LZ77 Compression/Decompression Routine

ACagliano · Super-Expert Joined: 08 Feb 2010 Posts: 924

I am working on a program that requires compression and decompression to be done on calc. I lack the programming skills to achieve compression/decompression, although I do understand the concept. Yet, I would rather not let another project fail. So, I ask... is there anyone with the time and expertise who would like to code the compression/decompression routines, and be listed on the project as a co-author? If not, I'll try again when everything else is done, but I doubt I'll be successful.
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-ACagliano

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Kaslai · Member Joined: 16 Nov 2011 Posts: 172 Location: ???, WA

What kind of data are you trying to compress? Could a simple Run Length Encoding suffice?
Most other (de)compression methods require a lot of ram to perform quickly.
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ACagliano · Super-Expert Joined: 08 Feb 2010 Posts: 924

This algorithm needs to compress all different data forms...in fact, a specially formatted "Archive". Here's the project in question:

http://clrhome.org/projects/calcrar
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-ACagliano

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Kaslai · Member Joined: 16 Nov 2011 Posts: 172 Location: ???, WA

Alright, so you're right, an LZ77 or LZ77-like solution would probably achieve the most satisfactory results. I'll try tinkering about during school writing a Z80 LZ77 codec.
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ACagliano · Super-Expert Joined: 08 Feb 2010 Posts: 924

Thank you. I do appreciate it.
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-ACagliano

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ACagliano · Super-Expert Joined: 08 Feb 2010 Posts: 924

Any progress on this Kaslai?
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-ACagliano

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Kaslai · Member Joined: 16 Nov 2011 Posts: 172 Location: ???, WA

I talked in IRC about some ideas. I'm not sure how BASIC programs are run, but what I'm thinking is that you could probably decompress files in-place. Just insertmem in to the running programs space to fit the size of the decompressed files, provided enough memory.

Decompressing in place is easy enough; you just need to write the compressor to run backwards instead of forwards. Then, decompress from the end of where the decompressed data will be. I don't think the TI-83+ uses memory caching, so going backwards shouldn't cut performance.
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ACagliano · Super-Expert Joined: 08 Feb 2010 Posts: 924

I haven't the slightest clue how to do this. 0x5.

Edit: Does anyone feel up to writing this for me? I can handle the rest on my own, I'm pretty sure.
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-ACagliano

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tr1p1ea · Advanced Newbie Joined: 23 Jul 2010 Posts: 57

puCrunch will be something of interest. There are various implementations on ticalc.org.

Tari · Posted: 22 Apr 2012 10:47:15 pm Post subject:

LZF is conceptually very similar to LZ77-- I've been working on an implementation to target the prizm.

My goal with that is maximal compression, so it's very slow. I've been slowly improving the speed, though.
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