Initial version

1 files changed, 50 insertions, 0 deletions

diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c
new file mode 100644
index 0000000..409b9c8
--- /dev/null
+++ b/src/stdio/vsnprintf.c
@@ -0,0 +1,50 @@
+#include "stdio_impl.h"
+#include <limits.h>
+#include <string.h>
+#include <errno.h>
+#include <stdint.h>
+
+struct cookie {
+	char *s;
+	size_t n;
+};
+
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+
+static size_t sn_write(FILE *f, const unsigned char *s, size_t l)
+{
+	struct cookie *c = f->cookie;
+	size_t k = MIN(c->n, f->wpos - f->wbase);
+	if (k) {
+		memcpy(c->s, f->wbase, k);
+		c->s += k;
+		c->n -= k;
+	}
+	k = MIN(c->n, l);
+	if (k) {
+		memcpy(c->s, s, k);
+		c->s += k;
+		c->n -= k;
+	}
+	*c->s = 0;
+	f->wpos = f->wbase = f->buf;
+	/* pretend to succeed, even if we discarded extra data */
+	return l;
+}
+
+int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
+{
+	unsigned char buf[1];
+	char dummy[1];
+	struct cookie c = { .s = n ? s : dummy, .n = n ? n-1 : 0 };
+	FILE f = {
+		.lbf = EOF,
+		.write = sn_write,
+		.lock = -1,
+		.buf = buf,
+		.cookie = &c,
+	};
+
+	*c.s = 0;
+	return vfprintf(&f, fmt, ap);
+}