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Add scan for X-ray attacks in piece_attacks_square()

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Used to avoid pruning interesting moves.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-02-13 15:29:24 +01:00
parent 52ed0e9563
commit e71d520758
1 changed files with 24 additions and 10 deletions
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34
src/position.cpp
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@ -420,30 +420,44 @@ bool Position::piece_attacks_square(Square f, Square t) const {
/// Position::move_attacks_square() tests whether a move from the current /// Position::move_attacks_square() tests whether a move from the current
/// position attacks a given square. Only attacks by the moving piece are /// position attacks a given square.
/// considered; the function does not handle X-ray attacks.
bool Position::move_attacks_square(Move m, Square s) const { bool Position::move_attacks_square(Move m, Square s) const {
assert(move_is_ok(m)); assert(move_is_ok(m));
assert(square_is_ok(s)); assert(square_is_ok(s));
bool is_attack;
Square f = move_from(m), t = move_to(m); Square f = move_from(m), t = move_to(m);
assert(square_is_occupied(f)); assert(square_is_occupied(f));
switch (piece_on(f)) switch (piece_on(f))
{ {
case WP: return pawn_attacks_square(WHITE, t, s); case WP: is_attack = pawn_attacks_square(WHITE, t, s); break;
case BP: return pawn_attacks_square(BLACK, t, s); case BP: is_attack = pawn_attacks_square(BLACK, t, s); break;
case WN: case BN: return piece_attacks_square<KNIGHT>(t, s); case WN: case BN: is_attack = piece_attacks_square<KNIGHT>(t, s); break;
case WB: case BB: return piece_attacks_square<BISHOP>(t, s); case WB: case BB: is_attack = piece_attacks_square<BISHOP>(t, s); break;
case WR: case BR: return piece_attacks_square<ROOK>(t, s); case WR: case BR: is_attack = piece_attacks_square<ROOK>(t, s); break;
case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s); case WQ: case BQ: is_attack = piece_attacks_square<QUEEN>(t, s); break;
case WK: case BK: return piece_attacks_square<KING>(t, s); case WK: case BK: is_attack = piece_attacks_square<KING>(t, s); break;
default: break; default: break;
} }
return false;
if (is_attack)
return true;
// Move the piece and scan for X-ray attacks behind it
Bitboard occ = occupied_squares();
Color us = color_of_piece_on(f);
clear_bit(&occ, f);
set_bit(&occ, t);
Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
|(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
// If we have attacks we need to verify that are caused by our move
// and are not already existent ones.
return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
} }