diff --git a/printf.c b/printf.c
index 8deb74d..13b0567 100644
--- a/printf.c
+++ b/printf.c
@@ -1,39 +1,94 @@
-/* printf.c -- format and print data    */
-/* Copyright (c) 2020 Renaud Fivet      */
+/* printf.c -- format and print data
+** Copyright (c) 2020-2021 Renaud Fivet
+** v3: %[flags][width]type
+** v2: zero padding and uppercase/lowercase for hexadecimal
+** v1: type=c,u,x,X,i,d,s,%
+*/
 
 #include <stdarg.h>
 #include <stdio.h>
+#include <string.h>
 #include "system.h" /* kputc(), kputs() */
 
-static int kputu( unsigned u, unsigned d, int padlen, char fmt) {
-    char s[ 12] ;                   /* room for 11 octal digit + EOS */
-    char *p = &s[ sizeof s - 1] ;   /* point to last byte */
+size_t strlen( const char *s) {
+    const char *end = s - 1 ;
+    while( *++end) ;
 
-    *p = 0 ;                        /* null terminated string */
-    fmt = fmt & 0x20 ;              /* set uppercase bit */
-    do {
-        unsigned r = u % d ;
-        u /= d ;
-        *--p = "0123456789ABCDEF"[ r] | fmt ;
-        padlen -= 1 ;
-    } while( u) ;
-
-    while( padlen-- > 0) {
-        kputc( '0') ;
-        u += 1 ;        /* use u to calculate output length */
-    }
-
-    return u + kputs( p) ;
+    return end - s ;
 }
 
-static int kputi( int i) {
-    int flag = i < 0 ;
-    if( flag) {
-        i = -i ;
-        kputc( '-') ;
+#define ZEROPAD     (1 << 3)
+#define LEFTALIGN   (3 << 2)
+#define LEFTMASK    4
+#define PLUSSIGN    (1 << 1)
+#define BLANKSIGN   (1 << 0)
+
+static const unsigned char base[] = {
+    16, /* Xx 0x58 0x78 */
+    10, /* iu 0x69 0x75 */
+    2,  /* b  0x62 unused */
+    8,  /* o  0x6F */
+} ;
+
+static const char signs[] = { 0, ' ', '+', '+'} ;
+
+static int kputpad( char c, int len) {
+    int cnt ;
+
+    if( len > 0) {
+        cnt = len ;
+        while( len--)
+            kputc( c) ;
+    } else
+        cnt = 0 ;
+
+    return cnt ;
+}
+
+static int kputu( unsigned u, int padlen, char fmt) {
+    char s[ 12] ;                   /* room for 11 octal digit + EOS */
+    char *p = &s[ sizeof s - 1] ;   /* point to last byte */
+    char signprefix ;
+
+    *p = 0 ;                        /* null terminated string */
+
+    int flags = padlen >> 28 ;
+    padlen &= 0x0FFFFFFF ;          /* clear flags */
+    if( fmt == 'i' && (0 > (int) u)) {
+        u = - (int) u ;
+        signprefix = '-' ;
+    } else
+        signprefix = signs[ flags & 3] ;
+
+    if( signprefix)
+        padlen -= 1 ;
+
+    unsigned d = base[ fmt & 3] ;
+    fmt = fmt & 0x20 ;              /* set uppercase bit */
+    do {
+        *--p = "0123456789ABCDEF"[ u % d] | fmt ;
+        padlen -= 1 ;
+        u /= d ;
+    } while( u) ;
+
+/* reuse u to calculate output length */
+    flags >>= 2 ;
+    if( !flags)     /* Right align */
+        u += kputpad( ' ', padlen) ;
+
+    if( signprefix) {
+        kputc( signprefix) ;
+        u += 1 ;
     }
 
-    return flag + kputu( i, 10, 0, 'u') ;
+    if( flags == (ZEROPAD >> 2))
+        u += kputpad( '0', padlen) ;
+
+    u += kputs( p) ;
+    if( flags == (LEFTALIGN >> 2))
+        u += kputpad( ' ', padlen) ;
+
+    return u ;
 }
 
 int printf( const char *fmt, ...) {
@@ -46,37 +101,77 @@ int printf( const char *fmt, ...) {
         if( c != '%') {
             cnt += 1 ; kputc( c) ;
         } else {
-            int len = 0 ;
+        /* %[flags][width]type */
+            int flags = 0 ;
+            int width = 0 ;
 
-            c = *fmt++ ;
-            while( c >= '0' && c <= '9') {
-                len = len * 10 + ( c - '0') ;
+        /* flags and width */
+            for( ;;) {
                 c = *fmt++ ;
+                switch( c) {
+                case ' ':
+                    flags |= BLANKSIGN ;
+                    continue ;
+                case '+':
+                    flags |= PLUSSIGN ;
+                    continue ;
+                case '-':
+                    flags |= LEFTALIGN ;
+                    continue ;
+                case '0':
+                    flags |= ZEROPAD ;
+                    continue ;
+                case '*':
+                    width = va_arg( ap, int) ;
+                    c = *fmt++ ;
+                    break ;
+                default:
+                    while( c >= '0' && c <= '9') {
+                        width = width * 10 + ( c - '0') ;
+                        c = *fmt++ ;
+                    }
+                }
+
+                break ;
             }
 
+        /* type */
             if( c == 0)
                 break ;
 
             switch( c) {
             case 'c':
+                flags >>= 2 ;
+                if( !flags) /* right aligned */
+                    cnt += kputpad( ' ', width - 1) ;
+
                 cnt += 1 ; kputc( va_arg( ap, int /* char */)) ;
+                if( flags == (LEFTALIGN >> 2))
+                    cnt += kputpad( ' ', width - 1) ;
+
                 break ;
+            case 'd':
+                c = 'i' ;
+                /* fallthrough */
+            case 'i':
             case 'o':
-                cnt += kputu( va_arg( ap, unsigned), 8, len, c) ;
-                break ;
             case 'u':
-                cnt += kputu( va_arg( ap, unsigned), 10, len, c) ;
-                break ;
             case 'x':
             case 'X':
-                cnt += kputu( va_arg( ap, unsigned), 16, len, c) ;
+                cnt += kputu( va_arg( ap, unsigned), width | flags << 28, c) ;
                 break ;
-            case 'i':
-            case 'd':
-                cnt += kputi( va_arg( ap, int)) ;
-                break ;
-            case 's':
-                cnt += kputs( va_arg( ap, char *)) ;
+            case 's': {
+                    char *argp = va_arg( ap, char *) ;
+                    flags >>= 2 ;
+                    if( !flags) /* right aligned */
+                        cnt += kputpad( ' ', width - strlen( argp)) ;
+
+                    int size = kputs( argp) ;
+                    cnt += size ;
+                    if( flags == (LEFTMASK >> 2))
+                        cnt += kputpad( ' ', width - size) ;
+                }
+
                 break ;
             default:
                 cnt += 1 ; kputc( '%') ;