Author: Robert Hyatt
Date: 11:32:43 05/18/01
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On May 18, 2001 at 14:12:19, Dan Andersson wrote: >>Probably a rewrite into bitmaps. The issue is information density. Bitmaps >>are dense pieces of information requiring 64 bits. A normal program will end >>up with most of the bits wasted since the upper 1/2 are _never_ used and in >>general, the lower 1/2 is only partially used, in any 64 bit register... > >Yes, one of the main problems when using a 64 bit processor is that many data >structures are smaller than 64 bits, many are 8 bits or less. Refactoring the >data to use the bigger size words is essential. But IMO that a 64 bit processor >chess program will have worse information density, and will need special data to >extract some information from the board. Thus some of the gain from making the >transition that will be eaten up by lessened data and instruction cashe >efficacy, but not all. An iteresting POV is that an attackboard program can be >rewritten fairly easy from 32 to 64 bits by having 32 words of 64 bits instead >of 64 words of 32 bits. And when I'm thinking about it an attackboard will gain >substantially from 64 bits, since the sparseness of the boards will be offset by >the fact that a captured pieces board is not needed longer. The only problem >with the attackboard as I see it, is that it will tax even a register rich RISC >architecture, at least in the opening. > >Regards Dan Andersson The registers might be less of a problem than you suspect. IE register-renaming solves many bitboard problems where I do something like this: bishops_queens^=something; white_occupied^=something; etc. Those two could be coded using one real register, and yet they can be pipelined at the same instant if the hardware does register renaming... The real wins are the shifts and stuff I do a lot of. Shifts are evil if you use 64 bits for the item, but only have 32 bit registers...
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