source: asp3_tinet_ecnl_arm/trunk/musl-1.1.18/src/string/wcsstr.c@ 352

#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);
}