SkTypes.h"
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;
}
/**
* Calculate 32-bit Murmur hash (murmur3).
* See en.wikipedia.org/wiki/MurmurHash.
*
* @param data Memory address of the data block to be processed.
* @param size Size of the data block in bytes.
* @param seed Initial hash seed. (optional)
* @return hash result
*/
static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0);
};
// 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 SkChecksum::Murmur3(&k, sizeof(K));
}
uint32_t operator()(const SkString& k) const {
return SkChecksum::Murmur3(k.c_str(), k.size());
}
};
#endif
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