Re: Wolfenstein 3D levels

[nparker@inferno.uoregon.edu (Neil Parker)]

In article <%tsK.86$Gn4.556416@ptah.visi.com>,
Nathan Mates <nathan@visi.com> wrote:
>In article <19980302043301.XAA25228@ladder02.news.aol.com>,
>Supertimer <supertimer@aol.com> wrote:
>>[...]
>>Why do .sit decoders break so often but .zip decoders don't?  .zip
>>is a proprietary format of pkZip, right?  Do they just don't update it
>>as much?
>
>   Initially developed by pkZip, but uses standard LZW compression
>(same as in .gif) so any good reference on compression should have the
>specs. From there, it's a simple matter of a little header for table
>of contents and each file and possibly some other stuff. Not rocket
>science by a long shot.

Sorry to pick nits here, but Zip compression (at least in its latest
incarnation) is *not* the same as GIF compression.  Zip uses an LZ77
algorithm, and then does Huffman compression in its output codes.  GIF uses
an LZ78 algorithm, quite similar to the UNIX "compress" algorithm.  (The
old, non-proprietary version of .sit, by the way, used the UNIX "compress"
algorithm verbatim, so writing a UNIX decompresser for old .sit files is 
really easy...just strip off a header, and feed what's left to "uncompress".)

Yes, they'll both be in any good compression reference.  But they're usually
discussed in different chapters...

               - Neil Parker
-- 
Neil Parker, nparker@inferno.uoregon.edu, nparker@axis.llx.com,
http://axis.llx.com/~nparker/     (Note new addresses and home page!)

Unsolicited commerical e-mail is not welcome, and will be discarded unread.