#ifndef MURMURHASH2_C #define MURMURHASH2_C #define MURMURHASH2_DIGEST_LENGTH 4 /* * ----------------------------------------------------------------------------- * MurmurHash2, by Austin Appleby * Note - This code makes a few assumptions about how your machine behaves - * 1. We can read a 4-byte value from any address without crashing * 2. sizeof(int) == 4 * And it has a few limitations - * 1. It will not work incrementally. * 2. It will not produce the same results on little-endian and big-endian * machines. */ unsigned int MurmurHash2 ( const void * key, int len, unsigned int seed ) { /* * 'm' and 'r' are mixing constants generated offline. * They're not really 'magic', they just happen to work well. */ const unsigned int m = 0x5bd1e995; const int r = 24; /* Initialize the hash to a 'random' value */ unsigned int h = seed ^ len; /* Mix 4 bytes at a time into the hash */ const unsigned char * data = (const unsigned char *)key; while(len >= 4) { unsigned int k = *(unsigned int *)data; k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; data += 4; len -= 4; } /* Handle the last few bytes of the input array */ switch(len) { case 3: h ^= data[2] << 16; case 2: h ^= data[1] << 8; case 1: h ^= data[0]; h *= m; }; /* Do a few final mixes of the hash to ensure the last few * bytes are well-incorporated. */ h ^= h >> 13; h *= m; h ^= h >> 15; return h; } #endif