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	libc/wchar: Fix unicode handling - scc - simple c99 compiler
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	---
	commit dee0c6f0c90f7d64fd45cb6e3c48321f4beaf81d
	parent 2eaef0900f5ebd9f00bebd8ce899423a0b37b4bb
	Author: Roberto E. Vargas Caballero <[email protected]>
	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 p…
	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;