scc

commit 68ad37c9bee5f12c0804f165a5176e4bbf4b4898
parent 29f51dd9ea6407ff5d6386d7dc82cd499185533e
Author: Roberto E. Vargas Caballero <k0ga@shike2.net>
Date:   Fri, 28 Mar 2025 09:42:13 +0100

libc/wchar: Simplify mbsrtowc() and mbstowc()

We only support UTF8, that is stateless, and as mbsrtowc() cannot return
-2 then we do know that the internal state of mbsrtowc() will be always
set to the initial state, so we can reuse it from mbstowcs().

Also, mbsrtowcs() had a bug and it was incrementing the number of wchar
stored in the output buffer when mbrtowc() returned -2. Not a big issue
because we try to read MB_LEN_MAX, and longer sequences will eventually
return -1 and the value of n will not be used.

Diffstat:
M
src/libc/stdlib/mbstowcs.c
 | 
10
+++++++---
M
src/libc/wchar/mbsrtowcs.c
 | 
18
++++++++++--------

2 files changed, 17 insertions(+), 11 deletions(-)
diff --git a/src/libc/stdlib/mbstowcs.c b/src/libc/stdlib/mbstowcs.c
@@ -4,10 +4,14 @@
 
 #undef mbstowcs
 
+/*
+ * we can reuse the internal state of mbstwocws() because
+ * we loop in case of having a -2 from mbrtowc(), that
+ * makes impossible to leave the function in a non initial
+ * state (or error that cleans the state).
+ */
 size_t
 mbstowcs(wchar_t *restrict dest, const char *restrict src, size_t n)
 {
-	static mbstate_t st;
-
-	return mbsrtowcs(dest, (void *) &src, n, &st);
+	return mbsrtowcs(dest, (void *) &src, n, NULL);
 }
diff --git a/src/libc/wchar/mbsrtowcs.c b/src/libc/wchar/mbsrtowcs.c
@@ -16,7 +16,8 @@ mbsrtowcs(wchar_t *restrict dest, const char **restrict src, size_t len,
 	if (!ps)
 		ps = &st;
 
-	for (n = 0; ; n++) {
+	n = 0;
+	for (;;) {
 		cnt = mbrtowc(&wc, s, MB_LEN_MAX, ps);
 		if (cnt == (size_t) -2) {
 			s += MB_LEN_MAX;
@@ -28,19 +29,20 @@ mbsrtowcs(wchar_t *restrict dest, const char **restrict src, size_t len,
 		if (dest) {
 			if (n == len) {
 				*src = s;
-				return n;
+				break;
 			}
 			*dest++ = wc;
 		}
-		s += cnt;
 
-		if (wc == 0)
+		if (wc == 0) {
+			if (dest)
+				*src = NULL;
 			break;
-	}
+		}
+
+		s += cnt;
+		n++;
 
-	if (dest) {
-		memset(ps, 0, sizeof(mbstate_t));
-		*src = NULL;
 	}
 
 	return n;