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From: Paul <nospam@needed.invalid>
Newsgroups: comp.lang.c
Subject: Re: ASCII to ASCII compression.
Date: Thu, 6 Jun 2024 15:23:33 -0400
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On 6/6/2024 12:25 PM, Malcolm McLean wrote:
> 
> Not strictly a C programming question, but smart people will see the relavance to the topicality, which is portability.
> 
> Is there a compresiion algorthim which converts human language ASCII text to compressed ASCII, preferably only "isgraph" characters?
> 
> So "Mary had a little lamb, its fleece was white as snow".
> 
> Would become
> 
> QWE£$543GtT£$"||x|VVBB?
> 

The purpose of doing this, is to satisfy transmission through a 7 bit channel.
In the history of networking, not all channels were eight-bit transparent.
(On the equipment in question, this was called "robbed-bit signaling.)
For example, BASE64 is valued for its 7 bit channel properties, the ability
to pass through a pipe which is not 8 bit transparent. Even to this day,
your email attachments may traverse the network in BASE64 format.

That is one reason, that email or USENET clients to this day, have
both 7 bit and 8 bit content encoding methods. It's to handle the
unlikely possibility that 7 bit transmission channels still exist.
They likely do exist.

   Paul