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(42,11), S(63,17) }, // Knights
136 { S(18, 5), S(27, 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(31, 8) }, // Knights
144 { S( 8, 2), S(13, 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(19, 10), S(43, 21) };
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(64), V(137), V(193) }
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( 7, 27);
185 const Score TrappedRook = S(92, 0);
186 const Score Checked = S(20, 20);
187 const Score ThreatByHangingPawn = S(70, 63);
188 const Score Hanging = S(48, 28);
189 const Score ThreatByPawnPush = S(31, 19);
190 const Score Unstoppable = S( 0, 20);
192 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
193 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
194 // happen in Chess960 games.
195 const Score TrappedBishopA1H1 = S(50, 50);
200 // King danger constants and variables. The king danger scores are looked-up
201 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
202 // of the enemy attack are added up into an integer, which is used as an
203 // index to KingDanger[].
204 Score KingDanger[512];
206 // KingAttackWeights[PieceType] contains king attack weights by piece type
207 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
209 // Penalties for enemy's safe checks
210 const int QueenContactCheck = 89;
211 const int QueenCheck = 50;
212 const int RookCheck = 45;
213 const int BishopCheck = 6;
214 const int KnightCheck = 14;
217 // eval_init() initializes king and attack bitboards for a given color
218 // adding pawn attacks. To be done at the beginning of the evaluation.
221 void eval_init(const Position& pos, EvalInfo& ei) {
223 const Color Them = (Us == WHITE ? BLACK : WHITE);
224 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
226 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
227 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
228 ei.attackedBy[Them][ALL_PIECES] |= b;
229 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
231 // Init king safety tables only if we are going to use them
232 if (pos.non_pawn_material(Us) >= QueenValueMg)
234 ei.kingRing[Them] = b | shift_bb<Down>(b);
235 b &= ei.attackedBy[Us][PAWN];
236 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
237 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
240 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
244 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
247 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
248 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
249 const Bitboard* mobilityArea) {
252 Score score = SCORE_ZERO;
254 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
255 const Color Them = (Us == WHITE ? BLACK : WHITE);
256 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
257 : Rank5BB | Rank4BB | Rank3BB);
258 const Square* pl = pos.squares<Pt>(Us);
260 ei.attackedBy[Us][Pt] = 0;
262 while ((s = *pl++) != SQ_NONE)
264 // Find attacked squares, including x-ray attacks for bishops and rooks
265 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
266 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
267 : pos.attacks_from<Pt>(s);
269 if (ei.pinnedPieces[Us] & s)
270 b &= LineBB[pos.square<KING>(Us)][s];
272 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
274 if (b & ei.kingRing[Them])
276 ei.kingAttackersCount[Us]++;
277 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
278 bb = b & ei.attackedBy[Them][KING];
280 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
284 b &= ~( ei.attackedBy[Them][KNIGHT]
285 | ei.attackedBy[Them][BISHOP]
286 | ei.attackedBy[Them][ROOK]);
288 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
290 mobility[Us] += MobilityBonus[Pt][mob];
292 if (Pt == BISHOP || Pt == KNIGHT)
294 // Bonus for outpost squares
295 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
297 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
300 bb &= b & ~pos.pieces(Us);
302 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
305 // Bonus when behind a pawn
306 if ( relative_rank(Us, s) < RANK_5
307 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
308 score += MinorBehindPawn;
310 // Penalty for pawns on the same color square as the bishop
312 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
314 // An important Chess960 pattern: A cornered bishop blocked by a friendly
315 // pawn diagonally in front of it is a very serious problem, especially
316 // when that pawn is also blocked.
319 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
321 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
322 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
323 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
324 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
331 // Bonus for aligning with enemy pawns on the same rank/file
332 if (relative_rank(Us, s) >= RANK_5)
334 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
336 score += RookOnPawn * popcount<Max15>(alignedPawns);
339 // Bonus when on an open or semi-open file
340 if (ei.pi->semiopen_file(Us, file_of(s)))
341 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
343 // Penalize when trapped by the king, even more if the king cannot castle
346 Square ksq = pos.square<KING>(Us);
348 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
349 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
350 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
351 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
357 Trace::add(Pt, Us, score);
359 // Recursively call evaluate_pieces() of next piece type until KING is excluded
360 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
364 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
366 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
369 // evaluate_king() assigns bonuses and penalties to a king of a given color
371 template<Color Us, bool DoTrace>
372 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
374 const Color Them = (Us == WHITE ? BLACK : WHITE);
376 Bitboard undefended, b, b1, b2, safe;
378 const Square ksq = pos.square<KING>(Us);
380 // King shelter and enemy pawns storm
381 Score score = ei.pi->king_safety<Us>(pos, ksq);
383 // Main king safety evaluation
384 if (ei.kingAttackersCount[Them])
386 // Find the attacked squares around the king which have no defenders
387 // apart from the king itself.
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 // Initialize the 'attackUnits' variable, which is used later on as an
395 // index into the KingDanger[] array. The initial value is based on the
396 // number and types of the enemy's attacking pieces, the number of
397 // attacked and undefended squares around our king and the quality of
398 // the pawn shelter (current 'score' value).
399 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
400 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
401 + 27 * popcount<Max15>(undefended)
402 + 11 * !!ei.pinnedPieces[Us]
403 - 64 * !pos.count<QUEEN>(Them)
404 - mg_value(score) / 8;
406 // Analyse the enemy's safe queen contact checks. Firstly, find the
407 // undefended squares around the king reachable by the enemy queen...
408 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
411 // ...and then remove squares not supported by another enemy piece
412 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
413 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
414 | ei.attackedBy[Them][KING];
417 attackUnits += QueenContactCheck * popcount<Max15>(b);
420 // Analyse the enemy's safe distance checks for sliders and knights
421 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
423 b1 = pos.attacks_from<ROOK >(ksq) & safe;
424 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
426 // Enemy queen safe checks
427 if ((b1 | b2) & ei.attackedBy[Them][QUEEN])
428 attackUnits += QueenCheck, score -= Checked;
430 // Enemy rooks safe checks
431 if (b1 & ei.attackedBy[Them][ROOK])
432 attackUnits += RookCheck, score -= Checked;
434 // Enemy bishops safe checks
435 if (b2 & ei.attackedBy[Them][BISHOP])
436 attackUnits += BishopCheck, score -= Checked;
438 // Enemy knights safe checks
439 if (pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe)
440 attackUnits += KnightCheck, score -= Checked;
442 // Finally, extract the king danger score from the KingDanger[]
443 // array and subtract the score from the evaluation.
444 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
448 Trace::add(KING, Us, score);
454 // evaluate_threats() assigns bonuses according to the types of the attacking
455 // and the attacked pieces.
457 template<Color Us, bool DoTrace>
458 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
460 const Color Them = (Us == WHITE ? BLACK : WHITE);
461 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
462 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
463 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
464 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
465 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
467 enum { Minor, Rook };
469 Bitboard b, weak, defended, safeThreats;
470 Score score = SCORE_ZERO;
472 // Non-pawn enemies attacked by a pawn
473 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
477 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
478 | ei.attackedBy[Us][ALL_PIECES]);
480 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
482 if (weak ^ safeThreats)
483 score += ThreatByHangingPawn;
486 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
489 // Non-pawn enemies defended by a pawn
490 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
492 // Enemies not defended by a pawn and under our attack
493 weak = pos.pieces(Them)
494 & ~ei.attackedBy[Them][PAWN]
495 & ei.attackedBy[Us][ALL_PIECES];
497 // Add a bonus according to the kind of attacking pieces
500 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
502 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
504 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
506 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
508 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
510 score += Hanging * popcount<Max15>(b);
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];
530 score += ThreatByPawnPush * popcount<Max15>(b);
533 Trace::add(THREAT, Us, score);
539 // evaluate_passed_pawns() evaluates the passed pawns of the given color
541 template<Color Us, bool DoTrace>
542 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
544 const Color Them = (Us == WHITE ? BLACK : WHITE);
546 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
547 Score score = SCORE_ZERO;
549 b = ei.pi->passed_pawns(Us);
553 Square s = pop_lsb(&b);
555 assert(pos.pawn_passed(Us, s));
557 int r = relative_rank(Us, s) - RANK_2;
558 int rr = r * (r - 1);
560 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
564 Square blockSq = s + pawn_push(Us);
566 // Adjust bonus based on the king's proximity
567 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
568 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
570 // If blockSq is not the queening square then consider also a second push
571 if (relative_rank(Us, blockSq) != RANK_8)
572 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
574 // If the pawn is free to advance, then increase the bonus
575 if (pos.empty(blockSq))
577 // If there is a rook or queen attacking/defending the pawn from behind,
578 // consider all the squaresToQueen. Otherwise consider only the squares
579 // in the pawn's path attacked or occupied by the enemy.
580 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
582 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
584 if (!(pos.pieces(Us) & bb))
585 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
587 if (!(pos.pieces(Them) & bb))
588 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
590 // If there aren't any enemy attacks, assign a big bonus. Otherwise
591 // assign a smaller bonus if the block square isn't attacked.
592 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
594 // If the path to the queen is fully defended, assign a big bonus.
595 // Otherwise assign a smaller bonus if the block square is defended.
596 if (defendedSquares == squaresToQueen)
599 else if (defendedSquares & blockSq)
602 mbonus += k * rr, ebonus += k * rr;
604 else if (pos.pieces(Us) & blockSq)
605 mbonus += rr + r * 2, ebonus += rr + r * 2;
608 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
609 ebonus += ebonus / 4;
611 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
615 Trace::add(PASSED, Us, score);
617 // Add the scores to the middlegame and endgame eval
622 // evaluate_space() computes the space evaluation for a given side. The
623 // space evaluation is a simple bonus based on the number of safe squares
624 // available for minor pieces on the central four files on ranks 2--4. Safe
625 // squares one, two or three squares behind a friendly pawn are counted
626 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
627 // improve play on game opening.
629 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
631 const Color Them = (Us == WHITE ? BLACK : WHITE);
632 const Bitboard SpaceMask =
633 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
634 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
636 // Find the safe squares for our pieces inside the area defined by
637 // SpaceMask. A square is unsafe if it is attacked by an enemy
638 // pawn, or if it is undefended and attacked by an enemy piece.
639 Bitboard safe = SpaceMask
640 & ~pos.pieces(Us, PAWN)
641 & ~ei.attackedBy[Them][PAWN]
642 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
644 // Find all squares which are at most three squares behind some friendly pawn
645 Bitboard behind = pos.pieces(Us, PAWN);
646 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
647 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
649 // Since SpaceMask[Us] is fully on our half of the board...
650 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
652 // ...count safe + (behind & safe) with a single popcount
653 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
654 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
655 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
657 return make_score(bonus * weight * weight * 2 / 11, 0);
661 // evaluate_initiative() computes the initiative correction value for the
662 // position, i.e., second order bonus/malus based on the known attacking/defending
663 // status of the players.
664 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
666 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
667 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
668 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
670 // Compute the initiative bonus for the attacking side
671 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
673 // Now apply the bonus: note that we find the attacking side by extracting
674 // the sign of the endgame value, and that we carefully cap the bonus so
675 // that the endgame score will never be divided by more than two.
676 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
678 return make_score(0, value);
682 // evaluate_scale_factor() computes the scale factor for the winning side
683 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
685 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
686 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
688 // If we don't already have an unusual scale factor, check for certain
689 // types of endgames, and use a lower scale for those.
690 if ( ei.me->game_phase() < PHASE_MIDGAME
691 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
693 if (pos.opposite_bishops())
695 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
696 // is almost a draw, in case of KBP vs KB, it is even more a draw.
697 if ( pos.non_pawn_material(WHITE) == BishopValueMg
698 && pos.non_pawn_material(BLACK) == BishopValueMg)
699 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
701 // Endgame with opposite-colored bishops, but also other pieces. Still
702 // a bit drawish, but not as drawish as with only the two bishops.
704 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
706 // Endings where weaker side can place his king in front of the opponent's
707 // pawns are drawish.
708 else if ( abs(eg) <= BishopValueEg
709 && ei.pi->pawn_span(strongSide) <= 1
710 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
711 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
720 /// evaluate() is the main evaluation function. It returns a static evaluation
721 /// of the position from the point of view of the side to move.
723 template<bool DoTrace>
724 Value Eval::evaluate(const Position& pos) {
726 assert(!pos.checkers());
729 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
731 // Initialize score by reading the incrementally updated scores included in
732 // the position object (material + piece square tables). Score is computed
733 // internally from the white point of view.
734 score = pos.psq_score();
736 // Probe the material hash table
737 ei.me = Material::probe(pos);
738 score += ei.me->imbalance();
740 // If we have a specialized evaluation function for the current material
741 // configuration, call it and return.
742 if (ei.me->specialized_eval_exists())
743 return ei.me->evaluate(pos);
745 // Probe the pawn hash table
746 ei.pi = Pawns::probe(pos);
747 score += ei.pi->pawns_score();
749 // Initialize attack and king safety bitboards
750 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
751 eval_init<WHITE>(pos, ei);
752 eval_init<BLACK>(pos, ei);
754 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
755 Bitboard blockedPawns[] = {
756 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
757 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
760 // Do not include in mobility area squares protected by enemy pawns, or occupied
761 // by our blocked pawns or king.
762 Bitboard mobilityArea[] = {
763 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
764 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
767 // Evaluate all pieces but king and pawns
768 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
769 score += mobility[WHITE] - mobility[BLACK];
771 // Evaluate kings after all other pieces because we need full attack
772 // information when computing the king safety evaluation.
773 score += evaluate_king<WHITE, DoTrace>(pos, ei)
774 - evaluate_king<BLACK, DoTrace>(pos, ei);
776 // Evaluate tactical threats, we need full attack information including king
777 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
778 - evaluate_threats<BLACK, DoTrace>(pos, ei);
780 // Evaluate passed pawns, we need full attack information including king
781 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
782 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
784 // If both sides have only pawns, score for potential unstoppable pawns
785 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
788 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
789 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
791 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
792 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
795 // Evaluate space for both sides, only during opening
796 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
797 score += evaluate_space<WHITE>(pos, ei)
798 - evaluate_space<BLACK>(pos, ei);
800 // Evaluate position potential for the winning side
801 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
803 // Evaluate scale factor for the winning side
804 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
806 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
807 Value v = mg_value(score) * int(ei.me->game_phase())
808 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
810 v /= int(PHASE_MIDGAME);
812 // In case of tracing add all remaining individual evaluation terms
815 Trace::add(MATERIAL, pos.psq_score());
816 Trace::add(IMBALANCE, ei.me->imbalance());
817 Trace::add(PAWN, ei.pi->pawns_score());
818 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
819 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
820 , evaluate_space<BLACK>(pos, ei));
821 Trace::add(TOTAL, score);
824 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
827 // Explicit template instantiations
828 template Value Eval::evaluate<true >(const Position&);
829 template Value Eval::evaluate<false>(const Position&);
832 /// trace() is like evaluate(), but instead of returning a value, it returns
833 /// a string (suitable for outputting to stdout) that contains the detailed
834 /// descriptions and values of each evaluation term. Useful for debugging.
836 std::string Eval::trace(const Position& pos) {
838 std::memset(scores, 0, sizeof(scores));
840 Value v = evaluate<true>(pos);
841 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
843 std::stringstream ss;
844 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
845 << " Eval term | White | Black | Total \n"
846 << " | MG EG | MG EG | MG EG \n"
847 << "----------------+-------------+-------------+-------------\n"
848 << " Material | " << Term(MATERIAL)
849 << " Imbalance | " << Term(IMBALANCE)
850 << " Pawns | " << Term(PAWN)
851 << " Knights | " << Term(KNIGHT)
852 << " Bishop | " << Term(BISHOP)
853 << " Rooks | " << Term(ROOK)
854 << " Queens | " << Term(QUEEN)
855 << " Mobility | " << Term(MOBILITY)
856 << " King safety | " << Term(KING)
857 << " Threats | " << Term(THREAT)
858 << " Passed pawns | " << Term(PASSED)
859 << " Space | " << Term(SPACE)
860 << "----------------+-------------+-------------+-------------\n"
861 << " Total | " << Term(TOTAL);
863 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
869 /// init() computes evaluation weights, usually at startup
873 const int MaxSlope = 322;
874 const int Peak = 47410;
877 for (int i = 0; i < 400; ++i)
879 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
880 KingDanger[i] = make_score(t * 268 / 7700, 0);