2 * Copyright 2012 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_BASE_HASH_H_
18 #define FOLLY_BASE_HASH_H_
25 #include "folly/SpookyHashV1.h"
26 #include "folly/SpookyHashV2.h"
29 * Various hashing functions.
32 namespace folly { namespace hash {
34 // This is a general-purpose way to create a single hash from multiple
35 // hashable objects. It relies on std::hash<T> being available for all
36 // relevant types and combines those hashes in an order-dependent way
37 // to yield a new hash.
39 // Never used, but gcc demands it.
40 inline size_t hash_combine() {
44 // This is the Hash128to64 function from Google's cityhash (available
45 // under the MIT License). We use it to reduce multiple 64 bit hashes
46 // into a single hash.
47 inline size_t hash_128_to_64(const size_t upper, const size_t lower) {
48 // Murmur-inspired hashing.
49 const size_t kMul = 0x9ddfea08eb382d69ULL;
50 size_t a = (lower ^ upper) * kMul;
52 size_t b = (upper ^ a) * kMul;
58 template <typename T, typename... Ts>
59 size_t hash_combine(const T& t, const Ts&... ts) {
60 size_t seed = std::hash<T>()(t);
61 if (sizeof...(ts) == 0) {
64 size_t remainder = hash_combine(ts...);
65 return hash_128_to_64(seed, remainder);
68 //////////////////////////////////////////////////////////////////////
71 * Thomas Wang 64 bit mix hash function
74 inline uint64_t twang_mix64(uint64_t key) {
75 key = (~key) + (key << 21); // key *= (1 << 21) - 1; key -= 1;
76 key = key ^ (key >> 24);
77 key = key + (key << 3) + (key << 8); // key *= 1 + (1 << 3) + (1 << 8)
78 key = key ^ (key >> 14);
79 key = key + (key << 2) + (key << 4); // key *= 1 + (1 << 2) + (1 << 4)
80 key = key ^ (key >> 28);
81 key = key + (key << 31); // key *= 1 + (1 << 31)
86 * Inverse of twang_mix64
88 * Note that twang_unmix64 is significantly slower than twang_mix64.
91 inline uint64_t twang_unmix64(uint64_t key) {
92 // See the comments in jenkins_rev_unmix32 for an explanation as to how this
94 key *= 4611686016279904257U;
95 key ^= (key >> 28) ^ (key >> 56);
96 key *= 14933078535860113213U;
97 key ^= (key >> 14) ^ (key >> 28) ^ (key >> 42) ^ (key >> 56);
98 key *= 15244667743933553977U;
99 key ^= (key >> 24) ^ (key >> 48);
100 key = (key + 1) * 9223367638806167551U;
105 * Thomas Wang downscaling hash function
108 inline uint32_t twang_32from64(uint64_t key) {
109 key = (~key) + (key << 18);
110 key = key ^ (key >> 31);
112 key = key ^ (key >> 11);
113 key = key + (key << 6);
114 key = key ^ (key >> 22);
115 return (uint32_t) key;
119 * Robert Jenkins' reversible 32 bit mix hash function
122 inline uint32_t jenkins_rev_mix32(uint32_t key) {
123 key += (key << 12); // key *= (1 + (1 << 12))
125 key += (key << 4); // key *= (1 + (1 << 4))
127 key += (key << 10); // key *= (1 + (1 << 10))
129 // key *= (1 + (1 << 7)) * (1 + (1 << 12))
136 * Inverse of jenkins_rev_mix32
138 * Note that jenkinks_rev_unmix32 is significantly slower than
142 inline uint32_t jenkins_rev_unmix32(uint32_t key) {
143 // These are the modular multiplicative inverses (in Z_2^32) of the
144 // multiplication factors in jenkins_rev_mix32, in reverse order. They were
145 // computed using the Extended Euclidean algorithm, see
146 // http://en.wikipedia.org/wiki/Modular_multiplicative_inverse
149 // The inverse of a ^= (a >> n) is
151 // for (int i = n; i < 32; i += n) {
155 (key >> 2) ^ (key >> 4) ^ (key >> 6) ^ (key >> 8) ^
156 (key >> 10) ^ (key >> 12) ^ (key >> 14) ^ (key >> 16) ^
157 (key >> 18) ^ (key >> 20) ^ (key >> 22) ^ (key >> 24) ^
158 (key >> 26) ^ (key >> 28) ^ (key >> 30);
160 key ^= (key >> 9) ^ (key >> 18) ^ (key >> 27);
168 * Fowler / Noll / Vo (FNV) Hash
169 * http://www.isthe.com/chongo/tech/comp/fnv/
172 const uint32_t FNV_32_HASH_START = 216613626UL;
173 const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
175 inline uint32_t fnv32(const char* s,
176 uint32_t hash = FNV_32_HASH_START) {
178 hash += (hash << 1) + (hash << 4) + (hash << 7) +
179 (hash << 8) + (hash << 24);
185 inline uint32_t fnv32_buf(const void* buf,
187 uint32_t hash = FNV_32_HASH_START) {
188 const char* char_buf = reinterpret_cast<const char*>(buf);
190 for (int i = 0; i < n; ++i) {
191 hash += (hash << 1) + (hash << 4) + (hash << 7) +
192 (hash << 8) + (hash << 24);
199 inline uint32_t fnv32(const std::string& str,
200 uint64_t hash = FNV_32_HASH_START) {
201 return fnv32_buf(str.data(), str.size(), hash);
204 inline uint64_t fnv64(const char* s,
205 uint64_t hash = FNV_64_HASH_START) {
207 hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
208 (hash << 8) + (hash << 40);
214 inline uint64_t fnv64_buf(const void* buf,
216 uint64_t hash = FNV_64_HASH_START) {
217 const char* char_buf = reinterpret_cast<const char*>(buf);
219 for (int i = 0; i < n; ++i) {
220 hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
221 (hash << 8) + (hash << 40);
227 inline uint64_t fnv64(const std::string& str,
228 uint64_t hash = FNV_64_HASH_START) {
229 return fnv64_buf(str.data(), str.size(), hash);
233 * Paul Hsieh: http://www.azillionmonkeys.com/qed/hash.html
236 #define get16bits(d) (*((const uint16_t*) (d)))
238 inline uint32_t hsieh_hash32_buf(const void* buf, int len) {
239 const char* s = reinterpret_cast<const char*>(buf);
244 if (len <= 0 || buf == 0) {
252 for (;len > 0; len--) {
253 hash += get16bits (s);
254 tmp = (get16bits (s+2) << 11) ^ hash;
255 hash = (hash << 16) ^ tmp;
256 s += 2*sizeof (uint16_t);
260 /* Handle end cases */
263 hash += get16bits(s);
265 hash ^= s[sizeof (uint16_t)] << 18;
269 hash += get16bits(s);
279 /* Force "avalanching" of final 127 bits */
292 inline uint32_t hsieh_hash32(const char* s) {
293 return hsieh_hash32_buf(s, std::strlen(s));
296 inline uint32_t hsieh_hash32_str(const std::string& str) {
297 return hsieh_hash32_buf(str.data(), str.size());
300 //////////////////////////////////////////////////////////////////////
307 template<> struct hasher<int32_t> {
308 size_t operator()(int32_t key) const {
309 return hash::jenkins_rev_mix32(uint32_t(key));
313 template<> struct hasher<uint32_t> {
314 size_t operator()(uint32_t key) const {
315 return hash::jenkins_rev_mix32(key);
319 template<> struct hasher<int64_t> {
320 size_t operator()(int64_t key) const {
321 return hash::twang_mix64(uint64_t(key));
325 template<> struct hasher<uint64_t> {
326 size_t operator()(uint64_t key) const {
327 return hash::twang_mix64(key);
333 // Custom hash functions.
335 // Hash function for pairs. Requires default hash functions for both
336 // items in the pair.
337 template <typename T1, typename T2>
338 class hash<std::pair<T1, T2> > {
340 size_t operator()(const std::pair<T1, T2>& x) const {
341 return folly::hash::hash_combine(x.first, x.second);