versions/v1_4_0/mynewt-core/libc/baselibc/src/memmem.c

/*
 * 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 || !m || !n)
		return NULL;

	if (1 != m) {
		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;
			}
		}
	} else
		do {
			if (*y == *x)
				return (void *)y;
			y++;
		} while (--n);

	return NULL;
}