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 Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
35 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
36 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
37 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
39 const Bitboard KingFlank[FILE_NB] = {
40 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
45 enum Tracing {NO_TRACE, TRACE};
47 enum Term { // The first 8 entries are for PieceType
48 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
51 double scores[TERM_NB][COLOR_NB][PHASE_NB];
53 double to_cp(Value v) { return double(v) / PawnValueEg; }
55 void add(int idx, Color c, Score s) {
56 scores[idx][c][MG] = to_cp(mg_value(s));
57 scores[idx][c][EG] = to_cp(eg_value(s));
60 void add(int idx, Score w, Score b = SCORE_ZERO) {
61 add(idx, WHITE, w); add(idx, BLACK, b);
64 std::ostream& operator<<(std::ostream& os, Term t) {
66 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == INITIATIVE || t == TOTAL)
67 os << " --- --- | --- --- | ";
69 os << std::setw(5) << scores[t][WHITE][MG] << " "
70 << std::setw(5) << scores[t][WHITE][EG] << " | "
71 << std::setw(5) << scores[t][BLACK][MG] << " "
72 << std::setw(5) << scores[t][BLACK][EG] << " | ";
74 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
75 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
81 using namespace Trace;
83 // Evaluation class contains various information computed and collected
84 // by the evaluation functions.
85 template<Tracing T = NO_TRACE>
89 Evaluation() = delete;
90 Evaluation(const Position& p) : pos(p) {}
91 Evaluation& operator=(const Evaluation&) = delete;
96 // Evaluation helpers (used when calling value())
97 template<Color Us> void initialize();
98 template<Color Us> Score evaluate_king();
99 template<Color Us> Score evaluate_threats();
100 template<Color Us> Score evaluate_passed_pawns();
101 template<Color Us> Score evaluate_space();
102 template<Color Us, PieceType Pt> Score evaluate_pieces();
103 ScaleFactor evaluate_scale_factor(Value eg);
104 Score evaluate_initiative(Value eg);
110 Bitboard mobilityArea[COLOR_NB];
111 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
113 // attackedBy[color][piece type] is a bitboard representing all squares
114 // attacked by a given color and piece type (can be also ALL_PIECES).
115 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
117 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
118 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
119 // pawn or squares attacked by 2 pawns are not explicitly added.
120 Bitboard attackedBy2[COLOR_NB];
122 // kingRing[color] is the zone around the king which is considered
123 // by the king safety evaluation. This consists of the squares directly
124 // adjacent to the king, and (only for a king on its first rank) the
125 // squares two ranks in front of the king. For instance, if black's king
126 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
127 // f7, g7, h7, f6, g6 and h6.
128 Bitboard kingRing[COLOR_NB];
130 // kingAttackersCount[color] is the number of pieces of the given color
131 // which attack a square in the kingRing of the enemy king.
132 int kingAttackersCount[COLOR_NB];
134 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
135 // given color which attack a square in the kingRing of the enemy king. The
136 // weights of the individual piece types are given by the elements in the
137 // KingAttackWeights array.
138 int kingAttackersWeight[COLOR_NB];
140 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
141 // color to squares directly adjacent to the enemy king. Pieces which attack
142 // more than one square are counted multiple times. For instance, if there is
143 // a white knight on g5 and black's king is on g8, this white knight adds 2
144 // to kingAdjacentZoneAttacksCount[WHITE].
145 int kingAdjacentZoneAttacksCount[COLOR_NB];
148 #define V(v) Value(v)
149 #define S(mg, eg) make_score(mg, eg)
151 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
152 // indexed by piece type and number of attacked squares in the mobility area.
153 const Score MobilityBonus[][32] = {
154 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
155 S( 22, 26), S( 29, 29), S( 36, 29) },
156 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
157 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
158 S( 91, 88), S( 98, 97) },
159 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
160 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
161 S( 46,166), S( 48,169), S( 58,171) },
162 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
163 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
164 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
165 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
166 S(106,184), S(109,191), S(113,206), S(116,212) }
169 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
170 // pieces if they can reach an outpost square, bigger if that square is
171 // supported by a pawn. If the minor piece occupies an outpost square
172 // then score is doubled.
173 const Score Outpost[][2] = {
174 { S(22, 6), S(36,12) }, // Knight
175 { S( 9, 2), S(15, 5) } // Bishop
178 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
179 // friendly pawn on the rook file.
180 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
182 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
183 // which piece type attacks which one. Attacks on lesser pieces which are
184 // pawn-defended are not considered.
185 const Score ThreatByMinor[PIECE_TYPE_NB] = {
186 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
189 const Score ThreatByRook[PIECE_TYPE_NB] = {
190 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)
193 // ThreatByKing[on one/on many] contains bonuses for king attacks on
194 // pawns or pieces which are not pawn-defended.
195 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
197 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
198 // We don't use a Score because we process the two components independently.
199 const Value Passed[][RANK_NB] = {
200 { V(5), V( 5), V(31), V(73), V(166), V(252) },
201 { V(7), V(14), V(38), V(73), V(166), V(252) }
204 // PassedFile[File] contains a bonus according to the file of a passed pawn
205 const Score PassedFile[FILE_NB] = {
206 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
207 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
210 // KingProtector[PieceType-2] contains a bonus according to distance from king
211 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
213 // Assorted bonuses and penalties used by evaluation
214 const Score MinorBehindPawn = S( 16, 0);
215 const Score BishopPawns = S( 8, 12);
216 const Score LongRangedBishop = S( 22, 0);
217 const Score RookOnPawn = S( 8, 24);
218 const Score TrappedRook = S( 92, 0);
219 const Score WeakQueen = S( 50, 10);
220 const Score OtherCheck = S( 10, 10);
221 const Score CloseEnemies = S( 7, 0);
222 const Score PawnlessFlank = S( 20, 80);
223 const Score ThreatByHangingPawn = S( 71, 61);
224 const Score ThreatBySafePawn = S(192,175);
225 const Score ThreatByRank = S( 16, 3);
226 const Score Hanging = S( 48, 27);
227 const Score WeakUnopposedPawn = S( 5, 25);
228 const Score ThreatByPawnPush = S( 38, 22);
229 const Score ThreatByAttackOnQueen = 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;
308 attackedBy[Us][QUEEN_DIAGONAL] = 0;
310 while ((s = *pl++) != SQ_NONE)
312 // Find attacked squares, including x-ray attacks for bishops and rooks
313 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
314 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
315 : pos.attacks_from<Pt>(s);
317 if (pos.pinned_pieces(Us) & s)
318 b &= LineBB[pos.square<KING>(Us)][s];
320 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
321 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
324 attackedBy[Us][QUEEN_DIAGONAL] |= b & PseudoAttacks[BISHOP][s];
326 if (b & kingRing[Them])
328 kingAttackersCount[Us]++;
329 kingAttackersWeight[Us] += KingAttackWeights[Pt];
330 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
333 int mob = popcount(b & mobilityArea[Us]);
335 mobility[Us] += MobilityBonus[Pt - 2][mob];
337 // Bonus for this piece as a king protector
338 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
340 if (Pt == BISHOP || Pt == KNIGHT)
342 // Bonus for outpost squares
343 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
345 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & s)] * 2;
348 bb &= b & ~pos.pieces(Us);
350 score += Outpost[Pt == BISHOP][!!(attackedBy[Us][PAWN] & bb)];
353 // Bonus when behind a pawn
354 if ( relative_rank(Us, s) < RANK_5
355 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
356 score += MinorBehindPawn;
360 // Penalty for pawns on the same color square as the bishop
361 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
363 // Bonus for bishop on a long diagonal which can "see" both center squares
364 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
365 score += LongRangedBishop;
368 // An important Chess960 pattern: A cornered bishop blocked by a friendly
369 // pawn diagonally in front of it is a very serious problem, especially
370 // when that pawn is also blocked.
373 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
375 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
376 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
377 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
378 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
385 // Bonus for aligning with enemy pawns on the same rank/file
386 if (relative_rank(Us, s) >= RANK_5)
387 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
389 // Bonus when on an open or semi-open file
390 if (pe->semiopen_file(Us, file_of(s)))
391 score += RookOnFile[!!pe->semiopen_file(Them, file_of(s))];
393 // Penalty when trapped by the king, even more if the king cannot castle
396 Square ksq = pos.square<KING>(Us);
398 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
399 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
400 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
406 // Penalty if any relative pin or discovered attack against the queen
408 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
414 Trace::add(Pt, Us, score);
420 // evaluate_king() assigns bonuses and penalties to a king of a given color
422 template<Tracing T> template<Color Us>
423 Score Evaluation<T>::evaluate_king() {
425 const Color Them = (Us == WHITE ? BLACK : WHITE);
426 const Square Up = (Us == WHITE ? NORTH : SOUTH);
427 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
428 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
430 const Square ksq = pos.square<KING>(Us);
431 Bitboard weak, b, b1, b2, safe, other;
434 // King shelter and enemy pawns storm
435 Score score = pe->king_safety<Us>(pos, ksq);
437 // Main king safety evaluation
438 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
440 // Attacked squares defended at most once by our queen or king
441 weak = attackedBy[Them][ALL_PIECES]
443 & (attackedBy[Us][KING] | attackedBy[Us][QUEEN] | ~attackedBy[Us][ALL_PIECES]);
445 // Initialize the 'kingDanger' variable, which will be transformed
446 // later into a king danger score. The initial value is based on the
447 // number and types of the enemy's attacking pieces, the number of
448 // attacked and weak squares around our king, the absence of queen and
449 // the quality of the pawn shelter (current 'score' value).
450 kingDanger = kingAttackersCount[Them] * kingAttackersWeight[Them]
451 + 102 * kingAdjacentZoneAttacksCount[Them]
452 + 191 * popcount(kingRing[Us] & weak)
453 + 143 * !!pos.pinned_pieces(Us)
454 - 848 * !pos.count<QUEEN>(Them)
455 - 9 * mg_value(score) / 8
458 // Analyse the safe enemy's checks which are possible on next move
459 safe = ~pos.pieces(Them);
460 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
462 b1 = pos.attacks_from< ROOK>(ksq);
463 b2 = pos.attacks_from<BISHOP>(ksq);
465 // Enemy queen safe checks
466 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
467 kingDanger += QueenCheck;
469 // Some other potential checks are also analysed, even from squares
470 // currently occupied by the opponent own pieces, as long as the square
471 // is not attacked by our pawns, and is not occupied by a blocked pawn.
472 other = ~( attackedBy[Us][PAWN]
473 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
475 // Enemy rooks safe and other checks
476 if (b1 & attackedBy[Them][ROOK] & safe)
477 kingDanger += RookCheck;
479 else if (b1 & attackedBy[Them][ROOK] & other)
482 // Enemy bishops safe and other checks
483 if (b2 & attackedBy[Them][BISHOP] & safe)
484 kingDanger += BishopCheck;
486 else if (b2 & attackedBy[Them][BISHOP] & other)
489 // Enemy knights safe and other checks
490 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
492 kingDanger += KnightCheck;
497 // Transform the kingDanger units into a Score, and substract it from the evaluation
499 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
502 // King tropism: firstly, find squares that opponent attacks in our king flank
503 File kf = file_of(ksq);
504 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
506 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
507 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
509 // Secondly, add the squares which are attacked twice in that flank and
510 // which are not defended by our pawns.
511 b = (Us == WHITE ? b << 4 : b >> 4)
512 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
514 score -= CloseEnemies * popcount(b);
516 // Penalty when our king is on a pawnless flank
517 if (!(pos.pieces(PAWN) & KingFlank[kf]))
518 score -= PawnlessFlank;
521 Trace::add(KING, Us, score);
527 // evaluate_threats() assigns bonuses according to the types of the attacking
528 // and the attacked pieces.
530 template<Tracing T> template<Color Us>
531 Score Evaluation<T>::evaluate_threats() {
533 const Color Them = (Us == WHITE ? BLACK : WHITE);
534 const Square Up = (Us == WHITE ? NORTH : SOUTH);
535 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
536 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
537 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
539 Bitboard b, weak, defended, stronglyProtected, safeThreats;
540 Score score = SCORE_ZERO;
542 // Non-pawn enemies attacked by a pawn
543 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
547 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
548 | attackedBy[Us][ALL_PIECES]);
550 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
552 score += ThreatBySafePawn * popcount(safeThreats);
554 if (weak ^ safeThreats)
555 score += ThreatByHangingPawn;
558 // Squares strongly protected by the opponent, either because they attack the
559 // square with a pawn, or because they attack the square twice and we don't.
560 stronglyProtected = attackedBy[Them][PAWN]
561 | (attackedBy2[Them] & ~attackedBy2[Us]);
563 // Non-pawn enemies, strongly protected
564 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
567 // Enemies not strongly protected and under our attack
568 weak = pos.pieces(Them)
570 & attackedBy[Us][ALL_PIECES];
572 // Add a bonus according to the kind of attacking pieces
575 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
578 Square s = pop_lsb(&b);
579 score += ThreatByMinor[type_of(pos.piece_on(s))];
580 if (type_of(pos.piece_on(s)) != PAWN)
581 score += ThreatByRank * (int)relative_rank(Them, s);
584 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
587 Square s = pop_lsb(&b);
588 score += ThreatByRook[type_of(pos.piece_on(s))];
589 if (type_of(pos.piece_on(s)) != PAWN)
590 score += ThreatByRank * (int)relative_rank(Them, s);
593 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
595 b = weak & attackedBy[Us][KING];
597 score += ThreatByKing[more_than_one(b)];
600 // Bonus for opponent unopposed weak pawns
601 if (pos.pieces(Us, ROOK, QUEEN))
602 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
604 // Find squares where our pawns can push on the next move
605 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
606 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
608 // Keep only the squares which are not completely unsafe
609 b &= ~attackedBy[Them][PAWN]
610 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
612 // Add a bonus for each new pawn threats from those squares
613 b = (shift<Left>(b) | shift<Right>(b))
615 & ~attackedBy[Us][PAWN];
617 score += ThreatByPawnPush * popcount(b);
619 // Add a bonus for safe slider attack threats on opponent queen
620 safeThreats = ~pos.pieces(Us) & ~attackedBy2[Them] & attackedBy2[Us];
621 b = (attackedBy[Us][BISHOP] & attackedBy[Them][QUEEN_DIAGONAL])
622 | (attackedBy[Us][ROOK ] & attackedBy[Them][QUEEN] & ~attackedBy[Them][QUEEN_DIAGONAL]);
624 score += ThreatByAttackOnQueen * popcount(b & safeThreats);
627 Trace::add(THREAT, Us, score);
633 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
634 // pawns of the given color.
636 template<Tracing T> template<Color Us>
637 Score Evaluation<T>::evaluate_passed_pawns() {
639 const Color Them = (Us == WHITE ? BLACK : WHITE);
640 const Square Up = (Us == WHITE ? NORTH : SOUTH);
642 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
643 Score score = SCORE_ZERO;
645 b = pe->passed_pawns(Us);
649 Square s = pop_lsb(&b);
651 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
653 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
654 score -= HinderPassedPawn * popcount(bb);
656 int r = relative_rank(Us, s) - RANK_2;
657 int rr = r * (r - 1);
659 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
663 Square blockSq = s + Up;
665 // Adjust bonus based on the king's proximity
666 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
667 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
669 // If blockSq is not the queening square then consider also a second push
670 if (relative_rank(Us, blockSq) != RANK_8)
671 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
673 // If the pawn is free to advance, then increase the bonus
674 if (pos.empty(blockSq))
676 // If there is a rook or queen attacking/defending the pawn from behind,
677 // consider all the squaresToQueen. Otherwise consider only the squares
678 // in the pawn's path attacked or occupied by the enemy.
679 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
681 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
683 if (!(pos.pieces(Us) & bb))
684 defendedSquares &= attackedBy[Us][ALL_PIECES];
686 if (!(pos.pieces(Them) & bb))
687 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
689 // If there aren't any enemy attacks, assign a big bonus. Otherwise
690 // assign a smaller bonus if the block square isn't attacked.
691 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
693 // If the path to the queen is fully defended, assign a big bonus.
694 // Otherwise assign a smaller bonus if the block square is defended.
695 if (defendedSquares == squaresToQueen)
698 else if (defendedSquares & blockSq)
701 mbonus += k * rr, ebonus += k * rr;
703 else if (pos.pieces(Us) & blockSq)
704 mbonus += rr + r * 2, ebonus += rr + r * 2;
707 // Scale down bonus for candidate passers which need more than one
708 // pawn push to become passed or have a pawn in front of them.
709 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
710 mbonus /= 2, ebonus /= 2;
712 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
716 Trace::add(PASSED, Us, score);
722 // evaluate_space() computes the space evaluation for a given side. The
723 // space evaluation is a simple bonus based on the number of safe squares
724 // available for minor pieces on the central four files on ranks 2--4. Safe
725 // squares one, two or three squares behind a friendly pawn are counted
726 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
727 // improve play on game opening.
729 template<Tracing T> template<Color Us>
730 Score Evaluation<T>::evaluate_space() {
732 const Color Them = (Us == WHITE ? BLACK : WHITE);
733 const Bitboard SpaceMask =
734 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
735 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
737 // Find the safe squares for our pieces inside the area defined by
738 // SpaceMask. A square is unsafe if it is attacked by an enemy
739 // pawn, or if it is undefended and attacked by an enemy piece.
740 Bitboard safe = SpaceMask
741 & ~pos.pieces(Us, PAWN)
742 & ~attackedBy[Them][PAWN]
743 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
745 // Find all squares which are at most three squares behind some friendly pawn
746 Bitboard behind = pos.pieces(Us, PAWN);
747 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
748 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
750 // Since SpaceMask[Us] is fully on our half of the board...
751 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
753 // ...count safe + (behind & safe) with a single popcount.
754 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
755 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
757 return make_score(bonus * weight * weight / 16, 0);
761 // evaluate_initiative() computes the initiative correction value for the
762 // position, i.e., second order bonus/malus based on the known attacking/defending
763 // status of the players.
766 Score Evaluation<T>::evaluate_initiative(Value eg) {
768 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
769 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
770 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
772 // Compute the initiative bonus for the attacking side
773 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
775 // Now apply the bonus: note that we find the attacking side by extracting
776 // the sign of the endgame value, and that we carefully cap the bonus so
777 // that the endgame score will never change sign after the bonus.
778 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
781 Trace::add(INITIATIVE, make_score(0, v));
783 return make_score(0, v);
787 // evaluate_scale_factor() computes the scale factor for the winning side
790 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
792 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
793 ScaleFactor sf = me->scale_factor(pos, strongSide);
795 // If we don't already have an unusual scale factor, check for certain
796 // types of endgames, and use a lower scale for those.
797 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
799 if (pos.opposite_bishops())
801 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
802 // is almost a draw, in case of KBP vs KB, it is even more a draw.
803 if ( pos.non_pawn_material(WHITE) == BishopValueMg
804 && pos.non_pawn_material(BLACK) == BishopValueMg)
805 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
807 // Endgame with opposite-colored bishops, but also other pieces. Still
808 // a bit drawish, but not as drawish as with only the two bishops.
809 return ScaleFactor(46);
811 // Endings where weaker side can place his king in front of the opponent's
812 // pawns are drawish.
813 else if ( abs(eg) <= BishopValueEg
814 && pos.count<PAWN>(strongSide) <= 2
815 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
816 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
823 // value() is the main function of the class. It computes the various parts of
824 // the evaluation and returns the value of the position from the point of view
825 // of the side to move.
828 Value Evaluation<T>::value() {
830 assert(!pos.checkers());
832 // Probe the material hash table
833 me = Material::probe(pos);
835 // If we have a specialized evaluation function for the current material
836 // configuration, call it and return.
837 if (me->specialized_eval_exists())
838 return me->evaluate(pos);
840 // Initialize score by reading the incrementally updated scores included in
841 // the position object (material + piece square tables) and the material
842 // imbalance. Score is computed internally from the white point of view.
843 Score score = pos.psq_score() + me->imbalance();
845 // Probe the pawn hash table
846 pe = Pawns::probe(pos);
847 score += pe->pawns_score();
849 // Early exit if score is high
850 Value v = (mg_value(score) + eg_value(score)) / 2;
851 if (abs(v) > LazyThreshold)
852 return pos.side_to_move() == WHITE ? v : -v;
854 // Main evaluation begins here
859 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
860 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
861 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
862 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
864 score += mobility[WHITE] - mobility[BLACK];
866 score += evaluate_king<WHITE>()
867 - evaluate_king<BLACK>();
869 score += evaluate_threats<WHITE>()
870 - evaluate_threats<BLACK>();
872 score += evaluate_passed_pawns<WHITE>()
873 - evaluate_passed_pawns<BLACK>();
875 if (pos.non_pawn_material() >= SpaceThreshold)
876 score += evaluate_space<WHITE>()
877 - evaluate_space<BLACK>();
879 score += evaluate_initiative(eg_value(score));
881 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
882 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
883 v = mg_value(score) * int(me->game_phase())
884 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
886 v /= int(PHASE_MIDGAME);
888 // In case of tracing add all remaining individual evaluation terms
891 Trace::add(MATERIAL, pos.psq_score());
892 Trace::add(IMBALANCE, me->imbalance());
893 Trace::add(PAWN, pe->pawns_score());
894 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
895 if (pos.non_pawn_material() >= SpaceThreshold)
896 Trace::add(SPACE, evaluate_space<WHITE>()
897 , evaluate_space<BLACK>());
898 Trace::add(TOTAL, score);
901 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
907 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
908 /// of the position from the point of view of the side to move.
910 Value Eval::evaluate(const Position& pos)
912 return Evaluation<>(pos).value();
915 /// trace() is like evaluate(), but instead of returning a value, it returns
916 /// a string (suitable for outputting to stdout) that contains the detailed
917 /// descriptions and values of each evaluation term. Useful for debugging.
919 std::string Eval::trace(const Position& pos) {
921 std::memset(scores, 0, sizeof(scores));
923 Value v = Evaluation<TRACE>(pos).value();
924 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
926 std::stringstream ss;
927 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
928 << " Eval term | White | Black | Total \n"
929 << " | MG EG | MG EG | MG EG \n"
930 << "----------------+-------------+-------------+-------------\n"
931 << " Material | " << Term(MATERIAL)
932 << " Imbalance | " << Term(IMBALANCE)
933 << " Pawns | " << Term(PAWN)
934 << " Knights | " << Term(KNIGHT)
935 << " Bishops | " << Term(BISHOP)
936 << " Rooks | " << Term(ROOK)
937 << " Queens | " << Term(QUEEN)
938 << " Mobility | " << Term(MOBILITY)
939 << " King safety | " << Term(KING)
940 << " Threats | " << Term(THREAT)
941 << " Passed pawns | " << Term(PASSED)
942 << " Space | " << Term(SPACE)
943 << " Initiative | " << Term(INITIATIVE)
944 << "----------------+-------------+-------------+-------------\n"
945 << " Total | " << Term(TOTAL);
947 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";