Groups > comp.compression > #1988

Re: Generating data that can be compressed with a known ratio

From	Ian Collins <ian-news@hotmail.com>
Newsgroups	comp.compression
Subject	Re: Generating data that can be compressed with a known ratio
Date	2013-06-25 13:58 +1200
Message-ID	<b2sbqoFd7h3U13@mid.individual.net> (permalink)
References	(1 earlier) <8a78d61d-c5aa-4e63-8437-96764a083073@googlegroups.com> <kqa5s1$40d$1@speranza.aioe.org> <5e3902bf-a25d-4fc8-839a-f1ba129003aa@googlegroups.com> <b2rutvFd7h3U12@mid.individual.net> <6b23588c-fa29-459f-b8a9-860f2a2213ce@googlegroups.com>

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hitchmanr@gmail.com wrote:
> On Monday, June 24, 2013 3:18:39 PM UTC-7, Ian Collins wrote:
>> The algorithms used by ZFS are LZJB, ZLE, and gzip.
>
> LZJB is almost identical to LZNT1 (used by NTFS). There are only so
> many ways to encode LZ77 in a byte-stream, I suppose.
>
> Snappy: Byte tag + optional extra data to indicate whether following
> bytes are literal or copy sequence LZ4: Encode pairs of sequences of
> literals and a copy operation. LZNT1/LZJB: Tag byte indicating
> whether next 8 elements are 1 byte literals or 2 byte copies. 2 byte
> copy: LZJB: 6 bit match length, 10 bit match offset; LZNT1: adjust
> length/offset sizes based on amount of uncompressed data processed.
>
> ZLE is an (almost useless?) RLE transform that only compresses
> zeros.

Useful if there plenty of sparse files.

-- 
Ian Collins

Thread

Generating data that can be compressed with a known ratio Ian Collins <ian-news@hotmail.com> - 2013-06-23 10:59 +1200
  Re: Generating data that can be compressed with a known ratio glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-06-22 23:24 +0000
  Re: Generating data that can be compressed with a known ratio SG <sgesemann@gmail.invalid> - 2013-06-23 01:45 +0200
  Re: Generating data that can be compressed with a known ratio hitchmanr@gmail.com - 2013-06-24 11:53 -0700
    Re: Generating data that can be compressed with a known ratio glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-06-24 19:15 +0000
      Re: Generating data that can be compressed with a known ratio hitchmanr@gmail.com - 2013-06-24 13:44 -0700
        Re: Generating data that can be compressed with a known ratio Ian Collins <ian-news@hotmail.com> - 2013-06-25 10:18 +1200
          Re: Generating data that can be compressed with a known ratio hitchmanr@gmail.com - 2013-06-24 16:57 -0700
            Re: Generating data that can be compressed with a known ratio Ian Collins <ian-news@hotmail.com> - 2013-06-25 13:58 +1200
  Re: Generating data that can be compressed with a known ratio Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2013-06-27 10:08 +0300

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