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

fusl/src/string/memmem.c

+#define _GNU_SOURCE
+#include <string.h>
+#include <stdint.h>
+
+static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+        uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
+        for (h++, k--; k; k--, hw = hw<<8 | *++h)
+                if (hw == nw) return (char *)h-1;
+        return 0;
+}
+
+static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+        uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
+        uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
+        for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
+                if (hw == nw) return (char *)h-2;
+        return 0;
+}
+
+static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
+{
+        uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
+        uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+        for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
+                if (hw == nw) return (char *)h-3;
+        return 0;
+}
+
+#define MAX(a,b) ((a)>(b)?(a):(b))
+#define MIN(a,b) ((a)<(b)?(a):(b))
+
+#define BITOP(a,b,op) \
+ ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
+
+static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
+{
+        size_t i, ip, jp, k, p, ms, p0, mem, mem0;
+        size_t byteset[32 / sizeof(size_t)] = { 0 };
+        size_t shift[256];
+
+        /* Computing length of needle and fill shift table */
+        for (i=0; i<l; i++)
+                BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
+
+        /* 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 (memcmp(n, n+p, ms+1)) {
+                mem0 = 0;
+                p = MAX(ms, l-ms-1) + 1;
+        } else mem0 = l-p;
+        mem = 0;
+
+        /* Search loop */
+        for (;;) {
+                /* If remainder of haystack is shorter than needle, done */
+                if (z-h < l) return 0;
+
+                /* Check last byte first; advance by shift on mismatch */
+                if (BITOP(byteset, h[l-1], &)) {
+                        k = l-shift[h[l-1]];
+                        if (k) {
+                                if (mem0 && mem && k < p) k = l-p;
+                                h += k;
+                                mem = 0;
+                                continue;
+                        }
+                } else {
+                        h += l;
+                        mem = 0;
+                        continue;
+                }
+
+                /* Compare right half */
+                for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
+                if (k < l) {
+                        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 (char *)h;
+                h += p;
+                mem = mem0;
+        }
+}
+
+void *memmem(const void *h0, size_t k, const void *n0, size_t l)
+{
+        const unsigned char *h = h0, *n = n0;
+
+        /* Return immediately on empty needle */
+        if (!l) return (void *)h;
+
+        /* Return immediately when needle is longer than haystack */
+        if (k<l) return 0;
+
+        /* Use faster algorithms for short needles */
+        h = memchr(h0, *n, k);
+        if (!h || l==1) return (void *)h;
+        k -= h - (const unsigned char *)h0;
+        if (l==2) return twobyte_memmem(h, k, n);
+        if (l==3) return threebyte_memmem(h, k, n);
+        if (l==4) return fourbyte_memmem(h, k, n);
+
+        return twoway_memmem(h, h+k, n, l);
+}