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, 8);
156 constexpr Score CloseEnemies = S( 7, 0);
157 constexpr Score CorneredBishop = S( 50, 50);
158 constexpr Score Hanging = S( 62, 34);
159 constexpr Score KingProtector = S( 6, 7);
160 constexpr Score KnightOnQueen = S( 20, 12);
161 constexpr Score LongDiagonalBishop = S( 44, 0);
162 constexpr Score MinorBehindPawn = S( 16, 0);
163 constexpr Score Overload = S( 12, 6);
164 constexpr Score PawnlessFlank = S( 18, 94);
165 constexpr Score RestrictedPiece = S( 7, 6);
166 constexpr Score RookOnPawn = S( 10, 28);
167 constexpr Score SliderOnQueen = S( 49, 21);
168 constexpr Score ThreatByKing = S( 21, 84);
169 constexpr Score ThreatByPawnPush = S( 48, 42);
170 constexpr Score ThreatByRank = S( 14, 3);
171 constexpr Score ThreatBySafePawn = S(169, 99);
172 constexpr Score TrappedRook = S( 98, 5);
173 constexpr Score WeakQueen = S( 51, 10);
174 constexpr Score WeakUnopposedPawn = S( 14, 20);
178 // Evaluation class computes and stores attacks tables and other working data
183 Evaluation() = delete;
184 explicit Evaluation(const Position& p) : pos(p) {}
185 Evaluation& operator=(const Evaluation&) = delete;
189 template<Color Us> void initialize();
190 template<Color Us, PieceType Pt> Score pieces();
191 template<Color Us> Score king() const;
192 template<Color Us> Score threats() const;
193 template<Color Us> Score passed() const;
194 template<Color Us> Score space() const;
195 ScaleFactor scale_factor(Value eg) const;
196 Score initiative(Value eg) const;
201 Bitboard mobilityArea[COLOR_NB];
202 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
204 // attackedBy[color][piece type] is a bitboard representing all squares
205 // attacked by a given color and piece type. Special "piece types" which
206 // is also calculated is ALL_PIECES.
207 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
209 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
210 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
211 // pawn or squares attacked by 2 pawns are not explicitly added.
212 Bitboard attackedBy2[COLOR_NB];
214 // kingRing[color] are the squares adjacent to the king, plus (only for a
215 // king on its first rank) the squares two ranks in front. For instance,
216 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
217 // and h6. It is set to 0 when king safety evaluation is skipped.
218 Bitboard kingRing[COLOR_NB];
220 // kingAttackersCount[color] is the number of pieces of the given color
221 // which attack a square in the kingRing of the enemy king.
222 int kingAttackersCount[COLOR_NB];
224 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
225 // the given color which attack a square in the kingRing of the enemy king.
226 // The weights of the individual piece types are given by the elements in
227 // the KingAttackWeights array.
228 int kingAttackersWeight[COLOR_NB];
230 // kingAttacksCount[color] is the number of attacks by the given color to
231 // squares directly adjacent to the enemy king. Pieces which attack more
232 // than one square are counted multiple times. For instance, if there is
233 // a white knight on g5 and black's king is on g8, this white knight adds 2
234 // to kingAttacksCount[WHITE].
235 int kingAttacksCount[COLOR_NB];
239 // Evaluation::initialize() computes king and pawn attacks, and the king ring
240 // bitboard for a given color. This is done at the beginning of the evaluation.
241 template<Tracing T> template<Color Us>
242 void Evaluation<T>::initialize() {
244 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
245 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
246 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
247 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
249 // Find our pawns that are blocked or on the first two ranks
250 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
252 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
253 // are excluded from the mobility area.
254 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
256 // Initialise attackedBy bitboards for kings and pawns
257 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
258 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
259 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
260 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
262 kingRing[Us] = kingAttackersCount[Them] = 0;
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;
283 // Evaluation::pieces() scores pieces of a given color and type
284 template<Tracing T> template<Color Us, PieceType Pt>
285 Score Evaluation<T>::pieces() {
287 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
288 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
289 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
290 : Rank5BB | Rank4BB | Rank3BB);
291 const Square* pl = pos.squares<Pt>(Us);
295 Score score = SCORE_ZERO;
297 attackedBy[Us][Pt] = 0;
299 while ((s = *pl++) != SQ_NONE)
301 // Find attacked squares, including x-ray attacks for bishops and rooks
302 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
303 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
304 : pos.attacks_from<Pt>(s);
306 if (pos.blockers_for_king(Us) & s)
307 b &= LineBB[pos.square<KING>(Us)][s];
309 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
310 attackedBy[Us][Pt] |= b;
311 attackedBy[Us][ALL_PIECES] |= b;
313 if (b & kingRing[Them])
315 kingAttackersCount[Us]++;
316 kingAttackersWeight[Us] += KingAttackWeights[Pt];
317 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
320 int mob = popcount(b & mobilityArea[Us]);
322 mobility[Us] += MobilityBonus[Pt - 2][mob];
324 if (Pt == BISHOP || Pt == KNIGHT)
326 // Bonus if piece is on an outpost square or can reach one
327 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
329 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
331 else if (bb &= b & ~pos.pieces(Us))
332 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
334 // Knight and Bishop bonus for being right behind a pawn
335 if (shift<Down>(pos.pieces(PAWN)) & s)
336 score += MinorBehindPawn;
338 // Penalty if the piece is far from the king
339 score -= KingProtector * distance(s, pos.square<KING>(Us));
343 // Penalty according to number of pawns on the same color square as the
344 // bishop, bigger when the center files are blocked with pawns.
345 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
347 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
348 * (1 + popcount(blocked & CenterFiles));
350 // Bonus for bishop on a long diagonal which can "see" both center squares
351 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
352 score += LongDiagonalBishop;
355 // An important Chess960 pattern: A cornered bishop blocked by a friendly
356 // pawn diagonally in front of it is a very serious problem, especially
357 // when that pawn is also blocked.
360 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
362 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
363 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
364 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
365 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
372 // Bonus for aligning rook with enemy pawns on the same rank/file
373 if (relative_rank(Us, s) >= RANK_5)
374 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
376 // Bonus for rook on an open or semi-open file
377 if (pe->semiopen_file(Us, file_of(s)))
378 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
380 // Penalty when trapped by the king, even more if the king cannot castle
383 File kf = file_of(pos.square<KING>(Us));
384 if ((kf < FILE_E) == (file_of(s) < kf))
385 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
391 // Penalty if any relative pin or discovered attack against the queen
392 Bitboard queenPinners;
393 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
398 Trace::add(Pt, Us, score);
404 // Evaluation::king() assigns bonuses and penalties to a king of a given color
405 template<Tracing T> template<Color Us>
406 Score Evaluation<T>::king() const {
408 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
409 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
410 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
412 const Square ksq = pos.square<KING>(Us);
413 Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
415 // King shelter and enemy pawns storm
416 Score score = pe->king_safety<Us>(pos);
418 // Find the squares that opponent attacks in our king flank, and the squares
419 // which are attacked twice in that flank.
420 kingFlank = KingFlank[file_of(ksq)];
421 b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
422 b2 = b1 & attackedBy2[Them];
424 int tropism = popcount(b1) + popcount(b2);
426 // Main king safety evaluation
427 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
432 // Attacked squares defended at most once by our queen or king
433 weak = attackedBy[Them][ALL_PIECES]
435 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
437 // Analyse the safe enemy's checks which are possible on next move
438 safe = ~pos.pieces(Them);
439 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
441 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
442 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
444 // Enemy queen safe checks
445 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
446 kingDanger += QueenSafeCheck;
448 b1 &= attackedBy[Them][ROOK];
449 b2 &= attackedBy[Them][BISHOP];
451 // Enemy rooks checks
453 kingDanger += RookSafeCheck;
457 // Enemy bishops checks
459 kingDanger += BishopSafeCheck;
463 // Enemy knights checks
464 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
466 kingDanger += KnightSafeCheck;
470 // Unsafe or occupied checking squares will also be considered, as long as
471 // the square is in the attacker's mobility area.
472 unsafeChecks &= mobilityArea[Them];
474 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
475 + 69 * kingAttacksCount[Them]
476 + 185 * popcount(kingRing[Us] & weak)
477 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
478 + tropism * tropism / 4
479 - 873 * !pos.count<QUEEN>(Them)
480 - 6 * mg_value(score) / 8
481 + mg_value(mobility[Them] - mobility[Us])
484 // Transform the kingDanger units into a Score, and subtract it from the evaluation
486 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
489 // Penalty when our king is on a pawnless flank
490 if (!(pos.pieces(PAWN) & kingFlank))
491 score -= PawnlessFlank;
493 // King tropism bonus, to anticipate slow motion attacks on our king
494 score -= CloseEnemies * tropism;
497 Trace::add(KING, Us, score);
503 // Evaluation::threats() assigns bonuses according to the types of the
504 // attacking and the attacked pieces.
505 template<Tracing T> template<Color Us>
506 Score Evaluation<T>::threats() const {
508 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
509 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
510 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
512 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe, restricted;
513 Score score = SCORE_ZERO;
516 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
518 // Squares strongly protected by the enemy, either because they defend the
519 // square with a pawn, or because they defend the square twice and we don't.
520 stronglyProtected = attackedBy[Them][PAWN]
521 | (attackedBy2[Them] & ~attackedBy2[Us]);
523 // Non-pawn enemies, strongly protected
524 defended = nonPawnEnemies & stronglyProtected;
526 // Enemies not strongly protected and under our attack
527 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
529 // Safe or protected squares
530 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
532 // Bonus according to the kind of attacking pieces
535 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
538 Square s = pop_lsb(&b);
539 score += ThreatByMinor[type_of(pos.piece_on(s))];
540 if (type_of(pos.piece_on(s)) != PAWN)
541 score += ThreatByRank * (int)relative_rank(Them, s);
544 b = weak & attackedBy[Us][ROOK];
547 Square s = pop_lsb(&b);
548 score += ThreatByRook[type_of(pos.piece_on(s))];
549 if (type_of(pos.piece_on(s)) != PAWN)
550 score += ThreatByRank * (int)relative_rank(Them, s);
553 if (weak & attackedBy[Us][KING])
554 score += ThreatByKing;
556 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
558 b = weak & nonPawnEnemies & attackedBy[Them][ALL_PIECES];
559 score += Overload * popcount(b);
562 // Bonus for restricting their piece moves
563 restricted = attackedBy[Them][ALL_PIECES]
564 & ~attackedBy[Them][PAWN]
566 & attackedBy[Us][ALL_PIECES];
567 score += RestrictedPiece * popcount(restricted);
569 // Bonus for enemy unopposed weak pawns
570 if (pos.pieces(Us, ROOK, QUEEN))
571 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
573 // Find squares where our pawns can push on the next move
574 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
575 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
577 // Keep only the squares which are relatively safe
578 b &= ~attackedBy[Them][PAWN] & safe;
580 // Bonus for safe pawn threats on the next move
581 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
582 score += ThreatByPawnPush * popcount(b);
584 // Our safe or protected pawns
585 b = pos.pieces(Us, PAWN) & safe;
587 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
588 score += ThreatBySafePawn * 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 safe = mobilityArea[Us] & ~stronglyProtected;
596 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
598 score += KnightOnQueen * popcount(b & safe);
600 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
601 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
603 score += SliderOnQueen * popcount(b & safe & 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 int r = relative_rank(Us, s);
638 Score bonus = PassedRank[r];
642 int w = (r-2) * (r-2) + 2;
643 Square blockSq = s + Up;
645 // Adjust bonus based on the king's proximity
646 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
647 - king_proximity(Us, blockSq) * 2) * w);
649 // If blockSq is not the queening square then consider also a second push
651 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
653 // If the pawn is free to advance, then increase the bonus
654 if (pos.empty(blockSq))
656 // If there is a rook or queen attacking/defending the pawn from behind,
657 // consider all the squaresToQueen. Otherwise consider only the squares
658 // in the pawn's path attacked or occupied by the enemy.
659 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
661 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
663 if (!(pos.pieces(Us) & bb))
664 defendedSquares &= attackedBy[Us][ALL_PIECES];
666 if (!(pos.pieces(Them) & bb))
667 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
669 // If there aren't any enemy attacks, assign a big bonus. Otherwise
670 // assign a smaller bonus if the block square isn't attacked.
671 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
673 // If the path to the queen is fully defended, assign a big bonus.
674 // Otherwise assign a smaller bonus if the block square is defended.
675 if (defendedSquares == squaresToQueen)
678 else if (defendedSquares & blockSq)
681 bonus += make_score(k * w, k * w);
685 // Scale down bonus for candidate passers which need more than one
686 // pawn push to become passed, or have a pawn in front of them.
687 if ( !pos.pawn_passed(Us, s + Up)
688 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
691 score += bonus + PassedFile[file_of(s)];
695 Trace::add(PASSED, Us, score);
701 // Evaluation::space() computes the space evaluation for a given side. The
702 // space evaluation is a simple bonus based on the number of safe squares
703 // available for minor pieces on the central four files on ranks 2--4. Safe
704 // squares one, two or three squares behind a friendly pawn are counted
705 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
706 // improve play on game opening.
708 template<Tracing T> template<Color Us>
709 Score Evaluation<T>::space() const {
711 if (pos.non_pawn_material() < SpaceThreshold)
714 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
715 constexpr Bitboard SpaceMask =
716 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
717 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
719 // Find the available squares for our pieces inside the area defined by SpaceMask
720 Bitboard safe = SpaceMask
721 & ~pos.pieces(Us, PAWN)
722 & ~attackedBy[Them][PAWN];
724 // Find all squares which are at most three squares behind some friendly pawn
725 Bitboard behind = pos.pieces(Us, PAWN);
726 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
727 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
729 int bonus = popcount(safe) + popcount(behind & safe);
730 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
732 Score score = make_score(bonus * weight * weight / 16, 0);
735 Trace::add(SPACE, Us, score);
741 // Evaluation::initiative() computes the initiative correction value
742 // for the position. It is a second order bonus/malus based on the
743 // known attacking/defending status of the players.
746 Score Evaluation<T>::initiative(Value eg) const {
748 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
749 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
751 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
752 && (pos.pieces(PAWN) & KingSide);
754 // Compute the initiative bonus for the attacking side
755 int complexity = 8 * pe->pawn_asymmetry()
756 + 12 * pos.count<PAWN>()
758 + 16 * pawnsOnBothFlanks
759 + 48 * !pos.non_pawn_material()
762 // Now apply the bonus: note that we find the attacking side by extracting
763 // the sign of the endgame value, and that we carefully cap the bonus so
764 // that the endgame score will never change sign after the bonus.
765 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
768 Trace::add(INITIATIVE, make_score(0, v));
770 return make_score(0, v);
774 // Evaluation::scale_factor() computes the scale factor for the winning side
777 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
779 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
780 int sf = me->scale_factor(pos, strongSide);
782 // If scale is not already specific, scale down the endgame via general heuristics
783 if (sf == SCALE_FACTOR_NORMAL)
785 if ( pos.opposite_bishops()
786 && pos.non_pawn_material(WHITE) == BishopValueMg
787 && pos.non_pawn_material(BLACK) == BishopValueMg)
788 sf = 8 + 4 * pe->pawn_asymmetry();
790 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
794 return ScaleFactor(sf);
798 // Evaluation::value() is the main function of the class. It computes the various
799 // parts of the evaluation and returns the value of the position from the point
800 // of view of the side to move.
803 Value Evaluation<T>::value() {
805 assert(!pos.checkers());
807 // Probe the material hash table
808 me = Material::probe(pos);
810 // If we have a specialized evaluation function for the current material
811 // configuration, call it and return.
812 if (me->specialized_eval_exists())
813 return me->evaluate(pos);
815 // Initialize score by reading the incrementally updated scores included in
816 // the position object (material + piece square tables) and the material
817 // imbalance. Score is computed internally from the white point of view.
818 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
820 // Probe the pawn hash table
821 pe = Pawns::probe(pos);
822 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
824 // Early exit if score is high
825 Value v = (mg_value(score) + eg_value(score)) / 2;
826 if (abs(v) > LazyThreshold)
827 return pos.side_to_move() == WHITE ? v : -v;
829 // Main evaluation begins here
834 // Pieces should be evaluated first (populate attack tables)
835 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
836 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
837 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
838 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
840 score += mobility[WHITE] - mobility[BLACK];
842 score += king< WHITE>() - king< BLACK>()
843 + threats<WHITE>() - threats<BLACK>()
844 + passed< WHITE>() - passed< BLACK>()
845 + space< WHITE>() - space< BLACK>();
847 score += initiative(eg_value(score));
849 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
850 ScaleFactor sf = scale_factor(eg_value(score));
851 v = mg_value(score) * int(me->game_phase())
852 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
854 v /= int(PHASE_MIDGAME);
856 // In case of tracing add all remaining individual evaluation terms
859 Trace::add(MATERIAL, pos.psq_score());
860 Trace::add(IMBALANCE, me->imbalance());
861 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
862 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
863 Trace::add(TOTAL, score);
866 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
873 /// evaluate() is the evaluator for the outer world. It returns a static
874 /// evaluation of the position from the point of view of the side to move.
876 Value Eval::evaluate(const Position& pos) {
877 return Evaluation<NO_TRACE>(pos).value();
881 /// trace() is like evaluate(), but instead of returning a value, it returns
882 /// a string (suitable for outputting to stdout) that contains the detailed
883 /// descriptions and values of each evaluation term. Useful for debugging.
885 std::string Eval::trace(const Position& pos) {
887 std::memset(scores, 0, sizeof(scores));
889 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
891 Value v = Evaluation<TRACE>(pos).value();
893 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
895 std::stringstream ss;
896 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
897 << " Term | White | Black | Total \n"
898 << " | MG EG | MG EG | MG EG \n"
899 << " ------------+-------------+-------------+------------\n"
900 << " Material | " << Term(MATERIAL)
901 << " Imbalance | " << Term(IMBALANCE)
902 << " Initiative | " << Term(INITIATIVE)
903 << " Pawns | " << Term(PAWN)
904 << " Knights | " << Term(KNIGHT)
905 << " Bishops | " << Term(BISHOP)
906 << " Rooks | " << Term(ROOK)
907 << " Queens | " << Term(QUEEN)
908 << " Mobility | " << Term(MOBILITY)
909 << " King safety | " << Term(KING)
910 << " Threats | " << Term(THREAT)
911 << " Passed | " << Term(PASSED)
912 << " Space | " << Term(SPACE)
913 << " ------------+-------------+-------------+------------\n"
914 << " Total | " << Term(TOTAL);
916 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";