musl/src/multibyte/wcsrtombs.c

/* 
 * 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 <wchar.h>

size_t wcsrtombs(char *restrict s, const wchar_t **restrict ws, size_t n, mbstate_t *restrict st)
{
	const wchar_t *ws2;
	char buf[4];
	size_t N = n, l;
	if (!s) {
		for (n=0, ws2=*ws; *ws2; ws2++) {
			if (*ws2 >= 0x80u) {
				l = wcrtomb(buf, *ws2, 0);
				if (!(l+1)) return -1;
				n += l;
			} else n++;
		}
		return n;
	}
	while (n>=4) {
		if (**ws-1u >= 0x7fu) {
			if (!**ws) {
				*s = 0;
				*ws = 0;
				return N-n;
			}
			l = wcrtomb(s, **ws, 0);
			if (!(l+1)) return -1;
			s += l;
			n -= l;
		} else {
			*s++ = **ws;
			n--;
		}
		(*ws)++;
	}
	while (n) {
		if (**ws-1u >= 0x7fu) {
			if (!**ws) {
				*s = 0;
				*ws = 0;
				return N-n;
			}
			l = wcrtomb(buf, **ws, 0);
			if (!(l+1)) return -1;
			if (l>n) return N-n;
			wcrtomb(s, **ws, 0);
			s += l;
			n -= l;
		} else {
			*s++ = **ws;
			n--;
		}
		(*ws)++;
	}
	return N;
}