[Syzygies]

Arithmetic coding is a drop-in replacement for Huffman coding that saves binary roundoff. It's less known because it was patented, and the (short) code to implement requires optimizing a tricky 1.0000 versus 0.9999 issue (in binary).

The usual application involves letter frequencies without context. Rather than a trie for deterministic context, one could in far less space compute a hidden Markov chain of small but effective dimension, to generate the probabilities for arithmetic coding.

[quicktwo]

Thanks, I'll look into it. This case is interesting though, because the Gameboy doesn't even have native mul/div operators, so I suspect that Huffman coding is as fancy as you're going to get while still having a small and efficient decoder that isn't taking up more space than its saving.