diff options
Diffstat (limited to 'City.h')
| -rw-r--r-- | City.h | 107 |
1 files changed, 107 insertions, 0 deletions
@@ -0,0 +1,107 @@ +// Copyright (c) 2011 Google, Inc. +// +// Permission is hereby granted, free of charge, to any person obtaining a copy +// of this software and associated documentation files (the "Software"), to deal +// in the Software without restriction, including without limitation the rights +// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +// copies of the Software, and to permit persons to whom the Software is +// furnished to do so, subject to the following conditions: +// +// The above copyright notice and this permission notice shall be included in +// all copies or substantial portions of the Software. +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +// THE SOFTWARE. +// +// CityHash, by Geoff Pike and Jyrki Alakuijala +// +// This file provides a few functions for hashing strings. On x86-64 +// hardware in 2011, CityHash64() is faster than other high-quality +// hash functions, such as Murmur. This is largely due to higher +// instruction-level parallelism. CityHash64() and CityHash128() also perform +// well on hash-quality tests. +// +// CityHash128() is optimized for relatively long strings and returns +// a 128-bit hash. For strings more than about 2000 bytes it can be +// faster than CityHash64(). +// +// Functions in the CityHash family are not suitable for cryptography. +// +// WARNING: This code has not been tested on big-endian platforms! +// It is known to work well on little-endian platforms that have a small penalty +// for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. +// +// By the way, for some hash functions, given strings a and b, the hash +// of a+b is easily derived from the hashes of a and b. This property +// doesn't hold for any hash functions in this file. + +#ifndef CITY_HASH_H_ +#define CITY_HASH_H_ + +#include "Platform.h" +#include <stdlib.h> // for size_t. +//#include <stdint.h> +#include <utility> + +typedef uint8_t uint8; +typedef uint32_t uint32; +typedef uint64_t uint64; +typedef std::pair<uint64, uint64> uint128; + +inline uint64 Uint128Low64(const uint128& x) { return x.first; } +inline uint64 Uint128High64(const uint128& x) { return x.second; } + +// Hash function for a byte array. +uint64 CityHash64(const char *buf, size_t len); + +// Hash function for a byte array. For convenience, a 64-bit seed is also +// hashed into the result. +uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed); + +// Hash function for a byte array. For convenience, two seeds are also +// hashed into the result. +uint64 CityHash64WithSeeds(const char *buf, size_t len, + uint64 seed0, uint64 seed1); + +// Hash function for a byte array. +uint128 CityHash128(const char *s, size_t len); + +// Hash function for a byte array. For convenience, a 128-bit seed is also +// hashed into the result. +uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed); + +// Hash 128 input bits down to 64 bits of output. +// This is intended to be a reasonably good hash function. +inline uint64 Hash128to64(const uint128& x) { + // Murmur-inspired hashing. + const uint64 kMul = 0x9ddfea08eb382d69ULL; + uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul; + a ^= (a >> 47); + uint64 b = (Uint128High64(x) ^ a) * kMul; + b ^= (b >> 47); + b *= kMul; + return b; +} + +// Conditionally include declarations for versions of City that require SSE4.2 +// instructions to be available. +#ifdef __SSE4_2__ + +// Hash function for a byte array. +uint128 CityHashCrc128(const char *s, size_t len); + +// Hash function for a byte array. For convenience, a 128-bit seed is also +// hashed into the result. +uint128 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed); + +// Hash function for a byte array. Sets result[0] ... result[3]. +void CityHashCrc256(const char *s, size_t len, uint64 *result); + +#endif // __SSE4_2__ + +#endif // CITY_HASH_H_ |