- Bitboard attacks(const Piece P, const Square sq, const Bitboard occ)
- {
- switch(P)
- {
- case WP:
- case BP:
- case WN:
- case BN:
- case WK:
- case BK:
- return StepAttackBB[P][sq];
- case WB:
- case BB:
- return bishop_attacks_bb(sq, occ);
- case WR:
- case BR:
- return rook_attacks_bb(sq, occ);
- case WQ:
- case BQ:
- return bishop_attacks_bb(sq, occ) | rook_attacks_bb(sq, occ);
- default:
- assert(false);
- return 0ULL;
- }
- }
-
- bool check_is_useless(Position &pos, Move move, Value eval, Value futilityBase, Value beta, Value *bValue)
- {
- Value bestValue = *bValue;
-
- /// Rule 1. Using checks to reposition pieces when close to beta
- if (eval + PawnValueMidgame / 4 < beta)
- {
- if (eval + PawnValueMidgame / 4 > bestValue)
- bestValue = eval + PawnValueMidgame / 4;
- }
- else
- return false;
-
- Square from = move_from(move);
- Square to = move_to(move);
- Color oppColor = opposite_color(pos.side_to_move());
- Square oppKing = pos.king_square(oppColor);
-
- Bitboard occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL <<oppKing);
- Bitboard oppOcc = pos.pieces_of_color(oppColor) & ~(1ULL <<oppKing);
- Bitboard oldAtt = attacks(pos.piece_on(from), from, occ);
- Bitboard newAtt = attacks(pos.piece_on(from), to, occ);
-
- // Rule 2. Checks which give opponent's king at most one escape square are dangerous
- Bitboard escapeBB = attacks(WK, oppKing, 0) & ~oppOcc & ~newAtt & ~(1ULL << to);
-
- if (!escapeBB)
- return false;
-
- if (!(escapeBB & (escapeBB - 1)))
- return false;
-
- /// Rule 3. Queen contact check is very dangerous
- if ( pos.type_of_piece_on(from) == QUEEN
- && bit_is_set(attacks(WK, oppKing, 0), to))
- return false;
-
- /// Rule 4. Creating new double threats with checks
- Bitboard newVictims = oppOcc & ~oldAtt & newAtt;
-
- while(newVictims)
- {
- Square victimSq = pop_1st_bit(&newVictims);
-
- Value futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
-
- // Note that here we generate illegal "double move"!
- if (futilityValue >= beta && pos.see_sign(make_move(from, victimSq)) >= 0)
- return false;
-
- if (futilityValue > bestValue)
- bestValue = futilityValue;
- }
-
- *bValue = bestValue;
- return true;
- }
-