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
32 std::atomic<Score> Eval::Contempt;
36 enum Tracing { NO_TRACE, TRACE };
38 enum Term { // The first 8 entries are reserved for PieceType
39 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
42 Score scores[TERM_NB][COLOR_NB];
44 double to_cp(Value v) { return double(v) / PawnValueEg; }
46 void add(int idx, Color c, Score s) {
50 void add(int idx, Score w, Score b = SCORE_ZERO) {
51 scores[idx][WHITE] = w;
52 scores[idx][BLACK] = b;
55 std::ostream& operator<<(std::ostream& os, Score s) {
56 os << std::setw(5) << to_cp(mg_value(s)) << " "
57 << std::setw(5) << to_cp(eg_value(s));
61 std::ostream& operator<<(std::ostream& os, Term t) {
63 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
64 os << " ---- ----" << " | " << " ---- ----";
66 os << scores[t][WHITE] << " | " << scores[t][BLACK];
68 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
73 using namespace Trace;
77 constexpr Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
78 constexpr Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
79 constexpr Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
80 constexpr Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
82 constexpr Bitboard KingFlank[FILE_NB] = {
83 QueenSide, QueenSide, QueenSide,
84 CenterFiles, CenterFiles,
85 KingSide, KingSide, KingSide
88 // Threshold for lazy and space evaluation
89 constexpr Value LazyThreshold = Value(1500);
90 constexpr Value SpaceThreshold = Value(12222);
92 // KingAttackWeights[PieceType] contains king attack weights by piece type
93 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
95 // Penalties for enemy's safe checks
96 constexpr int QueenSafeCheck = 780;
97 constexpr int RookSafeCheck = 880;
98 constexpr int BishopSafeCheck = 435;
99 constexpr int KnightSafeCheck = 790;
101 #define S(mg, eg) make_score(mg, eg)
103 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
104 // indexed by piece type and number of attacked squares in the mobility area.
105 constexpr Score MobilityBonus[][32] = {
106 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
107 S( 22, 26), S( 29, 29), S( 36, 29) },
108 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
109 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
110 S( 91, 88), S( 98, 97) },
111 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
112 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
113 S( 46,166), S( 48,169), S( 58,171) },
114 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
115 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
116 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
117 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
118 S(106,184), S(109,191), S(113,206), S(116,212) }
121 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
122 // pieces if they occupy or can reach an outpost square, bigger if that
123 // square is supported by a pawn.
124 constexpr Score Outpost[][2] = {
125 { S(22, 6), S(36,12) }, // Knight
126 { S( 9, 2), S(15, 5) } // Bishop
129 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
130 // no (friendly) pawn on the rook file.
131 constexpr Score RookOnFile[] = { S(20, 7), S(45, 20) };
133 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
134 // which piece type attacks which one. Attacks on lesser pieces which are
135 // pawn-defended are not considered.
136 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
137 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(47, 120)
140 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
141 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(36, 38)
144 // ThreatByKing[on one/on many] contains bonuses for king attacks on
145 // pawns or pieces which are not pawn-defended.
146 constexpr Score ThreatByKing[] = { S(3, 65), S(9, 145) };
148 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
149 constexpr Score PassedRank[RANK_NB] = {
150 S(0, 0), S(5, 7), S(5, 13), S(32, 42), S(70, 70), S(172, 170), S(217, 269)
153 // PassedFile[File] contains a bonus according to the file of a passed pawn
154 constexpr Score PassedFile[FILE_NB] = {
155 S( 9, 10), S(2, 10), S(1, -8), S(-20,-12),
156 S(-20,-12), S(1, -8), S(2, 10), S( 9, 10)
159 // PassedDanger[Rank] contains a term to weight the passed score
160 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 2, 7, 12, 19 };
162 // KingProtector[PieceType-2] contains a penalty according to distance from king
163 constexpr Score KingProtector[] = { S(3, 5), S(4, 3), S(3, 0), S(1, -1) };
165 // Assorted bonuses and penalties
166 constexpr Score BishopPawns = S( 8, 12);
167 constexpr Score CloseEnemies = S( 7, 0);
168 constexpr Score Connectivity = S( 3, 1);
169 constexpr Score CorneredBishop = S( 50, 50);
170 constexpr Score Hanging = S( 52, 30);
171 constexpr Score HinderPassedPawn = S( 8, 1);
172 constexpr Score KnightOnQueen = S( 21, 11);
173 constexpr Score LongDiagonalBishop = S( 22, 0);
174 constexpr Score MinorBehindPawn = S( 16, 0);
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( 47, 26);
179 constexpr Score ThreatByRank = S( 16, 3);
180 constexpr Score ThreatBySafePawn = S(175,168);
181 constexpr Score TrappedRook = S( 92, 0);
182 constexpr Score WeakQueen = S( 50, 10);
183 constexpr Score WeakUnopposedPawn = S( 5, 25);
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 controlled by enemy pawns
262 // are excluded from the mobility area.
263 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | 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 kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
279 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
282 kingRing[Us] = kingAttackersCount[Them] = 0;
286 // Evaluation::pieces() scores pieces of a given color and type
287 template<Tracing T> template<Color Us, PieceType Pt>
288 Score Evaluation<T>::pieces() {
290 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
291 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
292 : Rank5BB | Rank4BB | Rank3BB);
293 const Square* pl = pos.squares<Pt>(Us);
297 Score score = SCORE_ZERO;
299 attackedBy[Us][Pt] = 0;
301 while ((s = *pl++) != SQ_NONE)
303 // Find attacked squares, including x-ray attacks for bishops and rooks
304 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
305 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
306 : pos.attacks_from<Pt>(s);
308 if (pos.blockers_for_king(Us) & s)
309 b &= LineBB[pos.square<KING>(Us)][s];
311 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
312 attackedBy[Us][Pt] |= b;
313 attackedBy[Us][ALL_PIECES] |= b;
315 if (b & kingRing[Them])
317 kingAttackersCount[Us]++;
318 kingAttackersWeight[Us] += KingAttackWeights[Pt];
319 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
322 int mob = popcount(b & mobilityArea[Us]);
324 mobility[Us] += MobilityBonus[Pt - 2][mob];
326 // Penalty if the piece is far from the king
327 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
329 if (Pt == BISHOP || Pt == KNIGHT)
331 // Bonus if piece is on an outpost square or can reach one
332 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
334 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
336 else if (bb &= b & ~pos.pieces(Us))
337 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
339 // Bonus when behind a pawn
340 if ( relative_rank(Us, s) < RANK_5
341 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
342 score += MinorBehindPawn;
346 // Penalty according to number of pawns on the same color square as the bishop
347 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
349 // Bonus for bishop on a long diagonal which can "see" both center squares
350 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
351 score += LongDiagonalBishop;
354 // An important Chess960 pattern: A cornered bishop blocked by a friendly
355 // pawn diagonally in front of it is a very serious problem, especially
356 // when that pawn is also blocked.
359 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
361 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
362 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
363 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
364 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
371 // Bonus for aligning rook with with enemy pawns on the same rank/file
372 if (relative_rank(Us, s) >= RANK_5)
373 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
375 // Bonus for rook on an open or semi-open file
376 if (pe->semiopen_file(Us, file_of(s)))
377 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
379 // Penalty when trapped by the king, even more if the king cannot castle
382 File kf = file_of(pos.square<KING>(Us));
383 if ((kf < FILE_E) == (file_of(s) < kf))
384 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
390 // Penalty if any relative pin or discovered attack against the queen
391 Bitboard queenPinners;
392 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
397 Trace::add(Pt, Us, score);
403 // Evaluation::king() assigns bonuses and penalties to a king of a given color
404 template<Tracing T> template<Color Us>
405 Score Evaluation<T>::king() const {
407 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
408 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
409 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
411 const Square ksq = pos.square<KING>(Us);
412 Bitboard weak, b, b1, b2, safe, unsafeChecks, pinned;
414 // King shelter and enemy pawns storm
415 Score score = pe->king_safety<Us>(pos, ksq);
417 // Main king safety evaluation
418 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
423 // Attacked squares defended at most once by our queen or king
424 weak = attackedBy[Them][ALL_PIECES]
426 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
428 // Analyse the safe enemy's checks which are possible on next move
429 safe = ~pos.pieces(Them);
430 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
432 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
433 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
435 // Enemy queen safe checks
436 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
437 kingDanger += QueenSafeCheck;
439 b1 &= attackedBy[Them][ROOK];
440 b2 &= attackedBy[Them][BISHOP];
442 // Enemy rooks checks
444 kingDanger += RookSafeCheck;
448 // Enemy bishops checks
450 kingDanger += BishopSafeCheck;
454 // Enemy knights checks
455 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
457 kingDanger += KnightSafeCheck;
461 // Unsafe or occupied checking squares will also be considered, as long as
462 // the square is in the attacker's mobility area.
463 unsafeChecks &= mobilityArea[Them];
464 pinned = pos.blockers_for_king(Us) & pos.pieces(Us);
466 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
467 + 102 * kingAttacksCount[Them]
468 + 191 * popcount(kingRing[Us] & weak)
469 + 143 * popcount(pinned | unsafeChecks)
470 - 848 * !pos.count<QUEEN>(Them)
471 - 9 * mg_value(score) / 8
474 // Transform the kingDanger units into a Score, and subtract it from the evaluation
477 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
478 kingDanger = std::max(0, kingDanger + mobilityDanger);
479 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
483 Bitboard kf = KingFlank[file_of(ksq)];
485 // Penalty when our king is on a pawnless flank
486 if (!(pos.pieces(PAWN) & kf))
487 score -= PawnlessFlank;
489 // Find the squares that opponent attacks in our king flank, and the squares
490 // which are attacked twice in that flank but not defended by our pawns.
491 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
492 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
494 // King tropism, to anticipate slow motion attacks on our king
495 score -= CloseEnemies * (popcount(b1) + popcount(b2));
498 Trace::add(KING, Us, score);
504 // Evaluation::threats() assigns bonuses according to the types of the
505 // attacking and the attacked pieces.
506 template<Tracing T> template<Color Us>
507 Score Evaluation<T>::threats() const {
509 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
510 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
511 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
513 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
514 Score score = SCORE_ZERO;
516 // Non-pawn enemies attacked by a pawn
517 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
518 weak = nonPawnEnemies & attackedBy[Us][PAWN];
522 // Our safe or protected pawns
523 b = pos.pieces(Us, PAWN)
524 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
526 safeThreats = pawn_attacks_bb<Us>(b) & weak;
527 score += ThreatBySafePawn * popcount(safeThreats);
530 // Squares strongly protected by the enemy, either because they defend the
531 // square with a pawn, or because they defend the square twice and we don't.
532 stronglyProtected = attackedBy[Them][PAWN]
533 | (attackedBy2[Them] & ~attackedBy2[Us]);
535 // Non-pawn enemies, strongly protected
536 defended = nonPawnEnemies & stronglyProtected;
538 // Enemies not strongly protected and under our attack
539 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
541 // Bonus according to the kind of attacking pieces
544 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
547 Square s = pop_lsb(&b);
548 score += ThreatByMinor[type_of(pos.piece_on(s))];
549 if (type_of(pos.piece_on(s)) != PAWN)
550 score += ThreatByRank * (int)relative_rank(Them, s);
553 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
556 Square s = pop_lsb(&b);
557 score += ThreatByRook[type_of(pos.piece_on(s))];
558 if (type_of(pos.piece_on(s)) != PAWN)
559 score += ThreatByRank * (int)relative_rank(Them, s);
562 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
564 b = weak & attackedBy[Us][KING];
566 score += ThreatByKing[more_than_one(b)];
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 not completely unsafe
578 b &= ~attackedBy[Them][PAWN]
579 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
581 // Bonus for safe pawn threats on the next move
582 b = pawn_attacks_bb<Us>(b)
584 & ~attackedBy[Us][PAWN];
586 score += ThreatByPawnPush * popcount(b);
588 // Bonus for threats on the next moves against enemy queen
589 if (pos.count<QUEEN>(Them) == 1)
591 Square s = pos.square<QUEEN>(Them);
592 safeThreats = mobilityArea[Us] & ~stronglyProtected;
594 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
596 score += KnightOnQueen * popcount(b & safeThreats);
598 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
599 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
601 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
604 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
605 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
606 score += Connectivity * popcount(b);
609 Trace::add(THREAT, Us, score);
614 // Evaluation::passed() evaluates the passed pawns and candidate passed
615 // pawns of the given color.
617 template<Tracing T> template<Color Us>
618 Score Evaluation<T>::passed() const {
620 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
621 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
623 auto king_proximity = [&](Color c, Square s) {
624 return std::min(distance(pos.square<KING>(c), s), 5);
627 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
628 Score score = SCORE_ZERO;
630 b = pe->passed_pawns(Us);
634 Square s = pop_lsb(&b);
636 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
638 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
639 score -= HinderPassedPawn * popcount(bb);
641 int r = relative_rank(Us, s);
642 int w = PassedDanger[r];
644 Score bonus = PassedRank[r];
648 Square blockSq = s + Up;
650 // Adjust bonus based on the king's proximity
651 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
652 - king_proximity(Us, blockSq) * 2) * w);
654 // If blockSq is not the queening square then consider also a second push
656 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
658 // If the pawn is free to advance, then increase the bonus
659 if (pos.empty(blockSq))
661 // If there is a rook or queen attacking/defending the pawn from behind,
662 // consider all the squaresToQueen. Otherwise consider only the squares
663 // in the pawn's path attacked or occupied by the enemy.
664 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
666 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
668 if (!(pos.pieces(Us) & bb))
669 defendedSquares &= attackedBy[Us][ALL_PIECES];
671 if (!(pos.pieces(Them) & bb))
672 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
674 // If there aren't any enemy attacks, assign a big bonus. Otherwise
675 // assign a smaller bonus if the block square isn't attacked.
676 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
678 // If the path to the queen is fully defended, assign a big bonus.
679 // Otherwise assign a smaller bonus if the block square is defended.
680 if (defendedSquares == squaresToQueen)
683 else if (defendedSquares & blockSq)
686 bonus += make_score(k * w, k * w);
688 else if (pos.pieces(Us) & blockSq)
689 bonus += make_score(w + r * 2, w + r * 2);
692 // Scale down bonus for candidate passers which need more than one
693 // pawn push to become passed or have a pawn in front of them.
694 if ( !pos.pawn_passed(Us, s + Up)
695 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
698 score += bonus + PassedFile[file_of(s)];
702 Trace::add(PASSED, Us, score);
708 // Evaluation::space() computes the space evaluation for a given side. The
709 // space evaluation is a simple bonus based on the number of safe squares
710 // available for minor pieces on the central four files on ranks 2--4. Safe
711 // squares one, two or three squares behind a friendly pawn are counted
712 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
713 // improve play on game opening.
715 template<Tracing T> template<Color Us>
716 Score Evaluation<T>::space() const {
718 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
719 constexpr Bitboard SpaceMask =
720 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
721 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
723 if (pos.non_pawn_material() < SpaceThreshold)
726 // Find the safe squares for our pieces inside the area defined by
727 // SpaceMask. A square is unsafe if it is attacked by an enemy
728 // pawn, or if it is undefended and attacked by an enemy piece.
729 Bitboard safe = SpaceMask
730 & ~pos.pieces(Us, PAWN)
731 & ~attackedBy[Them][PAWN]
732 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
734 // Find all squares which are at most three squares behind some friendly pawn
735 Bitboard behind = pos.pieces(Us, PAWN);
736 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
737 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
739 int bonus = popcount(safe) + popcount(behind & safe);
740 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
742 Score score = make_score(bonus * weight * weight / 16, 0);
745 Trace::add(SPACE, Us, score);
751 // Evaluation::initiative() computes the initiative correction value
752 // for the position. It is a second order bonus/malus based on the
753 // known attacking/defending status of the players.
756 Score Evaluation<T>::initiative(Value eg) const {
758 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
759 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
761 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
762 && (pos.pieces(PAWN) & KingSide);
764 // Compute the initiative bonus for the attacking side
765 int complexity = 8 * outflanking
766 + 8 * pe->pawn_asymmetry()
767 + 12 * pos.count<PAWN>()
768 + 16 * pawnsOnBothFlanks
769 + 48 * !pos.non_pawn_material()
772 // Now apply the bonus: note that we find the attacking side by extracting
773 // the sign of the endgame value, and that we carefully cap the bonus so
774 // that the endgame score will never change sign after the bonus.
775 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
778 Trace::add(INITIATIVE, make_score(0, v));
780 return make_score(0, v);
784 // Evaluation::scale_factor() computes the scale factor for the winning side
787 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
789 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
790 int sf = me->scale_factor(pos, strongSide);
792 // If we don't already have an unusual scale factor, check for certain
793 // types of endgames, and use a lower scale for those.
794 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
796 if (pos.opposite_bishops())
798 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
799 // is almost a draw, in case of KBP vs KB, it is even more a draw.
800 if ( pos.non_pawn_material(WHITE) == BishopValueMg
801 && pos.non_pawn_material(BLACK) == BishopValueMg)
802 sf = more_than_one(pos.pieces(PAWN)) ? 31 : 9;
804 // Endgame with opposite-colored bishops, but also other pieces. Still
805 // a bit drawish, but not as drawish as with only the two bishops.
809 // Endings where weaker side can place his king in front of the enemy's
810 // pawns are drawish.
811 else if ( abs(eg) <= BishopValueEg
812 && pos.count<PAWN>(strongSide) <= 2
813 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
814 sf = 37 + 7 * pos.count<PAWN>(strongSide);
817 return ScaleFactor(sf);
821 // Evaluation::value() is the main function of the class. It computes the various
822 // parts of the evaluation and returns the value of the position from the point
823 // of view of the side to move.
826 Value Evaluation<T>::value() {
828 assert(!pos.checkers());
830 // Probe the material hash table
831 me = Material::probe(pos);
833 // If we have a specialized evaluation function for the current material
834 // configuration, call it and return.
835 if (me->specialized_eval_exists())
836 return me->evaluate(pos);
838 // Initialize score by reading the incrementally updated scores included in
839 // the position object (material + piece square tables) and the material
840 // imbalance. Score is computed internally from the white point of view.
841 Score score = pos.psq_score() + me->imbalance() + Eval::Contempt;
843 // Probe the pawn hash table
844 pe = Pawns::probe(pos);
845 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
847 // Early exit if score is high
848 Value v = (mg_value(score) + eg_value(score)) / 2;
849 if (abs(v) > LazyThreshold)
850 return pos.side_to_move() == WHITE ? v : -v;
852 // Main evaluation begins here
857 // Pieces should be evaluated first (populate attack tables)
858 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
859 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
860 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
861 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
863 score += mobility[WHITE] - mobility[BLACK];
865 score += king< WHITE>() - king< BLACK>()
866 + threats<WHITE>() - threats<BLACK>()
867 + passed< WHITE>() - passed< BLACK>()
868 + space< WHITE>() - space< BLACK>();
870 score += initiative(eg_value(score));
872 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
873 ScaleFactor sf = scale_factor(eg_value(score));
874 v = mg_value(score) * int(me->game_phase())
875 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
877 v /= int(PHASE_MIDGAME);
879 // In case of tracing add all remaining individual evaluation terms
882 Trace::add(MATERIAL, pos.psq_score());
883 Trace::add(IMBALANCE, me->imbalance());
884 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
885 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
886 Trace::add(TOTAL, score);
889 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
896 /// evaluate() is the evaluator for the outer world. It returns a static
897 /// evaluation of the position from the point of view of the side to move.
899 Value Eval::evaluate(const Position& pos) {
900 return Evaluation<NO_TRACE>(pos).value();
904 /// trace() is like evaluate(), but instead of returning a value, it returns
905 /// a string (suitable for outputting to stdout) that contains the detailed
906 /// descriptions and values of each evaluation term. Useful for debugging.
908 std::string Eval::trace(const Position& pos) {
910 std::memset(scores, 0, sizeof(scores));
912 Eval::Contempt = SCORE_ZERO; // Reset any dynamic contempt
914 Value v = Evaluation<TRACE>(pos).value();
916 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
918 std::stringstream ss;
919 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
920 << " Term | White | Black | Total \n"
921 << " | MG EG | MG EG | MG EG \n"
922 << " ------------+-------------+-------------+------------\n"
923 << " Material | " << Term(MATERIAL)
924 << " Imbalance | " << Term(IMBALANCE)
925 << " Initiative | " << Term(INITIATIVE)
926 << " Pawns | " << Term(PAWN)
927 << " Knights | " << Term(KNIGHT)
928 << " Bishops | " << Term(BISHOP)
929 << " Rooks | " << Term(ROOK)
930 << " Queens | " << Term(QUEEN)
931 << " Mobility | " << Term(MOBILITY)
932 << " King safety | " << Term(KING)
933 << " Threats | " << Term(THREAT)
934 << " Passed | " << Term(PASSED)
935 << " Space | " << Term(SPACE)
936 << " ------------+-------------+-------------+------------\n"
937 << " Total | " << Term(TOTAL);
939 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";