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) 2015-2019 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 ^ FileDBB, QueenSide, QueenSide,
83 CenterFiles, CenterFiles,
84 KingSide, KingSide, KingSide ^ FileEBB
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(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
106 S( 22, 23), S( 28, 27), S( 33, 33) },
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(18, 7), S(44, 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(62, 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(51, 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(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
148 // PassedFile[File] contains a bonus according to the file of a passed pawn
149 constexpr Score PassedFile[FILE_NB] = {
150 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
151 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
154 // Assorted bonuses and penalties
155 constexpr Score BishopPawns = S( 3, 7);
156 constexpr Score CloseEnemies = S( 8, 0);
157 constexpr Score CorneredBishop = S( 50, 50);
158 constexpr Score Hanging = S( 69, 36);
159 constexpr Score KingProtector = S( 7, 8);
160 constexpr Score KnightOnQueen = S( 16, 12);
161 constexpr Score LongDiagonalBishop = S( 45, 0);
162 constexpr Score MinorBehindPawn = S( 18, 3);
163 constexpr Score PawnlessFlank = S( 17, 95);
164 constexpr Score RestrictedPiece = S( 7, 7);
165 constexpr Score RookOnPawn = S( 10, 32);
166 constexpr Score SliderOnQueen = S( 59, 18);
167 constexpr Score ThreatByKing = S( 24, 89);
168 constexpr Score ThreatByPawnPush = S( 48, 39);
169 constexpr Score ThreatByRank = S( 13, 0);
170 constexpr Score ThreatBySafePawn = S(173, 94);
171 constexpr Score TrappedRook = S( 96, 4);
172 constexpr Score WeakQueen = S( 49, 15);
173 constexpr Score WeakUnopposedPawn = S( 12, 23);
177 // Evaluation class computes and stores attacks tables and other working data
182 Evaluation() = delete;
183 explicit Evaluation(const Position& p) : pos(p) {}
184 Evaluation& operator=(const Evaluation&) = delete;
188 template<Color Us> void initialize();
189 template<Color Us, PieceType Pt> Score pieces();
190 template<Color Us> Score king() const;
191 template<Color Us> Score threats() const;
192 template<Color Us> Score passed() const;
193 template<Color Us> Score space() const;
194 ScaleFactor scale_factor(Value eg) const;
195 Score initiative(Value eg) const;
200 Bitboard mobilityArea[COLOR_NB];
201 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
203 // attackedBy[color][piece type] is a bitboard representing all squares
204 // attacked by a given color and piece type. Special "piece types" which
205 // is also calculated is ALL_PIECES.
206 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
208 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
209 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
210 // pawn or squares attacked by 2 pawns are not explicitly added.
211 Bitboard attackedBy2[COLOR_NB];
213 // kingRing[color] are the squares adjacent to the king, plus (only for a
214 // king on its first rank) the squares two ranks in front. For instance,
215 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
216 // and h6. It is set to 0 when king safety evaluation is skipped.
217 Bitboard kingRing[COLOR_NB];
219 // kingAttackersCount[color] is the number of pieces of the given color
220 // which attack a square in the kingRing of the enemy king.
221 int kingAttackersCount[COLOR_NB];
223 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
224 // the given color which attack a square in the kingRing of the enemy king.
225 // The weights of the individual piece types are given by the elements in
226 // the KingAttackWeights array.
227 int kingAttackersWeight[COLOR_NB];
229 // kingAttacksCount[color] is the number of attacks by the given color to
230 // squares directly adjacent to the enemy king. Pieces which attack more
231 // than one square are counted multiple times. For instance, if there is
232 // a white knight on g5 and black's king is on g8, this white knight adds 2
233 // to kingAttacksCount[WHITE].
234 int kingAttacksCount[COLOR_NB];
238 // Evaluation::initialize() computes king and pawn attacks, and the king ring
239 // bitboard for a given color. This is done at the beginning of the evaluation.
240 template<Tracing T> template<Color Us>
241 void Evaluation<T>::initialize() {
243 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
244 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
245 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
246 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
248 // Find our pawns that are blocked or on the first two ranks
249 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
251 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
252 // are excluded from the mobility area.
253 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
255 // Initialise attackedBy bitboards for kings and pawns
256 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
257 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
258 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
259 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
261 kingRing[Us] = kingAttackersCount[Them] = 0;
263 // Init our king safety tables only if we are going to use them
264 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
266 kingRing[Us] = attackedBy[Us][KING];
267 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
268 kingRing[Us] |= shift<Up>(kingRing[Us]);
270 if (file_of(pos.square<KING>(Us)) == FILE_H)
271 kingRing[Us] |= shift<WEST>(kingRing[Us]);
273 else if (file_of(pos.square<KING>(Us)) == FILE_A)
274 kingRing[Us] |= shift<EAST>(kingRing[Us]);
276 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
277 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
282 // Evaluation::pieces() scores pieces of a given color and type
283 template<Tracing T> template<Color Us, PieceType Pt>
284 Score Evaluation<T>::pieces() {
286 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
287 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
288 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
289 : Rank5BB | Rank4BB | Rank3BB);
290 const Square* pl = pos.squares<Pt>(Us);
294 Score score = SCORE_ZERO;
296 attackedBy[Us][Pt] = 0;
298 while ((s = *pl++) != SQ_NONE)
300 // Find attacked squares, including x-ray attacks for bishops and rooks
301 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
302 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
303 : pos.attacks_from<Pt>(s);
305 if (pos.blockers_for_king(Us) & s)
306 b &= LineBB[pos.square<KING>(Us)][s];
308 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
309 attackedBy[Us][Pt] |= b;
310 attackedBy[Us][ALL_PIECES] |= b;
312 if (b & kingRing[Them] & ~double_pawn_attacks_bb<Them>(pos.pieces(Them, PAWN)))
314 kingAttackersCount[Us]++;
315 kingAttackersWeight[Us] += KingAttackWeights[Pt];
316 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
319 int mob = popcount(b & mobilityArea[Us]);
321 mobility[Us] += MobilityBonus[Pt - 2][mob];
323 if (Pt == BISHOP || Pt == KNIGHT)
325 // Bonus if piece is on an outpost square or can reach one
326 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
328 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
330 else if (bb &= b & ~pos.pieces(Us))
331 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
333 // Knight and Bishop bonus for being right behind a pawn
334 if (shift<Down>(pos.pieces(PAWN)) & s)
335 score += MinorBehindPawn;
337 // Penalty if the piece is far from the king
338 score -= KingProtector * distance(s, pos.square<KING>(Us));
342 // Penalty according to number of pawns on the same color square as the
343 // bishop, bigger when the center files are blocked with pawns.
344 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
346 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
347 * (1 + popcount(blocked & CenterFiles));
349 // Bonus for bishop on a long diagonal which can "see" both center squares
350 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
351 score += LongDiagonalBishop;
354 // An important Chess960 pattern: A cornered bishop blocked by a friendly
355 // pawn diagonally in front of it is a very serious problem, especially
356 // when that pawn is also blocked.
359 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
361 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
362 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
363 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
364 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
371 // Bonus for aligning rook with enemy pawns on the same rank/file
372 if (relative_rank(Us, s) >= RANK_5)
373 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
375 // Bonus for rook on an open or semi-open file
376 if (pe->semiopen_file(Us, file_of(s)))
377 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
379 // Penalty when trapped by the king, even more if the king cannot castle
382 File kf = file_of(pos.square<KING>(Us));
383 if ((kf < FILE_E) == (file_of(s) < kf))
384 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.castling_rights(Us));
390 // Penalty if any relative pin or discovered attack against the queen
391 Bitboard queenPinners;
392 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
397 Trace::add(Pt, Us, score);
403 // Evaluation::king() assigns bonuses and penalties to a king of a given color
404 template<Tracing T> template<Color Us>
405 Score Evaluation<T>::king() const {
407 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
408 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
409 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
411 const Square ksq = pos.square<KING>(Us);
412 Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
414 // King shelter and enemy pawns storm
415 Score score = pe->king_safety<Us>(pos);
417 // Find the squares that opponent attacks in our king flank, and the squares
418 // which are attacked twice in that flank.
419 kingFlank = KingFlank[file_of(ksq)];
420 b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
421 b2 = b1 & attackedBy2[Them];
423 int tropism = popcount(b1) + popcount(b2);
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 + 69 * kingAttacksCount[Them]
475 + 185 * popcount(kingRing[Us] & weak)
476 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
477 + tropism * tropism / 4
478 - 873 * !pos.count<QUEEN>(Them)
479 - 6 * mg_value(score) / 8
480 + mg_value(mobility[Them] - mobility[Us])
483 // Transform the kingDanger units into a Score, and subtract it from the evaluation
485 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
488 // Penalty when our king is on a pawnless flank
489 if (!(pos.pieces(PAWN) & kingFlank))
490 score -= PawnlessFlank;
492 // King tropism bonus, to anticipate slow motion attacks on our king
493 score -= CloseEnemies * tropism;
496 Trace::add(KING, Us, score);
502 // Evaluation::threats() assigns bonuses according to the types of the
503 // attacking and the attacked pieces.
504 template<Tracing T> template<Color Us>
505 Score Evaluation<T>::threats() const {
507 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
508 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
509 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
511 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe, restricted;
512 Score score = SCORE_ZERO;
515 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(Them, PAWN);
517 // Squares strongly protected by the enemy, either because they defend the
518 // square with a pawn, or because they defend the square twice and we don't.
519 stronglyProtected = attackedBy[Them][PAWN]
520 | (attackedBy2[Them] & ~attackedBy2[Us]);
522 // Non-pawn enemies, strongly protected
523 defended = nonPawnEnemies & stronglyProtected;
525 // Enemies not strongly protected and under our attack
526 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
528 // Safe or protected squares
529 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
531 // Bonus according to the kind of attacking pieces
534 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
537 Square s = pop_lsb(&b);
538 score += ThreatByMinor[type_of(pos.piece_on(s))];
539 if (type_of(pos.piece_on(s)) != PAWN)
540 score += ThreatByRank * (int)relative_rank(Them, s);
543 b = weak & attackedBy[Us][ROOK];
546 Square s = pop_lsb(&b);
547 score += ThreatByRook[type_of(pos.piece_on(s))];
548 if (type_of(pos.piece_on(s)) != PAWN)
549 score += ThreatByRank * (int)relative_rank(Them, s);
552 if (weak & attackedBy[Us][KING])
553 score += ThreatByKing;
555 b = ~attackedBy[Them][ALL_PIECES]
556 | (nonPawnEnemies & attackedBy2[Us]);
557 score += Hanging * popcount(weak & b);
560 // Bonus for restricting their piece moves
561 restricted = attackedBy[Them][ALL_PIECES]
562 & ~attackedBy[Them][PAWN]
564 & attackedBy[Us][ALL_PIECES];
565 score += RestrictedPiece * popcount(restricted);
567 // Bonus for enemy unopposed weak pawns
568 if (pos.pieces(Us, ROOK, QUEEN))
569 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
571 // Find squares where our pawns can push on the next move
572 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
573 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
575 // Keep only the squares which are relatively safe
576 b &= ~attackedBy[Them][PAWN] & safe;
578 // Bonus for safe pawn threats on the next move
579 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
580 score += ThreatByPawnPush * popcount(b);
582 // Our safe or protected pawns
583 b = pos.pieces(Us, PAWN) & safe;
585 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
586 score += ThreatBySafePawn * popcount(b);
588 // Bonus for threats on the next moves against enemy queen
589 if (pos.count<QUEEN>(Them) == 1)
591 Square s = pos.square<QUEEN>(Them);
592 safe = mobilityArea[Us] & ~stronglyProtected;
594 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
596 score += KnightOnQueen * popcount(b & safe);
598 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
599 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
601 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
605 Trace::add(THREAT, Us, score);
610 // Evaluation::passed() evaluates the passed pawns and candidate passed
611 // pawns of the given color.
613 template<Tracing T> template<Color Us>
614 Score Evaluation<T>::passed() const {
616 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
617 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
619 auto king_proximity = [&](Color c, Square s) {
620 return std::min(distance(pos.square<KING>(c), s), 5);
623 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
624 Score score = SCORE_ZERO;
626 b = pe->passed_pawns(Us);
630 Square s = pop_lsb(&b);
632 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
634 int r = relative_rank(Us, s);
636 Score bonus = PassedRank[r];
640 int w = (r-2) * (r-2) + 2;
641 Square blockSq = s + Up;
643 // Adjust bonus based on the king's proximity
644 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
645 - king_proximity(Us, blockSq) * 2) * w);
647 // If blockSq is not the queening square then consider also a second push
649 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
651 // If the pawn is free to advance, then increase the bonus
652 if (pos.empty(blockSq))
654 // If there is a rook or queen attacking/defending the pawn from behind,
655 // consider all the squaresToQueen. Otherwise consider only the squares
656 // in the pawn's path attacked or occupied by the enemy.
657 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
659 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
661 if (!(pos.pieces(Us) & bb))
662 defendedSquares &= attackedBy[Us][ALL_PIECES];
664 if (!(pos.pieces(Them) & bb))
665 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
667 // If there aren't any enemy attacks, assign a big bonus. Otherwise
668 // assign a smaller bonus if the block square isn't attacked.
669 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
671 // If the path to the queen is fully defended, assign a big bonus.
672 // Otherwise assign a smaller bonus if the block square is defended.
673 if (defendedSquares == squaresToQueen)
676 else if (defendedSquares & blockSq)
679 bonus += make_score(k * w, k * w);
683 // Scale down bonus for candidate passers which need more than one
684 // pawn push to become passed, or have a pawn in front of them.
685 if ( !pos.pawn_passed(Us, s + Up)
686 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
689 score += bonus + PassedFile[file_of(s)];
693 Trace::add(PASSED, Us, score);
699 // Evaluation::space() computes the space evaluation for a given side. The
700 // space evaluation is a simple bonus based on the number of safe squares
701 // available for minor pieces on the central four files on ranks 2--4. Safe
702 // squares one, two or three squares behind a friendly pawn are counted
703 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
704 // improve play on game opening.
706 template<Tracing T> template<Color Us>
707 Score Evaluation<T>::space() const {
709 if (pos.non_pawn_material() < SpaceThreshold)
712 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
713 constexpr Bitboard SpaceMask =
714 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
715 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
717 // Find the available squares for our pieces inside the area defined by SpaceMask
718 Bitboard safe = SpaceMask
719 & ~pos.pieces(Us, PAWN)
720 & ~attackedBy[Them][PAWN];
722 // Find all squares which are at most three squares behind some friendly pawn
723 Bitboard behind = pos.pieces(Us, PAWN);
724 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
725 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
727 int bonus = popcount(safe) + popcount(behind & safe);
728 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
730 Score score = make_score(bonus * weight * weight / 16, 0);
733 Trace::add(SPACE, Us, score);
739 // Evaluation::initiative() computes the initiative correction value
740 // for the position. It is a second order bonus/malus based on the
741 // known attacking/defending status of the players.
744 Score Evaluation<T>::initiative(Value eg) const {
746 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
747 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
749 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
750 && (pos.pieces(PAWN) & KingSide);
752 // Compute the initiative bonus for the attacking side
753 int complexity = 8 * pe->pawn_asymmetry()
754 + 12 * pos.count<PAWN>()
756 + 16 * pawnsOnBothFlanks
757 + 48 * !pos.non_pawn_material()
760 // Now apply the bonus: note that we find the attacking side by extracting
761 // the sign of the endgame value, and that we carefully cap the bonus so
762 // that the endgame score will never change sign after the bonus.
763 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
766 Trace::add(INITIATIVE, make_score(0, v));
768 return make_score(0, v);
772 // Evaluation::scale_factor() computes the scale factor for the winning side
775 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
777 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
778 int sf = me->scale_factor(pos, strongSide);
780 // If scale is not already specific, scale down the endgame via general heuristics
781 if (sf == SCALE_FACTOR_NORMAL)
783 if ( pos.opposite_bishops()
784 && pos.non_pawn_material(WHITE) == BishopValueMg
785 && pos.non_pawn_material(BLACK) == BishopValueMg)
786 sf = 8 + 4 * pe->pawn_asymmetry();
788 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
792 return ScaleFactor(sf);
796 // Evaluation::value() is the main function of the class. It computes the various
797 // parts of the evaluation and returns the value of the position from the point
798 // of view of the side to move.
801 Value Evaluation<T>::value() {
803 assert(!pos.checkers());
805 // Probe the material hash table
806 me = Material::probe(pos);
808 // If we have a specialized evaluation function for the current material
809 // configuration, call it and return.
810 if (me->specialized_eval_exists())
811 return me->evaluate(pos);
813 // Initialize score by reading the incrementally updated scores included in
814 // the position object (material + piece square tables) and the material
815 // imbalance. Score is computed internally from the white point of view.
816 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
818 // Probe the pawn hash table
819 pe = Pawns::probe(pos);
820 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
822 // Early exit if score is high
823 Value v = (mg_value(score) + eg_value(score)) / 2;
824 if (abs(v) > LazyThreshold)
825 return pos.side_to_move() == WHITE ? v : -v;
827 // Main evaluation begins here
832 // Pieces should be evaluated first (populate attack tables)
833 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
834 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
835 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
836 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
838 score += mobility[WHITE] - mobility[BLACK];
840 score += king< WHITE>() - king< BLACK>()
841 + threats<WHITE>() - threats<BLACK>()
842 + passed< WHITE>() - passed< BLACK>()
843 + space< WHITE>() - space< BLACK>();
845 score += initiative(eg_value(score));
847 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
848 ScaleFactor sf = scale_factor(eg_value(score));
849 v = mg_value(score) * int(me->game_phase())
850 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
852 v /= int(PHASE_MIDGAME);
854 // In case of tracing add all remaining individual evaluation terms
857 Trace::add(MATERIAL, pos.psq_score());
858 Trace::add(IMBALANCE, me->imbalance());
859 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
860 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
861 Trace::add(TOTAL, score);
864 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
871 /// evaluate() is the evaluator for the outer world. It returns a static
872 /// evaluation of the position from the point of view of the side to move.
874 Value Eval::evaluate(const Position& pos) {
875 return Evaluation<NO_TRACE>(pos).value();
879 /// trace() is like evaluate(), but instead of returning a value, it returns
880 /// a string (suitable for outputting to stdout) that contains the detailed
881 /// descriptions and values of each evaluation term. Useful for debugging.
883 std::string Eval::trace(const Position& pos) {
885 std::memset(scores, 0, sizeof(scores));
887 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
889 Value v = Evaluation<TRACE>(pos).value();
891 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
893 std::stringstream ss;
894 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
895 << " Term | White | Black | Total \n"
896 << " | MG EG | MG EG | MG EG \n"
897 << " ------------+-------------+-------------+------------\n"
898 << " Material | " << Term(MATERIAL)
899 << " Imbalance | " << Term(IMBALANCE)
900 << " Initiative | " << Term(INITIATIVE)
901 << " Pawns | " << Term(PAWN)
902 << " Knights | " << Term(KNIGHT)
903 << " Bishops | " << Term(BISHOP)
904 << " Rooks | " << Term(ROOK)
905 << " Queens | " << Term(QUEEN)
906 << " Mobility | " << Term(MOBILITY)
907 << " King safety | " << Term(KING)
908 << " Threats | " << Term(THREAT)
909 << " Passed | " << Term(PASSED)
910 << " Space | " << Term(SPACE)
911 << " ------------+-------------+-------------+------------\n"
912 << " Total | " << Term(TOTAL);
914 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";