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, 78, 56, 45, 11 };
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(3, 65), S(9, 145) };
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(5, 7), S(5, 13), S(32, 42), S(70, 70), S(172, 170), S(217, 269)
152 // PassedFile[File] contains a bonus according to the file of a passed pawn
153 constexpr Score PassedFile[FILE_NB] = {
154 S( 9, 10), S(2, 10), S(1, -8), S(-20,-12),
155 S(-20,-12), S(1, -8), S(2, 10), S( 9, 10)
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(3, 5), S(4, 3), S(3, 0), S(1, -1) };
164 // Assorted bonuses and penalties
165 constexpr Score BishopPawns = S( 8, 12);
166 constexpr Score CloseEnemies = S( 7, 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( 8, 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( 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 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(attackedBy[Us][KING] & 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 Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
298 : Rank5BB | Rank4BB | Rank3BB);
299 const Square* pl = pos.squares<Pt>(Us);
303 Score score = SCORE_ZERO;
305 attackedBy[Us][Pt] = 0;
307 while ((s = *pl++) != SQ_NONE)
309 // Find attacked squares, including x-ray attacks for bishops and rooks
310 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
311 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
312 : pos.attacks_from<Pt>(s);
314 if (pos.blockers_for_king(Us) & s)
315 b &= LineBB[pos.square<KING>(Us)][s];
317 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
318 attackedBy[Us][Pt] |= b;
319 attackedBy[Us][ALL_PIECES] |= b;
321 if (b & kingRing[Them])
323 kingAttackersCount[Us]++;
324 kingAttackersWeight[Us] += KingAttackWeights[Pt];
325 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
328 int mob = popcount(b & mobilityArea[Us]);
330 mobility[Us] += MobilityBonus[Pt - 2][mob];
332 // Penalty if the piece is far from the king
333 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
335 if (Pt == BISHOP || Pt == KNIGHT)
337 // Bonus if piece is on an outpost square or can reach one
338 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
340 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
342 else if (bb &= b & ~pos.pieces(Us))
343 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
345 // Bonus when behind a pawn
346 if ( relative_rank(Us, s) < RANK_5
347 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
348 score += MinorBehindPawn;
352 // Penalty according to number of pawns on the same color square as the bishop
353 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
355 // Bonus for bishop on a long diagonal which can "see" both center squares
356 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
357 score += LongDiagonalBishop;
360 // An important Chess960 pattern: A cornered bishop blocked by a friendly
361 // pawn diagonally in front of it is a very serious problem, especially
362 // when that pawn is also blocked.
365 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
367 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
368 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
369 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
370 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
377 // Bonus for aligning rook with enemy pawns on the same rank/file
378 if (relative_rank(Us, s) >= RANK_5)
379 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
381 // Bonus for rook on an open or semi-open file
382 if (pe->semiopen_file(Us, file_of(s)))
383 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
385 // Penalty when trapped by the king, even more if the king cannot castle
388 File kf = file_of(pos.square<KING>(Us));
389 if ((kf < FILE_E) == (file_of(s) < kf))
390 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
396 // Penalty if any relative pin or discovered attack against the queen
397 Bitboard queenPinners;
398 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
403 Trace::add(Pt, Us, score);
409 // Evaluation::king() assigns bonuses and penalties to a king of a given color
410 template<Tracing T> template<Color Us>
411 Score Evaluation<T>::king() const {
413 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
414 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
415 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
417 const Square ksq = pos.square<KING>(Us);
418 Bitboard weak, b, b1, b2, safe, unsafeChecks, pinned;
420 // King shelter and enemy pawns storm
421 Score score = pe->king_safety<Us>(pos, ksq);
423 // Main king safety evaluation
424 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
429 // Attacked squares defended at most once by our queen or king
430 weak = attackedBy[Them][ALL_PIECES]
432 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
434 // Analyse the safe enemy's checks which are possible on next move
435 safe = ~pos.pieces(Them);
436 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
438 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
439 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
441 // Enemy queen safe checks
442 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
443 kingDanger += QueenSafeCheck;
445 b1 &= attackedBy[Them][ROOK];
446 b2 &= attackedBy[Them][BISHOP];
448 // Enemy rooks checks
450 kingDanger += RookSafeCheck;
454 // Enemy bishops checks
456 kingDanger += BishopSafeCheck;
460 // Enemy knights checks
461 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
463 kingDanger += KnightSafeCheck;
467 // Unsafe or occupied checking squares will also be considered, as long as
468 // the square is in the attacker's mobility area.
469 unsafeChecks &= mobilityArea[Them];
470 pinned = pos.blockers_for_king(Us) & pos.pieces(Us);
472 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
473 + 102 * kingAttacksCount[Them]
474 + 191 * popcount(kingRing[Us] & weak)
475 + 143 * popcount(pinned | unsafeChecks)
476 - 848 * !pos.count<QUEEN>(Them)
477 - 9 * mg_value(score) / 8
480 // Transform the kingDanger units into a Score, and subtract it from the evaluation
483 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
484 kingDanger = std::max(0, kingDanger + mobilityDanger);
485 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
489 Bitboard kf = KingFlank[file_of(ksq)];
491 // Penalty when our king is on a pawnless flank
492 if (!(pos.pieces(PAWN) & kf))
493 score -= PawnlessFlank;
495 // Find the squares that opponent attacks in our king flank, and the squares
496 // which are attacked twice in that flank but not defended by our pawns.
497 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
498 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
500 // King tropism, to anticipate slow motion attacks on our king
501 score -= CloseEnemies * (popcount(b1) + popcount(b2));
504 Trace::add(KING, Us, score);
510 // Evaluation::threats() assigns bonuses according to the types of the
511 // attacking and the attacked pieces.
512 template<Tracing T> template<Color Us>
513 Score Evaluation<T>::threats() const {
515 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
516 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
517 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
519 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
520 Score score = SCORE_ZERO;
523 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
525 // Squares strongly protected by the enemy, either because they defend the
526 // square with a pawn, or because they defend the square twice and we don't.
527 stronglyProtected = attackedBy[Them][PAWN]
528 | (attackedBy2[Them] & ~attackedBy2[Us]);
530 // Non-pawn enemies, strongly protected
531 defended = nonPawnEnemies & stronglyProtected;
533 // Enemies not strongly protected and under our attack
534 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
536 // Bonus according to the kind of attacking pieces
539 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
542 Square s = pop_lsb(&b);
543 score += ThreatByMinor[type_of(pos.piece_on(s))];
544 if (type_of(pos.piece_on(s)) != PAWN)
545 score += ThreatByRank * (int)relative_rank(Them, s);
548 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
551 Square s = pop_lsb(&b);
552 score += ThreatByRook[type_of(pos.piece_on(s))];
553 if (type_of(pos.piece_on(s)) != PAWN)
554 score += ThreatByRank * (int)relative_rank(Them, s);
557 b = weak & attackedBy[Us][KING];
559 score += ThreatByKing[more_than_one(b)];
561 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
563 // Bonus for overload (non-pawn enemies attacked and defended exactly once)
565 & attackedBy[Us][ALL_PIECES] & ~attackedBy2[Us]
566 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
567 score += Overload * popcount(b);
570 // Bonus for enemy unopposed weak pawns
571 if (pos.pieces(Us, ROOK, QUEEN))
572 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
574 // Our safe or protected pawns
575 b = pos.pieces(Us, PAWN)
576 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
578 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
579 score += ThreatBySafePawn * popcount(safeThreats);
581 // Find squares where our pawns can push on the next move
582 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
583 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
585 // Keep only the squares which are not completely unsafe
586 b &= ~attackedBy[Them][PAWN]
587 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
589 // Bonus for safe pawn threats on the next move
590 b = pawn_attacks_bb<Us>(b)
592 & ~attackedBy[Us][PAWN];
594 score += ThreatByPawnPush * popcount(b);
596 // Bonus for threats on the next moves against enemy queen
597 if (pos.count<QUEEN>(Them) == 1)
599 Square s = pos.square<QUEEN>(Them);
600 safeThreats = mobilityArea[Us] & ~stronglyProtected;
602 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
604 score += KnightOnQueen * popcount(b & safeThreats);
606 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
607 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
609 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
612 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
613 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
614 score += Connectivity * popcount(b);
617 Trace::add(THREAT, Us, score);
622 // Evaluation::passed() evaluates the passed pawns and candidate passed
623 // pawns of the given color.
625 template<Tracing T> template<Color Us>
626 Score Evaluation<T>::passed() const {
628 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
629 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
631 auto king_proximity = [&](Color c, Square s) {
632 return std::min(distance(pos.square<KING>(c), s), 5);
635 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
636 Score score = SCORE_ZERO;
638 b = pe->passed_pawns(Us);
642 Square s = pop_lsb(&b);
644 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
646 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
647 score -= HinderPassedPawn * popcount(bb);
649 int r = relative_rank(Us, s);
650 int w = PassedDanger[r];
652 Score bonus = PassedRank[r];
656 Square blockSq = s + Up;
658 // Adjust bonus based on the king's proximity
659 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
660 - king_proximity(Us, blockSq) * 2) * w);
662 // If blockSq is not the queening square then consider also a second push
664 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
666 // If the pawn is free to advance, then increase the bonus
667 if (pos.empty(blockSq))
669 // If there is a rook or queen attacking/defending the pawn from behind,
670 // consider all the squaresToQueen. Otherwise consider only the squares
671 // in the pawn's path attacked or occupied by the enemy.
672 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
674 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
676 if (!(pos.pieces(Us) & bb))
677 defendedSquares &= attackedBy[Us][ALL_PIECES];
679 if (!(pos.pieces(Them) & bb))
680 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
682 // If there aren't any enemy attacks, assign a big bonus. Otherwise
683 // assign a smaller bonus if the block square isn't attacked.
684 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
686 // If the path to the queen is fully defended, assign a big bonus.
687 // Otherwise assign a smaller bonus if the block square is defended.
688 if (defendedSquares == squaresToQueen)
691 else if (defendedSquares & blockSq)
694 bonus += make_score(k * w, k * w);
696 else if (pos.pieces(Us) & blockSq)
697 bonus += make_score(w + r * 2, w + r * 2);
700 // Scale down bonus for candidate passers which need more than one
701 // pawn push to become passed, or have a pawn in front of them.
702 if ( !pos.pawn_passed(Us, s + Up)
703 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
706 score += bonus + PassedFile[file_of(s)];
710 Trace::add(PASSED, Us, score);
716 // Evaluation::space() computes the space evaluation for a given side. The
717 // space evaluation is a simple bonus based on the number of safe squares
718 // available for minor pieces on the central four files on ranks 2--4. Safe
719 // squares one, two or three squares behind a friendly pawn are counted
720 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
721 // improve play on game opening.
723 template<Tracing T> template<Color Us>
724 Score Evaluation<T>::space() const {
726 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
727 constexpr Bitboard SpaceMask =
728 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
729 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
731 if (pos.non_pawn_material() < SpaceThreshold)
734 // Find the available squares for our pieces inside the area defined by SpaceMask
735 Bitboard safe = SpaceMask
736 & ~pos.pieces(Us, PAWN)
737 & ~attackedBy[Them][PAWN];
739 // Find all squares which are at most three squares behind some friendly pawn
740 Bitboard behind = pos.pieces(Us, PAWN);
741 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
742 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
744 int bonus = popcount(safe) + popcount(behind & safe);
745 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
747 Score score = make_score(bonus * weight * weight / 16, 0);
750 Trace::add(SPACE, Us, score);
756 // Evaluation::initiative() computes the initiative correction value
757 // for the position. It is a second order bonus/malus based on the
758 // known attacking/defending status of the players.
761 Score Evaluation<T>::initiative(Value eg) const {
763 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
764 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
766 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
767 && (pos.pieces(PAWN) & KingSide);
769 // Compute the initiative bonus for the attacking side
770 int complexity = 8 * outflanking
771 + 8 * pe->pawn_asymmetry()
772 + 12 * pos.count<PAWN>()
773 + 16 * pawnsOnBothFlanks
774 + 48 * !pos.non_pawn_material()
777 // Now apply the bonus: note that we find the attacking side by extracting
778 // the sign of the endgame value, and that we carefully cap the bonus so
779 // that the endgame score will never change sign after the bonus.
780 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
783 Trace::add(INITIATIVE, make_score(0, v));
785 return make_score(0, v);
789 // Evaluation::scale_factor() computes the scale factor for the winning side
792 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
794 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
795 int sf = me->scale_factor(pos, strongSide);
797 // If we don't already have an unusual scale factor, check for certain
798 // types of endgames, and use a lower scale for those.
799 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
801 if (pos.opposite_bishops())
803 // Endgame with opposite-colored bishops and no other pieces is almost a draw
804 if ( pos.non_pawn_material(WHITE) == BishopValueMg
805 && pos.non_pawn_material(BLACK) == BishopValueMg)
808 // Endgame with opposite-colored bishops, but also other pieces. Still
809 // a bit drawish, but not as drawish as with only the two bishops.
813 // Endings where weaker side can place his king in front of the enemy's
814 // pawns are drawish.
815 else if ( abs(eg) <= BishopValueEg
816 && pos.count<PAWN>(strongSide) <= 2
817 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
818 sf = 37 + 7 * pos.count<PAWN>(strongSide);
821 return ScaleFactor(sf);
825 // Evaluation::value() is the main function of the class. It computes the various
826 // parts of the evaluation and returns the value of the position from the point
827 // of view of the side to move.
830 Value Evaluation<T>::value() {
832 assert(!pos.checkers());
834 // Probe the material hash table
835 me = Material::probe(pos);
837 // If we have a specialized evaluation function for the current material
838 // configuration, call it and return.
839 if (me->specialized_eval_exists())
840 return me->evaluate(pos);
842 // Initialize score by reading the incrementally updated scores included in
843 // the position object (material + piece square tables) and the material
844 // imbalance. Score is computed internally from the white point of view.
845 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
847 // Probe the pawn hash table
848 pe = Pawns::probe(pos);
849 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
851 // Early exit if score is high
852 Value v = (mg_value(score) + eg_value(score)) / 2;
853 if (abs(v) > LazyThreshold)
854 return pos.side_to_move() == WHITE ? v : -v;
856 // Main evaluation begins here
861 // Pieces should be evaluated first (populate attack tables)
862 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
863 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
864 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
865 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
867 score += mobility[WHITE] - mobility[BLACK];
869 score += king< WHITE>() - king< BLACK>()
870 + threats<WHITE>() - threats<BLACK>()
871 + passed< WHITE>() - passed< BLACK>()
872 + space< WHITE>() - space< BLACK>();
874 score += initiative(eg_value(score));
876 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
877 ScaleFactor sf = scale_factor(eg_value(score));
878 v = mg_value(score) * int(me->game_phase())
879 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
881 v /= int(PHASE_MIDGAME);
883 // In case of tracing add all remaining individual evaluation terms
886 Trace::add(MATERIAL, pos.psq_score());
887 Trace::add(IMBALANCE, me->imbalance());
888 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
889 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
890 Trace::add(TOTAL, score);
893 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
900 /// evaluate() is the evaluator for the outer world. It returns a static
901 /// evaluation of the position from the point of view of the side to move.
903 Value Eval::evaluate(const Position& pos) {
904 return Evaluation<NO_TRACE>(pos).value();
908 /// trace() is like evaluate(), but instead of returning a value, it returns
909 /// a string (suitable for outputting to stdout) that contains the detailed
910 /// descriptions and values of each evaluation term. Useful for debugging.
912 std::string Eval::trace(const Position& pos) {
914 std::memset(scores, 0, sizeof(scores));
916 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
918 Value v = Evaluation<TRACE>(pos).value();
920 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
922 std::stringstream ss;
923 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
924 << " Term | White | Black | Total \n"
925 << " | MG EG | MG EG | MG EG \n"
926 << " ------------+-------------+-------------+------------\n"
927 << " Material | " << Term(MATERIAL)
928 << " Imbalance | " << Term(IMBALANCE)
929 << " Initiative | " << Term(INITIATIVE)
930 << " Pawns | " << Term(PAWN)
931 << " Knights | " << Term(KNIGHT)
932 << " Bishops | " << Term(BISHOP)
933 << " Rooks | " << Term(ROOK)
934 << " Queens | " << Term(QUEEN)
935 << " Mobility | " << Term(MOBILITY)
936 << " King safety | " << Term(KING)
937 << " Threats | " << Term(THREAT)
938 << " Passed | " << Term(PASSED)
939 << " Space | " << Term(SPACE)
940 << " ------------+-------------+-------------+------------\n"
941 << " Total | " << Term(TOTAL);
943 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";