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Subject: Re: Bitbases- What are they? Tablebases?

Author: Dagh Nielsen

Date: 12:06:52 12/06/05

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On December 06, 2005 at 05:42:11, Vincent Lejeune wrote:

>On December 06, 2005 at 05:24:26, Steve Lim wrote:
>
>>On December 06, 2005 at 05:21:34, Daniel Shawul wrote:
>>
>>>On December 06, 2005 at 05:15:54, Steve Lim wrote:
>>>
>>>>Title says it all. Am just wondering how they differ from Eugene's EGTBs?
>>> They store only Win Draw Loss information, hence they are smaller and some
>>>of them can be loaded in to RAM, which makes them faster.
>>>
>>>>
>>>>Thanks.
>>
>>
>>Ahhh.. similar to the old Distance to Conversion vs Distance to Mate.
>>
>>This is DTC I guess.
>
>I'm trying to be more clear ...
>
>In the Bitbase endgame file only results is store, so there's only 3 values
>possible for each position 1) win 2) lost 3) draw
>In comparison, in the 5 pieces Nalimov files there's 256 (255?) possible value
>from -127 to +127 (-127 = mated in 127 moves ; 0 = draw ; +127 = mate in 127
>moves, not very sure about this values, but it's the logic)
>
>In bitbase one can store 4 positions per bytes but one don't know the best move.
>In Nalimov (5 pieces) one can store 1 positions per byte but one knows the best
>move(s).
>
>remark :
> I pointed Nalimov "5 pieces" because some 6 pieces endgame require more than 1
>bytes (mate > 127 moves). On one side that means that more pieces on the board
>give bigger size difference between Nalimov and bitbase but the drawback will be
>that with the bitbase, computer will not be able to find the mate because it's
>so long that the file with draw/win/lose will not be enough to find the path to
>the mate in 1.


Hi, I'm not sure I understand all the advantages of bitbases in full, but I'm
just wondering if one could not use an approach like this:

(1) Use bitbases during search
(2) Once won/lost position is reached, switch to Nalimov table bases.

The point would be to speed up things, but I don't know if I got something
wrong.

Regards, Dagh Nielsen



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