#define Q     33554393L   /* prime number */
#define LOG2D 8           /* 2^8 = 256 */

unsigned long rkHash(unsigned long *dm, char *pattern, int patlen)
{
    int      i;
    unsigned long h1;

    for (i = 1, *dm = 1; i < patlen; i++)
        *dm = (*dm << LOG2D) % Q;
    for (i = 0, h1 = 0; i < patlen; i++)
        h1 = ((h1 << LOG2D) + pattern[i]) % Q;
    return h1;
}

char *rkMatch(char *text, int len, int patlen,
     unsigned long patHash, unsigned long dm)
{
    int      i;
    char     *textEnd;
    unsigned long h2;

    if (patlen == 0)  return text;
    if (len < patlen) return NULL;

    for (i = 0, h2 = 0; i < patlen; i++)
        h2 = ((h2 << LOG2D) + text[i]) % Q;

    textEnd = text + (len - patlen) + 1;
    while (text != textEnd) {
        if (h2 == patHash) return text;
        h2 = (h2 + (Q << LOG2D) - *text * dm) % Q;
        h2 = ((h2 << LOG2D) + *(text + patlen)) % Q;
        text++;
    }
    return NULL;
}