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#include <wchar.h>
#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
static wchar_t *twoway_wcsstr(const wchar_t *h, const wchar_t *n)
{
const wchar_t *z;
size_t l, ip, jp, k, p, ms, p0, mem, mem0;
/* Computing length of needle */
for (l=0; n[l] && h[l]; l++);
if (n[l]) return 0; /* hit the end of h */
/* Compute maximal suffix */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] > n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
ms = ip;
p0 = p;
/* And with the opposite comparison */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] < n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
if (ip+1 > ms+1) ms = ip;
else p = p0;
/* Periodic needle? */
if (wmemcmp(n, n+p, ms+1)) {
mem0 = 0;
p = MAX(ms, l-ms-1) + 1;
} else mem0 = l-p;
mem = 0;
/* Initialize incremental end-of-haystack pointer */
z = h;
/* Search loop */
for (;;) {
/* Update incremental end-of-haystack pointer */
if (z-h < l) {
/* Fast estimate for MIN(l,63) */
size_t grow = l | 63;
const wchar_t *z2 = wmemchr(z, 0, grow);
if (z2) {
z = z2;
if (z-h < l) return 0;
} else z += grow;
}
/* Compare right half */
for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
if (n[k]) {
h += k-ms;
mem = 0;
continue;
}
/* Compare left half */
for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
if (k == mem) return (wchar_t *)h;
h += p;
mem = mem0;
}
}
wchar_t *wcsstr(const wchar_t *restrict h, const wchar_t *restrict n)
{
/* Return immediately on empty needle or haystack */
if (!n[0]) return (wchar_t *)h;
if (!h[0]) return 0;
/* Use faster algorithms for short needles */
h = wcschr(h, *n);
if (!h || !n[1]) return (wchar_t *)h;
if (!h[1]) return 0;
return twoway_wcsstr(h, n);
}
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