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From: keith@apple.UUCP (Keith Rollin)
Newsgroups: rec.games.misc,comp.sys.apple
Subject: Re: zork decoding
Message-ID: <6663@apple.UUCP>
Date: Sun, 8-Nov-87 15:11:59 EST
Article-I.D.: apple.6663
Posted: Sun Nov  8 15:11:59 1987
Date-Received: Tue, 10-Nov-87 04:19:35 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: keith@apple.UUCP (Keith Rollin)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 31
Keywords: zork,infocom
Xref: mnetor rec.games.misc:1110 comp.sys.apple:3226

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.
>

It doesn't seem like any of us can! I, too, spent some of the vigor of my
youth trying to comment the assembly code of one of InfoCom's interpreter. 
One feature that (I think) I found concerned this switching that Dyon just 
mentioned. Some of the more common words (about 180 in Hitchhiker's) are
stored separate from the rest of the encoded text. These special words
(common objects like 'towel', 'Arthur', etc. and words like 'the', 'into',
and so on) are then referenced by one of these 5 bit symbols. That way,
you can squeeze a whole word into just 5 bits.

To make matters worse, InfoCom has developed many different interpreters
(I assume tthey have at least 7, as I have seen versions A, B, and G). With
any bit of bad luck, they will have changed the encoding algorithm somewhere
along the way...

-- 

Keith Rollin                                               amdahl\
Sales Technical Support                               pyramid!sun !apple!keith
Apple Computer                                             decwrl/

Disclaimer: I read this board for fun, not profit. Anything I say is from the
            result of reading magazines, hacking, and soaking my head in acid.