- // King safety. This is quite complicated, and is almost certainly far
- // from optimally tuned.
- Color them = opposite_color(us);
- if(p.queen_count(them) >= 1 && ei.attackCount[them] >= 2
- && p.non_pawn_material(them) >= QueenValueMidgame + RookValueMidgame
- && ei.attacked[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 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.attackCount[them] * ei.attackWeight[them]) / 2, 25)
- + (ei.attacked[them] + count_1s_max_15(undefended)) * 3
- + InitKingDanger[relative_square(us, s)] - shelter / 32;
-
- // 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.king_attacks(s) & ~p.pieces_of_color(us) & ~attackedByOthers;
- while(b) {
- Square from, to = pop_1st_bit(&b);
- if(!(escapeSquares
- & ~queen_attacks_bb(to, occ & clear_mask_bb(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.queen_count(them); i++) {
- from = p.queen_list(them, i);
- if(bit_is_set(p.queen_attacks(from), to)
- && !bit_is_set(p.pinned_pieces(them), from)
- && !(rook_attacks_bb(to, occ & clear_mask_bb(from))
- & p.rooks_and_queens(us))
- && !(rook_attacks_bb(to, occ & clear_mask_bb(from))
- & p.rooks_and_queens(us)))
- ei.mateThreat[them] = make_move(from, to);
- }
- }
- }
- }
- }
- }