1#include <wchar.h>
  2
  3#define MAX(a,b) ((a)>(b)?(a):(b))
  4#define MIN(a,b) ((a)<(b)?(a):(b))
  5
  6static wchar_t *twoway_wcsstr(const wchar_t *h, const wchar_t *n)
  7{
  8	const wchar_t *z;
  9	size_t l, ip, jp, k, p, ms, p0, mem, mem0;
 10
 11	/* Computing length of needle */
 12	for (l=0; n[l] && h[l]; l++);
 13	if (n[l]) return 0; /* hit the end of h */
 14
 15	/* Compute maximal suffix */
 16	ip = -1; jp = 0; k = p = 1;
 17	while (jp+k<l) {
 18		if (n[ip+k] == n[jp+k]) {
 19			if (k == p) {
 20				jp += p;
 21				k = 1;
 22			} else k++;
 23		} else if (n[ip+k] > n[jp+k]) {
 24			jp += k;
 25			k = 1;
 26			p = jp - ip;
 27		} else {
 28			ip = jp++;
 29			k = p = 1;
 30		}
 31	}
 32	ms = ip;
 33	p0 = p;
 34
 35	/* And with the opposite comparison */
 36	ip = -1; jp = 0; k = p = 1;
 37	while (jp+k<l) {
 38		if (n[ip+k] == n[jp+k]) {
 39			if (k == p) {
 40				jp += p;
 41				k = 1;
 42			} else k++;
 43		} else if (n[ip+k] < n[jp+k]) {
 44			jp += k;
 45			k = 1;
 46			p = jp - ip;
 47		} else {
 48			ip = jp++;
 49			k = p = 1;
 50		}
 51	}
 52	if (ip+1 > ms+1) ms = ip;
 53	else p = p0;
 54
 55	/* Periodic needle? */
 56	if (wmemcmp(n, n+p, ms+1)) {
 57		mem0 = 0;
 58		p = MAX(ms, l-ms-1) + 1;
 59	} else mem0 = l-p;
 60	mem = 0;
 61
 62	/* Initialize incremental end-of-haystack pointer */
 63	z = h;
 64
 65	/* Search loop */
 66	for (;;) {
 67		/* Update incremental end-of-haystack pointer */
 68		if (z-h < l) {
 69			/* Fast estimate for MIN(l,63) */
 70			size_t grow = l | 63;
 71			const wchar_t *z2 = wmemchr(z, 0, grow);
 72			if (z2) {
 73				z = z2;
 74				if (z-h < l) return 0;
 75			} else z += grow;
 76		}
 77
 78		/* Compare right half */
 79		for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
 80		if (n[k]) {
 81			h += k-ms;
 82			mem = 0;
 83			continue;
 84		}
 85		/* Compare left half */
 86		for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
 87		if (k <= mem) return (wchar_t *)h;
 88		h += p;
 89		mem = mem0;
 90	}
 91}
 92
 93wchar_t *wcsstr(const wchar_t *restrict h, const wchar_t *restrict n)
 94{
 95	/* Return immediately on empty needle or haystack */
 96	if (!n[0]) return (wchar_t *)h;
 97	if (!h[0]) return 0;
 98
 99	/* Use faster algorithms for short needles */
100	h = wcschr(h, *n);
101	if (!h || !n[1]) return (wchar_t *)h;
102	if (!h[1]) return 0;
103
104	return twoway_wcsstr(h, n);
105}