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

fusl/src/multibyte/mbsrtowcs.c

Index: fusl/src/multibyte/mbsrtowcs.c
diff --git a/fusl/src/multibyte/mbsrtowcs.c b/fusl/src/multibyte/mbsrtowcs.c
new file mode 100644
index 0000000000000000000000000000000000000000..e23083d223fc4c5528d46730b7c12a936888ef64
--- /dev/null
+++ b/fusl/src/multibyte/mbsrtowcs.c
@@ -0,0 +1,120 @@
+/* 
+ * This code was written by Rich Felker in 2010; no copyright is claimed.
+ * This code is in the public domain. Attribution is appreciated but
+ * unnecessary.
+ */
+
+#include <stdint.h>
+#include <wchar.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include "internal.h"
+
+size_t mbsrtowcs(wchar_t *restrict ws, const char **restrict src, size_t wn, mbstate_t *restrict st)
+{
+	const unsigned char *s = (const void *)*src;
+	size_t wn0 = wn;
+	unsigned c = 0;
+
+	if (st && (c = *(unsigned *)st)) {
+		if (ws) {
+			*(unsigned *)st = 0;
+			goto resume;
+		} else {
+			goto resume0;
+		}
+	}
+
+	if (MB_CUR_MAX==1) {
+		if (!ws) return strlen((const char *)s);
+		for (;;) {
+			if (!wn) {
+				*src = (const void *)s;
+				return wn0;
+			}
+			if (!*s) break;
+			c = *s++;
+			*ws++ = CODEUNIT(c);
+			wn--;
+		}
+		*ws = 0;
+		*src = 0;
+		return wn0-wn;
+	}
+
+	if (!ws) for (;;) {
+		if (*s-1u < 0x7f && (uintptr_t)s%4 == 0) {
+			while (!(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
+				s += 4;
+				wn -= 4;
+			}
+		}
+		if (*s-1u < 0x7f) {
+			s++;
+			wn--;
+			continue;
+		}
+		if (*s-SA > SB-SA) break;
+		c = bittab[*s++-SA];
+resume0:
+		if (OOB(c,*s)) { s--; break; }
+		s++;
+		if (c&(1U<<25)) {
+			if (*s-0x80u >= 0x40) { s-=2; break; }
+			s++;
+			if (c&(1U<<19)) {
+				if (*s-0x80u >= 0x40) { s-=3; break; }
+				s++;
+			}
+		}
+		wn--;
+		c = 0;
+	} else for (;;) {
+		if (!wn) {
+			*src = (const void *)s;
+			return wn0;
+		}
+		if (*s-1u < 0x7f && (uintptr_t)s%4 == 0) {
+			while (wn>=5 && !(( *(uint32_t*)s | *(uint32_t*)s-0x01010101) & 0x80808080)) {
+				*ws++ = *s++;
+				*ws++ = *s++;
+				*ws++ = *s++;
+				*ws++ = *s++;
+				wn -= 4;
+			}
+		}
+		if (*s-1u < 0x7f) {
+			*ws++ = *s++;
+			wn--;
+			continue;
+		}
+		if (*s-SA > SB-SA) break;
+		c = bittab[*s++-SA];
+resume:
+		if (OOB(c,*s)) { s--; break; }
+		c = (c<<6) | *s++-0x80;
+		if (c&(1U<<31)) {
+			if (*s-0x80u >= 0x40) { s-=2; break; }
+			c = (c<<6) | *s++-0x80;
+			if (c&(1U<<31)) {
+				if (*s-0x80u >= 0x40) { s-=3; break; }
+				c = (c<<6) | *s++-0x80;
+			}
+		}
+		*ws++ = c;
+		wn--;
+		c = 0;
+	}
+
+	if (!c && !*s) {
+		if (ws) {
+			*ws = 0;
+			*src = 0;
+		}
+		return wn0-wn;
+	}
+	errno = EILSEQ;
+	if (ws) *src = (const void *)s;
+	return -1;
+}