2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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/>.
30 #include "ucioption.h"
34 // Struct EvalInfo contains various information computed and collected
35 // by the evaluation functions.
38 // Pointers to material and pawn hash table entries
42 // attackedBy[color][piece type] is a bitboard representing all squares
43 // attacked by a given color and piece type, attackedBy[color][ALL_PIECES]
44 // contains all squares attacked by the given color.
45 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
47 // kingRing[color] is the zone around the king which is considered
48 // by the king safety evaluation. This consists of the squares directly
49 // adjacent to the king, and the three (or two, for a king on an edge file)
50 // squares two ranks in front of the king. For instance, if black's king
51 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
52 // f7, g7, h7, f6, g6 and h6.
53 Bitboard kingRing[COLOR_NB];
55 // kingAttackersCount[color] is the number of pieces of the given color
56 // which attack a square in the kingRing of the enemy king.
57 int kingAttackersCount[COLOR_NB];
59 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
60 // given color which attack a square in the kingRing of the enemy king. The
61 // weights of the individual piece types are given by the variables
62 // QueenAttackWeight, RookAttackWeight, BishopAttackWeight and
63 // KnightAttackWeight in evaluate.cpp
64 int kingAttackersWeight[COLOR_NB];
66 // kingAdjacentZoneAttacksCount[color] is the number of attacks to squares
67 // directly adjacent to the king of the given color. Pieces which attack
68 // more than one square are counted multiple times. For instance, if black's
69 // king is on g8 and there's a white knight on g5, this knight adds
70 // 2 to kingAdjacentZoneAttacksCount[BLACK].
71 int kingAdjacentZoneAttacksCount[COLOR_NB];
73 Bitboard pinnedPieces[COLOR_NB];
78 enum Terms { // First 8 entries are for PieceType
79 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERMS_NB
82 Score scores[COLOR_NB][TERMS_NB];
86 double to_cp(Value v);
87 void write(int idx, Color c, Score s);
88 void write(int idx, Score w, Score b = SCORE_ZERO);
89 void print(std::stringstream& ss, const char* name, int idx);
90 std::string do_trace(const Position& pos);
93 // Evaluation weights, indexed by evaluation term
94 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
95 const struct Weight { int mg, eg; } Weights[] = {
96 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {318, 0}
100 #define S(mg, eg) make_score(mg, eg)
102 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
103 // game, indexed by piece type and number of attacked squares not occupied by
105 const Score MobilityBonus[][32] = {
107 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
108 S( 37, 28), S( 42, 31), S(44, 33) },
109 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
110 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
111 S( 84, 79), S( 86, 81) },
112 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
113 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
114 S( 35,122), S( 36,123), S(37,124) },
115 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
116 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
117 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
118 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
119 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
122 // Outpost[PieceType][Square] contains bonuses for knights and bishops outposts,
123 // indexed by piece type and square (from white's point of view).
124 const Value Outpost[][SQUARE_NB] = {
126 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
127 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
128 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
129 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
130 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
131 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
133 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
134 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
135 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
136 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
137 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
138 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
141 // Threat[attacking][attacked] contains bonuses according to which piece
142 // type attacks which one.
143 const Score Threat[][PIECE_TYPE_NB] = {
144 { S(0, 0), S( 7, 39), S(24, 49), S(24, 49), S(41,100), S(41,100) }, // Minor
145 { S(0, 0), S(15, 39), S(15, 45), S(15, 45), S(15, 45), S(24, 49) } // Major
148 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
149 // type is attacked by an enemy pawn.
150 const Score ThreatenedByPawn[] = {
151 S(0, 0), S(0, 0), S(80, 119), S(80, 119), S(117, 199), S(127, 218)
154 // Assorted bonuses and penalties used by evaluation
155 const Score KingOnOne = S(2 , 58);
156 const Score KingOnMany = S(6 ,125);
157 const Score RookOnPawn = S(10, 28);
158 const Score RookOpenFile = S(43, 21);
159 const Score RookSemiOpenFile = S(19, 10);
160 const Score BishopPawns = S( 8, 12);
161 const Score MinorBehindPawn = S(16, 0);
162 const Score TrappedRook = S(92, 0);
163 const Score Unstoppable = S( 0, 20);
164 const Score Hanging = S(23, 20);
166 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
167 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
168 // happen in Chess960 games.
169 const Score TrappedBishopA1H1 = S(50, 50);
173 // SpaceMask[Color] contains the area of the board which is considered
174 // by the space evaluation. In the middlegame, each side is given a bonus
175 // based on how many squares inside this area are safe and available for
176 // friendly minor pieces.
177 const Bitboard SpaceMask[] = {
178 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
179 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
182 // King danger constants and variables. The king danger scores are taken
183 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
184 // of the enemy attack are added up into an integer, which is used as an
185 // index to KingDanger[].
187 // KingAttackWeights[PieceType] contains king attack weights by piece type
188 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
190 // Bonuses for enemy's safe checks
191 const int QueenContactCheck = 24;
192 const int RookContactCheck = 16;
193 const int QueenCheck = 12;
194 const int RookCheck = 8;
195 const int BishopCheck = 2;
196 const int KnightCheck = 3;
198 // KingDanger[attackUnits] contains the actual king danger weighted
199 // scores, indexed by a calculated integer number.
200 Score KingDanger[128];
202 const int ScalePawnSpan[2] = { 38, 56 };
204 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
205 Score apply_weight(Score v, const Weight& w) {
206 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
210 // init_eval_info() initializes king bitboards for given color adding
211 // pawn attacks. To be done at the beginning of the evaluation.
214 void init_eval_info(const Position& pos, EvalInfo& ei) {
216 const Color Them = (Us == WHITE ? BLACK : WHITE);
217 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
219 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
221 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
222 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
224 // Init king safety tables only if we are going to use them
225 if (pos.non_pawn_material(Us) > QueenValueMg + PawnValueMg)
227 ei.kingRing[Them] = b | shift_bb<Down>(b);
228 b &= ei.attackedBy[Us][PAWN];
229 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
230 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
233 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
237 // evaluate_outpost() evaluates bishop and knight outpost squares
239 template<PieceType Pt, Color Us>
240 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
242 const Color Them = (Us == WHITE ? BLACK : WHITE);
244 assert (Pt == BISHOP || Pt == KNIGHT);
246 // Initial bonus based on square
247 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
249 // Increase bonus if supported by pawn, especially if the opponent has
250 // no minor piece which can trade with the outpost piece.
251 if (bonus && (ei.attackedBy[Us][PAWN] & s))
253 if ( !pos.pieces(Them, KNIGHT)
254 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
255 bonus += bonus + bonus / 2;
260 return make_score(bonus * 2, bonus / 2);
264 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
266 template<PieceType Pt, Color Us, bool Trace>
267 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
271 Score score = SCORE_ZERO;
273 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
274 const Color Them = (Us == WHITE ? BLACK : WHITE);
275 const Square* pl = pos.list<Pt>(Us);
277 ei.attackedBy[Us][Pt] = 0;
279 while ((s = *pl++) != SQ_NONE)
281 // Find attacked squares, including x-ray attacks for bishops and rooks
282 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
283 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
284 : pos.attacks_from<Pt>(s);
286 if (ei.pinnedPieces[Us] & s)
287 b &= LineBB[pos.king_square(Us)][s];
289 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
291 if (b & ei.kingRing[Them])
293 ei.kingAttackersCount[Us]++;
294 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
295 Bitboard bb = b & ei.attackedBy[Them][KING];
297 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
301 b &= ~( ei.attackedBy[Them][KNIGHT]
302 | ei.attackedBy[Them][BISHOP]
303 | ei.attackedBy[Them][ROOK]);
305 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
306 : popcount<Full >(b & mobilityArea[Us]);
308 mobility[Us] += MobilityBonus[Pt][mob];
310 // Decrease score if we are attacked by an enemy pawn. The remaining part
311 // of threat evaluation must be done later when we have full attack info.
312 if (ei.attackedBy[Them][PAWN] & s)
313 score -= ThreatenedByPawn[Pt];
315 if (Pt == BISHOP || Pt == KNIGHT)
317 // Penalty for bishop with same colored pawns
319 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
321 // Bishop and knight outpost square
322 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
323 score += evaluate_outpost<Pt, Us>(pos, ei, s);
325 // Bishop or knight behind a pawn
326 if ( relative_rank(Us, s) < RANK_5
327 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
328 score += MinorBehindPawn;
333 // Rook piece attacking enemy pawns on the same rank/file
334 if (relative_rank(Us, s) >= RANK_5)
336 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
338 score += popcount<Max15>(pawns) * RookOnPawn;
341 // Give a bonus for a rook on a open or semi-open file
342 if (ei.pi->semiopen_file(Us, file_of(s)))
343 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOpenFile : RookSemiOpenFile;
345 if (mob > 3 || ei.pi->semiopen_file(Us, file_of(s)))
348 Square ksq = pos.king_square(Us);
350 // Penalize rooks which are trapped by a king. Penalize more if the
351 // king has lost its castling capability.
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));
358 // An important Chess960 pattern: A cornered bishop blocked by a friendly
359 // pawn diagonally in front of it is a very serious problem, especially
360 // when that pawn is also blocked.
363 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
365 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
366 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
367 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
368 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
374 Tracing::write(Pt, Us, score);
376 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
380 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
382 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
385 // evaluate_king() assigns bonuses and penalties to a king of a given color
387 template<Color Us, bool Trace>
388 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
390 const Color Them = (Us == WHITE ? BLACK : WHITE);
392 Bitboard undefended, b, b1, b2, safe;
394 const Square ksq = pos.king_square(Us);
396 // King shelter and enemy pawns storm
397 Score score = ei.pi->king_safety<Us>(pos, ksq);
399 // Main king safety evaluation
400 if (ei.kingAttackersCount[Them])
402 // Find the attacked squares around the king which have no defenders
403 // apart from the king itself
404 undefended = ei.attackedBy[Them][ALL_PIECES]
405 & ei.attackedBy[Us][KING]
406 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
407 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
408 | ei.attackedBy[Us][QUEEN]);
410 // Initialize the 'attackUnits' variable, which is used later on as an
411 // index to the KingDanger[] array. The initial value is based on the
412 // number and types of the enemy's attacking pieces, the number of
413 // attacked and undefended squares around our king and the quality of
414 // the pawn shelter (current 'score' value).
415 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
416 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
417 + 2 * (ei.pinnedPieces[Us] != 0)
418 - mg_value(score) / 32
419 - !pos.count<QUEEN>(Them) * 15;
421 // Analyse the enemy's safe queen contact checks. Firstly, find the
422 // undefended squares around the king that are attacked by the enemy's
424 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
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] | ei.attackedBy[Them][ROOK]);
432 attackUnits += QueenContactCheck * popcount<Max15>(b);
435 // Analyse the enemy's safe rook contact checks. Firstly, find the
436 // undefended squares around the king that are attacked by the enemy's
438 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
440 // Consider only squares where the enemy's rook gives check
441 b &= PseudoAttacks[ROOK][ksq];
445 // ...and then remove squares not supported by another enemy piece
446 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
447 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
450 attackUnits += RookContactCheck * popcount<Max15>(b);
453 // Analyse the enemy's safe distance checks for sliders and knights
454 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
456 b1 = pos.attacks_from<ROOK>(ksq) & safe;
457 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
459 // Enemy queen safe checks
460 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
462 attackUnits += QueenCheck * popcount<Max15>(b);
464 // Enemy rooks safe checks
465 b = b1 & ei.attackedBy[Them][ROOK];
467 attackUnits += RookCheck * popcount<Max15>(b);
469 // Enemy bishops safe checks
470 b = b2 & ei.attackedBy[Them][BISHOP];
472 attackUnits += BishopCheck * popcount<Max15>(b);
474 // Enemy knights safe checks
475 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
477 attackUnits += KnightCheck * popcount<Max15>(b);
479 // To index KingDanger[] attackUnits must be in [0, 99] range
480 attackUnits = std::min(99, std::max(0, attackUnits));
482 // Finally, extract the king danger score from the KingDanger[]
483 // array and subtract the score from evaluation.
484 score -= KingDanger[attackUnits];
488 Tracing::write(KING, Us, score);
494 // evaluate_threats() assigns bonuses according to the type of attacking piece
495 // and the type of attacked one.
497 template<Color Us, bool Trace>
498 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
500 const Color Them = (Us == WHITE ? BLACK : WHITE);
502 Bitboard b, weakEnemies, protectedEnemies;
503 Score score = SCORE_ZERO;
504 enum { Minor, Major };
507 protectedEnemies = (pos.pieces(Them) ^ pos.pieces(Them,PAWN))
508 & ei.attackedBy[Them][PAWN]
509 & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
511 if (protectedEnemies)
512 score += Threat[Minor][type_of(pos.piece_on(lsb(protectedEnemies)))];
514 // Enemies not defended by a pawn and under our attack
515 weakEnemies = pos.pieces(Them)
516 & ~ei.attackedBy[Them][PAWN]
517 & ei.attackedBy[Us][ALL_PIECES];
519 // Add a bonus according if the attacking pieces are minor or major
522 b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
524 score += Threat[Minor][type_of(pos.piece_on(lsb(b)))];
526 b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
528 score += Threat[Major][type_of(pos.piece_on(lsb(b)))];
530 b = weakEnemies & ~ei.attackedBy[Them][ALL_PIECES];
532 score += more_than_one(b) ? Hanging * popcount<Max15>(b) : Hanging;
534 b = weakEnemies & ei.attackedBy[Us][KING];
536 score += more_than_one(b) ? KingOnMany : KingOnOne;
540 Tracing::write(Tracing::THREAT, Us, score);
546 // evaluate_passed_pawns() evaluates the passed pawns of the given color
548 template<Color Us, bool Trace>
549 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
551 const Color Them = (Us == WHITE ? BLACK : WHITE);
553 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
554 Score score = SCORE_ZERO;
556 b = ei.pi->passed_pawns(Us);
560 Square s = pop_lsb(&b);
562 assert(pos.pawn_passed(Us, s));
564 int r = relative_rank(Us, s) - RANK_2;
565 int rr = r * (r - 1);
567 // Base bonus based on rank
568 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
572 Square blockSq = s + pawn_push(Us);
574 // Adjust bonus based on the king's proximity
575 ebonus += square_distance(pos.king_square(Them), blockSq) * 5 * rr
576 - square_distance(pos.king_square(Us ), blockSq) * 2 * rr;
578 // If blockSq is not the queening square then consider also a second push
579 if (relative_rank(Us, blockSq) != RANK_8)
580 ebonus -= square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
582 // If the pawn is free to advance, then increase the bonus
583 if (pos.empty(blockSq))
585 // If there is a rook or queen attacking/defending the pawn from behind,
586 // consider all the squaresToQueen. Otherwise consider only the squares
587 // in the pawn's path attacked or occupied by the enemy.
588 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
590 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
592 if (!(pos.pieces(Us) & bb))
593 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
595 if (!(pos.pieces(Them) & bb))
596 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
598 // If there aren't any enemy attacks, assign a big bonus. Otherwise
599 // assign a smaller bonus if the block square isn't attacked.
600 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
602 // If the path to queen is fully defended, assign a big bonus.
603 // Otherwise assign a smaller bonus if the block square is defended.
604 if (defendedSquares == squaresToQueen)
607 else if (defendedSquares & blockSq)
610 mbonus += k * rr, ebonus += k * rr;
612 else if (pos.pieces(Us) & blockSq)
613 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
616 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
617 ebonus += ebonus / 4;
619 score += make_score(mbonus, ebonus);
623 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
625 // Add the scores to the middlegame and endgame eval
626 return apply_weight(score, Weights[PassedPawns]);
630 // evaluate_unstoppable_pawns() scores the most advanced passed pawn. In case
631 // both players have no pieces but pawns, this is somewhat related to the
632 // possibility that pawns are unstoppable.
634 Score evaluate_unstoppable_pawns(Color us, const EvalInfo& ei) {
636 Bitboard b = ei.pi->passed_pawns(us);
638 return b ? Unstoppable * int(relative_rank(us, frontmost_sq(us, b))) : SCORE_ZERO;
642 // evaluate_space() computes the space evaluation for a given side. The
643 // space evaluation is a simple bonus based on the number of safe squares
644 // available for minor pieces on the central four files on ranks 2--4. Safe
645 // squares one, two or three squares behind a friendly pawn are counted
646 // twice. Finally, the space bonus is scaled by a weight taken from the
647 // material hash table. The aim is to improve play on game opening.
649 int evaluate_space(const Position& pos, const EvalInfo& ei) {
651 const Color Them = (Us == WHITE ? BLACK : WHITE);
653 // Find the safe squares for our pieces inside the area defined by
654 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
655 // pawn, or if it is undefended and attacked by an enemy piece.
656 Bitboard safe = SpaceMask[Us]
657 & ~pos.pieces(Us, PAWN)
658 & ~ei.attackedBy[Them][PAWN]
659 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
661 // Find all squares which are at most three squares behind some friendly pawn
662 Bitboard behind = pos.pieces(Us, PAWN);
663 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
664 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
666 // Since SpaceMask[Us] is fully on our half of the board
667 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
669 // Count safe + (behind & safe) with a single popcount
670 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
674 // do_evaluate() is the evaluation entry point, called directly from evaluate()
677 Value do_evaluate(const Position& pos) {
679 assert(!pos.checkers());
682 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
683 Thread* thisThread = pos.this_thread();
685 // Initialize score by reading the incrementally updated scores included
686 // in the position object (material + piece square tables).
687 // Score is computed from the point of view of white.
688 score = pos.psq_score();
690 // Probe the material hash table
691 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
692 score += ei.mi->material_value();
694 // If we have a specialized evaluation function for the current material
695 // configuration, call it and return.
696 if (ei.mi->specialized_eval_exists())
697 return ei.mi->evaluate(pos) + Eval::Tempo;
699 // Probe the pawn hash table
700 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
701 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
703 // Initialize attack and king safety bitboards
704 init_eval_info<WHITE>(pos, ei);
705 init_eval_info<BLACK>(pos, ei);
707 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
708 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
710 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
711 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
712 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
714 // Evaluate pieces and mobility
715 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
716 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
718 // Evaluate kings after all other pieces because we need complete attack
719 // information when computing the king safety evaluation.
720 score += evaluate_king<WHITE, Trace>(pos, ei)
721 - evaluate_king<BLACK, Trace>(pos, ei);
723 // Evaluate tactical threats, we need full attack information including king
724 score += evaluate_threats<WHITE, Trace>(pos, ei)
725 - evaluate_threats<BLACK, Trace>(pos, ei);
727 // Evaluate passed pawns, we need full attack information including king
728 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
729 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
731 // If both sides have only pawns, score for potential unstoppable pawns
732 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
733 score += evaluate_unstoppable_pawns(WHITE, ei)
734 - evaluate_unstoppable_pawns(BLACK, ei);
736 // Evaluate space for both sides, only in middlegame
737 if (ei.mi->space_weight())
739 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
740 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
743 // Scale winning side if position is more drawish than it appears
744 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
745 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
747 // If we don't already have an unusual scale factor, check for certain
748 // types of endgames, and use a lower scale for those.
749 if ( ei.mi->game_phase() < PHASE_MIDGAME
750 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
752 if (pos.opposite_bishops()) {
753 // Ignoring any pawns, do both sides only have a single bishop and no
755 if ( pos.non_pawn_material(WHITE) == BishopValueMg
756 && pos.non_pawn_material(BLACK) == BishopValueMg)
758 // Check for KBP vs KB with only a single pawn that is almost
759 // certainly a draw or at least two pawns.
760 bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
761 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
764 // Endgame with opposite-colored bishops, but also other pieces. Still
765 // a bit drawish, but not as drawish as with only the two bishops.
766 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
767 } else if ( abs(eg_value(score)) <= BishopValueEg
768 && ei.pi->pawn_span(strongSide) <= 1
769 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide))) {
770 // Endings where weaker side can be place his king in front of the opponent's pawns are drawish.
771 sf = ScaleFactor(ScalePawnSpan[ei.pi->pawn_span(strongSide)]);
775 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
776 Value v = mg_value(score) * int(ei.mi->game_phase())
777 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
779 v /= int(PHASE_MIDGAME);
781 // In case of tracing add all single evaluation contributions for both white and black
784 Tracing::write(Tracing::MATERIAL, pos.psq_score());
785 Tracing::write(Tracing::IMBALANCE, ei.mi->material_value());
786 Tracing::write(PAWN, ei.pi->pawns_value());
787 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
788 , apply_weight(mobility[BLACK], Weights[Mobility]));
789 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
790 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
791 Tracing::write(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
792 Tracing::write(Tracing::TOTAL, score);
797 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
801 // Tracing function definitions
803 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
805 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
807 void Tracing::write(int idx, Score w, Score b) {
809 write(idx, WHITE, w);
810 write(idx, BLACK, b);
813 void Tracing::print(std::stringstream& ss, const char* name, int idx) {
815 Score wScore = scores[WHITE][idx];
816 Score bScore = scores[BLACK][idx];
819 case MATERIAL: case IMBALANCE: case PAWN: case TOTAL:
820 ss << std::setw(15) << name << " | --- --- | --- --- | "
821 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
822 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
825 ss << std::setw(15) << name << " | " << std::noshowpos
826 << std::setw(5) << to_cp(mg_value(wScore)) << " "
827 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
828 << std::setw(5) << to_cp(mg_value(bScore)) << " "
829 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
830 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
831 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
835 std::string Tracing::do_trace(const Position& pos) {
837 std::memset(scores, 0, sizeof(scores));
839 Value v = do_evaluate<true>(pos);
840 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
842 std::stringstream ss;
843 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
844 << " Eval term | White | Black | Total \n"
845 << " | MG EG | MG EG | MG EG \n"
846 << "----------------+-------------+-------------+-------------\n";
848 print(ss, "Material", MATERIAL);
849 print(ss, "Imbalance", IMBALANCE);
850 print(ss, "Pawns", PAWN);
851 print(ss, "Knights", KNIGHT);
852 print(ss, "Bishops", BISHOP);
853 print(ss, "Rooks", ROOK);
854 print(ss, "Queens", QUEEN);
855 print(ss, "Mobility", MOBILITY);
856 print(ss, "King safety", KING);
857 print(ss, "Threats", THREAT);
858 print(ss, "Passed pawns", PASSED);
859 print(ss, "Space", SPACE);
861 ss << "----------------+-------------+-------------+-------------\n";
862 print(ss, "Total", TOTAL);
864 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
874 /// evaluate() is the main evaluation function. It returns a static evaluation
875 /// of the position always from the point of view of the side to move.
877 Value evaluate(const Position& pos) {
878 return do_evaluate<false>(pos);
882 /// trace() is like evaluate(), but instead of returning a value, it returns
883 /// a string (suitable for outputting to stdout) that contains the detailed
884 /// descriptions and values of each evaluation term. It's mainly used for
886 std::string trace(const Position& pos) {
887 return Tracing::do_trace(pos);
891 /// init() computes evaluation weights from the corresponding UCI parameters
892 /// and setup king tables.
896 const double MaxSlope = 30;
897 const double Peak = 1280;
899 for (int t = 0, i = 1; i < 100; ++i)
901 t = int(std::min(Peak, std::min(0.4 * i * i, t + MaxSlope)));
902 KingDanger[i] = apply_weight(make_score(t, 0), Weights[KingSafety]);