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) 2015-2017 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
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
78 Bitboard mobilityArea[COLOR_NB];
80 // attackedBy[color][piece type] is a bitboard representing all squares
81 // attacked by a given color and piece type (can be also ALL_PIECES).
82 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
84 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
85 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
86 // pawn or squares attacked by 2 pawns are not explicitly added.
87 Bitboard attackedBy2[COLOR_NB];
89 // kingRing[color] is the zone around the king which is considered
90 // by the king safety evaluation. This consists of the squares directly
91 // adjacent to the king, and the three (or two, for a king on an edge file)
92 // squares two ranks in front of the king. For instance, if black's king
93 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
94 // f7, g7, h7, f6, g6 and h6.
95 Bitboard kingRing[COLOR_NB];
97 // kingAttackersCount[color] is the number of pieces of the given color
98 // which attack a square in the kingRing of the enemy king.
99 int kingAttackersCount[COLOR_NB];
101 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
102 // given color which attack a square in the kingRing of the enemy king. The
103 // weights of the individual piece types are given by the elements in the
104 // KingAttackWeights array.
105 int kingAttackersWeight[COLOR_NB];
107 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
108 // color to squares directly adjacent to the enemy king. Pieces which attack
109 // more than one square are counted multiple times. For instance, if there is
110 // a white knight on g5 and black's king is on g8, this white knight adds 2
111 // to kingAdjacentZoneAttacksCount[WHITE].
112 int kingAdjacentZoneAttacksCount[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end game,
119 // indexed by piece type and number of attacked squares in the mobility area.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
138 // pieces if they can reach an outpost square, bigger if that square is
139 // supported by a pawn. If the minor piece occupies an outpost square
140 // then score is doubled.
141 const Score Outpost[][2] = {
142 { S(22, 6), S(33, 9) }, // Knight
143 { S( 9, 2), S(14, 4) } // Bishop
146 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
147 // friendly pawn on the rook file.
148 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
150 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
151 // type is attacked by a pawn which is protected or is not attacked.
152 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
156 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
157 // which piece type attacks which one. Attacks on lesser pieces which are
158 // pawn-defended are not considered.
159 const Score ThreatByMinor[PIECE_TYPE_NB] = {
160 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
163 const Score ThreatByRook[PIECE_TYPE_NB] = {
164 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
167 // ThreatByKing[on one/on many] contains bonuses for king attacks on
168 // pawns or pieces which are not pawn-defended.
169 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
171 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
172 // We don't use a Score because we process the two components independently.
173 const Value Passed[][RANK_NB] = {
174 { V(5), V( 5), V(31), V(73), V(166), V(252) },
175 { V(7), V(14), V(38), V(73), V(166), V(252) }
178 // PassedFile[File] contains a bonus according to the file of a passed pawn
179 const Score PassedFile[FILE_NB] = {
180 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
181 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
184 // Assorted bonuses and penalties used by evaluation
185 const Score MinorBehindPawn = S(16, 0);
186 const Score BishopPawns = S( 8, 12);
187 const Score RookOnPawn = S( 8, 24);
188 const Score TrappedRook = S(92, 0);
189 const Score WeakQueen = S(50, 10);
190 const Score OtherCheck = S(10, 10);
191 const Score CloseEnemies = S( 7, 0);
192 const Score PawnlessFlank = S(20, 80);
193 const Score LooseEnemies = S( 0, 25);
194 const Score ThreatByHangingPawn = S(71, 61);
195 const Score ThreatByRank = S(16, 3);
196 const Score Hanging = S(48, 27);
197 const Score ThreatByPawnPush = S(38, 22);
198 const Score HinderPassedPawn = S( 7, 0);
200 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
201 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
202 // happen in Chess960 games.
203 const Score TrappedBishopA1H1 = S(50, 50);
208 // KingAttackWeights[PieceType] contains king attack weights by piece type
209 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
211 // Penalties for enemy's safe checks
212 const int QueenCheck = 745;
213 const int RookCheck = 688;
214 const int BishopCheck = 588;
215 const int KnightCheck = 924;
217 // Threshold for lazy evaluation
218 const Value LazyThreshold = Value(1500);
220 // eval_init() initializes king and attack bitboards for a given color
221 // adding pawn attacks. To be done at the beginning of the evaluation.
224 void eval_init(const Position& pos, EvalInfo& ei) {
226 const Color Them = (Us == WHITE ? BLACK : WHITE);
227 const Square Up = (Us == WHITE ? NORTH : SOUTH);
228 const Square Down = (Us == WHITE ? SOUTH : NORTH);
229 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
231 // Find our pawns on the first two ranks, and those which are blocked
232 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
234 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
235 // are excluded from the mobility area.
236 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
238 // Initialise the attack bitboards with the king and pawn information
239 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
240 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
242 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
243 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
245 // Init our king safety tables only if we are going to use them
246 if (pos.non_pawn_material(Them) >= QueenValueMg)
248 ei.kingRing[Us] = b | shift<Up>(b);
249 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
250 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
253 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
257 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
260 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
261 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
263 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
264 const Color Them = (Us == WHITE ? BLACK : WHITE);
265 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
266 : Rank5BB | Rank4BB | Rank3BB);
267 const Square* pl = pos.squares<Pt>(Us);
271 Score score = SCORE_ZERO;
273 ei.attackedBy[Us][Pt] = 0;
275 while ((s = *pl++) != SQ_NONE)
277 // Find attacked squares, including x-ray attacks for bishops and rooks
278 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
279 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
280 : pos.attacks_from<Pt>(s);
282 if (pos.pinned_pieces(Us) & s)
283 b &= LineBB[pos.square<KING>(Us)][s];
285 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
286 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
288 if (b & ei.kingRing[Them])
290 ei.kingAttackersCount[Us]++;
291 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
292 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
295 int mob = popcount(b & ei.mobilityArea[Us]);
297 mobility[Us] += MobilityBonus[Pt][mob];
299 if (Pt == BISHOP || Pt == KNIGHT)
301 // Bonus for outpost squares
302 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
304 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
307 bb &= b & ~pos.pieces(Us);
309 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
312 // Bonus when behind a pawn
313 if ( relative_rank(Us, s) < RANK_5
314 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
315 score += MinorBehindPawn;
317 // Penalty for pawns on the same color square as the bishop
319 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
321 // An important Chess960 pattern: A cornered bishop blocked by a friendly
322 // pawn diagonally in front of it is a very serious problem, especially
323 // when that pawn is also blocked.
326 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
328 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
329 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
330 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
331 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
338 // Bonus for aligning with enemy pawns on the same rank/file
339 if (relative_rank(Us, s) >= RANK_5)
340 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
342 // Bonus when on an open or semi-open file
343 if (ei.pe->semiopen_file(Us, file_of(s)))
344 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
346 // Penalty when trapped by the king, even more if the king cannot castle
349 Square ksq = pos.square<KING>(Us);
351 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
352 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
353 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
359 // Penalty if any relative pin or discovered attack against the queen
361 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
367 Trace::add(Pt, Us, score);
369 // Recursively call evaluate_pieces() of next piece type until KING is excluded
370 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
374 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
376 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
379 // evaluate_king() assigns bonuses and penalties to a king of a given color
381 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
383 const Bitboard KingFlank[FILE_NB] = {
384 CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
385 CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
388 template<Color Us, bool DoTrace>
389 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
391 const Color Them = (Us == WHITE ? BLACK : WHITE);
392 const Square Up = (Us == WHITE ? NORTH : SOUTH);
393 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
394 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
396 const Square ksq = pos.square<KING>(Us);
397 Bitboard undefended, b, b1, b2, safe, other;
400 // King shelter and enemy pawns storm
401 Score score = ei.pe->king_safety<Us>(pos, ksq);
403 // Main king safety evaluation
404 if (ei.kingAttackersCount[Them])
406 // Find the attacked squares which are defended only by our king...
407 undefended = ei.attackedBy[Them][ALL_PIECES]
408 & ei.attackedBy[Us][KING]
409 & ~ei.attackedBy2[Us];
411 // ... and those which are not defended at all in the larger king ring
412 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
413 & ei.kingRing[Us] & ~pos.pieces(Them);
415 // Initialize the 'kingDanger' variable, which will be transformed
416 // later into a king danger score. The initial value is based on the
417 // number and types of the enemy's attacking pieces, the number of
418 // attacked and undefended squares around our king and the quality of
419 // the pawn shelter (current 'score' value).
420 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
421 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
422 + 235 * popcount(undefended)
423 + 134 * (popcount(b) + !!pos.pinned_pieces(Us))
424 - 717 * !pos.count<QUEEN>(Them)
425 - 7 * mg_value(score) / 5 - 5;
427 // Analyse the safe enemy's checks which are possible on next move
428 safe = ~pos.pieces(Them);
429 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
431 b1 = pos.attacks_from<ROOK >(ksq);
432 b2 = pos.attacks_from<BISHOP>(ksq);
434 // Enemy queen safe checks
435 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
436 kingDanger += QueenCheck;
438 // For minors and rooks, also consider the square safe if attacked twice,
439 // and only defended by our queen.
440 safe |= ei.attackedBy2[Them]
441 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
442 & ei.attackedBy[Us][QUEEN];
444 // Some other potential checks are also analysed, even from squares
445 // currently occupied by the opponent own pieces, as long as the square
446 // is not attacked by our pawns, and is not occupied by a blocked pawn.
447 other = ~( ei.attackedBy[Us][PAWN]
448 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
450 // Enemy rooks safe and other checks
451 if (b1 & ei.attackedBy[Them][ROOK] & safe)
452 kingDanger += RookCheck;
454 else if (b1 & ei.attackedBy[Them][ROOK] & other)
457 // Enemy bishops safe and other checks
458 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
459 kingDanger += BishopCheck;
461 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
464 // Enemy knights safe and other checks
465 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
467 kingDanger += KnightCheck;
472 // Transform the kingDanger units into a Score, and substract it from the evaluation
474 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
477 // King tropism: firstly, find squares that opponent attacks in our king flank
478 File kf = file_of(ksq);
479 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
481 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
482 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
484 // Secondly, add the squares which are attacked twice in that flank and
485 // which are not defended by our pawns.
486 b = (Us == WHITE ? b << 4 : b >> 4)
487 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
489 score -= CloseEnemies * popcount(b);
491 // Penalty when our king is on a pawnless flank
492 if (!(pos.pieces(PAWN) & KingFlank[kf]))
493 score -= PawnlessFlank;
496 Trace::add(KING, Us, score);
502 // evaluate_threats() assigns bonuses according to the types of the attacking
503 // and the attacked pieces.
505 template<Color Us, bool DoTrace>
506 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
508 const Color Them = (Us == WHITE ? BLACK : WHITE);
509 const Square Up = (Us == WHITE ? NORTH : SOUTH);
510 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
511 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
512 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
513 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
515 Bitboard b, weak, defended, safeThreats;
516 Score score = SCORE_ZERO;
518 // Small bonus if the opponent has loose pawns or pieces
519 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
520 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
521 score += LooseEnemies;
523 // Non-pawn enemies attacked by a pawn
524 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
528 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
529 | ei.attackedBy[Us][ALL_PIECES]);
531 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
533 if (weak ^ safeThreats)
534 score += ThreatByHangingPawn;
537 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
540 // Non-pawn enemies defended by a pawn
541 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
543 // Enemies not defended by a pawn and under our attack
544 weak = pos.pieces(Them)
545 & ~ei.attackedBy[Them][PAWN]
546 & ei.attackedBy[Us][ALL_PIECES];
548 // Add a bonus according to the kind of attacking pieces
551 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
554 Square s = pop_lsb(&b);
555 score += ThreatByMinor[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 = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
563 Square s = pop_lsb(&b);
564 score += ThreatByRook[type_of(pos.piece_on(s))];
565 if (type_of(pos.piece_on(s)) != PAWN)
566 score += ThreatByRank * (int)relative_rank(Them, s);
569 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
571 b = weak & ei.attackedBy[Us][KING];
573 score += ThreatByKing[more_than_one(b)];
576 // Bonus if some pawns can safely push and attack an enemy piece
577 b = pos.pieces(Us, PAWN) & ~TRank7BB;
578 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
581 & ~ei.attackedBy[Them][PAWN]
582 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
584 b = (shift<Left>(b) | shift<Right>(b))
586 & ~ei.attackedBy[Us][PAWN];
588 score += ThreatByPawnPush * popcount(b);
591 Trace::add(THREAT, Us, score);
597 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
598 // pawns of the given color.
600 template<Color Us, bool DoTrace>
601 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
603 const Color Them = (Us == WHITE ? BLACK : WHITE);
605 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
606 Score score = SCORE_ZERO;
608 b = ei.pe->passed_pawns(Us);
612 Square s = pop_lsb(&b);
614 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
616 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
617 score -= HinderPassedPawn * popcount(bb);
619 int r = relative_rank(Us, s) - RANK_2;
620 int rr = r * (r - 1);
622 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
626 Square blockSq = s + pawn_push(Us);
628 // Adjust bonus based on the king's proximity
629 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
630 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
632 // If blockSq is not the queening square then consider also a second push
633 if (relative_rank(Us, blockSq) != RANK_8)
634 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
636 // If the pawn is free to advance, then increase the bonus
637 if (pos.empty(blockSq))
639 // If there is a rook or queen attacking/defending the pawn from behind,
640 // consider all the squaresToQueen. Otherwise consider only the squares
641 // in the pawn's path attacked or occupied by the enemy.
642 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
644 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
646 if (!(pos.pieces(Us) & bb))
647 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
649 if (!(pos.pieces(Them) & bb))
650 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
652 // If there aren't any enemy attacks, assign a big bonus. Otherwise
653 // assign a smaller bonus if the block square isn't attacked.
654 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
656 // If the path to the queen is fully defended, assign a big bonus.
657 // Otherwise assign a smaller bonus if the block square is defended.
658 if (defendedSquares == squaresToQueen)
661 else if (defendedSquares & blockSq)
664 mbonus += k * rr, ebonus += k * rr;
666 else if (pos.pieces(Us) & blockSq)
667 mbonus += rr + r * 2, ebonus += rr + r * 2;
670 // Assign a small bonus when the opponent has no pieces left
671 if (!pos.non_pawn_material(Them))
674 // Scale down bonus for candidate passers which need more than one pawn
675 // push to become passed.
676 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
677 mbonus /= 2, ebonus /= 2;
679 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
683 Trace::add(PASSED, Us, score);
685 // Add the scores to the middlegame and endgame eval
690 // evaluate_space() computes the space evaluation for a given side. The
691 // space evaluation is a simple bonus based on the number of safe squares
692 // available for minor pieces on the central four files on ranks 2--4. Safe
693 // squares one, two or three squares behind a friendly pawn are counted
694 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
695 // improve play on game opening.
697 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
699 const Color Them = (Us == WHITE ? BLACK : WHITE);
700 const Bitboard SpaceMask =
701 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
702 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
704 // Find the safe squares for our pieces inside the area defined by
705 // SpaceMask. A square is unsafe if it is attacked by an enemy
706 // pawn, or if it is undefended and attacked by an enemy piece.
707 Bitboard safe = SpaceMask
708 & ~pos.pieces(Us, PAWN)
709 & ~ei.attackedBy[Them][PAWN]
710 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
712 // Find all squares which are at most three squares behind some friendly pawn
713 Bitboard behind = pos.pieces(Us, PAWN);
714 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
715 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
717 // Since SpaceMask[Us] is fully on our half of the board...
718 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
720 // ...count safe + (behind & safe) with a single popcount.
721 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
722 bonus = std::min(16, bonus);
723 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
725 return make_score(bonus * weight * weight / 18, 0);
729 // evaluate_initiative() computes the initiative correction value for the
730 // position, i.e., second order bonus/malus based on the known attacking/defending
731 // status of the players.
732 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
734 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
735 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
736 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
738 // Compute the initiative bonus for the attacking side
739 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
741 // Now apply the bonus: note that we find the attacking side by extracting
742 // the sign of the endgame value, and that we carefully cap the bonus so
743 // that the endgame score will never be divided by more than two.
744 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
746 return make_score(0, value);
750 // evaluate_scale_factor() computes the scale factor for the winning side
751 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
753 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
754 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
756 // If we don't already have an unusual scale factor, check for certain
757 // types of endgames, and use a lower scale for those.
758 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
760 if (pos.opposite_bishops())
762 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
763 // is almost a draw, in case of KBP vs KB, it is even more a draw.
764 if ( pos.non_pawn_material(WHITE) == BishopValueMg
765 && pos.non_pawn_material(BLACK) == BishopValueMg)
766 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
768 // Endgame with opposite-colored bishops, but also other pieces. Still
769 // a bit drawish, but not as drawish as with only the two bishops.
770 return ScaleFactor(46);
772 // Endings where weaker side can place his king in front of the opponent's
773 // pawns are drawish.
774 else if ( abs(eg) <= BishopValueEg
775 && pos.count<PAWN>(strongSide) <= 2
776 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
777 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
786 /// evaluate() is the main evaluation function. It returns a static evaluation
787 /// of the position from the point of view of the side to move.
789 template<bool DoTrace>
790 Value Eval::evaluate(const Position& pos) {
792 assert(!pos.checkers());
794 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
798 // Probe the material hash table
799 ei.me = Material::probe(pos);
801 // If we have a specialized evaluation function for the current material
802 // configuration, call it and return.
803 if (ei.me->specialized_eval_exists())
804 return ei.me->evaluate(pos);
806 // Initialize score by reading the incrementally updated scores included in
807 // the position object (material + piece square tables) and the material
808 // imbalance. Score is computed internally from the white point of view.
809 Score score = pos.psq_score() + ei.me->imbalance();
811 // Probe the pawn hash table
812 ei.pe = Pawns::probe(pos);
813 score += ei.pe->pawns_score();
815 // Early exit if score is high
816 v = (mg_value(score) + eg_value(score)) / 2;
817 if (abs(v) > LazyThreshold)
818 return pos.side_to_move() == WHITE ? v : -v;
820 // Initialize attack and king safety bitboards
821 eval_init<WHITE>(pos, ei);
822 eval_init<BLACK>(pos, ei);
824 // Evaluate all pieces but king and pawns
825 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
826 score += mobility[WHITE] - mobility[BLACK];
828 // Evaluate kings after all other pieces because we need full attack
829 // information when computing the king safety evaluation.
830 score += evaluate_king<WHITE, DoTrace>(pos, ei)
831 - evaluate_king<BLACK, DoTrace>(pos, ei);
833 // Evaluate tactical threats, we need full attack information including king
834 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
835 - evaluate_threats<BLACK, DoTrace>(pos, ei);
837 // Evaluate passed pawns, we need full attack information including king
838 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
839 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
841 // Evaluate space for both sides, only during opening
842 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
843 score += evaluate_space<WHITE>(pos, ei)
844 - evaluate_space<BLACK>(pos, ei);
846 // Evaluate position potential for the winning side
847 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
849 // Evaluate scale factor for the winning side
850 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
852 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
853 v = mg_value(score) * int(ei.me->game_phase())
854 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
856 v /= int(PHASE_MIDGAME);
858 // In case of tracing add all remaining individual evaluation terms
861 Trace::add(MATERIAL, pos.psq_score());
862 Trace::add(IMBALANCE, ei.me->imbalance());
863 Trace::add(PAWN, ei.pe->pawns_score());
864 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
865 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
866 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
867 , evaluate_space<BLACK>(pos, ei));
868 Trace::add(TOTAL, score);
871 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
874 // Explicit template instantiations
875 template Value Eval::evaluate<true >(const Position&);
876 template Value Eval::evaluate<false>(const Position&);
879 /// trace() is like evaluate(), but instead of returning a value, it returns
880 /// a string (suitable for outputting to stdout) that contains the detailed
881 /// descriptions and values of each evaluation term. Useful for debugging.
883 std::string Eval::trace(const Position& pos) {
885 std::memset(scores, 0, sizeof(scores));
887 Value v = evaluate<true>(pos);
888 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
890 std::stringstream ss;
891 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
892 << " Eval term | White | Black | Total \n"
893 << " | MG EG | MG EG | MG EG \n"
894 << "----------------+-------------+-------------+-------------\n"
895 << " Material | " << Term(MATERIAL)
896 << " Imbalance | " << Term(IMBALANCE)
897 << " Pawns | " << Term(PAWN)
898 << " Knights | " << Term(KNIGHT)
899 << " Bishop | " << Term(BISHOP)
900 << " Rooks | " << Term(ROOK)
901 << " Queens | " << Term(QUEEN)
902 << " Mobility | " << Term(MOBILITY)
903 << " King safety | " << Term(KING)
904 << " Threats | " << Term(THREAT)
905 << " Passed pawns | " << Term(PASSED)
906 << " Space | " << Term(SPACE)
907 << "----------------+-------------+-------------+-------------\n"
908 << " Total | " << Term(TOTAL);
910 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";