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] = popcount(b);
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 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
283 b &= ~( ei.attackedBy[Them][KNIGHT]
284 | ei.attackedBy[Them][BISHOP]
285 | ei.attackedBy[Them][ROOK]);
287 int mob = popcount(b & mobilityArea[Us]);
289 mobility[Us] += MobilityBonus[Pt][mob];
291 if (Pt == BISHOP || Pt == KNIGHT)
293 // Bonus for outpost squares
294 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
296 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
299 bb &= b & ~pos.pieces(Us);
301 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
304 // Bonus when behind a pawn
305 if ( relative_rank(Us, s) < RANK_5
306 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
307 score += MinorBehindPawn;
309 // Penalty for pawns on the same color square as the bishop
311 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
313 // An important Chess960 pattern: A cornered bishop blocked by a friendly
314 // pawn diagonally in front of it is a very serious problem, especially
315 // when that pawn is also blocked.
318 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
320 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
321 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
322 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
323 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
330 // Bonus for aligning with enemy pawns on the same rank/file
331 if (relative_rank(Us, s) >= RANK_5)
332 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
334 // Bonus when on an open or semi-open file
335 if (ei.pi->semiopen_file(Us, file_of(s)))
336 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
338 // Penalize when trapped by the king, even more if the king cannot castle
341 Square ksq = pos.square<KING>(Us);
343 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
344 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
345 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
346 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
352 Trace::add(Pt, Us, score);
354 // Recursively call evaluate_pieces() of next piece type until KING is excluded
355 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
359 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
361 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
364 // evaluate_king() assigns bonuses and penalties to a king of a given color
366 template<Color Us, bool DoTrace>
367 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
369 const Color Them = (Us == WHITE ? BLACK : WHITE);
371 Bitboard undefended, b, b1, b2, safe;
373 const Square ksq = pos.square<KING>(Us);
375 // King shelter and enemy pawns storm
376 Score score = ei.pi->king_safety<Us>(pos, ksq);
378 // Main king safety evaluation
379 if (ei.kingAttackersCount[Them])
381 // Find the attacked squares which are defended only by the king...
382 undefended = ei.attackedBy[Them][ALL_PIECES]
383 & ei.attackedBy[Us][KING]
384 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
385 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
386 | ei.attackedBy[Us][QUEEN]);
388 // ... and those which are not defended at all in the larger king ring
389 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
390 & ei.kingRing[Us] & ~pos.pieces(Them);
392 // Initialize the 'attackUnits' variable, which is used later on as an
393 // index into the KingDanger[] array. The initial value is based on the
394 // number and types of the enemy's attacking pieces, the number of
395 // attacked and undefended squares around our king and the quality of
396 // the pawn shelter (current 'score' value).
397 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
398 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
399 + 27 * popcount(undefended)
400 + 11 * (popcount(b) + !!ei.pinnedPieces[Us])
401 - 64 * !pos.count<QUEEN>(Them)
402 - mg_value(score) / 8;
404 // Analyse the enemy's safe queen contact checks. Firstly, find the
405 // undefended squares around the king reachable by the enemy queen...
406 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
409 // ...and then remove squares not supported by another enemy piece
410 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
411 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
412 | ei.attackedBy[Them][KING];
414 attackUnits += QueenContactCheck * popcount(b);
417 // Analyse the enemy's safe distance checks for sliders and knights
418 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
420 b1 = pos.attacks_from<ROOK >(ksq) & safe;
421 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
423 // Enemy queen safe checks
424 if ((b1 | b2) & ei.attackedBy[Them][QUEEN])
425 attackUnits += QueenCheck, score -= Checked;
427 // Enemy rooks safe checks
428 if (b1 & ei.attackedBy[Them][ROOK])
429 attackUnits += RookCheck, score -= Checked;
431 // Enemy bishops safe checks
432 if (b2 & ei.attackedBy[Them][BISHOP])
433 attackUnits += BishopCheck, score -= Checked;
435 // Enemy knights safe checks
436 if (pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe)
437 attackUnits += KnightCheck, score -= Checked;
439 // Finally, extract the king danger score from the KingDanger[]
440 // array and subtract the score from the evaluation.
441 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
445 Trace::add(KING, Us, score);
451 // evaluate_threats() assigns bonuses according to the types of the attacking
452 // and the attacked pieces.
454 template<Color Us, bool DoTrace>
455 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
457 const Color Them = (Us == WHITE ? BLACK : WHITE);
458 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
459 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
460 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
461 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
462 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
464 enum { Minor, Rook };
466 Bitboard b, weak, defended, safeThreats;
467 Score score = SCORE_ZERO;
469 // Small bonus if the opponent has loose pawns or pieces
470 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
471 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
472 score += LooseEnemies;
474 // Non-pawn enemies attacked by a pawn
475 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
479 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
480 | ei.attackedBy[Us][ALL_PIECES]);
482 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
484 if (weak ^ safeThreats)
485 score += ThreatByHangingPawn;
488 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
491 // Non-pawn enemies defended by a pawn
492 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
494 // Enemies not defended by a pawn and under our attack
495 weak = pos.pieces(Them)
496 & ~ei.attackedBy[Them][PAWN]
497 & ei.attackedBy[Us][ALL_PIECES];
499 // Add a bonus according to the kind of attacking pieces
502 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
504 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
506 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
508 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
510 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
512 b = weak & ei.attackedBy[Us][KING];
514 score += ThreatByKing[more_than_one(b)];
517 // Bonus if some pawns can safely push and attack an enemy piece
518 b = pos.pieces(Us, PAWN) & ~TRank7BB;
519 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
522 & ~ei.attackedBy[Them][PAWN]
523 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
525 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
527 & ~ei.attackedBy[Us][PAWN];
529 score += ThreatByPawnPush * popcount(b);
532 Trace::add(THREAT, Us, score);
538 // evaluate_passed_pawns() evaluates the passed pawns of the given color
540 template<Color Us, bool DoTrace>
541 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
543 const Color Them = (Us == WHITE ? BLACK : WHITE);
545 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
546 Score score = SCORE_ZERO;
548 b = ei.pi->passed_pawns(Us);
552 Square s = pop_lsb(&b);
554 assert(pos.pawn_passed(Us, s));
556 int r = relative_rank(Us, s) - RANK_2;
557 int rr = r * (r - 1);
559 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
563 Square blockSq = s + pawn_push(Us);
565 // Adjust bonus based on the king's proximity
566 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
567 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
569 // If blockSq is not the queening square then consider also a second push
570 if (relative_rank(Us, blockSq) != RANK_8)
571 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
573 // If the pawn is free to advance, then increase the bonus
574 if (pos.empty(blockSq))
576 // If there is a rook or queen attacking/defending the pawn from behind,
577 // consider all the squaresToQueen. Otherwise consider only the squares
578 // in the pawn's path attacked or occupied by the enemy.
579 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
581 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
583 if (!(pos.pieces(Us) & bb))
584 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
586 if (!(pos.pieces(Them) & bb))
587 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
589 // If there aren't any enemy attacks, assign a big bonus. Otherwise
590 // assign a smaller bonus if the block square isn't attacked.
591 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
593 // If the path to the queen is fully defended, assign a big bonus.
594 // Otherwise assign a smaller bonus if the block square is defended.
595 if (defendedSquares == squaresToQueen)
598 else if (defendedSquares & blockSq)
601 mbonus += k * rr, ebonus += k * rr;
603 else if (pos.pieces(Us) & blockSq)
604 mbonus += rr + r * 2, ebonus += rr + r * 2;
607 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
611 Trace::add(PASSED, Us, score);
613 // Add the scores to the middlegame and endgame eval
618 // evaluate_space() computes the space evaluation for a given side. The
619 // space evaluation is a simple bonus based on the number of safe squares
620 // available for minor pieces on the central four files on ranks 2--4. Safe
621 // squares one, two or three squares behind a friendly pawn are counted
622 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
623 // improve play on game opening.
625 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
627 const Color Them = (Us == WHITE ? BLACK : WHITE);
628 const Bitboard SpaceMask =
629 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
630 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
632 // Find the safe squares for our pieces inside the area defined by
633 // SpaceMask. A square is unsafe if it is attacked by an enemy
634 // pawn, or if it is undefended and attacked by an enemy piece.
635 Bitboard safe = SpaceMask
636 & ~pos.pieces(Us, PAWN)
637 & ~ei.attackedBy[Them][PAWN]
638 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
640 // Find all squares which are at most three squares behind some friendly pawn
641 Bitboard behind = pos.pieces(Us, PAWN);
642 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
643 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
645 // Since SpaceMask[Us] is fully on our half of the board...
646 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
648 // ...count safe + (behind & safe) with a single popcount
649 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
650 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
651 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
653 return make_score(bonus * weight * weight * 2 / 11, 0);
657 // evaluate_initiative() computes the initiative correction value for the
658 // position, i.e., second order bonus/malus based on the known attacking/defending
659 // status of the players.
660 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
662 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
663 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
664 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
666 // Compute the initiative bonus for the attacking side
667 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
669 // Now apply the bonus: note that we find the attacking side by extracting
670 // the sign of the endgame value, and that we carefully cap the bonus so
671 // that the endgame score will never be divided by more than two.
672 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
674 return make_score(0, value);
678 // evaluate_scale_factor() computes the scale factor for the winning side
679 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
681 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
682 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
684 // If we don't already have an unusual scale factor, check for certain
685 // types of endgames, and use a lower scale for those.
686 if ( ei.me->game_phase() < PHASE_MIDGAME
687 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
689 if (pos.opposite_bishops())
691 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
692 // is almost a draw, in case of KBP vs KB, it is even more a draw.
693 if ( pos.non_pawn_material(WHITE) == BishopValueMg
694 && pos.non_pawn_material(BLACK) == BishopValueMg)
695 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
697 // Endgame with opposite-colored bishops, but also other pieces. Still
698 // a bit drawish, but not as drawish as with only the two bishops.
700 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
702 // Endings where weaker side can place his king in front of the opponent's
703 // pawns are drawish.
704 else if ( abs(eg) <= BishopValueEg
705 && ei.pi->pawn_span(strongSide) <= 1
706 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
707 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
716 /// evaluate() is the main evaluation function. It returns a static evaluation
717 /// of the position from the point of view of the side to move.
719 template<bool DoTrace>
720 Value Eval::evaluate(const Position& pos) {
722 assert(!pos.checkers());
725 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
727 // Initialize score by reading the incrementally updated scores included in
728 // the position object (material + piece square tables). Score is computed
729 // internally from the white point of view.
730 score = pos.psq_score();
732 // Probe the material hash table
733 ei.me = Material::probe(pos);
734 score += ei.me->imbalance();
736 // If we have a specialized evaluation function for the current material
737 // configuration, call it and return.
738 if (ei.me->specialized_eval_exists())
739 return ei.me->evaluate(pos);
741 // Probe the pawn hash table
742 ei.pi = Pawns::probe(pos);
743 score += ei.pi->pawns_score();
745 // Initialize attack and king safety bitboards
746 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
747 eval_init<WHITE>(pos, ei);
748 eval_init<BLACK>(pos, ei);
750 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
751 Bitboard blockedPawns[] = {
752 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
753 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
756 // Do not include in mobility area squares protected by enemy pawns, or occupied
757 // by our blocked pawns or king.
758 Bitboard mobilityArea[] = {
759 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
760 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
763 // Evaluate all pieces but king and pawns
764 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
765 score += mobility[WHITE] - mobility[BLACK];
767 // Evaluate kings after all other pieces because we need full attack
768 // information when computing the king safety evaluation.
769 score += evaluate_king<WHITE, DoTrace>(pos, ei)
770 - evaluate_king<BLACK, DoTrace>(pos, ei);
772 // Evaluate tactical threats, we need full attack information including king
773 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
774 - evaluate_threats<BLACK, DoTrace>(pos, ei);
776 // Evaluate passed pawns, we need full attack information including king
777 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
778 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
780 // If both sides have only pawns, score for potential unstoppable pawns
781 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
784 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
785 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
787 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
788 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
791 // Evaluate space for both sides, only during opening
792 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
793 score += evaluate_space<WHITE>(pos, ei)
794 - evaluate_space<BLACK>(pos, ei);
796 // Evaluate position potential for the winning side
797 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
799 // Evaluate scale factor for the winning side
800 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
802 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
803 Value v = mg_value(score) * int(ei.me->game_phase())
804 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
806 v /= int(PHASE_MIDGAME);
808 // In case of tracing add all remaining individual evaluation terms
811 Trace::add(MATERIAL, pos.psq_score());
812 Trace::add(IMBALANCE, ei.me->imbalance());
813 Trace::add(PAWN, ei.pi->pawns_score());
814 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
815 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
816 , evaluate_space<BLACK>(pos, ei));
817 Trace::add(TOTAL, score);
820 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
823 // Explicit template instantiations
824 template Value Eval::evaluate<true >(const Position&);
825 template Value Eval::evaluate<false>(const Position&);
828 /// trace() is like evaluate(), but instead of returning a value, it returns
829 /// a string (suitable for outputting to stdout) that contains the detailed
830 /// descriptions and values of each evaluation term. Useful for debugging.
832 std::string Eval::trace(const Position& pos) {
834 std::memset(scores, 0, sizeof(scores));
836 Value v = evaluate<true>(pos);
837 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
839 std::stringstream ss;
840 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
841 << " Eval term | White | Black | Total \n"
842 << " | MG EG | MG EG | MG EG \n"
843 << "----------------+-------------+-------------+-------------\n"
844 << " Material | " << Term(MATERIAL)
845 << " Imbalance | " << Term(IMBALANCE)
846 << " Pawns | " << Term(PAWN)
847 << " Knights | " << Term(KNIGHT)
848 << " Bishop | " << Term(BISHOP)
849 << " Rooks | " << Term(ROOK)
850 << " Queens | " << Term(QUEEN)
851 << " Mobility | " << Term(MOBILITY)
852 << " King safety | " << Term(KING)
853 << " Threats | " << Term(THREAT)
854 << " Passed pawns | " << Term(PASSED)
855 << " Space | " << Term(SPACE)
856 << "----------------+-------------+-------------+-------------\n"
857 << " Total | " << Term(TOTAL);
859 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
865 /// init() computes evaluation weights, usually at startup
869 const int MaxSlope = 322;
870 const int Peak = 47410;
873 for (int i = 0; i < 400; ++i)
875 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
876 KingDanger[i] = make_score(t * 268 / 7700, 0);