year/month/day upload dirc

how to customize upload directory with
year/month/day
im try to edit this code but not working properly, hope someone guide me thanks

// Generate the yearly and monthly dirs
if ( !$time )
	$time = current_time( 'mysql' );
	$y = substr( $time, 0, 4 );
	$m = substr( $time, 5, 2 );
	$d = substr( $time, 6, 2);
	$subdir = "/$y/$m/$d";
}