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-2][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] = {
121 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
122 S( 22, 26), S( 29, 29), S( 36, 29) },
123 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
124 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
125 S( 91, 88), S( 98, 97) },
126 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
127 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
128 S( 46,166), S( 48,169), S( 58,171) },
129 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
130 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
131 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
132 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
133 S(106,184), S(109,191), S(113,206), S(116,212) }
136 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
137 // pieces if they can reach an outpost square, bigger if that square is
138 // supported by a pawn. If the minor piece occupies an outpost square
139 // then score is doubled.
140 const Score Outpost[][2] = {
141 { S(22, 6), S(33, 9) }, // Knight
142 { S( 9, 2), S(14, 4) } // Bishop
145 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
146 // friendly pawn on the rook file.
147 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
149 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
150 // which piece type attacks which one. Attacks on lesser pieces which are
151 // pawn-defended are not considered.
152 const Score ThreatByMinor[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
156 const Score ThreatByRook[PIECE_TYPE_NB] = {
157 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
160 // ThreatByKing[on one/on many] contains bonuses for king attacks on
161 // pawns or pieces which are not pawn-defended.
162 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
164 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
165 // We don't use a Score because we process the two components independently.
166 const Value Passed[][RANK_NB] = {
167 { V(5), V( 5), V(31), V(73), V(166), V(252) },
168 { V(7), V(14), V(38), V(73), V(166), V(252) }
171 // PassedFile[File] contains a bonus according to the file of a passed pawn
172 const Score PassedFile[FILE_NB] = {
173 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
174 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
177 // KingProtector[PieceType-2] * "distance to own king" determines a bonus for each piece.
178 const Score KingProtector[] = {S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
180 // Assorted bonuses and penalties used by evaluation
181 const Score MinorBehindPawn = S( 16, 0);
182 const Score BishopPawns = S( 8, 12);
183 const Score RookOnPawn = S( 8, 24);
184 const Score TrappedRook = S( 92, 0);
185 const Score WeakQueen = S( 50, 10);
186 const Score OtherCheck = S( 10, 10);
187 const Score CloseEnemies = S( 7, 0);
188 const Score PawnlessFlank = S( 20, 80);
189 const Score ThreatByHangingPawn = S( 71, 61);
190 const Score ThreatBySafePawn = S(182,175);
191 const Score ThreatByRank = S( 16, 3);
192 const Score Hanging = S( 48, 27);
193 const Score ThreatByPawnPush = S( 38, 22);
194 const Score HinderPassedPawn = S( 7, 0);
196 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
197 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
198 // happen in Chess960 games.
199 const Score TrappedBishopA1H1 = S(50, 50);
204 // KingAttackWeights[PieceType] contains king attack weights by piece type
205 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
207 // Penalties for enemy's safe checks
208 const int QueenCheck = 780;
209 const int RookCheck = 880;
210 const int BishopCheck = 435;
211 const int KnightCheck = 790;
213 // Threshold for lazy and space evaluation
214 const Value LazyThreshold = Value(1500);
215 const Value SpaceThreshold = Value(12222);
217 // eval_init() initializes king and attack bitboards for a given color
218 // adding pawn attacks. To be done at the beginning of the evaluation.
221 void eval_init(const Position& pos, EvalInfo& ei) {
223 const Color Them = (Us == WHITE ? BLACK : WHITE);
224 const Square Up = (Us == WHITE ? NORTH : SOUTH);
225 const Square Down = (Us == WHITE ? SOUTH : NORTH);
226 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
228 // Find our pawns on the first two ranks, and those which are blocked
229 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
231 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
232 // are excluded from the mobility area.
233 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
235 // Initialise the attack bitboards with the king and pawn information
236 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
237 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
239 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
240 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
242 // Init our king safety tables only if we are going to use them
243 if (pos.non_pawn_material(Them) >= QueenValueMg)
245 ei.kingRing[Us] = b | shift<Up>(b);
246 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
247 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
250 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
254 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
257 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
260 const Color Them = (Us == WHITE ? BLACK : WHITE);
261 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
262 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
268 Score score = SCORE_ZERO;
270 ei.attackedBy[Us][Pt] = 0;
272 while ((s = *pl++) != SQ_NONE)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
277 : pos.attacks_from<Pt>(s);
279 if (pos.pinned_pieces(Us) & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
283 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
285 if (b & ei.kingRing[Them])
287 ei.kingAttackersCount[Us]++;
288 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
292 int mob = popcount(b & ei.mobilityArea[Us]);
294 mobility[Us] += MobilityBonus[Pt-2][mob];
296 score += KingProtector[Pt-2] * distance(s, pos.square<KING>(Us));
298 if (Pt == BISHOP || Pt == KNIGHT)
300 // Bonus for outpost squares
301 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
303 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
306 bb &= b & ~pos.pieces(Us);
308 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
311 // Bonus when behind a pawn
312 if ( relative_rank(Us, s) < RANK_5
313 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
314 score += MinorBehindPawn;
316 // Penalty for pawns on the same color square as the bishop
318 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
320 // An important Chess960 pattern: A cornered bishop blocked by a friendly
321 // pawn diagonally in front of it is a very serious problem, especially
322 // when that pawn is also blocked.
325 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
327 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
328 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
329 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
330 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
337 // Bonus for aligning with enemy pawns on the same rank/file
338 if (relative_rank(Us, s) >= RANK_5)
339 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
341 // Bonus when on an open or semi-open file
342 if (ei.pe->semiopen_file(Us, file_of(s)))
343 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
345 // Penalty when trapped by the king, even more if the king cannot castle
348 Square ksq = pos.square<KING>(Us);
350 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
351 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
352 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
358 // Penalty if any relative pin or discovered attack against the queen
360 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
366 Trace::add(Pt, Us, score);
368 // Recursively call evaluate_pieces() of next piece type until KING is excluded
369 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
373 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
375 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
378 // evaluate_king() assigns bonuses and penalties to a king of a given color
380 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
381 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
382 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
384 const Bitboard KingFlank[FILE_NB] = {
385 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
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 = ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]
421 + 102 * ei.kingAdjacentZoneAttacksCount[Them]
422 + 201 * popcount(undefended)
423 + 143 * (popcount(b) + !!pos.pinned_pieces(Us))
424 - 848 * !pos.count<QUEEN>(Them)
425 - 28 * mg_value(score) / 25 - 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(kingDanger * kingDanger / 4096, 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, stronglyProtected, safeThreats;
516 Score score = SCORE_ZERO;
518 // Non-pawn enemies attacked by a pawn
519 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
523 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
524 | ei.attackedBy[Us][ALL_PIECES]);
526 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
528 score += ThreatBySafePawn * popcount(safeThreats);
530 if (weak ^ safeThreats)
531 score += ThreatByHangingPawn;
534 // Squares strongly protected by the opponent, either because they attack the
535 // square with a pawn, or because they attack the square twice and we don't.
536 stronglyProtected = ei.attackedBy[Them][PAWN]
537 | (ei.attackedBy2[Them] & ~ei.attackedBy2[Us]);
539 // Non-pawn enemies, strongly protected
540 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
543 // Enemies not strongly protected and under our attack
544 weak = pos.pieces(Them)
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(Them, PAWN) & forward_bb(Us, s + pawn_push(Us))));
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 // Scale down bonus for candidate passers which need more than one
671 // pawn push to become passed or have a pawn in front of them.
672 if (!pos.pawn_passed(Us, s + pawn_push(Us)) || (pos.pieces(PAWN) & forward_bb(Us, s)))
673 mbonus /= 2, ebonus /= 2;
675 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
679 Trace::add(PASSED, Us, score);
685 // evaluate_space() computes the space evaluation for a given side. The
686 // space evaluation is a simple bonus based on the number of safe squares
687 // available for minor pieces on the central four files on ranks 2--4. Safe
688 // squares one, two or three squares behind a friendly pawn are counted
689 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
690 // improve play on game opening.
692 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
694 const Color Them = (Us == WHITE ? BLACK : WHITE);
695 const Bitboard SpaceMask =
696 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
697 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
699 // Find the safe squares for our pieces inside the area defined by
700 // SpaceMask. A square is unsafe if it is attacked by an enemy
701 // pawn, or if it is undefended and attacked by an enemy piece.
702 Bitboard safe = SpaceMask
703 & ~pos.pieces(Us, PAWN)
704 & ~ei.attackedBy[Them][PAWN]
705 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
707 // Find all squares which are at most three squares behind some friendly pawn
708 Bitboard behind = pos.pieces(Us, PAWN);
709 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
710 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
712 // Since SpaceMask[Us] is fully on our half of the board...
713 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
715 // ...count safe + (behind & safe) with a single popcount.
716 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
717 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
719 return make_score(bonus * weight * weight / 16, 0);
723 // evaluate_initiative() computes the initiative correction value for the
724 // position, i.e., second order bonus/malus based on the known attacking/defending
725 // status of the players.
726 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
728 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
729 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
730 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
732 // Compute the initiative bonus for the attacking side
733 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
735 // Now apply the bonus: note that we find the attacking side by extracting
736 // the sign of the endgame value, and that we carefully cap the bonus so
737 // that the endgame score will never change sign after the bonus.
738 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
740 return make_score(0, value);
744 // evaluate_scale_factor() computes the scale factor for the winning side
745 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
747 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
748 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
750 // If we don't already have an unusual scale factor, check for certain
751 // types of endgames, and use a lower scale for those.
752 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
754 if (pos.opposite_bishops())
756 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
757 // is almost a draw, in case of KBP vs KB, it is even more a draw.
758 if ( pos.non_pawn_material(WHITE) == BishopValueMg
759 && pos.non_pawn_material(BLACK) == BishopValueMg)
760 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
762 // Endgame with opposite-colored bishops, but also other pieces. Still
763 // a bit drawish, but not as drawish as with only the two bishops.
764 return ScaleFactor(46);
766 // Endings where weaker side can place his king in front of the opponent's
767 // pawns are drawish.
768 else if ( abs(eg) <= BishopValueEg
769 && pos.count<PAWN>(strongSide) <= 2
770 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
771 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
780 /// evaluate() is the main evaluation function. It returns a static evaluation
781 /// of the position from the point of view of the side to move.
783 template<bool DoTrace>
784 Value Eval::evaluate(const Position& pos) {
786 assert(!pos.checkers());
788 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
792 // Probe the material hash table
793 ei.me = Material::probe(pos);
795 // If we have a specialized evaluation function for the current material
796 // configuration, call it and return.
797 if (ei.me->specialized_eval_exists())
798 return ei.me->evaluate(pos);
800 // Initialize score by reading the incrementally updated scores included in
801 // the position object (material + piece square tables) and the material
802 // imbalance. Score is computed internally from the white point of view.
803 Score score = pos.psq_score() + ei.me->imbalance();
805 // Probe the pawn hash table
806 ei.pe = Pawns::probe(pos);
807 score += ei.pe->pawns_score();
809 // Early exit if score is high
810 v = (mg_value(score) + eg_value(score)) / 2;
811 if (abs(v) > LazyThreshold)
812 return pos.side_to_move() == WHITE ? v : -v;
814 // Initialize attack and king safety bitboards
815 eval_init<WHITE>(pos, ei);
816 eval_init<BLACK>(pos, ei);
818 // Evaluate all pieces but king and pawns
819 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
820 score += mobility[WHITE] - mobility[BLACK];
822 // Evaluate kings after all other pieces because we need full attack
823 // information when computing the king safety evaluation.
824 score += evaluate_king<WHITE, DoTrace>(pos, ei)
825 - evaluate_king<BLACK, DoTrace>(pos, ei);
827 // Evaluate tactical threats, we need full attack information including king
828 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
829 - evaluate_threats<BLACK, DoTrace>(pos, ei);
831 // Evaluate passed pawns, we need full attack information including king
832 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
833 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
835 // Evaluate space for both sides, only during opening
836 if (pos.non_pawn_material() >= SpaceThreshold)
837 score += evaluate_space<WHITE>(pos, ei)
838 - evaluate_space<BLACK>(pos, ei);
840 // Evaluate position potential for the winning side
841 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
843 // Evaluate scale factor for the winning side
844 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
846 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
847 v = mg_value(score) * int(ei.me->game_phase())
848 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
850 v /= int(PHASE_MIDGAME);
852 // In case of tracing add all remaining individual evaluation terms
855 Trace::add(MATERIAL, pos.psq_score());
856 Trace::add(IMBALANCE, ei.me->imbalance());
857 Trace::add(PAWN, ei.pe->pawns_score());
858 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
859 if (pos.non_pawn_material() >= SpaceThreshold)
860 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
861 , evaluate_space<BLACK>(pos, ei));
862 Trace::add(TOTAL, score);
865 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
868 // Explicit template instantiations
869 template Value Eval::evaluate<true >(const Position&);
870 template Value Eval::evaluate<false>(const Position&);
873 /// trace() is like evaluate(), but instead of returning a value, it returns
874 /// a string (suitable for outputting to stdout) that contains the detailed
875 /// descriptions and values of each evaluation term. Useful for debugging.
877 std::string Eval::trace(const Position& pos) {
879 std::memset(scores, 0, sizeof(scores));
881 Value v = evaluate<true>(pos);
882 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
884 std::stringstream ss;
885 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
886 << " Eval term | White | Black | Total \n"
887 << " | MG EG | MG EG | MG EG \n"
888 << "----------------+-------------+-------------+-------------\n"
889 << " Material | " << Term(MATERIAL)
890 << " Imbalance | " << Term(IMBALANCE)
891 << " Pawns | " << Term(PAWN)
892 << " Knights | " << Term(KNIGHT)
893 << " Bishop | " << Term(BISHOP)
894 << " Rooks | " << Term(ROOK)
895 << " Queens | " << Term(QUEEN)
896 << " Mobility | " << Term(MOBILITY)
897 << " King safety | " << Term(KING)
898 << " Threats | " << Term(THREAT)
899 << " Passed pawns | " << Term(PASSED)
900 << " Space | " << Term(SPACE)
901 << "----------------+-------------+-------------+-------------\n"
902 << " Total | " << Term(TOTAL);
904 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";