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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 #include <cstring> // For std::memset
35 enum Term { // First 8 entries are for PieceType
36 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
39 double scores[TERM_NB][COLOR_NB][PHASE_NB];
41 double to_cp(Value v) { return double(v) / PawnValueEg; }
43 void add(int idx, Color c, Score s) {
44 scores[idx][c][MG] = to_cp(mg_value(s));
45 scores[idx][c][EG] = to_cp(eg_value(s));
48 void add(int idx, Score w, Score b = SCORE_ZERO) {
49 add(idx, WHITE, w); add(idx, BLACK, b);
52 std::ostream& operator<<(std::ostream& os, Term t) {
54 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
55 os << " --- --- | --- --- | ";
57 os << std::setw(5) << scores[t][WHITE][MG] << " "
58 << std::setw(5) << scores[t][WHITE][EG] << " | "
59 << std::setw(5) << scores[t][BLACK][MG] << " "
60 << std::setw(5) << scores[t][BLACK][EG] << " | ";
62 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
63 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
69 using namespace Trace;
71 // Struct EvalInfo contains various information computed and collected
72 // by the evaluation functions.
75 // attackedBy[color][piece type] is a bitboard representing all squares
76 // attacked by a given color and piece type (can be also ALL_PIECES).
77 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
79 // kingRing[color] is the zone around the king which is considered
80 // by the king safety evaluation. This consists of the squares directly
81 // adjacent to the king, and the three (or two, for a king on an edge file)
82 // squares two ranks in front of the king. For instance, if black's king
83 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
84 // f7, g7, h7, f6, g6 and h6.
85 Bitboard kingRing[COLOR_NB];
87 // kingAttackersCount[color] is the number of pieces of the given color
88 // which attack a square in the kingRing of the enemy king.
89 int kingAttackersCount[COLOR_NB];
91 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
92 // given color which attack a square in the kingRing of the enemy king. The
93 // weights of the individual piece types are given by the elements in the
94 // KingAttackWeights array.
95 int kingAttackersWeight[COLOR_NB];
97 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
98 // color to squares directly adjacent to the enemy king. Pieces which attack
99 // more than one square are counted multiple times. For instance, if there is
100 // a white knight on g5 and black's king is on g8, this white knight adds 2
101 // to kingAdjacentZoneAttacksCount[WHITE].
102 int kingAdjacentZoneAttacksCount[COLOR_NB];
104 Bitboard pinnedPieces[COLOR_NB];
109 // Evaluation weights, indexed by the corresponding evaluation term
110 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
112 const struct Weight { int mg, eg; } Weights[] = {
113 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {322, 0}
116 Score operator*(Score s, const Weight& w) {
117 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
121 #define V(v) Value(v)
122 #define S(mg, eg) make_score(mg, eg)
124 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
125 // game, indexed by piece type and number of attacked squares not occupied by
127 const Score MobilityBonus[][32] = {
129 { S(-68,-49), S(-46,-33), S(-3,-12), S( 5, -4), S( 9, 11), S(15, 16), // Knights
130 S( 23, 27), S( 33, 28), S(37, 29) },
131 { S(-49,-44), S(-23,-16), S(16, 1), S(29, 16), S(40, 25), S(51, 34), // Bishops
132 S( 55, 43), S( 61, 49), S(64, 51), S(68, 52), S(73, 55), S(75, 60),
133 S( 80, 65), S( 86, 66) },
134 { S(-50,-57), S(-28,-22), S(-11, 7), S(-1, 29), S( 0, 39), S( 1, 46), // Rooks
135 S( 10, 66), S( 16, 79), S(22, 86), S(23,103), S(30,109), S(33,111),
136 S( 37,115), S( 38,119), S(48,124) },
137 { S(-43,-30), S(-27,-15), S( 1, -5), S( 2, -3), S(14, 10), S(18, 24), // Queens
138 S( 20, 27), S( 33, 37), S(33, 38), S(34, 43), S(40, 46), S(43, 56),
139 S( 46, 61), S( 52, 63), S(52, 63), S(57, 65), S(60, 70), S(61, 74),
140 S( 67, 80), S( 76, 82), S(77, 88), S(82, 94), S(86, 95), S(90, 96),
141 S( 94, 99), S( 96,100), S(99,111), S(99,112) }
144 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
145 // bishops outposts, bigger if outpost piece is supported by a pawn.
146 const Score Outpost[][2] = {
147 { S(42,11), S(63,17) }, // Knights
148 { S(18, 5), S(27, 8) } // Bishops
151 // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
152 // bonuses according to which piece type attacks which one.
153 const Score Threat[][2][PIECE_TYPE_NB] = {
154 { { S(0, 0), S( 0, 0), S(19, 37), S(24, 37), S(44, 97), S(35,106) }, // Defended Minor
155 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Defended Major
156 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Weak Minor
157 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Weak Major
160 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
161 // type is attacked by an enemy pawn.
162 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
163 S(0, 0), S(0, 0), S(107, 138), S(84, 122), S(114, 203), S(121, 217)
166 // Passed[mg/eg][rank] contains midgame and endgame bonuses for passed pawns.
167 // We don't use a Score because we process the two components independently.
168 const Value Passed[][RANK_NB] = {
169 { V(0), V( 1), V(34), V(90), V(214), V(328) },
170 { V(7), V(14), V(37), V(63), V(134), V(189) }
173 const Score ThreatenedByHangingPawn = S(40, 60);
175 // Assorted bonuses and penalties used by evaluation
176 const Score KingOnOne = S( 2, 58);
177 const Score KingOnMany = S( 6,125);
178 const Score RookOnPawn = S( 7, 27);
179 const Score RookOnOpenFile = S(43, 21);
180 const Score RookOnSemiOpenFile = S(19, 10);
181 const Score BishopPawns = S( 8, 12);
182 const Score MinorBehindPawn = S(16, 0);
183 const Score TrappedRook = S(92, 0);
184 const Score Unstoppable = S( 0, 20);
185 const Score Hanging = S(31, 26);
186 const Score PawnAttackThreat = S(20, 20);
187 const Score Checked = S(20, 20);
189 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
190 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
191 // happen in Chess960 games.
192 const Score TrappedBishopA1H1 = S(50, 50);
197 // SpaceMask[Color] contains the area of the board which is considered
198 // by the space evaluation. In the middlegame, each side is given a bonus
199 // based on how many squares inside this area are safe and available for
200 // friendly minor pieces.
201 const Bitboard SpaceMask[COLOR_NB] = {
202 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
203 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
206 // King danger constants and variables. The king danger scores are looked-up
207 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
208 // of the enemy attack are added up into an integer, which is used as an
209 // index to KingDanger[].
210 Score KingDanger[512];
212 // KingAttackWeights[PieceType] contains king attack weights by piece type
213 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
215 // Penalties for enemy's safe checks
216 const int QueenContactCheck = 89;
217 const int RookContactCheck = 71;
218 const int QueenCheck = 50;
219 const int RookCheck = 37;
220 const int BishopCheck = 6;
221 const int KnightCheck = 14;
224 // init_eval_info() initializes king bitboards for given color adding
225 // pawn attacks. To be done at the beginning of the evaluation.
228 void init_eval_info(const Position& pos, EvalInfo& ei) {
230 const Color Them = (Us == WHITE ? BLACK : WHITE);
231 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
233 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
234 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
235 ei.attackedBy[Them][ALL_PIECES] |= b;
236 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
238 // Init king safety tables only if we are going to use them
239 if (pos.non_pawn_material(Us) >= QueenValueMg)
241 ei.kingRing[Them] = b | shift_bb<Down>(b);
242 b &= ei.attackedBy[Us][PAWN];
243 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
244 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
247 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
251 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
253 template<PieceType Pt, Color Us, bool DoTrace>
254 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, const Bitboard* mobilityArea) {
258 Score score = SCORE_ZERO;
260 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
261 const Color Them = (Us == WHITE ? BLACK : WHITE);
262 const Square* pl = pos.squares<Pt>(Us);
264 ei.attackedBy[Us][Pt] = 0;
266 while ((s = *pl++) != SQ_NONE)
268 // Find attacked squares, including x-ray attacks for bishops and rooks
269 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
270 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
271 : pos.attacks_from<Pt>(s);
273 if (ei.pinnedPieces[Us] & s)
274 b &= LineBB[pos.square<KING>(Us)][s];
276 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
278 if (b & ei.kingRing[Them])
280 ei.kingAttackersCount[Us]++;
281 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
282 Bitboard bb = b & ei.attackedBy[Them][KING];
284 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
288 b &= ~( ei.attackedBy[Them][KNIGHT]
289 | ei.attackedBy[Them][BISHOP]
290 | ei.attackedBy[Them][ROOK]);
292 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
294 mobility[Us] += MobilityBonus[Pt][mob];
296 if (Pt == BISHOP || Pt == KNIGHT)
298 // Bonus for outpost square
299 if ( relative_rank(Us, s) >= RANK_4
300 && relative_rank(Us, s) <= RANK_6
301 && !(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
302 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
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 same color square of 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)
333 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
335 score += popcount<Max15>(alignedPawns) * RookOnPawn;
338 // Bonus when on an open or semi-open file
339 if (ei.pi->semiopen_file(Us, file_of(s)))
340 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
342 // Penalize when trapped by the king, even more if king cannot castle
343 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
345 Square ksq = pos.square<KING>(Us);
347 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
348 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
349 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
350 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
356 Trace::add(Pt, Us, score);
358 // Recursively call evaluate_pieces() of next piece type until KING excluded
359 return score - evaluate_pieces<NextPt, Them, DoTrace>(pos, ei, mobility, mobilityArea);
363 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
365 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
368 // evaluate_king() assigns bonuses and penalties to a king of a given color
370 template<Color Us, bool DoTrace>
371 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
373 const Color Them = (Us == WHITE ? BLACK : WHITE);
375 Bitboard undefended, b, b1, b2, safe;
377 const Square ksq = pos.square<KING>(Us);
379 // King shelter and enemy pawns storm
380 Score score = ei.pi->king_safety<Us>(pos, ksq);
382 // Main king safety evaluation
383 if (ei.kingAttackersCount[Them])
385 // Find the attacked squares around the king which have no defenders
386 // apart from the king itself
387 undefended = ei.attackedBy[Them][ALL_PIECES]
388 & ei.attackedBy[Us][KING]
389 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
390 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
391 | ei.attackedBy[Us][QUEEN]);
393 // Initialize the 'attackUnits' variable, which is used later on as an
394 // index into the KingDanger[] array. The initial value is based on the
395 // number and types of the enemy's attacking pieces, the number of
396 // attacked and undefended squares around our king and the quality of
397 // the pawn shelter (current 'score' value).
398 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
399 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
400 + 25 * popcount<Max15>(undefended)
401 + 11 * !!ei.pinnedPieces[Us]
402 - 60 * !pos.count<QUEEN>(Them)
403 - mg_value(score) / 8;
405 // Analyse the enemy's safe queen contact checks. Firstly, find the
406 // undefended squares around the king reachable by the enemy queen...
407 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
410 // ...and then remove squares not supported by another enemy piece
411 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
412 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
415 attackUnits += QueenContactCheck * popcount<Max15>(b);
418 // Analyse the enemy's safe rook contact checks. Firstly, find the
419 // undefended squares around the king reachable by the enemy rooks...
420 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
422 // Consider only squares where the enemy's rook gives check
423 b &= PseudoAttacks[ROOK][ksq];
427 // ...and then remove squares not supported by another enemy piece
428 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
429 | ei.attackedBy[Them][BISHOP]);
432 attackUnits += RookContactCheck * popcount<Max15>(b);
435 // Analyse the enemy's safe distance checks for sliders and knights
436 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
438 b1 = pos.attacks_from<ROOK >(ksq) & safe;
439 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
441 // Enemy queen safe checks
442 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
445 attackUnits += QueenCheck * popcount<Max15>(b);
449 // Enemy rooks safe checks
450 b = b1 & ei.attackedBy[Them][ROOK];
453 attackUnits += RookCheck * popcount<Max15>(b);
457 // Enemy bishops safe checks
458 b = b2 & ei.attackedBy[Them][BISHOP];
461 attackUnits += BishopCheck * popcount<Max15>(b);
465 // Enemy knights safe checks
466 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
469 attackUnits += KnightCheck * popcount<Max15>(b);
473 // Finally, extract the king danger score from the KingDanger[]
474 // array and subtract the score from evaluation.
475 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
479 Trace::add(KING, Us, score);
485 // evaluate_threats() assigns bonuses according to the type of attacking piece
486 // and the type of attacked one.
488 template<Color Us, bool DoTrace>
489 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
491 const Color Them = (Us == WHITE ? BLACK : WHITE);
492 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
493 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
494 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
495 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
496 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
498 enum { Defended, Weak };
499 enum { Minor, Major };
501 Bitboard b, weak, defended, safeThreats;
502 Score score = SCORE_ZERO;
504 // Non-pawn enemies attacked by a pawn
505 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
509 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
510 | ei.attackedBy[Us][ALL_PIECES]);
512 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
514 if (weak ^ safeThreats)
515 score += ThreatenedByHangingPawn;
518 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
521 // Non-pawn enemies defended by a pawn
522 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
524 // Add a bonus according to the kind of attacking pieces
527 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
529 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
531 b = defended & (ei.attackedBy[Us][ROOK]);
533 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
536 // Enemies not defended by a pawn and under our attack
537 weak = pos.pieces(Them)
538 & ~ei.attackedBy[Them][PAWN]
539 & ei.attackedBy[Us][ALL_PIECES];
541 // Add a bonus according to the kind of attacking pieces
544 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
546 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
548 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
550 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
552 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
554 score += Hanging * popcount<Max15>(b);
556 b = weak & ei.attackedBy[Us][KING];
558 score += more_than_one(b) ? KingOnMany : KingOnOne;
561 // Bonus if some pawns can safely push and attack an enemy piece
562 b = pos.pieces(Us, PAWN) & ~TRank7BB;
563 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
566 & ~ei.attackedBy[Them][PAWN]
567 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
569 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
571 & ~ei.attackedBy[Us][PAWN];
574 score += popcount<Max15>(b) * PawnAttackThreat;
577 Trace::add(THREAT, Us, score);
583 // evaluate_passed_pawns() evaluates the passed pawns of the given color
585 template<Color Us, bool DoTrace>
586 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
588 const Color Them = (Us == WHITE ? BLACK : WHITE);
590 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
591 Score score = SCORE_ZERO;
593 b = ei.pi->passed_pawns(Us);
597 Square s = pop_lsb(&b);
599 assert(pos.pawn_passed(Us, s));
601 int r = relative_rank(Us, s) - RANK_2;
602 int rr = r * (r - 1);
604 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
608 Square blockSq = s + pawn_push(Us);
610 // Adjust bonus based on the king's proximity
611 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
612 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
614 // If blockSq is not the queening square then consider also a second push
615 if (relative_rank(Us, blockSq) != RANK_8)
616 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
618 // If the pawn is free to advance, then increase the bonus
619 if (pos.empty(blockSq))
621 // If there is a rook or queen attacking/defending the pawn from behind,
622 // consider all the squaresToQueen. Otherwise consider only the squares
623 // in the pawn's path attacked or occupied by the enemy.
624 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
626 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
628 if (!(pos.pieces(Us) & bb))
629 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
631 if (!(pos.pieces(Them) & bb))
632 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
634 // If there aren't any enemy attacks, assign a big bonus. Otherwise
635 // assign a smaller bonus if the block square isn't attacked.
636 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
638 // If the path to queen is fully defended, assign a big bonus.
639 // Otherwise assign a smaller bonus if the block square is defended.
640 if (defendedSquares == squaresToQueen)
643 else if (defendedSquares & blockSq)
646 mbonus += k * rr, ebonus += k * rr;
648 else if (pos.pieces(Us) & blockSq)
649 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
652 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
653 ebonus += ebonus / 4;
655 score += make_score(mbonus, ebonus);
659 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
661 // Add the scores to the middlegame and endgame eval
662 return score * Weights[PassedPawns];
666 // evaluate_space() computes the space evaluation for a given side. The
667 // space evaluation is a simple bonus based on the number of safe squares
668 // available for minor pieces on the central four files on ranks 2--4. Safe
669 // squares one, two or three squares behind a friendly pawn are counted
670 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
671 // improve play on game opening.
673 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
675 const Color Them = (Us == WHITE ? BLACK : WHITE);
677 // Find the safe squares for our pieces inside the area defined by
678 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
679 // pawn, or if it is undefended and attacked by an enemy piece.
680 Bitboard safe = SpaceMask[Us]
681 & ~pos.pieces(Us, PAWN)
682 & ~ei.attackedBy[Them][PAWN]
683 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
685 // Find all squares which are at most three squares behind some friendly pawn
686 Bitboard behind = pos.pieces(Us, PAWN);
687 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
688 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
690 // Since SpaceMask[Us] is fully on our half of the board...
691 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
693 // ...count safe + (behind & safe) with a single popcount
694 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
695 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
696 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
698 return make_score(bonus * weight * weight, 0);
704 /// evaluate() is the main evaluation function. It returns a static evaluation
705 /// of the position always from the point of view of the side to move.
707 template<bool DoTrace>
708 Value Eval::evaluate(const Position& pos) {
710 assert(!pos.checkers());
713 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
715 // Initialize score by reading the incrementally updated scores included
716 // in the position object (material + piece square tables).
717 // Score is computed from the point of view of white.
718 score = pos.psq_score();
720 // Probe the material hash table
721 Material::Entry* me = Material::probe(pos);
722 score += me->imbalance();
724 // If we have a specialized evaluation function for the current material
725 // configuration, call it and return.
726 if (me->specialized_eval_exists())
727 return me->evaluate(pos);
729 // Probe the pawn hash table
730 ei.pi = Pawns::probe(pos);
731 score += ei.pi->pawns_score() * Weights[PawnStructure];
733 // Initialize attack and king safety bitboards
734 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
735 init_eval_info<WHITE>(pos, ei);
736 init_eval_info<BLACK>(pos, ei);
738 // Pawns blocked or on ranks 2 and 3. Will be excluded from the mobility area
739 Bitboard blockedPawns[] = {
740 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
741 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
744 // Do not include in mobility squares protected by enemy pawns, or occupied
745 // by our blocked pawns or king.
746 Bitboard mobilityArea[] = {
747 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
748 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
751 // Evaluate pieces and mobility
752 score += evaluate_pieces<KNIGHT, WHITE, DoTrace>(pos, ei, mobility, mobilityArea);
753 score += (mobility[WHITE] - mobility[BLACK]) * Weights[Mobility];
755 // Evaluate kings after all other pieces because we need complete attack
756 // information when computing the king safety evaluation.
757 score += evaluate_king<WHITE, DoTrace>(pos, ei)
758 - evaluate_king<BLACK, DoTrace>(pos, ei);
760 // Evaluate tactical threats, we need full attack information including king
761 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
762 - evaluate_threats<BLACK, DoTrace>(pos, ei);
764 // Evaluate passed pawns, we need full attack information including king
765 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
766 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
768 // If both sides have only pawns, score for potential unstoppable pawns
769 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
772 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
773 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
775 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
776 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
779 // Evaluate space for both sides, only during opening
780 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 11756)
781 score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
783 // Scale winning side if position is more drawish than it appears
784 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
785 ScaleFactor sf = me->scale_factor(pos, strongSide);
787 // If we don't already have an unusual scale factor, check for certain
788 // types of endgames, and use a lower scale for those.
789 if ( me->game_phase() < PHASE_MIDGAME
790 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
792 if (pos.opposite_bishops())
794 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
795 // is almost a draw, in case of KBP vs KB is even more a draw.
796 if ( pos.non_pawn_material(WHITE) == BishopValueMg
797 && pos.non_pawn_material(BLACK) == BishopValueMg)
798 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
800 // Endgame with opposite-colored bishops, but also other pieces. Still
801 // a bit drawish, but not as drawish as with only the two bishops.
803 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
805 // Endings where weaker side can place his king in front of the opponent's
806 // pawns are drawish.
807 else if ( abs(eg_value(score)) <= BishopValueEg
808 && ei.pi->pawn_span(strongSide) <= 1
809 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
810 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
813 // Scale endgame by number of pawns
814 int p = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
815 int v_eg = 1 + abs(int(eg_value(score)));
816 sf = ScaleFactor(std::max(sf / 2, sf - 7 * SCALE_FACTOR_NORMAL * (14 - p) / v_eg));
818 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
819 Value v = mg_value(score) * int(me->game_phase())
820 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
822 v /= int(PHASE_MIDGAME);
824 // In case of tracing add all single evaluation terms
827 Trace::add(MATERIAL, pos.psq_score());
828 Trace::add(IMBALANCE, me->imbalance());
829 Trace::add(PAWN, ei.pi->pawns_score());
830 Trace::add(MOBILITY, mobility[WHITE] * Weights[Mobility]
831 , mobility[BLACK] * Weights[Mobility]);
832 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
833 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
834 Trace::add(TOTAL, score);
837 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
840 // Explicit template instantiations
841 template Value Eval::evaluate<true >(const Position&);
842 template Value Eval::evaluate<false>(const Position&);
845 /// trace() is like evaluate(), but instead of returning a value, it returns
846 /// a string (suitable for outputting to stdout) that contains the detailed
847 /// descriptions and values of each evaluation term. Useful for debugging.
849 std::string Eval::trace(const Position& pos) {
851 std::memset(scores, 0, sizeof(scores));
853 Value v = evaluate<true>(pos);
854 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
856 std::stringstream ss;
857 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
858 << " Eval term | White | Black | Total \n"
859 << " | MG EG | MG EG | MG EG \n"
860 << "----------------+-------------+-------------+-------------\n"
861 << " Material | " << Term(MATERIAL)
862 << " Imbalance | " << Term(IMBALANCE)
863 << " Pawns | " << Term(PAWN)
864 << " Knights | " << Term(KNIGHT)
865 << " Bishop | " << Term(BISHOP)
866 << " Rooks | " << Term(ROOK)
867 << " Queens | " << Term(QUEEN)
868 << " Mobility | " << Term(MOBILITY)
869 << " King safety | " << Term(KING)
870 << " Threats | " << Term(THREAT)
871 << " Passed pawns | " << Term(PASSED)
872 << " Space | " << Term(SPACE)
873 << "----------------+-------------+-------------+-------------\n"
874 << " Total | " << Term(TOTAL);
876 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
882 /// init() computes evaluation weights, usually at startup
886 const int MaxSlope = 8700;
887 const int Peak = 1280000;
890 for (int i = 0; i < 400; ++i)
892 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
893 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];