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) 2015-2018 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
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 constexpr Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
77 constexpr Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
78 constexpr Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
79 constexpr Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
81 constexpr Bitboard KingFlank[FILE_NB] = {
82 QueenSide, QueenSide, QueenSide,
83 CenterFiles, CenterFiles,
84 KingSide, KingSide, KingSide
87 // Threshold for lazy and space evaluation
88 constexpr Value LazyThreshold = Value(1500);
89 constexpr Value SpaceThreshold = Value(12222);
91 // KingAttackWeights[PieceType] contains king attack weights by piece type
92 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
94 // Penalties for enemy's safe checks
95 constexpr int QueenSafeCheck = 780;
96 constexpr int RookSafeCheck = 880;
97 constexpr int BishopSafeCheck = 435;
98 constexpr int KnightSafeCheck = 790;
100 #define S(mg, eg) make_score(mg, eg)
102 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
103 // indexed by piece type and number of attacked squares in the mobility area.
104 constexpr Score MobilityBonus[][32] = {
105 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
106 S( 22, 26), S( 29, 29), S( 36, 29) },
107 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
108 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
109 S( 91, 88), S( 98, 97) },
110 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
111 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
112 S( 46,166), S( 48,169), S( 58,171) },
113 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
114 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
115 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
116 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
117 S(106,184), S(109,191), S(113,206), S(116,212) }
120 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
121 // pieces if they occupy or can reach an outpost square, bigger if that
122 // square is supported by a pawn.
123 constexpr Score Outpost[][2] = {
124 { S(22, 6), S(36,12) }, // Knight
125 { S( 9, 2), S(15, 5) } // Bishop
128 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
129 // no (friendly) pawn on the rook file.
130 constexpr Score RookOnFile[] = { S(20, 7), S(45, 20) };
132 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
133 // which piece type attacks which one. Attacks on lesser pieces which are
134 // pawn-defended are not considered.
135 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
136 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(47, 120)
139 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
140 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(36, 38)
143 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
144 constexpr Score PassedRank[RANK_NB] = {
145 S(0, 0), S(4, 17), S(7, 20), S(14, 36), S(42, 62), S(165, 171), S(279, 252)
148 // PassedFile[File] contains a bonus according to the file of a passed pawn
149 constexpr Score PassedFile[FILE_NB] = {
150 S( 11, 14), S( 0, -5), S(-2, -8), S(-25,-13),
151 S(-25,-13), S(-2, -8), S( 0, -5), S( 11, 14)
154 // PassedDanger[Rank] contains a term to weight the passed score
155 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 2, 7, 12, 19 };
157 // KingProtector[knight/bishop] contains a penalty according to distance from king
158 constexpr Score KingProtector[] = { S(4, 6), S(6, 3) };
160 // Assorted bonuses and penalties
161 constexpr Score BishopPawns = S( 3, 5);
162 constexpr Score CloseEnemies = S( 8, 0);
163 constexpr Score Connectivity = S( 3, 1);
164 constexpr Score CorneredBishop = S( 50, 50);
165 constexpr Score Hanging = S( 52, 30);
166 constexpr Score HinderPassedPawn = S( 5, -1);
167 constexpr Score KnightOnQueen = S( 21, 11);
168 constexpr Score LongDiagonalBishop = S( 22, 0);
169 constexpr Score MinorBehindPawn = S( 16, 0);
170 constexpr Score Overload = S( 10, 5);
171 constexpr Score PawnlessFlank = S( 20, 80);
172 constexpr Score RookOnPawn = S( 8, 24);
173 constexpr Score SliderOnQueen = S( 42, 21);
174 constexpr Score ThreatByKing = S( 31, 75);
175 constexpr Score ThreatByPawnPush = S( 49, 30);
176 constexpr Score ThreatByRank = S( 16, 3);
177 constexpr Score ThreatBySafePawn = S(165,133);
178 constexpr Score TrappedRook = S( 92, 0);
179 constexpr Score WeakQueen = S( 50, 10);
180 constexpr Score WeakUnopposedPawn = S( 5, 26);
184 // Evaluation class computes and stores attacks tables and other working data
189 Evaluation() = delete;
190 explicit Evaluation(const Position& p) : pos(p) {}
191 Evaluation& operator=(const Evaluation&) = delete;
195 template<Color Us> void initialize();
196 template<Color Us, PieceType Pt> Score pieces();
197 template<Color Us> Score king() const;
198 template<Color Us> Score threats() const;
199 template<Color Us> Score passed() const;
200 template<Color Us> Score space() const;
201 ScaleFactor scale_factor(Value eg) const;
202 Score initiative(Value eg) const;
207 Bitboard mobilityArea[COLOR_NB];
208 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
210 // attackedBy[color][piece type] is a bitboard representing all squares
211 // attacked by a given color and piece type. Special "piece types" which
212 // is also calculated is ALL_PIECES.
213 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
215 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
216 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
217 // pawn or squares attacked by 2 pawns are not explicitly added.
218 Bitboard attackedBy2[COLOR_NB];
220 // kingRing[color] are the squares adjacent to the king, plus (only for a
221 // king on its first rank) the squares two ranks in front. For instance,
222 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
223 // and h6. It is set to 0 when king safety evaluation is skipped.
224 Bitboard kingRing[COLOR_NB];
226 // kingAttackersCount[color] is the number of pieces of the given color
227 // which attack a square in the kingRing of the enemy king.
228 int kingAttackersCount[COLOR_NB];
230 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
231 // the given color which attack a square in the kingRing of the enemy king.
232 // The weights of the individual piece types are given by the elements in
233 // the KingAttackWeights array.
234 int kingAttackersWeight[COLOR_NB];
236 // kingAttacksCount[color] is the number of attacks by the given color to
237 // squares directly adjacent to the enemy king. Pieces which attack more
238 // than one square are counted multiple times. For instance, if there is
239 // a white knight on g5 and black's king is on g8, this white knight adds 2
240 // to kingAttacksCount[WHITE].
241 int kingAttacksCount[COLOR_NB];
245 // Evaluation::initialize() computes king and pawn attacks, and the king ring
246 // bitboard for a given color. This is done at the beginning of the evaluation.
247 template<Tracing T> template<Color Us>
248 void Evaluation<T>::initialize() {
250 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
251 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
252 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
253 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
255 // Find our pawns that are blocked or on the first two ranks
256 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
258 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
259 // are excluded from the mobility area.
260 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
262 // Initialise attackedBy bitboards for kings and pawns
263 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
264 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
265 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
266 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
268 // Init our king safety tables only if we are going to use them
269 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
271 kingRing[Us] = attackedBy[Us][KING];
272 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
273 kingRing[Us] |= shift<Up>(kingRing[Us]);
275 if (file_of(pos.square<KING>(Us)) == FILE_H)
276 kingRing[Us] |= shift<WEST>(kingRing[Us]);
278 else if (file_of(pos.square<KING>(Us)) == FILE_A)
279 kingRing[Us] |= shift<EAST>(kingRing[Us]);
281 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
282 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
285 kingRing[Us] = kingAttackersCount[Them] = 0;
289 // Evaluation::pieces() scores pieces of a given color and type
290 template<Tracing T> template<Color Us, PieceType Pt>
291 Score Evaluation<T>::pieces() {
293 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
294 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
295 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
296 : Rank5BB | Rank4BB | Rank3BB);
297 const Square* pl = pos.squares<Pt>(Us);
301 Score score = SCORE_ZERO;
303 attackedBy[Us][Pt] = 0;
305 while ((s = *pl++) != SQ_NONE)
307 // Find attacked squares, including x-ray attacks for bishops and rooks
308 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
309 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
310 : pos.attacks_from<Pt>(s);
312 if (pos.blockers_for_king(Us) & s)
313 b &= LineBB[pos.square<KING>(Us)][s];
315 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
316 attackedBy[Us][Pt] |= b;
317 attackedBy[Us][ALL_PIECES] |= b;
319 if (b & kingRing[Them])
321 kingAttackersCount[Us]++;
322 kingAttackersWeight[Us] += KingAttackWeights[Pt];
323 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
326 int mob = popcount(b & mobilityArea[Us]);
328 mobility[Us] += MobilityBonus[Pt - 2][mob];
330 if (Pt == BISHOP || Pt == KNIGHT)
332 // Bonus if piece is on an outpost square or can reach one
333 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
335 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
337 else if (bb &= b & ~pos.pieces(Us))
338 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
340 // Bonus when behind a pawn
341 if ( relative_rank(Us, s) < RANK_5
342 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
343 score += MinorBehindPawn;
345 // Penalty if the piece is far from the king
346 score -= KingProtector[Pt == BISHOP] * distance(s, pos.square<KING>(Us));
350 // Penalty according to number of pawns on the same color square as the
351 // bishop, bigger when the center files are blocked with pawns.
352 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
354 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
355 * (1 + popcount(blocked & CenterFiles));
357 // Bonus for bishop on a long diagonal which can "see" both center squares
358 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
359 score += LongDiagonalBishop;
362 // An important Chess960 pattern: A cornered bishop blocked by a friendly
363 // pawn diagonally in front of it is a very serious problem, especially
364 // when that pawn is also blocked.
367 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
369 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
370 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
371 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
372 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
379 // Bonus for aligning rook with enemy pawns on the same rank/file
380 if (relative_rank(Us, s) >= RANK_5)
381 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
383 // Bonus for rook on an open or semi-open file
384 if (pe->semiopen_file(Us, file_of(s)))
385 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
387 // Penalty when trapped by the king, even more if the king cannot castle
390 File kf = file_of(pos.square<KING>(Us));
391 if ((kf < FILE_E) == (file_of(s) < kf))
392 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
398 // Penalty if any relative pin or discovered attack against the queen
399 Bitboard queenPinners;
400 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
405 Trace::add(Pt, Us, score);
411 // Evaluation::king() assigns bonuses and penalties to a king of a given color
412 template<Tracing T> template<Color Us>
413 Score Evaluation<T>::king() const {
415 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
416 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
417 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
419 const Square ksq = pos.square<KING>(Us);
420 Bitboard weak, b, b1, b2, safe, unsafeChecks;
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))
431 // Attacked squares defended at most once by our queen or king
432 weak = attackedBy[Them][ALL_PIECES]
434 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
436 // Analyse the safe enemy's checks which are possible on next move
437 safe = ~pos.pieces(Them);
438 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
440 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
441 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
443 // Enemy queen safe checks
444 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
445 kingDanger += QueenSafeCheck;
447 b1 &= attackedBy[Them][ROOK];
448 b2 &= attackedBy[Them][BISHOP];
450 // Enemy rooks checks
452 kingDanger += RookSafeCheck;
456 // Enemy bishops checks
458 kingDanger += BishopSafeCheck;
462 // Enemy knights checks
463 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
465 kingDanger += KnightSafeCheck;
469 // Unsafe or occupied checking squares will also be considered, as long as
470 // the square is in the attacker's mobility area.
471 unsafeChecks &= mobilityArea[Them];
473 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
474 + 64 * kingAttacksCount[Them]
475 + 183 * popcount(kingRing[Us] & weak)
476 + 122 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
477 - 860 * !pos.count<QUEEN>(Them)
478 - 7 * mg_value(score) / 8
481 // Transform the kingDanger units into a Score, and subtract it from the evaluation
484 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
485 kingDanger = std::max(0, kingDanger + mobilityDanger);
486 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
490 Bitboard kf = KingFlank[file_of(ksq)];
492 // Penalty when our king is on a pawnless flank
493 if (!(pos.pieces(PAWN) & kf))
494 score -= PawnlessFlank;
496 // Find the squares that opponent attacks in our king flank, and the squares
497 // which are attacked twice in that flank but not defended by our pawns.
498 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
499 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
501 // King tropism, to anticipate slow motion attacks on our king
502 score -= CloseEnemies * (popcount(b1) + popcount(b2));
505 Trace::add(KING, Us, score);
511 // Evaluation::threats() assigns bonuses according to the types of the
512 // attacking and the attacked pieces.
513 template<Tracing T> template<Color Us>
514 Score Evaluation<T>::threats() const {
516 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
517 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
518 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
520 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
521 Score score = SCORE_ZERO;
524 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
526 // Squares strongly protected by the enemy, either because they defend the
527 // square with a pawn, or because they defend the square twice and we don't.
528 stronglyProtected = attackedBy[Them][PAWN]
529 | (attackedBy2[Them] & ~attackedBy2[Us]);
531 // Non-pawn enemies, strongly protected
532 defended = nonPawnEnemies & stronglyProtected;
534 // Enemies not strongly protected and under our attack
535 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
537 // Bonus according to the kind of attacking pieces
540 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
543 Square s = pop_lsb(&b);
544 score += ThreatByMinor[type_of(pos.piece_on(s))];
545 if (type_of(pos.piece_on(s)) != PAWN)
546 score += ThreatByRank * (int)relative_rank(Them, s);
549 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
552 Square s = pop_lsb(&b);
553 score += ThreatByRook[type_of(pos.piece_on(s))];
554 if (type_of(pos.piece_on(s)) != PAWN)
555 score += ThreatByRank * (int)relative_rank(Them, s);
558 // Bonus for king attacks on pawns or pieces which are not pawn-defended
559 if (weak & attackedBy[Us][KING])
560 score += ThreatByKing;
562 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
564 // Bonus for overload (non-pawn enemies attacked and defended exactly once)
566 & attackedBy[Us][ALL_PIECES] & ~attackedBy2[Us]
567 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
568 score += Overload * popcount(b);
571 // Bonus for enemy unopposed weak pawns
572 if (pos.pieces(Us, ROOK, QUEEN))
573 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
575 // Our safe or protected pawns
576 b = pos.pieces(Us, PAWN)
577 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
579 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
580 score += ThreatBySafePawn * popcount(safeThreats);
582 // Find squares where our pawns can push on the next move
583 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
584 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
586 // Keep only the squares which are not completely unsafe
587 b &= ~attackedBy[Them][PAWN]
588 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
590 // Bonus for safe pawn threats on the next move
591 b = pawn_attacks_bb<Us>(b)
593 & ~attackedBy[Us][PAWN];
595 score += ThreatByPawnPush * popcount(b);
597 // Bonus for threats on the next moves against enemy queen
598 if (pos.count<QUEEN>(Them) == 1)
600 Square s = pos.square<QUEEN>(Them);
601 safeThreats = mobilityArea[Us] & ~stronglyProtected;
603 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
605 score += KnightOnQueen * popcount(b & safeThreats);
607 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
608 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
610 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
613 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
614 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
615 score += Connectivity * popcount(b);
618 Trace::add(THREAT, Us, score);
623 // Evaluation::passed() evaluates the passed pawns and candidate passed
624 // pawns of the given color.
626 template<Tracing T> template<Color Us>
627 Score Evaluation<T>::passed() const {
629 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
630 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
632 auto king_proximity = [&](Color c, Square s) {
633 return std::min(distance(pos.square<KING>(c), s), 5);
636 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
637 Score score = SCORE_ZERO;
639 b = pe->passed_pawns(Us);
643 Square s = pop_lsb(&b);
645 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
647 bb = forward_file_bb(Us, s) & pos.pieces(Them);
648 score -= HinderPassedPawn * popcount(bb);
650 int r = relative_rank(Us, s);
651 int w = PassedDanger[r];
653 Score bonus = PassedRank[r];
657 Square blockSq = s + Up;
659 // Adjust bonus based on the king's proximity
660 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
661 - king_proximity(Us, blockSq) * 2) * w);
663 // If blockSq is not the queening square then consider also a second push
665 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
667 // If the pawn is free to advance, then increase the bonus
668 if (pos.empty(blockSq))
670 // If there is a rook or queen attacking/defending the pawn from behind,
671 // consider all the squaresToQueen. Otherwise consider only the squares
672 // in the pawn's path attacked or occupied by the enemy.
673 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
675 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
677 if (!(pos.pieces(Us) & bb))
678 defendedSquares &= attackedBy[Us][ALL_PIECES];
680 if (!(pos.pieces(Them) & bb))
681 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
683 // If there aren't any enemy attacks, assign a big bonus. Otherwise
684 // assign a smaller bonus if the block square isn't attacked.
685 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
687 // If the path to the queen is fully defended, assign a big bonus.
688 // Otherwise assign a smaller bonus if the block square is defended.
689 if (defendedSquares == squaresToQueen)
692 else if (defendedSquares & blockSq)
695 bonus += make_score(k * w, k * w);
697 else if (pos.pieces(Us) & blockSq)
698 bonus += make_score(w + r * 2, w + r * 2);
701 // Scale down bonus for candidate passers which need more than one
702 // pawn push to become passed, or have a pawn in front of them.
703 if ( !pos.pawn_passed(Us, s + Up)
704 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
707 score += bonus + PassedFile[file_of(s)];
711 Trace::add(PASSED, Us, score);
717 // Evaluation::space() computes the space evaluation for a given side. The
718 // space evaluation is a simple bonus based on the number of safe squares
719 // available for minor pieces on the central four files on ranks 2--4. Safe
720 // squares one, two or three squares behind a friendly pawn are counted
721 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
722 // improve play on game opening.
724 template<Tracing T> template<Color Us>
725 Score Evaluation<T>::space() const {
727 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
728 constexpr Bitboard SpaceMask =
729 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
730 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
732 if (pos.non_pawn_material() < SpaceThreshold)
735 // Find the available squares for our pieces inside the area defined by SpaceMask
736 Bitboard safe = SpaceMask
737 & ~pos.pieces(Us, PAWN)
738 & ~attackedBy[Them][PAWN];
740 // Find all squares which are at most three squares behind some friendly pawn
741 Bitboard behind = pos.pieces(Us, PAWN);
742 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
743 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
745 int bonus = popcount(safe) + popcount(behind & safe);
746 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
748 Score score = make_score(bonus * weight * weight / 16, 0);
751 Trace::add(SPACE, Us, score);
757 // Evaluation::initiative() computes the initiative correction value
758 // for the position. It is a second order bonus/malus based on the
759 // known attacking/defending status of the players.
762 Score Evaluation<T>::initiative(Value eg) const {
764 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
765 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
767 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
768 && (pos.pieces(PAWN) & KingSide);
770 // Compute the initiative bonus for the attacking side
771 int complexity = 8 * pe->pawn_asymmetry()
772 + 12 * pos.count<PAWN>()
774 + 16 * pawnsOnBothFlanks
775 + 48 * !pos.non_pawn_material()
778 // Now apply the bonus: note that we find the attacking side by extracting
779 // the sign of the endgame value, and that we carefully cap the bonus so
780 // that the endgame score will never change sign after the bonus.
781 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
784 Trace::add(INITIATIVE, make_score(0, v));
786 return make_score(0, v);
790 // Evaluation::scale_factor() computes the scale factor for the winning side
793 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
795 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
796 int sf = me->scale_factor(pos, strongSide);
798 // If scale is not already specific, scale down the endgame via general heuristics
799 if (sf == SCALE_FACTOR_NORMAL)
801 if ( pos.opposite_bishops()
802 && pos.non_pawn_material(WHITE) == BishopValueMg
803 && pos.non_pawn_material(BLACK) == BishopValueMg)
806 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
809 return ScaleFactor(sf);
813 // Evaluation::value() is the main function of the class. It computes the various
814 // parts of the evaluation and returns the value of the position from the point
815 // of view of the side to move.
818 Value Evaluation<T>::value() {
820 assert(!pos.checkers());
822 // Probe the material hash table
823 me = Material::probe(pos);
825 // If we have a specialized evaluation function for the current material
826 // configuration, call it and return.
827 if (me->specialized_eval_exists())
828 return me->evaluate(pos);
830 // Initialize score by reading the incrementally updated scores included in
831 // the position object (material + piece square tables) and the material
832 // imbalance. Score is computed internally from the white point of view.
833 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
835 // Probe the pawn hash table
836 pe = Pawns::probe(pos);
837 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
839 // Early exit if score is high
840 Value v = (mg_value(score) + eg_value(score)) / 2;
841 if (abs(v) > LazyThreshold)
842 return pos.side_to_move() == WHITE ? v : -v;
844 // Main evaluation begins here
849 // Pieces should be evaluated first (populate attack tables)
850 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
851 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
852 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
853 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
855 score += mobility[WHITE] - mobility[BLACK];
857 score += king< WHITE>() - king< BLACK>()
858 + threats<WHITE>() - threats<BLACK>()
859 + passed< WHITE>() - passed< BLACK>()
860 + space< WHITE>() - space< BLACK>();
862 score += initiative(eg_value(score));
864 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
865 ScaleFactor sf = scale_factor(eg_value(score));
866 v = mg_value(score) * int(me->game_phase())
867 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
869 v /= int(PHASE_MIDGAME);
871 // In case of tracing add all remaining individual evaluation terms
874 Trace::add(MATERIAL, pos.psq_score());
875 Trace::add(IMBALANCE, me->imbalance());
876 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
877 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
878 Trace::add(TOTAL, score);
881 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
888 /// evaluate() is the evaluator for the outer world. It returns a static
889 /// evaluation of the position from the point of view of the side to move.
891 Value Eval::evaluate(const Position& pos) {
892 return Evaluation<NO_TRACE>(pos).value();
896 /// trace() is like evaluate(), but instead of returning a value, it returns
897 /// a string (suitable for outputting to stdout) that contains the detailed
898 /// descriptions and values of each evaluation term. Useful for debugging.
900 std::string Eval::trace(const Position& pos) {
902 std::memset(scores, 0, sizeof(scores));
904 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
906 Value v = Evaluation<TRACE>(pos).value();
908 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
910 std::stringstream ss;
911 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
912 << " Term | White | Black | Total \n"
913 << " | MG EG | MG EG | MG EG \n"
914 << " ------------+-------------+-------------+------------\n"
915 << " Material | " << Term(MATERIAL)
916 << " Imbalance | " << Term(IMBALANCE)
917 << " Initiative | " << Term(INITIATIVE)
918 << " Pawns | " << Term(PAWN)
919 << " Knights | " << Term(KNIGHT)
920 << " Bishops | " << Term(BISHOP)
921 << " Rooks | " << Term(ROOK)
922 << " Queens | " << Term(QUEEN)
923 << " Mobility | " << Term(MOBILITY)
924 << " King safety | " << Term(KING)
925 << " Threats | " << Term(THREAT)
926 << " Passed | " << Term(PASSED)
927 << " Space | " << Term(SPACE)
928 << " ------------+-------------+-------------+------------\n"
929 << " Total | " << Term(TOTAL);
931 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";