This one is trying to calculate the total (t) bytes on the interface. The calculation was just weird - the number of bytes passed in plus the number of bytes blocked out. IMHO it has to be simple - total bytes passed plus total bytes blocked.
I think these are just cut-paste-change errors that slipped in because there are so many lines of similar calculations that it is really easy for the original coder to go into brain-fade mode while generate 1000 lines like this. I reviewed all the approx 1000 lines of this stuff looking for other similar cut-paste-change errors and these are all I could spot.