As part of getting a handle on OO in picolisp I implemented a basic arithmetic coder. This is just the Coder and a simple adaptive model.
https://github.com/thinknlive/picolisp-acdc It is slower than I expected it to be, but I was focused more on getting the implementation correct in this pass. Any optimization suggestions welcome. Maybe not use OO at all and leverage namespaces. /Lindsay