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

fusl/src/string/memcpy.c

+#include <string.h>
+#include <stdint.h>
+#include <endian.h>
+
+void *memcpy(void *restrict dest, const void *restrict src, size_t n)
+{
+        unsigned char *d = dest;
+        const unsigned char *s = src;
+
+#ifdef __GNUC__
+
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define LS >>
+#define RS <<
+#else
+#define LS <<
+#define RS >>
+#endif
+
+        typedef uint32_t __attribute__((__may_alias__)) u32;
+        uint32_t w, x;
+
+        for (; (uintptr_t)s % 4 && n; n--) *d++ = *s++;
+
+        if ((uintptr_t)d % 4 == 0) {
+                for (; n>=16; s+=16, d+=16, n-=16) {
+                        *(u32 *)(d+0) = *(u32 *)(s+0);
+                        *(u32 *)(d+4) = *(u32 *)(s+4);
+                        *(u32 *)(d+8) = *(u32 *)(s+8);
+                        *(u32 *)(d+12) = *(u32 *)(s+12);
+                }
+                if (n&8) {
+                        *(u32 *)(d+0) = *(u32 *)(s+0);
+                        *(u32 *)(d+4) = *(u32 *)(s+4);
+                        d += 8; s += 8;
+                }
+                if (n&4) {
+                        *(u32 *)(d+0) = *(u32 *)(s+0);
+                        d += 4; s += 4;
+                }
+                if (n&2) {
+                        *d++ = *s++; *d++ = *s++;
+                }
+                if (n&1) {
+                        *d = *s;
+                }
+                return dest;
+        }
+
+        if (n >= 32) switch ((uintptr_t)d % 4) {
+        case 1:
+                w = *(u32 *)s;
+                *d++ = *s++;
+                *d++ = *s++;
+                *d++ = *s++;
+                n -= 3;
+                for (; n>=17; s+=16, d+=16, n-=16) {
+                        x = *(u32 *)(s+1);
+                        *(u32 *)(d+0) = (w LS 24) | (x RS 8);
+                        w = *(u32 *)(s+5);
+                        *(u32 *)(d+4) = (x LS 24) | (w RS 8);
+                        x = *(u32 *)(s+9);
+                        *(u32 *)(d+8) = (w LS 24) | (x RS 8);
+                        w = *(u32 *)(s+13);
+                        *(u32 *)(d+12) = (x LS 24) | (w RS 8);
+                }
+                break;
+        case 2:
+                w = *(u32 *)s;
+                *d++ = *s++;
+                *d++ = *s++;
+                n -= 2;
+                for (; n>=18; s+=16, d+=16, n-=16) {
+                        x = *(u32 *)(s+2);
+                        *(u32 *)(d+0) = (w LS 16) | (x RS 16);
+                        w = *(u32 *)(s+6);
+                        *(u32 *)(d+4) = (x LS 16) | (w RS 16);
+                        x = *(u32 *)(s+10);
+                        *(u32 *)(d+8) = (w LS 16) | (x RS 16);
+                        w = *(u32 *)(s+14);
+                        *(u32 *)(d+12) = (x LS 16) | (w RS 16);
+                }
+                break;
+        case 3:
+                w = *(u32 *)s;
+                *d++ = *s++;
+                n -= 1;
+                for (; n>=19; s+=16, d+=16, n-=16) {
+                        x = *(u32 *)(s+3);
+                        *(u32 *)(d+0) = (w LS 8) | (x RS 24);
+                        w = *(u32 *)(s+7);
+                        *(u32 *)(d+4) = (x LS 8) | (w RS 24);
+                        x = *(u32 *)(s+11);
+                        *(u32 *)(d+8) = (w LS 8) | (x RS 24);
+                        w = *(u32 *)(s+15);
+                        *(u32 *)(d+12) = (x LS 8) | (w RS 24);
+                }
+                break;
+        }
+        if (n&16) {
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+        }
+        if (n&8) {
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+        }
+        if (n&4) {
+                *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+        }
+        if (n&2) {
+                *d++ = *s++; *d++ = *s++;
+        }
+        if (n&1) {
+                *d = *s;
+        }
+        return dest;
+#endif
+
+        for (; n; n--) *d++ = *s++;
+        return dest;
+}