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From: Lowell Gilbert <lgusenet@be-well.ilk.org>
Newsgroups: comp.lang.c
Subject: Re: ASCII to ASCII compression.
Date: Sun, 09 Jun 2024 19:20:16 -0400
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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:

> On 06/06/2024 20:23, Paul wrote:
>> 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.
>> 
> Yes. If yiu stire data as 8 but binaries then it's inherently
> risky. There's usually no recovery froma single bit gett corrupted.
>
> Whilst if you store as ASCII, the data can usually be recovered very
> easly if something goes wrong wit the phsyical storage. A "And God
> said"
> becomes "And G$d said", an even with this tiny text, you can still read
> it perfectly well.

That example only works because it doesn't include compression.


-- 
Lowell Gilbert, embedded/networking software engineer
	 http://be-well.ilk.org/~lowell/