Add a "fork" of musl as //fusl.

fusl/src/string/wcsstr.c

+#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);
+}