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
34 const Bitboard LongDiagonals = 0x8142241818244281ULL; // A1..H8 | H1..A8
35 const Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
36 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
37 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
38 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
40 const Bitboard KingFlank[FILE_NB] = {
41 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
46 enum Tracing {NO_TRACE, TRACE};
48 enum Term { // The first 8 entries are for PieceType
49 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
52 double scores[TERM_NB][COLOR_NB][PHASE_NB];
54 double to_cp(Value v) { return double(v) / PawnValueEg; }
56 void add(int idx, Color c, Score s) {
57 scores[idx][c][MG] = to_cp(mg_value(s));
58 scores[idx][c][EG] = to_cp(eg_value(s));
61 void add(int idx, Score w, Score b = SCORE_ZERO) {
62 add(idx, WHITE, w); add(idx, BLACK, b);
65 std::ostream& operator<<(std::ostream& os, Term t) {
67 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
68 os << " --- --- | --- --- | ";
70 os << std::setw(5) << scores[t][WHITE][MG] << " "
71 << std::setw(5) << scores[t][WHITE][EG] << " | "
72 << std::setw(5) << scores[t][BLACK][MG] << " "
73 << std::setw(5) << scores[t][BLACK][EG] << " | ";
75 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
76 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
82 using namespace Trace;
84 // Evaluation class contains various information computed and collected
85 // by the evaluation functions.
86 template<Tracing T = NO_TRACE>
90 Evaluation() = delete;
91 Evaluation(const Position& p) : pos(p) {}
92 Evaluation& operator=(const Evaluation&) = delete;
97 // Evaluation helpers (used when calling value())
98 template<Color Us> void initialize();
99 template<Color Us> Score evaluate_king();
100 template<Color Us> Score evaluate_threats();
101 template<Color Us> Score evaluate_passed_pawns();
102 template<Color Us> Score evaluate_space();
103 template<Color Us, PieceType Pt> Score evaluate_pieces();
104 ScaleFactor evaluate_scale_factor(Value eg);
105 Score evaluate_initiative(Value eg);
111 Bitboard mobilityArea[COLOR_NB];
112 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
114 // attackedBy[color][piece type] is a bitboard representing all squares
115 // attacked by a given color and piece type (can be also ALL_PIECES).
116 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
118 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
119 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
120 // pawn or squares attacked by 2 pawns are not explicitly added.
121 Bitboard attackedBy2[COLOR_NB];
123 // kingRing[color] is the zone around the king which is considered
124 // by the king safety evaluation. This consists of the squares directly
125 // adjacent to the king, and (only for a king on its first rank) the
126 // squares two ranks in front of the king. For instance, if black's king
127 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
128 // f7, g7, h7, f6, g6 and h6.
129 Bitboard kingRing[COLOR_NB];
131 // kingAttackersCount[color] is the number of pieces of the given color
132 // which attack a square in the kingRing of the enemy king.
133 int kingAttackersCount[COLOR_NB];
135 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
136 // given color which attack a square in the kingRing of the enemy king. The
137 // weights of the individual piece types are given by the elements in the
138 // KingAttackWeights array.
139 int kingAttackersWeight[COLOR_NB];
141 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
142 // color to squares directly adjacent to the enemy king. Pieces which attack
143 // more than one square are counted multiple times. For instance, if there is
144 // a white knight on g5 and black's king is on g8, this white knight adds 2
145 // to kingAdjacentZoneAttacksCount[WHITE].
146 int kingAdjacentZoneAttacksCount[COLOR_NB];
149 #define V(v) Value(v)
150 #define S(mg, eg) make_score(mg, eg)
152 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
153 // indexed by piece type and number of attacked squares in the mobility area.
154 const Score MobilityBonus[][32] = {
155 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
156 S( 22, 26), S( 29, 29), S( 36, 29) },
157 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
158 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
159 S( 91, 88), S( 98, 97) },
160 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
161 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
162 S( 46,166), S( 48,169), S( 58,171) },
163 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
164 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
165 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
166 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
167 S(106,184), S(109,191), S(113,206), S(116,212) }
170 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
171 // pieces if they can reach an outpost square, bigger if that square is
172 // supported by a pawn. If the minor piece occupies an outpost square
173 // then score is doubled.
174 const Score Outpost[][2] = {
175 { S(22, 6), S(36,12) }, // Knight
176 { S( 9, 2), S(15, 5) } // Bishop
179 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
180 // friendly pawn on the rook file.
181 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
183 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
184 // which piece type attacks which one. Attacks on lesser pieces which are
185 // pawn-defended are not considered.
186 const Score ThreatByMinor[PIECE_TYPE_NB] = {
187 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
190 const Score ThreatByRook[PIECE_TYPE_NB] = {
191 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)
194 // ThreatByKing[on one/on many] contains bonuses for king attacks on
195 // pawns or pieces which are not pawn-defended.
196 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
198 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
199 // We don't use a Score because we process the two components independently.
200 const Value Passed[][RANK_NB] = {
201 { V(5), V( 5), V(31), V(73), V(166), V(252) },
202 { V(7), V(14), V(38), V(73), V(166), V(252) }
205 // PassedFile[File] contains a bonus according to the file of a passed pawn
206 const Score PassedFile[FILE_NB] = {
207 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
208 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
211 // KingProtector[PieceType-2] contains a bonus according to distance from king
212 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
214 // Assorted bonuses and penalties used by evaluation
215 const Score MinorBehindPawn = S( 16, 0);
216 const Score BishopPawns = S( 8, 12);
217 const Score LongRangedBishop = S( 22, 0);
218 const Score RookOnPawn = S( 8, 24);
219 const Score TrappedRook = S( 92, 0);
220 const Score WeakQueen = S( 50, 10);
221 const Score OtherCheck = S( 10, 10);
222 const Score CloseEnemies = S( 7, 0);
223 const Score PawnlessFlank = S( 20, 80);
224 const Score ThreatByHangingPawn = S( 71, 61);
225 const Score ThreatBySafePawn = S(182,175);
226 const Score ThreatByRank = S( 16, 3);
227 const Score Hanging = S( 48, 27);
228 const Score WeakUnopposedPawn = S( 5, 25);
229 const Score ThreatByPawnPush = S( 38, 22);
230 const Score HinderPassedPawn = S( 7, 0);
231 const Score TrappedBishopA1H1 = S( 50, 50);
236 // KingAttackWeights[PieceType] contains king attack weights by piece type
237 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
239 // Penalties for enemy's safe checks
240 const int QueenCheck = 780;
241 const int RookCheck = 880;
242 const int BishopCheck = 435;
243 const int KnightCheck = 790;
245 // Threshold for lazy and space evaluation
246 const Value LazyThreshold = Value(1500);
247 const Value SpaceThreshold = Value(12222);
250 // initialize() computes king and pawn attacks, and the king ring bitboard
251 // for a given color. This is done at the beginning of the evaluation.
253 template<Tracing T> template<Color Us>
254 void Evaluation<T>::initialize() {
256 const Color Them = (Us == WHITE ? BLACK : WHITE);
257 const Square Up = (Us == WHITE ? NORTH : SOUTH);
258 const Square Down = (Us == WHITE ? SOUTH : NORTH);
259 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
261 // Find our pawns on the first two ranks, and those which are blocked
262 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
264 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
265 // are excluded from the mobility area.
266 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
268 // Initialise the attack bitboards with the king and pawn information
269 b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
270 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
272 attackedBy2[Us] = b & attackedBy[Us][PAWN];
273 attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];
275 // Init our king safety tables only if we are going to use them
276 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
279 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
280 kingRing[Us] |= shift<Up>(b);
282 kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));
283 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
286 kingRing[Us] = kingAttackersCount[Them] = 0;
290 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
293 template<Tracing T> template<Color Us, PieceType Pt>
294 Score Evaluation<T>::evaluate_pieces() {
296 const Color Them = (Us == WHITE ? BLACK : WHITE);
297 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
298 : Rank5BB | Rank4BB | Rank3BB);
299 const Square* pl = pos.squares<Pt>(Us);
303 Score score = SCORE_ZERO;
305 attackedBy[Us][Pt] = 0;
307 while ((s = *pl++) != SQ_NONE)
309 // Find attacked squares, including x-ray attacks for bishops and rooks
310 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
311 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
312 : pos.attacks_from<Pt>(s);
314 if (pos.pinned_pieces(Us) & s)
315 b &= LineBB[pos.square<KING>(Us)][s];
317 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
318 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
320 if (b & kingRing[Them])
322 kingAttackersCount[Us]++;
323 kingAttackersWeight[Us] += KingAttackWeights[Pt];
324 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
327 int mob = popcount(b & mobilityArea[Us]);
329 mobility[Us] += MobilityBonus[Pt - 2][mob];
331 // Bonus for this piece as a king protector
332 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
334 if (Pt == BISHOP || Pt == KNIGHT)
336 // Bonus for outpost squares
337 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
339 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & s)] * 2;
342 bb &= b & ~pos.pieces(Us);
344 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & bb)];
347 // Bonus when behind a pawn
348 if ( relative_rank(Us, s) < RANK_5
349 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
350 score += MinorBehindPawn;
354 // Penalty for pawns on the same color square as the bishop
355 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
357 // Bonus for bishop on a long diagonal without pawns in the center
358 if ( (LongDiagonals & s)
359 && !(attackedBy[Them][PAWN] & s)
360 && !(Center & PseudoAttacks[BISHOP][s] & pos.pieces(PAWN)))
361 score += LongRangedBishop;
364 // An important Chess960 pattern: A cornered bishop blocked by a friendly
365 // pawn diagonally in front of it is a very serious problem, especially
366 // when that pawn is also blocked.
369 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
371 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
372 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
373 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
374 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
381 // Bonus for aligning with enemy pawns on the same rank/file
382 if (relative_rank(Us, s) >= RANK_5)
383 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
385 // Bonus when on an open or semi-open file
386 if (pe->semiopen_file(Us, file_of(s)))
387 score += RookOnFile[!!pe->semiopen_file(Them, file_of(s))];
389 // Penalty when trapped by the king, even more if the king cannot castle
392 Square ksq = pos.square<KING>(Us);
394 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
395 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
396 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
402 // Penalty if any relative pin or discovered attack against the queen
404 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
410 Trace::add(Pt, Us, score);
416 // evaluate_king() assigns bonuses and penalties to a king of a given color
418 template<Tracing T> template<Color Us>
419 Score Evaluation<T>::evaluate_king() {
421 const Color Them = (Us == WHITE ? BLACK : WHITE);
422 const Square Up = (Us == WHITE ? NORTH : SOUTH);
423 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
424 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
426 const Square ksq = pos.square<KING>(Us);
427 Bitboard kingOnlyDefended, undefended, b, b1, b2, safe, other;
430 // King shelter and enemy pawns storm
431 Score score = pe->king_safety<Us>(pos, ksq);
433 // Main king safety evaluation
434 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
436 // Find the attacked squares which are defended only by our king...
437 kingOnlyDefended = attackedBy[Them][ALL_PIECES]
438 & attackedBy[Us][KING]
441 // ... and those which are not defended at all in the larger king ring
442 undefended = attackedBy[Them][ALL_PIECES]
443 & ~attackedBy[Us][ALL_PIECES]
447 // Initialize the 'kingDanger' variable, which will be transformed
448 // later into a king danger score. The initial value is based on the
449 // number and types of the enemy's attacking pieces, the number of
450 // attacked and weak squares around our king, the absence of queen and
451 // the quality of the pawn shelter (current 'score' value).
452 kingDanger = kingAttackersCount[Them] * kingAttackersWeight[Them]
453 + 102 * kingAdjacentZoneAttacksCount[Them]
454 + 191 * popcount(kingOnlyDefended | undefended)
455 + 143 * !!pos.pinned_pieces(Us)
456 - 848 * !pos.count<QUEEN>(Them)
457 - 9 * mg_value(score) / 8
460 // Analyse the safe enemy's checks which are possible on next move
461 safe = ~pos.pieces(Them);
462 safe &= ~attackedBy[Us][ALL_PIECES] | (kingOnlyDefended & attackedBy2[Them]);
464 b1 = pos.attacks_from< ROOK>(ksq);
465 b2 = pos.attacks_from<BISHOP>(ksq);
467 // Enemy queen safe checks
468 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe)
469 kingDanger += QueenCheck;
471 // For minors and rooks, also consider the square safe if attacked twice,
472 // and only defended by our queen.
473 safe |= attackedBy2[Them]
474 & ~(attackedBy2[Us] | pos.pieces(Them))
475 & attackedBy[Us][QUEEN];
477 // Some other potential checks are also analysed, even from squares
478 // currently occupied by the opponent own pieces, as long as the square
479 // is not attacked by our pawns, and is not occupied by a blocked pawn.
480 other = ~( attackedBy[Us][PAWN]
481 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
483 // Enemy rooks safe and other checks
484 if (b1 & attackedBy[Them][ROOK] & safe)
485 kingDanger += RookCheck;
487 else if (b1 & attackedBy[Them][ROOK] & other)
490 // Enemy bishops safe and other checks
491 if (b2 & attackedBy[Them][BISHOP] & safe)
492 kingDanger += BishopCheck;
494 else if (b2 & attackedBy[Them][BISHOP] & other)
497 // Enemy knights safe and other checks
498 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
500 kingDanger += KnightCheck;
505 // Transform the kingDanger units into a Score, and substract it from the evaluation
507 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
510 // King tropism: firstly, find squares that opponent attacks in our king flank
511 File kf = file_of(ksq);
512 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
514 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
515 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
517 // Secondly, add the squares which are attacked twice in that flank and
518 // which are not defended by our pawns.
519 b = (Us == WHITE ? b << 4 : b >> 4)
520 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
522 score -= CloseEnemies * popcount(b);
524 // Penalty when our king is on a pawnless flank
525 if (!(pos.pieces(PAWN) & KingFlank[kf]))
526 score -= PawnlessFlank;
529 Trace::add(KING, Us, score);
535 // evaluate_threats() assigns bonuses according to the types of the attacking
536 // and the attacked pieces.
538 template<Tracing T> template<Color Us>
539 Score Evaluation<T>::evaluate_threats() {
541 const Color Them = (Us == WHITE ? BLACK : WHITE);
542 const Square Up = (Us == WHITE ? NORTH : SOUTH);
543 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
544 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
545 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
547 Bitboard b, weak, defended, stronglyProtected, safeThreats;
548 Score score = SCORE_ZERO;
550 // Non-pawn enemies attacked by a pawn
551 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
555 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
556 | attackedBy[Us][ALL_PIECES]);
558 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
560 score += ThreatBySafePawn * popcount(safeThreats);
562 if (weak ^ safeThreats)
563 score += ThreatByHangingPawn;
566 // Squares strongly protected by the opponent, either because they attack the
567 // square with a pawn, or because they attack the square twice and we don't.
568 stronglyProtected = attackedBy[Them][PAWN]
569 | (attackedBy2[Them] & ~attackedBy2[Us]);
571 // Non-pawn enemies, strongly protected
572 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
575 // Enemies not strongly protected and under our attack
576 weak = pos.pieces(Them)
578 & attackedBy[Us][ALL_PIECES];
580 // Add a bonus according to the kind of attacking pieces
583 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
586 Square s = pop_lsb(&b);
587 score += ThreatByMinor[type_of(pos.piece_on(s))];
588 if (type_of(pos.piece_on(s)) != PAWN)
589 score += ThreatByRank * (int)relative_rank(Them, s);
592 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
595 Square s = pop_lsb(&b);
596 score += ThreatByRook[type_of(pos.piece_on(s))];
597 if (type_of(pos.piece_on(s)) != PAWN)
598 score += ThreatByRank * (int)relative_rank(Them, s);
601 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
603 b = weak & attackedBy[Us][KING];
605 score += ThreatByKing[more_than_one(b)];
608 // Bonus for opponent unopposed weak pawns
609 if (pos.pieces(Us, ROOK, QUEEN))
610 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
612 // Find squares where our pawns can push on the next move
613 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
614 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
616 // Keep only the squares which are not completely unsafe
617 b &= ~attackedBy[Them][PAWN]
618 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
620 // Add a bonus for each new pawn threats from those squares
621 b = (shift<Left>(b) | shift<Right>(b))
623 & ~attackedBy[Us][PAWN];
625 score += ThreatByPawnPush * popcount(b);
628 Trace::add(THREAT, Us, score);
634 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
635 // pawns of the given color.
637 template<Tracing T> template<Color Us>
638 Score Evaluation<T>::evaluate_passed_pawns() {
640 const Color Them = (Us == WHITE ? BLACK : WHITE);
641 const Square Up = (Us == WHITE ? NORTH : SOUTH);
643 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
644 Score score = SCORE_ZERO;
646 b = pe->passed_pawns(Us);
650 Square s = pop_lsb(&b);
652 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
654 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
655 score -= HinderPassedPawn * popcount(bb);
657 int r = relative_rank(Us, s) - RANK_2;
658 int rr = r * (r - 1);
660 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
664 Square blockSq = s + Up;
666 // Adjust bonus based on the king's proximity
667 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
668 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
670 // If blockSq is not the queening square then consider also a second push
671 if (relative_rank(Us, blockSq) != RANK_8)
672 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
674 // If the pawn is free to advance, then increase the bonus
675 if (pos.empty(blockSq))
677 // If there is a rook or queen attacking/defending the pawn from behind,
678 // consider all the squaresToQueen. Otherwise consider only the squares
679 // in the pawn's path attacked or occupied by the enemy.
680 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
682 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
684 if (!(pos.pieces(Us) & bb))
685 defendedSquares &= attackedBy[Us][ALL_PIECES];
687 if (!(pos.pieces(Them) & bb))
688 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
690 // If there aren't any enemy attacks, assign a big bonus. Otherwise
691 // assign a smaller bonus if the block square isn't attacked.
692 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
694 // If the path to the queen is fully defended, assign a big bonus.
695 // Otherwise assign a smaller bonus if the block square is defended.
696 if (defendedSquares == squaresToQueen)
699 else if (defendedSquares & blockSq)
702 mbonus += k * rr, ebonus += k * rr;
704 else if (pos.pieces(Us) & blockSq)
705 mbonus += rr + r * 2, ebonus += rr + r * 2;
708 // Scale down bonus for candidate passers which need more than one
709 // pawn push to become passed or have a pawn in front of them.
710 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
711 mbonus /= 2, ebonus /= 2;
713 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
717 Trace::add(PASSED, Us, score);
723 // evaluate_space() computes the space evaluation for a given side. The
724 // space evaluation is a simple bonus based on the number of safe squares
725 // available for minor pieces on the central four files on ranks 2--4. Safe
726 // squares one, two or three squares behind a friendly pawn are counted
727 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
728 // improve play on game opening.
730 template<Tracing T> template<Color Us>
731 Score Evaluation<T>::evaluate_space() {
733 const Color Them = (Us == WHITE ? BLACK : WHITE);
734 const Bitboard SpaceMask =
735 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
736 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
738 // Find the safe squares for our pieces inside the area defined by
739 // SpaceMask. A square is unsafe if it is attacked by an enemy
740 // pawn, or if it is undefended and attacked by an enemy piece.
741 Bitboard safe = SpaceMask
742 & ~pos.pieces(Us, PAWN)
743 & ~attackedBy[Them][PAWN]
744 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
746 // Find all squares which are at most three squares behind some friendly pawn
747 Bitboard behind = pos.pieces(Us, PAWN);
748 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
749 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
751 // Since SpaceMask[Us] is fully on our half of the board...
752 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
754 // ...count safe + (behind & safe) with a single popcount.
755 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
756 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
758 return make_score(bonus * weight * weight / 16, 0);
762 // evaluate_initiative() computes the initiative correction value for the
763 // position, i.e., second order bonus/malus based on the known attacking/defending
764 // status of the players.
767 Score Evaluation<T>::evaluate_initiative(Value eg) {
769 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
770 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
771 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
773 // Compute the initiative bonus for the attacking side
774 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
776 // Now apply the bonus: note that we find the attacking side by extracting
777 // the sign of the endgame value, and that we carefully cap the bonus so
778 // that the endgame score will never change sign after the bonus.
779 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
781 return make_score(0, v);
785 // evaluate_scale_factor() computes the scale factor for the winning side
788 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
790 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
791 ScaleFactor sf = me->scale_factor(pos, strongSide);
793 // If we don't already have an unusual scale factor, check for certain
794 // types of endgames, and use a lower scale for those.
795 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
797 if (pos.opposite_bishops())
799 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
800 // is almost a draw, in case of KBP vs KB, it is even more a draw.
801 if ( pos.non_pawn_material(WHITE) == BishopValueMg
802 && pos.non_pawn_material(BLACK) == BishopValueMg)
803 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
805 // Endgame with opposite-colored bishops, but also other pieces. Still
806 // a bit drawish, but not as drawish as with only the two bishops.
807 return ScaleFactor(46);
809 // Endings where weaker side can place his king in front of the opponent's
810 // pawns are drawish.
811 else if ( abs(eg) <= BishopValueEg
812 && pos.count<PAWN>(strongSide) <= 2
813 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
814 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
821 // value() is the main function of the class. It computes the various parts of
822 // the evaluation and returns the value of the position from the point of view
823 // of the side to move.
826 Value Evaluation<T>::value() {
828 assert(!pos.checkers());
830 // Probe the material hash table
831 me = Material::probe(pos);
833 // If we have a specialized evaluation function for the current material
834 // configuration, call it and return.
835 if (me->specialized_eval_exists())
836 return me->evaluate(pos);
838 // Initialize score by reading the incrementally updated scores included in
839 // the position object (material + piece square tables) and the material
840 // imbalance. Score is computed internally from the white point of view.
841 Score score = pos.psq_score() + me->imbalance();
843 // Probe the pawn hash table
844 pe = Pawns::probe(pos);
845 score += pe->pawns_score();
847 // Early exit if score is high
848 Value v = (mg_value(score) + eg_value(score)) / 2;
849 if (abs(v) > LazyThreshold)
850 return pos.side_to_move() == WHITE ? v : -v;
852 // Main evaluation begins here
857 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
858 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
859 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
860 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
862 score += mobility[WHITE] - mobility[BLACK];
864 score += evaluate_king<WHITE>()
865 - evaluate_king<BLACK>();
867 score += evaluate_threats<WHITE>()
868 - evaluate_threats<BLACK>();
870 score += evaluate_passed_pawns<WHITE>()
871 - evaluate_passed_pawns<BLACK>();
873 if (pos.non_pawn_material() >= SpaceThreshold)
874 score += evaluate_space<WHITE>()
875 - evaluate_space<BLACK>();
877 score += evaluate_initiative(eg_value(score));
879 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
880 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
881 v = mg_value(score) * int(me->game_phase())
882 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
884 v /= int(PHASE_MIDGAME);
886 // In case of tracing add all remaining individual evaluation terms
889 Trace::add(MATERIAL, pos.psq_score());
890 Trace::add(IMBALANCE, me->imbalance());
891 Trace::add(PAWN, pe->pawns_score());
892 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
893 if (pos.non_pawn_material() >= SpaceThreshold)
894 Trace::add(SPACE, evaluate_space<WHITE>()
895 , evaluate_space<BLACK>());
896 Trace::add(TOTAL, score);
899 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
905 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
906 /// of the position from the point of view of the side to move.
908 Value Eval::evaluate(const Position& pos)
910 return Evaluation<>(pos).value();
913 /// trace() is like evaluate(), but instead of returning a value, it returns
914 /// a string (suitable for outputting to stdout) that contains the detailed
915 /// descriptions and values of each evaluation term. Useful for debugging.
917 std::string Eval::trace(const Position& pos) {
919 std::memset(scores, 0, sizeof(scores));
921 Value v = Evaluation<TRACE>(pos).value();
922 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
924 std::stringstream ss;
925 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
926 << " Eval term | White | Black | Total \n"
927 << " | MG EG | MG EG | MG EG \n"
928 << "----------------+-------------+-------------+-------------\n"
929 << " Material | " << Term(MATERIAL)
930 << " Imbalance | " << Term(IMBALANCE)
931 << " Pawns | " << Term(PAWN)
932 << " Knights | " << Term(KNIGHT)
933 << " Bishops | " << Term(BISHOP)
934 << " Rooks | " << Term(ROOK)
935 << " Queens | " << Term(QUEEN)
936 << " Mobility | " << Term(MOBILITY)
937 << " King safety | " << Term(KING)
938 << " Threats | " << Term(THREAT)
939 << " Passed pawns | " << Term(PASSED)
940 << " Space | " << Term(SPACE)
941 << "----------------+-------------+-------------+-------------\n"
942 << " Total | " << Term(TOTAL);
944 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";