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(-70,-52), S(-52,-37), S( -7,-17), S( 0, -6), S( 8, 5), S( 16, 9), // Knights
130 S( 23, 20), S( 31, 21), S( 36, 22) },
131 { S(-49,-44), S(-22,-13), S( 16, 0), S( 27, 11), S( 38, 19), S( 52, 34), // Bishops
132 S( 56, 44), S( 65, 47), S( 67, 51), S( 73, 56), S( 81, 59), S( 83, 69),
133 S( 95, 72), S(100, 75) },
134 { S(-49,-57), S(-22,-14), S(-10, 18), S( -5, 39), S( -4, 50), S( -2, 58), // Rooks
135 S( 6, 78), S( 11, 86), S( 17, 92), S( 19,103), S( 26,111), S( 27,115),
136 S( 36,119), S( 41,121), S( 50,122) },
137 { S(-41,-24), S(-26, -8), S( 0, 6), S( 2, 14), S( 12, 27), S( 21, 40), // Queens
138 S( 22, 45), S( 37, 55), S( 40, 57), S( 43, 63), S( 50, 68), S( 52, 74),
139 S( 56, 80), S( 66, 84), S( 68, 85), S( 69, 88), S( 71, 92), S( 72, 94),
140 S( 80, 96), S( 89, 98), S( 94,101), S(102,113), S(106,114), S(107,116),
141 S(112,125), S(113,127), S(117,137), S(122,143) }
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[minor/rook][attacked PieceType] contains
152 // bonuses according to which piece type attacks which one.
153 // Attacks on lesser pieces which are pawn defended are not considered.
154 const Score Threat[2][PIECE_TYPE_NB] = {
155 { S(0, 0), S(0, 32), S(25, 39), S(28, 44), S(42, 98), S(35,105) }, // Minor attacks
156 { S(0, 0), S(0, 27), S(26, 57), S(26, 57), S( 0, 30), S(23, 51) } // Rook attacks
159 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
160 // type is attacked by a pawn.
161 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
162 S(0, 0), S(0, 0), S(107, 138), S(84, 122), S(114, 203), S(121, 217)
165 // Passed[mg/eg][rank] contains midgame and endgame bonuses for passed pawns.
166 // We don't use a Score because we process the two components independently.
167 const Value Passed[][RANK_NB] = {
168 { V(0), V( 1), V(34), V(90), V(214), V(328) },
169 { V(7), V(14), V(37), V(63), V(134), V(189) }
172 // PassedFile[File] contains a bonus according to the file of a passed pawn.
173 const Score PassedFile[] = {
174 S( 12, 10), S( 3, 10), S( 1, -8), S(-27, -12),
175 S(-27, -12), S( 1, -8), S( 3, 10), S( 12, 10)
178 const Score ThreatenedByHangingPawn = S(40, 60);
180 // Assorted bonuses and penalties used by evaluation
181 const Score KingOnOne = S( 2, 58);
182 const Score KingOnMany = S( 6,125);
183 const Score RookOnPawn = S( 7, 27);
184 const Score RookOnOpenFile = S(43, 21);
185 const Score RookOnSemiOpenFile = S(19, 10);
186 const Score BishopPawns = S( 8, 12);
187 const Score MinorBehindPawn = S(16, 0);
188 const Score TrappedRook = S(92, 0);
189 const Score Unstoppable = S( 0, 20);
190 const Score Hanging = S(31, 26);
191 const Score PawnAttackThreat = S(20, 20);
192 const Score Checked = S(20, 20);
194 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
195 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
196 // happen in Chess960 games.
197 const Score TrappedBishopA1H1 = S(50, 50);
202 // SpaceMask[Color] contains the area of the board which is considered
203 // by the space evaluation. In the middlegame, each side is given a bonus
204 // based on how many squares inside this area are safe and available for
205 // friendly minor pieces.
206 const Bitboard SpaceMask[COLOR_NB] = {
207 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
208 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
211 // King danger constants and variables. The king danger scores are looked-up
212 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
213 // of the enemy attack are added up into an integer, which is used as an
214 // index to KingDanger[].
215 Score KingDanger[512];
217 // KingAttackWeights[PieceType] contains king attack weights by piece type
218 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
220 // Penalties for enemy's safe checks
221 const int QueenContactCheck = 89;
222 const int QueenCheck = 50;
223 const int RookCheck = 45;
224 const int BishopCheck = 6;
225 const int KnightCheck = 14;
228 // init_eval_info() initializes king bitboards for given color adding
229 // pawn attacks. To be done at the beginning of the evaluation.
232 void init_eval_info(const Position& pos, EvalInfo& ei) {
234 const Color Them = (Us == WHITE ? BLACK : WHITE);
235 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
237 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
238 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
239 ei.attackedBy[Them][ALL_PIECES] |= b;
240 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
242 // Init king safety tables only if we are going to use them
243 if (pos.non_pawn_material(Us) >= QueenValueMg)
245 ei.kingRing[Them] = b | shift_bb<Down>(b);
246 b &= ei.attackedBy[Us][PAWN];
247 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
248 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
251 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
255 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
257 template<PieceType Pt, Color Us, bool DoTrace>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, const Bitboard* mobilityArea) {
262 Score score = SCORE_ZERO;
264 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
265 const Color Them = (Us == WHITE ? BLACK : WHITE);
266 const Square* pl = pos.squares<Pt>(Us);
268 ei.attackedBy[Us][Pt] = 0;
270 while ((s = *pl++) != SQ_NONE)
272 // Find attacked squares, including x-ray attacks for bishops and rooks
273 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
274 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
275 : pos.attacks_from<Pt>(s);
277 if (ei.pinnedPieces[Us] & s)
278 b &= LineBB[pos.square<KING>(Us)][s];
280 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
282 if (b & ei.kingRing[Them])
284 ei.kingAttackersCount[Us]++;
285 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
286 Bitboard bb = b & ei.attackedBy[Them][KING];
288 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
292 b &= ~( ei.attackedBy[Them][KNIGHT]
293 | ei.attackedBy[Them][BISHOP]
294 | ei.attackedBy[Them][ROOK]);
296 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
298 mobility[Us] += MobilityBonus[Pt][mob];
300 if (Pt == BISHOP || Pt == KNIGHT)
302 // Bonus for outpost square
303 if ( relative_rank(Us, s) >= RANK_4
304 && relative_rank(Us, s) <= RANK_6
305 && !(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
306 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
308 // Bonus when behind a pawn
309 if ( relative_rank(Us, s) < RANK_5
310 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
311 score += MinorBehindPawn;
313 // Penalty for pawns on same color square of bishop
315 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
317 // An important Chess960 pattern: A cornered bishop blocked by a friendly
318 // pawn diagonally in front of it is a very serious problem, especially
319 // when that pawn is also blocked.
322 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
324 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
325 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
326 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
327 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
334 // Bonus for aligning with enemy pawns on the same rank/file
335 if (relative_rank(Us, s) >= RANK_5)
337 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
339 score += popcount<Max15>(alignedPawns) * RookOnPawn;
342 // Bonus when on an open or semi-open file
343 if (ei.pi->semiopen_file(Us, file_of(s)))
344 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
346 // Penalize when trapped by the king, even more if king cannot castle
347 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
349 Square ksq = pos.square<KING>(Us);
351 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
352 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
353 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
354 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
360 Trace::add(Pt, Us, score);
362 // Recursively call evaluate_pieces() of next piece type until KING excluded
363 return score - evaluate_pieces<NextPt, Them, DoTrace>(pos, ei, mobility, mobilityArea);
367 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
369 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
372 // evaluate_king() assigns bonuses and penalties to a king of a given color
374 template<Color Us, bool DoTrace>
375 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
377 const Color Them = (Us == WHITE ? BLACK : WHITE);
379 Bitboard undefended, b, b1, b2, safe;
381 const Square ksq = pos.square<KING>(Us);
383 // King shelter and enemy pawns storm
384 Score score = ei.pi->king_safety<Us>(pos, ksq);
386 // Main king safety evaluation
387 if (ei.kingAttackersCount[Them])
389 // Find the attacked squares around the king which have no defenders
390 // apart from the king itself
391 undefended = ei.attackedBy[Them][ALL_PIECES]
392 & ei.attackedBy[Us][KING]
393 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
394 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
395 | ei.attackedBy[Us][QUEEN]);
397 // Initialize the 'attackUnits' variable, which is used later on as an
398 // index into the KingDanger[] array. The initial value is based on the
399 // number and types of the enemy's attacking pieces, the number of
400 // attacked and undefended squares around our king and the quality of
401 // the pawn shelter (current 'score' value).
402 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
403 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
404 + 27 * popcount<Max15>(undefended)
405 + 11 * !!ei.pinnedPieces[Us]
406 - 64 * !pos.count<QUEEN>(Them)
407 - mg_value(score) / 8;
409 // Analyse the enemy's safe queen contact checks. Firstly, find the
410 // undefended squares around the king reachable by the enemy queen...
411 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
414 // ...and then remove squares not supported by another enemy piece
415 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
416 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
417 | ei.attackedBy[Them][KING];
420 attackUnits += QueenContactCheck * popcount<Max15>(b);
423 // Analyse the enemy's safe distance checks for sliders and knights
424 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
426 b1 = pos.attacks_from<ROOK >(ksq) & safe;
427 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
429 // Enemy queen safe checks
430 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
433 attackUnits += QueenCheck * popcount<Max15>(b);
437 // Enemy rooks safe checks
438 b = b1 & ei.attackedBy[Them][ROOK];
441 attackUnits += RookCheck * popcount<Max15>(b);
445 // Enemy bishops safe checks
446 b = b2 & ei.attackedBy[Them][BISHOP];
449 attackUnits += BishopCheck * popcount<Max15>(b);
453 // Enemy knights safe checks
454 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
457 attackUnits += KnightCheck * popcount<Max15>(b);
461 // Finally, extract the king danger score from the KingDanger[]
462 // array and subtract the score from evaluation.
463 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
467 Trace::add(KING, Us, score);
473 // evaluate_threats() assigns bonuses according to the type of attacking piece
474 // and the type of attacked one.
476 template<Color Us, bool DoTrace>
477 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
479 const Color Them = (Us == WHITE ? BLACK : WHITE);
480 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
481 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
482 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
483 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
484 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
486 enum { Minor, Rook };
488 Bitboard b, weak, defended, safeThreats;
489 Score score = SCORE_ZERO;
491 // Non-pawn enemies attacked by a pawn
492 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
496 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
497 | ei.attackedBy[Us][ALL_PIECES]);
499 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
501 if (weak ^ safeThreats)
502 score += ThreatenedByHangingPawn;
505 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
508 // Non-pawn enemies defended by a pawn
509 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
511 // Enemies not defended by a pawn and under our attack
512 weak = pos.pieces(Them)
513 & ~ei.attackedBy[Them][PAWN]
514 & ei.attackedBy[Us][ALL_PIECES];
516 // Add a bonus according to the kind of attacking pieces
519 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
521 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
523 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
525 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
527 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
529 score += Hanging * popcount<Max15>(b);
531 b = weak & ei.attackedBy[Us][KING];
533 score += more_than_one(b) ? KingOnMany : KingOnOne;
536 // Bonus if some pawns can safely push and attack an enemy piece
537 b = pos.pieces(Us, PAWN) & ~TRank7BB;
538 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
541 & ~ei.attackedBy[Them][PAWN]
542 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
544 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
546 & ~ei.attackedBy[Us][PAWN];
549 score += popcount<Max15>(b) * PawnAttackThreat;
552 Trace::add(THREAT, Us, score);
558 // evaluate_passed_pawns() evaluates the passed pawns of the given color
560 template<Color Us, bool DoTrace>
561 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
563 const Color Them = (Us == WHITE ? BLACK : WHITE);
565 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
566 Score score = SCORE_ZERO;
568 b = ei.pi->passed_pawns(Us);
572 Square s = pop_lsb(&b);
574 assert(pos.pawn_passed(Us, s));
576 int r = relative_rank(Us, s) - RANK_2;
577 int rr = r * (r - 1);
579 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
583 Square blockSq = s + pawn_push(Us);
585 // Adjust bonus based on the king's proximity
586 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
587 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
589 // If blockSq is not the queening square then consider also a second push
590 if (relative_rank(Us, blockSq) != RANK_8)
591 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
593 // If the pawn is free to advance, then increase the bonus
594 if (pos.empty(blockSq))
596 // If there is a rook or queen attacking/defending the pawn from behind,
597 // consider all the squaresToQueen. Otherwise consider only the squares
598 // in the pawn's path attacked or occupied by the enemy.
599 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
601 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
603 if (!(pos.pieces(Us) & bb))
604 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
606 if (!(pos.pieces(Them) & bb))
607 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
609 // If there aren't any enemy attacks, assign a big bonus. Otherwise
610 // assign a smaller bonus if the block square isn't attacked.
611 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
613 // If the path to queen is fully defended, assign a big bonus.
614 // Otherwise assign a smaller bonus if the block square is defended.
615 if (defendedSquares == squaresToQueen)
618 else if (defendedSquares & blockSq)
621 mbonus += k * rr, ebonus += k * rr;
623 else if (pos.pieces(Us) & blockSq)
624 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
627 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
628 ebonus += ebonus / 4;
630 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
634 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
636 // Add the scores to the middlegame and endgame eval
637 return score * Weights[PassedPawns];
641 // evaluate_space() computes the space evaluation for a given side. The
642 // space evaluation is a simple bonus based on the number of safe squares
643 // available for minor pieces on the central four files on ranks 2--4. Safe
644 // squares one, two or three squares behind a friendly pawn are counted
645 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
646 // improve play on game opening.
648 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
650 const Color Them = (Us == WHITE ? BLACK : WHITE);
652 // Find the safe squares for our pieces inside the area defined by
653 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
654 // pawn, or if it is undefended and attacked by an enemy piece.
655 Bitboard safe = SpaceMask[Us]
656 & ~pos.pieces(Us, PAWN)
657 & ~ei.attackedBy[Them][PAWN]
658 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
660 // Find all squares which are at most three squares behind some friendly pawn
661 Bitboard behind = pos.pieces(Us, PAWN);
662 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
663 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
665 // Since SpaceMask[Us] is fully on our half of the board...
666 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
668 // ...count safe + (behind & safe) with a single popcount
669 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
670 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
671 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
673 return make_score(bonus * weight * weight, 0);
677 // evaluate_initiative() computes the initiative correction value for the
678 // position, i.e. second order bonus/malus based on the known attacking/defending
679 // status of the players.
680 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
682 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
683 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
685 // Compute the initiative bonus for the attacking side
686 int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
688 // Now apply the bonus: note that we find the attacking side by extracting
689 // the sign of the endgame value, and that we carefully cap the bonus so
690 // that the endgame score will never be divided by more than two.
691 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
693 return make_score(0, value);
699 /// evaluate() is the main evaluation function. It returns a static evaluation
700 /// of the position always from the point of view of the side to move.
702 template<bool DoTrace>
703 Value Eval::evaluate(const Position& pos) {
705 assert(!pos.checkers());
708 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
710 // Initialize score by reading the incrementally updated scores included
711 // in the position object (material + piece square tables).
712 // Score is computed from the point of view of white.
713 score = pos.psq_score();
715 // Probe the material hash table
716 Material::Entry* me = Material::probe(pos);
717 score += me->imbalance();
719 // If we have a specialized evaluation function for the current material
720 // configuration, call it and return.
721 if (me->specialized_eval_exists())
722 return me->evaluate(pos);
724 // Probe the pawn hash table
725 ei.pi = Pawns::probe(pos);
726 score += ei.pi->pawns_score() * Weights[PawnStructure];
728 // Initialize attack and king safety bitboards
729 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
730 init_eval_info<WHITE>(pos, ei);
731 init_eval_info<BLACK>(pos, ei);
733 // Pawns blocked or on ranks 2 and 3. Will be excluded from the mobility area
734 Bitboard blockedPawns[] = {
735 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
736 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
739 // Do not include in mobility squares protected by enemy pawns, or occupied
740 // by our blocked pawns or king.
741 Bitboard mobilityArea[] = {
742 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
743 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
746 // Evaluate pieces and mobility
747 score += evaluate_pieces<KNIGHT, WHITE, DoTrace>(pos, ei, mobility, mobilityArea);
748 score += (mobility[WHITE] - mobility[BLACK]) * Weights[Mobility];
750 // Evaluate kings after all other pieces because we need complete attack
751 // information when computing the king safety evaluation.
752 score += evaluate_king<WHITE, DoTrace>(pos, ei)
753 - evaluate_king<BLACK, DoTrace>(pos, ei);
755 // Evaluate tactical threats, we need full attack information including king
756 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
757 - evaluate_threats<BLACK, DoTrace>(pos, ei);
759 // Evaluate passed pawns, we need full attack information including king
760 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
761 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
763 // If both sides have only pawns, score for potential unstoppable pawns
764 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
767 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
768 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
770 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
771 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
774 // Evaluate space for both sides, only during opening
775 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
776 score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
778 // Evaluate position potential for the winning side
779 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
781 // Scale winning side if position is more drawish than it appears
782 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
783 ScaleFactor sf = me->scale_factor(pos, strongSide);
785 // If we don't already have an unusual scale factor, check for certain
786 // types of endgames, and use a lower scale for those.
787 if ( me->game_phase() < PHASE_MIDGAME
788 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
790 if (pos.opposite_bishops())
792 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
793 // is almost a draw, in case of KBP vs KB is even more a draw.
794 if ( pos.non_pawn_material(WHITE) == BishopValueMg
795 && pos.non_pawn_material(BLACK) == BishopValueMg)
796 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
798 // Endgame with opposite-colored bishops, but also other pieces. Still
799 // a bit drawish, but not as drawish as with only the two bishops.
801 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
803 // Endings where weaker side can place his king in front of the opponent's
804 // pawns are drawish.
805 else if ( abs(eg_value(score)) <= BishopValueEg
806 && ei.pi->pawn_span(strongSide) <= 1
807 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
808 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
811 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
812 Value v = mg_value(score) * int(me->game_phase())
813 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
815 v /= int(PHASE_MIDGAME);
817 // In case of tracing add all single evaluation terms
820 Trace::add(MATERIAL, pos.psq_score());
821 Trace::add(IMBALANCE, me->imbalance());
822 Trace::add(PAWN, ei.pi->pawns_score());
823 Trace::add(MOBILITY, mobility[WHITE] * Weights[Mobility]
824 , mobility[BLACK] * Weights[Mobility]);
825 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
826 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
827 Trace::add(TOTAL, score);
830 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
833 // Explicit template instantiations
834 template Value Eval::evaluate<true >(const Position&);
835 template Value Eval::evaluate<false>(const Position&);
838 /// trace() is like evaluate(), but instead of returning a value, it returns
839 /// a string (suitable for outputting to stdout) that contains the detailed
840 /// descriptions and values of each evaluation term. Useful for debugging.
842 std::string Eval::trace(const Position& pos) {
844 std::memset(scores, 0, sizeof(scores));
846 Value v = evaluate<true>(pos);
847 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
849 std::stringstream ss;
850 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
851 << " Eval term | White | Black | Total \n"
852 << " | MG EG | MG EG | MG EG \n"
853 << "----------------+-------------+-------------+-------------\n"
854 << " Material | " << Term(MATERIAL)
855 << " Imbalance | " << Term(IMBALANCE)
856 << " Pawns | " << Term(PAWN)
857 << " Knights | " << Term(KNIGHT)
858 << " Bishop | " << Term(BISHOP)
859 << " Rooks | " << Term(ROOK)
860 << " Queens | " << Term(QUEEN)
861 << " Mobility | " << Term(MOBILITY)
862 << " King safety | " << Term(KING)
863 << " Threats | " << Term(THREAT)
864 << " Passed pawns | " << Term(PASSED)
865 << " Space | " << Term(SPACE)
866 << "----------------+-------------+-------------+-------------\n"
867 << " Total | " << Term(TOTAL);
869 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
875 /// init() computes evaluation weights, usually at startup
879 const int MaxSlope = 8700;
880 const int Peak = 1280000;
883 for (int i = 0; i < 400; ++i)
885 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
886 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];