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(-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 // 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, 29);
169 constexpr Score SliderOnQueen = S( 42, 21);
170 constexpr Score ThreatByKing = S( 22, 78);
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( 96, 5);
175 constexpr Score WeakQueen = S( 50, 10);
176 constexpr Score WeakUnopposedPawn = S( 15, 19);
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 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
481 - 873 * !pos.count<QUEEN>(Them)
482 - 6 * mg_value(score) / 8
483 + mg_value(mobility[Them] - mobility[Us])
486 // Transform the kingDanger units into a Score, and subtract it from the evaluation
488 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
491 // Penalty when our king is on a pawnless flank
492 if (!(pos.pieces(PAWN) & kingFlank))
493 score -= PawnlessFlank;
495 // King tropism bonus, to anticipate slow motion attacks on our king
496 score -= CloseEnemies * tropism;
499 Trace::add(KING, Us, score);
505 // Evaluation::threats() assigns bonuses according to the types of the
506 // attacking and the attacked pieces.
507 template<Tracing T> template<Color Us>
508 Score Evaluation<T>::threats() const {
510 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
511 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
512 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
514 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
515 Score score = SCORE_ZERO;
518 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
520 // Squares strongly protected by the enemy, either because they defend the
521 // square with a pawn, or because they defend the square twice and we don't.
522 stronglyProtected = attackedBy[Them][PAWN]
523 | (attackedBy2[Them] & ~attackedBy2[Us]);
525 // Non-pawn enemies, strongly protected
526 defended = nonPawnEnemies & stronglyProtected;
528 // Enemies not strongly protected and under our attack
529 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
531 // Safe or protected squares
532 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
534 // Bonus according to the kind of attacking pieces
537 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
540 Square s = pop_lsb(&b);
541 score += ThreatByMinor[type_of(pos.piece_on(s))];
542 if (type_of(pos.piece_on(s)) != PAWN)
543 score += ThreatByRank * (int)relative_rank(Them, s);
546 b = weak & attackedBy[Us][ROOK];
549 Square s = pop_lsb(&b);
550 score += ThreatByRook[type_of(pos.piece_on(s))];
551 if (type_of(pos.piece_on(s)) != PAWN)
552 score += ThreatByRank * (int)relative_rank(Them, s);
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 // Find squares where our pawns can push on the next move
569 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
570 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
572 // Keep only the squares which are relatively safe
573 b &= ~attackedBy[Them][PAWN] & safe;
575 // Bonus for safe pawn threats on the next move
576 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
577 score += ThreatByPawnPush * popcount(b);
579 // Our safe or protected pawns
580 b = pos.pieces(Us, PAWN) & safe;
582 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
583 score += ThreatBySafePawn * popcount(b);
585 // Bonus for threats on the next moves against enemy queen
586 if (pos.count<QUEEN>(Them) == 1)
588 Square s = pos.square<QUEEN>(Them);
589 safe = mobilityArea[Us] & ~stronglyProtected;
591 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
593 score += KnightOnQueen * popcount(b & safe);
595 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
596 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
598 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
602 Trace::add(THREAT, Us, score);
607 // Evaluation::passed() evaluates the passed pawns and candidate passed
608 // pawns of the given color.
610 template<Tracing T> template<Color Us>
611 Score Evaluation<T>::passed() const {
613 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
614 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
616 auto king_proximity = [&](Color c, Square s) {
617 return std::min(distance(pos.square<KING>(c), s), 5);
620 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
621 Score score = SCORE_ZERO;
623 b = pe->passed_pawns(Us);
627 Square s = pop_lsb(&b);
629 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
631 int r = relative_rank(Us, s);
632 int w = PassedDanger[r];
634 Score bonus = PassedRank[r];
638 Square blockSq = s + Up;
640 // Adjust bonus based on the king's proximity
641 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
642 - king_proximity(Us, blockSq) * 2) * w);
644 // If blockSq is not the queening square then consider also a second push
646 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
648 // If the pawn is free to advance, then increase the bonus
649 if (pos.empty(blockSq))
651 // If there is a rook or queen attacking/defending the pawn from behind,
652 // consider all the squaresToQueen. Otherwise consider only the squares
653 // in the pawn's path attacked or occupied by the enemy.
654 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
656 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
658 if (!(pos.pieces(Us) & bb))
659 defendedSquares &= attackedBy[Us][ALL_PIECES];
661 if (!(pos.pieces(Them) & bb))
662 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
664 // If there aren't any enemy attacks, assign a big bonus. Otherwise
665 // assign a smaller bonus if the block square isn't attacked.
666 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
668 // If the path to the queen is fully defended, assign a big bonus.
669 // Otherwise assign a smaller bonus if the block square is defended.
670 if (defendedSquares == squaresToQueen)
673 else if (defendedSquares & blockSq)
676 bonus += make_score(k * w, k * w);
680 // Scale down bonus for candidate passers which need more than one
681 // pawn push to become passed, or have a pawn in front of them.
682 if ( !pos.pawn_passed(Us, s + Up)
683 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
686 score += bonus + PassedFile[file_of(s)];
690 Trace::add(PASSED, Us, score);
696 // Evaluation::space() computes the space evaluation for a given side. The
697 // space evaluation is a simple bonus based on the number of safe squares
698 // available for minor pieces on the central four files on ranks 2--4. Safe
699 // squares one, two or three squares behind a friendly pawn are counted
700 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
701 // improve play on game opening.
703 template<Tracing T> template<Color Us>
704 Score Evaluation<T>::space() const {
706 if (pos.non_pawn_material() < SpaceThreshold)
709 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
710 constexpr Bitboard SpaceMask =
711 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
712 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
714 // Find the available squares for our pieces inside the area defined by SpaceMask
715 Bitboard safe = SpaceMask
716 & ~pos.pieces(Us, PAWN)
717 & ~attackedBy[Them][PAWN];
719 // Find all squares which are at most three squares behind some friendly pawn
720 Bitboard behind = pos.pieces(Us, PAWN);
721 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
722 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
724 int bonus = popcount(safe) + popcount(behind & safe);
725 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
727 Score score = make_score(bonus * weight * weight / 16, 0);
730 Trace::add(SPACE, Us, score);
736 // Evaluation::initiative() computes the initiative correction value
737 // for the position. It is a second order bonus/malus based on the
738 // known attacking/defending status of the players.
741 Score Evaluation<T>::initiative(Value eg) const {
743 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
744 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
746 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
747 && (pos.pieces(PAWN) & KingSide);
749 // Compute the initiative bonus for the attacking side
750 int complexity = 8 * pe->pawn_asymmetry()
751 + 12 * pos.count<PAWN>()
753 + 16 * pawnsOnBothFlanks
754 + 48 * !pos.non_pawn_material()
757 // Now apply the bonus: note that we find the attacking side by extracting
758 // the sign of the endgame value, and that we carefully cap the bonus so
759 // that the endgame score will never change sign after the bonus.
760 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
763 Trace::add(INITIATIVE, make_score(0, v));
765 return make_score(0, v);
769 // Evaluation::scale_factor() computes the scale factor for the winning side
772 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
774 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
775 int sf = me->scale_factor(pos, strongSide);
777 // If scale is not already specific, scale down the endgame via general heuristics
778 if (sf == SCALE_FACTOR_NORMAL)
780 if ( pos.opposite_bishops()
781 && pos.non_pawn_material(WHITE) == BishopValueMg
782 && pos.non_pawn_material(BLACK) == BishopValueMg)
783 sf = 8 + 4 * pe->pawn_asymmetry();
785 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
789 return ScaleFactor(sf);
793 // Evaluation::value() is the main function of the class. It computes the various
794 // parts of the evaluation and returns the value of the position from the point
795 // of view of the side to move.
798 Value Evaluation<T>::value() {
800 assert(!pos.checkers());
802 // Probe the material hash table
803 me = Material::probe(pos);
805 // If we have a specialized evaluation function for the current material
806 // configuration, call it and return.
807 if (me->specialized_eval_exists())
808 return me->evaluate(pos);
810 // Initialize score by reading the incrementally updated scores included in
811 // the position object (material + piece square tables) and the material
812 // imbalance. Score is computed internally from the white point of view.
813 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
815 // Probe the pawn hash table
816 pe = Pawns::probe(pos);
817 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
819 // Early exit if score is high
820 Value v = (mg_value(score) + eg_value(score)) / 2;
821 if (abs(v) > LazyThreshold)
822 return pos.side_to_move() == WHITE ? v : -v;
824 // Main evaluation begins here
829 // Pieces should be evaluated first (populate attack tables)
830 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
831 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
832 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
833 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
835 score += mobility[WHITE] - mobility[BLACK];
837 score += king< WHITE>() - king< BLACK>()
838 + threats<WHITE>() - threats<BLACK>()
839 + passed< WHITE>() - passed< BLACK>()
840 + space< WHITE>() - space< BLACK>();
842 score += initiative(eg_value(score));
844 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
845 ScaleFactor sf = scale_factor(eg_value(score));
846 v = mg_value(score) * int(me->game_phase())
847 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
849 v /= int(PHASE_MIDGAME);
851 // In case of tracing add all remaining individual evaluation terms
854 Trace::add(MATERIAL, pos.psq_score());
855 Trace::add(IMBALANCE, me->imbalance());
856 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
857 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
858 Trace::add(TOTAL, score);
861 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
868 /// evaluate() is the evaluator for the outer world. It returns a static
869 /// evaluation of the position from the point of view of the side to move.
871 Value Eval::evaluate(const Position& pos) {
872 return Evaluation<NO_TRACE>(pos).value();
876 /// trace() is like evaluate(), but instead of returning a value, it returns
877 /// a string (suitable for outputting to stdout) that contains the detailed
878 /// descriptions and values of each evaluation term. Useful for debugging.
880 std::string Eval::trace(const Position& pos) {
882 std::memset(scores, 0, sizeof(scores));
884 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
886 Value v = Evaluation<TRACE>(pos).value();
888 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
890 std::stringstream ss;
891 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
892 << " Term | White | Black | Total \n"
893 << " | MG EG | MG EG | MG EG \n"
894 << " ------------+-------------+-------------+------------\n"
895 << " Material | " << Term(MATERIAL)
896 << " Imbalance | " << Term(IMBALANCE)
897 << " Initiative | " << Term(INITIATIVE)
898 << " Pawns | " << Term(PAWN)
899 << " Knights | " << Term(KNIGHT)
900 << " Bishops | " << Term(BISHOP)
901 << " Rooks | " << Term(ROOK)
902 << " Queens | " << Term(QUEEN)
903 << " Mobility | " << Term(MOBILITY)
904 << " King safety | " << Term(KING)
905 << " Threats | " << Term(THREAT)
906 << " Passed | " << Term(PASSED)
907 << " Space | " << Term(SPACE)
908 << " ------------+-------------+-------------+------------\n"
909 << " Total | " << Term(TOTAL);
911 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";