Nginx源码完全注释（6）core/murmurhash

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

1. Murmurhash2