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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 07:12:57 +0100
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On 10/06/2024 01:45, Lew Pitcher wrote:
> On Thu, 06 Jun 2024 17:25:37 +0100, 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?
> 
> I'm afraid that you have conflicting requirements here. In effect,
> you want to take an array of values (each within the range of
> 0 to 127) and
> a) make the array shorter ("compress it"), and
> b) express the individual elements of this shorter array with
>     a range of 96 values ("isgraph() characters")
> 
> Because you reduce the number of values each result element
> can carry, each result element can only express a fraction
> (96/128'ths) of the corresponding source element. Thus,
> with the isgraph() requirement, the result will take /more/
> elements to express the same data as the source did.
> 
> However, you want /compression/, which implies that you want
> the result to be smaller than the source. And, therein lies
> the conflict.
> 
> Can you help clarify this for me?
 >
We have a fixed Huffman tree which is part of the algorithm and optmised 
for ASCII. And we take each line otext, and comress it to a binary 
string, using the Huffman table. The we code the binary string six bytes 
ar a time using a 64 character dubset of ASCCI. And the we append a 
special character which is chosen to be visually distinctive..

So the inout is

Mary had a little lamb,
it's fleece was white as snow,
and eveywhere that Mary went,
the lamb was sure to. go.

And we get the output.

CVbGNh£-H$£*MMH&-VVdsE3w2as3-vv$G^&ggf-


And if it shorter or not depends on whether the fixed Huffman table is 
any good.

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