libstdc%2B%2B-v3/libsupc%2B%2B/hash_bytes.cc

25 // This file defines Hash_bytes, a primitive used for defining hash
30 // exactly the same interface but using a different hash algorithm,
31 // Fowler / Noll / Vo (FNV) Hash (type FNV-1a). The Murmur hash
32 // function apears to be better in both speed and hash quality, and
72   // Implementation of Murmur hash for 32-bit size_t.
77     size_t hash = seed ^ len;
80     // Mix 4 bytes at a time into the hash.
87 	hash *= m;
88 	hash ^= k;
97 	hash ^= static_cast<unsigned char>(buf[2]) << 16;
100 	hash ^= static_cast<unsigned char>(buf[1]) << 8;
103 	hash ^= static_cast<unsigned char>(buf[0]);
104 	hash *= m;
107     // Do a few final mixes of the hash.
108     hash ^= hash >> 13;
109     hash *= m;
110     hash ^= hash >> 15;
111     return hash;
114   // Implementation of FNV hash for 32-bit size_t.
119   _Fnv_hash_bytes(const void* ptr, size_t len, size_t hash)
124 	hash ^= static_cast<size_t>(*cptr++);
125 	hash *= static_cast<size_t>(16777619UL);
127     return hash;
132   // Implementation of Murmur hash for 64-bit size_t.
144     size_t hash = seed ^ (len * mul);
148 	hash ^= data;
149 	hash *= mul;
154 	hash ^= data;
155 	hash *= mul;
157     hash = shift_mix(hash) * mul;
158     hash = shift_mix(hash);
159     return hash;
162   // Implementation of FNV hash for 64-bit size_t.
167   _Fnv_hash_bytes(const void* ptr, size_t len, size_t hash)
172 	hash ^= static_cast<size_t>(*cptr++);
173 	hash *= static_cast<size_t>(1099511628211ULL);
175     return hash;
180   // Dummy hash implementation for unusual sizeof(size_t).
184     size_t hash = seed;
187       hash = (hash * 131) + *cptr++;
188     return hash;