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Thread: Free software to support RARv3

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    Free software to support RARv3

    The RARv3 archive format provides a high compression rate, supports split volumes, and other features. The only free software presently available for it is unrarlib, which can only read rar archives, not write them, and only up to rar v2.9, not the now-prevalent rar v3. Supporting it will take some effort, since the file format is not publicly documented , it will have to be reverse-engineered from rar files.
    Ways to help. If you know of an existing project or you wish to spearhead the creation of such a project please contact campaigns@fsf.org letting us know the details.

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    Ilya, it's an archive structure and this document is part of unrar distribution. closed-source part is compression algorithms

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    IIRC RAR license disallows reversing.

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    Quote Originally Posted by m^2 View Post
    IIRC RAR license disallows reversing.
    I don t know .If you use unrar source to reverse enginering is illegal.

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    The Founder encode's Avatar
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    Quote Originally Posted by lunaris View Post
    The only free software presently available for it is unrarlib, which can only read rar archives, not write them, and only up to rar v2.9, not the now-prevalent rar v3.
    RAR v3 and RAR v2.9 are the same! i.e. nothing new since v2.9!

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    Yes, compatibility is maitained, but are *compression* algoritms been decompiled?
    BTW, encode, you have done an improved compress, what about improved RAR

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    compress is opensource, RAR isn't. Only improved decompressor could be done
    I am... Black_Fox... my discontinued benchmark
    "No one involved in computers would ever say that a certain amount of memory is enough for all time? I keep bumping into that silly quotation attributed to me that says 640K of memory is enough. There's never a citation; the quotation just floats like a rumor, repeated again and again." -- Bill Gates

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    It's illegal to improve RAR compression. Anyway, it would be cool if author will add:
    • Optimal parsing to RAR's LZH algorithm. This will give an extra compression with no decompression speed loss.
    • PPMd var.J with auto-parameters (variable model order and model size). This will improve compression further. Currently RAR uses an obsolete version of the PPMd compression library.
    • A few specialized MM codecs. Say, more advanced image and audio ones.

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    Someone can give some details about rar algos?

    Someone have documentation about rar algos?



    Thanks.

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    The Founder encode's Avatar
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    Quote Originally Posted by lunaris View Post
    Someone can give some details about rar algos?
    Briefly:
    RAR has so called RARVM - RAR Virtual Machine which applies various algorithms and filters on certain data block. i.e. Beginning of a file can be compressed with one algorithm, and other part or parts with another algorithm(s) and filter(s). Such switching are done dynamically.

    RAR algorithms are:
    • RAR's LZH
    • PPMd var. H
    RAR filters are:
    • E8/E8E9
    • ITANIUM
    • DELTA
    • RGB
    • AUDIO
    • UPCASE

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    Quote Originally Posted by encode View Post
    Briefly:
    RAR has so called RARVM - RAR Virtual Machine which applies various algorithms and filters on certain data block. i.e. Beginning of a file can be compressed with one algorithm, and other part or parts with another algorithm(s) and filter(s). Such switching are done dynamically.

    RAR algorithms are:
    • RAR's LZH
    • PPMd var. H
    RAR filters are:
    • E8/E8E9
    • ITANIUM
    • DELTA
    • RGB
    • AUDIO
    • UPCASE
    Thanks!

    I will send a email to Free software Foundation.
    Last edited by lunaris; 21st January 2009 at 20:16.

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