/*
- * Copyright 2012 Facebook, Inc.
+ * Copyright 2014 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#ifndef FOLLY_BASE_HASH_H_
#define FOLLY_BASE_HASH_H_
-#include <stdint.h>
#include <cstring>
+#include <stdint.h>
#include <string>
+#include <utility>
+#include <tuple>
+
+#include "folly/SpookyHashV1.h"
+#include "folly/SpookyHashV2.h"
/*
* Various hashing functions.
namespace folly { namespace hash {
+// This is a general-purpose way to create a single hash from multiple
+// hashable objects. hash_combine_generic takes a class Hasher implementing
+// hash<T>; hash_combine uses a default hasher StdHasher that uses std::hash.
+// hash_combine_generic hashes each argument and combines those hashes in
+// an order-dependent way to yield a new hash.
+
+
+// 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;
+}
+
+// Never used, but gcc demands it.
+template <class Hasher>
+inline size_t hash_combine_generic() {
+ return 0;
+}
+
+template <class Hasher, typename T, typename... Ts>
+size_t hash_combine_generic(const T& t, const Ts&... ts) {
+ size_t seed = Hasher::hash(t);
+ if (sizeof...(ts) == 0) {
+ return seed;
+ }
+ size_t remainder = hash_combine_generic<Hasher>(ts...);
+ return hash_128_to_64(seed, remainder);
+}
+
+// Simply uses std::hash to hash. Note that std::hash is not guaranteed
+// to be a very good hash function; provided std::hash doesn't collide on
+// the individual inputs, you are fine, but that won't be true for, say,
+// strings or pairs
+class StdHasher {
+ public:
+ template <typename T>
+ static size_t hash(const T& t) {
+ return std::hash<T>()(t);
+ }
+};
+
+template <typename T, typename... Ts>
+size_t hash_combine(const T& t, const Ts&... ts) {
+ return hash_combine_generic<StdHasher>(t, ts...);
+}
+
//////////////////////////////////////////////////////////////////////
/*
*/
inline uint64_t twang_mix64(uint64_t key) {
- key = (~key) + (key << 21);
+ key = (~key) + (key << 21); // key *= (1 << 21) - 1; key -= 1;
key = key ^ (key >> 24);
- key = (key + (key << 3)) + (key << 8);
+ key = key + (key << 3) + (key << 8); // key *= 1 + (1 << 3) + (1 << 8)
key = key ^ (key >> 14);
- key = (key + (key << 2)) + (key << 4);
+ key = key + (key << 2) + (key << 4); // key *= 1 + (1 << 2) + (1 << 4)
key = key ^ (key >> 28);
- key = key + (key << 31);
+ 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;
}
*/
inline uint32_t jenkins_rev_mix32(uint32_t key) {
- key += (key << 12);
+ key += (key << 12); // key *= (1 + (1 << 12))
key ^= (key >> 22);
- key += (key << 4);
+ key += (key << 4); // key *= (1 + (1 << 4))
key ^= (key >> 9);
- key += (key << 10);
+ 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 uint32_t FNV_32_HASH_START = 2166136261UL;
const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
inline uint32_t fnv32(const char* s,
}
inline uint32_t fnv32(const std::string& str,
- uint64_t hash = FNV_32_HASH_START) {
+ uint32_t hash = FNV_32_HASH_START) {
return fnv32_buf(str.data(), str.size(), hash);
}
}
};
+// recursion
+template <size_t index, typename... Ts>
+struct TupleHasher {
+ size_t operator()(std::tuple<Ts...> const& key) const {
+ return hash::hash_combine(
+ TupleHasher<index - 1, Ts...>()(key),
+ std::get<index>(key));
+ }
+};
+
+// base
+template <typename... Ts>
+struct TupleHasher<0, Ts...> {
+ size_t operator()(std::tuple<Ts...> const& key) const {
+ // we could do std::hash here directly, but hash_combine hides all the
+ // ugly templating implicitly
+ return hash::hash_combine(std::get<0>(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);
+ }
+ };
+
+ // Hash function for tuples. Requires default hash functions for all types.
+ template <typename... Ts>
+ struct hash<std::tuple<Ts...>> {
+ size_t operator()(std::tuple<Ts...> const& key) const {
+ folly::TupleHasher<
+ std::tuple_size<std::tuple<Ts...>>::value - 1, // start index
+ Ts...> hasher;
+
+ return hasher(key);
+ }
+ };
+} // namespace std
+
#endif
projects / folly.git / blobdiff