常用字符串hash方法——转自杭电BBS

虽然看不懂……但是还是先存下吧~~~

// 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 );
}

// SDBM Hash Function
unsigned int SDBMHash(char* str)
{
    unsigned int hash = 0 ;
    while (*str)
    {
        hash = (*str ++ ) + (hash << 6 ) + (hash << 16 ) - hash;
    }
    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 );
}