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From: minow@mountn.dec.com (Martin Minow)
Newsgroups: comp.sys.mac
Subject: Re: Stuffit loses my files!!  Crystal Cave closed for repairs.
Message-ID: <958@mountn.dec.com>
Date: 17 Oct 89 12:59:47 GMT
References: <994@kosman.UUCP>
Reply-To: minow@mountn.UUCP (Martin Minow)
Organization: Digital Equipment Corporation
Lines: 24

In article <994@kosman.UUCP> kevin@kosman.UUCP (Kevin O'Gorman) says that
he had archived some source files using Stuffit, but when he extracts the
archive, Stuffit complains about "checksum errors" and bombs the Mac.

Welcome to Lempel-Ziv-Welch compression.  It compresses your file by an elegant
(and hard to describe) method.  The bad news is that a single bit error
cascades -- and everything "downstream" of the error is total garbage.
LZW works by -- essentially -- building a dictionary of subsequences and
storing dictionary indexes in the compressed file.  The decompressor rebuilds
the dictionary as it expands the file.  One consequence of this is that
a single-bit error can result an illegal dictionary index and, ultimately,
an illegal memory reference.

I suspect you're out of luck.  If you had source code for UnStuffit (or
knew the archive format and had access to Unix compress to get the LZW
algorithm), you *might* be able to extract parts of your files.

>Lest you think I'm a total nitwit, let me assure you that there is another
>form of backup, but it's one update level old,

That was a smart move.  Good luck.

Martin Minow
minow@thundr.enet.dec.com