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(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( 52, 30);
162 constexpr Score HinderPassedPawn = S( 4, 0);
163 constexpr Score KingProtector = S( 6, 6);
164 constexpr Score KnightOnQueen = S( 21, 11);
165 constexpr Score LongDiagonalBishop = S( 22, 0);
166 constexpr Score MinorBehindPawn = S( 16, 0);
167 constexpr Score Overload = S( 16, 7);
168 constexpr Score PawnlessFlank = S( 20, 80);
169 constexpr Score RookOnPawn = S( 8, 24);
170 constexpr Score SliderOnQueen = S( 42, 21);
171 constexpr Score ThreatByKing = S( 23, 76);
172 constexpr Score ThreatByPawnPush = S( 45, 40);
173 constexpr Score ThreatByRank = S( 16, 3);
174 constexpr Score ThreatBySafePawn = S(173,102);
175 constexpr Score TrappedRook = S( 92, 0);
176 constexpr Score WeakQueen = S( 50, 10);
177 constexpr Score WeakUnopposedPawn = S( 5, 29);
181 // Evaluation class computes and stores attacks tables and other working data
186 Evaluation() = delete;
187 explicit Evaluation(const Position& p) : pos(p) {}
188 Evaluation& operator=(const Evaluation&) = delete;
192 template<Color Us> void initialize();
193 template<Color Us, PieceType Pt> Score pieces();
194 template<Color Us> Score king() const;
195 template<Color Us> Score threats() const;
196 template<Color Us> Score passed() const;
197 template<Color Us> Score space() const;
198 ScaleFactor scale_factor(Value eg) const;
199 Score initiative(Value eg) const;
204 Bitboard mobilityArea[COLOR_NB];
205 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
207 // attackedBy[color][piece type] is a bitboard representing all squares
208 // attacked by a given color and piece type. Special "piece types" which
209 // is also calculated is ALL_PIECES.
210 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
212 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
213 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
214 // pawn or squares attacked by 2 pawns are not explicitly added.
215 Bitboard attackedBy2[COLOR_NB];
217 // kingRing[color] are the squares adjacent to the king, plus (only for a
218 // king on its first rank) the squares two ranks in front. For instance,
219 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
220 // and h6. It is set to 0 when king safety evaluation is skipped.
221 Bitboard kingRing[COLOR_NB];
223 // kingAttackersCount[color] is the number of pieces of the given color
224 // which attack a square in the kingRing of the enemy king.
225 int kingAttackersCount[COLOR_NB];
227 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
228 // the given color which attack a square in the kingRing of the enemy king.
229 // The weights of the individual piece types are given by the elements in
230 // the KingAttackWeights array.
231 int kingAttackersWeight[COLOR_NB];
233 // kingAttacksCount[color] is the number of attacks by the given color to
234 // squares directly adjacent to the enemy king. Pieces which attack more
235 // than one square are counted multiple times. For instance, if there is
236 // a white knight on g5 and black's king is on g8, this white knight adds 2
237 // to kingAttacksCount[WHITE].
238 int kingAttacksCount[COLOR_NB];
242 // Evaluation::initialize() computes king and pawn attacks, and the king ring
243 // bitboard for a given color. This is done at the beginning of the evaluation.
244 template<Tracing T> template<Color Us>
245 void Evaluation<T>::initialize() {
247 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
248 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
249 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
250 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
252 // Find our pawns that are blocked or on the first two ranks
253 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
255 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
256 // are excluded from the mobility area.
257 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
259 // Initialise attackedBy bitboards for kings and pawns
260 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
261 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
262 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
263 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
265 // Init our king safety tables only if we are going to use them
266 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
268 kingRing[Us] = attackedBy[Us][KING];
269 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
270 kingRing[Us] |= shift<Up>(kingRing[Us]);
272 if (file_of(pos.square<KING>(Us)) == FILE_H)
273 kingRing[Us] |= shift<WEST>(kingRing[Us]);
275 else if (file_of(pos.square<KING>(Us)) == FILE_A)
276 kingRing[Us] |= shift<EAST>(kingRing[Us]);
278 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
279 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
282 kingRing[Us] = kingAttackersCount[Them] = 0;
286 // Evaluation::pieces() scores pieces of a given color and type
287 template<Tracing T> template<Color Us, PieceType Pt>
288 Score Evaluation<T>::pieces() {
290 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
291 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
292 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
293 : Rank5BB | Rank4BB | Rank3BB);
294 const Square* pl = pos.squares<Pt>(Us);
298 Score score = SCORE_ZERO;
300 attackedBy[Us][Pt] = 0;
302 while ((s = *pl++) != SQ_NONE)
304 // Find attacked squares, including x-ray attacks for bishops and rooks
305 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
306 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
307 : pos.attacks_from<Pt>(s);
309 if (pos.blockers_for_king(Us) & s)
310 b &= LineBB[pos.square<KING>(Us)][s];
312 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
313 attackedBy[Us][Pt] |= b;
314 attackedBy[Us][ALL_PIECES] |= b;
316 if (b & kingRing[Them])
318 kingAttackersCount[Us]++;
319 kingAttackersWeight[Us] += KingAttackWeights[Pt];
320 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
323 int mob = popcount(b & mobilityArea[Us]);
325 mobility[Us] += MobilityBonus[Pt - 2][mob];
327 if (Pt == BISHOP || Pt == KNIGHT)
329 // Bonus if piece is on an outpost square or can reach one
330 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
332 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
334 else if (bb &= b & ~pos.pieces(Us))
335 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
337 // Knight and Bishop bonus for being right behind a pawn
338 if (shift<Down>(pos.pieces(PAWN)) & s)
339 score += MinorBehindPawn;
341 // Penalty if the piece is far from the king
342 score -= KingProtector * distance(s, pos.square<KING>(Us));
346 // Penalty according to number of pawns on the same color square as the
347 // bishop, bigger when the center files are blocked with pawns.
348 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
350 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
351 * (1 + popcount(blocked & CenterFiles));
353 // Bonus for bishop on a long diagonal which can "see" both center squares
354 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
355 score += LongDiagonalBishop;
358 // An important Chess960 pattern: A cornered bishop blocked by a friendly
359 // pawn diagonally in front of it is a very serious problem, especially
360 // when that pawn is also blocked.
363 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
365 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
366 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
367 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
368 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
375 // Bonus for aligning rook with enemy pawns on the same rank/file
376 if (relative_rank(Us, s) >= RANK_5)
377 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
379 // Bonus for rook on an open or semi-open file
380 if (pe->semiopen_file(Us, file_of(s)))
381 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
383 // Penalty when trapped by the king, even more if the king cannot castle
386 File kf = file_of(pos.square<KING>(Us));
387 if ((kf < FILE_E) == (file_of(s) < kf))
388 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
394 // Penalty if any relative pin or discovered attack against the queen
395 Bitboard queenPinners;
396 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
401 Trace::add(Pt, Us, score);
407 // Evaluation::king() assigns bonuses and penalties to a king of a given color
408 template<Tracing T> template<Color Us>
409 Score Evaluation<T>::king() const {
411 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
412 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
413 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
415 const Square ksq = pos.square<KING>(Us);
416 Bitboard weak, b, b1, b2, safe, unsafeChecks;
418 // King shelter and enemy pawns storm
419 Score score = pe->king_safety<Us>(pos, ksq);
421 // Main king safety evaluation
422 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
427 // Attacked squares defended at most once by our queen or king
428 weak = attackedBy[Them][ALL_PIECES]
430 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
432 // Analyse the safe enemy's checks which are possible on next move
433 safe = ~pos.pieces(Them);
434 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
436 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
437 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
439 // Enemy queen safe checks
440 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
441 kingDanger += QueenSafeCheck;
443 b1 &= attackedBy[Them][ROOK];
444 b2 &= attackedBy[Them][BISHOP];
446 // Enemy rooks checks
448 kingDanger += RookSafeCheck;
452 // Enemy bishops checks
454 kingDanger += BishopSafeCheck;
458 // Enemy knights checks
459 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
461 kingDanger += KnightSafeCheck;
465 // Unsafe or occupied checking squares will also be considered, as long as
466 // the square is in the attacker's mobility area.
467 unsafeChecks &= mobilityArea[Them];
469 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
470 + 69 * kingAttacksCount[Them]
471 + 185 * popcount(kingRing[Us] & weak)
472 + 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
473 - 873 * !pos.count<QUEEN>(Them)
474 - 6 * mg_value(score) / 8
477 // Transform the kingDanger units into a Score, and subtract it from the evaluation
480 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
481 kingDanger = std::max(0, kingDanger + mobilityDanger);
482 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
486 Bitboard kf = KingFlank[file_of(ksq)];
488 // Penalty when our king is on a pawnless flank
489 if (!(pos.pieces(PAWN) & kf))
490 score -= PawnlessFlank;
492 // Find the squares that opponent attacks in our king flank, and the squares
493 // which are attacked twice in that flank but not defended by our pawns.
494 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
495 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
497 // King tropism, to anticipate slow motion attacks on our king
498 score -= CloseEnemies * (popcount(b1) + popcount(b2));
501 Trace::add(KING, Us, score);
507 // Evaluation::threats() assigns bonuses according to the types of the
508 // attacking and the attacked pieces.
509 template<Tracing T> template<Color Us>
510 Score Evaluation<T>::threats() const {
512 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
513 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
514 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
516 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
517 Score score = SCORE_ZERO;
520 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
522 // Squares strongly protected by the enemy, either because they defend the
523 // square with a pawn, or because they defend the square twice and we don't.
524 stronglyProtected = attackedBy[Them][PAWN]
525 | (attackedBy2[Them] & ~attackedBy2[Us]);
527 // Non-pawn enemies, strongly protected
528 defended = nonPawnEnemies & stronglyProtected;
530 // Enemies not strongly protected and under our attack
531 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
533 // Bonus according to the kind of attacking pieces
536 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
539 Square s = pop_lsb(&b);
540 score += ThreatByMinor[type_of(pos.piece_on(s))];
541 if (type_of(pos.piece_on(s)) != PAWN)
542 score += ThreatByRank * (int)relative_rank(Them, s);
545 b = weak & attackedBy[Us][ROOK];
548 Square s = pop_lsb(&b);
549 score += ThreatByRook[type_of(pos.piece_on(s))];
550 if (type_of(pos.piece_on(s)) != PAWN)
551 score += ThreatByRank * (int)relative_rank(Them, s);
554 // Bonus for king attacks on pawns or pieces which are not pawn-defended
555 if (weak & attackedBy[Us][KING])
556 score += ThreatByKing;
558 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
560 b = weak & nonPawnEnemies & attackedBy[Them][ALL_PIECES];
561 score += Overload * popcount(b);
564 // Bonus for enemy unopposed weak pawns
565 if (pos.pieces(Us, ROOK, QUEEN))
566 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
568 // Our safe or protected pawns
569 b = pos.pieces(Us, PAWN)
570 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
572 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
573 score += ThreatBySafePawn * popcount(safeThreats);
575 // Find squares where our pawns can push on the next move
576 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
577 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
579 // Keep only the squares which are not completely unsafe
580 b &= ~attackedBy[Them][PAWN]
581 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
583 // Bonus for safe pawn threats on the next move
584 b = pawn_attacks_bb<Us>(b)
586 & ~attackedBy[Us][PAWN];
588 score += ThreatByPawnPush * popcount(b);
590 // Bonus for threats on the next moves against enemy queen
591 if (pos.count<QUEEN>(Them) == 1)
593 Square s = pos.square<QUEEN>(Them);
594 safeThreats = mobilityArea[Us] & ~stronglyProtected;
596 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
598 score += KnightOnQueen * popcount(b & safeThreats);
600 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
601 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
603 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
607 Trace::add(THREAT, Us, score);
612 // Evaluation::passed() evaluates the passed pawns and candidate passed
613 // pawns of the given color.
615 template<Tracing T> template<Color Us>
616 Score Evaluation<T>::passed() const {
618 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
619 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
621 auto king_proximity = [&](Color c, Square s) {
622 return std::min(distance(pos.square<KING>(c), s), 5);
625 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
626 Score score = SCORE_ZERO;
628 b = pe->passed_pawns(Us);
632 Square s = pop_lsb(&b);
634 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
636 bb = forward_file_bb(Us, s) & pos.pieces(Them);
637 score -= HinderPassedPawn * popcount(bb);
639 int r = relative_rank(Us, s);
640 int w = PassedDanger[r];
642 Score bonus = PassedRank[r];
646 Square blockSq = s + Up;
648 // Adjust bonus based on the king's proximity
649 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
650 - king_proximity(Us, blockSq) * 2) * w);
652 // If blockSq is not the queening square then consider also a second push
654 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
656 // If the pawn is free to advance, then increase the bonus
657 if (pos.empty(blockSq))
659 // If there is a rook or queen attacking/defending the pawn from behind,
660 // consider all the squaresToQueen. Otherwise consider only the squares
661 // in the pawn's path attacked or occupied by the enemy.
662 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
664 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
666 if (!(pos.pieces(Us) & bb))
667 defendedSquares &= attackedBy[Us][ALL_PIECES];
669 if (!(pos.pieces(Them) & bb))
670 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
672 // If there aren't any enemy attacks, assign a big bonus. Otherwise
673 // assign a smaller bonus if the block square isn't attacked.
674 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
676 // If the path to the queen is fully defended, assign a big bonus.
677 // Otherwise assign a smaller bonus if the block square is defended.
678 if (defendedSquares == squaresToQueen)
681 else if (defendedSquares & blockSq)
684 bonus += make_score(k * w, k * w);
686 else if (pos.pieces(Us) & blockSq)
687 bonus += make_score(w + r * 2, w + r * 2);
690 // Scale down bonus for candidate passers which need more than one
691 // pawn push to become passed, or have a pawn in front of them.
692 if ( !pos.pawn_passed(Us, s + Up)
693 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
696 score += bonus + PassedFile[file_of(s)];
700 Trace::add(PASSED, Us, score);
706 // Evaluation::space() computes the space evaluation for a given side. The
707 // space evaluation is a simple bonus based on the number of safe squares
708 // available for minor pieces on the central four files on ranks 2--4. Safe
709 // squares one, two or three squares behind a friendly pawn are counted
710 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
711 // improve play on game opening.
713 template<Tracing T> template<Color Us>
714 Score Evaluation<T>::space() const {
716 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
717 constexpr Bitboard SpaceMask =
718 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
719 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
721 if (pos.non_pawn_material() < SpaceThreshold)
724 // Find the available squares for our pieces inside the area defined by SpaceMask
725 Bitboard safe = SpaceMask
726 & ~pos.pieces(Us, PAWN)
727 & ~attackedBy[Them][PAWN];
729 // Find all squares which are at most three squares behind some friendly pawn
730 Bitboard behind = pos.pieces(Us, PAWN);
731 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
732 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
734 int bonus = popcount(safe) + popcount(behind & safe);
735 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
737 Score score = make_score(bonus * weight * weight / 16, 0);
740 Trace::add(SPACE, Us, score);
746 // Evaluation::initiative() computes the initiative correction value
747 // for the position. It is a second order bonus/malus based on the
748 // known attacking/defending status of the players.
751 Score Evaluation<T>::initiative(Value eg) const {
753 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
754 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
756 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
757 && (pos.pieces(PAWN) & KingSide);
759 // Compute the initiative bonus for the attacking side
760 int complexity = 8 * pe->pawn_asymmetry()
761 + 12 * pos.count<PAWN>()
763 + 16 * pawnsOnBothFlanks
764 + 48 * !pos.non_pawn_material()
767 // Now apply the bonus: note that we find the attacking side by extracting
768 // the sign of the endgame value, and that we carefully cap the bonus so
769 // that the endgame score will never change sign after the bonus.
770 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
773 Trace::add(INITIATIVE, make_score(0, v));
775 return make_score(0, v);
779 // Evaluation::scale_factor() computes the scale factor for the winning side
782 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
784 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
785 int sf = me->scale_factor(pos, strongSide);
787 // If scale is not already specific, scale down the endgame via general heuristics
788 if (sf == SCALE_FACTOR_NORMAL)
790 if ( pos.opposite_bishops()
791 && pos.non_pawn_material(WHITE) == BishopValueMg
792 && pos.non_pawn_material(BLACK) == BishopValueMg)
795 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";