1 #include <wchar.h>
2
3 #define MAX(a,b) ((a)>(b)?(a):(b))
4 #define MIN(a,b) ((a)<(b)?(a):(b))
5
twoway_wcsstr(const wchar_t * h,const wchar_t * n)6 static 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
wcsstr(const wchar_t * restrict h,const wchar_t * restrict n)93 wchar_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