Author: Poschmann
Date: 00:50:56 10/28/01
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On October 28, 2001 at 02:19:31, Paul Byrne wrote: >I've been looking at tablebases lately and was wondering if anyone >has ever played with this idea (before I spend too much time on it!) > >Basically, take the normal (Nalimov or whatever) tablebases in their >uncompressed form and divide the mate-in-x or loss-in-x values by some >number N. So mate-in-1 through N become (+1) mate-in-(N+1) through 2*N >become (+2), etc. Then compress the resulting files as usual. > >The idea being to reduce the number of different values to make the file >more compressible. > >This would, of course, make life a little more difficult for the engine. :) >When the position is not yet into a tablebase, there would be little effect -- >other than any mate/loss scores being a little inaccurate. Once the position >on the board is actually a tablebase position, a short search would have to >be done to determine the correct move. For example, if the position OTB is >scored as (+5), then one would search for the move that forces a (+4) position >the quickest. > >I did a little test to see if the space savings is worthwhile... >Using the kbbkn.nbb/nbw tablebases (something with long mates) and the >kqnkn.nbb/nbw tablebases (mostly short mates) with various N's -- the >numbers are the percentage of the regular _compressed_ tablebases: > > N=2 N=3 N=4 N=5 N=10 N=100 >kbbkn.nbb 84.67 75.00 68.26 63.74 52.08 23.11 >kbbkn.nbw 82.96 73.21 66.98 62.13 47.80 9.10 >kqnkn.nbb 64.40 48.51 40.58 31.93 19.21 5.86 >kqnkn.nbw 63.51 46.43 37.20 28.70 6.36 2.57 > >The last 2 columns were just out of curiousity. :) > >The question is, how large can N be made while still allowing tablebase >positions to be played out in a reasonable amount of time? Don't know (yet). > >None of this would help for generating tablebases, of course. You still need >the normal tablebases to generate the reduced ones. And I'd imagine most >engine authors would prefer the full tablebases, but for the average >player I don't know they'd notice much difference and could save a few GB >of disk space... less stuff to distribute or download too. > >I suppose a lot of folks have enough disk space for 3/4/5 man tables >nowadays, but when the 6 man tables become more complete/common, this may >help some. > >-paul If a program uses tablebaeses it do it in the following way: 1. Look into the tablebases to find the current position. For example mate in
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