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From: mdavis@CHEM.UCSD.EDU (Morgan Davis)
Newsgroups: comp.sys.apple
Subject: Bit packing and squeezing
Message-ID: <8707312136.AA02715@crash.CTS.COM>
Date: Fri, 31-Jul-87 16:35:36 EDT
Article-I.D.: crash.8707312136.AA02715
Posted: Fri Jul 31 16:35:36 1987
Date-Received: Sun, 2-Aug-87 08:48:38 EDT
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This is mainly directed to Larry Virden, though I suspect that others have
already beaten me to the punch...

The net cannot handle 8-bit binary data through the various mailers. 
Therefore, a SQueeze type program, which creates 8-bit binary data files, is
not useful for passing information through the net as regular mail.

The Executioner will take 8-bit data and create a special text version of a
file by using a 6-bit packing scheme.  This allows all the printable ASCII
characters to make up the contents of the file so that they can be passed
through a regular text network without getting munged.

Almost all text mailers will strip the high-bit off of each byte, and they
may act up if spurious control characters are found in messages.

While one would be correct in saying that Executioner doesn't do any
compression, technically speaking, its 6-bit packing mode will create smaller
text files than would an ordinary hex dump.  In fact, a 49-block object file
(like TIC) will create a 158-block hex dump file.  But if a 6-bit encoding
scheme is used, TIC can be converted to a 68-block text file - - a SIGNIFICANT
savings.  In that sense, Executioner does provide compression for a text-based
network.

The ULTIMATE method would be to use an 8-bit squeezing program (like Don
Elton's ASQ utility) to compress a binary file first.  Then use Executioner to
convert it to a transmittable text file with 6-bit encoding.  Not everyone has
the ASQ/AUSQ utilities, though.  And the overall savings may or may not be
that big of a deal.

UUCP: [ ihnp4 cbosgd hplabs!hp-sdd sdcsvax nosc ] !crash!pnet01!pro-sol!mdavis
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INET: mdavis@pro-sol.CTS.COM
BITNET: mdavis%pro-sol.cts.com@ucbvax.berkeley.edu      (I hope this works)