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/>.
33 // Struct EvalInfo contains various information computed and collected
34 // by the evaluation functions.
37 // Pointers to material and pawn hash table entries
41 // attackedBy[color][piece type] is a bitboard representing all squares
42 // attacked by a given color and piece type, attackedBy[color][ALL_PIECES]
43 // contains all squares attacked by the given color.
44 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
46 // kingRing[color] is the zone around the king which is considered
47 // by the king safety evaluation. This consists of the squares directly
48 // adjacent to the king, and the three (or two, for a king on an edge file)
49 // squares two ranks in front of the king. For instance, if black's king
50 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
51 // f7, g7, h7, f6, g6 and h6.
52 Bitboard kingRing[COLOR_NB];
54 // kingAttackersCount[color] is the number of pieces of the given color
55 // which attack a square in the kingRing of the enemy king.
56 int kingAttackersCount[COLOR_NB];
58 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
59 // given color which attack a square in the kingRing of the enemy king. The
60 // weights of the individual piece types are given by the variables
61 // QueenAttackWeight, RookAttackWeight, BishopAttackWeight and
62 // KnightAttackWeight in evaluate.cpp
63 int kingAttackersWeight[COLOR_NB];
65 // kingAdjacentZoneAttacksCount[color] is the number of attacks to squares
66 // directly adjacent to the king of the given color. Pieces which attack
67 // more than one square are counted multiple times. For instance, if black's
68 // king is on g8 and there's a white knight on g5, this knight adds
69 // 2 to kingAdjacentZoneAttacksCount[BLACK].
70 int kingAdjacentZoneAttacksCount[COLOR_NB];
72 Bitboard pinnedPieces[COLOR_NB];
77 enum Terms { // First 8 entries are for PieceType
78 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERMS_NB
81 Score scores[COLOR_NB][TERMS_NB];
85 double to_cp(Value v);
86 void write(int idx, Color c, Score s);
87 void write(int idx, Score w, Score b = SCORE_ZERO);
88 void print(std::stringstream& ss, const char* name, int idx);
89 std::string do_trace(const Position& pos);
92 // Evaluation weights, indexed by evaluation term
93 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
94 const struct Weight { int mg, eg; } Weights[] = {
95 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {318, 0}
99 #define S(mg, eg) make_score(mg, eg)
101 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
102 // game, indexed by piece type and number of attacked squares not occupied by
104 const Score MobilityBonus[][32] = {
106 { S(-65,-50), S(-42,-30), S(-9,-10), S( 3, 0), S(15, 10), S(27, 20), // Knights
107 S( 37, 28), S( 42, 31), S(44, 33) },
108 { S(-52,-47), S(-28,-23), S( 6, 1), S(20, 15), S(34, 29), S(48, 43), // Bishops
109 S( 60, 55), S( 68, 63), S(74, 68), S(77, 72), S(80, 75), S(82, 77),
110 S( 84, 79), S( 86, 81) },
111 { S(-47,-53), S(-31,-26), S(-5, 0), S( 1, 16), S( 7, 32), S(13, 48), // Rooks
112 S( 18, 64), S( 22, 80), S(26, 96), S(29,109), S(31,115), S(33,119),
113 S( 35,122), S( 36,123), S(37,124) },
114 { S(-42,-40), S(-28,-23), S(-5, -7), S( 0, 0), S( 6, 10), S(11, 19), // Queens
115 S( 13, 29), S( 18, 38), S(20, 40), S(21, 41), S(22, 41), S(22, 41),
116 S( 22, 41), S( 23, 41), S(24, 41), S(25, 41), S(25, 41), S(25, 41),
117 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41), S(25, 41), S(25, 41),
118 S( 25, 41), S( 25, 41), S(25, 41), S(25, 41) }
121 // Outpost[PieceType][Square] contains bonuses for knights and bishops outposts,
122 // indexed by piece type and square (from white's point of view).
123 const Value Outpost[][SQUARE_NB] = {
125 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
126 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
127 V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0),
128 V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0),
129 V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0),
130 V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0) },
132 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
133 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
134 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
135 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
136 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
137 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0) }
140 // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
141 // bonuses according to which piece type attacks which one.
142 const Score Threat[][2][PIECE_TYPE_NB] = {
143 { { S(0, 0), S( 0, 0), S(19, 37), S(24, 37), S(44, 97), S(35,106) }, // Defended Minor
144 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Defended Major
145 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Weak Minor
146 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Weak Major
149 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
150 // type is attacked by an enemy pawn.
151 const Score ThreatenedByPawn[] = {
152 S(0, 0), S(0, 0), S(87, 118), S(84, 122), S(114, 203), S(121, 217)
155 // Assorted bonuses and penalties used by evaluation
156 const Score KingOnOne = S( 2, 58);
157 const Score KingOnMany = S( 6,125);
158 const Score RookOnPawn = S( 7, 27);
159 const Score RookOpenFile = S(43, 21);
160 const Score RookSemiOpenFile = S(19, 10);
161 const Score BishopPawns = S( 8, 12);
162 const Score MinorBehindPawn = S(16, 0);
163 const Score TrappedRook = S(92, 0);
164 const Score Unstoppable = S( 0, 20);
165 const Score Hanging = S(31, 26);
167 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
168 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
169 // happen in Chess960 games.
170 const Score TrappedBishopA1H1 = S(50, 50);
174 // SpaceMask[Color] contains the area of the board which is considered
175 // by the space evaluation. In the middlegame, each side is given a bonus
176 // based on how many squares inside this area are safe and available for
177 // friendly minor pieces.
178 const Bitboard SpaceMask[] = {
179 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
180 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
183 // King danger constants and variables. The king danger scores are taken
184 // from KingDanger[]. Various little "meta-bonuses" measuring the strength
185 // of the enemy attack are added up into an integer, which is used as an
186 // index to KingDanger[].
188 // KingAttackWeights[PieceType] contains king attack weights by piece type
189 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
191 // Bonuses for enemy's safe checks
192 const int QueenContactCheck = 24;
193 const int RookContactCheck = 16;
194 const int QueenCheck = 12;
195 const int RookCheck = 8;
196 const int BishopCheck = 2;
197 const int KnightCheck = 3;
199 // KingDanger[attackUnits] contains the actual king danger weighted
200 // scores, indexed by a calculated integer number.
201 Score KingDanger[128];
203 // apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
204 Score apply_weight(Score v, const Weight& w) {
205 return make_score(mg_value(v) * w.mg / 256, eg_value(v) * w.eg / 256);
209 // init_eval_info() initializes king bitboards for given color adding
210 // pawn attacks. To be done at the beginning of the evaluation.
213 void init_eval_info(const Position& pos, EvalInfo& ei) {
215 const Color Them = (Us == WHITE ? BLACK : WHITE);
216 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
218 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
220 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
221 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
223 // Init king safety tables only if we are going to use them
224 if (pos.non_pawn_material(Us) >= QueenValueMg)
226 ei.kingRing[Them] = b | shift_bb<Down>(b);
227 b &= ei.attackedBy[Us][PAWN];
228 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
229 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
232 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
236 // evaluate_outpost() evaluates bishop and knight outpost squares
238 template<PieceType Pt, Color Us>
239 Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
241 const Color Them = (Us == WHITE ? BLACK : WHITE);
243 assert (Pt == BISHOP || Pt == KNIGHT);
245 // Initial bonus based on square
246 Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
248 // Increase bonus if supported by pawn, especially if the opponent has
249 // no minor piece which can trade with the outpost piece.
250 if (bonus && (ei.attackedBy[Us][PAWN] & s))
252 if ( !pos.pieces(Them, KNIGHT)
253 && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
254 bonus += bonus + bonus / 2;
259 return make_score(bonus * 2, bonus / 2);
263 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
265 template<PieceType Pt, Color Us, bool Trace>
266 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
270 Score score = SCORE_ZERO;
272 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
273 const Color Them = (Us == WHITE ? BLACK : WHITE);
274 const Square* pl = pos.list<Pt>(Us);
276 ei.attackedBy[Us][Pt] = 0;
278 while ((s = *pl++) != SQ_NONE)
280 // Find attacked squares, including x-ray attacks for bishops and rooks
281 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
282 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
283 : pos.attacks_from<Pt>(s);
285 if (ei.pinnedPieces[Us] & s)
286 b &= LineBB[pos.king_square(Us)][s];
288 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
290 if (b & ei.kingRing[Them])
292 ei.kingAttackersCount[Us]++;
293 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
294 Bitboard bb = b & ei.attackedBy[Them][KING];
296 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
300 b &= ~( ei.attackedBy[Them][KNIGHT]
301 | ei.attackedBy[Them][BISHOP]
302 | ei.attackedBy[Them][ROOK]);
304 int mob = Pt != QUEEN ? popcount<Max15>(b & mobilityArea[Us])
305 : popcount<Full >(b & mobilityArea[Us]);
307 mobility[Us] += MobilityBonus[Pt][mob];
309 // Decrease score if we are attacked by an enemy pawn. The remaining part
310 // of threat evaluation must be done later when we have full attack info.
311 if (ei.attackedBy[Them][PAWN] & s)
312 score -= ThreatenedByPawn[Pt];
314 if (Pt == BISHOP || Pt == KNIGHT)
316 // Penalty for bishop with same colored pawns
318 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
320 // Bishop and knight outpost square
321 if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
322 score += evaluate_outpost<Pt, Us>(pos, ei, s);
324 // Bishop or knight behind a pawn
325 if ( relative_rank(Us, s) < RANK_5
326 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
327 score += MinorBehindPawn;
332 // Rook piece attacking enemy pawns on the same rank/file
333 if (relative_rank(Us, s) >= RANK_5)
335 Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
337 score += popcount<Max15>(pawns) * RookOnPawn;
340 // Give a bonus for a rook on a open or semi-open file
341 if (ei.pi->semiopen_file(Us, file_of(s)))
342 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOpenFile : RookSemiOpenFile;
344 if (mob > 3 || ei.pi->semiopen_file(Us, file_of(s)))
347 Square ksq = pos.king_square(Us);
349 // Penalize rooks which are trapped by a king. Penalize more if the
350 // king has lost its castling capability.
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));
357 // An important Chess960 pattern: A cornered bishop blocked by a friendly
358 // pawn diagonally in front of it is a very serious problem, especially
359 // when that pawn is also blocked.
362 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
364 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
365 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
366 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
367 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
373 Tracing::write(Pt, Us, score);
375 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
379 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
381 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
384 // evaluate_king() assigns bonuses and penalties to a king of a given color
386 template<Color Us, bool Trace>
387 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
389 const Color Them = (Us == WHITE ? BLACK : WHITE);
391 Bitboard undefended, b, b1, b2, safe;
393 const Square ksq = pos.king_square(Us);
395 // King shelter and enemy pawns storm
396 Score score = ei.pi->king_safety<Us>(pos, ksq);
398 // Main king safety evaluation
399 if (ei.kingAttackersCount[Them])
401 // Find the attacked squares around the king which have no defenders
402 // apart from the king itself
403 undefended = ei.attackedBy[Them][ALL_PIECES]
404 & ei.attackedBy[Us][KING]
405 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
406 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
407 | ei.attackedBy[Us][QUEEN]);
409 // Initialize the 'attackUnits' variable, which is used later on as an
410 // index to the KingDanger[] array. The initial value is based on the
411 // number and types of the enemy's attacking pieces, the number of
412 // attacked and undefended squares around our king and the quality of
413 // the pawn shelter (current 'score' value).
414 attackUnits = std::min(20, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
415 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
416 + 2 * (ei.pinnedPieces[Us] != 0)
417 - mg_value(score) / 32
418 - !pos.count<QUEEN>(Them) * 15;
420 // Analyse the enemy's safe queen contact checks. Firstly, find the
421 // undefended squares around the king that are attacked by the enemy's
423 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
426 // ...and then remove squares not supported by another enemy piece
427 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
428 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
431 attackUnits += QueenContactCheck * popcount<Max15>(b);
434 // Analyse the enemy's safe rook contact checks. Firstly, find the
435 // undefended squares around the king that are attacked by the enemy's
437 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
439 // Consider only squares where the enemy's rook gives check
440 b &= PseudoAttacks[ROOK][ksq];
444 // ...and then remove squares not supported by another enemy piece
445 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
446 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
449 attackUnits += RookContactCheck * popcount<Max15>(b);
452 // Analyse the enemy's safe distance checks for sliders and knights
453 safe = ~(pos.pieces(Them) | ei.attackedBy[Us][ALL_PIECES]);
455 b1 = pos.attacks_from<ROOK>(ksq) & safe;
456 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
458 // Enemy queen safe checks
459 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
461 attackUnits += QueenCheck * popcount<Max15>(b);
463 // Enemy rooks safe checks
464 b = b1 & ei.attackedBy[Them][ROOK];
466 attackUnits += RookCheck * popcount<Max15>(b);
468 // Enemy bishops safe checks
469 b = b2 & ei.attackedBy[Them][BISHOP];
471 attackUnits += BishopCheck * popcount<Max15>(b);
473 // Enemy knights safe checks
474 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
476 attackUnits += KnightCheck * popcount<Max15>(b);
478 // To index KingDanger[] attackUnits must be in [0, 99] range
479 attackUnits = std::min(99, std::max(0, attackUnits));
481 // Finally, extract the king danger score from the KingDanger[]
482 // array and subtract the score from evaluation.
483 score -= KingDanger[attackUnits];
487 Tracing::write(KING, Us, score);
493 // evaluate_threats() assigns bonuses according to the type of attacking piece
494 // and the type of attacked one.
496 template<Color Us, bool Trace>
497 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
499 const Color Them = (Us == WHITE ? BLACK : WHITE);
501 enum { Defended, Weak };
502 enum { Minor, Major };
504 Bitboard b, weak, defended;
505 Score score = SCORE_ZERO;
507 // Non-pawn enemies defended by a pawn and under our attack
508 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
509 & ei.attackedBy[Them][PAWN]
510 & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]);
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][Major][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] | ei.attackedBy[Us][QUEEN]);
538 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
540 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
542 score += more_than_one(b) ? Hanging * popcount<Max15>(b) : Hanging;
544 b = weak & ei.attackedBy[Us][KING];
546 score += more_than_one(b) ? KingOnMany : KingOnOne;
550 Tracing::write(Tracing::THREAT, Us, score);
556 // evaluate_passed_pawns() evaluates the passed pawns of the given color
558 template<Color Us, bool Trace>
559 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
561 const Color Them = (Us == WHITE ? BLACK : WHITE);
563 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
564 Score score = SCORE_ZERO;
566 b = ei.pi->passed_pawns(Us);
570 Square s = pop_lsb(&b);
572 assert(pos.pawn_passed(Us, s));
574 int r = relative_rank(Us, s) - RANK_2;
575 int rr = r * (r - 1);
577 // Base bonus based on rank
578 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
582 Square blockSq = s + pawn_push(Us);
584 // Adjust bonus based on the king's proximity
585 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
586 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
588 // If blockSq is not the queening square then consider also a second push
589 if (relative_rank(Us, blockSq) != RANK_8)
590 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
592 // If the pawn is free to advance, then increase the bonus
593 if (pos.empty(blockSq))
595 // If there is a rook or queen attacking/defending the pawn from behind,
596 // consider all the squaresToQueen. Otherwise consider only the squares
597 // in the pawn's path attacked or occupied by the enemy.
598 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
600 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
602 if (!(pos.pieces(Us) & bb))
603 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
605 if (!(pos.pieces(Them) & bb))
606 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
608 // If there aren't any enemy attacks, assign a big bonus. Otherwise
609 // assign a smaller bonus if the block square isn't attacked.
610 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
612 // If the path to queen is fully defended, assign a big bonus.
613 // Otherwise assign a smaller bonus if the block square is defended.
614 if (defendedSquares == squaresToQueen)
617 else if (defendedSquares & blockSq)
620 mbonus += k * rr, ebonus += k * rr;
622 else if (pos.pieces(Us) & blockSq)
623 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
626 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
627 ebonus += ebonus / 4;
629 score += make_score(mbonus, ebonus);
633 Tracing::write(Tracing::PASSED, Us, apply_weight(score, Weights[PassedPawns]));
635 // Add the scores to the middlegame and endgame eval
636 return apply_weight(score, Weights[PassedPawns]);
640 // evaluate_unstoppable_pawns() scores the most advanced passed pawn. In case
641 // both players have no pieces but pawns, this is somewhat related to the
642 // possibility that pawns are unstoppable.
644 Score evaluate_unstoppable_pawns(Color us, const EvalInfo& ei) {
646 Bitboard b = ei.pi->passed_pawns(us);
648 return b ? Unstoppable * int(relative_rank(us, frontmost_sq(us, b))) : SCORE_ZERO;
652 // evaluate_space() computes the space evaluation for a given side. The
653 // space evaluation is a simple bonus based on the number of safe squares
654 // available for minor pieces on the central four files on ranks 2--4. Safe
655 // squares one, two or three squares behind a friendly pawn are counted
656 // twice. Finally, the space bonus is scaled by a weight taken from the
657 // material hash table. The aim is to improve play on game opening.
659 int evaluate_space(const Position& pos, const EvalInfo& ei) {
661 const Color Them = (Us == WHITE ? BLACK : WHITE);
663 // Find the safe squares for our pieces inside the area defined by
664 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
665 // pawn, or if it is undefended and attacked by an enemy piece.
666 Bitboard safe = SpaceMask[Us]
667 & ~pos.pieces(Us, PAWN)
668 & ~ei.attackedBy[Them][PAWN]
669 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
671 // Find all squares which are at most three squares behind some friendly pawn
672 Bitboard behind = pos.pieces(Us, PAWN);
673 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
674 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
676 // Since SpaceMask[Us] is fully on our half of the board
677 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
679 // Count safe + (behind & safe) with a single popcount
680 return popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
684 // do_evaluate() is the evaluation entry point, called directly from evaluate()
687 Value do_evaluate(const Position& pos) {
689 assert(!pos.checkers());
692 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
693 Thread* thisThread = pos.this_thread();
695 // Initialize score by reading the incrementally updated scores included
696 // in the position object (material + piece square tables).
697 // Score is computed from the point of view of white.
698 score = pos.psq_score();
700 // Probe the material hash table
701 ei.mi = Material::probe(pos, thisThread->materialTable, thisThread->endgames);
702 score += ei.mi->material_value();
704 // If we have a specialized evaluation function for the current material
705 // configuration, call it and return.
706 if (ei.mi->specialized_eval_exists())
707 return ei.mi->evaluate(pos) + Eval::Tempo;
709 // Probe the pawn hash table
710 ei.pi = Pawns::probe(pos, thisThread->pawnsTable);
711 score += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
713 // Initialize attack and king safety bitboards
714 init_eval_info<WHITE>(pos, ei);
715 init_eval_info<BLACK>(pos, ei);
717 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
718 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
720 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
721 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
722 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
724 // Evaluate pieces and mobility
725 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
726 score += apply_weight(mobility[WHITE] - mobility[BLACK], Weights[Mobility]);
728 // Evaluate kings after all other pieces because we need complete attack
729 // information when computing the king safety evaluation.
730 score += evaluate_king<WHITE, Trace>(pos, ei)
731 - evaluate_king<BLACK, Trace>(pos, ei);
733 // Evaluate tactical threats, we need full attack information including king
734 score += evaluate_threats<WHITE, Trace>(pos, ei)
735 - evaluate_threats<BLACK, Trace>(pos, ei);
737 // Evaluate passed pawns, we need full attack information including king
738 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
739 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
741 // If both sides have only pawns, score for potential unstoppable pawns
742 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
743 score += evaluate_unstoppable_pawns(WHITE, ei)
744 - evaluate_unstoppable_pawns(BLACK, ei);
746 // Evaluate space for both sides, only in middlegame
747 if (ei.mi->space_weight())
749 int s = evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei);
750 score += apply_weight(s * ei.mi->space_weight(), Weights[Space]);
753 // Scale winning side if position is more drawish than it appears
754 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
755 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
757 // If we don't already have an unusual scale factor, check for certain
758 // types of endgames, and use a lower scale for those.
759 if ( ei.mi->game_phase() < PHASE_MIDGAME
760 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
762 if (pos.opposite_bishops())
764 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
765 // is almost a draw, in case of KBP vs KB is even more a draw.
766 if ( pos.non_pawn_material(WHITE) == BishopValueMg
767 && pos.non_pawn_material(BLACK) == BishopValueMg)
768 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
770 // Endgame with opposite-colored bishops, but also other pieces. Still
771 // a bit drawish, but not as drawish as with only the two bishops.
773 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
775 // Endings where weaker side can place his king in front of the opponent's
776 // pawns are drawish.
777 else if ( abs(eg_value(score)) <= BishopValueEg
778 && ei.pi->pawn_span(strongSide) <= 1
779 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
780 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
783 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
784 Value v = mg_value(score) * int(ei.mi->game_phase())
785 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
787 v /= int(PHASE_MIDGAME);
789 // In case of tracing add all single evaluation contributions for both white and black
792 Tracing::write(Tracing::MATERIAL, pos.psq_score());
793 Tracing::write(Tracing::IMBALANCE, ei.mi->material_value());
794 Tracing::write(PAWN, ei.pi->pawns_value());
795 Tracing::write(Tracing::MOBILITY, apply_weight(mobility[WHITE], Weights[Mobility])
796 , apply_weight(mobility[BLACK], Weights[Mobility]));
797 Score w = ei.mi->space_weight() * evaluate_space<WHITE>(pos, ei);
798 Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
799 Tracing::write(Tracing::SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
800 Tracing::write(Tracing::TOTAL, score);
805 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
809 // Tracing function definitions
811 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
813 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
815 void Tracing::write(int idx, Score w, Score b) {
817 write(idx, WHITE, w);
818 write(idx, BLACK, b);
821 void Tracing::print(std::stringstream& ss, const char* name, int idx) {
823 Score wScore = scores[WHITE][idx];
824 Score bScore = scores[BLACK][idx];
827 case MATERIAL: case IMBALANCE: case PAWN: case TOTAL:
828 ss << std::setw(15) << name << " | --- --- | --- --- | "
829 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
830 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
833 ss << std::setw(15) << name << " | " << std::noshowpos
834 << std::setw(5) << to_cp(mg_value(wScore)) << " "
835 << std::setw(5) << to_cp(eg_value(wScore)) << " | "
836 << std::setw(5) << to_cp(mg_value(bScore)) << " "
837 << std::setw(5) << to_cp(eg_value(bScore)) << " | "
838 << std::setw(5) << to_cp(mg_value(wScore - bScore)) << " "
839 << std::setw(5) << to_cp(eg_value(wScore - bScore)) << " \n";
843 std::string Tracing::do_trace(const Position& pos) {
845 std::memset(scores, 0, sizeof(scores));
847 Value v = do_evaluate<true>(pos);
848 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
850 std::stringstream ss;
851 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
852 << " Eval term | White | Black | Total \n"
853 << " | MG EG | MG EG | MG EG \n"
854 << "----------------+-------------+-------------+-------------\n";
856 print(ss, "Material", MATERIAL);
857 print(ss, "Imbalance", IMBALANCE);
858 print(ss, "Pawns", PAWN);
859 print(ss, "Knights", KNIGHT);
860 print(ss, "Bishops", BISHOP);
861 print(ss, "Rooks", ROOK);
862 print(ss, "Queens", QUEEN);
863 print(ss, "Mobility", MOBILITY);
864 print(ss, "King safety", KING);
865 print(ss, "Threats", THREAT);
866 print(ss, "Passed pawns", PASSED);
867 print(ss, "Space", SPACE);
869 ss << "----------------+-------------+-------------+-------------\n";
870 print(ss, "Total", TOTAL);
872 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
882 /// evaluate() is the main evaluation function. It returns a static evaluation
883 /// of the position always from the point of view of the side to move.
885 Value evaluate(const Position& pos) {
886 return do_evaluate<false>(pos);
890 /// trace() is like evaluate(), but instead of returning a value, it returns
891 /// a string (suitable for outputting to stdout) that contains the detailed
892 /// descriptions and values of each evaluation term. It's mainly used for
894 std::string trace(const Position& pos) {
895 return Tracing::do_trace(pos);
899 /// init() computes evaluation weights.
903 const double MaxSlope = 30;
904 const double Peak = 1280;
906 for (int t = 0, i = 1; i < 100; ++i)
908 t = int(std::min(Peak, std::min(0.4 * i * i, t + MaxSlope)));
909 KingDanger[i] = apply_weight(make_score(t, 0), Weights[KingSafety]);