Re: ASCII to ASCII compression.

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.
--
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http://malcolmmclean.github.io/babyxrc