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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: ASCII to ASCII compression.
Date: Mon, 10 Jun 2024 01:22:45 +0100
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On 10/06/2024 00:20, Lowell Gilbert wrote:
> 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.
> 
> 
Yes, so the ASCII to ASCCI compression scheme needs to be almost as 
robust. Any corruption will corrupt only a single line. And you can 
examine near-nonsense ASCII in a way you can't examine binary. Yiu can 
lod it into a text editor and look for the difference between two versions.

-- 
Check out my hobby project.
http://malcolmmclean.github.io/babyxrc