From: Marco Costalba Date: Thu, 12 Nov 2009 18:01:44 +0000 (+0100) Subject: Better document king safety evaluation X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=7d0e0ff95eef8e38eb0b07f2e499d650e7680909 Better document king safety evaluation No functional change. Signed-off-by: Marco Costalba --- diff --git a/src/evaluate.cpp b/src/evaluate.cpp index 25d3ed03..21bd97b0 100644 --- a/src/evaluate.cpp +++ b/src/evaluate.cpp @@ -720,8 +720,12 @@ namespace { void evaluate_king(const Position& pos, EvalInfo& ei) { const Color Them = (Us == WHITE ? BLACK : WHITE); + + Bitboard undefended, attackedByOthers, escapeSquares, occ, b, b2, safe; + Square from, to; + bool sente; + int attackUnits, count, shelter = 0; const Square s = pos.king_square(Us); - int shelter = 0; // King shelter if (relative_rank(Us, s) <= RANK_4) @@ -738,77 +742,80 @@ namespace { && ei.kingAdjacentZoneAttacksCount[Them]) { // Is it the attackers turn to move? - bool sente = (Them == pos.side_to_move()); + 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; + undefended = ei.attacked_by(Them) & ei.attacked_by(Us, KING); + undefended &= ~( 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)); // Initialize the 'attackUnits' variable, which is used later on as an - // index to the SafetyTable[] array. The initial value is based on the + // 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); + attackUnits = Min(25, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2) + + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + count_1s_max_15(undefended)) + + 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); + attackedByOthers = ei.attacked_by(Them, PAWN) | ei.attacked_by(Them, KNIGHT) + | ei.attacked_by(Them, BISHOP) | ei.attacked_by(Them, ROOK); b &= attackedByOthers; + + // Squares attacked by the queen and supported by another enemy piece and + // not defended by other pieces but our king. 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 && !pos.is_check()) - { - Bitboard escapeSquares = - pos.attacks_from(s) & ~pos.pieces_of_color(Us) & ~attackedByOthers; - - while (b) + // The bitboard b now contains the squares available for safe queen + // contact checks. + count = count_1s_max_15(b); + attackUnits += QueenContactCheckBonus * count * (sente ? 2 : 1); + + // Is there a mate threat? + if (QueenContactMates && !pos.is_check()) { - Square from, to = pop_1st_bit(&b); - if (!(escapeSquares & ~queen_attacks_bb(to, occ & ClearMaskBB[s]))) + escapeSquares = pos.attacks_from(s) & ~pos.pieces_of_color(Us) & ~attackedByOthers; + occ = pos.occupied_squares(); + while (b) { - // 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(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))) + to = pop_1st_bit(&b); - ei.mateThreat[Them] = make_move(from, to); + // Do we have escape squares from queen contact check attack ? + 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(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))) + + // Set the mate threat move + ei.mateThreat[Them] = make_move(from, to); + } } } } - } } } // Analyse safe distance checks + safe = ~(pos.pieces_of_color(Them) | ei.attacked_by(Us)); + if (QueenCheckBonus > 0 || RookCheckBonus > 0) { - b = pos.attacks_from(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us); + b = pos.attacks_from(s) & safe; // Queen checks b2 = b & ei.attacked_by(Them, QUEEN); @@ -822,7 +829,7 @@ namespace { } if (QueenCheckBonus > 0 || BishopCheckBonus > 0) { - b = pos.attacks_from(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us); + b = pos.attacks_from(s) & safe; // Queen checks b2 = b & ei.attacked_by(Them, QUEEN); @@ -836,7 +843,7 @@ namespace { } if (KnightCheckBonus > 0) { - b = pos.attacks_from(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us); + b = pos.attacks_from(s) & safe; // Knight checks b2 = b & ei.attacked_by(Them, KNIGHT); @@ -848,12 +855,12 @@ namespace { // adding pawns later). if (DiscoveredCheckBonus) { - b = pos.discovered_check_candidates(Them) & ~pos.pieces(PAWN); - if (b) - attackUnits += DiscoveredCheckBonus * count_1s_max_15(b) * (sente ? 2 : 1); + b = pos.discovered_check_candidates(Them) & ~pos.pieces(PAWN); + 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 + // 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. @@ -861,15 +868,11 @@ namespace { 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; + // out of bounds errors. + attackUnits = Min(99, Max(0, attackUnits)); // Finally, extract the king safety score from the SafetyTable[] array. - // Add the score to the evaluation, and also to ei.futilityMargin. The + // 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