基本哈希函数

// SDBM Hash
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 
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 
unsigned int JSHash(char *str)
{
    unsigned int hash = 1315423911;
 
    while (*str)
    {
         hash ^= ((hash << 5) + (*str++) + (hash >> 2));
    }
 
    return (hash & 0x7FFFFFFF);
}
 
// P. J. Weinberger Hash 
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 unsigned int SDBMHash(char *str) - 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 
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 
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 
unsigned int DJBHash(char *str)
{
    unsigned int hash = 5381;
 
    while (*str)
    {
        hash += (hash << 5) + (*str++);
    }
 
    return (hash & 0x7FFFFFFF);
}
 
// AP Hash 
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);
}