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/rook 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) }, // Minor on Defended
155 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Rook on Defended
156 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Minor on Weak
157 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Rook on Weak
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 // PassedFile[File] contains a bonus according to the file of a passed pawn.
174 const Score PassedFile[] = {
175 S( 14, 13), S( 2, 5), S(-3, -4), S(-19, -14),
176 S(-19, -14), S(-3, -4), S( 2, 5), S( 14, 13)
179 const Score ThreatenedByHangingPawn = S(40, 60);
181 // Assorted bonuses and penalties used by evaluation
182 const Score KingOnOne = S( 2, 58);
183 const Score KingOnMany = S( 6,125);
184 const Score RookOnPawn = S( 7, 27);
185 const Score RookOnOpenFile = S(43, 21);
186 const Score RookOnSemiOpenFile = S(19, 10);
187 const Score BishopPawns = S( 8, 12);
188 const Score MinorBehindPawn = S(16, 0);
189 const Score TrappedRook = S(92, 0);
190 const Score Unstoppable = S( 0, 20);
191 const Score Hanging = S(31, 26);
192 const Score PawnAttackThreat = S(20, 20);
193 const Score Checked = S(20, 20);
195 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
196 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
197 // happen in Chess960 games.
198 const Score TrappedBishopA1H1 = S(50, 50);
203 // SpaceMask[Color] contains the area of the board which is considered
204 // by the space evaluation. In the middlegame, each side is given a bonus
205 // based on how many squares inside this area are safe and available for
206 // friendly minor pieces.
207 const Bitboard SpaceMask[COLOR_NB] = {
208 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
209 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
212 // King danger constants and variables. The king danger scores are looked-up
213 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
214 // of the enemy attack are added up into an integer, which is used as an
215 // index to KingDanger[].
216 Score KingDanger[512];
218 // KingAttackWeights[PieceType] contains king attack weights by piece type
219 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
221 // Penalties for enemy's safe checks
222 const int QueenContactCheck = 89;
223 const int QueenCheck = 50;
224 const int RookCheck = 45;
225 const int BishopCheck = 6;
226 const int KnightCheck = 14;
229 // init_eval_info() initializes king bitboards for given color adding
230 // pawn attacks. To be done at the beginning of the evaluation.
233 void init_eval_info(const Position& pos, EvalInfo& ei) {
235 const Color Them = (Us == WHITE ? BLACK : WHITE);
236 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
238 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
239 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
240 ei.attackedBy[Them][ALL_PIECES] |= b;
241 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
243 // Init king safety tables only if we are going to use them
244 if (pos.non_pawn_material(Us) >= QueenValueMg)
246 ei.kingRing[Them] = b | shift_bb<Down>(b);
247 b &= ei.attackedBy[Us][PAWN];
248 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
249 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
252 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
256 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
258 template<PieceType Pt, Color Us, bool DoTrace>
259 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, const Bitboard* mobilityArea) {
263 Score score = SCORE_ZERO;
265 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
266 const Color Them = (Us == WHITE ? BLACK : WHITE);
267 const Square* pl = pos.squares<Pt>(Us);
269 ei.attackedBy[Us][Pt] = 0;
271 while ((s = *pl++) != SQ_NONE)
273 // Find attacked squares, including x-ray attacks for bishops and rooks
274 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
275 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
276 : pos.attacks_from<Pt>(s);
278 if (ei.pinnedPieces[Us] & s)
279 b &= LineBB[pos.square<KING>(Us)][s];
281 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
283 if (b & ei.kingRing[Them])
285 ei.kingAttackersCount[Us]++;
286 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
287 Bitboard bb = b & ei.attackedBy[Them][KING];
289 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
293 b &= ~( ei.attackedBy[Them][KNIGHT]
294 | ei.attackedBy[Them][BISHOP]
295 | ei.attackedBy[Them][ROOK]);
297 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
299 mobility[Us] += MobilityBonus[Pt][mob];
301 if (Pt == BISHOP || Pt == KNIGHT)
303 // Bonus for outpost square
304 if ( relative_rank(Us, s) >= RANK_4
305 && relative_rank(Us, s) <= RANK_6
306 && !(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
307 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
309 // Bonus when behind a pawn
310 if ( relative_rank(Us, s) < RANK_5
311 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
312 score += MinorBehindPawn;
314 // Penalty for pawns on same color square of bishop
316 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
318 // An important Chess960 pattern: A cornered bishop blocked by a friendly
319 // pawn diagonally in front of it is a very serious problem, especially
320 // when that pawn is also blocked.
323 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
325 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
326 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
327 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
328 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
335 // Bonus for aligning with enemy pawns on the same rank/file
336 if (relative_rank(Us, s) >= RANK_5)
338 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
340 score += popcount<Max15>(alignedPawns) * RookOnPawn;
343 // Bonus when on an open or semi-open file
344 if (ei.pi->semiopen_file(Us, file_of(s)))
345 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
347 // Penalize when trapped by the king, even more if king cannot castle
348 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
350 Square ksq = pos.square<KING>(Us);
352 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
353 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
354 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
355 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
361 Trace::add(Pt, Us, score);
363 // Recursively call evaluate_pieces() of next piece type until KING excluded
364 return score - evaluate_pieces<NextPt, Them, DoTrace>(pos, ei, mobility, mobilityArea);
368 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
370 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
373 // evaluate_king() assigns bonuses and penalties to a king of a given color
375 template<Color Us, bool DoTrace>
376 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
378 const Color Them = (Us == WHITE ? BLACK : WHITE);
380 Bitboard undefended, b, b1, b2, safe;
382 const Square ksq = pos.square<KING>(Us);
384 // King shelter and enemy pawns storm
385 Score score = ei.pi->king_safety<Us>(pos, ksq);
387 // Main king safety evaluation
388 if (ei.kingAttackersCount[Them])
390 // Find the attacked squares around the king which have no defenders
391 // apart from the king itself
392 undefended = ei.attackedBy[Them][ALL_PIECES]
393 & ei.attackedBy[Us][KING]
394 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
395 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
396 | ei.attackedBy[Us][QUEEN]);
398 // Initialize the 'attackUnits' variable, which is used later on as an
399 // index into the KingDanger[] array. The initial value is based on the
400 // number and types of the enemy's attacking pieces, the number of
401 // attacked and undefended squares around our king and the quality of
402 // the pawn shelter (current 'score' value).
403 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
404 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
405 + 27 * popcount<Max15>(undefended)
406 + 11 * !!ei.pinnedPieces[Us]
407 - 64 * !pos.count<QUEEN>(Them)
408 - mg_value(score) / 8;
410 // Analyse the enemy's safe queen contact checks. Firstly, find the
411 // undefended squares around the king reachable by the enemy queen...
412 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
415 // ...and then remove squares not supported by another enemy piece
416 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
417 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
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 { Defended, Weak };
487 enum { Minor, Rook };
489 Bitboard b, weak, defended, safeThreats;
490 Score score = SCORE_ZERO;
492 // Non-pawn enemies attacked by a pawn
493 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
497 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
498 | ei.attackedBy[Us][ALL_PIECES]);
500 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
502 if (weak ^ safeThreats)
503 score += ThreatenedByHangingPawn;
506 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
509 // Non-pawn enemies defended by a pawn
510 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
512 // Add a bonus according to the kind of attacking pieces
515 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
517 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
519 b = defended & ei.attackedBy[Us][ROOK];
521 score += Threat[Defended][Rook][type_of(pos.piece_on(pop_lsb(&b)))];
524 // Enemies not defended by a pawn and under our attack
525 weak = pos.pieces(Them)
526 & ~ei.attackedBy[Them][PAWN]
527 & ei.attackedBy[Us][ALL_PIECES];
529 // Add a bonus according to the kind of attacking pieces
532 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
534 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
536 b = weak & ei.attackedBy[Us][ROOK];
538 score += Threat[Weak][Rook][type_of(pos.piece_on(pop_lsb(&b)))];
540 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
542 score += Hanging * popcount<Max15>(b);
544 b = weak & ei.attackedBy[Us][KING];
546 score += more_than_one(b) ? KingOnMany : KingOnOne;
549 // Bonus if some pawns can safely push and attack an enemy piece
550 b = pos.pieces(Us, PAWN) & ~TRank7BB;
551 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
554 & ~ei.attackedBy[Them][PAWN]
555 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
557 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
559 & ~ei.attackedBy[Us][PAWN];
562 score += popcount<Max15>(b) * PawnAttackThreat;
565 Trace::add(THREAT, Us, score);
571 // evaluate_passed_pawns() evaluates the passed pawns of the given color
573 template<Color Us, bool DoTrace>
574 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
576 const Color Them = (Us == WHITE ? BLACK : WHITE);
578 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
579 Score score = SCORE_ZERO;
581 b = ei.pi->passed_pawns(Us);
585 Square s = pop_lsb(&b);
587 assert(pos.pawn_passed(Us, s));
589 int r = relative_rank(Us, s) - RANK_2;
590 int rr = r * (r - 1);
592 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
596 Square blockSq = s + pawn_push(Us);
598 // Adjust bonus based on the king's proximity
599 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
600 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
602 // If blockSq is not the queening square then consider also a second push
603 if (relative_rank(Us, blockSq) != RANK_8)
604 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
606 // If the pawn is free to advance, then increase the bonus
607 if (pos.empty(blockSq))
609 // If there is a rook or queen attacking/defending the pawn from behind,
610 // consider all the squaresToQueen. Otherwise consider only the squares
611 // in the pawn's path attacked or occupied by the enemy.
612 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
614 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
616 if (!(pos.pieces(Us) & bb))
617 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
619 if (!(pos.pieces(Them) & bb))
620 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
622 // If there aren't any enemy attacks, assign a big bonus. Otherwise
623 // assign a smaller bonus if the block square isn't attacked.
624 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
626 // If the path to queen is fully defended, assign a big bonus.
627 // Otherwise assign a smaller bonus if the block square is defended.
628 if (defendedSquares == squaresToQueen)
631 else if (defendedSquares & blockSq)
634 mbonus += k * rr, ebonus += k * rr;
636 else if (pos.pieces(Us) & blockSq)
637 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
640 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
641 ebonus += ebonus / 4;
643 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
647 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
649 // Add the scores to the middlegame and endgame eval
650 return score * Weights[PassedPawns];
654 // evaluate_space() computes the space evaluation for a given side. The
655 // space evaluation is a simple bonus based on the number of safe squares
656 // available for minor pieces on the central four files on ranks 2--4. Safe
657 // squares one, two or three squares behind a friendly pawn are counted
658 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
659 // improve play on game opening.
661 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
663 const Color Them = (Us == WHITE ? BLACK : WHITE);
665 // Find the safe squares for our pieces inside the area defined by
666 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
667 // pawn, or if it is undefended and attacked by an enemy piece.
668 Bitboard safe = SpaceMask[Us]
669 & ~pos.pieces(Us, PAWN)
670 & ~ei.attackedBy[Them][PAWN]
671 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
673 // Find all squares which are at most three squares behind some friendly pawn
674 Bitboard behind = pos.pieces(Us, PAWN);
675 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
676 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
678 // Since SpaceMask[Us] is fully on our half of the board...
679 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
681 // ...count safe + (behind & safe) with a single popcount
682 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
683 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
684 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
686 return make_score(bonus * weight * weight, 0);
690 // evaluate_initiative() computes the initiative correction value for the position, i.e.
691 // second order bonus/malus based on the known attacking/defending status of the players.
692 Score evaluate_initiative(const Position& pos, const EvalInfo& ei, const Score positional_score) {
694 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
695 int king_separation = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
696 int asymmetry = ei.pi->pawn_asymmetry();
698 // Compute the initiative bonus for the attacking side
699 int attacker_bonus = 8 * (pawns + asymmetry + king_separation) - 120;
701 // Now apply the bonus: note that we find the attacking side by extracting the sign
702 // of the endgame value of "positional_score", and that we carefully cap the bonus so
703 // that the endgame score with the correction will never be divided by more than two.
704 int eg = eg_value(positional_score);
705 int value = ((eg > 0) - (eg < 0)) * std::max( attacker_bonus , -abs( eg / 2 ) );
707 return make_score( 0 , value ) ;
713 /// evaluate() is the main evaluation function. It returns a static evaluation
714 /// of the position always from the point of view of the side to move.
716 template<bool DoTrace>
717 Value Eval::evaluate(const Position& pos) {
719 assert(!pos.checkers());
722 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
724 // Initialize score by reading the incrementally updated scores included
725 // in the position object (material + piece square tables).
726 // Score is computed from the point of view of white.
727 score = pos.psq_score();
729 // Probe the material hash table
730 Material::Entry* me = Material::probe(pos);
731 score += me->imbalance();
733 // If we have a specialized evaluation function for the current material
734 // configuration, call it and return.
735 if (me->specialized_eval_exists())
736 return me->evaluate(pos);
738 // Probe the pawn hash table
739 ei.pi = Pawns::probe(pos);
740 score += ei.pi->pawns_score() * Weights[PawnStructure];
742 // Initialize attack and king safety bitboards
743 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
744 init_eval_info<WHITE>(pos, ei);
745 init_eval_info<BLACK>(pos, ei);
747 // Pawns blocked or on ranks 2 and 3. Will be excluded from the mobility area
748 Bitboard blockedPawns[] = {
749 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
750 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
753 // Do not include in mobility squares protected by enemy pawns, or occupied
754 // by our blocked pawns or king.
755 Bitboard mobilityArea[] = {
756 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
757 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
760 // Evaluate pieces and mobility
761 score += evaluate_pieces<KNIGHT, WHITE, DoTrace>(pos, ei, mobility, mobilityArea);
762 score += (mobility[WHITE] - mobility[BLACK]) * Weights[Mobility];
764 // Evaluate kings after all other pieces because we need complete attack
765 // information when computing the king safety evaluation.
766 score += evaluate_king<WHITE, DoTrace>(pos, ei)
767 - evaluate_king<BLACK, DoTrace>(pos, ei);
769 // Evaluate tactical threats, we need full attack information including king
770 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
771 - evaluate_threats<BLACK, DoTrace>(pos, ei);
773 // Evaluate passed pawns, we need full attack information including king
774 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
775 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
777 // If both sides have only pawns, score for potential unstoppable pawns
778 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
781 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
782 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
784 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
785 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
788 // Evaluate space for both sides, only during opening
789 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
790 score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
792 // Evaluate initiative
793 score += evaluate_initiative(pos, ei, score);
795 // Scale winning side if position is more drawish than it appears
796 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
797 ScaleFactor sf = me->scale_factor(pos, strongSide);
799 // If we don't already have an unusual scale factor, check for certain
800 // types of endgames, and use a lower scale for those.
801 if ( me->game_phase() < PHASE_MIDGAME
802 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
804 if (pos.opposite_bishops())
806 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
807 // is almost a draw, in case of KBP vs KB is even more a draw.
808 if ( pos.non_pawn_material(WHITE) == BishopValueMg
809 && pos.non_pawn_material(BLACK) == BishopValueMg)
810 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
812 // Endgame with opposite-colored bishops, but also other pieces. Still
813 // a bit drawish, but not as drawish as with only the two bishops.
815 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
817 // Endings where weaker side can place his king in front of the opponent's
818 // pawns are drawish.
819 else if ( abs(eg_value(score)) <= BishopValueEg
820 && ei.pi->pawn_span(strongSide) <= 1
821 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
822 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
825 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
826 Value v = mg_value(score) * int(me->game_phase())
827 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
829 v /= int(PHASE_MIDGAME);
831 // In case of tracing add all single evaluation terms
834 Trace::add(MATERIAL, pos.psq_score());
835 Trace::add(IMBALANCE, me->imbalance());
836 Trace::add(PAWN, ei.pi->pawns_score());
837 Trace::add(MOBILITY, mobility[WHITE] * Weights[Mobility]
838 , mobility[BLACK] * Weights[Mobility]);
839 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
840 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
841 Trace::add(TOTAL, score);
844 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
847 // Explicit template instantiations
848 template Value Eval::evaluate<true >(const Position&);
849 template Value Eval::evaluate<false>(const Position&);
852 /// trace() is like evaluate(), but instead of returning a value, it returns
853 /// a string (suitable for outputting to stdout) that contains the detailed
854 /// descriptions and values of each evaluation term. Useful for debugging.
856 std::string Eval::trace(const Position& pos) {
858 std::memset(scores, 0, sizeof(scores));
860 Value v = evaluate<true>(pos);
861 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
863 std::stringstream ss;
864 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
865 << " Eval term | White | Black | Total \n"
866 << " | MG EG | MG EG | MG EG \n"
867 << "----------------+-------------+-------------+-------------\n"
868 << " Material | " << Term(MATERIAL)
869 << " Imbalance | " << Term(IMBALANCE)
870 << " Pawns | " << Term(PAWN)
871 << " Knights | " << Term(KNIGHT)
872 << " Bishop | " << Term(BISHOP)
873 << " Rooks | " << Term(ROOK)
874 << " Queens | " << Term(QUEEN)
875 << " Mobility | " << Term(MOBILITY)
876 << " King safety | " << Term(KING)
877 << " Threats | " << Term(THREAT)
878 << " Passed pawns | " << Term(PASSED)
879 << " Space | " << Term(SPACE)
880 << "----------------+-------------+-------------+-------------\n"
881 << " Total | " << Term(TOTAL);
883 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
889 /// init() computes evaluation weights, usually at startup
893 const int MaxSlope = 8700;
894 const int Peak = 1280000;
897 for (int i = 0; i < 400; ++i)
899 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
900 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];