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 // The SpaceMask[Color] contains the area of the board which is considered
172 // by the space evaluation. In the middle game, each side is given a bonus
173 // based on how many squares inside this area are safe and available for
174 // friendly minor pieces.
175 const Bitboard SpaceMask[] = {
176 (1ULL << SQ_C2) | (1ULL << SQ_D2) | (1ULL << SQ_E2) | (1ULL << SQ_F2) |
177 (1ULL << SQ_C3) | (1ULL << SQ_D3) | (1ULL << SQ_E3) | (1ULL << SQ_F3) |
178 (1ULL << SQ_C4) | (1ULL << SQ_D4) | (1ULL << SQ_E4) | (1ULL << SQ_F4),
179 (1ULL << SQ_C7) | (1ULL << SQ_D7) | (1ULL << SQ_E7) | (1ULL << SQ_F7) |
180 (1ULL << SQ_C6) | (1ULL << SQ_D6) | (1ULL << SQ_E6) | (1ULL << SQ_F6) |
181 (1ULL << SQ_C5) | (1ULL << SQ_D5) | (1ULL << SQ_E5) | (1ULL << SQ_F5)
184 // King danger constants and variables. The king danger scores are taken
185 // from the KingDangerTable[]. Various little "meta-bonuses" measuring
186 // the strength of the enemy attack are added up into an integer, which
187 // is used as an index to KingDangerTable[].
189 // KingAttackWeights[PieceType] contains king attack weights by piece type
190 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
192 // Bonuses for enemy's safe checks
193 const int QueenContactCheckBonus = 6;
194 const int RookContactCheckBonus = 4;
195 const int QueenCheckBonus = 3;
196 const int RookCheckBonus = 2;
197 const int BishopCheckBonus = 1;
198 const int KnightCheckBonus = 1;
200 // InitKingDanger[Square] contains penalties based on the position of the
201 // defending king, indexed by king's square (from white's point of view).
202 const int InitKingDanger[] = {
203 2, 0, 2, 5, 5, 2, 0, 2,
204 2, 2, 4, 8, 8, 4, 2, 2,
205 7, 10, 12, 12, 12, 12, 10, 7,
206 15, 15, 15, 15, 15, 15, 15, 15,
207 15, 15, 15, 15, 15, 15, 15, 15,
208 15, 15, 15, 15, 15, 15, 15, 15,
209 15, 15, 15, 15, 15, 15, 15, 15,
210 15, 15, 15, 15, 15, 15, 15, 15
213 // KingDangerTable[Color][attackUnits] contains the actual king danger
214 // weighted scores, indexed by color and by a calculated integer number.
215 Score KingDangerTable[2][128];
217 // Pawn and material hash tables, indexed by the current thread id.
218 // Note that they will be initialized at 0 being global variables.
219 MaterialInfoTable* MaterialTable[MAX_THREADS];
220 PawnInfoTable* PawnTable[MAX_THREADS];
222 // Function prototypes
223 template<bool HasPopCnt>
224 Value do_evaluate(const Position& pos, Value& margin);
226 template<Color Us, bool HasPopCnt>
227 void init_eval_info(const Position& pos, EvalInfo& ei);
229 template<Color Us, bool HasPopCnt>
230 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility);
232 template<Color Us, bool HasPopCnt>
233 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]);
236 Score evaluate_threats(const Position& pos, EvalInfo& ei);
238 template<Color Us, bool HasPopCnt>
239 int evaluate_space(const Position& pos, EvalInfo& ei);
242 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei);
244 inline Score apply_weight(Score v, Score weight);
245 Value scale_by_game_phase(const Score& v, Phase ph, ScaleFactor sf);
246 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight);
256 /// Prefetches in pawn hash tables
258 void prefetchPawn(Key key, int threadID) {
260 PawnTable[threadID]->prefetch(key);
264 /// evaluate() is the main evaluation function. It always computes two
265 /// values, an endgame score and a middle game score, and interpolates
266 /// between them based on the remaining material.
267 Value evaluate(const Position& pos, Value& margin) {
269 return CpuHasPOPCNT ? do_evaluate<true>(pos, margin)
270 : do_evaluate<false>(pos, margin);
275 template<bool HasPopCnt>
276 Value do_evaluate(const Position& pos, Value& margin) {
280 Score mobilityWhite, mobilityBlack;
283 assert(pos.thread() >= 0 && pos.thread() < MAX_THREADS);
284 assert(!pos.is_check());
286 // Initialize value by reading the incrementally updated scores included
287 // in the position object (material + piece square tables).
288 Score bonus = pos.value();
290 // margins[] store the uncertainty estimation of position's evaluation
291 // that typically is used by the search for pruning decisions.
292 margins[WHITE] = margins[BLACK] = VALUE_ZERO;
294 // Probe the material hash table
295 MaterialInfo* mi = MaterialTable[pos.thread()]->get_material_info(pos);
296 bonus += mi->material_value();
298 // If we have a specialized evaluation function for the current material
299 // configuration, call it and return.
300 if (mi->specialized_eval_exists())
303 return mi->evaluate(pos);
306 // Probe the pawn hash table
307 ei.pi = PawnTable[pos.thread()]->get_pawn_info(pos);
308 bonus += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
310 // Initialize attack and king safety bitboards
311 init_eval_info<WHITE, HasPopCnt>(pos, ei);
312 init_eval_info<BLACK, HasPopCnt>(pos, ei);
314 // Evaluate pieces and mobility
315 bonus += evaluate_pieces_of_color<WHITE, HasPopCnt>(pos, ei, mobilityWhite)
316 - evaluate_pieces_of_color<BLACK, HasPopCnt>(pos, ei, mobilityBlack);
318 bonus += apply_weight(mobilityWhite - mobilityBlack, Weights[Mobility]);
320 // Evaluate kings after all other pieces because we need complete attack
321 // information when computing the king safety evaluation.
322 bonus += evaluate_king<WHITE, HasPopCnt>(pos, ei, margins)
323 - evaluate_king<BLACK, HasPopCnt>(pos, ei, margins);
325 // Evaluate tactical threats, we need full attack information including king
326 bonus += evaluate_threats<WHITE>(pos, ei)
327 - evaluate_threats<BLACK>(pos, ei);
329 // Evaluate passed pawns, we need full attack information including king
330 bonus += evaluate_passed_pawns<WHITE>(pos, ei)
331 - evaluate_passed_pawns<BLACK>(pos, ei);
333 // Evaluate space for both sides, only in middle-game.
334 if (mi->space_weight())
336 int s = evaluate_space<WHITE, HasPopCnt>(pos, ei) - evaluate_space<BLACK, HasPopCnt>(pos, ei);
337 bonus += apply_weight(make_score(s * mi->space_weight(), 0), Weights[Space]);
340 // Scale winning side if position is more drawish that what it appears
341 ScaleFactor sf = eg_value(bonus) > VALUE_DRAW ? mi->scale_factor(pos, WHITE)
342 : mi->scale_factor(pos, BLACK);
343 Phase phase = mi->game_phase();
345 // If we don't already have an unusual scale factor, check for opposite
346 // colored bishop endgames, and use a lower scale for those.
347 if ( phase < PHASE_MIDGAME
348 && pos.opposite_colored_bishops()
349 && sf == SCALE_FACTOR_NORMAL)
351 // Only the two bishops ?
352 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
353 && pos.non_pawn_material(BLACK) == BishopValueMidgame)
355 // Check for KBP vs KB with only a single pawn that is almost
356 // certainly a draw or at least two pawns.
357 bool one_pawn = (pos.piece_count(WHITE, PAWN) + pos.piece_count(BLACK, PAWN) == 1);
358 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
361 // Endgame with opposite-colored bishops, but also other pieces. Still
362 // a bit drawish, but not as drawish as with only the two bishops.
363 sf = ScaleFactor(50);
366 // Interpolate between the middle game and the endgame score
367 margin = margins[pos.side_to_move()];
368 Value v = scale_by_game_phase(bonus, phase, sf);
369 return pos.side_to_move() == WHITE ? v : -v;
375 /// init_eval() initializes various tables used by the evaluation function
377 void init_eval(int threads) {
379 assert(threads <= MAX_THREADS);
381 for (int i = 0; i < MAX_THREADS; i++)
386 delete MaterialTable[i];
388 MaterialTable[i] = NULL;
392 PawnTable[i] = new PawnInfoTable();
394 if (!MaterialTable[i])
395 MaterialTable[i] = new MaterialInfoTable();
400 /// quit_eval() releases heap-allocated memory at program termination
408 /// read_weights() reads evaluation weights from the corresponding UCI parameters
410 void read_weights(Color us) {
412 // King safety is asymmetrical. Our king danger level is weighted by
413 // "Cowardice" UCI parameter, instead the opponent one by "Aggressiveness".
414 const int kingDangerUs = (us == WHITE ? KingDangerUs : KingDangerThem);
415 const int kingDangerThem = (us == WHITE ? KingDangerThem : KingDangerUs);
417 Weights[Mobility] = weight_option("Mobility (Middle Game)", "Mobility (Endgame)", WeightsInternal[Mobility]);
418 Weights[PawnStructure] = weight_option("Pawn Structure (Middle Game)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
419 Weights[PassedPawns] = weight_option("Passed Pawns (Middle Game)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
420 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
421 Weights[kingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
422 Weights[kingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
424 // If running in analysis mode, make sure we use symmetrical king safety. We do this
425 // by replacing both Weights[kingDangerUs] and Weights[kingDangerThem] by their average.
426 if (get_option_value_bool("UCI_AnalyseMode"))
427 Weights[kingDangerUs] = Weights[kingDangerThem] = (Weights[kingDangerUs] + Weights[kingDangerThem]) / 2;
435 // init_eval_info() initializes king bitboards for given color adding
436 // pawn attacks. To be done at the beginning of the evaluation.
438 template<Color Us, bool HasPopCnt>
439 void init_eval_info(const Position& pos, EvalInfo& ei) {
441 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
442 const Color Them = (Us == WHITE ? BLACK : WHITE);
444 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
445 ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
447 // Init king safety tables only if we are going to use them
448 if ( pos.piece_count(Us, QUEEN)
449 && pos.non_pawn_material(Us) >= QueenValueMidgame + RookValueMidgame)
451 ei.kingZone[Us] = (b | (Us == WHITE ? b >> 8 : b << 8));
452 b &= ei.attackedBy[Us][PAWN];
453 ei.kingAttackersCount[Us] = b ? count_1s<Max15>(b) / 2 : 0;
454 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
456 ei.kingZone[Us] = ei.kingAttackersCount[Us] = 0;
460 // evaluate_outposts() evaluates bishop and knight outposts squares
462 template<PieceType Piece, Color Us>
463 Score evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {
465 const Color Them = (Us == WHITE ? BLACK : WHITE);
467 assert (Piece == BISHOP || Piece == KNIGHT);
469 // Initial bonus based on square
470 Value bonus = OutpostBonus[Piece == BISHOP][relative_square(Us, s)];
472 // Increase bonus if supported by pawn, especially if the opponent has
473 // no minor piece which can exchange the outpost piece.
474 if (bonus && bit_is_set(ei.attackedBy[Us][PAWN], s))
476 if ( pos.pieces(KNIGHT, Them) == EmptyBoardBB
477 && (SquaresByColorBB[square_color(s)] & pos.pieces(BISHOP, Them)) == EmptyBoardBB)
478 bonus += bonus + bonus / 2;
482 return make_score(bonus, bonus);
486 // evaluate_pieces<>() assigns bonuses and penalties to the pieces of a given color
488 template<PieceType Piece, Color Us, bool HasPopCnt>
489 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score& mobility, Bitboard mobilityArea) {
495 Score bonus = SCORE_ZERO;
497 const BitCountType Full = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64 : CNT32;
498 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
499 const Color Them = (Us == WHITE ? BLACK : WHITE);
500 const Square* ptr = pos.piece_list_begin(Us, Piece);
502 ei.attackedBy[Us][Piece] = EmptyBoardBB;
504 while ((s = *ptr++) != SQ_NONE)
506 // Find attacked squares, including x-ray attacks for bishops and rooks
507 if (Piece == KNIGHT || Piece == QUEEN)
508 b = pos.attacks_from<Piece>(s);
509 else if (Piece == BISHOP)
510 b = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
511 else if (Piece == ROOK)
512 b = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
516 // Update attack info
517 ei.attackedBy[Us][Piece] |= b;
520 if (b & ei.kingZone[Us])
522 ei.kingAttackersCount[Us]++;
523 ei.kingAttackersWeight[Us] += KingAttackWeights[Piece];
524 Bitboard bb = (b & ei.attackedBy[Them][KING]);
526 ei.kingAdjacentZoneAttacksCount[Us] += count_1s<Max15>(bb);
530 mob = (Piece != QUEEN ? count_1s<Max15>(b & mobilityArea)
531 : count_1s<Full >(b & mobilityArea));
533 mobility += MobilityBonus[Piece][mob];
535 // Decrease score if we are attacked by an enemy pawn. Remaining part
536 // of threat evaluation must be done later when we have full attack info.
537 if (bit_is_set(ei.attackedBy[Them][PAWN], s))
538 bonus -= ThreatedByPawnPenalty[Piece];
540 // Bishop and knight outposts squares
541 if ((Piece == BISHOP || Piece == KNIGHT) && pos.square_is_weak(s, Us))
542 bonus += evaluate_outposts<Piece, Us>(pos, ei, s);
544 // Queen or rook on 7th rank
545 if ( (Piece == ROOK || Piece == QUEEN)
546 && relative_rank(Us, s) == RANK_7
547 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
549 bonus += (Piece == ROOK ? RookOn7thBonus : QueenOn7thBonus);
552 // Special extra evaluation for rooks
555 // Open and half-open files
557 if (ei.pi->file_is_half_open(Us, f))
559 if (ei.pi->file_is_half_open(Them, f))
560 bonus += RookOpenFileBonus;
562 bonus += RookHalfOpenFileBonus;
565 // Penalize rooks which are trapped inside a king. Penalize more if
566 // king has lost right to castle.
567 if (mob > 6 || ei.pi->file_is_half_open(Us, f))
570 ksq = pos.king_square(Us);
572 if ( square_file(ksq) >= FILE_E
573 && square_file(s) > square_file(ksq)
574 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
576 // Is there a half-open file between the king and the edge of the board?
577 if (!ei.pi->has_open_file_to_right(Us, square_file(ksq)))
578 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
579 : (TrappedRookPenalty - mob * 16), 0);
581 else if ( square_file(ksq) <= FILE_D
582 && square_file(s) < square_file(ksq)
583 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
585 // Is there a half-open file between the king and the edge of the board?
586 if (!ei.pi->has_open_file_to_left(Us, square_file(ksq)))
587 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
588 : (TrappedRookPenalty - mob * 16), 0);
596 // evaluate_threats<>() assigns bonuses according to the type of attacking piece
597 // and the type of attacked one.
600 Score evaluate_threats(const Position& pos, EvalInfo& ei) {
602 const Color Them = (Us == WHITE ? BLACK : WHITE);
605 Score bonus = SCORE_ZERO;
607 // Enemy pieces not defended by a pawn and under our attack
608 Bitboard weakEnemies = pos.pieces_of_color(Them)
609 & ~ei.attackedBy[Them][PAWN]
610 & ei.attackedBy[Us][0];
614 // Add bonus according to type of attacked enemy piece and to the
615 // type of attacking piece, from knights to queens. Kings are not
616 // considered because are already handled in king evaluation.
617 for (PieceType pt1 = KNIGHT; pt1 < KING; pt1++)
619 b = ei.attackedBy[Us][pt1] & weakEnemies;
621 for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
622 if (b & pos.pieces(pt2))
623 bonus += ThreatBonus[pt1][pt2];
629 // evaluate_pieces_of_color<>() assigns bonuses and penalties to all the
630 // pieces of a given color.
632 template<Color Us, bool HasPopCnt>
633 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility) {
635 const Color Them = (Us == WHITE ? BLACK : WHITE);
637 Score bonus = mobility = SCORE_ZERO;
639 // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
640 const Bitboard mobilityArea = ~(ei.attackedBy[Them][PAWN] | pos.pieces_of_color(Us));
642 bonus += evaluate_pieces<KNIGHT, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
643 bonus += evaluate_pieces<BISHOP, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
644 bonus += evaluate_pieces<ROOK, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
645 bonus += evaluate_pieces<QUEEN, Us, HasPopCnt>(pos, ei, mobility, mobilityArea);
647 // Sum up all attacked squares
648 ei.attackedBy[Us][0] = ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
649 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
650 | ei.attackedBy[Us][QUEEN] | ei.attackedBy[Us][KING];
655 // evaluate_king<>() assigns bonuses and penalties to a king of a given color
657 template<Color Us, bool HasPopCnt>
658 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]) {
660 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
661 const Color Them = (Us == WHITE ? BLACK : WHITE);
663 Bitboard undefended, b, b1, b2, safe;
665 const Square ksq = pos.king_square(Us);
668 Score bonus = ei.pi->king_shelter<Us>(pos, ksq);
670 // King safety. This is quite complicated, and is almost certainly far
671 // from optimally tuned.
672 if ( ei.kingAttackersCount[Them] >= 2
673 && ei.kingAdjacentZoneAttacksCount[Them])
675 // Find the attacked squares around the king which has no defenders
676 // apart from the king itself
677 undefended = ei.attackedBy[Them][0] & ei.attackedBy[Us][KING];
678 undefended &= ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
679 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
680 | ei.attackedBy[Us][QUEEN]);
682 // Initialize the 'attackUnits' variable, which is used later on as an
683 // index to the KingDangerTable[] array. The initial value is based on
684 // the number and types of the enemy's attacking pieces, the number of
685 // attacked and undefended squares around our king, the square of the
686 // king, and the quality of the pawn shelter.
687 attackUnits = Min(25, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
688 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + count_1s<Max15>(undefended))
689 + InitKingDanger[relative_square(Us, ksq)]
690 - mg_value(ei.pi->king_shelter<Us>(pos, ksq)) / 32;
692 // Analyse enemy's safe queen contact checks. First find undefended
693 // squares around the king attacked by enemy queen...
694 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces_of_color(Them);
697 // ...then remove squares not supported by another enemy piece
698 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
699 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
701 attackUnits += QueenContactCheckBonus
703 * (Them == pos.side_to_move() ? 2 : 1);
706 // Analyse enemy's safe rook contact checks. First find undefended
707 // squares around the king attacked by enemy rooks...
708 b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces_of_color(Them);
710 // Consider only squares where the enemy rook gives check
711 b &= RookPseudoAttacks[ksq];
715 // ...then remove squares not supported by another enemy piece
716 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
717 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
719 attackUnits += RookContactCheckBonus
721 * (Them == pos.side_to_move() ? 2 : 1);
724 // Analyse enemy's safe distance checks for sliders and knights
725 safe = ~(pos.pieces_of_color(Them) | ei.attackedBy[Us][0]);
727 b1 = pos.attacks_from<ROOK>(ksq) & safe;
728 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
730 // Enemy queen safe checks
731 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
733 attackUnits += QueenCheckBonus * count_1s<Max15>(b);
735 // Enemy rooks safe checks
736 b = b1 & ei.attackedBy[Them][ROOK];
738 attackUnits += RookCheckBonus * count_1s<Max15>(b);
740 // Enemy bishops safe checks
741 b = b2 & ei.attackedBy[Them][BISHOP];
743 attackUnits += BishopCheckBonus * count_1s<Max15>(b);
745 // Enemy knights safe checks
746 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
748 attackUnits += KnightCheckBonus * count_1s<Max15>(b);
750 // To index KingDangerTable[] attackUnits must be in [0, 99] range
751 attackUnits = Min(99, Max(0, attackUnits));
753 // Finally, extract the king danger score from the KingDangerTable[]
754 // array and subtract the score from evaluation. Set also margins[]
755 // value that will be used for pruning because this value can sometimes
756 // be very big, and so capturing a single attacking piece can therefore
757 // result in a score change far bigger than the value of the captured piece.
758 bonus -= KingDangerTable[Us][attackUnits];
759 margins[Us] += mg_value(KingDangerTable[Us][attackUnits]);
765 // evaluate_passed_pawns<>() evaluates the passed pawns of the given color
768 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei) {
770 const Color Them = (Us == WHITE ? BLACK : WHITE);
772 Score bonus = SCORE_ZERO;
773 Bitboard squaresToQueen, defendedSquares, unsafeSquares, supportingPawns;
774 Bitboard b = ei.pi->passed_pawns(Us);
780 Square s = pop_1st_bit(&b);
782 assert(pos.pawn_is_passed(Us, s));
784 int r = int(relative_rank(Us, s) - RANK_2);
785 int rr = r * (r - 1);
787 // Base bonus based on rank
788 Value mbonus = Value(20 * rr);
789 Value ebonus = Value(10 * (rr + r + 1));
793 Square blockSq = s + pawn_push(Us);
795 // Adjust bonus based on kings proximity
796 ebonus -= Value(square_distance(pos.king_square(Us), blockSq) * 3 * rr);
797 ebonus -= Value(square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr);
798 ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 6 * rr);
800 // If the pawn is free to advance, increase bonus
801 if (pos.square_is_empty(blockSq))
803 squaresToQueen = squares_in_front_of(Us, s);
804 defendedSquares = squaresToQueen & ei.attackedBy[Us][0];
806 // If there is an enemy rook or queen attacking the pawn from behind,
807 // add all X-ray attacks by the rook or queen. Otherwise consider only
808 // the squares in the pawn's path attacked or occupied by the enemy.
809 if ( (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them))
810 && (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<ROOK>(s)))
811 unsafeSquares = squaresToQueen;
813 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][0] | pos.pieces_of_color(Them));
815 // If there aren't enemy attacks or pieces along the path to queen give
816 // huge bonus. Even bigger if we protect the pawn's path.
818 ebonus += Value(rr * (squaresToQueen == defendedSquares ? 17 : 15));
820 // OK, there are enemy attacks or pieces (but not pawns). Are those
821 // squares which are attacked by the enemy also attacked by us ?
822 // If yes, big bonus (but smaller than when there are no enemy attacks),
823 // if no, somewhat smaller bonus.
824 ebonus += Value(rr * ((unsafeSquares & defendedSquares) == unsafeSquares ? 13 : 8));
826 // At last, add a small bonus when there are no *friendly* pieces
827 // in the pawn's path.
828 if (!(squaresToQueen & pos.pieces_of_color(Us)))
833 // Increase the bonus if the passed pawn is supported by a friendly pawn
834 // on the same rank and a bit smaller if it's on the previous rank.
835 supportingPawns = pos.pieces(PAWN, Us) & neighboring_files_bb(s);
836 if (supportingPawns & rank_bb(s))
837 ebonus += Value(r * 20);
838 else if (supportingPawns & rank_bb(s - pawn_push(Us)))
839 ebonus += Value(r * 12);
841 // Rook pawns are a special case: They are sometimes worse, and
842 // sometimes better than other passed pawns. It is difficult to find
843 // good rules for determining whether they are good or bad. For now,
844 // we try the following: Increase the value for rook pawns if the
845 // other side has no pieces apart from a knight, and decrease the
846 // value if the other side has a rook or queen.
847 if (square_file(s) == FILE_A || square_file(s) == FILE_H)
849 if (pos.non_pawn_material(Them) <= KnightValueMidgame)
850 ebonus += ebonus / 4;
851 else if (pos.pieces(ROOK, QUEEN, Them))
852 ebonus -= ebonus / 4;
854 bonus += make_score(mbonus, ebonus);
858 // Add the scores to the middle game and endgame eval
859 return apply_weight(bonus, Weights[PassedPawns]);
863 // evaluate_space() computes the space evaluation for a given side. The
864 // space evaluation is a simple bonus based on the number of safe squares
865 // available for minor pieces on the central four files on ranks 2--4. Safe
866 // squares one, two or three squares behind a friendly pawn are counted
867 // twice. Finally, the space bonus is scaled by a weight taken from the
868 // material hash table. The aim is to improve play on game opening.
869 template<Color Us, bool HasPopCnt>
870 int evaluate_space(const Position& pos, EvalInfo& ei) {
872 const BitCountType Max15 = HasPopCnt ? CNT_POPCNT : CpuIs64Bit ? CNT64_MAX15 : CNT32_MAX15;
873 const Color Them = (Us == WHITE ? BLACK : WHITE);
875 // Find the safe squares for our pieces inside the area defined by
876 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
877 // pawn, or if it is undefended and attacked by an enemy piece.
878 Bitboard safe = SpaceMask[Us]
879 & ~pos.pieces(PAWN, Us)
880 & ~ei.attackedBy[Them][PAWN]
881 & (ei.attackedBy[Us][0] | ~ei.attackedBy[Them][0]);
883 // Find all squares which are at most three squares behind some friendly pawn
884 Bitboard behind = pos.pieces(PAWN, Us);
885 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
886 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
888 return count_1s<Max15>(safe) + count_1s<Max15>(behind & safe);
892 // apply_weight() applies an evaluation weight to a value trying to prevent overflow
894 inline Score apply_weight(Score v, Score w) {
895 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
896 (int(eg_value(v)) * eg_value(w)) / 0x100);
900 // scale_by_game_phase() interpolates between a middle game and an endgame score,
901 // based on game phase. It also scales the return value by a ScaleFactor array.
903 Value scale_by_game_phase(const Score& v, Phase ph, ScaleFactor sf) {
905 assert(mg_value(v) > -VALUE_INFINITE && mg_value(v) < VALUE_INFINITE);
906 assert(eg_value(v) > -VALUE_INFINITE && eg_value(v) < VALUE_INFINITE);
907 assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
909 Value eg = eg_value(v);
910 Value ev = Value((eg * int(sf)) / SCALE_FACTOR_NORMAL);
912 int result = (mg_value(v) * int(ph) + ev * int(128 - ph)) / 128;
913 return Value(result & ~(GrainSize - 1));
917 // weight_option() computes the value of an evaluation weight, by combining
918 // two UCI-configurable weights (midgame and endgame) with an internal weight.
920 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
922 // Scale option value from 100 to 256
923 int mg = get_option_value_int(mgOpt) * 256 / 100;
924 int eg = get_option_value_int(egOpt) * 256 / 100;
926 return apply_weight(make_score(mg, eg), internalWeight);
930 // init_safety() initizes the king safety evaluation, based on UCI
931 // parameters. It is called from read_weights().
935 const Value MaxSlope = Value(30);
936 const Value Peak = Value(1280);
939 // First setup the base table
940 for (int i = 0; i < 100; i++)
942 t[i] = Value(int(0.4 * i * i));
945 t[i] = Min(t[i], t[i - 1] + MaxSlope);
947 t[i] = Min(t[i], Peak);
950 // Then apply the weights and get the final KingDangerTable[] array
951 for (Color c = WHITE; c <= BLACK; c++)
952 for (int i = 0; i < 100; i++)
953 KingDangerTable[c][i] = apply_weight(make_score(t[i], 0), Weights[KingDangerUs + c]);