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From: reeves@amd.AMD.COM (James Reeves)
Newsgroups: rec.games.misc,comp.sys.apple
Subject: Re: zork decoding
Message-ID: <4651@amd.AMD.COM>
Date: Tue, 10-Nov-87 10:27:21 EST
Article-I.D.: amd.4651
Posted: Tue Nov 10 10:27:21 1987
Date-Received: Thu, 12-Nov-87 22:58:31 EST
References: <2804@batcomputer.tn.cornell.edu> <7639@reed.UUCP> <434@ur-tut.UUCP> <436@ur-tut.UUCP> <2846@batcomputer.tn.cornell.edu>
Reply-To: reeves@amd.UUCP (James Reeves)
Organization: Advanced Micro Devices
Lines: 31
Keywords: zork,infocom
Xref: mnetor rec.games.misc:1130 comp.sys.apple:3251

In article <2846@batcomputer.tn.cornell.edu> dyon@tcgould.tn.cornell.edu (Dyon Anniballi) writes:
>
>  Back in the old days, a friend and I made some headway in disassembling
>the Zork interpreter.  If I recall correctly, they used 5 bits per char.
>for encoding text.  Only 32 combinations you say?  Well, the first 26
>were the lower case alphabet, and the other 6 were for switching character
>sets.  That is, one would switch to upper case, another to punctuation type
>stuff, etc.  I don't remember the specifics though, sorry.
>
>-- 
>--Dyon Anniballi

I'm sorry to get involved in this but this last statement was truly 
ridiculous. with 2^5 you have 32 combinations. That's it. Done. No more.

I have spent hours trying to decode the Infocom files and have found some very
interesting thing. First of all I am almost positive that they DO NOT USE 
A 5 bit encodeing scheme. (Actually I should say that they do not solely
use a 5 nit encoding scheme) I have played around weth some of the bits in
the .DAT file and watched how the text changed. It definitely didn't react
in a way that would indicate a 5 bit encoding scheme. It think that there
is a tokenizing scheme as well as a compression method. When I attempted 
to debug the code I found some nasty GOTCHAs in the code. The loop for creating a text sentence apparently pushes a whole lot of SH*T on the stack and then
goes through some calculations as it pops it off. I also seem to remeber that
there is some initial code that scans the memory for INT 3 instructions
that make it very difficult to place breakpoints in the code.

Anyway, the person who wrote ZORK Tools should be able to help 
where is he/she when you need them.

James