Author: Dave Gomboc
Date: 14:50:50 02/10/00
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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. Maybe you could use empty = 0, R=1, B=2, Q=3, K=4, N=5, P=6? Advantages (?): * Your piece arrays don't have an extra element * Bit 2 indicates whether the piece is a slider or not (when piece!=empty) * If a slider, * Bit 0 indicates whether the piece does manhattan slides. * Bit 1 indicates whether the piece does diagonal slides. Disadvantages (?): * the pieces are not in material worth order >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. :) My opinion is that none of this matters much, relative to whether your program understands what to do in an isolated d-pawn position. Dave
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