#include <errno.h>
#include "internal.h"
-
-int mbtowc(wchar_t *restrict wc, const char *restrict s, size_t n)
+#include <stdio.h>
+int mbtowc(wchar_t *restrict wc, const char *restrict src, size_t n)
{
- mbstate_t st = { 0 };
- n = mbrtowc(wc, s, n, &st);
- return n+2 ? n : -1;
+ unsigned c;
+ const unsigned char *s = (const void *)src;
+
+ if (!s) return 0;
+ if (!n) goto ilseq;
+ if (!wc) wc = (void *)&wc;
+
+ if (*s < 0x80) return !!(*wc = *s);
+ if (*s-SA > SB-SA) goto ilseq;
+ c = bittab[*s++-SA];
+
+ /* Avoid excessive checks against n: If shifting the state n-1
+ * times does not clear the high bit, then the value of n is
+ * insufficient to read a character */
+ if (n<4 && ((c<<(6*n-6)) & (1U<<31))) goto ilseq;
+
+ if (OOB(c,*s)) goto ilseq;
+ c = c<<6 | *s++-0x80;
+ if (!(c&(1U<<31))) {
+ *wc = c;
+ return 2;
+ }
+
+ if (*s-0x80u >= 0x40) goto ilseq;
+ c = c<<6 | *s++-0x80;
+ if (!(c&(1U<<31))) {
+ *wc = c;
+ return 3;
+ }
+
+ if (*s-0x80u >= 0x40) goto ilseq;
+ *wc = c<<6 | *s++-0x80;
+ return 4;
+
+ilseq:
+ errno = EILSEQ;
+ return -1;
}