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 // ThreatByKing[on one/on many] contains bonuses for king attacks on
144 // pawns or pieces which are not pawn-defended.
145 constexpr Score ThreatByKing[] = { S(30, 62), S(-9, 160) };
147 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
148 constexpr Score PassedRank[RANK_NB] = {
149 S(0, 0), S(4, 17), S(7, 20), S(14, 36), S(42, 62), S(165, 171), S(279, 252)
152 // PassedFile[File] contains a bonus according to the file of a passed pawn
153 constexpr Score PassedFile[FILE_NB] = {
154 S( 11, 14), S( 0, -5), S(-2, -8), S(-25,-13),
155 S(-25,-13), S(-2, -8), S( 0, -5), S( 11, 14)
158 // PassedDanger[Rank] contains a term to weight the passed score
159 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 2, 7, 12, 19 };
161 // KingProtector[PieceType-2] contains a penalty according to distance from king
162 constexpr Score KingProtector[] = { S(4, 6), S(6, 3), S(1, 0), S(0, -2) };
164 // Assorted bonuses and penalties
165 constexpr Score BishopPawns = S( 3, 5);
166 constexpr Score CloseEnemies = S( 8, 0);
167 constexpr Score Connectivity = S( 3, 1);
168 constexpr Score CorneredBishop = S( 50, 50);
169 constexpr Score Hanging = S( 52, 30);
170 constexpr Score HinderPassedPawn = S( 5, -1);
171 constexpr Score KnightOnQueen = S( 21, 11);
172 constexpr Score LongDiagonalBishop = S( 22, 0);
173 constexpr Score MinorBehindPawn = S( 16, 0);
174 constexpr Score Overload = S( 10, 5);
175 constexpr Score PawnlessFlank = S( 20, 80);
176 constexpr Score RookOnPawn = S( 8, 24);
177 constexpr Score SliderOnQueen = S( 42, 21);
178 constexpr Score ThreatByPawnPush = S( 49, 30);
179 constexpr Score ThreatByRank = S( 16, 3);
180 constexpr Score ThreatBySafePawn = S(165,133);
181 constexpr Score TrappedRook = S( 92, 0);
182 constexpr Score WeakQueen = S( 50, 10);
183 constexpr Score WeakUnopposedPawn = S( 5, 26);
187 // Evaluation class computes and stores attacks tables and other working data
192 Evaluation() = delete;
193 explicit Evaluation(const Position& p) : pos(p) {}
194 Evaluation& operator=(const Evaluation&) = delete;
198 template<Color Us> void initialize();
199 template<Color Us, PieceType Pt> Score pieces();
200 template<Color Us> Score king() const;
201 template<Color Us> Score threats() const;
202 template<Color Us> Score passed() const;
203 template<Color Us> Score space() const;
204 ScaleFactor scale_factor(Value eg) const;
205 Score initiative(Value eg) const;
210 Bitboard mobilityArea[COLOR_NB];
211 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
213 // attackedBy[color][piece type] is a bitboard representing all squares
214 // attacked by a given color and piece type. Special "piece types" which
215 // is also calculated is ALL_PIECES.
216 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
218 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
219 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
220 // pawn or squares attacked by 2 pawns are not explicitly added.
221 Bitboard attackedBy2[COLOR_NB];
223 // kingRing[color] are the squares adjacent to the king, plus (only for a
224 // king on its first rank) the squares two ranks in front. For instance,
225 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
226 // and h6. It is set to 0 when king safety evaluation is skipped.
227 Bitboard kingRing[COLOR_NB];
229 // kingAttackersCount[color] is the number of pieces of the given color
230 // which attack a square in the kingRing of the enemy king.
231 int kingAttackersCount[COLOR_NB];
233 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
234 // the given color which attack a square in the kingRing of the enemy king.
235 // The weights of the individual piece types are given by the elements in
236 // the KingAttackWeights array.
237 int kingAttackersWeight[COLOR_NB];
239 // kingAttacksCount[color] is the number of attacks by the given color to
240 // squares directly adjacent to the enemy king. Pieces which attack more
241 // than one square are counted multiple times. For instance, if there is
242 // a white knight on g5 and black's king is on g8, this white knight adds 2
243 // to kingAttacksCount[WHITE].
244 int kingAttacksCount[COLOR_NB];
248 // Evaluation::initialize() computes king and pawn attacks, and the king ring
249 // bitboard for a given color. This is done at the beginning of the evaluation.
250 template<Tracing T> template<Color Us>
251 void Evaluation<T>::initialize() {
253 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
254 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
255 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
256 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
258 // Find our pawns that are blocked or on the first two ranks
259 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
261 // Squares occupied by those pawns, by our king or queen, or controlled by enemy pawns
262 // are excluded from the mobility area.
263 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
265 // Initialise attackedBy bitboards for kings and pawns
266 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
267 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
268 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
269 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
271 // Init our king safety tables only if we are going to use them
272 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
274 kingRing[Us] = attackedBy[Us][KING];
275 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
276 kingRing[Us] |= shift<Up>(kingRing[Us]);
278 if (file_of(pos.square<KING>(Us)) == FILE_H)
279 kingRing[Us] |= shift<WEST>(kingRing[Us]);
281 else if (file_of(pos.square<KING>(Us)) == FILE_A)
282 kingRing[Us] |= shift<EAST>(kingRing[Us]);
284 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
285 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
288 kingRing[Us] = kingAttackersCount[Them] = 0;
292 // Evaluation::pieces() scores pieces of a given color and type
293 template<Tracing T> template<Color Us, PieceType Pt>
294 Score Evaluation<T>::pieces() {
296 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
297 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
298 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
299 : Rank5BB | Rank4BB | Rank3BB);
300 const Square* pl = pos.squares<Pt>(Us);
304 Score score = SCORE_ZERO;
306 attackedBy[Us][Pt] = 0;
308 while ((s = *pl++) != SQ_NONE)
310 // Find attacked squares, including x-ray attacks for bishops and rooks
311 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
312 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
313 : pos.attacks_from<Pt>(s);
315 if (pos.blockers_for_king(Us) & s)
316 b &= LineBB[pos.square<KING>(Us)][s];
318 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
319 attackedBy[Us][Pt] |= b;
320 attackedBy[Us][ALL_PIECES] |= b;
322 if (b & kingRing[Them])
324 kingAttackersCount[Us]++;
325 kingAttackersWeight[Us] += KingAttackWeights[Pt];
326 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
329 int mob = popcount(b & mobilityArea[Us]);
331 mobility[Us] += MobilityBonus[Pt - 2][mob];
333 // Penalty if the piece is far from the king
334 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
336 if (Pt == BISHOP || Pt == KNIGHT)
338 // Bonus if piece is on an outpost square or can reach one
339 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
341 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
343 else if (bb &= b & ~pos.pieces(Us))
344 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
346 // Bonus when behind a pawn
347 if ( relative_rank(Us, s) < RANK_5
348 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
349 score += MinorBehindPawn;
353 // Penalty according to number of pawns on the same color square as the
354 // bishop, bigger when the center files are blocked with pawns.
355 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
357 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
358 * (1 + popcount(blocked & CenterFiles));
360 // Bonus for bishop on a long diagonal which can "see" both center squares
361 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
362 score += LongDiagonalBishop;
365 // An important Chess960 pattern: A cornered bishop blocked by a friendly
366 // pawn diagonally in front of it is a very serious problem, especially
367 // when that pawn is also blocked.
370 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
372 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
373 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
374 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
375 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
382 // Bonus for aligning rook with enemy pawns on the same rank/file
383 if (relative_rank(Us, s) >= RANK_5)
384 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
386 // Bonus for rook on an open or semi-open file
387 if (pe->semiopen_file(Us, file_of(s)))
388 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
390 // Penalty when trapped by the king, even more if the king cannot castle
393 File kf = file_of(pos.square<KING>(Us));
394 if ((kf < FILE_E) == (file_of(s) < kf))
395 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
401 // Penalty if any relative pin or discovered attack against the queen
402 Bitboard queenPinners;
403 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
408 Trace::add(Pt, Us, score);
414 // Evaluation::king() assigns bonuses and penalties to a king of a given color
415 template<Tracing T> template<Color Us>
416 Score Evaluation<T>::king() const {
418 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
419 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
420 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
422 const Square ksq = pos.square<KING>(Us);
423 Bitboard weak, b, b1, b2, safe, unsafeChecks;
425 // King shelter and enemy pawns storm
426 Score score = pe->king_safety<Us>(pos, ksq);
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 + 64 * kingAttacksCount[Them]
478 + 183 * popcount(kingRing[Us] & weak)
479 + 122 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
480 - 860 * !pos.count<QUEEN>(Them)
481 - 7 * mg_value(score) / 8
484 // Transform the kingDanger units into a Score, and subtract it from the evaluation
487 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
488 kingDanger = std::max(0, kingDanger + mobilityDanger);
489 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
493 Bitboard kf = KingFlank[file_of(ksq)];
495 // Penalty when our king is on a pawnless flank
496 if (!(pos.pieces(PAWN) & kf))
497 score -= PawnlessFlank;
499 // Find the squares that opponent attacks in our king flank, and the squares
500 // which are attacked twice in that flank but not defended by our pawns.
501 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
502 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
504 // King tropism, to anticipate slow motion attacks on our king
505 score -= CloseEnemies * (popcount(b1) + popcount(b2));
508 Trace::add(KING, Us, score);
514 // Evaluation::threats() assigns bonuses according to the types of the
515 // attacking and the attacked pieces.
516 template<Tracing T> template<Color Us>
517 Score Evaluation<T>::threats() const {
519 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
520 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
521 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
523 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
524 Score score = SCORE_ZERO;
527 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
529 // Squares strongly protected by the enemy, either because they defend the
530 // square with a pawn, or because they defend the square twice and we don't.
531 stronglyProtected = attackedBy[Them][PAWN]
532 | (attackedBy2[Them] & ~attackedBy2[Us]);
534 // Non-pawn enemies, strongly protected
535 defended = nonPawnEnemies & stronglyProtected;
537 // Enemies not strongly protected and under our attack
538 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
540 // Bonus according to the kind of attacking pieces
543 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
546 Square s = pop_lsb(&b);
547 score += ThreatByMinor[type_of(pos.piece_on(s))];
548 if (type_of(pos.piece_on(s)) != PAWN)
549 score += ThreatByRank * (int)relative_rank(Them, s);
552 b = (pos.pieces(Them, QUEEN) | 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);
561 b = weak & attackedBy[Us][KING];
563 score += ThreatByKing[more_than_one(b)];
565 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
567 // Bonus for overload (non-pawn enemies attacked and defended exactly once)
569 & attackedBy[Us][ALL_PIECES] & ~attackedBy2[Us]
570 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
571 score += Overload * popcount(b);
574 // Bonus for enemy unopposed weak pawns
575 if (pos.pieces(Us, ROOK, QUEEN))
576 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
578 // Our safe or protected pawns
579 b = pos.pieces(Us, PAWN)
580 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
582 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
583 score += ThreatBySafePawn * popcount(safeThreats);
585 // Find squares where our pawns can push on the next move
586 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
587 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
589 // Keep only the squares which are not completely unsafe
590 b &= ~attackedBy[Them][PAWN]
591 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
593 // Bonus for safe pawn threats on the next move
594 b = pawn_attacks_bb<Us>(b)
596 & ~attackedBy[Us][PAWN];
598 score += ThreatByPawnPush * popcount(b);
600 // Bonus for threats on the next moves against enemy queen
601 if (pos.count<QUEEN>(Them) == 1)
603 Square s = pos.square<QUEEN>(Them);
604 safeThreats = mobilityArea[Us] & ~stronglyProtected;
606 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
608 score += KnightOnQueen * popcount(b & safeThreats);
610 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
611 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
613 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
616 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
617 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
618 score += Connectivity * popcount(b);
621 Trace::add(THREAT, Us, score);
626 // Evaluation::passed() evaluates the passed pawns and candidate passed
627 // pawns of the given color.
629 template<Tracing T> template<Color Us>
630 Score Evaluation<T>::passed() const {
632 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
633 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
635 auto king_proximity = [&](Color c, Square s) {
636 return std::min(distance(pos.square<KING>(c), s), 5);
639 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
640 Score score = SCORE_ZERO;
642 b = pe->passed_pawns(Us);
646 Square s = pop_lsb(&b);
648 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
650 bb = forward_file_bb(Us, s) & pos.pieces(Them);
651 score -= HinderPassedPawn * popcount(bb);
653 int r = relative_rank(Us, s);
654 int w = PassedDanger[r];
656 Score bonus = PassedRank[r];
660 Square blockSq = s + Up;
662 // Adjust bonus based on the king's proximity
663 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
664 - king_proximity(Us, blockSq) * 2) * w);
666 // If blockSq is not the queening square then consider also a second push
668 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
670 // If the pawn is free to advance, then increase the bonus
671 if (pos.empty(blockSq))
673 // If there is a rook or queen attacking/defending the pawn from behind,
674 // consider all the squaresToQueen. Otherwise consider only the squares
675 // in the pawn's path attacked or occupied by the enemy.
676 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
678 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
680 if (!(pos.pieces(Us) & bb))
681 defendedSquares &= attackedBy[Us][ALL_PIECES];
683 if (!(pos.pieces(Them) & bb))
684 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
686 // If there aren't any enemy attacks, assign a big bonus. Otherwise
687 // assign a smaller bonus if the block square isn't attacked.
688 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
690 // If the path to the queen is fully defended, assign a big bonus.
691 // Otherwise assign a smaller bonus if the block square is defended.
692 if (defendedSquares == squaresToQueen)
695 else if (defendedSquares & blockSq)
698 bonus += make_score(k * w, k * w);
700 else if (pos.pieces(Us) & blockSq)
701 bonus += make_score(w + r * 2, w + r * 2);
704 // Scale down bonus for candidate passers which need more than one
705 // pawn push to become passed, or have a pawn in front of them.
706 if ( !pos.pawn_passed(Us, s + Up)
707 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
710 score += bonus + PassedFile[file_of(s)];
714 Trace::add(PASSED, Us, score);
720 // Evaluation::space() computes the space evaluation for a given side. The
721 // space evaluation is a simple bonus based on the number of safe squares
722 // available for minor pieces on the central four files on ranks 2--4. Safe
723 // squares one, two or three squares behind a friendly pawn are counted
724 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
725 // improve play on game opening.
727 template<Tracing T> template<Color Us>
728 Score Evaluation<T>::space() const {
730 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
731 constexpr Bitboard SpaceMask =
732 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
733 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
735 if (pos.non_pawn_material() < SpaceThreshold)
738 // Find the available squares for our pieces inside the area defined by SpaceMask
739 Bitboard safe = SpaceMask
740 & ~pos.pieces(Us, PAWN)
741 & ~attackedBy[Them][PAWN];
743 // Find all squares which are at most three squares behind some friendly pawn
744 Bitboard behind = pos.pieces(Us, PAWN);
745 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
746 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
748 int bonus = popcount(safe) + popcount(behind & safe);
749 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
751 Score score = make_score(bonus * weight * weight / 16, 0);
754 Trace::add(SPACE, Us, score);
760 // Evaluation::initiative() computes the initiative correction value
761 // for the position. It is a second order bonus/malus based on the
762 // known attacking/defending status of the players.
765 Score Evaluation<T>::initiative(Value eg) const {
767 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
768 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
770 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
771 && (pos.pieces(PAWN) & KingSide);
773 // Compute the initiative bonus for the attacking side
774 int complexity = 8 * pe->pawn_asymmetry()
775 + 12 * pos.count<PAWN>()
777 + 16 * pawnsOnBothFlanks
778 + 48 * !pos.non_pawn_material()
781 // Now apply the bonus: note that we find the attacking side by extracting
782 // the sign of the endgame value, and that we carefully cap the bonus so
783 // that the endgame score will never change sign after the bonus.
784 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
787 Trace::add(INITIATIVE, make_score(0, v));
789 return make_score(0, v);
793 // Evaluation::scale_factor() computes the scale factor for the winning side
796 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
798 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
799 int sf = me->scale_factor(pos, strongSide);
801 // If scale is not already specific, scale down the endgame via general heuristics
802 if (sf == SCALE_FACTOR_NORMAL)
804 if ( pos.opposite_bishops()
805 && pos.non_pawn_material(WHITE) == BishopValueMg
806 && pos.non_pawn_material(BLACK) == BishopValueMg)
809 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
812 return ScaleFactor(sf);
816 // Evaluation::value() is the main function of the class. It computes the various
817 // parts of the evaluation and returns the value of the position from the point
818 // of view of the side to move.
821 Value Evaluation<T>::value() {
823 assert(!pos.checkers());
825 // Probe the material hash table
826 me = Material::probe(pos);
828 // If we have a specialized evaluation function for the current material
829 // configuration, call it and return.
830 if (me->specialized_eval_exists())
831 return me->evaluate(pos);
833 // Initialize score by reading the incrementally updated scores included in
834 // the position object (material + piece square tables) and the material
835 // imbalance. Score is computed internally from the white point of view.
836 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
838 // Probe the pawn hash table
839 pe = Pawns::probe(pos);
840 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
842 // Early exit if score is high
843 Value v = (mg_value(score) + eg_value(score)) / 2;
844 if (abs(v) > LazyThreshold)
845 return pos.side_to_move() == WHITE ? v : -v;
847 // Main evaluation begins here
852 // Pieces should be evaluated first (populate attack tables)
853 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
854 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
855 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
856 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
858 score += mobility[WHITE] - mobility[BLACK];
860 score += king< WHITE>() - king< BLACK>()
861 + threats<WHITE>() - threats<BLACK>()
862 + passed< WHITE>() - passed< BLACK>()
863 + space< WHITE>() - space< BLACK>();
865 score += initiative(eg_value(score));
867 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
868 ScaleFactor sf = scale_factor(eg_value(score));
869 v = mg_value(score) * int(me->game_phase())
870 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
872 v /= int(PHASE_MIDGAME);
874 // In case of tracing add all remaining individual evaluation terms
877 Trace::add(MATERIAL, pos.psq_score());
878 Trace::add(IMBALANCE, me->imbalance());
879 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
880 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
881 Trace::add(TOTAL, score);
884 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
891 /// evaluate() is the evaluator for the outer world. It returns a static
892 /// evaluation of the position from the point of view of the side to move.
894 Value Eval::evaluate(const Position& pos) {
895 return Evaluation<NO_TRACE>(pos).value();
899 /// trace() is like evaluate(), but instead of returning a value, it returns
900 /// a string (suitable for outputting to stdout) that contains the detailed
901 /// descriptions and values of each evaluation term. Useful for debugging.
903 std::string Eval::trace(const Position& pos) {
905 std::memset(scores, 0, sizeof(scores));
907 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
909 Value v = Evaluation<TRACE>(pos).value();
911 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
913 std::stringstream ss;
914 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
915 << " Term | White | Black | Total \n"
916 << " | MG EG | MG EG | MG EG \n"
917 << " ------------+-------------+-------------+------------\n"
918 << " Material | " << Term(MATERIAL)
919 << " Imbalance | " << Term(IMBALANCE)
920 << " Initiative | " << Term(INITIATIVE)
921 << " Pawns | " << Term(PAWN)
922 << " Knights | " << Term(KNIGHT)
923 << " Bishops | " << Term(BISHOP)
924 << " Rooks | " << Term(ROOK)
925 << " Queens | " << Term(QUEEN)
926 << " Mobility | " << Term(MOBILITY)
927 << " King safety | " << Term(KING)
928 << " Threats | " << Term(THREAT)
929 << " Passed | " << Term(PASSED)
930 << " Space | " << Term(SPACE)
931 << " ------------+-------------+-------------+------------\n"
932 << " Total | " << Term(TOTAL);
934 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";