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Thread: LZW with unbounded dictionary

  1. #31
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    You may try to. But Z files are not GIF ones - have different header and slightly different LZW stream. And if seriously, current OPTZ compresses to .z files only.

  2. #32
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    Hi,

    Quote Originally Posted by encode View Post
    OK, it's a dummy version of OPTZ. It is compatible with UNIX COMPRESS but in most cases provides a little bit more compression due to better dictionary reset. No advanced parsing yet. In addition, it should be FAST!
    Thank you so much!!

    First quick test. Application logfile in binary form (got from office), 130 241 536 bytes.

    Original .Z, generated on AiX 4.3, don't know compress version (don't have access to the computer now) : 54 768 927
    (N)compress 4.2.4 on Windows : 56 126 713
    (N)compress 4.2.4 on Linux : 56 037 953
    optz 0.01 : 54 790 115

    So optz performs very well but it's not the ultimate Z compressor (yet ? )

    Thanks again and have a nice day,


    AiZ

  3. #33
    The Founder encode's Avatar
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    Yep! Basically, LZW is bad algorithm. Good LZSS is much better even on text files. Even with a huge dictionary the performance of well designed LZW is not impressive. I may use OPTZ with a larger dictionary - 24-bit instead of 16, but current Z unpackers will unable to unpack such files, although with a small changes all stuff will work... Anyway, baseline LZW is a waste of time these days. Back in 1984, LZW was impressive, now we have CM and other stuff...

    Quote Originally Posted by AiZ View Post
    Hi,

    Thank you so much!!

    First quick test. Application logfile in binary form (got from office), 130 241 536 bytes.

    Original .Z, generated on AiX 4.3, don't know compress version (don't have access to the computer now) : 54 768 927
    (N)compress 4.2.4 on Windows : 56 126 713
    (N)compress 4.2.4 on Linux : 56 037 953
    optz 0.01 : 54 790 115

    So optz performs very well but it's not the ultimate Z compressor (yet ? )

    Thanks again and have a nice day,

    AiZ

  4. #34
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    *bump*
    any news about it, encode?

  5. #35
    The Founder encode's Avatar
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    Well, some LZW parts was written some time ago... Now, I don't like the idea about LZW and LZW-related stuff. GIF images and Z files are something from the past. The biggest and the worst thing adding advanced parsing to LZW is - LZW is not LZ77. Encoder's choice is also affects the dictionary contents, unlike LZ77. With LZ77 all phrases will be added regardless of the encoder's choice. Making such weird LZW parser may cause unexpected results with the third party unpackers like image viewers. LZW is bad algorithm. Even simplest LZSS with proper parsing may beat LZW at text file and picture compression, providing higher decompression speed and with no need in extra resources for the decoder. Proof of concept is great, but only if you have some inspiration and ideas to check. All of my ideas I've checked... and lost interest in LZW.
    I have not that much of spare time these days. And better I will check my new and fresh ideas, instead of wasting my time...

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