sub id2path_boftx
{
    my $id = shift or return q();

#    my $chunk_length = length $id > 6 ? 3 : 2;
    my $chunk_length = $id < 1e6 ? 2 : 3;
    my $path_pat = '%0' . $chunk_length . 'd';
    $path_pat = join('/', $path_pat, $path_pat, $path_pat);

    my $chunk_power = 10 ** $chunk_length;

    my $path = sprintf $path_pat, $id / ($chunk_power ** 2),
      ($id / $chunk_power) % $chunk_power, $id % $chunk_power;

    return $path;
}