Redis中散列函数的实现：
Redis针对整数key和字符串key，采用了不同的散列函数
对于整数key，redis使用了 Thomas Wang的 32 bit Mix Function，实现了dict.c/dictIntHashFunction函数：
/* Thomas Wang's 32 bit Mix Function */
unsigned int dictIntHashFunction(unsigned int key)
{
key += ~(key << );
key ^= (key >> );
key += (key << );
key ^= (key >> );
key += ~(key << );
key ^= (key >> );
return key;
}
这段代码的妙处我还没来得及仔细研究，等研究好了会在这里补上，不过找到了两个初看还不错的链接：
首先是Thomas Wang大神本人的链接:
http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
再者是他人根据上面链接和其他资料写的总结
http://blog.csdn.net/jasper_xulei/article/details/18364313
对于字符串形式的key，redis使用了MurmurHash2算法和djb算法:
MurmurHash2算法对于key是大小写敏感的，而且在大端机器和小端机器上生成结果不一致
redis的dict.c/dictGenHashFunction是MurmurHash2算法的C语言实现：
unsigned int dictGenHashFunction(const void *key, int len) {
/* 'm' and 'r' are mixing constants generated offline.
They're not really 'magic', they just happen to work well. */
uint32_t seed = dict_hash_function_seed;
const uint32_t m = 0x5bd1e995;
const int r = ;
/* 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 >= ) {
uint32_t k = *(uint32_t*)data;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += ;
len -= ;
}
/* Handle the last few bytes of the input array */
switch(len) {
case : h ^= data[] << ;
case : h ^= data[] << ;
case : h ^= data[]; h *= m;
};
/* Do a few final mixes of the hash to ensure the last few
* bytes are well-incorporated. */
h ^= h >> ;
h *= m;
h ^= h >> ;
return (unsigned int)h;
}
而redis则借助djb函数实现了不区分大小写的散列函数dict.c/dictGenCaseHashFunction：
unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len) {
unsigned int hash = (unsigned int)dict_hash_function_seed;
while (len--)
hash = ((hash << ) + hash) + (tolower(*buf++)); /* hash * 33 + c */
return hash;
}
以上三个散列函数(dictIntHashFunction, dictIntHashFunction, dictGenCaseHashFunction)分别用在了redis的不同地方，用以实现了不同场合下的散列需求，接下来的文章将会详细介绍。