From 611f098bc38256adf2efadbc0b98138a5b4489de Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.xyz>
Date: Sun, 17 Jan 2021 20:18:37 -0600
Subject: kernel: implement a basic printf function

Implement a basic printf function using primitives from the TTY library.

Signed-off-by: Danny Holman <dholman@gymli.xyz>
---
 include/kernel/io.h | 10 ++++++++
 kernel/io.c         | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 include/kernel/io.h
 create mode 100644 kernel/io.c

diff --git a/include/kernel/io.h b/include/kernel/io.h
new file mode 100644
index 0000000..bef87af
--- /dev/null
+++ b/include/kernel/io.h
@@ -0,0 +1,10 @@
+#ifndef IO_H
+#define IO_H
+
+#include <kernel/tty.h>
+#include <stdarg.h>
+
+int vprintf(const char *fmt, va_list args);
+int printf(const char *fmt, ...);
+
+#endif
diff --git a/kernel/io.c b/kernel/io.c
new file mode 100644
index 0000000..ca787b3
--- /dev/null
+++ b/kernel/io.c
@@ -0,0 +1,72 @@
+#include <kernel/io.h>
+#include <kernel/string.h>
+
+char* convert(unsigned int num, int base) {
+        static char rep[] = "0123456789ABCDEF";
+        static char buffer[50];
+        char *ptr;
+
+        ptr = &buffer[49];
+        *ptr = '\0';
+
+        do {
+                *--ptr = rep[num%base];
+                num /= base;
+        } while (num != 0);
+
+        return ptr;
+}
+
+int vprintf(const char *fmt, va_list args) {
+        char *traverse;
+        char *s;
+        int i;
+
+        for (traverse = fmt; *traverse != '\0'; traverse++) {
+                if (*traverse != '%') {
+                        tty_putchar(*traverse);
+                        continue;
+                } else {
+                        traverse++;
+                }
+
+                switch (*traverse) {
+                        case 'c':
+                                i = va_arg(args, int);
+                                tty_putchar(i);
+                                break;
+                        case 'd':
+                                i = va_arg(args, int);
+                                if (i < 0) {
+                                        i = -i;
+                                        tty_putchar('-');
+                                }
+                                tty_writestring(convert(i, 10));
+                                break;
+                        case 'o':
+                                i = va_arg(args, unsigned int);
+                                tty_writestring(convert(i, 8));
+                                break;
+                        case 's':
+                                s = va_arg(args, char*);
+                                tty_writestring(s);
+                                break;
+                        case 'x':
+                                i = va_arg(args, unsigned int);
+                                tty_writestring(convert(i, 16));
+                                break;
+                }
+        }
+        return 0;
+}
+
+int printf(const char *fmt, ...) {
+        va_list args;
+        int done;
+
+        va_start(args, fmt);
+        done = vprintf(fmt, args);
+        va_end(args);
+
+        return done;
+}
-- 
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