Re: ASCII to ASCII compression.

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