sub id2path3 {
    my $id = shift || return '';
    my $path;
    my( $pat, $bit ) = $id < 1e6 ? ( '%06u', '..' ) : ( '%09u', '...' );
    $path = sprintf $pat, $id;
    $path =~ s[($bit)($bit)$][/$1/$2];
    return $path;
}