Author: Dan Newman
Date: 00:02:31 02/12/00
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On February 12, 2000 at 00:32:51, Bruce Moreland wrote: >On February 10, 2000 at 17:34:52, Tom Kerrigan wrote: > >>There seems to be a huge pro-bitboard movement underway... But for those of us >>not jumping on the bandwagon, I have some thoughts. >> >>Let's say you have an array to represent the board: >>int board[64]; >> >>If you make white pieces positive (i.e., pawn = 1, knight = 2) and black pieces >>negative, you can use the following macros: >> >>#define COLOR(x) (x < 0) >>#define TYPE(x) (x < 0 ? -x: x) >> >>I don't like the TYPE macro because it has a branch. So let's say you set bit #4 >>if the piece is black. Then you can use these macros: >> >>#define COLOR(x) (x >> 3) >>#define TYPE(x) (x & 7) >> >>This seems pretty good, but I still have a minor complaint: a pawn = 1, so all >>the arrays that are indexed by piece type have to have an unused element at the >>beginning. >> >>You can set the pawn = 0, but then the empty square value has to be non-zero. On >>some proessors, this increases the time it takes to see if a square is empty. >> >>If you're using the 0x88 trick, you get two boards to play with, so the color of >>the piece on square x can be board[x] and the piece type can be board[x+8]. I >>think this is a pretty good solution, but it involves some extra memory >>accesses, not only when you're examining the board, but also when you're moving >>pieces around. >> >>If you have a piece struct, your board can be pointers to the structs: >>piece_struct *board[64]; >> >>Then the color of the piece on square x is board[x]->color and the piece type is >>board[x]->type. I think this solution is pretty cool, but it involves some extra >>memory accesses. Plus, every time you want to check the piece type of square x, >>you have to make sure that board[x] isn't NULL. That's not cool. >> >>So... each method has its minor advantages and disadvantages. I can't really >>decide which I like more. What do other programmers do? Is there some really >>elegant solution that I'm missing? I hope so. :) >> >>-Tom > >I don't think it matters what you do, and starting out with intent to save a few >cycles is like being extremely concerned about making sure that the first step >you take on the way to work each morning is absolutely perfect. > >bruce Yeah, but I always have to pound my head against a brick wall to figure things like that out :). (I seem to have a compulsion to fiddle and tweek code--just to get that extra 1%--and have continued to do so even after I figured out what you said above...) -Dan.
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