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Title: Board representation in Bomb Post by fotland on Feb 11th, 2007, 5:43pm Bomb uses one bitmap for each piece type with a bit set for each square containing that piece. It also has an array for the board giving the piece on each square. This is a single dimension array since a two dimension array would be slower. It tracks the strongest piece adjacent to each square, and has a bitmap for pieces that are frozen. It has a 64-bit zobrist hash used to detect repetiion and to index into the transposition table during search. It keeps track of the current step and push/pull status. It has some incremental evaluation values, for material balance, and number of rabbits for each side. The full board data structue is: bmap p[NUMBITMAPS]; // locations of pieces, by PIECE NAMES (inluding one for empty squares) bmap frozen; // bit set if that piece is frozen char pieces[64]; // piece on each point, 0 is upper left (black side of board ) char strongest[2][64]; // strongest piece next to each square, by color (or EMPTY) unsigned int hashindex, hashkey1; // transposition table values int material; // material balance, 1000 per pawn, positive for gold int bestmateval; // best pawn matestep value char bestmateloc; // best mate location char tm; // side to move (0-white, 1-black) char phase; // phase of the the move, 0-3 char wtotmat, btotmat; // white and black total material, 1, 2, 3, 5, 9, 11 unsigned char pullsquare, pullpiece; // last move's pulling square (empty square where piece was) // and piece doing the pulling - unless pullpiece is empty unsigned char pushsquare, pushpiece; // last move pushed square (empty point where piece was) // and enemy piece that was pushed - // unless pushpiece is empty - next step is forced unsigned char pawncount[2]; // how many pawns left by color char matesearch; // doing a mate search now |
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Title: Re: Board representation in Bomb Post by fotland on Feb 11th, 2007, 5:46pm When doing a search we have to make a move, evaluate (possibly with more search), and unmake the move. I find it fastest to only write code for making the move. During search I make a copy of the board before making a move, so unmaking a move is not needed. This saves a lot of code to do incremental unmakes, and since the board data is small, the copy takes very little time. |
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