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(25, 57), S(4, 139) };
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(7, 10), S(7, 26), S(14, 31), S(42, 63), S(178, 167), S(279, 244)
152 // PassedFile[File] contains a bonus according to the file of a passed pawn
153 constexpr Score PassedFile[FILE_NB] = {
154 S( 17, 6), S(-4, 7), S( 2,-12), S(-17,-14),
155 S(-17,-14), S( 2,-12), S(-4, 7), S( 17, 6)
158 // PassedDanger[Rank] contains a term to weight the passed score
159 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 3, 6, 12, 21 };
161 // KingProtector[PieceType-2] contains a penalty according to distance from king
162 constexpr Score KingProtector[] = { S(3, 5), S(5, 3), S(3, 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, 2);
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(186,140);
181 constexpr Score TrappedRook = S( 92, 0);
182 constexpr Score WeakQueen = S( 50, 10);
183 constexpr Score WeakUnopposedPawn = S( 14, 19);
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))
431 int kingDanger = -mg_value(score);
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 + 182 * popcount(kingRing[Us] & weak)
479 + 128 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
480 - 857 * !pos.count<QUEEN>(Them)
483 // Transform the kingDanger units into a Score, and subtract it from the evaluation
486 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
487 kingDanger = std::max(0, kingDanger + mobilityDanger);
488 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
492 Bitboard kf = KingFlank[file_of(ksq)];
494 // Penalty when our king is on a pawnless flank
495 if (!(pos.pieces(PAWN) & kf))
496 score -= PawnlessFlank;
498 // Find the squares that opponent attacks in our king flank, and the squares
499 // which are attacked twice in that flank but not defended by our pawns.
500 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
501 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
503 // King tropism, to anticipate slow motion attacks on our king
504 score -= CloseEnemies * (popcount(b1) + popcount(b2));
507 Trace::add(KING, Us, score);
513 // Evaluation::threats() assigns bonuses according to the types of the
514 // attacking and the attacked pieces.
515 template<Tracing T> template<Color Us>
516 Score Evaluation<T>::threats() const {
518 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
519 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
520 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
522 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
523 Score score = SCORE_ZERO;
526 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
528 // Squares strongly protected by the enemy, either because they defend the
529 // square with a pawn, or because they defend the square twice and we don't.
530 stronglyProtected = attackedBy[Them][PAWN]
531 | (attackedBy2[Them] & ~attackedBy2[Us]);
533 // Non-pawn enemies, strongly protected
534 defended = nonPawnEnemies & stronglyProtected;
536 // Enemies not strongly protected and under our attack
537 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
539 // Bonus according to the kind of attacking pieces
542 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
545 Square s = pop_lsb(&b);
546 score += ThreatByMinor[type_of(pos.piece_on(s))];
547 if (type_of(pos.piece_on(s)) != PAWN)
548 score += ThreatByRank * (int)relative_rank(Them, s);
551 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
554 Square s = pop_lsb(&b);
555 score += ThreatByRook[type_of(pos.piece_on(s))];
556 if (type_of(pos.piece_on(s)) != PAWN)
557 score += ThreatByRank * (int)relative_rank(Them, s);
560 b = weak & attackedBy[Us][KING];
562 score += ThreatByKing[more_than_one(b)];
564 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
566 // Bonus for overload (non-pawn enemies attacked and defended exactly once)
568 & attackedBy[Us][ALL_PIECES] & ~attackedBy2[Us]
569 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
570 score += Overload * popcount(b);
573 // Bonus for enemy unopposed weak pawns
574 if (pos.pieces(Us, ROOK, QUEEN))
575 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
577 // Our safe or protected pawns
578 b = pos.pieces(Us, PAWN)
579 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
581 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
582 score += ThreatBySafePawn * popcount(safeThreats);
584 // Find squares where our pawns can push on the next move
585 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
586 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
588 // Keep only the squares which are not completely unsafe
589 b &= ~attackedBy[Them][PAWN]
590 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
592 // Bonus for safe pawn threats on the next move
593 b = pawn_attacks_bb<Us>(b)
595 & ~attackedBy[Us][PAWN];
597 score += ThreatByPawnPush * popcount(b);
599 // Bonus for threats on the next moves against enemy queen
600 if (pos.count<QUEEN>(Them) == 1)
602 Square s = pos.square<QUEEN>(Them);
603 safeThreats = mobilityArea[Us] & ~stronglyProtected;
605 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
607 score += KnightOnQueen * popcount(b & safeThreats);
609 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
610 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
612 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
615 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
616 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
617 score += Connectivity * popcount(b);
620 Trace::add(THREAT, Us, score);
625 // Evaluation::passed() evaluates the passed pawns and candidate passed
626 // pawns of the given color.
628 template<Tracing T> template<Color Us>
629 Score Evaluation<T>::passed() const {
631 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
632 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
634 auto king_proximity = [&](Color c, Square s) {
635 return std::min(distance(pos.square<KING>(c), s), 5);
638 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
639 Score score = SCORE_ZERO;
641 b = pe->passed_pawns(Us);
645 Square s = pop_lsb(&b);
647 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
649 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
650 score -= HinderPassedPawn * popcount(bb);
652 int r = relative_rank(Us, s);
653 int w = PassedDanger[r];
655 Score bonus = PassedRank[r];
659 Square blockSq = s + Up;
661 // Adjust bonus based on the king's proximity
662 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
663 - king_proximity(Us, blockSq) * 2) * w);
665 // If blockSq is not the queening square then consider also a second push
667 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
669 // If the pawn is free to advance, then increase the bonus
670 if (pos.empty(blockSq))
672 // If there is a rook or queen attacking/defending the pawn from behind,
673 // consider all the squaresToQueen. Otherwise consider only the squares
674 // in the pawn's path attacked or occupied by the enemy.
675 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
677 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
679 if (!(pos.pieces(Us) & bb))
680 defendedSquares &= attackedBy[Us][ALL_PIECES];
682 if (!(pos.pieces(Them) & bb))
683 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
685 // If there aren't any enemy attacks, assign a big bonus. Otherwise
686 // assign a smaller bonus if the block square isn't attacked.
687 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
689 // If the path to the queen is fully defended, assign a big bonus.
690 // Otherwise assign a smaller bonus if the block square is defended.
691 if (defendedSquares == squaresToQueen)
694 else if (defendedSquares & blockSq)
697 bonus += make_score(k * w, k * w);
699 else if (pos.pieces(Us) & blockSq)
700 bonus += make_score(w + r * 2, w + r * 2);
703 // Scale down bonus for candidate passers which need more than one
704 // pawn push to become passed, or have a pawn in front of them.
705 if ( !pos.pawn_passed(Us, s + Up)
706 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
709 score += bonus + PassedFile[file_of(s)];
713 Trace::add(PASSED, Us, score);
719 // Evaluation::space() computes the space evaluation for a given side. The
720 // space evaluation is a simple bonus based on the number of safe squares
721 // available for minor pieces on the central four files on ranks 2--4. Safe
722 // squares one, two or three squares behind a friendly pawn are counted
723 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
724 // improve play on game opening.
726 template<Tracing T> template<Color Us>
727 Score Evaluation<T>::space() const {
729 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
730 constexpr Bitboard SpaceMask =
731 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
732 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
734 if (pos.non_pawn_material() < SpaceThreshold)
737 // Find the available squares for our pieces inside the area defined by SpaceMask
738 Bitboard safe = SpaceMask
739 & ~pos.pieces(Us, PAWN)
740 & ~attackedBy[Them][PAWN];
742 // Find all squares which are at most three squares behind some friendly pawn
743 Bitboard behind = pos.pieces(Us, PAWN);
744 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
745 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
747 int bonus = popcount(safe) + popcount(behind & safe);
748 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
750 Score score = make_score(bonus * weight * weight / 16, 0);
753 Trace::add(SPACE, Us, score);
759 // Evaluation::initiative() computes the initiative correction value
760 // for the position. It is a second order bonus/malus based on the
761 // known attacking/defending status of the players.
764 Score Evaluation<T>::initiative(Value eg) const {
766 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
767 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
769 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
770 && (pos.pieces(PAWN) & KingSide);
772 // Compute the initiative bonus for the attacking side
773 int complexity = 8 * pe->pawn_asymmetry()
774 + 12 * pos.count<PAWN>()
776 + 16 * pawnsOnBothFlanks
777 + 48 * !pos.non_pawn_material()
780 // Now apply the bonus: note that we find the attacking side by extracting
781 // the sign of the endgame value, and that we carefully cap the bonus so
782 // that the endgame score will never change sign after the bonus.
783 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
786 Trace::add(INITIATIVE, make_score(0, v));
788 return make_score(0, v);
792 // Evaluation::scale_factor() computes the scale factor for the winning side
795 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
797 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
798 int sf = me->scale_factor(pos, strongSide);
800 // If scale is not already specific, scale down the endgame via general heuristics
801 if (sf == SCALE_FACTOR_NORMAL)
803 if ( pos.opposite_bishops()
804 && pos.non_pawn_material(WHITE) == BishopValueMg
805 && pos.non_pawn_material(BLACK) == BishopValueMg)
808 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
811 return ScaleFactor(sf);
815 // Evaluation::value() is the main function of the class. It computes the various
816 // parts of the evaluation and returns the value of the position from the point
817 // of view of the side to move.
820 Value Evaluation<T>::value() {
822 assert(!pos.checkers());
824 // Probe the material hash table
825 me = Material::probe(pos);
827 // If we have a specialized evaluation function for the current material
828 // configuration, call it and return.
829 if (me->specialized_eval_exists())
830 return me->evaluate(pos);
832 // Initialize score by reading the incrementally updated scores included in
833 // the position object (material + piece square tables) and the material
834 // imbalance. Score is computed internally from the white point of view.
835 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
837 // Probe the pawn hash table
838 pe = Pawns::probe(pos);
839 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
841 // Early exit if score is high
842 Value v = (mg_value(score) + eg_value(score)) / 2;
843 if (abs(v) > LazyThreshold)
844 return pos.side_to_move() == WHITE ? v : -v;
846 // Main evaluation begins here
851 // Pieces should be evaluated first (populate attack tables)
852 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
853 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
854 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
855 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
857 score += mobility[WHITE] - mobility[BLACK];
859 score += king< WHITE>() - king< BLACK>()
860 + threats<WHITE>() - threats<BLACK>()
861 + passed< WHITE>() - passed< BLACK>()
862 + space< WHITE>() - space< BLACK>();
864 score += initiative(eg_value(score));
866 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
867 ScaleFactor sf = scale_factor(eg_value(score));
868 v = mg_value(score) * int(me->game_phase())
869 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
871 v /= int(PHASE_MIDGAME);
873 // In case of tracing add all remaining individual evaluation terms
876 Trace::add(MATERIAL, pos.psq_score());
877 Trace::add(IMBALANCE, me->imbalance());
878 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
879 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
880 Trace::add(TOTAL, score);
883 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
890 /// evaluate() is the evaluator for the outer world. It returns a static
891 /// evaluation of the position from the point of view of the side to move.
893 Value Eval::evaluate(const Position& pos) {
894 return Evaluation<NO_TRACE>(pos).value();
898 /// trace() is like evaluate(), but instead of returning a value, it returns
899 /// a string (suitable for outputting to stdout) that contains the detailed
900 /// descriptions and values of each evaluation term. Useful for debugging.
902 std::string Eval::trace(const Position& pos) {
904 std::memset(scores, 0, sizeof(scores));
906 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
908 Value v = Evaluation<TRACE>(pos).value();
910 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
912 std::stringstream ss;
913 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
914 << " Term | White | Black | Total \n"
915 << " | MG EG | MG EG | MG EG \n"
916 << " ------------+-------------+-------------+------------\n"
917 << " Material | " << Term(MATERIAL)
918 << " Imbalance | " << Term(IMBALANCE)
919 << " Initiative | " << Term(INITIATIVE)
920 << " Pawns | " << Term(PAWN)
921 << " Knights | " << Term(KNIGHT)
922 << " Bishops | " << Term(BISHOP)
923 << " Rooks | " << Term(ROOK)
924 << " Queens | " << Term(QUEEN)
925 << " Mobility | " << Term(MOBILITY)
926 << " King safety | " << Term(KING)
927 << " Threats | " << Term(THREAT)
928 << " Passed | " << Term(PASSED)
929 << " Space | " << Term(SPACE)
930 << " ------------+-------------+-------------+------------\n"
931 << " Total | " << Term(TOTAL);
933 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";