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Z80 & 68k Assembly =>
z80 & ez80 Assembly
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hotdog1234
Advanced Member
Joined: 14 Aug 2009
Posts: 291
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 Posted: 22 Oct 2009 06:44:39 pm Post subject: |
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| Buckeye Dude and I had a discussion, we're probably doing pucrunch. |
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FloppusMaximus
Advanced Member
Joined: 22 Aug 2008
Posts: 472
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| Posted: 22 Oct 2009 09:24:53 pm Post subject: |
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Graphmastur wrote: Hmmm. Is Lz77 the same as zlib .zip compression? It looks like it works the same way.
Most zip files use the Deflate algorithm, which is basically a combination of an LZ77-like technique with Huffman coding, applied on a block-by-block basis. zlib is an implementation of that algorithm.
Strictly speaking, LZ77 refers specifically to the algorithm described by Lempel and Ziv in their 1977 paper, which is very inefficient for most real-world data and you should never use it. But LZ77-like compression schemes are quite popular (pucrunch being another example.) The basic idea of encoding strings by references into a "sliding window" is a very powerful and useful one.
(The term LZ77 is used to distinguish this type of technique from the somewhat related "LZ78-like" dictionary compression techniques, which can be more effective, but also require considerably more memory and time to decompress.) |
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darkstone knight
Advanced Member
Joined: 07 Sep 2008
Posts: 438
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| Posted: 23 Oct 2009 03:40:12 am Post subject: |
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thats right, im using lz77 with an 131-byte sliding windows and a max string lengt of 32
coupeled with von-haufmann, each "string pointer" is just 16 bits, and decompressing is FAAAST
just about 50 cc' per tile, AKA 14 miliseconds to decompress an 58*22 map (~1300 bytes)
well, decompressing is verry slow (~1 min in 15 mhz mode) but its worth it |
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tr1p1ea
Elite
Joined: 03 Aug 2003
Posts: 870
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| Posted: 23 Oct 2009 04:09:03 am Post subject: |
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| Ive made use of puCrunch before and i must say that i am impressed with the results. Of course as has been previoulsy mentioned, it all depends on your data. |
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DigiTan
Unregistered HyperCam 2
Super Elite (Last Title)
Joined: 10 Nov 2003
Posts: 4468
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| Posted: 23 Oct 2009 06:33:08 pm Post subject: |
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| About how well would you say Lz77 and pucrunch compress text? Factoring in the size of the algorithm does it usually pay off? (Maybe I should look at those TI eBook projects are doing.) |
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FloppusMaximus
Advanced Member
Joined: 22 Aug 2008
Posts: 472
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| Posted: 23 Oct 2009 09:18:26 pm Post subject: |
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The TICT eBook reader, I believe, uses a slightly modified version of pucrunch.
My eBook project uses an LZ77-and-Huffman approach of my own design (which I've been thinking about trying to improve, but it works OK.) I found it significantly better than pucrunch, particularly for small block sizes.
I never figured out the format for TI's eBook reader app for the 68ks, but whatever it is, it gives you something like -100% compression.  |
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darkstone knight
Advanced Member
Joined: 07 Sep 2008
Posts: 438
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| Posted: 24 Oct 2009 06:50:14 pm Post subject: |
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maybe it's trying to reduce the size by decompressing it, that would be cool  |
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