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From: fir <fir@grunge.pl>
Newsgroups: comp.lang.c
Subject: Re: simple compression mathod to code itself?
Date: Sat, 06 Apr 2024 16:02:12 +0200
Organization: i2pn2 (i2pn.org)
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bart wrote:
> On 06/04/2024 13:16, fir wrote:
>> fir wrote:
>>> David LaRue wrote:
>>>> fir <fir@grunge.pl> wrote in news:uupflr$5t1n$1@i2pn2.org:
>>>>
>>>>> i not code at all in recent years
>>>>> (recently i coded half of my compuler with a plan to write second half
>>>>> but its to ambitious to lazy coding mood i got recently)
>>>>> but recently i started this slamm coding modd and found
>>>>> ite pleasurable
>>>>>
>>>>> searching for lazy side things i could code in such mood
>>>>> i thought maybe i wopuld like to have compression routine
>>>>> but i would like to write it myself sortla like i use quicksort
>>>>> or so but i also want to write it myself
>>>>>
>>>>> so is there maybe some method i could use i mean some simple
>>>>> routine that compresses and uncompresses an array of bytes but
>>>>> maybe something a bit more complex than RLE (rune length encoding)
>>>>> - only thing i know from this domain
>>>>>
>>>>
>>>> Hello fir,
>>>>
>>>> A method a bit more complex that you might try builds a table of all
>>>> bytes
>>>> as you scan them from the input.  The compressed output is a
>>>> reference to
>>>> the table you just built (wnhem repeated byte strings are found,
>>>> otherwise
>>>> feed the input to the compressed image so that the expansion method can
>>>> build the sme dynamic table the encoder built.  The table generally
>>>> has a
>>>> limit on the number of entries (usually a good size) and allows the
>>>> table
>>>> of bytes to dynamically change as new patterns are read from the input.
>>>>
>>>> This is a well known and documented compression/expansion algorithm.
>>>> PKZIP
>>>> and other engines use this as one of their compression methodz.
>>>> Look for
>>>> the description of that if you need more details to figure out what you
>>>> need to write.
>>>>
>>>> Expansion is the reverse.  Read the source (now the compressed
>>>> image) and
>>>> build the compression table from the bytes.  As encoded references
>>>> to the
>>>> compression table are read from the compressed image output the source
>>>> byte
>>>> sequences.  The output should be the same as what your encoder
>>>> originally
>>>> read.
>>>>
>>>> A good check on the final code is to compare the original input with
>>>> the
>>>> eventual output and make sure they agree exactly.
>>>>
>>>> Have fun,
>>>>
>>>> David
>>>>
>>> this could be good but i dont quite understood that .. but eventually
>>> could be good...
>>>
>>> i thinged something abut that if rle search for repetitions of 1
>>> byte then maybe after that search for repetitions of 2 bytes, then 3
>>> bytes, 4 bytes and so on.. then do some "report" how many found and then
>>> find a way to encode that
>>>
>>>   need to think a bit becouse if rle only stores repetitions that are
>>> one after another then this method should store  repetitions that have
>>> various distances among them
>>>
>>>
>>> i also do nto want to spend a much time on this 1-2 days eventually
>>
>>
>> though maybe i should start from RLE indeed..in fact ihis shouldnt be
>> so bad as for some of my eventuall funny needs - also it maybe seem ok
>> to be first step until something more elaborate
>
> What sort of data are you compressing?
>
> If it is computer generated imagery with no noise or artefacts, then RLE
> will probably work well.
>
> If it is a noisy image captured from a camera then it'll be rubbish.
>
> Stuff like text files will likely be mildly compressed, but probably not
> enough to be worth the trouble.
>
> Decent compression is hard; you're not going to come up with anything in
> 1-2 days that will give worthwhile results across a range of inputs.
>
>> if someone want to talk on compression adn how to code it i could like
>> to read it (as reading net articles on this may be seem to hard for my
>> old sick head and posts are much are easier to get into it)
>
at the initial idea i want to add this as a method to my "bytes" 
microcontainer (where you could put or load anything)

i just tried to think what usebale metods i could add and some 
pack/unpack method caould be handy

though even i dont know if to do it todaye/tomorrow or maybe more in 
future..discussing something abut it would be interesting imo