implement mbtowc directly, not as a wrapper for mbrtowc

[musl] / src / multibyte / mbtowc.c

diff --git a/src/multibyte/mbtowc.c b/src/multibyte/mbtowc.c
index b5dd7e3..ec9e54a 100644 (file)
--- a/src/multibyte/mbtowc.c
+++ b/src/multibyte/mbtowc.c
@@ -10,10 +10,44 @@
 #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;
 }