Author: Sander de Zoete
Date: 13:16:11 01/13/03
Does anyone use reverse bitboards? I'm writing a new chess program "Preatorian",
which uses reverse bitboards. Up till now it looks good, but is still 10% slower
on capture generation than my 0x88 program "Shark". And Shark is slow, it must
say.
I add some code to see if i'm doing it correct? What could be improved?
//---------------------------------------------------------------------------
// Generate Rook Moves for Move List
// Bit Manipulation Trick for REVERSE Bitboard use
// BITBOARD x, y;
// y = x ^ (x - 4);
// Starting from bit 3 (4 = 0100) up, all bits are set to 1 until the
// first bit of x, which is 1. Also including this bit.
// eg. x = 0101 0011, y will be 0011 1100.
// Steps to use bit manipulation x ^ (x -2)
// 1. Shift allpieces bitboard to the right until the bit with the attacking
// piece is bit zero
// 2. Mask the rank/file (for offboard problems)
// (BITBOARD rank_mask = 0xFF; BITBOARD file_mask = 0x0101010101010101;)
// 3.1 Perform the bit manipulation
// 3.2 If file or diagonal: use file_mask/diagonal_mask again!
// 4.1 Shift back to the left
// 4.2 Use clear_right half of diagonal if bit 3 (int 4) is set to remove
// redundant/wrong squares in upper right corner
// 5 Result is attacks by piece without piece itself
// 6. Use same steps 1 - 5 for reverse bitboard
//---------------------------------------------------------------------------
void RookRankMoves(TBoard *pos, BITBOARD rooksqueen_bitboard, BITBOARD
all_pieces,
int reverse, BITBOARD capture_board, int capture )
{
BITBOARD h1_bitboard, h2_bitboard;
int sq_to, sq_fr;
h1_bitboard = rq_bitboard;
while(h1_bitboard)
{ sq_fr = LSB(h1_bitboard);
h2_bitboard = all_pieces;
h2_bitboard = h2_bitboard>>sq_fr;
h2_bitboard = h2_bitboard ^ (h2_bitboard - 2);
h2_bitboard = h2_bitboard<<sq_fr;
h2_bitboard = h2_bitboard & (mask_rank_1<<(8*(sq_fr>>3))) ;
//h1_bitboard = Clear_LSB(h1_bitboard);
h1_bitboard ^= bit_mask[sq_fr];
// remove captures/own pieces from non capture board
if (capture)
h2_bitboard &= capture_board;
else
h2_bitboard &= ~all_pieces;
while(h2_bitboard)
{ sq_to = LSB(h2_bitboard);
//h2_bitboard = Clear_LSB(h2_bitboard);
h2_bitboard ^= bit_mask[sq_to];
if (reverse)
AddMoveToList((63-sq_fr), (63-sq_to),
(pos->piece_on_square[(63-sq_fr)]>>2),
(pos->piece_on_square[(63-sq_to)]>>2), 0, 0, 0);
else
AddMoveToList(sq_fr, sq_to,
(pos->piece_on_square[sq_fr]>>2),
(pos->piece_on_square[sq_to]>>2), 0, 0, 0);
g_move_list_counter++;
}// while h2_board
}// while h1_board
}
Thanks for any input,
Sander de Zoete
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