This ftp site contains arithmetic coding source from Michael Schindler. The library code consists of a a byte oriented arithmetic coder. The arithmetic coder is based on Alstair Moffat’s paper “Arithmetic Coding Revisited,” presented at the Data Compression Conference 95 (Snowbird, UT). The source is stored in both tar.z and zip format. The 1.101 release has a bug fix at the end of the encoder.
For new versions see http://www.compressconsult.com/rangecoder/

ftp://eiunix.tuwien.ac.at/pub/michael/arith/