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An excellent resource for data compression compiled by Mark Nelson that includes libraries, documentations, and source code for Huffman Coding, Adaptive Huffman Coding, LZW, Arithmetic Coding, etc.

Adaptive Arithmetic Coding source code:

The Theory of Data Compression webpage at

This site introduces basic theories behind both lossless and lossy data compression. Shannon's original 1948 paper on information theory can be downloaded from this site as well.

The FAQ for the comp.compression and comp.compression.research groups can be found at

This FAQ answers most of the commonly asked questions about data compression in general.

A set of applets for lossless compression contained at the link ("Squeeze Page")

These applets very effectively show interactive demonstrations of Adaptive Huffman, LZW, and so on. (As well, and impressively, this webpage is the fruit of a student final project in a third-year undergraduate Multimedia course based on the material in this text.)

Finally, a good introduction to Arithmetic coding is contained in the link

Fundamentals of Multimedia