2 files changed, 53 insertions, 9 deletions

diff --git a/kernel/kmain.c b/kernel/kmain.c
index a854c12..793ca17 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -8,5 +8,5 @@ void kmain(void) {
   printf("Kernel booting...\n");
   printf("Kernel booted!\n");
 
-  printf("Number: %x\n", 0x80);
+  printf("Number: %04x\n", 0x18C);
 }
diff --git a/kernel/vsprintf.c b/kernel/vsprintf.c
index 20489f4..93a2ada 100644
--- a/kernel/vsprintf.c
+++ b/kernel/vsprintf.c
@@ -8,22 +8,51 @@ enum TYPE {
   TYPE_STRING = 4
 };
 
-static void hex(char **str, int x) {
-  int n;
+enum FLAGS {
+  FL_ZERO     = 1, /* zero padded */
+};
+
+static void hex(char **str, char flags, int fwidth, int size, int x) {
+  int i, y, len;
+  char c;
   char *s = "0x";
 
   while(*s)
     *(*str)++ = *s++;
 
-  n = sizeof(x) << 1;
-  while(n--) {
-    *(*str)++ = ((unsigned int) x >> 28) + 0x30;
+  /* calculate the number of digits */
+  len = 0;
+  y = x;
+  for(i = 0; i < sizeof(y) << 1; i++) {
+    c = ((unsigned int) y >> 28);
+    if(c)
+      len++;
+    y = y << 4;
+  }
+
+  /* print the padding characters (if any) */
+  c = ' ';
+  if(flags & FL_ZERO)
+    c = '0';
+  for(i = 0; i < fwidth - len; i++)
+    *(*str)++ = c;
+
+  /* actually print the digits */
+  for(i = 0; i < sizeof(x) << 1; i++) {
+    c = ((unsigned int) x >> 28) + '0';
+    if(c > '9')
+      c += 7;
+
+    if(c != '0')
+      *(*str)++ = c;
+
     x = x << 4;
   }
 }
 
 int vsprintf(char *str, char *fmt, va_list ap) {
-  int x;
+  int x, fwidth;
+  char flags;
   char *s;
   char *start = str;
   uint8_t type;
@@ -35,8 +64,10 @@ int vsprintf(char *str, char *fmt, va_list ap) {
     }
 
     type = 0;
+    flags = 0;
+    fwidth = 0;
 
-    fmt++;    
+    fmt++;
     while(1) {
       switch(*fmt) {
         case 's':
@@ -50,9 +81,22 @@ int vsprintf(char *str, char *fmt, va_list ap) {
           type = TYPE_HEX;
           break;
         default:
+          /* the first zero enables zero-padding */
+          if(*fmt == '0' && !fwidth) {
+            flags |= FL_ZERO;
+            goto next;;
+          }
+
+          /* subsequent numbers indicate field width */
+          if(*fmt >= '0' && *fmt <= '9') {
+            fwidth = (fwidth * 10) + (*fmt - '0');
+            goto next;;
+          }
+
           goto done;
           break;
       }
+next:
       fmt++;
     }
 
@@ -66,7 +110,7 @@ done:
         break;
       case TYPE_HEX:
         x = va_arg(ap, int);
-        hex(&str, x);
+        hex(&str, flags, fwidth, 4, x);
         break;
     }
   }