Author: Robert Hyatt
Date: 20:18:19 08/07/01
Go up one level in this thread
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.
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