uptime -- tells how long the system has been running

printf.c

@@ -0,0 +1,77 @@
+/* printf.c -- format and print data    */
+/* Copyright (c) 2020 Renaud Fivet      */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include "system.h" /* kputc(), kputs() */
+
+static int kputu( unsigned u, unsigned d) {
+    char s[ 12] ;                   /* room for 11 octal digit + EOS */
+    char *p = &s[ sizeof s - 1] ;   /* point to last byte */
+
+    *p = 0 ;                        /* null terminated string */
+    do {
+        unsigned r = u % d ;
+        u /= d ;
+        *--p = "0123456789ABCDEF"[ r] ;
+    } while( u) ;
+
+    return kputs( p) ;
+}
+
+static int kputi( int i) {
+    int flag = i < 0 ;
+    if( flag) {
+        i = -i ;
+        kputc( '-') ;
+    }
+
+    return flag + kputu( i, 10) ;
+}
+
+int printf( const char *fmt, ...) {
+    va_list ap ;
+    int cnt = 0 ;
+    int c ; /* current char in format string */
+
+    va_start( ap, fmt) ;
+    while( ( c = *fmt++) != 0)
+        if( c != '%') {
+            cnt += 1 ; kputc( c) ;
+        } else if( ( c = *fmt++) == 0) {
+            cnt += 1 ; kputc( '%') ;
+            break ;
+        } else
+            switch( c) {
+            case 'c':
+                cnt += 1 ; kputc( va_arg( ap, int /* char */)) ;
+                break ;
+            case 'o':
+                cnt += kputu( va_arg( ap, unsigned), 8) ;
+                break ;
+            case 'u':
+                cnt += kputu( va_arg( ap, unsigned), 10) ;
+                break ;
+            case 'x':
+            case 'X':
+                cnt += kputu( va_arg( ap, unsigned), 16) ;
+                break ;
+            case 'i':
+            case 'd':
+                cnt += kputi( va_arg( ap, int)) ;
+                break ;
+            case 's':
+                cnt += kputs( va_arg( ap, char *)) ;
+                break ;
+            default:
+                cnt += 1 ; kputc( '%') ;
+                /* fallthrough */
+            case '%':
+                cnt += 1 ; kputc( c) ;
+            }
+
+    va_end( ap) ;
+    return cnt ;
+}
+
+/* end of printf.c */