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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