- // King safety. This is quite complicated, and is almost certainly far
- // from optimally tuned.
- if ( pos.piece_count(Them, QUEEN) >= 1
- && ei.kingAttackersCount[Them] >= 2
- && pos.non_pawn_material(Them) >= QueenValueMidgame + RookValueMidgame
- && ei.kingAdjacentZoneAttacksCount[Them])
- {
- // Is it the attackers turn to move?
- bool sente = (Them == pos.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 = pos.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<HasPopCnt>(undefended)) * 3
- + InitKingDanger[relative_square(Us, s)] - (shelter >> 5);
-
- // Analyse safe queen contact checks
- b = undefended & ei.attacked_by(Them, QUEEN) & ~pos.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<HasPopCnt>(b);
- attackUnits += QueenContactCheckBonus * count * (sente ? 2 : 1);
-
- // Is there a mate threat?
- if (QueenContactMates && !pos.is_check())
- {
- Bitboard escapeSquares =
- pos.attacks_from<KING>(s) & ~pos.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 < pos.piece_count(Them, QUEEN); i++)
- {
- from = pos.piece_list(Them, QUEEN, i);
- if ( bit_is_set(pos.attacks_from<QUEEN>(from), to)
- && !bit_is_set(pos.pinned_pieces(Them), from)
- && !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(ROOK, QUEEN, Us))
- && !(bishop_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(BISHOP, QUEEN, Us)))
-
- ei.mateThreat[Them] = make_move(from, to);
- }
- }
- }
- }
- }
- }
-
- // Analyse safe distance checks
- if (QueenCheckBonus > 0 || RookCheckBonus > 0)
- {
- b = pos.attacks_from<ROOK>(s) & ~pos.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<HasPopCnt>(b2);
-
- // Rook checks
- b2 = b & ei.attacked_by(Them, ROOK);
- if (b2)
- attackUnits += RookCheckBonus * count_1s_max_15<HasPopCnt>(b2);
- }
- if (QueenCheckBonus > 0 || BishopCheckBonus > 0)
- {
- b = pos.attacks_from<BISHOP>(s) & ~pos.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<HasPopCnt>(b2);
-
- // Bishop checks
- b2 = b & ei.attacked_by(Them, BISHOP);
- if (b2)
- attackUnits += BishopCheckBonus * count_1s_max_15<HasPopCnt>(b2);
- }
- if (KnightCheckBonus > 0)
- {
- b = pos.attacks_from<KNIGHT>(s) & ~pos.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<HasPopCnt>(b2);
- }
-
- // Analyse discovered checks (only for non-pawns right now, consider
- // adding pawns later).
- if (DiscoveredCheckBonus)
- {
- b = pos.discovered_check_candidates(Them) & ~pos.pieces(PAWN);
- if (b)
- attackUnits += DiscoveredCheckBonus * count_1s_max_15<HasPopCnt>(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[Us] * v;
-
- if (Us == pos.side_to_move())
- ei.futilityMargin += v;
- }