diff --git a/srv/format.c b/srv/format.c
index f3bc2c1..ec4de76 100644
--- a/srv/format.c
+++ b/srv/format.c
@@ -21,9 +21,9 @@ static uint32_t buffer_write(uint8_t byte, void* arg);
 static uint32_t render_format(FormatCallback callback, void* arg,
 		const char* restrict format, va_list va);
 static uint32_t render_signed(FormatCallback callback, void* arg,
-		int32_t number, uint8_t base);
+		int32_t number, uint8_t base, uint8_t width, bool zero_padding);
 static uint32_t render_unsigned(FormatCallback callback, void* arg,
-		uint32_t number, uint8_t base);
+		uint32_t number, uint8_t base, uint8_t width, bool zero_padding);
 
 
 //--local variables-------------------------------------------------------------
@@ -74,7 +74,9 @@ static uint32_t buffer_write(uint8_t byte, void* arg)
 static uint32_t render_format(FormatCallback callback, void* arg,
 		const char* restrict format, va_list va)
 {
+	uint8_t width = 0;
 	bool in_format = false;
+	bool zero_padding = false;
 
 	for (const char* c = format; *c != '\0'; ++c) {
 
@@ -97,22 +99,40 @@ static uint32_t render_format(FormatCallback callback, void* arg,
 					}
 					break;
 				case 'i':
-					if (render_signed(callback, arg, va_arg(va, int32_t), 10)) {
+					if (render_signed(callback, arg, va_arg(va, int32_t),
+								10, width, zero_padding)) {
 						return 1;
 					}
 					break;
 				case 'u':
-					if (render_unsigned(callback, arg,
-								va_arg(va, uint32_t), 10)) {
+					if (render_unsigned(callback, arg, va_arg(va, uint32_t),
+								10, width, zero_padding)) {
 						return 1;
 					}
 					break;
 				case 'x':
-					if (render_unsigned(callback, arg,
-								va_arg(va, uint32_t), 16)) {
+					if (render_unsigned(callback, arg, va_arg(va, uint32_t),
+								16, width, zero_padding)) {
 						return 1;
 					}
 					break;
+				case '0':
+					if (width == 0) {
+						zero_padding = true;
+						continue;
+					}
+				case '1':
+				case '2':
+				case '3':
+				case '4':
+				case '5':
+				case '6':
+				case '7':
+				case '8':
+				case '9':
+					width *= 10;
+					width += (*c - '0');
+					continue;
 				default:
 					//TODO manage error
 					break;
@@ -121,6 +141,8 @@ static uint32_t render_format(FormatCallback callback, void* arg,
 			switch (*c) {
 				case '%':
 					in_format = true;
+					zero_padding = false;
+					width = 0;
 					continue;
 				default:
 					if (callback(*c, arg)) return 1;
@@ -135,23 +157,70 @@ static uint32_t render_format(FormatCallback callback, void* arg,
 }
 
 static uint32_t render_signed(FormatCallback callback, void* arg,
-		int32_t number, uint8_t base)
+		int32_t number, uint8_t base, uint8_t width, bool zero_padding)
 {
+	if (width > 0 && number < 0) {
+		--width;
+	}
+
+	if (width > 0) {
+		uint32_t abs_number;
+		if (number < 0) {
+			abs_number = -number;
+		} else {
+			abs_number = number;
+		}
+
+		uint32_t base_power = base;
+		while (width > 0 && base_power <= abs_number) {
+			base_power *= base;
+			--width;
+		}
+		if (width > 0) {
+			--width;
+		}
+
+		while (width > 0) {
+			--width;
+			if (zero_padding) {
+				if (callback('0', arg)) return 1;
+			} else {
+				if (callback(' ', arg)) return 1;
+			}
+		}
+	}
+
 	if (number < 0) {
 		callback('-', arg);
 		number = -number;
 	}
 
-	return render_unsigned(callback, arg, (uint32_t)number, base);
+	return render_unsigned(callback, arg, (uint32_t)number, base, 0,
+			zero_padding);
 }
 
 static uint32_t render_unsigned(FormatCallback callback, void* arg,
-		 uint32_t number, uint8_t base)
+		 uint32_t number, uint8_t base, uint8_t width, bool zero_padding)
 {
 	uint32_t base_power = base;
 
 	while (base_power <= number) {
 		base_power *= base;
+		if (width > 0) {
+			--width;
+		}
+	}
+	if (width > 0) {
+		--width;
+	}
+
+	while (width > 0) {
+		--width;
+		if (zero_padding) {
+			if (callback('0', arg)) return 1;
+		} else {
+			if (callback(' ', arg)) return 1;
+		}
 	}
 
 	while (base_power > 1) {