1 // Copyright (c) 2011 Google, Inc. 2 // 3 // Permission is hereby granted, free of charge, to any person obtaining a copy 4 // of this software and associated documentation files (the "Software"), to deal 5 // in the Software without restriction, including without limitation the rights 6 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 7 // copies of the Software, and to permit persons to whom the Software is 8 // furnished to do so, subject to the following conditions: 9 // 10 // The above copyright notice and this permission notice shall be included in 11 // all copies or substantial portions of the Software. 12 // 13 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 14 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 15 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 16 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 17 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 18 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 19 // THE SOFTWARE. 20 // 21 // CityHash, by Geoff Pike and Jyrki Alakuijala 22 // 23 // This file provides a few functions for hashing strings. On x86-64 24 // hardware in 2011, CityHash64() is faster than other high-quality 25 // hash functions, such as Murmur. This is largely due to higher 26 // instruction-level parallelism. CityHash64() and CityHash128() also perform 27 // well on hash-quality tests. 28 // 29 // CityHash128() is optimized for relatively long strings and returns 30 // a 128-bit hash. For strings more than about 2000 bytes it can be 31 // faster than CityHash64(). 32 // 33 // Functions in the CityHash family are not suitable for cryptography. 34 // 35 // WARNING: This code has not been tested on big-endian platforms! 36 // It is known to work well on little-endian platforms that have a small penalty 37 // for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. 38 // 39 // By the way, for some hash functions, given strings a and b, the hash 40 // of a+b is easily derived from the hashes of a and b. This property 41 // doesn't hold for any hash functions in this file. 42 43 #ifndef CITY_HASH_H_ 44 #define CITY_HASH_H_ 45 46 #include <stdlib.h> // for size_t. 47 #include <utility> 48 49 // Microsoft Visual Studio may not have stdint.h. 50 #if defined(_MSC_VER) && (_MSC_VER < 1600) 51 typedef unsigned char uint8_t; 52 typedef unsigned int uint32_t; 53 typedef unsigned __int64 uint64_t; 54 #else // defined(_MSC_VER) 55 #include <stdint.h> 56 #endif // !defined(_MSC_VER) 57 58 typedef uint8_t uint8; 59 typedef uint32_t uint32; 60 typedef uint64_t uint64; 61 typedef std::pair<uint64, uint64> uint128; 62 63 inline uint64 Uint128Low64(const uint128& x) { return x.first; } 64 inline uint64 Uint128High64(const uint128& x) { return x.second; } 65 66 // Hash function for a byte array. 67 uint64 CityHash64(const char *buf, size_t len); 68 69 // Hash function for a byte array. For convenience, a 64-bit seed is also 70 // hashed into the result. 71 uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed); 72 73 // Hash function for a byte array. For convenience, two seeds are also 74 // hashed into the result. 75 uint64 CityHash64WithSeeds(const char *buf, size_t len, 76 uint64 seed0, uint64 seed1); 77 78 // Hash function for a byte array. 79 uint128 CityHash128(const char *s, size_t len); 80 81 // Hash function for a byte array. For convenience, a 128-bit seed is also 82 // hashed into the result. 83 uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed); 84 85 // Hash 128 input bits down to 64 bits of output. 86 // This is intended to be a reasonably good hash function. 87 inline uint64 Hash128to64(const uint128& x) { 88 // Murmur-inspired hashing. 89 const uint64 kMul = 0x9ddfea08eb382d69ULL; 90 uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul; 91 a ^= (a >> 47); 92 uint64 b = (Uint128High64(x) ^ a) * kMul; 93 b ^= (b >> 47); 94 b *= kMul; 95 return b; 96 } 97 98 // Conditionally include declarations for versions of City that require SSE4.2 99 // instructions to be available. 100 #if defined(__SSE4_2__) && defined(__x86_64__) 101 102 // Hash function for a byte array. 103 uint128 CityHashCrc128(const char *s, size_t len); 104 105 // Hash function for a byte array. For convenience, a 128-bit seed is also 106 // hashed into the result. 107 uint128 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed); 108 109 // Hash function for a byte array. Sets result[0] ... result[3]. 110 void CityHashCrc256(const char *s, size_t len, uint64 *result); 111 112 #endif // __SSE4_2__ 113 114 #endif // CITY_HASH_H_ 115
