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 // kingRing[color] is the zone around the king which is considered
81 // by the king safety evaluation. This consists of the squares directly
82 // adjacent to the king, and the three (or two, for a king on an edge file)
83 // squares two ranks in front of the king. For instance, if black's king
84 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
85 // f7, g7, h7, f6, g6 and h6.
86 Bitboard kingRing[COLOR_NB];
88 // kingAttackersCount[color] is the number of pieces of the given color
89 // which attack a square in the kingRing of the enemy king.
90 int kingAttackersCount[COLOR_NB];
92 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
93 // given color which attack a square in the kingRing of the enemy king. The
94 // weights of the individual piece types are given by the elements in the
95 // KingAttackWeights array.
96 int kingAttackersWeight[COLOR_NB];
98 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
99 // color to squares directly adjacent to the enemy king. Pieces which attack
100 // more than one square are counted multiple times. For instance, if there is
101 // a white knight on g5 and black's king is on g8, this white knight adds 2
102 // to kingAdjacentZoneAttacksCount[WHITE].
103 int kingAdjacentZoneAttacksCount[COLOR_NB];
105 Bitboard pinnedPieces[COLOR_NB];
110 #define V(v) Value(v)
111 #define S(mg, eg) make_score(mg, eg)
113 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
114 // game, indexed by piece type and number of attacked squares in the MobilityArea.
115 const Score MobilityBonus[][32] = {
117 { S(-75,-76), S(-56,-54), S(- 9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
118 S( 22, 26), S( 30, 28), S( 36, 29) },
119 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
120 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
121 S( 92, 90), S( 97, 94) },
122 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
123 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
124 S( 43,165), S( 49,168), S( 59,169) },
125 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
126 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
127 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
128 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
129 S(118,174), S(119,177), S(123,191), S(128,199) }
132 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
133 // bishops outposts, bigger if outpost piece is supported by a pawn.
134 const Score Outpost[][2] = {
135 { S(43,11), S(65,20) }, // Knights
136 { S(20, 3), S(29, 8) } // Bishops
139 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
140 // knights and bishops which can reach an outpost square in one move, bigger
141 // if outpost square is supported by a pawn.
142 const Score ReachableOutpost[][2] = {
143 { S(21, 5), S(35, 8) }, // Knights
144 { S( 8, 0), S(14, 4) } // Bishops
147 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
148 // friendly pawn on the rook file.
149 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
151 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
152 // type is attacked by a pawn which is protected or is not attacked.
153 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
154 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215) };
156 // Threat[by minor/by rook][attacked PieceType] contains
157 // bonuses according to which piece type attacks which one.
158 // Attacks on lesser pieces which are pawn-defended are not considered.
159 const Score Threat[][PIECE_TYPE_NB] = {
160 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
161 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
164 // ThreatByKing[on one/on many] contains bonuses for King attacks on
165 // pawns or pieces which are not pawn-defended.
166 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
168 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
169 // We don't use a Score because we process the two components independently.
170 const Value Passed[][RANK_NB] = {
171 { V(5), V( 5), V(31), V(73), V(166), V(252) },
172 { V(7), V(14), V(38), V(73), V(166), V(252) }
175 // PassedFile[File] contains a bonus according to the file of a passed pawn
176 const Score PassedFile[FILE_NB] = {
177 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
178 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
181 // Assorted bonuses and penalties used by evaluation
182 const Score MinorBehindPawn = S(16, 0);
183 const Score BishopPawns = S( 8, 12);
184 const Score RookOnPawn = S( 8, 24);
185 const Score TrappedRook = S(92, 0);
186 const Score Checked = S(20, 20);
187 const Score ThreatByHangingPawn = S(71, 61);
188 const Score LooseEnemies = S( 0, 25);
189 const Score Hanging = S(48, 27);
190 const Score ThreatByPawnPush = S(38, 22);
191 const Score Unstoppable = S( 0, 20);
193 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
194 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
195 // happen in Chess960 games.
196 const Score TrappedBishopA1H1 = S(50, 50);
201 // King danger constants and variables. The king danger scores are looked-up
202 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
203 // of the enemy attack are added up into an integer, which is used as an
204 // index to KingDanger[].
205 Score KingDanger[512];
207 // KingAttackWeights[PieceType] contains king attack weights by piece type
208 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
210 // Penalties for enemy's safe checks
211 const int QueenContactCheck = 89;
212 const int QueenCheck = 52;
213 const int RookCheck = 45;
214 const int BishopCheck = 5;
215 const int KnightCheck = 17;
218 // eval_init() initializes king and attack bitboards for a given color
219 // adding pawn attacks. To be done at the beginning of the evaluation.
222 void eval_init(const Position& pos, EvalInfo& ei) {
224 const Color Them = (Us == WHITE ? BLACK : WHITE);
225 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
227 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
228 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
229 ei.attackedBy[Them][ALL_PIECES] |= b;
230 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
232 // Init king safety tables only if we are going to use them
233 if (pos.non_pawn_material(Us) >= QueenValueMg)
235 ei.kingRing[Them] = b | shift_bb<Down>(b);
236 b &= ei.attackedBy[Us][PAWN];
237 ei.kingAttackersCount[Us] = b ? popcount(b) : 0;
238 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
241 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
245 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
248 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
249 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
250 const Bitboard* mobilityArea) {
253 Score score = SCORE_ZERO;
255 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
256 const Color Them = (Us == WHITE ? BLACK : WHITE);
257 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
258 : Rank5BB | Rank4BB | Rank3BB);
259 const Square* pl = pos.squares<Pt>(Us);
261 ei.attackedBy[Us][Pt] = 0;
263 while ((s = *pl++) != SQ_NONE)
265 // Find attacked squares, including x-ray attacks for bishops and rooks
266 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
267 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
268 : pos.attacks_from<Pt>(s);
270 if (ei.pinnedPieces[Us] & s)
271 b &= LineBB[pos.square<KING>(Us)][s];
273 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
275 if (b & ei.kingRing[Them])
277 ei.kingAttackersCount[Us]++;
278 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
279 bb = b & ei.attackedBy[Them][KING];
281 ei.kingAdjacentZoneAttacksCount[Us] += popcount(bb);
285 b &= ~( ei.attackedBy[Them][KNIGHT]
286 | ei.attackedBy[Them][BISHOP]
287 | ei.attackedBy[Them][ROOK]);
289 int mob = popcount(b & mobilityArea[Us]);
291 mobility[Us] += MobilityBonus[Pt][mob];
293 if (Pt == BISHOP || Pt == KNIGHT)
295 // Bonus for outpost squares
296 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
298 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
301 bb &= b & ~pos.pieces(Us);
303 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
306 // Bonus when behind a pawn
307 if ( relative_rank(Us, s) < RANK_5
308 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
309 score += MinorBehindPawn;
311 // Penalty for pawns on the same color square as the bishop
313 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
315 // An important Chess960 pattern: A cornered bishop blocked by a friendly
316 // pawn diagonally in front of it is a very serious problem, especially
317 // when that pawn is also blocked.
320 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
322 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
323 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
324 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
325 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
332 // Bonus for aligning with enemy pawns on the same rank/file
333 if (relative_rank(Us, s) >= RANK_5)
335 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
337 score += RookOnPawn * popcount(alignedPawns);
340 // Bonus when on an open or semi-open file
341 if (ei.pi->semiopen_file(Us, file_of(s)))
342 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
344 // Penalize when trapped by the king, even more if the king cannot castle
347 Square ksq = pos.square<KING>(Us);
349 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
350 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
351 && !ei.pi->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 Trace::add(Pt, Us, score);
360 // Recursively call evaluate_pieces() of next piece type until KING is excluded
361 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
365 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
367 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
370 // evaluate_king() assigns bonuses and penalties to a king of a given color
372 template<Color Us, bool DoTrace>
373 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
375 const Color Them = (Us == WHITE ? BLACK : WHITE);
377 Bitboard undefended, b, b1, b2, safe;
379 const Square ksq = pos.square<KING>(Us);
381 // King shelter and enemy pawns storm
382 Score score = ei.pi->king_safety<Us>(pos, ksq);
384 // Main king safety evaluation
385 if (ei.kingAttackersCount[Them])
387 // Find the attacked squares which are defended only by the king...
388 undefended = ei.attackedBy[Them][ALL_PIECES]
389 & ei.attackedBy[Us][KING]
390 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
391 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
392 | ei.attackedBy[Us][QUEEN]);
394 // ... and those which are not defended at all in the larger king ring
395 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
396 & ei.kingRing[Us] & ~pos.pieces(Them);
398 // Initialize the 'attackUnits' variable, which is used later on as an
399 // index into the KingDanger[] array. The initial value is based on the
400 // number and types of the enemy's attacking pieces, the number of
401 // attacked and undefended squares around our king and the quality of
402 // the pawn shelter (current 'score' value).
403 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
404 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
405 + 27 * popcount(undefended)
406 + 11 * (popcount(b) + !!ei.pinnedPieces[Us])
407 - 64 * !pos.count<QUEEN>(Them)
408 - mg_value(score) / 8;
410 // Analyse the enemy's safe queen contact checks. Firstly, find the
411 // undefended squares around the king reachable by the enemy queen...
412 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
415 // ...and then remove squares not supported by another enemy piece
416 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
417 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
418 | ei.attackedBy[Them][KING];
421 attackUnits += QueenContactCheck * popcount(b);
424 // Analyse the enemy's safe distance checks for sliders and knights
425 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
427 b1 = pos.attacks_from<ROOK >(ksq) & safe;
428 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
430 // Enemy queen safe checks
431 if ((b1 | b2) & ei.attackedBy[Them][QUEEN])
432 attackUnits += QueenCheck, score -= Checked;
434 // Enemy rooks safe checks
435 if (b1 & ei.attackedBy[Them][ROOK])
436 attackUnits += RookCheck, score -= Checked;
438 // Enemy bishops safe checks
439 if (b2 & ei.attackedBy[Them][BISHOP])
440 attackUnits += BishopCheck, score -= Checked;
442 // Enemy knights safe checks
443 if (pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe)
444 attackUnits += KnightCheck, score -= Checked;
446 // Finally, extract the king danger score from the KingDanger[]
447 // array and subtract the score from the evaluation.
448 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
452 Trace::add(KING, Us, score);
458 // evaluate_threats() assigns bonuses according to the types of the attacking
459 // and the attacked pieces.
461 template<Color Us, bool DoTrace>
462 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
464 const Color Them = (Us == WHITE ? BLACK : WHITE);
465 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
466 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
467 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
468 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
469 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
471 enum { Minor, Rook };
473 Bitboard b, weak, defended, safeThreats;
474 Score score = SCORE_ZERO;
476 // Small bonus if the opponent has loose pawns or pieces
477 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
478 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
479 score += LooseEnemies;
481 // Non-pawn enemies attacked by a pawn
482 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
486 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
487 | ei.attackedBy[Us][ALL_PIECES]);
489 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
491 if (weak ^ safeThreats)
492 score += ThreatByHangingPawn;
495 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
498 // Non-pawn enemies defended by a pawn
499 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
501 // Enemies not defended by a pawn and under our attack
502 weak = pos.pieces(Them)
503 & ~ei.attackedBy[Them][PAWN]
504 & ei.attackedBy[Us][ALL_PIECES];
506 // Add a bonus according to the kind of attacking pieces
509 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
511 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
513 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
515 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
517 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
519 score += Hanging * popcount(b);
521 b = weak & ei.attackedBy[Us][KING];
523 score += ThreatByKing[more_than_one(b)];
526 // Bonus if some pawns can safely push and attack an enemy piece
527 b = pos.pieces(Us, PAWN) & ~TRank7BB;
528 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
531 & ~ei.attackedBy[Them][PAWN]
532 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
534 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
536 & ~ei.attackedBy[Us][PAWN];
539 score += ThreatByPawnPush * popcount(b);
542 Trace::add(THREAT, Us, score);
548 // evaluate_passed_pawns() evaluates the passed pawns of the given color
550 template<Color Us, bool DoTrace>
551 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
553 const Color Them = (Us == WHITE ? BLACK : WHITE);
555 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
556 Score score = SCORE_ZERO;
558 b = ei.pi->passed_pawns(Us);
562 Square s = pop_lsb(&b);
564 assert(pos.pawn_passed(Us, s));
566 int r = relative_rank(Us, s) - RANK_2;
567 int rr = r * (r - 1);
569 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
573 Square blockSq = s + pawn_push(Us);
575 // Adjust bonus based on the king's proximity
576 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
577 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
579 // If blockSq is not the queening square then consider also a second push
580 if (relative_rank(Us, blockSq) != RANK_8)
581 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
583 // If the pawn is free to advance, then increase the bonus
584 if (pos.empty(blockSq))
586 // If there is a rook or queen attacking/defending the pawn from behind,
587 // consider all the squaresToQueen. Otherwise consider only the squares
588 // in the pawn's path attacked or occupied by the enemy.
589 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
591 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
593 if (!(pos.pieces(Us) & bb))
594 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
596 if (!(pos.pieces(Them) & bb))
597 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
599 // If there aren't any enemy attacks, assign a big bonus. Otherwise
600 // assign a smaller bonus if the block square isn't attacked.
601 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
603 // If the path to the queen is fully defended, assign a big bonus.
604 // Otherwise assign a smaller bonus if the block square is defended.
605 if (defendedSquares == squaresToQueen)
608 else if (defendedSquares & blockSq)
611 mbonus += k * rr, ebonus += k * rr;
613 else if (pos.pieces(Us) & blockSq)
614 mbonus += rr + r * 2, ebonus += rr + r * 2;
617 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
621 Trace::add(PASSED, Us, score);
623 // Add the scores to the middlegame and endgame eval
628 // evaluate_space() computes the space evaluation for a given side. The
629 // space evaluation is a simple bonus based on the number of safe squares
630 // available for minor pieces on the central four files on ranks 2--4. Safe
631 // squares one, two or three squares behind a friendly pawn are counted
632 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
633 // improve play on game opening.
635 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
637 const Color Them = (Us == WHITE ? BLACK : WHITE);
638 const Bitboard SpaceMask =
639 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
640 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
642 // Find the safe squares for our pieces inside the area defined by
643 // SpaceMask. A square is unsafe if it is attacked by an enemy
644 // pawn, or if it is undefended and attacked by an enemy piece.
645 Bitboard safe = SpaceMask
646 & ~pos.pieces(Us, PAWN)
647 & ~ei.attackedBy[Them][PAWN]
648 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
650 // Find all squares which are at most three squares behind some friendly pawn
651 Bitboard behind = pos.pieces(Us, PAWN);
652 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
653 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
655 // Since SpaceMask[Us] is fully on our half of the board...
656 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
658 // ...count safe + (behind & safe) with a single popcount
659 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
660 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
661 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
663 return make_score(bonus * weight * weight * 2 / 11, 0);
667 // evaluate_initiative() computes the initiative correction value for the
668 // position, i.e., second order bonus/malus based on the known attacking/defending
669 // status of the players.
670 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
672 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
673 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
674 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
676 // Compute the initiative bonus for the attacking side
677 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
679 // Now apply the bonus: note that we find the attacking side by extracting
680 // the sign of the endgame value, and that we carefully cap the bonus so
681 // that the endgame score will never be divided by more than two.
682 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
684 return make_score(0, value);
688 // evaluate_scale_factor() computes the scale factor for the winning side
689 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
691 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
692 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
694 // If we don't already have an unusual scale factor, check for certain
695 // types of endgames, and use a lower scale for those.
696 if ( ei.me->game_phase() < PHASE_MIDGAME
697 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
699 if (pos.opposite_bishops())
701 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
702 // is almost a draw, in case of KBP vs KB, it is even more a draw.
703 if ( pos.non_pawn_material(WHITE) == BishopValueMg
704 && pos.non_pawn_material(BLACK) == BishopValueMg)
705 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
707 // Endgame with opposite-colored bishops, but also other pieces. Still
708 // a bit drawish, but not as drawish as with only the two bishops.
710 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
712 // Endings where weaker side can place his king in front of the opponent's
713 // pawns are drawish.
714 else if ( abs(eg) <= BishopValueEg
715 && ei.pi->pawn_span(strongSide) <= 1
716 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
717 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
726 /// evaluate() is the main evaluation function. It returns a static evaluation
727 /// of the position from the point of view of the side to move.
729 template<bool DoTrace>
730 Value Eval::evaluate(const Position& pos) {
732 assert(!pos.checkers());
735 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
737 // Initialize score by reading the incrementally updated scores included in
738 // the position object (material + piece square tables). Score is computed
739 // internally from the white point of view.
740 score = pos.psq_score();
742 // Probe the material hash table
743 ei.me = Material::probe(pos);
744 score += ei.me->imbalance();
746 // If we have a specialized evaluation function for the current material
747 // configuration, call it and return.
748 if (ei.me->specialized_eval_exists())
749 return ei.me->evaluate(pos);
751 // Probe the pawn hash table
752 ei.pi = Pawns::probe(pos);
753 score += ei.pi->pawns_score();
755 // Initialize attack and king safety bitboards
756 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
757 eval_init<WHITE>(pos, ei);
758 eval_init<BLACK>(pos, ei);
760 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
761 Bitboard blockedPawns[] = {
762 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
763 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
766 // Do not include in mobility area squares protected by enemy pawns, or occupied
767 // by our blocked pawns or king.
768 Bitboard mobilityArea[] = {
769 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
770 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
773 // Evaluate all pieces but king and pawns
774 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
775 score += mobility[WHITE] - mobility[BLACK];
777 // Evaluate kings after all other pieces because we need full attack
778 // information when computing the king safety evaluation.
779 score += evaluate_king<WHITE, DoTrace>(pos, ei)
780 - evaluate_king<BLACK, DoTrace>(pos, ei);
782 // Evaluate tactical threats, we need full attack information including king
783 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
784 - evaluate_threats<BLACK, DoTrace>(pos, ei);
786 // Evaluate passed pawns, we need full attack information including king
787 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
788 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
790 // If both sides have only pawns, score for potential unstoppable pawns
791 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
794 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
795 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
797 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
798 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
801 // Evaluate space for both sides, only during opening
802 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
803 score += evaluate_space<WHITE>(pos, ei)
804 - evaluate_space<BLACK>(pos, ei);
806 // Evaluate position potential for the winning side
807 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
809 // Evaluate scale factor for the winning side
810 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
812 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
813 Value v = mg_value(score) * int(ei.me->game_phase())
814 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
816 v /= int(PHASE_MIDGAME);
818 // In case of tracing add all remaining individual evaluation terms
821 Trace::add(MATERIAL, pos.psq_score());
822 Trace::add(IMBALANCE, ei.me->imbalance());
823 Trace::add(PAWN, ei.pi->pawns_score());
824 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
825 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
826 , evaluate_space<BLACK>(pos, ei));
827 Trace::add(TOTAL, score);
830 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
833 // Explicit template instantiations
834 template Value Eval::evaluate<true >(const Position&);
835 template Value Eval::evaluate<false>(const Position&);
838 /// trace() is like evaluate(), but instead of returning a value, it returns
839 /// a string (suitable for outputting to stdout) that contains the detailed
840 /// descriptions and values of each evaluation term. Useful for debugging.
842 std::string Eval::trace(const Position& pos) {
844 std::memset(scores, 0, sizeof(scores));
846 Value v = evaluate<true>(pos);
847 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
849 std::stringstream ss;
850 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
851 << " Eval term | White | Black | Total \n"
852 << " | MG EG | MG EG | MG EG \n"
853 << "----------------+-------------+-------------+-------------\n"
854 << " Material | " << Term(MATERIAL)
855 << " Imbalance | " << Term(IMBALANCE)
856 << " Pawns | " << Term(PAWN)
857 << " Knights | " << Term(KNIGHT)
858 << " Bishop | " << Term(BISHOP)
859 << " Rooks | " << Term(ROOK)
860 << " Queens | " << Term(QUEEN)
861 << " Mobility | " << Term(MOBILITY)
862 << " King safety | " << Term(KING)
863 << " Threats | " << Term(THREAT)
864 << " Passed pawns | " << Term(PASSED)
865 << " Space | " << Term(SPACE)
866 << "----------------+-------------+-------------+-------------\n"
867 << " Total | " << Term(TOTAL);
869 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
875 /// init() computes evaluation weights, usually at startup
879 const int MaxSlope = 322;
880 const int Peak = 47410;
883 for (int i = 0; i < 400; ++i)
885 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
886 KingDanger[i] = make_score(t * 268 / 7700, 0);