There's lots of literature on quantizing weights (including trits and binary) going back 15+ years. Nothing to hand right now but it's all on arxiv.

The relevant trit arithmetic should be on display in the linked repo (I haven't checked). Or try working it out for the uncompressed 2 bit form with a pen and paper. It's quite trivial. Try starting with a couple bitfields (inputs and weights), a couple masks, and see if you can figure it out without any help.