Visual basic 6.0 hash function

static unsigned long
sdbm(str)
unsigned char *str;
{
    unsigned long hash = 0;
    int c;

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

    return hash;
}

newHash = the character (c) + (previousHashValue * 2^6) +
                              (previousHashValue * 2^16) -
                               previousHashValue**
previousHashValue = newHash