This is from old version. I think it has something to do with command line parse. This loop_size is set with "-b" and followed by "-1 to -4", while "-b" is also used to set fixed packet size. When the value following "-b" is larger than 0, it specify a fixed packet size, otherwise, it should between "-1" to "-4" indicating loop through different packet size... If you think -1 to -4 is terrible, we could change it..