./Source/roboconfig.c

Configuration/Hash_Keyword [ Functions ]

FUNCTION

Calculate the hash value for a string

The hash value is a 32 bit integer based on the hash function written by Bob Jenkins. It is then reduced by an AND operation to the actual size of the hash table.

SYNOPSIS

unsigned long Hash_Keyword(
    char *key,
    unsigned long keylen )

INPUTS

key -- The keyword string
keylen -- The length of the keyword string

RETURN VALUE

The hash value for the keyword.

SOURCE

{
    unsigned long       bkt, i, j, k;

    bkt = 0xfeedbeef;
    i = j = 0x9e3779b9;
    k = keylen;

    while ( k >= 12 )
    {
        i += ( key[0] + ( ( unsigned ) key[1] << 8 )
               + ( ( unsigned ) key[2] << 16 )
               + ( ( unsigned ) key[3] << 24 ) );
        j += ( key[4] + ( ( unsigned ) key[5] << 8 )
               + ( ( unsigned ) key[6] << 16 )
               + ( ( unsigned ) key[7] << 24 ) );
        bkt += ( key[8] + ( ( unsigned ) key[9] << 8 )
                 + ( ( unsigned ) key[10] << 16 )
                 + ( ( unsigned ) key[11] << 24 ) );

        HASH_MIX( i, j, bkt );

        key += 12;
        k -= 12;
    }

    bkt += keylen;

    switch ( k )
    {
    case 11:
        bkt += ( ( unsigned ) key[10] << 24 );
    case 10:
        bkt += ( ( unsigned ) key[9] << 16 );
    case 9:
        bkt += ( ( unsigned ) key[8] << 8 );
    case 8:
        j += ( ( unsigned ) key[7] << 24 );
    case 7:
        j += ( ( unsigned ) key[6] << 16 );
    case 6:
        j += ( ( unsigned ) key[5] << 8 );
    case 5:
        j += key[4];
    case 4:
        i += ( ( unsigned ) key[3] << 24 );
    case 3:
        i += ( ( unsigned ) key[2] << 16 );
    case 2:
        i += ( ( unsigned ) key[1] << 8 );
    case 1:
        i += key[0];
    }

    HASH_MIX( i, j, bkt );

    return ( bkt & keywords_hash_mask );
}