2 files changed, 85 insertions, 0 deletions
diff --git a/lib/libc/include/stdio.h b/lib/libc/include/stdio.h
index b19230c..e701de0 100644
--- a/lib/libc/include/stdio.h
+++ b/lib/libc/include/stdio.h
@@ -31,6 +31,7 @@
 #define _STDIO_H
 
 #include <stddef.h>
+#include <stdarg.h>
 
 #define EOF (int)-1
 
@@ -64,4 +65,6 @@ int puts(const char *s);
 int fflush(FILE *stream);
 int fclose(FILE *stream);
 
+int vsnprintf(char *s, size_t size, const char *fmt, va_list ap);
+
 #endif  /* !_STDIO_H */
diff --git a/lib/libc/src/stdio/vsnprintf.c b/lib/libc/src/stdio/vsnprintf.c
new file mode 100644
index 0000000..6cc0a04
--- /dev/null
+++ b/lib/libc/src/stdio/vsnprintf.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <stdio.h>
+
+static inline void
+printc(char *buf, size_t size, size_t *off, char c)
+{
+    if (*off < size - 1) {
+        buf[(*off)++] = c;
+    }
+    buf[*off] = 0;
+}
+
+static void
+printstr(char *buf, size_t size, size_t *off, const char *s)
+{
+    while (*off < size - 1 && *s != '\0') {
+        buf[(*off)++] = *(s)++;
+    }
+    buf[*off] = 0;
+}
+
+int
+vsnprintf(char *s, size_t size, const char *fmt, va_list ap)
+{
+    size_t tmp_len, off = 0;
+    ssize_t num = 0;
+    char c, c1;
+    const char *tmp_str;
+
+    while (off < (size - 1)) {
+        while (*fmt && *fmt != '%') {
+            printc(s, size, &off, *fmt++);
+        }
+
+        if (*(fmt)++ == '\0' || off == size - 1) {
+            return off;
+        }
+
+        c = *fmt++;
+        switch (c) {
+        case 'c':
+            c1 = (char)va_arg(ap, int);
+            printc(s, size, &off, c1);
+            break;
+        case 's':
+            tmp_str = va_arg(ap, const char *);
+            printstr(s, size, &off, tmp_str);
+            break;
+        }
+    }
+
+    return 0;
+}