From fc00c656c96528112d05cf0edf8631bd5eaea446 Mon Sep 17 00:00:00 2001
From: Kacper <kacper@mail.openlinux.dev>
Date: Sun, 7 Dec 2025 20:10:31 +0100
Subject: Add build system scaffolding and libc headers

---
 lib/libc/stdio/vsnprintf.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 lib/libc/stdio/vsnprintf.c

(limited to 'lib/libc/stdio/vsnprintf.c')

diff --git a/lib/libc/stdio/vsnprintf.c b/lib/libc/stdio/vsnprintf.c
new file mode 100644
index 00000000..b7a59064
--- /dev/null
+++ b/lib/libc/stdio/vsnprintf.c
@@ -0,0 +1,45 @@
+#include <io.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdatomic.h>
+
+int vsnprintf(char *restrict s, size_t n, const char *restrict format,
+	      va_list ap)
+{
+	int r;
+	FILE f;
+
+	if (n == 0) {
+		return 0;
+	}
+
+	if (!s) {
+		return -1;
+	}
+
+	memset(&f, 0, sizeof(f));
+	f.fd = -1;
+	f.flags = O_WRONLY;
+	f.type = _IONBF;
+	atomic_flag_clear(&f.lock);
+	f.buf = s;
+	f.buf_size = n;
+	f.buf_len = 0;
+	f.buf_pos = 0;
+	f.eof = 0;
+	f.unget_cnt = 0;
+	f.offset = 0;
+	f.next = NULL;
+
+	r = vfprintf(&f, format, ap);
+
+	if (f.buf_len < n) {
+		s[f.buf_len] = '\0';
+	} else if (n > 0) {
+		s[n - 1] = '\0';
+		r = n - 1;
+	}
+
+	return r;
+}
-- 
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