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}
106