rms@GNU.AI.MIT.EDU (Richard Stallman) (04/13/91)
An Emacs mode to examine zip files probably must do lzw uncompression, which means that distributing one could get you lawsuit threats from Unisys. I don't know what lzh format is; it may have the same problem, or it may not, depending on what kind of algorithm is needed to work with those files. In the long run, the community will be better off if it makes a clean break and eliminates entirely the use of patented algorithms (unless we can overturn the patents). For more information on the problems of software patents, send mail to league@prep.ai.mit.edu.
EVERHART@arisia.dnet.ge.com (04/15/91)
Lharc sources (which create .lzh files) are readily available. The algorithm is adaptive Huffman coding, not LZW; that much is clear from the sources. The code has been dedicated, I believe, to public domain. It originated, by the way, in Japan, though the comments have by now been translated to English. The commenter who replied he thinks lharc uses LZW as an algorithm has obviously not looked at the code. ZIP uses different algorithms. I've heard comments about the zip system using two algorithms, one of which is lzw, in series. However this remains hearsay and I have not examined the pd unzip programs to check. Lharc performs comparably to Zip, but not identically. In fact it tends to compress better. I have not examined the lzw patent, but if it is specific to the lzw algorithm, I'd say lharc is and will remain in the clear. Its' roots appear to lie in some PD code off JApanese bulletin board systems, and is a recent development. Incidentally, I find lharc archives easier to work with than compressed tar, since extraction of individual files is trivial, and directories can be listed without decompressing everything. I believe you'll find the code needed to pull apart lharc files considerably more complex than needed to do LZW uncompression, but have not checked this in any detail. Lharc source for unix have appeared in comp.sources.misc, I believe, or alt.sources. Glenn Everhart