分享一个新的对字符串的哈希算法之FastHash

来源：互联网发布：制作蹭饭地图软件编辑：程序博客网时间：2024/05/16 13:04

算法如下：

#if OGRE_ENDIAN == OGRE_ENDIAN_LITTLE 大端小端自己定义一下
# define OGRE_GET16BITS(d) (*((const uint16 *) (d)))
#else
# define OGRE_GET16BITS(d) (*((const uint8 *) (d)) + (*((const uint8 *) (d+1))<<8))
#endif

//说明：一般情况下，hashSoFar 设置为0.
uint32 FastHash (const char * data, int len, uint32 hashSoFar)
{
uint32 hash;
uint32 tmp;
int rem;

if (hashSoFar)
hash = hashSoFar;
else
hash = len;

if (len <= 0 || data == NULL) return 0;

rem = len & 3;
len >>= 2;

/* Main loop */
for (;len > 0; len--) {
hash += OGRE_GET16BITS (data);
tmp = (OGRE_GET16BITS (data+2) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
data += 2*sizeof (uint16);
hash += hash >> 11;
}

/* Handle end cases */
switch (rem) {
case 3: hash += OGRE_GET16BITS (data);
hash ^= hash << 16;
hash ^= data[sizeof (uint16)] << 18;
hash += hash >> 11;
break;
case 2: hash += OGRE_GET16BITS (data);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1: hash += *data;
hash ^= hash << 10;
hash += hash >> 1;
}

/* Force "avalanching" of final 127 bits */
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;

return hash;
}

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