10个经典的字符串hash函数的C代码实现

以下总共给出了10种字符串hash函数，在上面的链接中可以找到各个Hash函数的描述，以及一些其它的关于hash函数的资料下载。

这些hash函数各自的优缺点不详。其中，ELFHash函数是在unix系统中被广泛使用的，也是《算法艺术与信息学竞赛》中作者推荐的一个字符串hash函数。DEKHash函数是Knuth在其《The Art of Computer Programming》第三卷中引入的。

 

unsigned int RSHash(char* str, unsigned int len)
{
unsigned int b    = 378551;
unsigned int a    = 63689;
unsigned int hash = 0;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = hash * a + (*str);
a    = a * b;
}
return hash;
}
/* End Of RS Hash Function */

unsigned int JSHash(char* str, unsigned int len)
{
unsigned int hash = 1315423911;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash ^= ((hash << 5) + (*str) + (hash >> 2));
}
return hash;
}
/* End Of JS Hash Function */

unsigned int PJWHash(char* str, unsigned int len)
{
const unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);
const unsigned int ThreeQuarters     = (unsigned int)((BitsInUnsignedInt  * 3) / 4);
const unsigned int OneEighth         = (unsigned int)(BitsInUnsignedInt / 8);
const unsigned int HighBits          = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
unsigned int hash              = 0;
unsigned int test              = 0;
unsigned int i                 = 0;
for(i = 0; i < len; str++, i++)
{
hash = (hash << OneEighth) + (*str);
if((test = hash & HighBits)  != 0)
{
hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
}
return hash;
}
/* End Of  P. J. Weinberger Hash Function */

unsigned int ELFHash(char* str, unsigned int len)
{
unsigned int hash = 0;
unsigned int x    = 0;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = (hash << 4) + (*str);
if((x = hash & 0xF0000000L) != 0)
{
hash ^= (x >> 24);
}
hash &= ~x;
}
return hash;
}
/* End Of ELF Hash Function */

unsigned int BKDRHash(char* str, unsigned int len)
{
unsigned int seed = 131; /* 31 131 1313 13131 131313 etc.. */
unsigned int hash = 0;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = (hash * seed) + (*str);
}
return hash;
}
/* End Of BKDR Hash Function */

unsigned int SDBMHash(char* str, unsigned int len)
{
unsigned int hash = 0;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = (*str) + (hash << 6) + (hash << 16) - hash;
}
return hash;
}
/* End Of SDBM Hash Function */

unsigned int DJBHash(char* str, unsigned int len)
{
unsigned int hash = 5381;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = ((hash << 5) + hash) + (*str);
}
return hash;
}
/* End Of DJB Hash Function */

unsigned int DEKHash(char* str, unsigned int len)
{
unsigned int hash = len;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = ((hash << 5) ^ (hash >> 27)) ^ (*str);
}
return hash;
}
/* End Of DEK Hash Function */

unsigned int BPHash(char* str, unsigned int len)
{
unsigned int hash = 0;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash = hash << 7 ^ (*str);
}
return hash;
}
/* End Of BP Hash Function */

unsigned int FNVHash(char* str, unsigned int len)
{
const unsigned int fnv_prime = 0x811C9DC5;
unsigned int hash      = 0;
unsigned int i         = 0;
for(i = 0; i < len; str++, i++)
{
hash *= fnv_prime;
hash ^= (*str);
}
return hash;
}
/* End Of FNV Hash Function */

unsigned int APHash(char* str, unsigned int len)
{
unsigned int hash = 0xAAAAAAAA;
unsigned int i    = 0;
for(i = 0; i < len; str++, i++)
{
hash ^= ((i & 1) == 0) ? (  (hash <<  7) ^ (*str) * (hash >> 3)) :
(~((hash << 11) + (*str) ^ (hash >> 5)));
}
return hash;
}
/* End Of AP Hash Function */

转自http://blog.csdn.net/jcwkyl/article/details/4088436