/*
 * memmem.c
 *
 * Find a byte string inside a longer byte string
 *
 * This uses the "Not So Naive" algorithm, a very simple but
 * usually effective algorithm, see:
 *
 * http://www-igm.univ-mlv.fr/~lecroq/string/
 */

#include <string.h>

void *memmem(const void *haystack, size_t n, const void *needle, size_t m)
{
    const unsigned char *y = (const unsigned char *)haystack;
    const unsigned char *x = (const unsigned char *)needle;

    size_t j, k, l;

    if (m > n)
	return NULL;

    if (x[0] == x[1]) {
	k = 2;
	l = 1;
    } else {
	k = 1;
	l = 2;
    }

    j = 0;
    while (j <= n - m) {
	if (x[1] != y[j + 1]) {
	    j += k;
	} else {
	    if (!memcmp(x + 2, y + j + 2, m - 2) && x[0] == y[j])
		return (void *)&y[j];
	    j += l;
	}
    }

    return NULL;
}
