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 "Platform.h"
47 #include <stdlib.h> // for size_t.
48 //#include <stdint.h>
49 #include <utility>
50
51 typedef uint8_t uint8;
52 typedef uint32_t uint32;
53 typedef uint64_t uint64;
54 typedef std::pair<uint64, uint64> uint128;
55
Uint128Low64(const uint128 & x)56 inline uint64 Uint128Low64(const uint128& x) { return x.first; }
Uint128High64(const uint128 & x)57 inline uint64 Uint128High64(const uint128& x) { return x.second; }
58
59 // Hash function for a byte array.
60 uint64 CityHash64(const char *buf, size_t len);
61
62 // Hash function for a byte array. For convenience, a 64-bit seed is also
63 // hashed into the result.
64 uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);
65
66 // Hash function for a byte array. For convenience, two seeds are also
67 // hashed into the result.
68 uint64 CityHash64WithSeeds(const char *buf, size_t len,
69 uint64 seed0, uint64 seed1);
70
71 // Hash function for a byte array.
72 uint128 CityHash128(const char *s, size_t len);
73
74 // Hash function for a byte array. For convenience, a 128-bit seed is also
75 // hashed into the result.
76 uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);
77
78 // Hash 128 input bits down to 64 bits of output.
79 // This is intended to be a reasonably good hash function.
Hash128to64(const uint128 & x)80 inline uint64 Hash128to64(const uint128& x) {
81 // Murmur-inspired hashing.
82 const uint64 kMul = 0x9ddfea08eb382d69ULL;
83 uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
84 a ^= (a >> 47);
85 uint64 b = (Uint128High64(x) ^ a) * kMul;
86 b ^= (b >> 47);
87 b *= kMul;
88 return b;
89 }
90
91 // Conditionally include declarations for versions of City that require SSE4.2
92 // instructions to be available.
93 #if defined(__SSE4_2__) && defined(__x86_64__)
94
95 // Hash function for a byte array.
96 uint128 CityHashCrc128(const char *s, size_t len);
97
98 // Hash function for a byte array. For convenience, a 128-bit seed is also
99 // hashed into the result.
100 uint128 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed);
101
102 // Hash function for a byte array. Sets result[0] ... result[3].
103 void CityHashCrc256(const char *s, size_t len, uint64 *result);
104
105 #endif // __SSE4_2__
106
107 #endif // CITY_HASH_H_
108