From 6b0d42789839614d19a0406b596326f2c8227f8b Mon Sep 17 00:00:00 2001
From: Ali Mashtizadeh <mashti@cs.stanford.edu>
Date: Sun, 13 Jul 2014 14:09:36 -0700
Subject: [PATCH] Improving libc and printf

---
 sys/kern/libc.c   | 14 +++++++++++
 sys/kern/printf.c | 61 ++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/sys/kern/libc.c b/sys/kern/libc.c
index 092e1ef..8b5afe5 100644
--- a/sys/kern/libc.c
+++ b/sys/kern/libc.c
@@ -4,9 +4,23 @@
  * All rights reserved.
  */
 
+#include <stddef.h>
 #include <stdint.h>
 #include <string.h>
 
+char *
+strchr(const char *s, int c)
+{
+    int i;
+    for (i = 0; ; i++)
+    {
+	if (s[i] == c)
+	    return (char *)s + i;
+	if (s[i] == '\0')
+	    return NULL;
+    }
+}
+
 char *
 strcpy(char *to, const char *from)
 {
diff --git a/sys/kern/printf.c b/sys/kern/printf.c
index c0b672e..12aff0f 100644
--- a/sys/kern/printf.c
+++ b/sys/kern/printf.c
@@ -4,8 +4,9 @@
  * All rights reserved.
  */
 
-#include <stdarg.h>
 #include <stdint.h>
+#include <stdarg.h>
+#include <string.h>
 
 #include <kassert.h>
 
@@ -48,12 +49,14 @@ static void printnum(void (*func)(int, void*),void *handle,
         } while (num /= base);
     }
 
-    // Print Spacers
+    // Print spacers (pre-number)
     spaces = width - (p - buf);
-    while (spaces > 0)
-    {
-        func(padc, handle);
-        spaces--;
+    if (padc == ' ' || padc == '0') {
+	while (spaces > 0)
+	{
+	    func(padc, handle);
+	    spaces--;
+	}
     }
 
     // Print Number
@@ -61,6 +64,15 @@ static void printnum(void (*func)(int, void*),void *handle,
         p--;
         func((int)*p, handle);
     }
+
+    // Print spacers (post-number)
+    if (padc == '-') {
+	while (spaces > 0)
+	{
+	    func(' ', handle);
+	    spaces--;
+	}
+    }
 }
 
 int kvprintf(char const *fmt, void (*func)(int,void *), void *handle, va_list ap)
@@ -117,14 +129,35 @@ again:
             case 'c':
                 func(va_arg(ap, int) & 0xff, handle);
                 break;
-            case 's':
-                p = va_arg(ap, char *);
-                ASSERT(p != 0);
-                while (*p != '\0')
-                {
-                    func(*p++, handle);
-                }
-                break;
+            case 's': {
+		int spaces;
+
+		p = va_arg(ap, char *);
+		ASSERT(p != 0);
+		spaces = width - strlen(p);
+
+		if (padc == ' ') {
+		    while (spaces > 0)
+		    {
+			func(' ', handle);
+			spaces--;
+		    }
+		}
+
+		while (*p != '\0')
+		{
+		    func(*p++, handle);
+		}
+
+		if (padc == '-') {
+		    while (spaces > 0)
+		    {
+			func(' ', handle);
+			spaces--;
+		    }
+		}
+		break;
+            }
             case 'd':
                 num = getint(ap, lflag);
                 if (num < 0) {