scc

commit dee0c6f0c90f7d64fd45cb6e3c48321f4beaf81d
parent 2eaef0900f5ebd9f00bebd8ce899423a0b37b4bb
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Wed, 26 Feb 2025 10:31:51 +0100

libc/wchar: Fix unicode handling

* mbrtowc: validate input, handle 4-byte UTF-8 code points, set errno
* wcrtomb: if a UTF-8 sequence has N bytes, the leading byte has the first
  N bits set (with ASCII characters a special case), not the first N-1 bits
* _validutf8: negate condition

Diffstat:
M
src/libc/wchar/_validutf8.c
 | 
2
+-
M
src/libc/wchar/mbrtowc.c
 | 
26
+++++++++++++++++---------
M
src/libc/wchar/wcrtomb.c
 | 
9
+++++++--

3 files changed, 25 insertions(+), 12 deletions(-)
diff --git a/src/libc/wchar/_validutf8.c b/src/libc/wchar/_validutf8.c
@@ -23,7 +23,7 @@ _validutf8(wchar_t wc, int *nbytes)
 	};
 	struct range *bp;
 
-	for (bp = ranges; bp->begin <= wc && bp->end > wc; ++bp)
+	for (bp = ranges; bp->begin > wc || bp->end <= wc; ++bp)
 		;
 	*nbytes = bp->nbytes;
 
diff --git a/src/libc/wchar/mbrtowc.c b/src/libc/wchar/mbrtowc.c
@@ -1,3 +1,5 @@
+#include <errno.h>
+#include <stdlib.h>
 #include <wchar.h>
 
 #include "../libc.h"
@@ -8,37 +10,43 @@ size_t
 mbrtowc(wchar_t *restrict pwc, const char *restrict s, size_t n,
         mbstate_t *restrict ps)
 {
-	unsigned char *t = (unsigned char *) s;
+	const unsigned char *t = (const unsigned char *) s;
 	unsigned long wc;
 	unsigned c;
 	int i, len, maxlen;
 
-	if (s == NULL)
+	if (t == NULL)
 		return 0;
+	if ((wc = *t) == 0)
+		goto return_code;
 
-	wc = c = *t++;
+	c = *t++;
 	for (len = 0; n > 0 && c & 0x80; --n, ++len)
 		c <<= 1;
-	if (n == 0 || len == 1 || len == 8)
-		return -1;
+	if (n == 0 && c & 0x80)
+		return -2;
+	if (len == 1 || len > MB_CUR_MAX)
+		goto return_error;
 	if (len == 0)
 		goto return_code;
 
 	wc = (c & 0xFF) >> len;
 	for (i = 0; i < len-1; i++) {
 		if (((c = *t++) & 0xC0) != 0x80)
-			return -1;
+			goto return_error;
 		wc <<= 6;
 		wc |= c & 0x3F;
 	}
 
 	if (!_validutf8(wc, &maxlen) || len != maxlen)
-		return -1;
+		goto return_error;
 
 return_code:
 	if (pwc)
 		*pwc = wc;
-	if (*s == '\0')
-		return 0;
 	return t - (unsigned char *) s;
+
+return_error:
+	errno = EILSEQ;
+	return -1;
 }
diff --git a/src/libc/wchar/wcrtomb.c b/src/libc/wchar/wcrtomb.c
@@ -14,13 +14,18 @@ wcrtomb(char *restrict s, wchar_t wc, mbstate_t *restrict ps)
 	if (!s)
 		return 1;
 
+	if (c < 0x80) {
+		*s = wc;
+		return 1;
+	}
+
 	if (!_validutf8(wc, &n)) {
 		errno = EILSEQ;
 		return -1;
 	}
-
 	n--;
-	*s = 0;
+
+	*s = 0x80;
 	for (i = 0; i < n; i++) {
 		*s >>= 1;
 		*s |= 0x80;