哈希字符串函数

unsigned int SDBMHash(char *str)

{

unsigned int hash = 0;

while (*str)

{

// equivalent to: hash = 65599*hash + (*str++);

hash = (*str++) + (hash << 6) + (hash << 16) - hash;

}

return (hash & 0x7FFFFFFF);

}

// RS Hash Function

unsigned int RSHash(char *str)

{

unsigned int b = 378551;

unsigned int a = 63689;

unsigned int hash = 0;

while (*str)

{

hash = hash * a + (*str++);

a *= b;

}

return (hash & 0x7FFFFFFF);

}

// JS Hash Function

unsigned int JSHash(char *str)

{

unsigned int hash = 1315423911;

while (*str)

{

hash ^= ((hash << 5) + (*str++) + (hash >> 2));

}

return (hash & 0x7FFFFFFF);

}

// P. J. Weinberger Hash Function

unsigned int PJWHash(char *str)

{

unsigned int BitsInUnignedInt = (unsigned int)(sizeof(unsigned int) * 8);

unsigned int ThreeQuarters = (unsigned int)((BitsInUnignedInt  * 3) / 4);

unsigned int OneEighth = (unsigned int)(BitsInUnignedInt / 8);

unsigned int HighBits = (unsigned int)(0xFFFFFFFF) << (BitsInUnignedInt - OneEighth);

unsigned int hash = 0;

unsigned int test = 0;

while (*str)

{

hash = (hash << OneEighth) + (*str++);

if ((test = hash & HighBits) != 0)

{

hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));

}

}

return (hash & 0x7FFFFFFF);

}

// ELF Hash Function

unsigned int ELFHash(char *str)

{

unsigned int hash = 0;

unsigned int x = 0;

while (*str)

{

hash = (hash << 4) + (*str++);

if ((x = hash & 0xF0000000L) != 0)

{

hash ^= (x >> 24);

hash &= ~x;

}

}

return (hash & 0x7FFFFFFF);

}

// BKDR Hash Function

unsigned int BKDRHash(char *str)

{

unsigned int seed = 131; // 31 131 1313 13131 131313 etc..

unsigned int hash = 0;

while (*str)

{

hash = hash * seed + (*str++);

}

return (hash & 0x7FFFFFFF);

}

// DJB Hash Function

unsigned int DJBHash(char *str)

{

unsigned int hash = 5381;

while (*str)

{

hash += (hash << 5) + (*str++);

}

return (hash & 0x7FFFFFFF);

}

// AP Hash Function

unsigned int APHash(char *str)

{

unsigned int hash = 0;

int i;

for (i=0; *str; i++)

{

if ((i & 1) == 0)

{

hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));

}

else

{

hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));

}

}

return (hash & 0x7FFFFFFF);

}