sub encode_2 {
  $_=sprintf "%04d", shift;
  /(\d)(\d)(\d)(\d)/;
  return chr($1<<4|$2).chr($3<<4|$4);
}

sub encode_3 {
  $_=sprintf "%06d", shift;
  /(\d)(\d)(\d)(\d)(\d)(\d)/;
  return chr($1<<4|$2).chr($3<<4|$4).chr($5<<4|$6);
}

sub decode_2 {
  ($a,$c)=unpack("A" x 2, shift);
  return (ord($a)>>4)*1000+(ord($a)&0x0f)*100+(ord($c)>>4)*10+(ord($c)&0x0f);
}

sub decode_3 {
  ($a,$b,$c)=unpack("A" x 3, shift);
  return (ord($a)>>4)*100000+(ord($a)&0x0f)*10000+(ord($b)>>4)*1000+(ord($b)&0x0f)*100+(ord($c)>>4)*10+(ord($c)&0x0f);
}