3 files changed, 61 insertions, 1 deletions
diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
index 13e5cfd9..4e6d3503 100644
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -50,7 +50,7 @@ struct __FILE_s {
 	signed char lbf;
 	int lock;
 	int lockcount;
-	void *dummy5;
+	void *cookie;
 	off_t off;
 	int (*flush)(FILE *);
 	void **wide_data; /* must be NULL */
diff --git a/src/stdio/swprintf.c b/src/stdio/swprintf.c
new file mode 100644
index 00000000..5ece97c4
--- /dev/null
+++ b/src/stdio/swprintf.c
@@ -0,0 +1,14 @@
+#include <stdio.h>
+#include <stdarg.h>
+#include <wchar.h>
+
+int swprintf(wchar_t *s, size_t n, const wchar_t *fmt, ...)
+{
+	int ret;
+	va_list ap;
+	va_start(ap, fmt);
+	ret = vswprintf(s, n, fmt, ap);
+	va_end(ap);
+	return ret;
+}
+
diff --git a/src/stdio/vswprintf.c b/src/stdio/vswprintf.c
new file mode 100644
index 00000000..4ad581fb
--- /dev/null
+++ b/src/stdio/vswprintf.c
@@ -0,0 +1,46 @@
+#include "stdio_impl.h"
+
+struct cookie {
+	wchar_t *ws;
+	size_t l;
+};
+
+static size_t sw_write(FILE *f, const unsigned char *s, size_t l)
+{
+	size_t l0 = l;
+	int i = 0;
+	struct cookie *c = f->cookie;
+	while (c->l && l && (i=mbtowc(c->ws, s, l))>=0) {
+		s+=i;
+		l-=i;
+		c->l--;
+		c->ws++;
+	}
+	*c->ws = 0;
+	return i<0 ? i : l0;
+}
+
+int vswprintf(wchar_t *s, size_t n, const wchar_t *fmt, va_list ap)
+{
+	int r;
+	FILE f;
+	unsigned char buf[256];
+	struct cookie c = { s, n-1 };
+
+	memset(&f, 0, sizeof(FILE));
+	f.lbf = EOF;
+	f.write = sw_write;
+	f.buf_size = sizeof buf;
+	f.buf = buf;
+	f.owner = -1;
+	f.cookie = &c;
+	if (!n) {
+		return -1;
+	} else if (n > INT_MAX) {
+		errno = EOVERFLOW;
+		return -1;
+	}
+	r = vfwprintf(&f, fmt, ap);
+	__oflow(&f);
+	return r>=n ? -1 : r;
+}