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From: knutsen@aramis.rutgers.edu (Mark Knutsen)
Newsgroups: comp.sys.atari.8bit
Subject: Re: ARC file format?
Message-ID: <1688@aramis.rutgers.edu>
Date: Sat, 26-Sep-87 20:05:11 EDT
Article-I.D.: aramis.1688
Posted: Sat Sep 26 20:05:11 1987
Date-Received: Sun, 27-Sep-87 11:38:16 EDT
References: <870925172005.1.JRD@GRACKLE.SCRC.Symbolics.COM>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 32

In article <870925172005.1.JRD@GRACKLE.SCRC.Symbolics.COM> jrd@STONY-BROOK.SCRC.SYMBOLICS.COM (John R. Dunning) writes:

> Does anyone know the format of .ARC files, as hacked by the ARCX and ARC
> that were posted a while ago?  
>   Failing that, does anyone know how to contact the authors?

  I've read articles on the format of .ARC files, but none were in-depth
enough for your purposes.  In a nutshell, however, ARC determines
which of four compression techniques to use on each file it's asked to
archive, compresses them, and sticks them together.  The 8-bit version
of ARC never uses the 4th technique ("crunching") due to memory
restrictions, but the 8-bit ARCX can unARC files compressed with all
four techniques.
  I believe that the 8-bit ARC and ARCX were written in Lightspeed C
by the authors of that language, who frequent the GEnie Atari
Roundtable.  I can recall reading a message by one of the authors
explaining that it's pointless to attempt to improve on the speed of
the 8-bit ARC.  It's a very calculation-intensive application, and the
Atari is only so fast at these things.
  Still, if you're willing to tackle the task in assembler, you may be
able to speed it up a bit...

  On another note: I have discovered by much experimentation that ARC
1.2 tends to compress text files such that they contain an extra copy
of their last byte when unARCed.  This causes ARCX to generate
checksum errors, which can safely be ignored.  Regardless, I find it
safest to ARC things with ARC 1.1 and deARC them with ARCX 1.2.
-- 
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