Author: Vincent Diepeveen
Date: 03:48:04 05/12/02
Go up one level in this thread
On May 12, 2002 at 00:26:03, Robert Hyatt wrote: >On May 11, 2002 at 21:12:35, David Dory wrote: > >> >>Vince wrote: >>>>Bitboards is a tradeoff. You put less information into >>>>a single 64 bits word. So you can use instructions like AND and OR >>>>more easily. >> >>>>Gnuchess is putting more information into a single word for each >>>>square. The advantage is you can faster work with complex knowledge. >> >>You wrote: >>>So in short it means, bitboard helps put more information (==more knowledge)in >>>single square (64 bits?), if that is what I understand. >> >> >>You have it exactly backward. Bitboards put less info than the design used by >>Gnuchess 4, but they are faster, and you have the opportunity to be quite >>creative with their use, without a big penalty in speed. > > >Actually Vincent has it backward. Bitmaps are "dense" in terms of information. >For example, in the opening position, 1/2 the bits are 1's and 1/2 are 0's. >That seems to suggest 50% density but that is _wrong_. The zero bits also >have significant meaning (squares that are empty). Bitmaps are by far the >best way to represent a chess board when you have a 64 bit machine. Just >compare a 32 bit program to a bitmapper on a 64 bit machine to see why. Every >internal instruction moves 64 bits around, and 1/2 of the bits are totally >useless on a 32 bit program. On a bitmapper, _every_ bit counts... They ask about attack information Bob, as already 2 years ago proven, also at a 64 bits machine bitboards are not the way to use for attack information gnuchess 4.0 style, because you use 1 bit of information a square, so in 1 integer for a square it takes a while to collect information, whereas i have incremental attacktables which keep track of a lot of things for each square. So to get number of attackers at a square X in for example gnuchess 4.0 all you do is: attackers = attack[0]&31; That's pretty unbeatable if you have 1 bit of information a bitmap! This gets used in evaluation. Crafty doesn't use it in evaluation, so i do not see why it needs it. It's a trade-off decision IMHO. > > >> >>Dave
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.