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/*
* Copyright 2012 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef FOLLY_BASE_HASH_H_
#define FOLLY_BASE_HASH_H_
#include <cstring>
#include <stdint.h>
#include <string>
#include <utility>
#include "folly/SpookyHash.h"
/*
* Various hashing functions.
*/
namespace folly { namespace hash {
// This is a general-purpose way to create a single hash from multiple
// hashable objects. It relies on std::hash<T> being available for all
// relevant types and combines those hashes in an order-dependent way
// to yield a new hash.
// Never used, but gcc demands it.
inline size_t hash_combine() {
return 0;
}
// This is the Hash128to64 function from Google's cityhash (available
// under the MIT License). We use it to reduce multiple 64 bit hashes
// into a single hash.
inline size_t hash_128_to_64(const size_t upper, const size_t lower) {
// Murmur-inspired hashing.
const size_t kMul = 0x9ddfea08eb382d69ULL;
size_t a = (lower ^ upper) * kMul;
a ^= (a >> 47);
size_t b = (upper ^ a) * kMul;
b ^= (b >> 47);
b *= kMul;
return b;
}
template <typename T, typename... Ts>
size_t hash_combine(const T& t, const Ts&... ts) {
size_t seed = std::hash<T>()(t);
if (sizeof...(ts) == 0) {
return seed;
}
size_t remainder = hash_combine(ts...);
return hash_128_to_64(seed, remainder);
}
//////////////////////////////////////////////////////////////////////
/*
* Thomas Wang 64 bit mix hash function
*/
inline uint64_t twang_mix64(uint64_t key) {
key = (~key) + (key << 21); // key *= (1 << 21) - 1; key -= 1;
key = key ^ (key >> 24);
key = key + (key << 3) + (key << 8); // key *= 1 + (1 << 3) + (1 << 8)
key = key ^ (key >> 14);
key = key + (key << 2) + (key << 4); // key *= 1 + (1 << 2) + (1 << 4)
key = key ^ (key >> 28);
key = key + (key << 31); // key *= 1 + (1 << 31)
return key;
}
/*
* Inverse of twang_mix64
*
* Note that twang_unmix64 is significantly slower than twang_mix64.
*/
inline uint64_t twang_unmix64(uint64_t key) {
// See the comments in jenkins_rev_unmix32 for an explanation as to how this
// was generated
key *= 4611686016279904257U;
key ^= (key >> 28) ^ (key >> 56);
key *= 14933078535860113213U;
key ^= (key >> 14) ^ (key >> 28) ^ (key >> 42) ^ (key >> 56);
key *= 15244667743933553977U;
key ^= (key >> 24) ^ (key >> 48);
key = (key + 1) * 9223367638806167551U;
return key;
}
/*
* Thomas Wang downscaling hash function
*/
inline uint32_t twang_32from64(uint64_t key) {
key = (~key) + (key << 18);
key = key ^ (key >> 31);
key = key * 21;
key = key ^ (key >> 11);
key = key + (key << 6);
key = key ^ (key >> 22);
return (uint32_t) key;
}
/*
* Robert Jenkins' reversible 32 bit mix hash function
*/
inline uint32_t jenkins_rev_mix32(uint32_t key) {
key += (key << 12); // key *= (1 + (1 << 12))
key ^= (key >> 22);
key += (key << 4); // key *= (1 + (1 << 4))
key ^= (key >> 9);
key += (key << 10); // key *= (1 + (1 << 10))
key ^= (key >> 2);
// key *= (1 + (1 << 7)) * (1 + (1 << 12))
key += (key << 7);
key += (key << 12);
return key;
}
/*
* Inverse of jenkins_rev_mix32
*
* Note that jenkinks_rev_unmix32 is significantly slower than
* jenkins_rev_mix32.
*/
inline uint32_t jenkins_rev_unmix32(uint32_t key) {
// These are the modular multiplicative inverses (in Z_2^32) of the
// multiplication factors in jenkins_rev_mix32, in reverse order. They were
// computed using the Extended Euclidean algorithm, see
// http://en.wikipedia.org/wiki/Modular_multiplicative_inverse
key *= 2364026753U;
// The inverse of a ^= (a >> n) is
// b = a
// for (int i = n; i < 32; i += n) {
// b ^= (a >> i);
// }
key ^=
(key >> 2) ^ (key >> 4) ^ (key >> 6) ^ (key >> 8) ^
(key >> 10) ^ (key >> 12) ^ (key >> 14) ^ (key >> 16) ^
(key >> 18) ^ (key >> 20) ^ (key >> 22) ^ (key >> 24) ^
(key >> 26) ^ (key >> 28) ^ (key >> 30);
key *= 3222273025U;
key ^= (key >> 9) ^ (key >> 18) ^ (key >> 27);
key *= 4042322161U;
key ^= (key >> 22);
key *= 16773121U;
return key;
}
/*
* Fowler / Noll / Vo (FNV) Hash
* http://www.isthe.com/chongo/tech/comp/fnv/
*/
const uint32_t FNV_32_HASH_START = 216613626UL;
const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
inline uint32_t fnv32(const char* s,
uint32_t hash = FNV_32_HASH_START) {
for (; *s; ++s) {
hash += (hash << 1) + (hash << 4) + (hash << 7) +
(hash << 8) + (hash << 24);
hash ^= *s;
}
return hash;
}
inline uint32_t fnv32_buf(const void* buf,
int n,
uint32_t hash = FNV_32_HASH_START) {
const char* char_buf = reinterpret_cast<const char*>(buf);
for (int i = 0; i < n; ++i) {
hash += (hash << 1) + (hash << 4) + (hash << 7) +
(hash << 8) + (hash << 24);
hash ^= char_buf[i];
}
return hash;
}
inline uint32_t fnv32(const std::string& str,
uint64_t hash = FNV_32_HASH_START) {
return fnv32_buf(str.data(), str.size(), hash);
}
inline uint64_t fnv64(const char* s,
uint64_t hash = FNV_64_HASH_START) {
for (; *s; ++s) {
hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
(hash << 8) + (hash << 40);
hash ^= *s;
}
return hash;
}
inline uint64_t fnv64_buf(const void* buf,
int n,
uint64_t hash = FNV_64_HASH_START) {
const char* char_buf = reinterpret_cast<const char*>(buf);
for (int i = 0; i < n; ++i) {
hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
(hash << 8) + (hash << 40);
hash ^= char_buf[i];
}
return hash;
}
inline uint64_t fnv64(const std::string& str,
uint64_t hash = FNV_64_HASH_START) {
return fnv64_buf(str.data(), str.size(), hash);
}
/*
* Paul Hsieh: http://www.azillionmonkeys.com/qed/hash.html
*/
#define get16bits(d) (*((const uint16_t*) (d)))
inline uint32_t hsieh_hash32_buf(const void* buf, int len) {
const char* s = reinterpret_cast<const char*>(buf);
uint32_t hash = len;
uint32_t tmp;
int rem;
if (len <= 0 || buf == 0) {
return 0;
}
rem = len & 3;
len >>= 2;
/* Main loop */
for (;len > 0; len--) {
hash += get16bits (s);
tmp = (get16bits (s+2) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
s += 2*sizeof (uint16_t);
hash += hash >> 11;
}
/* Handle end cases */
switch (rem) {
case 3:
hash += get16bits(s);
hash ^= hash << 16;
hash ^= s[sizeof (uint16_t)] << 18;
hash += hash >> 11;
break;
case 2:
hash += get16bits(s);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1:
hash += *s;
hash ^= hash << 10;
hash += hash >> 1;
}
/* Force "avalanching" of final 127 bits */
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;
return hash;
};
#undef get16bits
inline uint32_t hsieh_hash32(const char* s) {
return hsieh_hash32_buf(s, std::strlen(s));
}
inline uint32_t hsieh_hash32_str(const std::string& str) {
return hsieh_hash32_buf(str.data(), str.size());
}
//////////////////////////////////////////////////////////////////////
} // namespace hash
template<class Key>
struct hasher;
template<> struct hasher<int32_t> {
size_t operator()(int32_t key) const {
return hash::jenkins_rev_mix32(uint32_t(key));
}
};
template<> struct hasher<uint32_t> {
size_t operator()(uint32_t key) const {
return hash::jenkins_rev_mix32(key);
}
};
template<> struct hasher<int64_t> {
size_t operator()(int64_t key) const {
return hash::twang_mix64(uint64_t(key));
}
};
template<> struct hasher<uint64_t> {
size_t operator()(uint64_t key) const {
return hash::twang_mix64(key);
}
};
} // namespace folly
// Custom hash functions.
namespace std {
// Hash function for pairs. Requires default hash functions for both
// items in the pair.
template <typename T1, typename T2>
class hash<std::pair<T1, T2> > {
public:
size_t operator()(const std::pair<T1, T2>& x) const {
return folly::hash::hash_combine(x.first, x.second);
}
};
} // namespace std
#endif
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