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 Score scores[COLOR_NB][TERM_NB];
41 std::ostream& operator<<(std::ostream& os, Term idx);
43 double to_cp(Value v);
44 void write(int idx, Color c, Score s);
45 void write(int idx, Score w, Score b = SCORE_ZERO);
46 std::string do_trace(const Position& pos);
50 // Struct EvalInfo contains various information computed and collected
51 // by the evaluation functions.
54 // Pointers to material and pawn hash table entries
58 // attackedBy[color][piece type] is a bitboard representing all squares
59 // attacked by a given color and piece type, attackedBy[color][ALL_PIECES]
60 // contains all squares attacked by the given color.
61 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
63 // kingRing[color] is the zone around the king which is considered
64 // by the king safety evaluation. This consists of the squares directly
65 // adjacent to the king, and the three (or two, for a king on an edge file)
66 // squares two ranks in front of the king. For instance, if black's king
67 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
68 // f7, g7, h7, f6, g6 and h6.
69 Bitboard kingRing[COLOR_NB];
71 // kingAttackersCount[color] is the number of pieces of the given color
72 // which attack a square in the kingRing of the enemy king.
73 int kingAttackersCount[COLOR_NB];
75 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
76 // given color which attack a square in the kingRing of the enemy king. The
77 // weights of the individual piece types are given by the elements in the
78 // KingAttackWeights array.
79 int kingAttackersWeight[COLOR_NB];
81 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
82 // color to squares directly adjacent to the enemy king. Pieces which attack
83 // more than one square are counted multiple times. For instance, if there is
84 // a white knight on g5 and black's king is on g8, this white knight adds 2
85 // to kingAdjacentZoneAttacksCount[WHITE].
86 int kingAdjacentZoneAttacksCount[COLOR_NB];
88 Bitboard pinnedPieces[COLOR_NB];
92 // Evaluation weights, indexed by the corresponding evaluation term
93 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
95 const struct Weight { int mg, eg; } Weights[] = {
96 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {322, 0}
99 Score operator*(Score s, const Weight& w) {
100 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
104 #define V(v) Value(v)
105 #define S(mg, eg) make_score(mg, eg)
107 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
108 // game, indexed by piece type and number of attacked squares not occupied by
110 const Score MobilityBonus[][32] = {
112 { S(-68,-49), S(-46,-33), S(-3,-12), S( 5, -4), S( 9, 11), S(15, 16), // Knights
113 S( 23, 27), S( 33, 28), S(37, 29) },
114 { S(-49,-44), S(-23,-16), S(16, 1), S(29, 16), S(40, 25), S(51, 34), // Bishops
115 S( 55, 43), S( 61, 49), S(64, 51), S(68, 52), S(73, 55), S(75, 60),
116 S( 80, 65), S( 86, 66) },
117 { S(-50,-57), S(-28,-22), S(-11, 7), S(-1, 29), S( 0, 39), S( 1, 46), // Rooks
118 S( 10, 66), S( 16, 79), S(22, 86), S(23,103), S(30,109), S(33,111),
119 S( 37,115), S( 38,119), S(48,124) },
120 { S(-43,-30), S(-27,-15), S( 1, -5), S( 2, -3), S(14, 10), S(18, 24), // Queens
121 S( 20, 27), S( 33, 37), S(33, 38), S(34, 43), S(40, 46), S(43, 56),
122 S( 46, 61), S( 52, 63), S(52, 63), S(57, 65), S(60, 70), S(61, 74),
123 S( 67, 80), S( 76, 82), S(77, 88), S(82, 94), S(86, 95), S(90, 96),
124 S( 94, 99), S( 96,100), S(99,111), S(99,112) }
127 // Outpost[knight/bishop][supported by pawn]
128 const Score Outpost[2][2] = {{S(28,7), S(42,11)}, {S(12,3), S(18,5)}};
130 // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
131 // bonuses according to which piece type attacks which one.
132 const Score Threat[][2][PIECE_TYPE_NB] = {
133 { { S(0, 0), S( 0, 0), S(19, 37), S(24, 37), S(44, 97), S(35,106) }, // Defended Minor
134 { S(0, 0), S( 0, 0), S( 9, 14), S( 9, 14), S( 7, 14), S(24, 48) } }, // Defended Major
135 { { S(0, 0), S( 0,32), S(33, 41), S(31, 50), S(41,100), S(35,104) }, // Weak Minor
136 { S(0, 0), S( 0,27), S(26, 57), S(26, 57), S(0 , 43), S(23, 51) } } // Weak Major
139 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
140 // type is attacked by an enemy pawn.
141 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
142 S(0, 0), S(0, 0), S(107, 138), S(84, 122), S(114, 203), S(121, 217)
145 const Score ThreatenedByHangingPawn = S(40, 60);
147 // Assorted bonuses and penalties used by evaluation
148 const Score KingOnOne = S( 2, 58);
149 const Score KingOnMany = S( 6,125);
150 const Score RookOnPawn = S( 7, 27);
151 const Score RookOnOpenFile = S(43, 21);
152 const Score RookOnSemiOpenFile = S(19, 10);
153 const Score BishopPawns = S( 8, 12);
154 const Score MinorBehindPawn = S(16, 0);
155 const Score TrappedRook = S(92, 0);
156 const Score Unstoppable = S( 0, 20);
157 const Score Hanging = S(31, 26);
158 const Score PawnAttackThreat = S(20, 20);
159 const Score PawnSafePush = S( 5, 5);
161 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
162 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
163 // happen in Chess960 games.
164 const Score TrappedBishopA1H1 = S(50, 50);
169 // SpaceMask[Color] contains the area of the board which is considered
170 // by the space evaluation. In the middlegame, each side is given a bonus
171 // based on how many squares inside this area are safe and available for
172 // friendly minor pieces.
173 const Bitboard SpaceMask[COLOR_NB] = {
174 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
175 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
178 // King danger constants and variables. The king danger scores are looked-up
179 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
180 // of the enemy attack are added up into an integer, which is used as an
181 // index to KingDanger[].
182 Score KingDanger[512];
184 // KingAttackWeights[PieceType] contains king attack weights by piece type
185 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
187 // Penalties for enemy's safe checks
188 const int QueenContactCheck = 89;
189 const int RookContactCheck = 71;
190 const int QueenCheck = 50;
191 const int RookCheck = 37;
192 const int BishopCheck = 6;
193 const int KnightCheck = 14;
196 // init_eval_info() initializes king bitboards for given color adding
197 // pawn attacks. To be done at the beginning of the evaluation.
200 void init_eval_info(const Position& pos, EvalInfo& ei) {
202 const Color Them = (Us == WHITE ? BLACK : WHITE);
203 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
205 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
206 ei.attackedBy[Us][ALL_PIECES] = ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
207 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
209 // Init king safety tables only if we are going to use them
210 if (pos.non_pawn_material(Us) >= QueenValueMg)
212 ei.kingRing[Them] = b | shift_bb<Down>(b);
213 b &= ei.attackedBy[Us][PAWN];
214 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
215 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
218 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
222 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
224 template<PieceType Pt, Color Us, bool Trace>
225 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, Bitboard* mobilityArea) {
229 Score score = SCORE_ZERO;
231 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
232 const Color Them = (Us == WHITE ? BLACK : WHITE);
233 const Square* pl = pos.list<Pt>(Us);
235 ei.attackedBy[Us][Pt] = 0;
237 while ((s = *pl++) != SQ_NONE)
239 // Find attacked squares, including x-ray attacks for bishops and rooks
240 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
241 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
242 : pos.attacks_from<Pt>(s);
244 if (ei.pinnedPieces[Us] & s)
245 b &= LineBB[pos.king_square(Us)][s];
247 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
249 if (b & ei.kingRing[Them])
251 ei.kingAttackersCount[Us]++;
252 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
253 Bitboard bb = b & ei.attackedBy[Them][KING];
255 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
259 b &= ~( ei.attackedBy[Them][KNIGHT]
260 | ei.attackedBy[Them][BISHOP]
261 | ei.attackedBy[Them][ROOK]);
263 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
265 mobility[Us] += MobilityBonus[Pt][mob];
267 if (Pt == BISHOP || Pt == KNIGHT)
269 // Bonus for outpost square
270 if ( relative_rank(Us, s) >= RANK_4
271 && !(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
272 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
274 // Bonus when behind a pawn
275 if ( relative_rank(Us, s) < RANK_5
276 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
277 score += MinorBehindPawn;
279 // Penalty for pawns on same color square of bishop
281 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
283 // An important Chess960 pattern: A cornered bishop blocked by a friendly
284 // pawn diagonally in front of it is a very serious problem, especially
285 // when that pawn is also blocked.
288 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
290 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
291 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
292 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
293 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
300 // Bonus for aligning with enemy pawns on the same rank/file
301 if (relative_rank(Us, s) >= RANK_5)
303 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
305 score += popcount<Max15>(alignedPawns) * RookOnPawn;
308 // Bonus when on an open or semi-open file
309 if (ei.pi->semiopen_file(Us, file_of(s)))
310 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
312 // Penalize when trapped by the king, even more if king cannot castle
313 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
315 Square ksq = pos.king_square(Us);
317 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
318 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
319 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
320 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
326 Tracing::write(Pt, Us, score);
328 // Recursively call evaluate_pieces() of next piece type until KING excluded
329 return score - evaluate_pieces<NextPt, Them, Trace>(pos, ei, mobility, mobilityArea);
333 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
335 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, Bitboard*) { return SCORE_ZERO; }
338 // evaluate_king() assigns bonuses and penalties to a king of a given color
340 template<Color Us, bool Trace>
341 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
343 const Color Them = (Us == WHITE ? BLACK : WHITE);
345 Bitboard undefended, b, b1, b2, safe;
347 const Square ksq = pos.king_square(Us);
349 // King shelter and enemy pawns storm
350 Score score = ei.pi->king_safety<Us>(pos, ksq);
352 // Main king safety evaluation
353 if (ei.kingAttackersCount[Them])
355 // Find the attacked squares around the king which have no defenders
356 // apart from the king itself
357 undefended = ei.attackedBy[Them][ALL_PIECES]
358 & ei.attackedBy[Us][KING]
359 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
360 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
361 | ei.attackedBy[Us][QUEEN]);
363 // Initialize the 'attackUnits' variable, which is used later on as an
364 // index into the KingDanger[] array. The initial value is based on the
365 // number and types of the enemy's attacking pieces, the number of
366 // attacked and undefended squares around our king and the quality of
367 // the pawn shelter (current 'score' value).
368 attackUnits = std::min(74, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
369 + 8 * ei.kingAdjacentZoneAttacksCount[Them]
370 + 25 * popcount<Max15>(undefended)
371 + 11 * (ei.pinnedPieces[Us] != 0)
372 - mg_value(score) / 8
373 - !pos.count<QUEEN>(Them) * 60;
375 // Analyse the enemy's safe queen contact checks. Firstly, find the
376 // undefended squares around the king reachable by the enemy queen...
377 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
380 // ...and then remove squares not supported by another enemy piece
381 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
382 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK];
385 attackUnits += QueenContactCheck * popcount<Max15>(b);
388 // Analyse the enemy's safe rook contact checks. Firstly, find the
389 // undefended squares around the king reachable by the enemy rooks...
390 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces(Them);
392 // Consider only squares where the enemy's rook gives check
393 b &= PseudoAttacks[ROOK][ksq];
397 // ...and then remove squares not supported by another enemy piece
398 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
399 | ei.attackedBy[Them][BISHOP]);
402 attackUnits += RookContactCheck * popcount<Max15>(b);
405 // Analyse the enemy's safe distance checks for sliders and knights
406 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
408 b1 = pos.attacks_from<ROOK >(ksq) & safe;
409 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
411 // Enemy queen safe checks
412 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
414 attackUnits += QueenCheck * popcount<Max15>(b);
416 // Enemy rooks safe checks
417 b = b1 & ei.attackedBy[Them][ROOK];
419 attackUnits += RookCheck * popcount<Max15>(b);
421 // Enemy bishops safe checks
422 b = b2 & ei.attackedBy[Them][BISHOP];
424 attackUnits += BishopCheck * popcount<Max15>(b);
426 // Enemy knights safe checks
427 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
429 attackUnits += KnightCheck * popcount<Max15>(b);
431 // Finally, extract the king danger score from the KingDanger[]
432 // array and subtract the score from evaluation.
433 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
437 Tracing::write(KING, Us, score);
443 // evaluate_threats() assigns bonuses according to the type of attacking piece
444 // and the type of attacked one.
446 template<Color Us, bool Trace>
447 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
449 const Color Them = (Us == WHITE ? BLACK : WHITE);
450 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
451 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
452 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
453 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
454 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
456 enum { Defended, Weak };
457 enum { Minor, Major };
459 Bitboard b, weak, defended, safeThreats;
460 Score score = SCORE_ZERO;
462 // Non-pawn enemies attacked by a pawn
463 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
467 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
468 | ei.attackedBy[Us][ALL_PIECES]);
470 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
472 if (weak ^ safeThreats)
473 score += ThreatenedByHangingPawn;
476 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
479 // Non-pawn enemies defended by a pawn
480 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
482 // Add a bonus according to the kind of attacking pieces
485 b = defended & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
487 score += Threat[Defended][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
489 b = defended & (ei.attackedBy[Us][ROOK]);
491 score += Threat[Defended][Major][type_of(pos.piece_on(pop_lsb(&b)))];
494 // Enemies not defended by a pawn and under our attack
495 weak = pos.pieces(Them)
496 & ~ei.attackedBy[Them][PAWN]
497 & ei.attackedBy[Us][ALL_PIECES];
499 // Add a bonus according to the kind of attacking pieces
502 b = weak & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
504 score += Threat[Weak][Minor][type_of(pos.piece_on(pop_lsb(&b)))];
506 b = weak & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
508 score += Threat[Weak][Major][type_of(pos.piece_on(pop_lsb(&b)))];
510 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
512 score += Hanging * popcount<Max15>(b);
514 b = weak & ei.attackedBy[Us][KING];
516 score += more_than_one(b) ? KingOnMany : KingOnOne;
519 // Add a small bonus for safe pawn pushes
520 b = pos.pieces(Us, PAWN) & ~TRank7BB;
521 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
524 & ~ei.attackedBy[Them][PAWN]
525 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
528 score += popcount<Full>(b) * PawnSafePush;
530 // Add another bonus if the pawn push attacks an enemy piece
531 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
533 & ~ei.attackedBy[Us][PAWN];
536 score += popcount<Max15>(b) * PawnAttackThreat;
539 Tracing::write(Tracing::THREAT, Us, score);
545 // evaluate_passed_pawns() evaluates the passed pawns of the given color
547 template<Color Us, bool Trace>
548 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
550 const Color Them = (Us == WHITE ? BLACK : WHITE);
552 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
553 Score score = SCORE_ZERO;
555 b = ei.pi->passed_pawns(Us);
559 Square s = pop_lsb(&b);
561 assert(pos.pawn_passed(Us, s));
563 int r = relative_rank(Us, s) - RANK_2;
564 int rr = r * (r - 1);
566 // Base bonus based on rank
567 Value mbonus = Value(17 * rr), ebonus = Value(7 * (rr + r + 1));
571 Square blockSq = s + pawn_push(Us);
573 // Adjust bonus based on the king's proximity
574 ebonus += distance(pos.king_square(Them), blockSq) * 5 * rr
575 - distance(pos.king_square(Us ), blockSq) * 2 * rr;
577 // If blockSq is not the queening square then consider also a second push
578 if (relative_rank(Us, blockSq) != RANK_8)
579 ebonus -= distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr;
581 // If the pawn is free to advance, then increase the bonus
582 if (pos.empty(blockSq))
584 // If there is a rook or queen attacking/defending the pawn from behind,
585 // consider all the squaresToQueen. Otherwise consider only the squares
586 // in the pawn's path attacked or occupied by the enemy.
587 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
589 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
591 if (!(pos.pieces(Us) & bb))
592 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
594 if (!(pos.pieces(Them) & bb))
595 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
597 // If there aren't any enemy attacks, assign a big bonus. Otherwise
598 // assign a smaller bonus if the block square isn't attacked.
599 int k = !unsafeSquares ? 15 : !(unsafeSquares & blockSq) ? 9 : 0;
601 // If the path to queen is fully defended, assign a big bonus.
602 // Otherwise assign a smaller bonus if the block square is defended.
603 if (defendedSquares == squaresToQueen)
606 else if (defendedSquares & blockSq)
609 mbonus += k * rr, ebonus += k * rr;
611 else if (pos.pieces(Us) & blockSq)
612 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
615 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
616 ebonus += ebonus / 4;
618 score += make_score(mbonus, ebonus);
622 Tracing::write(Tracing::PASSED, Us, score * Weights[PassedPawns]);
624 // Add the scores to the middlegame and endgame eval
625 return score * Weights[PassedPawns];
629 // evaluate_space() computes the space evaluation for a given side. The
630 // space evaluation is a simple bonus based on the number of safe squares
631 // available for minor pieces on the central four files on ranks 2--4. Safe
632 // squares one, two or three squares behind a friendly pawn are counted
633 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
634 // improve play on game opening.
636 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
638 const Color Them = (Us == WHITE ? BLACK : WHITE);
640 // Find the safe squares for our pieces inside the area defined by
641 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
642 // pawn, or if it is undefended and attacked by an enemy piece.
643 Bitboard safe = SpaceMask[Us]
644 & ~pos.pieces(Us, PAWN)
645 & ~ei.attackedBy[Them][PAWN]
646 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
648 // Find all squares which are at most three squares behind some friendly pawn
649 Bitboard behind = pos.pieces(Us, PAWN);
650 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
651 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
653 // Since SpaceMask[Us] is fully on our half of the board
654 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
656 // Count safe + (behind & safe) with a single popcount
657 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
658 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
659 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
661 return make_score(bonus * weight * weight, 0);
665 // do_evaluate() is the evaluation entry point, called directly from evaluate()
668 Value do_evaluate(const Position& pos) {
670 assert(!pos.checkers());
673 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
675 // Initialize score by reading the incrementally updated scores included
676 // in the position object (material + piece square tables).
677 // Score is computed from the point of view of white.
678 score = pos.psq_score();
680 // Probe the material hash table
681 ei.mi = Material::probe(pos);
682 score += ei.mi->imbalance();
684 // If we have a specialized evaluation function for the current material
685 // configuration, call it and return.
686 if (ei.mi->specialized_eval_exists())
687 return ei.mi->evaluate(pos);
689 // Probe the pawn hash table
690 ei.pi = Pawns::probe(pos);
691 score += ei.pi->pawns_score() * Weights[PawnStructure];
693 // Initialize attack and king safety bitboards
694 init_eval_info<WHITE>(pos, ei);
695 init_eval_info<BLACK>(pos, ei);
697 ei.attackedBy[WHITE][ALL_PIECES] |= ei.attackedBy[WHITE][KING];
698 ei.attackedBy[BLACK][ALL_PIECES] |= ei.attackedBy[BLACK][KING];
700 // Do not include in mobility squares protected by enemy pawns or occupied by our pawns or king
701 Bitboard mobilityArea[] = { ~(ei.attackedBy[BLACK][PAWN] | pos.pieces(WHITE, PAWN, KING)),
702 ~(ei.attackedBy[WHITE][PAWN] | pos.pieces(BLACK, PAWN, KING)) };
704 // Evaluate pieces and mobility
705 score += evaluate_pieces<KNIGHT, WHITE, Trace>(pos, ei, mobility, mobilityArea);
706 score += (mobility[WHITE] - mobility[BLACK]) * Weights[Mobility];
708 // Evaluate kings after all other pieces because we need complete attack
709 // information when computing the king safety evaluation.
710 score += evaluate_king<WHITE, Trace>(pos, ei)
711 - evaluate_king<BLACK, Trace>(pos, ei);
713 // Evaluate tactical threats, we need full attack information including king
714 score += evaluate_threats<WHITE, Trace>(pos, ei)
715 - evaluate_threats<BLACK, Trace>(pos, ei);
717 // Evaluate passed pawns, we need full attack information including king
718 score += evaluate_passed_pawns<WHITE, Trace>(pos, ei)
719 - evaluate_passed_pawns<BLACK, Trace>(pos, ei);
721 // If both sides have only pawns, score for potential unstoppable pawns
722 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
725 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
726 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
728 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
729 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
732 // Evaluate space for both sides, only during opening
733 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 11756)
734 score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
736 // Scale winning side if position is more drawish than it appears
737 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
738 ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
740 // If we don't already have an unusual scale factor, check for certain
741 // types of endgames, and use a lower scale for those.
742 if ( ei.mi->game_phase() < PHASE_MIDGAME
743 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
745 if (pos.opposite_bishops())
747 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
748 // is almost a draw, in case of KBP vs KB is even more a draw.
749 if ( pos.non_pawn_material(WHITE) == BishopValueMg
750 && pos.non_pawn_material(BLACK) == BishopValueMg)
751 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(32) : ScaleFactor(8);
753 // Endgame with opposite-colored bishops, but also other pieces. Still
754 // a bit drawish, but not as drawish as with only the two bishops.
756 sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
758 // Endings where weaker side can place his king in front of the opponent's
759 // pawns are drawish.
760 else if ( abs(eg_value(score)) <= BishopValueEg
761 && ei.pi->pawn_span(strongSide) <= 1
762 && !pos.pawn_passed(~strongSide, pos.king_square(~strongSide)))
763 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(56) : ScaleFactor(38);
766 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
767 Value v = mg_value(score) * int(ei.mi->game_phase())
768 + eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;
770 v /= int(PHASE_MIDGAME);
772 // In case of tracing add all single evaluation terms for both white and black
775 Tracing::write(Tracing::MATERIAL, pos.psq_score());
776 Tracing::write(Tracing::IMBALANCE, ei.mi->imbalance());
777 Tracing::write(PAWN, ei.pi->pawns_score());
778 Tracing::write(Tracing::MOBILITY, mobility[WHITE] * Weights[Mobility]
779 , mobility[BLACK] * Weights[Mobility]);
780 Tracing::write(Tracing::SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
781 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
782 Tracing::write(Tracing::TOTAL, score);
785 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
791 double Tracing::to_cp(Value v) { return double(v) / PawnValueEg; }
793 void Tracing::write(int idx, Color c, Score s) { scores[c][idx] = s; }
795 void Tracing::write(int idx, Score w, Score b) {
796 scores[WHITE][idx] = w, scores[BLACK][idx] = b;
799 std::ostream& Tracing::operator<<(std::ostream& os, Term t) {
801 double wScore[] = { to_cp(mg_value(scores[WHITE][t])), to_cp(eg_value(scores[WHITE][t])) };
802 double bScore[] = { to_cp(mg_value(scores[BLACK][t])), to_cp(eg_value(scores[BLACK][t])) };
804 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
805 os << " --- --- | --- --- | ";
807 os << std::setw(5) << wScore[MG] << " " << std::setw(5) << wScore[EG] << " | "
808 << std::setw(5) << bScore[MG] << " " << std::setw(5) << bScore[EG] << " | ";
810 os << std::setw(5) << wScore[MG] - bScore[MG] << " "
811 << std::setw(5) << wScore[EG] - bScore[EG] << " \n";
816 std::string Tracing::do_trace(const Position& pos) {
818 std::memset(scores, 0, sizeof(scores));
820 Value v = do_evaluate<true>(pos);
821 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
823 std::stringstream ss;
824 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
825 << " Eval term | White | Black | Total \n"
826 << " | MG EG | MG EG | MG EG \n"
827 << "----------------+-------------+-------------+-------------\n"
828 << " Material | " << Term(MATERIAL)
829 << " Imbalance | " << Term(IMBALANCE)
830 << " Pawns | " << Term(PAWN)
831 << " Knights | " << Term(KNIGHT)
832 << " Bishop | " << Term(BISHOP)
833 << " Rooks | " << Term(ROOK)
834 << " Queens | " << Term(QUEEN)
835 << " Mobility | " << Term(MOBILITY)
836 << " King safety | " << Term(KING)
837 << " Threats | " << Term(THREAT)
838 << " Passed pawns | " << Term(PASSED)
839 << " Space | " << Term(SPACE)
840 << "----------------+-------------+-------------+-------------\n"
841 << " Total | " << Term(TOTAL);
843 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
853 /// evaluate() is the main evaluation function. It returns a static evaluation
854 /// of the position always from the point of view of the side to move.
856 Value evaluate(const Position& pos) {
857 return do_evaluate<false>(pos);
861 /// trace() is like evaluate(), but instead of returning a value, it returns
862 /// a string (suitable for outputting to stdout) that contains the detailed
863 /// descriptions and values of each evaluation term. It's mainly used for
865 std::string trace(const Position& pos) {
866 return Tracing::do_trace(pos);
870 /// init() computes evaluation weights, usually at startup
874 const int MaxSlope = 8700;
875 const int Peak = 1280000;
878 for (int i = 0; i < 400; ++i)
880 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
881 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];