2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 enum Tracing {NO_TRACE, TRACE};
38 enum Term { // The first 8 entries are for PieceType
39 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
42 double scores[TERM_NB][COLOR_NB][PHASE_NB];
44 double to_cp(Value v) { return double(v) / PawnValueEg; }
46 void add(int idx, Color c, Score s) {
47 scores[idx][c][MG] = to_cp(mg_value(s));
48 scores[idx][c][EG] = to_cp(eg_value(s));
51 void add(int idx, Score w, Score b = SCORE_ZERO) {
52 add(idx, WHITE, w); add(idx, BLACK, b);
55 std::ostream& operator<<(std::ostream& os, Term t) {
57 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
58 os << " --- --- | --- --- | ";
60 os << std::setw(5) << scores[t][WHITE][MG] << " "
61 << std::setw(5) << scores[t][WHITE][EG] << " | "
62 << std::setw(5) << scores[t][BLACK][MG] << " "
63 << std::setw(5) << scores[t][BLACK][EG] << " | ";
65 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
66 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
72 using namespace Trace;
74 // Evaluation class contains various information computed and collected
75 // by the evaluation functions.
76 template<Tracing T = NO_TRACE>
80 Evaluation() = delete;
81 Evaluation(const Position& p) : pos(p) {}
82 Evaluation& operator=(const Evaluation&) = delete;
87 // Evaluation helpers (used when calling value())
88 template<Color Us> void initialize();
89 template<Color Us> Score evaluate_king();
90 template<Color Us> Score evaluate_threats();
91 template<Color Us> Score evaluate_passed_pawns();
92 template<Color Us> Score evaluate_space();
93 template<Color Us, PieceType Pt> Score evaluate_pieces();
94 ScaleFactor evaluate_scale_factor(Value eg);
95 Score evaluate_initiative(Value eg);
101 Bitboard mobilityArea[COLOR_NB];
102 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
104 // attackedBy[color][piece type] is a bitboard representing all squares
105 // attacked by a given color and piece type (can be also ALL_PIECES).
106 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
108 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
109 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
110 // pawn or squares attacked by 2 pawns are not explicitly added.
111 Bitboard attackedBy2[COLOR_NB];
113 // kingRing[color] is the zone around the king which is considered
114 // by the king safety evaluation. This consists of the squares directly
115 // adjacent to the king, and (only for a king on its first rank) the
116 // squares two ranks in front of the king. For instance, if black's king
117 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
118 // f7, g7, h7, f6, g6 and h6.
119 Bitboard kingRing[COLOR_NB];
121 // kingAttackersCount[color] is the number of pieces of the given color
122 // which attack a square in the kingRing of the enemy king.
123 int kingAttackersCount[COLOR_NB];
125 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
126 // given color which attack a square in the kingRing of the enemy king. The
127 // weights of the individual piece types are given by the elements in the
128 // KingAttackWeights array.
129 int kingAttackersWeight[COLOR_NB];
131 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
132 // color to squares directly adjacent to the enemy king. Pieces which attack
133 // more than one square are counted multiple times. For instance, if there is
134 // a white knight on g5 and black's king is on g8, this white knight adds 2
135 // to kingAdjacentZoneAttacksCount[WHITE].
136 int kingAdjacentZoneAttacksCount[COLOR_NB];
139 #define V(v) Value(v)
140 #define S(mg, eg) make_score(mg, eg)
142 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
143 // indexed by piece type and number of attacked squares in the mobility area.
144 const Score MobilityBonus[][32] = {
145 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
146 S( 22, 26), S( 29, 29), S( 36, 29) },
147 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
148 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
149 S( 91, 88), S( 98, 97) },
150 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
151 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
152 S( 46,166), S( 48,169), S( 58,171) },
153 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
154 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
155 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
156 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
157 S(106,184), S(109,191), S(113,206), S(116,212) }
160 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
161 // pieces if they can reach an outpost square, bigger if that square is
162 // supported by a pawn. If the minor piece occupies an outpost square
163 // then score is doubled.
164 const Score Outpost[][2] = {
165 { S(22, 6), S(33, 9) }, // Knight
166 { S( 9, 2), S(14, 4) } // Bishop
169 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
170 // friendly pawn on the rook file.
171 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
173 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
174 // which piece type attacks which one. Attacks on lesser pieces which are
175 // pawn-defended are not considered.
176 const Score ThreatByMinor[PIECE_TYPE_NB] = {
177 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
180 const Score ThreatByRook[PIECE_TYPE_NB] = {
181 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)
184 // ThreatByKing[on one/on many] contains bonuses for king attacks on
185 // pawns or pieces which are not pawn-defended.
186 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
188 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
189 // We don't use a Score because we process the two components independently.
190 const Value Passed[][RANK_NB] = {
191 { V(5), V( 5), V(31), V(73), V(166), V(252) },
192 { V(7), V(14), V(38), V(73), V(166), V(252) }
195 // PassedFile[File] contains a bonus according to the file of a passed pawn
196 const Score PassedFile[FILE_NB] = {
197 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
198 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
201 // KingProtector[PieceType-2] contains a bonus according to distance from king
202 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
204 // Assorted bonuses and penalties used by evaluation
205 const Score MinorBehindPawn = S( 16, 0);
206 const Score BishopPawns = S( 8, 12);
207 const Score RookOnPawn = S( 8, 24);
208 const Score TrappedRook = S( 92, 0);
209 const Score WeakQueen = S( 50, 10);
210 const Score OtherCheck = S( 10, 10);
211 const Score CloseEnemies = S( 7, 0);
212 const Score PawnlessFlank = S( 20, 80);
213 const Score ThreatByHangingPawn = S( 71, 61);
214 const Score ThreatBySafePawn = S(182,175);
215 const Score ThreatByRank = S( 16, 3);
216 const Score Hanging = S( 48, 27);
217 const Score ThreatByPawnPush = S( 38, 22);
218 const Score HinderPassedPawn = S( 7, 0);
219 const Score TrappedBishopA1H1 = S( 50, 50);
224 // KingAttackWeights[PieceType] contains king attack weights by piece type
225 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
227 // Penalties for enemy's safe checks
228 const int QueenCheck = 780;
229 const int RookCheck = 880;
230 const int BishopCheck = 435;
231 const int KnightCheck = 790;
233 // Threshold for lazy and space evaluation
234 const Value LazyThreshold = Value(1500);
235 const Value SpaceThreshold = Value(12222);
238 // initialize() computes king and pawn attacks, and the king ring bitboard
239 // for a given color. This is done at the beginning of the evaluation.
241 template<Tracing T> template<Color Us>
242 void Evaluation<T>::initialize() {
244 const Color Them = (Us == WHITE ? BLACK : WHITE);
245 const Square Up = (Us == WHITE ? NORTH : SOUTH);
246 const Square Down = (Us == WHITE ? SOUTH : NORTH);
247 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
249 // Find our pawns on the first two ranks, and those which are blocked
250 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
252 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
253 // are excluded from the mobility area.
254 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
256 // Initialise the attack bitboards with the king and pawn information
257 b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
258 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
260 attackedBy2[Us] = b & attackedBy[Us][PAWN];
261 attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];
263 // Init our king safety tables only if we are going to use them
264 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
267 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
268 kingRing[Us] |= shift<Up>(b);
270 kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));
271 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
274 kingRing[Us] = kingAttackersCount[Them] = 0;
278 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
281 template<Tracing T> template<Color Us, PieceType Pt>
282 Score Evaluation<T>::evaluate_pieces() {
284 const Color Them = (Us == WHITE ? BLACK : WHITE);
285 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
286 : Rank5BB | Rank4BB | Rank3BB);
287 const Square* pl = pos.squares<Pt>(Us);
291 Score score = SCORE_ZERO;
293 attackedBy[Us][Pt] = 0;
295 while ((s = *pl++) != SQ_NONE)
297 // Find attacked squares, including x-ray attacks for bishops and rooks
298 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
299 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
300 : pos.attacks_from<Pt>(s);
302 if (pos.pinned_pieces(Us) & s)
303 b &= LineBB[pos.square<KING>(Us)][s];
305 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
306 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
308 if (b & kingRing[Them])
310 kingAttackersCount[Us]++;
311 kingAttackersWeight[Us] += KingAttackWeights[Pt];
312 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
315 int mob = popcount(b & mobilityArea[Us]);
317 mobility[Us] += MobilityBonus[Pt - 2][mob];
319 // Bonus for this piece as a king protector
320 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
322 if (Pt == BISHOP || Pt == KNIGHT)
324 // Bonus for outpost squares
325 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
327 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & s)] * 2;
330 bb &= b & ~pos.pieces(Us);
332 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & bb)];
335 // Bonus when behind a pawn
336 if ( relative_rank(Us, s) < RANK_5
337 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
338 score += MinorBehindPawn;
340 // Penalty for pawns on the same color square as the bishop
342 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
344 // An important Chess960 pattern: A cornered bishop blocked by a friendly
345 // pawn diagonally in front of it is a very serious problem, especially
346 // when that pawn is also blocked.
349 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
351 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
352 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
353 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
354 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
361 // Bonus for aligning with enemy pawns on the same rank/file
362 if (relative_rank(Us, s) >= RANK_5)
363 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
365 // Bonus when on an open or semi-open file
366 if (pe->semiopen_file(Us, file_of(s)))
367 score += RookOnFile[!!pe->semiopen_file(Them, file_of(s))];
369 // Penalty when trapped by the king, even more if the king cannot castle
372 Square ksq = pos.square<KING>(Us);
374 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
375 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
376 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
382 // Penalty if any relative pin or discovered attack against the queen
384 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
390 Trace::add(Pt, Us, score);
396 // evaluate_king() assigns bonuses and penalties to a king of a given color
398 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
399 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
400 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
402 const Bitboard KingFlank[FILE_NB] = {
403 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
406 template<Tracing T> template<Color Us>
407 Score Evaluation<T>::evaluate_king() {
409 const Color Them = (Us == WHITE ? BLACK : WHITE);
410 const Square Up = (Us == WHITE ? NORTH : SOUTH);
411 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
412 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
414 const Square ksq = pos.square<KING>(Us);
415 Bitboard kingOnlyDefended, undefended, b, b1, b2, safe, other;
418 // King shelter and enemy pawns storm
419 Score score = pe->king_safety<Us>(pos, ksq);
421 // Main king safety evaluation
422 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
424 // Find the attacked squares which are defended only by our king...
425 kingOnlyDefended = attackedBy[Them][ALL_PIECES]
426 & attackedBy[Us][KING]
429 // ... and those which are not defended at all in the larger king ring
430 undefended = attackedBy[Them][ALL_PIECES]
431 & ~attackedBy[Us][ALL_PIECES]
435 // Initialize the 'kingDanger' variable, which will be transformed
436 // later into a king danger score. The initial value is based on the
437 // number and types of the enemy's attacking pieces, the number of
438 // attacked and weak squares around our king, the absence of queen and
439 // the quality of the pawn shelter (current 'score' value).
440 kingDanger = kingAttackersCount[Them] * kingAttackersWeight[Them]
441 + 102 * kingAdjacentZoneAttacksCount[Them]
442 + 191 * popcount(kingOnlyDefended | undefended)
443 + 143 * !!pos.pinned_pieces(Us)
444 - 848 * !pos.count<QUEEN>(Them)
445 - 9 * mg_value(score) / 8
448 // Analyse the safe enemy's checks which are possible on next move
449 safe = ~pos.pieces(Them);
450 safe &= ~attackedBy[Us][ALL_PIECES] | (kingOnlyDefended & attackedBy2[Them]);
452 b1 = pos.attacks_from< ROOK>(ksq);
453 b2 = pos.attacks_from<BISHOP>(ksq);
455 // Enemy queen safe checks
456 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe)
457 kingDanger += QueenCheck;
459 // For minors and rooks, also consider the square safe if attacked twice,
460 // and only defended by our queen.
461 safe |= attackedBy2[Them]
462 & ~(attackedBy2[Us] | pos.pieces(Them))
463 & attackedBy[Us][QUEEN];
465 // Some other potential checks are also analysed, even from squares
466 // currently occupied by the opponent own pieces, as long as the square
467 // is not attacked by our pawns, and is not occupied by a blocked pawn.
468 other = ~( attackedBy[Us][PAWN]
469 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
471 // Enemy rooks safe and other checks
472 if (b1 & attackedBy[Them][ROOK] & safe)
473 kingDanger += RookCheck;
475 else if (b1 & attackedBy[Them][ROOK] & other)
478 // Enemy bishops safe and other checks
479 if (b2 & attackedBy[Them][BISHOP] & safe)
480 kingDanger += BishopCheck;
482 else if (b2 & attackedBy[Them][BISHOP] & other)
485 // Enemy knights safe and other checks
486 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
488 kingDanger += KnightCheck;
493 // Transform the kingDanger units into a Score, and substract it from the evaluation
495 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
498 // King tropism: firstly, find squares that opponent attacks in our king flank
499 File kf = file_of(ksq);
500 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
502 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
503 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
505 // Secondly, add the squares which are attacked twice in that flank and
506 // which are not defended by our pawns.
507 b = (Us == WHITE ? b << 4 : b >> 4)
508 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
510 score -= CloseEnemies * popcount(b);
512 // Penalty when our king is on a pawnless flank
513 if (!(pos.pieces(PAWN) & KingFlank[kf]))
514 score -= PawnlessFlank;
517 Trace::add(KING, Us, score);
523 // evaluate_threats() assigns bonuses according to the types of the attacking
524 // and the attacked pieces.
526 template<Tracing T> template<Color Us>
527 Score Evaluation<T>::evaluate_threats() {
529 const Color Them = (Us == WHITE ? BLACK : WHITE);
530 const Square Up = (Us == WHITE ? NORTH : SOUTH);
531 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
532 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
533 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
535 Bitboard b, weak, defended, stronglyProtected, safeThreats;
536 Score score = SCORE_ZERO;
538 // Non-pawn enemies attacked by a pawn
539 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
543 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
544 | attackedBy[Us][ALL_PIECES]);
546 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
548 score += ThreatBySafePawn * popcount(safeThreats);
550 if (weak ^ safeThreats)
551 score += ThreatByHangingPawn;
554 // Squares strongly protected by the opponent, either because they attack the
555 // square with a pawn, or because they attack the square twice and we don't.
556 stronglyProtected = attackedBy[Them][PAWN]
557 | (attackedBy2[Them] & ~attackedBy2[Us]);
559 // Non-pawn enemies, strongly protected
560 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
563 // Enemies not strongly protected and under our attack
564 weak = pos.pieces(Them)
566 & attackedBy[Us][ALL_PIECES];
568 // Add a bonus according to the kind of attacking pieces
571 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
574 Square s = pop_lsb(&b);
575 score += ThreatByMinor[type_of(pos.piece_on(s))];
576 if (type_of(pos.piece_on(s)) != PAWN)
577 score += ThreatByRank * (int)relative_rank(Them, s);
580 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
583 Square s = pop_lsb(&b);
584 score += ThreatByRook[type_of(pos.piece_on(s))];
585 if (type_of(pos.piece_on(s)) != PAWN)
586 score += ThreatByRank * (int)relative_rank(Them, s);
589 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
591 b = weak & attackedBy[Us][KING];
593 score += ThreatByKing[more_than_one(b)];
596 // Find squares where our pawns can push on the next move
597 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
598 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
600 // Keep only the squares which are not completely unsafe
601 b &= ~attackedBy[Them][PAWN]
602 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
604 // Add a bonus for each new pawn threats from those squares
605 b = (shift<Left>(b) | shift<Right>(b))
607 & ~attackedBy[Us][PAWN];
609 score += ThreatByPawnPush * popcount(b);
612 Trace::add(THREAT, Us, score);
618 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
619 // pawns of the given color.
621 template<Tracing T> template<Color Us>
622 Score Evaluation<T>::evaluate_passed_pawns() {
624 const Color Them = (Us == WHITE ? BLACK : WHITE);
625 const Square Up = (Us == WHITE ? NORTH : SOUTH);
627 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
628 Score score = SCORE_ZERO;
630 b = pe->passed_pawns(Us);
634 Square s = pop_lsb(&b);
636 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
638 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
639 score -= HinderPassedPawn * popcount(bb);
641 int r = relative_rank(Us, s) - RANK_2;
642 int rr = r * (r - 1);
644 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
648 Square blockSq = s + Up;
650 // Adjust bonus based on the king's proximity
651 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
652 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
654 // If blockSq is not the queening square then consider also a second push
655 if (relative_rank(Us, blockSq) != RANK_8)
656 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
658 // If the pawn is free to advance, then increase the bonus
659 if (pos.empty(blockSq))
661 // If there is a rook or queen attacking/defending the pawn from behind,
662 // consider all the squaresToQueen. Otherwise consider only the squares
663 // in the pawn's path attacked or occupied by the enemy.
664 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
666 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
668 if (!(pos.pieces(Us) & bb))
669 defendedSquares &= attackedBy[Us][ALL_PIECES];
671 if (!(pos.pieces(Them) & bb))
672 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
674 // If there aren't any enemy attacks, assign a big bonus. Otherwise
675 // assign a smaller bonus if the block square isn't attacked.
676 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
678 // If the path to the queen is fully defended, assign a big bonus.
679 // Otherwise assign a smaller bonus if the block square is defended.
680 if (defendedSquares == squaresToQueen)
683 else if (defendedSquares & blockSq)
686 mbonus += k * rr, ebonus += k * rr;
688 else if (pos.pieces(Us) & blockSq)
689 mbonus += rr + r * 2, ebonus += rr + r * 2;
692 // Scale down bonus for candidate passers which need more than one
693 // pawn push to become passed or have a pawn in front of them.
694 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
695 mbonus /= 2, ebonus /= 2;
697 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
701 Trace::add(PASSED, Us, score);
707 // evaluate_space() computes the space evaluation for a given side. The
708 // space evaluation is a simple bonus based on the number of safe squares
709 // available for minor pieces on the central four files on ranks 2--4. Safe
710 // squares one, two or three squares behind a friendly pawn are counted
711 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
712 // improve play on game opening.
714 template<Tracing T> template<Color Us>
715 Score Evaluation<T>::evaluate_space() {
717 const Color Them = (Us == WHITE ? BLACK : WHITE);
718 const Bitboard SpaceMask =
719 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
720 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
722 // Find the safe squares for our pieces inside the area defined by
723 // SpaceMask. A square is unsafe if it is attacked by an enemy
724 // pawn, or if it is undefended and attacked by an enemy piece.
725 Bitboard safe = SpaceMask
726 & ~pos.pieces(Us, PAWN)
727 & ~attackedBy[Them][PAWN]
728 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
730 // Find all squares which are at most three squares behind some friendly pawn
731 Bitboard behind = pos.pieces(Us, PAWN);
732 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
733 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
735 // Since SpaceMask[Us] is fully on our half of the board...
736 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
738 // ...count safe + (behind & safe) with a single popcount.
739 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
740 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
742 return make_score(bonus * weight * weight / 16, 0);
746 // evaluate_initiative() computes the initiative correction value for the
747 // position, i.e., second order bonus/malus based on the known attacking/defending
748 // status of the players.
751 Score Evaluation<T>::evaluate_initiative(Value eg) {
753 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
754 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
755 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
757 // Compute the initiative bonus for the attacking side
758 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
760 // Now apply the bonus: note that we find the attacking side by extracting
761 // the sign of the endgame value, and that we carefully cap the bonus so
762 // that the endgame score will never change sign after the bonus.
763 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
765 return make_score(0, v);
769 // evaluate_scale_factor() computes the scale factor for the winning side
772 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
774 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
775 ScaleFactor sf = me->scale_factor(pos, strongSide);
777 // If we don't already have an unusual scale factor, check for certain
778 // types of endgames, and use a lower scale for those.
779 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
781 if (pos.opposite_bishops())
783 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
784 // is almost a draw, in case of KBP vs KB, it is even more a draw.
785 if ( pos.non_pawn_material(WHITE) == BishopValueMg
786 && pos.non_pawn_material(BLACK) == BishopValueMg)
787 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
789 // Endgame with opposite-colored bishops, but also other pieces. Still
790 // a bit drawish, but not as drawish as with only the two bishops.
791 return ScaleFactor(46);
793 // Endings where weaker side can place his king in front of the opponent's
794 // pawns are drawish.
795 else if ( abs(eg) <= BishopValueEg
796 && pos.count<PAWN>(strongSide) <= 2
797 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
798 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
805 // value() is the main function of the class. It computes the various parts of
806 // the evaluation and returns the value of the position from the point of view
807 // of the side to move.
810 Value Evaluation<T>::value() {
812 assert(!pos.checkers());
814 // Probe the material hash table
815 me = Material::probe(pos);
817 // If we have a specialized evaluation function for the current material
818 // configuration, call it and return.
819 if (me->specialized_eval_exists())
820 return me->evaluate(pos);
822 // Initialize score by reading the incrementally updated scores included in
823 // the position object (material + piece square tables) and the material
824 // imbalance. Score is computed internally from the white point of view.
825 Score score = pos.psq_score() + me->imbalance();
827 // Probe the pawn hash table
828 pe = Pawns::probe(pos);
829 score += pe->pawns_score();
831 // Early exit if score is high
832 Value v = (mg_value(score) + eg_value(score)) / 2;
833 if (abs(v) > LazyThreshold)
834 return pos.side_to_move() == WHITE ? v : -v;
836 // Main evaluation begins here
841 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
842 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
843 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
844 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
846 score += mobility[WHITE] - mobility[BLACK];
848 score += evaluate_king<WHITE>()
849 - evaluate_king<BLACK>();
851 score += evaluate_threats<WHITE>()
852 - evaluate_threats<BLACK>();
854 score += evaluate_passed_pawns<WHITE>()
855 - evaluate_passed_pawns<BLACK>();
857 if (pos.non_pawn_material() >= SpaceThreshold)
858 score += evaluate_space<WHITE>()
859 - evaluate_space<BLACK>();
861 score += evaluate_initiative(eg_value(score));
863 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
864 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
865 v = mg_value(score) * int(me->game_phase())
866 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
868 v /= int(PHASE_MIDGAME);
870 // In case of tracing add all remaining individual evaluation terms
873 Trace::add(MATERIAL, pos.psq_score());
874 Trace::add(IMBALANCE, me->imbalance());
875 Trace::add(PAWN, pe->pawns_score());
876 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
877 if (pos.non_pawn_material() >= SpaceThreshold)
878 Trace::add(SPACE, evaluate_space<WHITE>()
879 , evaluate_space<BLACK>());
880 Trace::add(TOTAL, score);
883 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
889 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
890 /// of the position from the point of view of the side to move.
892 Value Eval::evaluate(const Position& pos)
894 return Evaluation<>(pos).value();
897 /// trace() is like evaluate(), but instead of returning a value, it returns
898 /// a string (suitable for outputting to stdout) that contains the detailed
899 /// descriptions and values of each evaluation term. Useful for debugging.
901 std::string Eval::trace(const Position& pos) {
903 std::memset(scores, 0, sizeof(scores));
905 Value v = Evaluation<TRACE>(pos).value();
906 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
908 std::stringstream ss;
909 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
910 << " Eval term | White | Black | Total \n"
911 << " | MG EG | MG EG | MG EG \n"
912 << "----------------+-------------+-------------+-------------\n"
913 << " Material | " << Term(MATERIAL)
914 << " Imbalance | " << Term(IMBALANCE)
915 << " Pawns | " << Term(PAWN)
916 << " Knights | " << Term(KNIGHT)
917 << " Bishops | " << Term(BISHOP)
918 << " Rooks | " << Term(ROOK)
919 << " Queens | " << Term(QUEEN)
920 << " Mobility | " << Term(MOBILITY)
921 << " King safety | " << Term(KING)
922 << " Threats | " << Term(THREAT)
923 << " Passed pawns | " << Term(PASSED)
924 << " Space | " << Term(SPACE)
925 << "----------------+-------------+-------------+-------------\n"
926 << " Total | " << Term(TOTAL);
928 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";