- if ( p.piece_count(them, QUEEN) >= 1
- && ei.kingAttackersCount[them] >= 2
- && p.non_pawn_material(them) >= QueenValueMidgame + RookValueMidgame
- && ei.kingAdjacentZoneAttacksCount[them])
- {
- // Is it the attackers turn to move?
- bool sente = (them == p.side_to_move());
-
- // Find the attacked squares around the king which has no defenders
- // apart from the king itself
- Bitboard undefended =
- ei.attacked_by(them) & ~ei.attacked_by(us, PAWN)
- & ~ei.attacked_by(us, KNIGHT) & ~ei.attacked_by(us, BISHOP)
- & ~ei.attacked_by(us, ROOK) & ~ei.attacked_by(us, QUEEN)
- & ei.attacked_by(us, KING);
-
- Bitboard occ = p.occupied_squares(), b, b2;
-
- // Initialize the 'attackUnits' variable, which is used later on as an
- // index to the SafetyTable[] array. The initial value is based on the
- // number and types of the attacking pieces, the number of attacked and
- // undefended squares around the king, the square of the king, and the
- // quality of the pawn shelter.
- int attackUnits =
- Min((ei.kingAttackersCount[them] * ei.kingAttackersWeight[them]) / 2, 25)
- + (ei.kingAdjacentZoneAttacksCount[them] + count_1s_max_15(undefended)) * 3
- + InitKingDanger[relative_square(us, s)] - (shelter >> 5);
-
- // Analyse safe queen contact checks
- b = undefended & ei.attacked_by(them, QUEEN) & ~p.pieces_of_color(them);
- if (b)
- {
- Bitboard attackedByOthers =
- ei.attacked_by(them, PAWN) | ei.attacked_by(them, KNIGHT)
- | ei.attacked_by(them, BISHOP) | ei.attacked_by(them, ROOK);
-
- b &= attackedByOthers;
- if (b)
- {
- // The bitboard b now contains the squares available for safe queen
- // contact checks.
- int count = count_1s_max_15(b);
- attackUnits += QueenContactCheckBonus * count * (sente ? 2 : 1);
-
- // Is there a mate threat?
- if (QueenContactMates && !p.is_check())
- {
- Bitboard escapeSquares =
- p.piece_attacks<KING>(s) & ~p.pieces_of_color(us) & ~attackedByOthers;
-
- while (b)
- {
- Square from, to = pop_1st_bit(&b);
- if (!(escapeSquares & ~queen_attacks_bb(to, occ & ClearMaskBB[s])))
- {
- // We have a mate, unless the queen is pinned or there
- // is an X-ray attack through the queen.
- for (int i = 0; i < p.piece_count(them, QUEEN); i++)
- {
- from = p.piece_list(them, QUEEN, i);
- if ( bit_is_set(p.piece_attacks<QUEEN>(from), to)
- && !bit_is_set(p.pinned_pieces(them), from)
- && !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & p.rooks_and_queens(us))
- && !(bishop_attacks_bb(to, occ & ClearMaskBB[from]) & p.bishops_and_queens(us)))
-
- ei.mateThreat[them] = make_move(from, to);
- }
- }
- }
- }
- }
- }
-
- // Analyse safe distance checks
- if (QueenCheckBonus > 0 || RookCheckBonus > 0)
- {
- b = p.piece_attacks<ROOK>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
-
- // Queen checks
- b2 = b & ei.attacked_by(them, QUEEN);
- if( b2)
- attackUnits += QueenCheckBonus * count_1s_max_15(b2);
-
- // Rook checks
- b2 = b & ei.attacked_by(them, ROOK);
- if (b2)
- attackUnits += RookCheckBonus * count_1s_max_15(b2);
- }
- if (QueenCheckBonus > 0 || BishopCheckBonus > 0)
- {
- b = p.piece_attacks<BISHOP>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
-
- // Queen checks
- b2 = b & ei.attacked_by(them, QUEEN);
- if (b2)
- attackUnits += QueenCheckBonus * count_1s_max_15(b2);
-
- // Bishop checks
- b2 = b & ei.attacked_by(them, BISHOP);
- if (b2)
- attackUnits += BishopCheckBonus * count_1s_max_15(b2);
- }
- if (KnightCheckBonus > 0)
- {
- b = p.piece_attacks<KNIGHT>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
-
- // Knight checks
- b2 = b & ei.attacked_by(them, KNIGHT);
- if (b2)
- attackUnits += KnightCheckBonus * count_1s_max_15(b2);
- }
-
- // Analyse discovered checks (only for non-pawns right now, consider
- // adding pawns later).
- if (DiscoveredCheckBonus)
- {
- b = p.discovered_check_candidates(them) & ~p.pawns();
- if (b)
- attackUnits += DiscoveredCheckBonus * count_1s_max_15(b) * (sente? 2 : 1);
- }
-
- // Has a mate threat been found? We don't do anything here if the
- // side with the mating move is the side to move, because in that
- // case the mating side will get a huge bonus at the end of the main
- // evaluation function instead.
- if (ei.mateThreat[them] != MOVE_NONE)
- attackUnits += MateThreatBonus;
-
- // Ensure that attackUnits is between 0 and 99, in order to avoid array
- // out of bounds errors:
- if (attackUnits < 0)
- attackUnits = 0;
-
- if (attackUnits >= 100)
- attackUnits = 99;
-
- // Finally, extract the king safety score from the SafetyTable[] array.
- // Add the score to the evaluation, and also to ei.futilityMargin. The
- // reason for adding the king safety score to the futility margin is
- // that the king safety scores can sometimes be very big, and that
- // capturing a single attacking piece can therefore result in a score
- // change far bigger than the value of the captured piece.
- Value v = apply_weight(SafetyTable[attackUnits], WeightKingSafety[us]);
-
- ei.mgValue -= sign * v;
-
- if (us == p.side_to_move())
- ei.futilityMargin += v;
- }