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) 2015-2016 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.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[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
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
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 knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
162 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
163 // which piece type attacks which one. Attacks on lesser pieces which are
164 // pawn-defended are not considered.
165 const Score ThreatByMinor[PIECE_TYPE_NB] = {
166 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
169 const Score ThreatByRook[PIECE_TYPE_NB] = {
170 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
173 // ThreatByKing[on one/on many] contains bonuses for king attacks on
174 // pawns or pieces which are not pawn-defended.
175 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
177 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
178 // We don't use a Score because we process the two components independently.
179 const Value Passed[][RANK_NB] = {
180 { V(5), V( 5), V(31), V(73), V(166), V(252) },
181 { V(7), V(14), V(38), V(73), V(166), V(252) }
184 // PassedFile[File] contains a bonus according to the file of a passed pawn
185 const Score PassedFile[FILE_NB] = {
186 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
187 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
190 // Assorted bonuses and penalties used by evaluation
191 const Score MinorBehindPawn = S(16, 0);
192 const Score BishopPawns = S( 8, 12);
193 const Score RookOnPawn = S( 8, 24);
194 const Score TrappedRook = S(92, 0);
195 const Score WeakQueen = S(50, 10);
196 const Score OtherCheck = S(10, 10);
197 const Score CloseEnemies = S( 7, 0);
198 const Score PawnlessFlank = S(20, 80);
199 const Score LooseEnemies = S( 0, 25);
200 const Score ThreatByHangingPawn = S(71, 61);
201 const Score ThreatByRank = S(16, 3);
202 const Score Hanging = S(48, 27);
203 const Score ThreatByPawnPush = S(38, 22);
204 const Score HinderPassedPawn = S( 7, 0);
206 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
207 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
208 // happen in Chess960 games.
209 const Score TrappedBishopA1H1 = S(50, 50);
214 // KingAttackWeights[PieceType] contains king attack weights by piece type
215 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
217 // Penalties for enemy's safe checks
218 const int QueenContactCheck = 997;
219 const int QueenCheck = 745;
220 const int RookCheck = 688;
221 const int BishopCheck = 588;
222 const int KnightCheck = 924;
225 // eval_init() initializes king and attack bitboards for a given color
226 // adding pawn attacks. To be done at the beginning of the evaluation.
229 void eval_init(const Position& pos, EvalInfo& ei) {
231 const Color Them = (Us == WHITE ? BLACK : WHITE);
232 const Square Down = (Us == WHITE ? SOUTH : NORTH);
234 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
235 Bitboard b = ei.attackedBy[Them][KING];
236 ei.attackedBy[Them][ALL_PIECES] |= b;
237 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
238 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
240 // Init king safety tables only if we are going to use them
241 if (pos.non_pawn_material(Us) >= QueenValueMg)
243 ei.kingRing[Them] = b | shift<Down>(b);
244 ei.kingAttackersCount[Us] = popcount(b & ei.attackedBy[Us][PAWN]);
245 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
248 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
252 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
255 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
256 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
257 const Bitboard* mobilityArea) {
258 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
259 const Color Them = (Us == WHITE ? BLACK : WHITE);
260 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
261 : Rank5BB | Rank4BB | Rank3BB);
262 const Square* pl = pos.squares<Pt>(Us);
266 Score score = SCORE_ZERO;
268 ei.attackedBy[Us][Pt] = 0;
270 while ((s = *pl++) != SQ_NONE)
272 // Find attacked squares, including x-ray attacks for bishops and rooks
273 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
274 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
275 : pos.attacks_from<Pt>(s);
277 if (ei.pinnedPieces[Us] & s)
278 b &= LineBB[pos.square<KING>(Us)][s];
280 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
281 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
283 if (b & ei.kingRing[Them])
285 ei.kingAttackersCount[Us]++;
286 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
287 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
291 b &= ~( ei.attackedBy[Them][KNIGHT]
292 | ei.attackedBy[Them][BISHOP]
293 | ei.attackedBy[Them][ROOK]);
295 int mob = popcount(b & mobilityArea[Us]);
297 mobility[Us] += MobilityBonus[Pt][mob];
299 if (Pt == BISHOP || Pt == KNIGHT)
301 // Bonus for outpost squares
302 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
304 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
307 bb &= b & ~pos.pieces(Us);
309 score += ReachableOutpost[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.pi->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.pi->semiopen_file(Us, file_of(s)))
344 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
346 // Penalize 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.pi->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, mobilityArea);
374 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
376 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { 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.pi->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 the 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) + !!ei.pinnedPieces[Us])
424 - 717 * !pos.count<QUEEN>(Them)
425 - 7 * mg_value(score) / 5 - 5;
427 // Analyse the enemy's safe queen contact checks. Firstly, find the
428 // undefended squares around the king reachable by the enemy queen...
429 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
431 // ...and keep squares supported by another enemy piece
432 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
434 // Analyse the safe enemy's checks which are possible on next move...
435 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
437 // ... and some other potential checks, only requiring the square to be
438 // safe from pawn-attacks, and not being occupied by a blocked pawn.
439 other = ~( ei.attackedBy[Us][PAWN]
440 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
442 b1 = pos.attacks_from<ROOK >(ksq);
443 b2 = pos.attacks_from<BISHOP>(ksq);
445 // Enemy queen safe checks
446 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
447 kingDanger += QueenCheck;
449 // For other pieces, also consider the square safe if attacked twice,
450 // and only defended by a queen.
451 safe |= ei.attackedBy2[Them]
452 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
453 & ei.attackedBy[Us][QUEEN];
455 // Enemy rooks safe and other checks
456 if (b1 & ei.attackedBy[Them][ROOK] & safe)
457 kingDanger += RookCheck;
459 else if (b1 & ei.attackedBy[Them][ROOK] & other)
462 // Enemy bishops safe and other checks
463 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
464 kingDanger += BishopCheck;
466 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
469 // Enemy knights safe and other checks
470 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
472 kingDanger += KnightCheck;
477 // Compute the king danger score and subtract it from the evaluation
479 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
482 // King tropism: firstly, find squares that opponent attacks in our king flank
483 File kf = file_of(ksq);
484 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
486 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
487 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
489 // Secondly, add the squares which are attacked twice in that flank and
490 // which are not defended by our pawns.
491 b = (Us == WHITE ? b << 4 : b >> 4)
492 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
494 score -= CloseEnemies * popcount(b);
496 // Penalty when our king is on a pawnless flank
497 if (!(pos.pieces(PAWN) & KingFlank[kf]))
498 score -= PawnlessFlank;
501 Trace::add(KING, Us, score);
507 // evaluate_threats() assigns bonuses according to the types of the attacking
508 // and the attacked pieces.
510 template<Color Us, bool DoTrace>
511 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
513 const Color Them = (Us == WHITE ? BLACK : WHITE);
514 const Square Up = (Us == WHITE ? NORTH : SOUTH);
515 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
516 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
517 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
518 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
520 Bitboard b, weak, defended, safeThreats;
521 Score score = SCORE_ZERO;
523 // Small bonus if the opponent has loose pawns or pieces
524 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
525 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
526 score += LooseEnemies;
528 // Non-pawn enemies attacked by a pawn
529 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
533 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
534 | ei.attackedBy[Us][ALL_PIECES]);
536 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
538 if (weak ^ safeThreats)
539 score += ThreatByHangingPawn;
542 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
545 // Non-pawn enemies defended by a pawn
546 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
548 // Enemies not defended by a pawn and under our attack
549 weak = pos.pieces(Them)
550 & ~ei.attackedBy[Them][PAWN]
551 & ei.attackedBy[Us][ALL_PIECES];
553 // Add a bonus according to the kind of attacking pieces
556 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
559 Square s = pop_lsb(&b);
560 score += ThreatByMinor[type_of(pos.piece_on(s))];
561 if (type_of(pos.piece_on(s)) != PAWN)
562 score += ThreatByRank * (int)relative_rank(Them, s);
565 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
568 Square s = pop_lsb(&b);
569 score += ThreatByRook[type_of(pos.piece_on(s))];
570 if (type_of(pos.piece_on(s)) != PAWN)
571 score += ThreatByRank * (int)relative_rank(Them, s);
574 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
576 b = weak & ei.attackedBy[Us][KING];
578 score += ThreatByKing[more_than_one(b)];
581 // Bonus if some pawns can safely push and attack an enemy piece
582 b = pos.pieces(Us, PAWN) & ~TRank7BB;
583 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
586 & ~ei.attackedBy[Them][PAWN]
587 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
589 b = (shift<Left>(b) | shift<Right>(b))
591 & ~ei.attackedBy[Us][PAWN];
593 score += ThreatByPawnPush * popcount(b);
596 Trace::add(THREAT, Us, score);
602 // evaluate_passed_pawns() evaluates the passed pawns of the given color
604 template<Color Us, bool DoTrace>
605 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
607 const Color Them = (Us == WHITE ? BLACK : WHITE);
609 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
610 Score score = SCORE_ZERO;
612 b = ei.pi->passed_pawns(Us);
616 Square s = pop_lsb(&b);
618 assert(pos.pawn_passed(Us, s));
619 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
621 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
622 score -= HinderPassedPawn * popcount(bb);
624 int r = relative_rank(Us, s) - RANK_2;
625 int rr = r * (r - 1);
627 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
631 Square blockSq = s + pawn_push(Us);
633 // Adjust bonus based on the king's proximity
634 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
635 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
637 // If blockSq is not the queening square then consider also a second push
638 if (relative_rank(Us, blockSq) != RANK_8)
639 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
641 // If the pawn is free to advance, then increase the bonus
642 if (pos.empty(blockSq))
644 // If there is a rook or queen attacking/defending the pawn from behind,
645 // consider all the squaresToQueen. Otherwise consider only the squares
646 // in the pawn's path attacked or occupied by the enemy.
647 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
649 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
651 if (!(pos.pieces(Us) & bb))
652 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
654 if (!(pos.pieces(Them) & bb))
655 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
657 // If there aren't any enemy attacks, assign a big bonus. Otherwise
658 // assign a smaller bonus if the block square isn't attacked.
659 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
661 // If the path to the queen is fully defended, assign a big bonus.
662 // Otherwise assign a smaller bonus if the block square is defended.
663 if (defendedSquares == squaresToQueen)
666 else if (defendedSquares & blockSq)
669 mbonus += k * rr, ebonus += k * rr;
671 else if (pos.pieces(Us) & blockSq)
672 mbonus += rr + r * 2, ebonus += rr + r * 2;
675 // Assign a small bonus when the opponent has no pieces left
676 if (!pos.non_pawn_material(Them))
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.pi->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 ( ei.me->game_phase() < PHASE_MIDGAME
759 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
761 if (pos.opposite_bishops())
763 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
764 // is almost a draw, in case of KBP vs KB, it is even more a draw.
765 if ( pos.non_pawn_material(WHITE) == BishopValueMg
766 && pos.non_pawn_material(BLACK) == BishopValueMg)
767 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
769 // Endgame with opposite-colored bishops, but also other pieces. Still
770 // a bit drawish, but not as drawish as with only the two bishops.
772 sf = ScaleFactor(46);
774 // Endings where weaker side can place his king in front of the opponent's
775 // pawns are drawish.
776 else if ( abs(eg) <= BishopValueEg
777 && pos.count<PAWN>(strongSide) <= 2
778 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
779 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
788 /// evaluate() is the main evaluation function. It returns a static evaluation
789 /// of the position from the point of view of the side to move.
791 template<bool DoTrace>
792 Value Eval::evaluate(const Position& pos) {
794 assert(!pos.checkers());
796 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
799 // Probe the material hash table
800 ei.me = Material::probe(pos);
802 // If we have a specialized evaluation function for the current material
803 // configuration, call it and return.
804 if (ei.me->specialized_eval_exists())
805 return ei.me->evaluate(pos);
807 // Initialize score by reading the incrementally updated scores included in
808 // the position object (material + piece square tables) and the material
809 // imbalance. Score is computed internally from the white point of view.
810 Score score = pos.psq_score() + ei.me->imbalance();
812 // Probe the pawn hash table
813 ei.pi = Pawns::probe(pos);
814 score += ei.pi->pawns_score();
816 // Initialize attack and king safety bitboards
817 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
818 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
819 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
820 eval_init<WHITE>(pos, ei);
821 eval_init<BLACK>(pos, ei);
823 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
824 Bitboard blockedPawns[] = {
825 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
826 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
829 // Do not include in mobility area squares protected by enemy pawns, or occupied
830 // by our blocked pawns or king.
831 Bitboard mobilityArea[] = {
832 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
833 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
836 // Evaluate all pieces but king and pawns
837 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
838 score += mobility[WHITE] - mobility[BLACK];
840 // Evaluate kings after all other pieces because we need full attack
841 // information when computing the king safety evaluation.
842 score += evaluate_king<WHITE, DoTrace>(pos, ei)
843 - evaluate_king<BLACK, DoTrace>(pos, ei);
845 // Evaluate tactical threats, we need full attack information including king
846 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
847 - evaluate_threats<BLACK, DoTrace>(pos, ei);
849 // Evaluate passed pawns, we need full attack information including king
850 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
851 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
853 // Evaluate space for both sides, only during opening
854 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
855 score += evaluate_space<WHITE>(pos, ei)
856 - evaluate_space<BLACK>(pos, ei);
858 // Evaluate position potential for the winning side
859 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
861 // Evaluate scale factor for the winning side
862 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
864 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
865 Value v = mg_value(score) * int(ei.me->game_phase())
866 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
868 v /= int(PHASE_MIDGAME);
870 // In case of tracing add all remaining individual evaluation terms
873 Trace::add(MATERIAL, pos.psq_score());
874 Trace::add(IMBALANCE, ei.me->imbalance());
875 Trace::add(PAWN, ei.pi->pawns_score());
876 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
877 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
878 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
879 , evaluate_space<BLACK>(pos, ei));
880 Trace::add(TOTAL, score);
883 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
886 // Explicit template instantiations
887 template Value Eval::evaluate<true >(const Position&);
888 template Value Eval::evaluate<false>(const Position&);
891 /// trace() is like evaluate(), but instead of returning a value, it returns
892 /// a string (suitable for outputting to stdout) that contains the detailed
893 /// descriptions and values of each evaluation term. Useful for debugging.
895 std::string Eval::trace(const Position& pos) {
897 std::memset(scores, 0, sizeof(scores));
899 Value v = evaluate<true>(pos);
900 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
902 std::stringstream ss;
903 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
904 << " Eval term | White | Black | Total \n"
905 << " | MG EG | MG EG | MG EG \n"
906 << "----------------+-------------+-------------+-------------\n"
907 << " Material | " << Term(MATERIAL)
908 << " Imbalance | " << Term(IMBALANCE)
909 << " Pawns | " << Term(PAWN)
910 << " Knights | " << Term(KNIGHT)
911 << " Bishop | " << Term(BISHOP)
912 << " Rooks | " << Term(ROOK)
913 << " Queens | " << Term(QUEEN)
914 << " Mobility | " << Term(MOBILITY)
915 << " King safety | " << Term(KING)
916 << " Threats | " << Term(THREAT)
917 << " Passed pawns | " << Term(PASSED)
918 << " Space | " << Term(SPACE)
919 << "----------------+-------------+-------------+-------------\n"
920 << " Total | " << Term(TOTAL);
922 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";