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

fusl/src/string/memset.c

+#include <string.h>
+#include <stdint.h>
+
+void *memset(void *dest, int c, size_t n)
+{
+        unsigned char *s = dest;
+        size_t k;
+
+        /* Fill head and tail with minimal branching. Each
+         * conditional ensures that all the subsequently used
+         * offsets are well-defined and in the dest region. */
+
+        if (!n) return dest;
+        s[0] = s[n-1] = c;
+        if (n <= 2) return dest;
+        s[1] = s[n-2] = c;
+        s[2] = s[n-3] = c;
+        if (n <= 6) return dest;
+        s[3] = s[n-4] = c;
+        if (n <= 8) return dest;
+
+        /* Advance pointer to align it at a 4-byte boundary,
+         * and truncate n to a multiple of 4. The previous code
+         * already took care of any head/tail that get cut off
+         * by the alignment. */
+
+        k = -(uintptr_t)s & 3;
+        s += k;
+        n -= k;
+        n &= -4;
+
+#ifdef __GNUC__
+        typedef uint32_t __attribute__((__may_alias__)) u32;
+        typedef uint64_t __attribute__((__may_alias__)) u64;
+
+        u32 c32 = ((u32)-1)/255 * (unsigned char)c;
+
+        /* In preparation to copy 32 bytes at a time, aligned on
+         * an 8-byte bounary, fill head/tail up to 28 bytes each.
+         * As in the initial byte-based head/tail fill, each
+         * conditional below ensures that the subsequent offsets
+         * are valid (e.g. !(n<=24) implies n>=28). */
+
+        *(u32 *)(s+0) = c32;
+        *(u32 *)(s+n-4) = c32;
+        if (n <= 8) return dest;
+        *(u32 *)(s+4) = c32;
+        *(u32 *)(s+8) = c32;
+        *(u32 *)(s+n-12) = c32;
+        *(u32 *)(s+n-8) = c32;
+        if (n <= 24) return dest;
+        *(u32 *)(s+12) = c32;
+        *(u32 *)(s+16) = c32;
+        *(u32 *)(s+20) = c32;
+        *(u32 *)(s+24) = c32;
+        *(u32 *)(s+n-28) = c32;
+        *(u32 *)(s+n-24) = c32;
+        *(u32 *)(s+n-20) = c32;
+        *(u32 *)(s+n-16) = c32;
+
+        /* Align to a multiple of 8 so we can fill 64 bits at a time,
+         * and avoid writing the same bytes twice as much as is
+         * practical without introducing additional branching. */
+
+        k = 24 + ((uintptr_t)s & 4);
+        s += k;
+        n -= k;
+
+        /* If this loop is reached, 28 tail bytes have already been
+         * filled, so any remainder when n drops below 32 can be
+         * safely ignored. */
+
+        u64 c64 = c32 | ((u64)c32 << 32);
+        for (; n >= 32; n-=32, s+=32) {
+                *(u64 *)(s+0) = c64;
+                *(u64 *)(s+8) = c64;
+                *(u64 *)(s+16) = c64;
+                *(u64 *)(s+24) = c64;
+        }
+#else
+        /* Pure C fallback with no aliasing violations. */
+        for (; n; n--, s++) *s = c;
+#endif
+
+        return dest;
+}