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Subject: Re: EGTB - dumb questions?

Author: Marc Bourzutschky

Date: 10:30:12 08/07/01

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On August 07, 2001 at 10:45:47, Robert Hyatt wrote:

>On August 07, 2001 at 01:02:51, Pham Minh Tri wrote:
>
>>[snip]
>>>>4) Could someone explain the technique of compressing TBs (how good/fast, what
>>>>kind and how different from normal one)?
>>>>Many thanks in advance.
>>>
>>>
>>>
>>>Pretty similar to normal compression.  But if you know you are compressing
>>>bytes, particularly when you have lots of "zeroes" (draw scores) then you can
>>>compress more efficiently than if you are trying to compress other types of
>>>data (say ASCII which has many zero bits).
>>
>>But normal compression is required to de-compress before use. In other hand, I
>>know that we could use compressed TBs when computing. Maybe we need a more
>>efficient method (fast or partly de-compress) for TBs?
>
>
>The nalimov (.emd) tables are compressed using a tablebase-specific compression
>algorithm.  It is different from normal compression in two distinct ways.
>
>(1) it is specific to the type of data stored in tablebases, which lets it do a
>better job of compression than a general-purpose compression algorithm.
>
>(2) it compresses in "chunks" so that a single chunk can be decompressed as
>needed without having to decompress the entire file. This is why most find that
>using the compressed (.emd) files are actually faster than using the files that
>have been previously uncompressed and saved on disk.  The compressed versions
>require less total I/O bandwidth since when you read in an 8K block, you get
>way more than 8K of real table data.
>
>I don't think there is a faster or more efficient way of doing this than what is
>already being done.  We played with the "chunk size" quite a bit, with me
>running lots of test games, to find the "optimal value".

Is the source code for the compression algorithm available?  I'm only aware of
the x86 executable.



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