下面是摘自 Google Code 的 Murmurhash 开源项目主页上的 Murmurhash2,Nginx 就是采用的这个。
uint32_t MurmurHash2 ( const void * key, int len, uint32_t seed )
{
// ‘m‘ and ‘r‘ are mixing constants generated offline.
// They‘re not really ‘magic‘, they just happen to work well.
const uint32_t m = 0x5bd1e995;
const int r = 24;
// Initialize the hash to a ‘random‘ value
uint32_t h = seed ^ len;
// Mix 4 bytes at a time into the hash
const unsigned char * data = (const unsigned char *)key;
while(len >= 4)
{
uint32_t k = *(uint32_t*)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;
}
下面是 Nginx 中 Murmurhash 的源码,基本与上面无异。
uint32_t
ngx_murmur_hash2(u_char *data, size_t len)
{
uint32_t h, k;
h = 0 ^ len;
while (len >= 4) {
k = data[0];
k |= data[1] << 8;
k |= data[2] << 16;
k |= data[3] << 24;
k *= 0x5bd1e995;
k ^= k >> 24;
k *= 0x5bd1e995;
h *= 0x5bd1e995;
h ^= k;
data += 4;
len -= 4;
}
switch (len) {
case 3:
h ^= data[2] << 16;
case 2:
h ^= data[1] << 8;
case 1:
h ^= data[0];
h *= 0x5bd1e995;
}
h ^= h >> 13;
h *= 0x5bd1e995;
h ^= h >> 15;
return h;
}
Reference
时间: 2024-11-09 14:44:22