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
51typedef uint8_t uint8;
52typedef uint32_t uint32;
53typedef uint64_t uint64;
54typedef std::pair<uint64, uint64> uint128;
55
56inline uint64 Uint128Low64(const uint128& x) { return x.first; }
57inline uint64 Uint128High64(const uint128& x) { return x.second; }
58
59// Hash function for a byte array.
60uint64 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.
64uint64 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.
68uint64 CityHash64WithSeeds(const char *buf, size_t len,
69                           uint64 seed0, uint64 seed1);
70
71// Hash function for a byte array.
72uint128 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.
76uint128 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.
80inline 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.
96uint128 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.
100uint128 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed);
101
102// Hash function for a byte array.  Sets result[0] ... result[3].
103void CityHashCrc256(const char *s, size_t len, uint64 *result);
104
105#endif  // __SSE4_2__
106
107#endif  // CITY_HASH_H_
108