2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
32 #include "ucioption.h"
36 //// Local definitions
41 // Struct EvalInfo contains various information computed and collected
42 // by the evaluation functions.
45 // Pointer to pawn hash table entry
48 // attackedBy[color][piece type] is a bitboard representing all squares
49 // attacked by a given color and piece type, attackedBy[color][0] contains
50 // all squares attacked by the given color.
51 Bitboard attackedBy[2][8];
53 // kingZone[color] is the zone around the enemy king which is considered
54 // by the king safety evaluation. This consists of the squares directly
55 // adjacent to the king, and the three (or two, for a king on an edge file)
56 // squares two ranks in front of the king. For instance, if black's king
57 // is on g8, kingZone[WHITE] is a bitboard containing the squares f8, h8,
58 // f7, g7, h7, f6, g6 and h6.
61 // kingAttackersCount[color] is the number of pieces of the given color
62 // which attack a square in the kingZone of the enemy king.
63 int kingAttackersCount[2];
65 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
66 // given color which attack a square in the kingZone of the enemy king. The
67 // weights of the individual piece types are given by the variables
68 // QueenAttackWeight, RookAttackWeight, BishopAttackWeight and
69 // KnightAttackWeight in evaluate.cpp
70 int kingAttackersWeight[2];
72 // kingAdjacentZoneAttacksCount[color] is the number of attacks to squares
73 // directly adjacent to the king of the given color. Pieces which attack
74 // more than one square are counted multiple times. For instance, if black's
75 // king is on g8 and there's a white knight on g5, this knight adds
76 // 2 to kingAdjacentZoneAttacksCount[BLACK].
77 int kingAdjacentZoneAttacksCount[2];
80 // Evaluation grain size, must be a power of 2
81 const int GrainSize = 8;
83 // Evaluation weights, initialized from UCI options
84 enum { Mobility, PawnStructure, PassedPawns, Space, KingDangerUs, KingDangerThem };
88 #define S(mg, eg) make_score(mg, eg)
90 // Internal evaluation weights. These are applied on top of the evaluation
91 // weights read from UCI parameters. The purpose is to be able to change
92 // the evaluation weights while keeping the default values of the UCI
93 // parameters at 100, which looks prettier.
95 // Values modified by Joona Kiiski
96 const Score WeightsInternal[] = {
97 S(248, 271), S(233, 201), S(252, 259), S(46, 0), S(247, 0), S(259, 0)
100 // MobilityBonus[PieceType][attacked] contains mobility bonuses for middle and
101 // end game, indexed by piece type and number of attacked squares not occupied
102 // by friendly pieces.
103 const Score MobilityBonus[][32] = {
105 { S(-38,-33), S(-25,-23), S(-12,-13), S( 0, -3), S(12, 7), S(25, 17), // Knights
106 S( 31, 22), S( 38, 27), S( 38, 27) },
107 { S(-25,-30), S(-11,-16), S( 3, -2), S(17, 12), S(31, 26), S(45, 40), // Bishops
108 S( 57, 52), S( 65, 60), S( 71, 65), S(74, 69), S(76, 71), S(78, 73),
109 S( 79, 74), S( 80, 75), S( 81, 76), S(81, 76) },
110 { S(-20,-36), S(-14,-19), S( -8, -3), S(-2, 13), S( 4, 29), S(10, 46), // Rooks
111 S( 14, 62), S( 19, 79), S( 23, 95), S(26,106), S(27,111), S(28,114),
112 S( 29,116), S( 30,117), S( 31,118), S(32,118) },
113 { S(-10,-18), S( -8,-13), S( -6, -7), S(-3, -2), S(-1, 3), S( 1, 8), // Queens
114 S( 3, 13), S( 5, 19), S( 8, 23), S(10, 27), S(12, 32), S(15, 34),
115 S( 16, 35), S( 17, 35), S( 18, 35), S(20, 35), S(20, 35), S(20, 35),
116 S( 20, 35), S( 20, 35), S( 20, 35), S(20, 35), S(20, 35), S(20, 35),
117 S( 20, 35), S( 20, 35), S( 20, 35), S(20, 35), S(20, 35), S(20, 35),
118 S( 20, 35), S( 20, 35) }
121 // OutpostBonus[PieceType][Square] contains outpost bonuses of knights and
122 // bishops, indexed by piece type and square (from white's point of view).
123 const Value OutpostBonus[][64] = {
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 // ThreatBonus[attacking][attacked] contains threat bonuses according to
142 // which piece type attacks which one.
143 const Score ThreatBonus[][8] = {
145 { S(0, 0), S( 7, 39), S( 0, 0), S(24, 49), S(41,100), S(41,100) }, // KNIGHT
146 { S(0, 0), S( 7, 39), S(24, 49), S( 0, 0), S(41,100), S(41,100) }, // BISHOP
147 { S(0, 0), S(-1, 29), S(15, 49), S(15, 49), S( 0, 0), S(24, 49) }, // ROOK
148 { S(0, 0), S(15, 39), S(15, 39), S(15, 39), S(15, 39), S( 0, 0) } // QUEEN
151 // ThreatedByPawnPenalty[PieceType] contains a penalty according to which
152 // piece type is attacked by an enemy pawn.
153 const Score ThreatedByPawnPenalty[] = {
154 S(0, 0), S(0, 0), S(56, 70), S(56, 70), S(76, 99), S(86, 118)
159 // Rooks and queens on the 7th rank (modified by Joona Kiiski)
160 const Score RookOn7thBonus = make_score(47, 98);
161 const Score QueenOn7thBonus = make_score(27, 54);
163 // Rooks on open files (modified by Joona Kiiski)
164 const Score RookOpenFileBonus = make_score(43, 43);
165 const Score RookHalfOpenFileBonus = make_score(19, 19);
167 // Penalty for rooks trapped inside a friendly king which has lost the
169 const Value TrappedRookPenalty = Value(180);
171 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
172 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
173 // happen in Chess960 games.
174 const Score TrappedBishopA1H1Penalty = make_score(100, 100);
176 // The SpaceMask[Color] contains the area of the board which is considered
177 // by the space evaluation. In the middle game, each side is given a bonus
178 // based on how many squares inside this area are safe and available for
179 // friendly minor pieces.
180 const Bitboard SpaceMask[] = {
181 (1ULL << SQ_C2) | (1ULL << SQ_D2) | (1ULL << SQ_E2) | (1ULL << SQ_F2) |
182 (1ULL << SQ_C3) | (1ULL << SQ_D3) | (1ULL << SQ_E3) | (1ULL << SQ_F3) |
183 (1ULL << SQ_C4) | (1ULL << SQ_D4) | (1ULL << SQ_E4) | (1ULL << SQ_F4),
184 (1ULL << SQ_C7) | (1ULL << SQ_D7) | (1ULL << SQ_E7) | (1ULL << SQ_F7) |
185 (1ULL << SQ_C6) | (1ULL << SQ_D6) | (1ULL << SQ_E6) | (1ULL << SQ_F6) |
186 (1ULL << SQ_C5) | (1ULL << SQ_D5) | (1ULL << SQ_E5) | (1ULL << SQ_F5)
189 // King danger constants and variables. The king danger scores are taken
190 // from the KingDangerTable[]. Various little "meta-bonuses" measuring
191 // the strength of the enemy attack are added up into an integer, which
192 // is used as an index to KingDangerTable[].
194 // KingAttackWeights[PieceType] contains king attack weights by piece type
195 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
197 // Bonuses for enemy's safe checks
198 const int QueenContactCheckBonus = 6;
199 const int RookContactCheckBonus = 4;
200 const int QueenCheckBonus = 3;
201 const int RookCheckBonus = 2;
202 const int BishopCheckBonus = 1;
203 const int KnightCheckBonus = 1;
205 // InitKingDanger[Square] contains penalties based on the position of the
206 // defending king, indexed by king's square (from white's point of view).
207 const int InitKingDanger[] = {
208 2, 0, 2, 5, 5, 2, 0, 2,
209 2, 2, 4, 8, 8, 4, 2, 2,
210 7, 10, 12, 12, 12, 12, 10, 7,
211 15, 15, 15, 15, 15, 15, 15, 15,
212 15, 15, 15, 15, 15, 15, 15, 15,
213 15, 15, 15, 15, 15, 15, 15, 15,
214 15, 15, 15, 15, 15, 15, 15, 15,
215 15, 15, 15, 15, 15, 15, 15, 15
218 // KingDangerTable[Color][attackUnits] contains the actual king danger
219 // weighted scores, indexed by color and by a calculated integer number.
220 Score KingDangerTable[2][128];
222 // Pawn and material hash tables, indexed by the current thread id.
223 // Note that they will be initialized at 0 being global variables.
224 MaterialInfoTable* MaterialTable[MAX_THREADS];
225 PawnInfoTable* PawnTable[MAX_THREADS];
227 // Function prototypes
228 template<bool HasPopCnt>
229 Value do_evaluate(const Position& pos, Value& margin);
231 template<Color Us, bool HasPopCnt>
232 void init_eval_info(const Position& pos, EvalInfo& ei);
234 template<Color Us, bool HasPopCnt>
235 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility);
237 template<Color Us, bool HasPopCnt>
238 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]);
241 Score evaluate_threats(const Position& pos, EvalInfo& ei);
243 template<Color Us, bool HasPopCnt>
244 int evaluate_space(const Position& pos, EvalInfo& ei);
247 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei);
249 template<bool HasPopCnt>
250 Score evaluate_unstoppable_pawns(const Position& pos, EvalInfo& ei);
252 inline Score apply_weight(Score v, Score weight);
253 Value scale_by_game_phase(const Score& v, Phase ph, ScaleFactor sf);
254 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight);
264 /// Prefetches in pawn hash tables
266 void prefetchPawn(Key key, int threadID) {
268 PawnTable[threadID]->prefetch(key);
272 /// evaluate() is the main evaluation function. It always computes two
273 /// values, an endgame score and a middle game score, and interpolates
274 /// between them based on the remaining material.
275 Value evaluate(const Position& pos, Value& margin) {
277 return CpuHasPOPCNT ? do_evaluate<true>(pos, margin)
278 : do_evaluate<false>(pos, margin);
283 template<bool HasPopCnt>
284 Value do_evaluate(const Position& pos, Value& margin) {
288 Score mobilityWhite, mobilityBlack;
291 assert(pos.thread() >= 0 && pos.thread() < MAX_THREADS);
292 assert(!pos.is_check());
294 // Initialize value by reading the incrementally updated scores included
295 // in the position object (material + piece square tables).
296 Score bonus = pos.value();
298 // margins[] store the uncertainty estimation of position's evaluation
299 // that typically is used by the search for pruning decisions.
300 margins[WHITE] = margins[BLACK] = VALUE_ZERO;
302 // Probe the material hash table
303 MaterialInfo* mi = MaterialTable[pos.thread()]->get_material_info(pos);
304 bonus += mi->material_value();
306 // If we have a specialized evaluation function for the current material
307 // configuration, call it and return.
308 if (mi->specialized_eval_exists())
311 return mi->evaluate(pos);
314 // Probe the pawn hash table
315 ei.pi = PawnTable[pos.thread()]->get_pawn_info(pos);
316 bonus += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
318 // Initialize attack and king safety bitboards
319 init_eval_info<WHITE, HasPopCnt>(pos, ei);
320 init_eval_info<BLACK, HasPopCnt>(pos, ei);
322 // Evaluate pieces and mobility
323 bonus += evaluate_pieces_of_color<WHITE, HasPopCnt>(pos, ei, mobilityWhite)
324 - evaluate_pieces_of_color<BLACK, HasPopCnt>(pos, ei, mobilityBlack);
326 bonus += apply_weight(mobilityWhite - mobilityBlack, Weights[Mobility]);
328 // Evaluate kings after all other pieces because we need complete attack
329 // information when computing the king safety evaluation.
330 bonus += evaluate_king<WHITE, HasPopCnt>(pos, ei, margins)
331 - evaluate_king<BLACK, HasPopCnt>(pos, ei, margins);
333 // Evaluate tactical threats, we need full attack information including king
334 bonus += evaluate_threats<WHITE>(pos, ei)
335 - evaluate_threats<BLACK>(pos, ei);
337 // Evaluate passed pawns, we need full attack information including king
338 bonus += evaluate_passed_pawns<WHITE>(pos, ei)
339 - evaluate_passed_pawns<BLACK>(pos, ei);
341 // If one side has only a king, check whether exists any unstoppable passed pawn
342 if (!pos.non_pawn_material(WHITE) || !pos.non_pawn_material(BLACK))
343 bonus += evaluate_unstoppable_pawns<HasPopCnt>(pos, ei);
345 // Evaluate space for both sides, only in middle-game.
346 if (mi->space_weight())
348 int s = evaluate_space<WHITE, HasPopCnt>(pos, ei) - evaluate_space<BLACK, HasPopCnt>(pos, ei);
349 bonus += apply_weight(make_score(s * mi->space_weight(), 0), Weights[Space]);
352 // Scale winning side if position is more drawish that what it appears
353 ScaleFactor sf = eg_value(bonus) > VALUE_DRAW ? mi->scale_factor(pos, WHITE)
354 : mi->scale_factor(pos, BLACK);
355 Phase phase = mi->game_phase();
357 // If we don't already have an unusual scale factor, check for opposite
358 // colored bishop endgames, and use a lower scale for those.
359 if ( phase < PHASE_MIDGAME
360 && pos.opposite_colored_bishops()
361 && sf == SCALE_FACTOR_NORMAL)
363 // Only the two bishops ?
364 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
365 && pos.non_pawn_material(BLACK) == BishopValueMidgame)
367 // Check for KBP vs KB with only a single pawn that is almost
368 // certainly a draw or at least two pawns.
369 bool one_pawn = (pos.piece_count(WHITE, PAWN) + pos.piece_count(BLACK, PAWN) == 1);
370 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
373 // Endgame with opposite-colored bishops, but also other pieces. Still
374 // a bit drawish, but not as drawish as with only the two bishops.
375 sf = ScaleFactor(50);
378 // Interpolate between the middle game and the endgame score
379 margin = margins[pos.side_to_move()];
380 Value v = scale_by_game_phase(bonus, phase, sf);
381 return pos.side_to_move() == WHITE ? v : -v;
387 /// init_eval() initializes various tables used by the evaluation function
389 void init_eval(int threads) {
391 assert(threads <= MAX_THREADS);
393 for (int i = 0; i < MAX_THREADS; i++)
398 delete MaterialTable[i];
400 MaterialTable[i] = NULL;
404 PawnTable[i] = new PawnInfoTable();
406 if (!MaterialTable[i])
407 MaterialTable[i] = new MaterialInfoTable();
412 /// quit_eval() releases heap-allocated memory at program termination
420 /// read_weights() reads evaluation weights from the corresponding UCI parameters
422 void read_evaluation_uci_options(Color us) {
424 // King safety is asymmetrical. Our king danger level is weighted by
425 // "Cowardice" UCI parameter, instead the opponent one by "Aggressiveness".
426 const int kingDangerUs = (us == WHITE ? KingDangerUs : KingDangerThem);
427 const int kingDangerThem = (us == WHITE ? KingDangerThem : KingDangerUs);
429 Weights[Mobility] = weight_option("Mobility (Middle Game)", "Mobility (Endgame)", WeightsInternal[Mobility]);
430 Weights[PawnStructure] = weight_option("Pawn Structure (Middle Game)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
431 Weights[PassedPawns] = weight_option("Passed Pawns (Middle Game)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
432 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
433 Weights[kingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
434 Weights[kingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
436 // If running in analysis mode, make sure we use symmetrical king safety. We do this
437 // by replacing both Weights[kingDangerUs] and Weights[kingDangerThem] by their average.
438 if (Options["UCI_AnalyseMode"].value<bool>())
439 Weights[kingDangerUs] = Weights[kingDangerThem] = (Weights[kingDangerUs] + Weights[kingDangerThem]) / 2;
447 // init_eval_info() initializes king bitboards for given color adding
448 // pawn attacks. To be done at the beginning of the evaluation.
450 template<Color Us, bool HasPopCnt>
451 void init_eval_info(const Position& pos, EvalInfo& ei) {
453 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
454 const Color Them = (Us == WHITE ? BLACK : WHITE);
456 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
457 ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
459 // Init king safety tables only if we are going to use them
460 if ( pos.piece_count(Us, QUEEN)
461 && pos.non_pawn_material(Us) >= QueenValueMidgame + RookValueMidgame)
463 ei.kingZone[Us] = (b | (Us == WHITE ? b >> 8 : b << 8));
464 b &= ei.attackedBy[Us][PAWN];
465 ei.kingAttackersCount[Us] = b ? count_1s<Max15>(b) / 2 : 0;
466 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
468 ei.kingZone[Us] = ei.kingAttackersCount[Us] = 0;
472 // evaluate_outposts() evaluates bishop and knight outposts squares
474 template<PieceType Piece, Color Us>
475 Score evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {
477 const Color Them = (Us == WHITE ? BLACK : WHITE);
479 assert (Piece == BISHOP || Piece == KNIGHT);
481 // Initial bonus based on square
482 Value bonus = OutpostBonus[Piece == BISHOP][relative_square(Us, s)];
484 // Increase bonus if supported by pawn, especially if the opponent has
485 // no minor piece which can exchange the outpost piece.
486 if (bonus && bit_is_set(ei.attackedBy[Us][PAWN], s))
488 if ( pos.pieces(KNIGHT, Them) == EmptyBoardBB
489 && (SquaresByColorBB[square_color(s)] & pos.pieces(BISHOP, Them)) == EmptyBoardBB)
490 bonus += bonus + bonus / 2;
494 return make_score(bonus, bonus);
498 // evaluate_pieces<>() assigns bonuses and penalties to the pieces of a given color
500 template<PieceType Piece, Color Us, bool HasPopCnt>
501 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score& mobility, Bitboard mobilityArea) {
507 Score bonus = SCORE_ZERO;
509 const BitCountType Full = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64 : CNT32;
510 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
511 const Color Them = (Us == WHITE ? BLACK : WHITE);
512 const Square* ptr = pos.piece_list_begin(Us, Piece);
514 ei.attackedBy[Us][Piece] = EmptyBoardBB;
516 while ((s = *ptr++) != SQ_NONE)
518 // Find attacked squares, including x-ray attacks for bishops and rooks
519 if (Piece == KNIGHT || Piece == QUEEN)
520 b = pos.attacks_from<Piece>(s);
521 else if (Piece == BISHOP)
522 b = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
523 else if (Piece == ROOK)
524 b = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
528 // Update attack info
529 ei.attackedBy[Us][Piece] |= b;
532 if (b & ei.kingZone[Us])
534 ei.kingAttackersCount[Us]++;
535 ei.kingAttackersWeight[Us] += KingAttackWeights[Piece];
536 Bitboard bb = (b & ei.attackedBy[Them][KING]);
538 ei.kingAdjacentZoneAttacksCount[Us] += count_1s<Max15>(bb);
542 mob = (Piece != QUEEN ? count_1s<Max15>(b & mobilityArea)
543 : count_1s<Full >(b & mobilityArea));
545 mobility += MobilityBonus[Piece][mob];
547 // Decrease score if we are attacked by an enemy pawn. Remaining part
548 // of threat evaluation must be done later when we have full attack info.
549 if (bit_is_set(ei.attackedBy[Them][PAWN], s))
550 bonus -= ThreatedByPawnPenalty[Piece];
552 // Bishop and knight outposts squares
553 if ((Piece == BISHOP || Piece == KNIGHT) && pos.square_is_weak(s, Us))
554 bonus += evaluate_outposts<Piece, Us>(pos, ei, s);
556 // Queen or rook on 7th rank
557 if ( (Piece == ROOK || Piece == QUEEN)
558 && relative_rank(Us, s) == RANK_7
559 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
561 bonus += (Piece == ROOK ? RookOn7thBonus : QueenOn7thBonus);
564 // Special extra evaluation for bishops
565 if (Piece == BISHOP && pos.is_chess960())
567 // An important Chess960 pattern: A cornered bishop blocked by
568 // a friendly pawn diagonally in front of it is a very serious
569 // problem, especially when that pawn is also blocked.
570 if (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1))
572 Square d = pawn_push(Us) + (square_file(s) == FILE_A ? DELTA_E : DELTA_W);
573 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
575 if (!pos.square_is_empty(s + d + pawn_push(Us)))
576 bonus -= 2*TrappedBishopA1H1Penalty;
577 else if (pos.piece_on(s + 2*d) == make_piece(Us, PAWN))
578 bonus -= TrappedBishopA1H1Penalty;
580 bonus -= TrappedBishopA1H1Penalty / 2;
585 // Special extra evaluation for rooks
588 // Open and half-open files
590 if (ei.pi->file_is_half_open(Us, f))
592 if (ei.pi->file_is_half_open(Them, f))
593 bonus += RookOpenFileBonus;
595 bonus += RookHalfOpenFileBonus;
598 // Penalize rooks which are trapped inside a king. Penalize more if
599 // king has lost right to castle.
600 if (mob > 6 || ei.pi->file_is_half_open(Us, f))
603 ksq = pos.king_square(Us);
605 if ( square_file(ksq) >= FILE_E
606 && square_file(s) > square_file(ksq)
607 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
609 // Is there a half-open file between the king and the edge of the board?
610 if (!ei.pi->has_open_file_to_right(Us, square_file(ksq)))
611 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
612 : (TrappedRookPenalty - mob * 16), 0);
614 else if ( square_file(ksq) <= FILE_D
615 && square_file(s) < square_file(ksq)
616 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
618 // Is there a half-open file between the king and the edge of the board?
619 if (!ei.pi->has_open_file_to_left(Us, square_file(ksq)))
620 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
621 : (TrappedRookPenalty - mob * 16), 0);
629 // evaluate_threats<>() assigns bonuses according to the type of attacking piece
630 // and the type of attacked one.
633 Score evaluate_threats(const Position& pos, EvalInfo& ei) {
635 const Color Them = (Us == WHITE ? BLACK : WHITE);
638 Score bonus = SCORE_ZERO;
640 // Enemy pieces not defended by a pawn and under our attack
641 Bitboard weakEnemies = pos.pieces_of_color(Them)
642 & ~ei.attackedBy[Them][PAWN]
643 & ei.attackedBy[Us][0];
647 // Add bonus according to type of attacked enemy piece and to the
648 // type of attacking piece, from knights to queens. Kings are not
649 // considered because are already handled in king evaluation.
650 for (PieceType pt1 = KNIGHT; pt1 < KING; pt1++)
652 b = ei.attackedBy[Us][pt1] & weakEnemies;
654 for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
655 if (b & pos.pieces(pt2))
656 bonus += ThreatBonus[pt1][pt2];
662 // evaluate_pieces_of_color<>() assigns bonuses and penalties to all the
663 // pieces of a given color.
665 template<Color Us, bool HasPopCnt>
666 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility) {
668 const Color Them = (Us == WHITE ? BLACK : WHITE);
670 Score bonus = mobility = SCORE_ZERO;
672 // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
673 const Bitboard mobilityArea = ~(ei.attackedBy[Them][PAWN] | pos.pieces_of_color(Us));
675 bonus += evaluate_pieces<KNIGHT, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
676 bonus += evaluate_pieces<BISHOP, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
677 bonus += evaluate_pieces<ROOK, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
678 bonus += evaluate_pieces<QUEEN, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
680 // Sum up all attacked squares
681 ei.attackedBy[Us][0] = ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
682 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
683 | ei.attackedBy[Us][QUEEN] | ei.attackedBy[Us][KING];
688 // evaluate_king<>() assigns bonuses and penalties to a king of a given color
690 template<Color Us, bool HasPopCnt>
691 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]) {
693 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
694 const Color Them = (Us == WHITE ? BLACK : WHITE);
696 Bitboard undefended, b, b1, b2, safe;
698 const Square ksq = pos.king_square(Us);
701 Score bonus = ei.pi->king_shelter<Us>(pos, ksq);
703 // King safety. This is quite complicated, and is almost certainly far
704 // from optimally tuned.
705 if ( ei.kingAttackersCount[Them] >= 2
706 && ei.kingAdjacentZoneAttacksCount[Them])
708 // Find the attacked squares around the king which has no defenders
709 // apart from the king itself
710 undefended = ei.attackedBy[Them][0] & ei.attackedBy[Us][KING];
711 undefended &= ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
712 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
713 | ei.attackedBy[Us][QUEEN]);
715 // Initialize the 'attackUnits' variable, which is used later on as an
716 // index to the KingDangerTable[] array. The initial value is based on
717 // the number and types of the enemy's attacking pieces, the number of
718 // attacked and undefended squares around our king, the square of the
719 // king, and the quality of the pawn shelter.
720 attackUnits = Min(25, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
721 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + count_1s<Max15>(undefended))
722 + InitKingDanger[relative_square(Us, ksq)]
723 - mg_value(ei.pi->king_shelter<Us>(pos, ksq)) / 32;
725 // Analyse enemy's safe queen contact checks. First find undefended
726 // squares around the king attacked by enemy queen...
727 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces_of_color(Them);
730 // ...then remove squares not supported by another enemy piece
731 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
732 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
734 attackUnits += QueenContactCheckBonus
736 * (Them == pos.side_to_move() ? 2 : 1);
739 // Analyse enemy's safe rook contact checks. First find undefended
740 // squares around the king attacked by enemy rooks...
741 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces_of_color(Them);
743 // Consider only squares where the enemy rook gives check
744 b &= RookPseudoAttacks[ksq];
748 // ...then remove squares not supported by another enemy piece
749 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
750 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
752 attackUnits += RookContactCheckBonus
754 * (Them == pos.side_to_move() ? 2 : 1);
757 // Analyse enemy's safe distance checks for sliders and knights
758 safe = ~(pos.pieces_of_color(Them) | ei.attackedBy[Us][0]);
760 b1 = pos.attacks_from<ROOK>(ksq) & safe;
761 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
763 // Enemy queen safe checks
764 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
766 attackUnits += QueenCheckBonus * count_1s<Max15>(b);
768 // Enemy rooks safe checks
769 b = b1 & ei.attackedBy[Them][ROOK];
771 attackUnits += RookCheckBonus * count_1s<Max15>(b);
773 // Enemy bishops safe checks
774 b = b2 & ei.attackedBy[Them][BISHOP];
776 attackUnits += BishopCheckBonus * count_1s<Max15>(b);
778 // Enemy knights safe checks
779 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
781 attackUnits += KnightCheckBonus * count_1s<Max15>(b);
783 // To index KingDangerTable[] attackUnits must be in [0, 99] range
784 attackUnits = Min(99, Max(0, attackUnits));
786 // Finally, extract the king danger score from the KingDangerTable[]
787 // array and subtract the score from evaluation. Set also margins[]
788 // value that will be used for pruning because this value can sometimes
789 // be very big, and so capturing a single attacking piece can therefore
790 // result in a score change far bigger than the value of the captured piece.
791 bonus -= KingDangerTable[Us][attackUnits];
792 margins[Us] += mg_value(KingDangerTable[Us][attackUnits]);
798 // evaluate_passed_pawns<>() evaluates the passed pawns of the given color
801 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei) {
803 const Color Them = (Us == WHITE ? BLACK : WHITE);
805 Score bonus = SCORE_ZERO;
806 Bitboard squaresToQueen, defendedSquares, unsafeSquares, supportingPawns;
807 Bitboard b = ei.pi->passed_pawns(Us);
813 Square s = pop_1st_bit(&b);
815 assert(pos.pawn_is_passed(Us, s));
817 int r = int(relative_rank(Us, s) - RANK_2);
818 int rr = r * (r - 1);
820 // Base bonus based on rank
821 Value mbonus = Value(20 * rr);
822 Value ebonus = Value(10 * (rr + r + 1));
826 Square blockSq = s + pawn_push(Us);
828 // Adjust bonus based on kings proximity
829 ebonus -= Value(square_distance(pos.king_square(Us), blockSq) * 3 * rr);
830 ebonus -= Value(square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr);
831 ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 6 * rr);
833 // If the pawn is free to advance, increase bonus
834 if (pos.square_is_empty(blockSq))
836 squaresToQueen = squares_in_front_of(Us, s);
837 defendedSquares = squaresToQueen & ei.attackedBy[Us][0];
839 // If there is an enemy rook or queen attacking the pawn from behind,
840 // add all X-ray attacks by the rook or queen. Otherwise consider only
841 // the squares in the pawn's path attacked or occupied by the enemy.
842 if ( (squares_in_front_of(Them, s) & pos.pieces(ROOK, QUEEN, Them))
843 && (squares_in_front_of(Them, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<ROOK>(s)))
844 unsafeSquares = squaresToQueen;
846 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][0] | pos.pieces_of_color(Them));
848 // If there aren't enemy attacks or pieces along the path to queen give
849 // huge bonus. Even bigger if we protect the pawn's path.
851 ebonus += Value(rr * (squaresToQueen == defendedSquares ? 17 : 15));
853 // OK, there are enemy attacks or pieces (but not pawns). Are those
854 // squares which are attacked by the enemy also attacked by us ?
855 // If yes, big bonus (but smaller than when there are no enemy attacks),
856 // if no, somewhat smaller bonus.
857 ebonus += Value(rr * ((unsafeSquares & defendedSquares) == unsafeSquares ? 13 : 8));
859 // At last, add a small bonus when there are no *friendly* pieces
860 // in the pawn's path.
861 if (!(squaresToQueen & pos.pieces_of_color(Us)))
866 // Increase the bonus if the passed pawn is supported by a friendly pawn
867 // on the same rank and a bit smaller if it's on the previous rank.
868 supportingPawns = pos.pieces(PAWN, Us) & neighboring_files_bb(s);
869 if (supportingPawns & rank_bb(s))
870 ebonus += Value(r * 20);
871 else if (supportingPawns & rank_bb(s - pawn_push(Us)))
872 ebonus += Value(r * 12);
874 // Rook pawns are a special case: They are sometimes worse, and
875 // sometimes better than other passed pawns. It is difficult to find
876 // good rules for determining whether they are good or bad. For now,
877 // we try the following: Increase the value for rook pawns if the
878 // other side has no pieces apart from a knight, and decrease the
879 // value if the other side has a rook or queen.
880 if (square_file(s) == FILE_A || square_file(s) == FILE_H)
882 if (pos.non_pawn_material(Them) <= KnightValueMidgame)
883 ebonus += ebonus / 4;
884 else if (pos.pieces(ROOK, QUEEN, Them))
885 ebonus -= ebonus / 4;
887 bonus += make_score(mbonus, ebonus);
891 // Add the scores to the middle game and endgame eval
892 return apply_weight(bonus, Weights[PassedPawns]);
895 // evaluate_unstoppable_pawns() evaluates the unstoppable passed pawns for both sides
896 template<bool HasPopCnt>
897 Score evaluate_unstoppable_pawns(const Position& pos, EvalInfo& ei) {
899 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
901 // Step 1. Hunt for unstoppable pawns. If we find at least one, record how many plies
902 // are required for promotion
903 int pliesToGo[2] = {256, 256};
905 for (Color c = WHITE; c <= BLACK; c++)
907 // Skip if other side has non-pawn pieces
908 if (pos.non_pawn_material(opposite_color(c)))
911 Bitboard b = ei.pi->passed_pawns(c);
915 Square s = pop_1st_bit(&b);
916 Square queeningSquare = relative_square(c, make_square(square_file(s), RANK_8));
918 int mtg = RANK_8 - relative_rank(c, s) - int(relative_rank(c, s) == RANK_2);
919 int oppmtg = square_distance(pos.king_square(opposite_color(c)), queeningSquare) - int(c != pos.side_to_move());
920 bool pathDefended = ((ei.attackedBy[c][0] & squares_in_front_of(c, s)) == squares_in_front_of(c, s));
922 if (mtg >= oppmtg && !pathDefended)
925 int blockerCount = count_1s<Max15>(squares_in_front_of(c, s) & pos.occupied_squares());
928 if (mtg >= oppmtg && !pathDefended)
931 int ptg = 2 * mtg - int(c == pos.side_to_move());
933 if (ptg < pliesToGo[c])
938 // Step 2. If either side cannot promote at least three plies before the other side then
939 // situation becomes too complex and we give up. Otherwise we determine the possibly "winning side"
940 if (abs(pliesToGo[WHITE] - pliesToGo[BLACK]) < 3)
941 return make_score(0, 0);
943 Color winnerSide = (pliesToGo[WHITE] < pliesToGo[BLACK] ? WHITE : BLACK);
944 Color loserSide = opposite_color(winnerSide);
946 // Step 3. Can the losing side possibly create a new passed pawn and thus prevent the loss?
947 // We collect the potential candidates in potentialBB.
948 Bitboard pawnBB = pos.pieces(PAWN, loserSide);
949 Bitboard potentialBB = pawnBB;
950 const Bitboard passedBB = ei.pi->passed_pawns(loserSide);
954 Square psq = pop_1st_bit(&pawnBB);
956 // Check direct advancement
957 int mtg = RANK_8 - relative_rank(loserSide, psq) - int(relative_rank(loserSide, psq) == RANK_2);
958 int ptg = 2 * mtg - int(loserSide == pos.side_to_move());
960 // Check if (without even considering any obstacles) we're too far away
961 if (pliesToGo[winnerSide] + 3 <= ptg)
963 clear_bit(&potentialBB, psq);
967 // If this is passed pawn, then it _may_ promote in time. We give up.
968 if (bit_is_set(passedBB, psq))
969 return make_score(0, 0);
971 // Doubled pawn is worthless
972 if (squares_in_front_of(loserSide, psq) & (pos.pieces(PAWN, loserSide)))
974 clear_bit(&potentialBB, psq);
979 // Step 4. Check new passed pawn creation through king capturing and sacrifises
980 pawnBB = potentialBB;
984 Square psq = pop_1st_bit(&pawnBB);
986 int mtg = RANK_8 - relative_rank(loserSide, psq) - int(relative_rank(loserSide, psq) == RANK_2);
987 int ptg = 2 * mtg - int(loserSide == pos.side_to_move());
989 // Generate list of obstacles
990 Bitboard obsBB = passed_pawn_mask(loserSide, psq) & pos.pieces(PAWN, winnerSide);
991 const bool pawnIsOpposed = squares_in_front_of(loserSide, psq) & obsBB;
994 // How many plies does it take to remove all the obstacles?
996 int realObsCount = 0;
997 int minKingDist = 256;
1001 Square obSq = pop_1st_bit(&obsBB);
1004 // Check pawns that can give support to overcome obstacle (Eg. wp: a4,b4 bp: b2. b4 is giving support)
1005 if (!pawnIsOpposed && square_file(psq) != square_file(obSq))
1007 Bitboard supBB = in_front_bb(winnerSide, Square(obSq + (winnerSide == WHITE ? 8 : -8)))
1008 & neighboring_files_bb(psq) & potentialBB;
1010 while(supBB) // This while-loop could be replaced with supSq = LSB/MSB(supBB) (depending on color)
1012 Square supSq = pop_1st_bit(&supBB);
1013 int dist = square_distance(obSq, supSq);
1014 minMoves = Min(minMoves, dist - 2);
1019 // Check pawns that can be sacrifised
1020 Bitboard sacBB = passed_pawn_mask(winnerSide, obSq) & neighboring_files_bb(obSq) & potentialBB & ~(1ULL << psq);
1022 while(sacBB) // This while-loop could be replaced with sacSq = LSB/MSB(sacBB) (depending on color)
1024 Square sacSq = pop_1st_bit(&sacBB);
1025 int dist = square_distance(obSq, sacSq);
1026 minMoves = Min(minMoves, dist - 2);
1029 // If obstacle can be destroyed with immediate pawn sacrifise, it's not real obstacle
1033 // Pawn sac calculations
1034 sacptg += minMoves * 2;
1036 // King capture calc
1038 int kingDist = square_distance(pos.king_square(loserSide), obSq);
1039 minKingDist = Min(minKingDist, kingDist);
1042 // Check if pawn sac plan _may_ save the day
1043 if (pliesToGo[winnerSide] + 3 > ptg + sacptg)
1044 return make_score(0, 0);
1046 // Check if king capture plan _may_ save the day (contains some false positives)
1047 int kingptg = (minKingDist + realObsCount) * 2;
1048 if (pliesToGo[winnerSide] + 3 > ptg + kingptg)
1049 return make_score(0, 0);
1052 // Step 5. Assign bonus
1053 const int Sign[2] = {1, -1};
1054 return Sign[winnerSide] * make_score(0, (Value) 0x500 - 0x20 * pliesToGo[winnerSide]);
1058 // evaluate_space() computes the space evaluation for a given side. The
1059 // space evaluation is a simple bonus based on the number of safe squares
1060 // available for minor pieces on the central four files on ranks 2--4. Safe
1061 // squares one, two or three squares behind a friendly pawn are counted
1062 // twice. Finally, the space bonus is scaled by a weight taken from the
1063 // material hash table. The aim is to improve play on game opening.
1064 template<Color Us, bool HasPopCnt>
1065 int evaluate_space(const Position& pos, EvalInfo& ei) {
1067 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
1068 const Color Them = (Us == WHITE ? BLACK : WHITE);
1070 // Find the safe squares for our pieces inside the area defined by
1071 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
1072 // pawn, or if it is undefended and attacked by an enemy piece.
1073 Bitboard safe = SpaceMask[Us]
1074 & ~pos.pieces(PAWN, Us)
1075 & ~ei.attackedBy[Them][PAWN]
1076 & (ei.attackedBy[Us][0] | ~ei.attackedBy[Them][0]);
1078 // Find all squares which are at most three squares behind some friendly pawn
1079 Bitboard behind = pos.pieces(PAWN, Us);
1080 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
1081 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
1083 return count_1s<Max15>(safe) + count_1s<Max15>(behind & safe);
1087 // apply_weight() applies an evaluation weight to a value trying to prevent overflow
1089 inline Score apply_weight(Score v, Score w) {
1090 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
1091 (int(eg_value(v)) * eg_value(w)) / 0x100);
1095 // scale_by_game_phase() interpolates between a middle game and an endgame score,
1096 // based on game phase. It also scales the return value by a ScaleFactor array.
1098 Value scale_by_game_phase(const Score& v, Phase ph, ScaleFactor sf) {
1100 assert(mg_value(v) > -VALUE_INFINITE && mg_value(v) < VALUE_INFINITE);
1101 assert(eg_value(v) > -VALUE_INFINITE && eg_value(v) < VALUE_INFINITE);
1102 assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
1104 Value eg = eg_value(v);
1105 Value ev = Value((eg * int(sf)) / SCALE_FACTOR_NORMAL);
1107 int result = (mg_value(v) * int(ph) + ev * int(128 - ph)) / 128;
1108 return Value(result & ~(GrainSize - 1));
1112 // weight_option() computes the value of an evaluation weight, by combining
1113 // two UCI-configurable weights (midgame and endgame) with an internal weight.
1115 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
1117 // Scale option value from 100 to 256
1118 int mg = Options[mgOpt].value<int>() * 256 / 100;
1119 int eg = Options[egOpt].value<int>() * 256 / 100;
1121 return apply_weight(make_score(mg, eg), internalWeight);
1125 // init_safety() initizes the king safety evaluation, based on UCI
1126 // parameters. It is called from read_weights().
1128 void init_safety() {
1130 const Value MaxSlope = Value(30);
1131 const Value Peak = Value(1280);
1134 // First setup the base table
1135 for (int i = 0; i < 100; i++)
1137 t[i] = Value(int(0.4 * i * i));
1140 t[i] = Min(t[i], t[i - 1] + MaxSlope);
1142 t[i] = Min(t[i], Peak);
1145 // Then apply the weights and get the final KingDangerTable[] array
1146 for (Color c = WHITE; c <= BLACK; c++)
1147 for (int i = 0; i < 100; i++)
1148 KingDangerTable[c][i] = apply_weight(make_score(t[i], 0), Weights[KingDangerUs + c]);