常用hash函数介绍

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);
}