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);
220 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
221 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
222 // happen in Chess960 games.
223 const Score TrappedBishopA1H1 = S(50, 50);
228 // KingAttackWeights[PieceType] contains king attack weights by piece type
229 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
231 // Penalties for enemy's safe checks
232 const int QueenCheck = 780;
233 const int RookCheck = 880;
234 const int BishopCheck = 435;
235 const int KnightCheck = 790;
237 // Threshold for lazy and space evaluation
238 const Value LazyThreshold = Value(1500);
239 const Value SpaceThreshold = Value(12222);
242 // initialize() computes king and pawn attacks, and the king ring bitboard
243 // for a given color. This is done at the beginning of the evaluation.
245 template<Tracing T> template<Color Us>
246 void Evaluation<T>::initialize() {
248 const Color Them = (Us == WHITE ? BLACK : WHITE);
249 const Square Up = (Us == WHITE ? NORTH : SOUTH);
250 const Square Down = (Us == WHITE ? SOUTH : NORTH);
251 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
253 // Find our pawns on the first two ranks, and those which are blocked
254 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
256 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
257 // are excluded from the mobility area.
258 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
260 // Initialise the attack bitboards with the king and pawn information
261 b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
262 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
264 attackedBy2[Us] = b & attackedBy[Us][PAWN];
265 attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];
267 // Init our king safety tables only if we are going to use them
268 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
271 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
272 kingRing[Us] |= shift<Up>(b);
274 kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));
275 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
278 kingRing[Us] = kingAttackersCount[Them] = 0;
282 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
285 template<Tracing T> template<Color Us, PieceType Pt>
286 Score Evaluation<T>::evaluate_pieces() {
288 const Color Them = (Us == WHITE ? BLACK : WHITE);
289 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
290 : Rank5BB | Rank4BB | Rank3BB);
291 const Square* pl = pos.squares<Pt>(Us);
295 Score score = SCORE_ZERO;
297 attackedBy[Us][Pt] = 0;
299 while ((s = *pl++) != SQ_NONE)
301 // Find attacked squares, including x-ray attacks for bishops and rooks
302 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
303 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
304 : pos.attacks_from<Pt>(s);
306 if (pos.pinned_pieces(Us) & s)
307 b &= LineBB[pos.square<KING>(Us)][s];
309 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
310 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
312 if (b & kingRing[Them])
314 kingAttackersCount[Us]++;
315 kingAttackersWeight[Us] += KingAttackWeights[Pt];
316 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
319 int mob = popcount(b & mobilityArea[Us]);
321 mobility[Us] += MobilityBonus[Pt - 2][mob];
323 // Bonus for this piece as a king protector
324 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
326 if (Pt == BISHOP || Pt == KNIGHT)
328 // Bonus for outpost squares
329 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
331 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & s)] * 2;
334 bb &= b & ~pos.pieces(Us);
336 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & bb)];
339 // Bonus when behind a pawn
340 if ( relative_rank(Us, s) < RANK_5
341 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
342 score += MinorBehindPawn;
344 // Penalty for pawns on the same color square as the bishop
346 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
348 // An important Chess960 pattern: A cornered bishop blocked by a friendly
349 // pawn diagonally in front of it is a very serious problem, especially
350 // when that pawn is also blocked.
353 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
355 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
356 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
357 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
358 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
365 // Bonus for aligning with enemy pawns on the same rank/file
366 if (relative_rank(Us, s) >= RANK_5)
367 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
369 // Bonus when on an open or semi-open file
370 if (pe->semiopen_file(Us, file_of(s)))
371 score += RookOnFile[!!pe->semiopen_file(Them, file_of(s))];
373 // Penalty when trapped by the king, even more if the king cannot castle
376 Square ksq = pos.square<KING>(Us);
378 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
379 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
380 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
386 // Penalty if any relative pin or discovered attack against the queen
388 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
394 Trace::add(Pt, Us, score);
400 // evaluate_king() assigns bonuses and penalties to a king of a given color
402 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
403 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
404 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
406 const Bitboard KingFlank[FILE_NB] = {
407 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
410 template<Tracing T> template<Color Us>
411 Score Evaluation<T>::evaluate_king() {
413 const Color Them = (Us == WHITE ? BLACK : WHITE);
414 const Square Up = (Us == WHITE ? NORTH : SOUTH);
415 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
416 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
418 const Square ksq = pos.square<KING>(Us);
419 Bitboard kingOnlyDefended, b, b1, b2, safe, other;
422 // King shelter and enemy pawns storm
423 Score score = pe->king_safety<Us>(pos, ksq);
425 // Main king safety evaluation
426 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
428 // Find the attacked squares which are defended only by our king...
429 kingOnlyDefended = attackedBy[Them][ALL_PIECES]
430 & attackedBy[Us][KING]
433 // ... and those which are not defended at all in the larger king ring
434 b = attackedBy[Them][ALL_PIECES] & ~attackedBy[Us][ALL_PIECES]
435 & kingRing[Us] & ~pos.pieces(Them);
437 // Initialize the 'kingDanger' variable, which will be transformed
438 // later into a king danger score. The initial value is based on the
439 // number and types of the enemy's attacking pieces, the number of
440 // attacked and weak squares around our king, the absence of queen and
441 // the quality of the pawn shelter (current 'score' value).
442 kingDanger = kingAttackersCount[Them] * kingAttackersWeight[Them]
443 + 102 * kingAdjacentZoneAttacksCount[Them]
444 + 201 * popcount(kingOnlyDefended)
445 + 143 * (popcount(b) + !!pos.pinned_pieces(Us))
446 - 848 * !pos.count<QUEEN>(Them)
447 - 9 * mg_value(score) / 8
450 // Analyse the safe enemy's checks which are possible on next move
451 safe = ~pos.pieces(Them);
452 safe &= ~attackedBy[Us][ALL_PIECES] | (kingOnlyDefended & attackedBy2[Them]);
454 b1 = pos.attacks_from< ROOK>(ksq);
455 b2 = pos.attacks_from<BISHOP>(ksq);
457 // Enemy queen safe checks
458 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe)
459 kingDanger += QueenCheck;
461 // For minors and rooks, also consider the square safe if attacked twice,
462 // and only defended by our queen.
463 safe |= attackedBy2[Them]
464 & ~(attackedBy2[Us] | pos.pieces(Them))
465 & attackedBy[Us][QUEEN];
467 // Some other potential checks are also analysed, even from squares
468 // currently occupied by the opponent own pieces, as long as the square
469 // is not attacked by our pawns, and is not occupied by a blocked pawn.
470 other = ~( attackedBy[Us][PAWN]
471 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
473 // Enemy rooks safe and other checks
474 if (b1 & attackedBy[Them][ROOK] & safe)
475 kingDanger += RookCheck;
477 else if (b1 & attackedBy[Them][ROOK] & other)
480 // Enemy bishops safe and other checks
481 if (b2 & attackedBy[Them][BISHOP] & safe)
482 kingDanger += BishopCheck;
484 else if (b2 & attackedBy[Them][BISHOP] & other)
487 // Enemy knights safe and other checks
488 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
490 kingDanger += KnightCheck;
495 // Transform the kingDanger units into a Score, and substract it from the evaluation
497 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
500 // King tropism: firstly, find squares that opponent attacks in our king flank
501 File kf = file_of(ksq);
502 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
504 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
505 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
507 // Secondly, add the squares which are attacked twice in that flank and
508 // which are not defended by our pawns.
509 b = (Us == WHITE ? b << 4 : b >> 4)
510 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
512 score -= CloseEnemies * popcount(b);
514 // Penalty when our king is on a pawnless flank
515 if (!(pos.pieces(PAWN) & KingFlank[kf]))
516 score -= PawnlessFlank;
519 Trace::add(KING, Us, score);
525 // evaluate_threats() assigns bonuses according to the types of the attacking
526 // and the attacked pieces.
528 template<Tracing T> template<Color Us>
529 Score Evaluation<T>::evaluate_threats() {
531 const Color Them = (Us == WHITE ? BLACK : WHITE);
532 const Square Up = (Us == WHITE ? NORTH : SOUTH);
533 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
534 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
535 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
537 Bitboard b, weak, defended, stronglyProtected, safeThreats;
538 Score score = SCORE_ZERO;
540 // Non-pawn enemies attacked by a pawn
541 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
545 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
546 | attackedBy[Us][ALL_PIECES]);
548 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
550 score += ThreatBySafePawn * popcount(safeThreats);
552 if (weak ^ safeThreats)
553 score += ThreatByHangingPawn;
556 // Squares strongly protected by the opponent, either because they attack the
557 // square with a pawn, or because they attack the square twice and we don't.
558 stronglyProtected = attackedBy[Them][PAWN]
559 | (attackedBy2[Them] & ~attackedBy2[Us]);
561 // Non-pawn enemies, strongly protected
562 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
565 // Enemies not strongly protected and under our attack
566 weak = pos.pieces(Them)
568 & attackedBy[Us][ALL_PIECES];
570 // Add a bonus according to the kind of attacking pieces
573 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
576 Square s = pop_lsb(&b);
577 score += ThreatByMinor[type_of(pos.piece_on(s))];
578 if (type_of(pos.piece_on(s)) != PAWN)
579 score += ThreatByRank * (int)relative_rank(Them, s);
582 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
585 Square s = pop_lsb(&b);
586 score += ThreatByRook[type_of(pos.piece_on(s))];
587 if (type_of(pos.piece_on(s)) != PAWN)
588 score += ThreatByRank * (int)relative_rank(Them, s);
591 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
593 b = weak & attackedBy[Us][KING];
595 score += ThreatByKing[more_than_one(b)];
598 // Find squares where our pawns can push on the next move
599 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
600 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
602 // Keep only the squares which are not completely unsafe
603 b &= ~attackedBy[Them][PAWN]
604 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
606 // Add a bonus for each new pawn threats from those squares
607 b = (shift<Left>(b) | shift<Right>(b))
609 & ~attackedBy[Us][PAWN];
611 score += ThreatByPawnPush * popcount(b);
614 Trace::add(THREAT, Us, score);
620 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
621 // pawns of the given color.
623 template<Tracing T> template<Color Us>
624 Score Evaluation<T>::evaluate_passed_pawns() {
626 const Color Them = (Us == WHITE ? BLACK : WHITE);
627 const Square Up = (Us == WHITE ? NORTH : SOUTH);
629 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
630 Score score = SCORE_ZERO;
632 b = pe->passed_pawns(Us);
636 Square s = pop_lsb(&b);
638 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
640 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
641 score -= HinderPassedPawn * popcount(bb);
643 int r = relative_rank(Us, s) - RANK_2;
644 int rr = r * (r - 1);
646 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
650 Square blockSq = s + Up;
652 // Adjust bonus based on the king's proximity
653 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
654 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
656 // If blockSq is not the queening square then consider also a second push
657 if (relative_rank(Us, blockSq) != RANK_8)
658 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
660 // If the pawn is free to advance, then increase the bonus
661 if (pos.empty(blockSq))
663 // If there is a rook or queen attacking/defending the pawn from behind,
664 // consider all the squaresToQueen. Otherwise consider only the squares
665 // in the pawn's path attacked or occupied by the enemy.
666 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
668 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
670 if (!(pos.pieces(Us) & bb))
671 defendedSquares &= attackedBy[Us][ALL_PIECES];
673 if (!(pos.pieces(Them) & bb))
674 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
676 // If there aren't any enemy attacks, assign a big bonus. Otherwise
677 // assign a smaller bonus if the block square isn't attacked.
678 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
680 // If the path to the queen is fully defended, assign a big bonus.
681 // Otherwise assign a smaller bonus if the block square is defended.
682 if (defendedSquares == squaresToQueen)
685 else if (defendedSquares & blockSq)
688 mbonus += k * rr, ebonus += k * rr;
690 else if (pos.pieces(Us) & blockSq)
691 mbonus += rr + r * 2, ebonus += rr + r * 2;
694 // Scale down bonus for candidate passers which need more than one
695 // pawn push to become passed or have a pawn in front of them.
696 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
697 mbonus /= 2, ebonus /= 2;
699 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
703 Trace::add(PASSED, Us, score);
709 // evaluate_space() computes the space evaluation for a given side. The
710 // space evaluation is a simple bonus based on the number of safe squares
711 // available for minor pieces on the central four files on ranks 2--4. Safe
712 // squares one, two or three squares behind a friendly pawn are counted
713 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
714 // improve play on game opening.
716 template<Tracing T> template<Color Us>
717 Score Evaluation<T>::evaluate_space() {
719 const Color Them = (Us == WHITE ? BLACK : WHITE);
720 const Bitboard SpaceMask =
721 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
722 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
724 // Find the safe squares for our pieces inside the area defined by
725 // SpaceMask. A square is unsafe if it is attacked by an enemy
726 // pawn, or if it is undefended and attacked by an enemy piece.
727 Bitboard safe = SpaceMask
728 & ~pos.pieces(Us, PAWN)
729 & ~attackedBy[Them][PAWN]
730 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
732 // Find all squares which are at most three squares behind some friendly pawn
733 Bitboard behind = pos.pieces(Us, PAWN);
734 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
735 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
737 // Since SpaceMask[Us] is fully on our half of the board...
738 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
740 // ...count safe + (behind & safe) with a single popcount.
741 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
742 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
744 return make_score(bonus * weight * weight / 16, 0);
748 // evaluate_initiative() computes the initiative correction value for the
749 // position, i.e., second order bonus/malus based on the known attacking/defending
750 // status of the players.
753 Score Evaluation<T>::evaluate_initiative(Value eg) {
755 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
756 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
757 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
759 // Compute the initiative bonus for the attacking side
760 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
762 // Now apply the bonus: note that we find the attacking side by extracting
763 // the sign of the endgame value, and that we carefully cap the bonus so
764 // that the endgame score will never change sign after the bonus.
765 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
767 return make_score(0, v);
771 // evaluate_scale_factor() computes the scale factor for the winning side
774 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
776 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
777 ScaleFactor sf = me->scale_factor(pos, strongSide);
779 // If we don't already have an unusual scale factor, check for certain
780 // types of endgames, and use a lower scale for those.
781 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
783 if (pos.opposite_bishops())
785 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
786 // is almost a draw, in case of KBP vs KB, it is even more a draw.
787 if ( pos.non_pawn_material(WHITE) == BishopValueMg
788 && pos.non_pawn_material(BLACK) == BishopValueMg)
789 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
791 // Endgame with opposite-colored bishops, but also other pieces. Still
792 // a bit drawish, but not as drawish as with only the two bishops.
793 return ScaleFactor(46);
795 // Endings where weaker side can place his king in front of the opponent's
796 // pawns are drawish.
797 else if ( abs(eg) <= BishopValueEg
798 && pos.count<PAWN>(strongSide) <= 2
799 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
800 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
807 // value() is the main function of the class. It computes the various parts of
808 // the evaluation and returns the value of the position from the point of view
809 // of the side to move.
812 Value Evaluation<T>::value() {
814 assert(!pos.checkers());
816 // Probe the material hash table
817 me = Material::probe(pos);
819 // If we have a specialized evaluation function for the current material
820 // configuration, call it and return.
821 if (me->specialized_eval_exists())
822 return me->evaluate(pos);
824 // Initialize score by reading the incrementally updated scores included in
825 // the position object (material + piece square tables) and the material
826 // imbalance. Score is computed internally from the white point of view.
827 Score score = pos.psq_score() + me->imbalance();
829 // Probe the pawn hash table
830 pe = Pawns::probe(pos);
831 score += pe->pawns_score();
833 // Early exit if score is high
834 Value v = (mg_value(score) + eg_value(score)) / 2;
835 if (abs(v) > LazyThreshold)
836 return pos.side_to_move() == WHITE ? v : -v;
838 // Main evaluation begins here
843 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
844 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
845 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
846 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
848 score += mobility[WHITE] - mobility[BLACK];
850 score += evaluate_king<WHITE>()
851 - evaluate_king<BLACK>();
853 score += evaluate_threats<WHITE>()
854 - evaluate_threats<BLACK>();
856 score += evaluate_passed_pawns<WHITE>()
857 - evaluate_passed_pawns<BLACK>();
859 if (pos.non_pawn_material() >= SpaceThreshold)
860 score += evaluate_space<WHITE>()
861 - evaluate_space<BLACK>();
863 score += evaluate_initiative(eg_value(score));
865 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
866 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
867 v = mg_value(score) * int(me->game_phase())
868 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
870 v /= int(PHASE_MIDGAME);
872 // In case of tracing add all remaining individual evaluation terms
875 Trace::add(MATERIAL, pos.psq_score());
876 Trace::add(IMBALANCE, me->imbalance());
877 Trace::add(PAWN, pe->pawns_score());
878 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
879 if (pos.non_pawn_material() >= SpaceThreshold)
880 Trace::add(SPACE, evaluate_space<WHITE>()
881 , evaluate_space<BLACK>());
882 Trace::add(TOTAL, score);
885 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
891 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
892 /// of the position from the point of view of the side to move.
894 Value Eval::evaluate(const Position& pos)
896 return Evaluation<>(pos).value();
899 /// trace() is like evaluate(), but instead of returning a value, it returns
900 /// a string (suitable for outputting to stdout) that contains the detailed
901 /// descriptions and values of each evaluation term. Useful for debugging.
903 std::string Eval::trace(const Position& pos) {
905 std::memset(scores, 0, sizeof(scores));
907 Value v = Evaluation<TRACE>(pos).value();
908 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
910 std::stringstream ss;
911 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
912 << " Eval term | White | Black | Total \n"
913 << " | MG EG | MG EG | MG EG \n"
914 << "----------------+-------------+-------------+-------------\n"
915 << " Material | " << Term(MATERIAL)
916 << " Imbalance | " << Term(IMBALANCE)
917 << " Pawns | " << Term(PAWN)
918 << " Knights | " << Term(KNIGHT)
919 << " Bishops | " << Term(BISHOP)
920 << " Rooks | " << Term(ROOK)
921 << " Queens | " << Term(QUEEN)
922 << " Mobility | " << Term(MOBILITY)
923 << " King safety | " << Term(KING)
924 << " Threats | " << Term(THREAT)
925 << " Passed pawns | " << Term(PASSED)
926 << " Space | " << Term(SPACE)
927 << "----------------+-------------+-------------+-------------\n"
928 << " Total | " << Term(TOTAL);
930 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";