Author: Marc Bourzutschky
Date: 02:00:53 08/08/01
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On August 07, 2001 at 23:18:19, Robert Hyatt wrote: >On August 07, 2001 at 13:30:12, Marc Bourzutschky wrote: > >>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. > > >Its gotta be. As the probe code does the decompression, and it is part of >the source distribution for the egtb stuff. The decompression is indeed part of the source distribution, but the compression itself does not seem to be.
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