musl/src/multibyte/wcrtomb.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>
#include <errno.h>

size_t wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict st)
{
	if (!s) return 1;
	if ((unsigned)wc < 0x80) {
		*s = wc;
		return 1;
	} else if ((unsigned)wc < 0x800) {
		*s++ = 0xc0 | (wc>>6);
		*s = 0x80 | (wc&0x3f);
		return 2;
	} else if ((unsigned)wc < 0xd800 || (unsigned)wc-0xe000 < 0x2000) {
		*s++ = 0xe0 | (wc>>12);
		*s++ = 0x80 | ((wc>>6)&0x3f);
		*s = 0x80 | (wc&0x3f);
		return 3;
	} else if ((unsigned)wc-0x10000 < 0x100000) {
		*s++ = 0xf0 | (wc>>18);
		*s++ = 0x80 | ((wc>>12)&0x3f);
		*s++ = 0x80 | ((wc>>6)&0x3f);
		*s = 0x80 | (wc&0x3f);
		return 4;
	}
	errno = EILSEQ;
	return -1;
}