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 <stdint.h>
48#include <utility>
49
50/** This is a version of CityHash that predates v1.0.3 algorithm change.
51 * Why we need exactly this version?
52 * Although hash values of CityHash are not recommended for storing persistently anywhere,
53 * it has already been used this way in ClickHouse:
54 * - for calculation of checksums of compressed chunks and for data parts;
55 * - this version of CityHash is exposed in cityHash64 function in ClickHouse SQL language;
56 * - and already used by many users for data ordering, sampling and sharding.
57 */
58namespace CityHash_v1_0_2
59{
60
61typedef uint8_t uint8;
62typedef uint32_t uint32;
63typedef uint64_t uint64;
64typedef std::pair<uint64, uint64> uint128;
65
66
67inline uint64 Uint128Low64(const uint128& x) { return x.first; }
68inline uint64 Uint128High64(const uint128& x) { return x.second; }
69
70// Hash function for a byte array.
71uint64 CityHash64(const char *buf, size_t len);
72
73// Hash function for a byte array. For convenience, a 64-bit seed is also
74// hashed into the result.
75uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);
76
77// Hash function for a byte array. For convenience, two seeds are also
78// hashed into the result.
79uint64 CityHash64WithSeeds(const char *buf, size_t len,
80 uint64 seed0, uint64 seed1);
81
82// Hash function for a byte array.
83uint128 CityHash128(const char *s, size_t len);
84
85// Hash function for a byte array. For convenience, a 128-bit seed is also
86// hashed into the result.
87uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);
88
89// Hash 128 input bits down to 64 bits of output.
90// This is intended to be a reasonably good hash function.
91inline uint64 Hash128to64(const uint128& x) {
92 // Murmur-inspired hashing.
93 const uint64 kMul = 0x9ddfea08eb382d69ULL;
94 uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
95 a ^= (a >> 47);
96 uint64 b = (Uint128High64(x) ^ a) * kMul;
97 b ^= (b >> 47);
98 b *= kMul;
99 return b;
100}
101
102}
103
104#endif // CITY_HASH_H_
105