- unsafeChecks |= knightChecks;
-
- // Find the squares that opponent attacks in our king flank, the squares
- // which they attack twice in that flank, and the squares that we defend.
- b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
- b2 = b1 & attackedBy2[Them];
- b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
-
- int kingFlankAttack = popcount(b1) + popcount(b2);
- int kingFlankDefense = popcount(b3);
-
- kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them] // (~10 Elo)
- + 183 * popcount(kingRing[Us] & weak) // (~15 Elo)
- + 148 * popcount(unsafeChecks) // (~4 Elo)
- + 98 * popcount(pos.blockers_for_king(Us)) // (~2 Elo)
- + 69 * kingAttacksCount[Them] // (~0.5 Elo)
- + 3 * kingFlankAttack * kingFlankAttack / 8 // (~0.5 Elo)
- + mg_value(mobility[Them] - mobility[Us]) // (~0.5 Elo)
- - 873 * !pos.count<QUEEN>(Them) // (~24 Elo)
- - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING]) // (~5 Elo)
- - 6 * mg_value(score) / 8 // (~8 Elo)
- - 4 * kingFlankDefense // (~5 Elo)
- + 37; // (~0.5 Elo)
-
- // Transform the kingDanger units into a Score, and subtract it from the evaluation
- if (kingDanger > 100)
- score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
-
- // Penalty when our king is on a pawnless flank
- if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
- score -= PawnlessFlank;
-
- // Penalty if king flank is under attack, potentially moving toward the king
- score -= FlankAttacks * kingFlankAttack;
-
- if constexpr (T)
- Trace::add(KING, Us, score);
-
- return score;
- }
-
-
- // Evaluation::threats() assigns bonuses according to the types of the
- // attacking and the attacked pieces.
-
- template<Tracing T> template<Color Us>
- Score Evaluation<T>::threats() const {
-
- constexpr Color Them = ~Us;
- constexpr Direction Up = pawn_push(Us);
- constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
-
- Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
- Score score = SCORE_ZERO;
-
- // Non-pawn enemies
- nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
-
- // Squares strongly protected by the enemy, either because they defend the
- // square with a pawn, or because they defend the square twice and we don't.
- stronglyProtected = attackedBy[Them][PAWN]
- | (attackedBy2[Them] & ~attackedBy2[Us]);
-
- // Non-pawn enemies, strongly protected
- defended = nonPawnEnemies & stronglyProtected;
-
- // Enemies not strongly protected and under our attack
- weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
-
- // Bonus according to the kind of attacking pieces
- if (defended | weak)
- {
- b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
- while (b)
- score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(b)))];
-
- b = weak & attackedBy[Us][ROOK];
- while (b)
- score += ThreatByRook[type_of(pos.piece_on(pop_lsb(b)))];
-
- if (weak & attackedBy[Us][KING])
- score += ThreatByKing;
-
- b = ~attackedBy[Them][ALL_PIECES]
- | (nonPawnEnemies & attackedBy2[Us]);
- score += Hanging * popcount(weak & b);
-
- // Additional bonus if weak piece is only protected by a queen
- score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
- }
-
- // Bonus for restricting their piece moves
- b = attackedBy[Them][ALL_PIECES]
- & ~stronglyProtected
- & attackedBy[Us][ALL_PIECES];
- score += RestrictedPiece * popcount(b);
-
- // Protected or unattacked squares
- safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
-
- // Bonus for attacking enemy pieces with our relatively safe pawns
- b = pos.pieces(Us, PAWN) & safe;
- b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
- score += ThreatBySafePawn * popcount(b);
-
- // Find squares where our pawns can push on the next move
- b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
- b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
-
- // Keep only the squares which are relatively safe
- b &= ~attackedBy[Them][PAWN] & safe;
-
- // Bonus for safe pawn threats on the next move
- b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
- score += ThreatByPawnPush * popcount(b);
-
- // Bonus for threats on the next moves against enemy queen
- if (pos.count<QUEEN>(Them) == 1)
- {
- bool queenImbalance = pos.count<QUEEN>() == 1;
-
- Square s = pos.square<QUEEN>(Them);
- safe = mobilityArea[Us]
- & ~pos.pieces(Us, PAWN)
- & ~stronglyProtected;
-
- b = attackedBy[Us][KNIGHT] & attacks_bb<KNIGHT>(s);
-
- score += KnightOnQueen * popcount(b & safe) * (1 + queenImbalance);
-
- b = (attackedBy[Us][BISHOP] & attacks_bb<BISHOP>(s, pos.pieces()))
- | (attackedBy[Us][ROOK ] & attacks_bb<ROOK >(s, pos.pieces()));
-
- score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]) * (1 + queenImbalance);
- }
-
- if constexpr (T)
- Trace::add(THREAT, Us, score);
-
- return score;
- }
-
- // Evaluation::passed() evaluates the passed pawns and candidate passed
- // pawns of the given color.
-
- template<Tracing T> template<Color Us>
- Score Evaluation<T>::passed() const {
-
- constexpr Color Them = ~Us;
- constexpr Direction Up = pawn_push(Us);
- constexpr Direction Down = -Up;
-
- auto king_proximity = [&](Color c, Square s) {
- return std::min(distance(pos.square<KING>(c), s), 5);
- };
-
- Bitboard b, bb, squaresToQueen, unsafeSquares, blockedPassers, helpers;
- Score score = SCORE_ZERO;
-
- b = pe->passed_pawns(Us);
-
- blockedPassers = b & shift<Down>(pos.pieces(Them, PAWN));
- if (blockedPassers)
- {
- helpers = shift<Up>(pos.pieces(Us, PAWN))
- & ~pos.pieces(Them)
- & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES]);
-
- // Remove blocked candidate passers that don't have help to pass
- b &= ~blockedPassers
- | shift<WEST>(helpers)
- | shift<EAST>(helpers);
- }
-
- while (b)
- {
- Square s = pop_lsb(b);
-
- assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
-
- int r = relative_rank(Us, s);
-
- Score bonus = PassedRank[r];
-
- if (r > RANK_3)
- {
- int w = 5 * r - 13;
- Square blockSq = s + Up;
-
- // Adjust bonus based on the king's proximity
- bonus += make_score(0, ( king_proximity(Them, blockSq) * 19 / 4
- - king_proximity(Us, blockSq) * 2) * w);
-
- // If blockSq is not the queening square then consider also a second push
- if (r != RANK_7)
- bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
-
- // If the pawn is free to advance, then increase the bonus
- if (pos.empty(blockSq))
- {
- squaresToQueen = forward_file_bb(Us, s);
- unsafeSquares = passed_pawn_span(Us, s);
-
- bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
-
- if (!(pos.pieces(Them) & bb))
- unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
-
- // If there are no enemy pieces or attacks on passed pawn span, assign a big bonus.
- // Or if there is some, but they are all attacked by our pawns, assign a bit smaller bonus.
- // Otherwise assign a smaller bonus if the path to queen is not attacked
- // and even smaller bonus if it is attacked but block square is not.
- int k = !unsafeSquares ? 36 :
- !(unsafeSquares & ~attackedBy[Us][PAWN]) ? 30 :
- !(unsafeSquares & squaresToQueen) ? 17 :
- !(unsafeSquares & blockSq) ? 7 :
- 0 ;
-
- // Assign a larger bonus if the block square is defended
- if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
- k += 5;
-
- bonus += make_score(k * w, k * w);
- }
- } // r > RANK_3
-
- score += bonus - PassedFile * edge_distance(file_of(s));
- }
-
- if constexpr (T)
- Trace::add(PASSED, Us, score);
-
- return score;
- }
-
-
- // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
- // play in the opening. It is based on the number of safe squares on the four central files
- // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
- // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
-
- template<Tracing T> template<Color Us>
- Score Evaluation<T>::space() const {
-
- // Early exit if, for example, both queens or 6 minor pieces have been exchanged
- if (pos.non_pawn_material() < SpaceThreshold)
- return SCORE_ZERO;
-
- constexpr Color Them = ~Us;
- constexpr Direction Down = -pawn_push(Us);
- constexpr Bitboard SpaceMask =
- Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
- : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
-
- // Find the available squares for our pieces inside the area defined by SpaceMask
- Bitboard safe = SpaceMask
- & ~pos.pieces(Us, PAWN)
- & ~attackedBy[Them][PAWN];
-
- // Find all squares which are at most three squares behind some friendly pawn
- Bitboard behind = pos.pieces(Us, PAWN);
- behind |= shift<Down>(behind);
- behind |= shift<Down+Down>(behind);
-
- // Compute space score based on the number of safe squares and number of our pieces
- // increased with number of total blocked pawns in position.
- int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
- int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
- Score score = make_score(bonus * weight * weight / 16, 0);
-
- if constexpr (T)
- Trace::add(SPACE, Us, score);
-
- return score;
- }
-
-
- // Evaluation::winnable() adjusts the midgame and endgame score components, based on
- // the known attacking/defending status of the players. The final value is derived
- // by interpolation from the midgame and endgame values.
-
- template<Tracing T>
- Value Evaluation<T>::winnable(Score score) const {
-
- int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
- + int(rank_of(pos.square<KING>(WHITE)) - rank_of(pos.square<KING>(BLACK)));
-
- bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
- && (pos.pieces(PAWN) & KingSide);
-
- bool almostUnwinnable = outflanking < 0
- && !pawnsOnBothFlanks;
-
- bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
- || rank_of(pos.square<KING>(BLACK)) < RANK_5;
-
- // Compute the initiative bonus for the attacking side
- int complexity = 9 * pe->passed_count()
- + 12 * pos.count<PAWN>()
- + 9 * outflanking
- + 21 * pawnsOnBothFlanks
- + 24 * infiltration
- + 51 * !pos.non_pawn_material()
- - 43 * almostUnwinnable
- -110 ;
-
- Value mg = mg_value(score);
- Value eg = eg_value(score);
-
- // Now apply the bonus: note that we find the attacking side by extracting the
- // sign of the midgame or endgame values, and that we carefully cap the bonus
- // so that the midgame and endgame scores do not change sign after the bonus.
- int u = ((mg > 0) - (mg < 0)) * std::clamp(complexity + 50, -abs(mg), 0);
- int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
-
- mg += u;
- eg += v;
-
- // Compute the scale factor for the winning side
- Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
- int sf = me->scale_factor(pos, strongSide);
-
- // If scale factor is not already specific, scale up/down via general heuristics
- if (sf == SCALE_FACTOR_NORMAL)