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 ^ 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(-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(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 // PassedDanger[Rank] contains a term to weight the passed score
155 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 3, 7, 11, 20 };
157 // Assorted bonuses and penalties
158 constexpr Score BishopPawns = S( 3, 7);
159 constexpr Score CloseEnemies = S( 6, 0);
160 constexpr Score CorneredBishop = S( 50, 50);
161 constexpr Score Hanging = S( 57, 32);
162 constexpr Score KingProtector = S( 6, 6);
163 constexpr Score KnightOnQueen = S( 21, 11);
164 constexpr Score LongDiagonalBishop = S( 46, 0);
165 constexpr Score MinorBehindPawn = S( 16, 0);
166 constexpr Score Overload = S( 13, 6);
167 constexpr Score PawnlessFlank = S( 19, 84);
168 constexpr Score RookOnPawn = S( 10, 30);
169 constexpr Score SliderOnQueen = S( 42, 21);
170 constexpr Score ThreatByKing = S( 23, 76);
171 constexpr Score ThreatByPawnPush = S( 45, 40);
172 constexpr Score ThreatByRank = S( 16, 3);
173 constexpr Score ThreatBySafePawn = S(173,102);
174 constexpr Score TrappedRook = S( 92, 0);
175 constexpr Score WeakQueen = S( 50, 10);
176 constexpr Score WeakUnopposedPawn = S( 5, 29);
180 // Evaluation class computes and stores attacks tables and other working data
185 Evaluation() = delete;
186 explicit Evaluation(const Position& p) : pos(p) {}
187 Evaluation& operator=(const Evaluation&) = delete;
191 template<Color Us> void initialize();
192 template<Color Us, PieceType Pt> Score pieces();
193 template<Color Us> Score king() const;
194 template<Color Us> Score threats() const;
195 template<Color Us> Score passed() const;
196 template<Color Us> Score space() const;
197 ScaleFactor scale_factor(Value eg) const;
198 Score initiative(Value eg) const;
203 Bitboard mobilityArea[COLOR_NB];
204 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
206 // attackedBy[color][piece type] is a bitboard representing all squares
207 // attacked by a given color and piece type. Special "piece types" which
208 // is also calculated is ALL_PIECES.
209 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
211 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
212 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
213 // pawn or squares attacked by 2 pawns are not explicitly added.
214 Bitboard attackedBy2[COLOR_NB];
216 // kingRing[color] are the squares adjacent to the king, plus (only for a
217 // king on its first rank) the squares two ranks in front. For instance,
218 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
219 // and h6. It is set to 0 when king safety evaluation is skipped.
220 Bitboard kingRing[COLOR_NB];
222 // kingAttackersCount[color] is the number of pieces of the given color
223 // which attack a square in the kingRing of the enemy king.
224 int kingAttackersCount[COLOR_NB];
226 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
227 // the given color which attack a square in the kingRing of the enemy king.
228 // The weights of the individual piece types are given by the elements in
229 // the KingAttackWeights array.
230 int kingAttackersWeight[COLOR_NB];
232 // kingAttacksCount[color] is the number of attacks by the given color to
233 // squares directly adjacent to the enemy king. Pieces which attack more
234 // than one square are counted multiple times. For instance, if there is
235 // a white knight on g5 and black's king is on g8, this white knight adds 2
236 // to kingAttacksCount[WHITE].
237 int kingAttacksCount[COLOR_NB];
241 // Evaluation::initialize() computes king and pawn attacks, and the king ring
242 // bitboard for a given color. This is done at the beginning of the evaluation.
243 template<Tracing T> template<Color Us>
244 void Evaluation<T>::initialize() {
246 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
247 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
248 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
249 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
251 // Find our pawns that are blocked or on the first two ranks
252 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
254 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
255 // are excluded from the mobility area.
256 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
258 // Initialise attackedBy bitboards for kings and pawns
259 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
260 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
261 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
262 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
264 // Init our king safety tables only if we are going to use them
265 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
267 kingRing[Us] = attackedBy[Us][KING];
268 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
269 kingRing[Us] |= shift<Up>(kingRing[Us]);
271 if (file_of(pos.square<KING>(Us)) == FILE_H)
272 kingRing[Us] |= shift<WEST>(kingRing[Us]);
274 else if (file_of(pos.square<KING>(Us)) == FILE_A)
275 kingRing[Us] |= shift<EAST>(kingRing[Us]);
277 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
278 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
281 kingRing[Us] = kingAttackersCount[Them] = 0;
285 // Evaluation::pieces() scores pieces of a given color and type
286 template<Tracing T> template<Color Us, PieceType Pt>
287 Score Evaluation<T>::pieces() {
289 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
290 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
291 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
292 : Rank5BB | Rank4BB | Rank3BB);
293 const Square* pl = pos.squares<Pt>(Us);
297 Score score = SCORE_ZERO;
299 attackedBy[Us][Pt] = 0;
301 while ((s = *pl++) != SQ_NONE)
303 // Find attacked squares, including x-ray attacks for bishops and rooks
304 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
305 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
306 : pos.attacks_from<Pt>(s);
308 if (pos.blockers_for_king(Us) & s)
309 b &= LineBB[pos.square<KING>(Us)][s];
311 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
312 attackedBy[Us][Pt] |= b;
313 attackedBy[Us][ALL_PIECES] |= b;
315 if (b & kingRing[Them])
317 kingAttackersCount[Us]++;
318 kingAttackersWeight[Us] += KingAttackWeights[Pt];
319 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
322 int mob = popcount(b & mobilityArea[Us]);
324 mobility[Us] += MobilityBonus[Pt - 2][mob];
326 if (Pt == BISHOP || Pt == KNIGHT)
328 // Bonus if piece is on an outpost square or can reach one
329 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
331 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
333 else if (bb &= b & ~pos.pieces(Us))
334 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
336 // Knight and Bishop bonus for being right behind a pawn
337 if (shift<Down>(pos.pieces(PAWN)) & s)
338 score += MinorBehindPawn;
340 // Penalty if the piece is far from the king
341 score -= KingProtector * distance(s, pos.square<KING>(Us));
345 // Penalty according to number of pawns on the same color square as the
346 // bishop, bigger when the center files are blocked with pawns.
347 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
349 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
350 * (1 + popcount(blocked & CenterFiles));
352 // Bonus for bishop on a long diagonal which can "see" both center squares
353 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
354 score += LongDiagonalBishop;
357 // An important Chess960 pattern: A cornered bishop blocked by a friendly
358 // pawn diagonally in front of it is a very serious problem, especially
359 // when that pawn is also blocked.
362 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
364 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
365 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
366 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
367 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
374 // Bonus for aligning rook with enemy pawns on the same rank/file
375 if (relative_rank(Us, s) >= RANK_5)
376 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
378 // Bonus for rook on an open or semi-open file
379 if (pe->semiopen_file(Us, file_of(s)))
380 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
382 // Penalty when trapped by the king, even more if the king cannot castle
385 File kf = file_of(pos.square<KING>(Us));
386 if ((kf < FILE_E) == (file_of(s) < kf))
387 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
393 // Penalty if any relative pin or discovered attack against the queen
394 Bitboard queenPinners;
395 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
400 Trace::add(Pt, Us, score);
406 // Evaluation::king() assigns bonuses and penalties to a king of a given color
407 template<Tracing T> template<Color Us>
408 Score Evaluation<T>::king() const {
410 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
411 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
412 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
414 const Square ksq = pos.square<KING>(Us);
415 Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
417 // King shelter and enemy pawns storm
418 Score score = pe->king_safety<Us>(pos, ksq);
420 // Find the squares that opponent attacks in our king flank, and the squares
421 // which are attacked twice in that flank but not defended by our pawns.
422 kingFlank = KingFlank[file_of(ksq)];
423 b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
424 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
426 int tropism = popcount(b1) + popcount(b2);
428 // Main king safety evaluation
429 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
434 // Attacked squares defended at most once by our queen or king
435 weak = attackedBy[Them][ALL_PIECES]
437 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
439 // Analyse the safe enemy's checks which are possible on next move
440 safe = ~pos.pieces(Them);
441 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
443 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
444 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
446 // Enemy queen safe checks
447 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
448 kingDanger += QueenSafeCheck;
450 b1 &= attackedBy[Them][ROOK];
451 b2 &= attackedBy[Them][BISHOP];
453 // Enemy rooks checks
455 kingDanger += RookSafeCheck;
459 // Enemy bishops checks
461 kingDanger += BishopSafeCheck;
465 // Enemy knights checks
466 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
468 kingDanger += KnightSafeCheck;
472 // Unsafe or occupied checking squares will also be considered, as long as
473 // the square is in the attacker's mobility area.
474 unsafeChecks &= mobilityArea[Them];
476 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
477 + 69 * kingAttacksCount[Them]
478 + 185 * popcount(kingRing[Us] & weak)
479 + 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
481 - 873 * !pos.count<QUEEN>(Them)
482 - 6 * mg_value(score) / 8
485 // Transform the kingDanger units into a Score, and subtract it from the evaluation
488 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
489 kingDanger = std::max(0, kingDanger + mobilityDanger);
490 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
494 // Penalty when our king is on a pawnless flank
495 if (!(pos.pieces(PAWN) & kingFlank))
496 score -= PawnlessFlank;
498 // King tropism bonus, to anticipate slow motion attacks on our king
499 score -= CloseEnemies * tropism;
502 Trace::add(KING, Us, score);
508 // Evaluation::threats() assigns bonuses according to the types of the
509 // attacking and the attacked pieces.
510 template<Tracing T> template<Color Us>
511 Score Evaluation<T>::threats() const {
513 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
514 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
515 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
517 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
518 Score score = SCORE_ZERO;
521 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
523 // Squares strongly protected by the enemy, either because they defend the
524 // square with a pawn, or because they defend the square twice and we don't.
525 stronglyProtected = attackedBy[Them][PAWN]
526 | (attackedBy2[Them] & ~attackedBy2[Us]);
528 // Non-pawn enemies, strongly protected
529 defended = nonPawnEnemies & stronglyProtected;
531 // Enemies not strongly protected and under our attack
532 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
534 // Safe or protected squares
535 safe = ~attackedBy[Them][ALL_PIECES] | 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);
548 else if (pos.blockers_for_king(Them) & s)
549 score += ThreatByRank * (int)relative_rank(Them, s) / 2;
552 b = weak & attackedBy[Us][ROOK];
555 Square s = pop_lsb(&b);
556 score += ThreatByRook[type_of(pos.piece_on(s))];
557 if (type_of(pos.piece_on(s)) != PAWN)
558 score += ThreatByRank * (int)relative_rank(Them, s);
560 else if (pos.blockers_for_king(Them) & s)
561 score += ThreatByRank * (int)relative_rank(Them, s) / 2;
564 if (weak & attackedBy[Us][KING])
565 score += ThreatByKing;
567 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
569 b = weak & nonPawnEnemies & attackedBy[Them][ALL_PIECES];
570 score += Overload * popcount(b);
573 // Bonus for enemy unopposed weak pawns
574 if (pos.pieces(Us, ROOK, QUEEN))
575 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
577 // Find squares where our pawns can push on the next move
578 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
579 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
581 // Keep only the squares which are relatively safe
582 b &= ~attackedBy[Them][PAWN] & safe;
584 // Bonus for safe pawn threats on the next move
585 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
586 score += ThreatByPawnPush * popcount(b);
588 // Our safe or protected pawns
589 b = pos.pieces(Us, PAWN) & safe;
591 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
592 score += ThreatBySafePawn * popcount(b);
594 // Bonus for threats on the next moves against enemy queen
595 if (pos.count<QUEEN>(Them) == 1)
597 Square s = pos.square<QUEEN>(Them);
598 safe = mobilityArea[Us] & ~stronglyProtected;
600 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
602 score += KnightOnQueen * popcount(b & safe);
604 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
605 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
607 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
611 Trace::add(THREAT, Us, score);
616 // Evaluation::passed() evaluates the passed pawns and candidate passed
617 // pawns of the given color.
619 template<Tracing T> template<Color Us>
620 Score Evaluation<T>::passed() const {
622 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
623 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
625 auto king_proximity = [&](Color c, Square s) {
626 return std::min(distance(pos.square<KING>(c), s), 5);
629 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
630 Score score = SCORE_ZERO;
632 b = pe->passed_pawns(Us);
636 Square s = pop_lsb(&b);
638 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
640 int r = relative_rank(Us, s);
641 int w = PassedDanger[r];
643 Score bonus = PassedRank[r];
647 Square blockSq = s + Up;
649 // Adjust bonus based on the king's proximity
650 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
651 - king_proximity(Us, blockSq) * 2) * w);
653 // If blockSq is not the queening square then consider also a second push
655 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
657 // If the pawn is free to advance, then increase the bonus
658 if (pos.empty(blockSq))
660 // If there is a rook or queen attacking/defending the pawn from behind,
661 // consider all the squaresToQueen. Otherwise consider only the squares
662 // in the pawn's path attacked or occupied by the enemy.
663 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
665 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
667 if (!(pos.pieces(Us) & bb))
668 defendedSquares &= attackedBy[Us][ALL_PIECES];
670 if (!(pos.pieces(Them) & bb))
671 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
673 // If there aren't any enemy attacks, assign a big bonus. Otherwise
674 // assign a smaller bonus if the block square isn't attacked.
675 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
677 // If the path to the queen is fully defended, assign a big bonus.
678 // Otherwise assign a smaller bonus if the block square is defended.
679 if (defendedSquares == squaresToQueen)
682 else if (defendedSquares & blockSq)
685 bonus += make_score(k * w, k * w);
689 // Scale down bonus for candidate passers which need more than one
690 // pawn push to become passed, or have a pawn in front of them.
691 if ( !pos.pawn_passed(Us, s + Up)
692 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
695 score += bonus + PassedFile[file_of(s)];
699 Trace::add(PASSED, Us, score);
705 // Evaluation::space() computes the space evaluation for a given side. The
706 // space evaluation is a simple bonus based on the number of safe squares
707 // available for minor pieces on the central four files on ranks 2--4. Safe
708 // squares one, two or three squares behind a friendly pawn are counted
709 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
710 // improve play on game opening.
712 template<Tracing T> template<Color Us>
713 Score Evaluation<T>::space() const {
715 if (pos.non_pawn_material() < SpaceThreshold)
718 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
719 constexpr Bitboard SpaceMask =
720 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
721 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
723 // Find the available squares for our pieces inside the area defined by SpaceMask
724 Bitboard safe = SpaceMask
725 & ~pos.pieces(Us, PAWN)
726 & ~attackedBy[Them][PAWN];
728 // Find all squares which are at most three squares behind some friendly pawn
729 Bitboard behind = pos.pieces(Us, PAWN);
730 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
731 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
733 int bonus = popcount(safe) + popcount(behind & safe);
734 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
736 Score score = make_score(bonus * weight * weight / 16, 0);
739 Trace::add(SPACE, Us, score);
745 // Evaluation::initiative() computes the initiative correction value
746 // for the position. It is a second order bonus/malus based on the
747 // known attacking/defending status of the players.
750 Score Evaluation<T>::initiative(Value eg) const {
752 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
753 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
755 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
756 && (pos.pieces(PAWN) & KingSide);
758 // Compute the initiative bonus for the attacking side
759 int complexity = 8 * pe->pawn_asymmetry()
760 + 12 * pos.count<PAWN>()
762 + 16 * pawnsOnBothFlanks
763 + 48 * !pos.non_pawn_material()
766 // Now apply the bonus: note that we find the attacking side by extracting
767 // the sign of the endgame value, and that we carefully cap the bonus so
768 // that the endgame score will never change sign after the bonus.
769 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
772 Trace::add(INITIATIVE, make_score(0, v));
774 return make_score(0, v);
778 // Evaluation::scale_factor() computes the scale factor for the winning side
781 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
783 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
784 int sf = me->scale_factor(pos, strongSide);
786 // If scale is not already specific, scale down the endgame via general heuristics
787 if (sf == SCALE_FACTOR_NORMAL)
789 if ( pos.opposite_bishops()
790 && pos.non_pawn_material(WHITE) == BishopValueMg
791 && pos.non_pawn_material(BLACK) == BishopValueMg)
792 sf = 8 + 4 * pe->pawn_asymmetry();
794 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
798 return ScaleFactor(sf);
802 // Evaluation::value() is the main function of the class. It computes the various
803 // parts of the evaluation and returns the value of the position from the point
804 // of view of the side to move.
807 Value Evaluation<T>::value() {
809 assert(!pos.checkers());
811 // Probe the material hash table
812 me = Material::probe(pos);
814 // If we have a specialized evaluation function for the current material
815 // configuration, call it and return.
816 if (me->specialized_eval_exists())
817 return me->evaluate(pos);
819 // Initialize score by reading the incrementally updated scores included in
820 // the position object (material + piece square tables) and the material
821 // imbalance. Score is computed internally from the white point of view.
822 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
824 // Probe the pawn hash table
825 pe = Pawns::probe(pos);
826 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
828 // Early exit if score is high
829 Value v = (mg_value(score) + eg_value(score)) / 2;
830 if (abs(v) > LazyThreshold)
831 return pos.side_to_move() == WHITE ? v : -v;
833 // Main evaluation begins here
838 // Pieces should be evaluated first (populate attack tables)
839 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
840 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
841 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
842 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
844 score += mobility[WHITE] - mobility[BLACK];
846 score += king< WHITE>() - king< BLACK>()
847 + threats<WHITE>() - threats<BLACK>()
848 + passed< WHITE>() - passed< BLACK>()
849 + space< WHITE>() - space< BLACK>();
851 score += initiative(eg_value(score));
853 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
854 ScaleFactor sf = scale_factor(eg_value(score));
855 v = mg_value(score) * int(me->game_phase())
856 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
858 v /= int(PHASE_MIDGAME);
860 // In case of tracing add all remaining individual evaluation terms
863 Trace::add(MATERIAL, pos.psq_score());
864 Trace::add(IMBALANCE, me->imbalance());
865 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
866 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
867 Trace::add(TOTAL, score);
870 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
877 /// evaluate() is the evaluator for the outer world. It returns a static
878 /// evaluation of the position from the point of view of the side to move.
880 Value Eval::evaluate(const Position& pos) {
881 return Evaluation<NO_TRACE>(pos).value();
885 /// trace() is like evaluate(), but instead of returning a value, it returns
886 /// a string (suitable for outputting to stdout) that contains the detailed
887 /// descriptions and values of each evaluation term. Useful for debugging.
889 std::string Eval::trace(const Position& pos) {
891 std::memset(scores, 0, sizeof(scores));
893 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
895 Value v = Evaluation<TRACE>(pos).value();
897 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
899 std::stringstream ss;
900 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
901 << " Term | White | Black | Total \n"
902 << " | MG EG | MG EG | MG EG \n"
903 << " ------------+-------------+-------------+------------\n"
904 << " Material | " << Term(MATERIAL)
905 << " Imbalance | " << Term(IMBALANCE)
906 << " Initiative | " << Term(INITIATIVE)
907 << " Pawns | " << Term(PAWN)
908 << " Knights | " << Term(KNIGHT)
909 << " Bishops | " << Term(BISHOP)
910 << " Rooks | " << Term(ROOK)
911 << " Queens | " << Term(QUEEN)
912 << " Mobility | " << Term(MOBILITY)
913 << " King safety | " << Term(KING)
914 << " Threats | " << Term(THREAT)
915 << " Passed | " << Term(PASSED)
916 << " Space | " << Term(SPACE)
917 << " ------------+-------------+-------------+------------\n"
918 << " Total | " << Term(TOTAL);
920 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";