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),
132 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
133 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0) },
135 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
136 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
137 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0),
138 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0),
139 V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0),
140 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0),
141 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
142 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0) }
145 // ThreatBonus[attacking][attacked] contains threat bonuses according to
146 // which piece type attacks which one.
147 const Score ThreatBonus[][8] = {
149 { S(0, 0), S( 7, 39), S( 0, 0), S(24, 49), S(41,100), S(41,100) }, // KNIGHT
150 { S(0, 0), S( 7, 39), S(24, 49), S( 0, 0), S(41,100), S(41,100) }, // BISHOP
151 { S(0, 0), S(-1, 29), S(15, 49), S(15, 49), S( 0, 0), S(24, 49) }, // ROOK
152 { S(0, 0), S(15, 39), S(15, 39), S(15, 39), S(15, 39), S( 0, 0) } // QUEEN
155 // ThreatedByPawnPenalty[PieceType] contains a penalty according to which
156 // piece type is attacked by an enemy pawn.
157 const Score ThreatedByPawnPenalty[] = {
158 S(0, 0), S(0, 0), S(56, 70), S(56, 70), S(76, 99), S(86, 118)
163 // Rooks and queens on the 7th rank (modified by Joona Kiiski)
164 const Score RookOn7thBonus = make_score(47, 98);
165 const Score QueenOn7thBonus = make_score(27, 54);
167 // Rooks on open files (modified by Joona Kiiski)
168 const Score RookOpenFileBonus = make_score(43, 43);
169 const Score RookHalfOpenFileBonus = make_score(19, 19);
171 // Penalty for rooks trapped inside a friendly king which has lost the
173 const Value TrappedRookPenalty = Value(180);
175 // The SpaceMask[Color] contains the area of the board which is considered
176 // by the space evaluation. In the middle game, each side is given a bonus
177 // based on how many squares inside this area are safe and available for
178 // friendly minor pieces.
179 const Bitboard SpaceMask[] = {
180 (1ULL << SQ_C2) | (1ULL << SQ_D2) | (1ULL << SQ_E2) | (1ULL << SQ_F2) |
181 (1ULL << SQ_C3) | (1ULL << SQ_D3) | (1ULL << SQ_E3) | (1ULL << SQ_F3) |
182 (1ULL << SQ_C4) | (1ULL << SQ_D4) | (1ULL << SQ_E4) | (1ULL << SQ_F4),
183 (1ULL << SQ_C7) | (1ULL << SQ_D7) | (1ULL << SQ_E7) | (1ULL << SQ_F7) |
184 (1ULL << SQ_C6) | (1ULL << SQ_D6) | (1ULL << SQ_E6) | (1ULL << SQ_F6) |
185 (1ULL << SQ_C5) | (1ULL << SQ_D5) | (1ULL << SQ_E5) | (1ULL << SQ_F5)
188 // King danger constants and variables. The king danger scores are taken
189 // from the KingDangerTable[]. Various little "meta-bonuses" measuring
190 // the strength of the enemy attack are added up into an integer, which
191 // is used as an index to KingDangerTable[].
193 // KingAttackWeights[PieceType] contains king attack weights by piece type
194 const int KingAttackWeights[] = { 0, 0, 2, 2, 3, 5 };
196 // Bonuses for enemy's safe checks
197 const int QueenContactCheckBonus = 3;
198 const int QueenCheckBonus = 2;
199 const int RookCheckBonus = 1;
200 const int BishopCheckBonus = 1;
201 const int KnightCheckBonus = 1;
203 // InitKingDanger[Square] contains penalties based on the position of the
204 // defending king, indexed by king's square (from white's point of view).
205 const int InitKingDanger[] = {
206 2, 0, 2, 5, 5, 2, 0, 2,
207 2, 2, 4, 8, 8, 4, 2, 2,
208 7, 10, 12, 12, 12, 12, 10, 7,
209 15, 15, 15, 15, 15, 15, 15, 15,
210 15, 15, 15, 15, 15, 15, 15, 15,
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
216 // KingDangerTable[Color][attackUnits] contains the actual king danger
217 // weighted scores, indexed by color and by a calculated integer number.
218 Score KingDangerTable[2][128];
220 // Pawn and material hash tables, indexed by the current thread id.
221 // Note that they will be initialized at 0 being global variables.
222 MaterialInfoTable* MaterialTable[MAX_THREADS];
223 PawnInfoTable* PawnTable[MAX_THREADS];
225 // Function prototypes
226 template<bool HasPopCnt>
227 Value do_evaluate(const Position& pos, Value margins[]);
229 template<Color Us, bool HasPopCnt>
230 void init_eval_info(const Position& pos, EvalInfo& ei);
232 template<Color Us, bool HasPopCnt>
233 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility);
235 template<Color Us, bool HasPopCnt>
236 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]);
239 Score evaluate_threats(const Position& pos, EvalInfo& ei);
241 template<Color Us, bool HasPopCnt>
242 int evaluate_space(const Position& pos, EvalInfo& ei);
245 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei);
247 Score apply_weight(Score v, Score weight);
248 Value scale_by_game_phase(const Score& v, Phase ph, const ScaleFactor sf[]);
249 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight);
259 /// Prefetches in pawn hash tables
261 void prefetchPawn(Key key, int threadID) {
263 PawnTable[threadID]->prefetch(key);
267 /// evaluate() is the main evaluation function. It always computes two
268 /// values, an endgame score and a middle game score, and interpolates
269 /// between them based on the remaining material.
270 Value evaluate(const Position& pos, Value margins[]) {
272 return CpuHasPOPCNT ? do_evaluate<true>(pos, margins)
273 : do_evaluate<false>(pos, margins);
278 template<bool HasPopCnt>
279 Value do_evaluate(const Position& pos, Value margins[]) {
282 ScaleFactor factor[2];
283 Score mobilityWhite, mobilityBlack;
286 assert(pos.thread() >= 0 && pos.thread() < MAX_THREADS);
287 assert(!pos.is_check());
289 // Initialize value by reading the incrementally updated scores included
290 // in the position object (material + piece square tables).
291 Score bonus = pos.value();
293 // margins[color] is the uncertainty estimation of position's evaluation
294 // and typically is used by the search for pruning decisions.
295 margins[WHITE] = margins[BLACK] = VALUE_ZERO;
297 // Probe the material hash table
298 MaterialInfo* mi = MaterialTable[pos.thread()]->get_material_info(pos);
299 bonus += mi->material_value();
301 // If we have a specialized evaluation function for the current material
302 // configuration, call it and return.
303 if (mi->specialized_eval_exists())
304 return mi->evaluate(pos);
306 // After get_material_info() call that modifies them
307 factor[WHITE] = mi->scale_factor(pos, WHITE);
308 factor[BLACK] = mi->scale_factor(pos, BLACK);
310 // Probe the pawn hash table
311 ei.pi = PawnTable[pos.thread()]->get_pawn_info(pos);
312 bonus += apply_weight(ei.pi->pawns_value(), Weights[PawnStructure]);
314 // Initialize attack and king safety bitboards
315 init_eval_info<WHITE, HasPopCnt>(pos, ei);
316 init_eval_info<BLACK, HasPopCnt>(pos, ei);
318 // Evaluate pieces and mobility
319 bonus += evaluate_pieces_of_color<WHITE, HasPopCnt>(pos, ei, mobilityWhite)
320 - evaluate_pieces_of_color<BLACK, HasPopCnt>(pos, ei, mobilityBlack);
322 bonus += apply_weight(mobilityWhite - mobilityBlack, Weights[Mobility]);
324 // Evaluate kings after all other pieces because we need complete attack
325 // information when computing the king safety evaluation.
326 bonus += evaluate_king<WHITE, HasPopCnt>(pos, ei, margins)
327 - evaluate_king<BLACK, HasPopCnt>(pos, ei, margins);
329 // Evaluate tactical threats, we need full attack information including king
330 bonus += evaluate_threats<WHITE>(pos, ei)
331 - evaluate_threats<BLACK>(pos, ei);
333 // Evaluate passed pawns, we need full attack information including king
334 bonus += evaluate_passed_pawns<WHITE>(pos, ei)
335 - evaluate_passed_pawns<BLACK>(pos, ei);
337 Phase phase = mi->game_phase();
339 // Evaluate space for both sides, only in middle-game.
340 if (phase > PHASE_ENDGAME && mi->space_weight() > 0)
342 int s = evaluate_space<WHITE, HasPopCnt>(pos, ei) - evaluate_space<BLACK, HasPopCnt>(pos, ei);
343 bonus += apply_weight(make_score(s * mi->space_weight(), 0), Weights[Space]);
346 // If we don't already have an unusual scale factor, check for opposite
347 // colored bishop endgames, and use a lower scale for those
348 if ( phase < PHASE_MIDGAME
349 && pos.opposite_colored_bishops()
350 && ( (factor[WHITE] == SCALE_FACTOR_NORMAL && eg_value(bonus) > VALUE_ZERO)
351 || (factor[BLACK] == SCALE_FACTOR_NORMAL && eg_value(bonus) < VALUE_ZERO)))
355 // Only the two bishops ?
356 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
357 && pos.non_pawn_material(BLACK) == BishopValueMidgame)
359 // Check for KBP vs KB with only a single pawn that is almost
360 // certainly a draw or at least two pawns.
361 bool one_pawn = (pos.piece_count(WHITE, PAWN) + pos.piece_count(BLACK, PAWN) == 1);
362 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
365 // Endgame with opposite-colored bishops, but also other pieces. Still
366 // a bit drawish, but not as drawish as with only the two bishops.
367 sf = ScaleFactor(50);
369 if (factor[WHITE] == SCALE_FACTOR_NORMAL)
371 if (factor[BLACK] == SCALE_FACTOR_NORMAL)
375 // Interpolate between the middle game and the endgame score
376 Value v = scale_by_game_phase(bonus, phase, factor);
377 return pos.side_to_move() == WHITE ? v : -v;
383 /// init_eval() initializes various tables used by the evaluation function
385 void init_eval(int threads) {
387 assert(threads <= MAX_THREADS);
389 for (int i = 0; i < MAX_THREADS; i++)
394 delete MaterialTable[i];
396 MaterialTable[i] = NULL;
400 PawnTable[i] = new PawnInfoTable();
402 if (!MaterialTable[i])
403 MaterialTable[i] = new MaterialInfoTable();
408 /// quit_eval() releases heap-allocated memory at program termination
416 /// read_weights() reads evaluation weights from the corresponding UCI parameters
418 void read_weights(Color us) {
420 // King safety is asymmetrical. Our king danger level is weighted by
421 // "Cowardice" UCI parameter, instead the opponent one by "Aggressiveness".
422 const int kingDangerUs = (us == WHITE ? KingDangerUs : KingDangerThem);
423 const int kingDangerThem = (us == WHITE ? KingDangerThem : KingDangerUs);
425 Weights[Mobility] = weight_option("Mobility (Middle Game)", "Mobility (Endgame)", WeightsInternal[Mobility]);
426 Weights[PawnStructure] = weight_option("Pawn Structure (Middle Game)", "Pawn Structure (Endgame)", WeightsInternal[PawnStructure]);
427 Weights[PassedPawns] = weight_option("Passed Pawns (Middle Game)", "Passed Pawns (Endgame)", WeightsInternal[PassedPawns]);
428 Weights[Space] = weight_option("Space", "Space", WeightsInternal[Space]);
429 Weights[kingDangerUs] = weight_option("Cowardice", "Cowardice", WeightsInternal[KingDangerUs]);
430 Weights[kingDangerThem] = weight_option("Aggressiveness", "Aggressiveness", WeightsInternal[KingDangerThem]);
432 // If running in analysis mode, make sure we use symmetrical king safety. We do this
433 // by replacing both Weights[kingDangerUs] and Weights[kingDangerThem] by their average.
434 if (get_option_value_bool("UCI_AnalyseMode"))
435 Weights[kingDangerUs] = Weights[kingDangerThem] = (Weights[kingDangerUs] + Weights[kingDangerThem]) / 2;
443 // init_eval_info() initializes king bitboards for given color adding
444 // pawn attacks. To be done at the beginning of the evaluation.
446 template<Color Us, bool HasPopCnt>
447 void init_eval_info(const Position& pos, EvalInfo& ei) {
449 const Color Them = (Us == WHITE ? BLACK : WHITE);
451 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.king_square(Them));
452 ei.kingZone[Us] = (b | (Us == WHITE ? b >> 8 : b << 8));
453 ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
454 b &= ei.attackedBy[Us][PAWN];
455 ei.kingAttackersCount[Us] = b ? count_1s_max_15<HasPopCnt>(b) / 2 : EmptyBoardBB;
456 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = EmptyBoardBB;
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 no_mob_area) {
495 Score bonus = SCORE_ZERO;
497 const Color Them = (Us == WHITE ? BLACK : WHITE);
498 const Square* ptr = pos.piece_list_begin(Us, Piece);
500 ei.attackedBy[Us][Piece] = EmptyBoardBB;
502 while ((s = *ptr++) != SQ_NONE)
504 // Find attacked squares, including x-ray attacks for bishops and rooks
505 if (Piece == KNIGHT || Piece == QUEEN)
506 b = pos.attacks_from<Piece>(s);
507 else if (Piece == BISHOP)
508 b = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
509 else if (Piece == ROOK)
510 b = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
514 // Update attack info
515 ei.attackedBy[Us][Piece] |= b;
518 if (b & ei.kingZone[Us])
520 ei.kingAttackersCount[Us]++;
521 ei.kingAttackersWeight[Us] += KingAttackWeights[Piece];
522 Bitboard bb = (b & ei.attackedBy[Them][KING]);
524 ei.kingAdjacentZoneAttacksCount[Us] += count_1s_max_15<HasPopCnt>(bb);
528 mob = (Piece != QUEEN ? count_1s_max_15<HasPopCnt>(b & no_mob_area)
529 : count_1s<HasPopCnt>(b & no_mob_area));
531 mobility += MobilityBonus[Piece][mob];
533 // Decrease score if we are attacked by an enemy pawn. Remaining part
534 // of threat evaluation must be done later when we have full attack info.
535 if (bit_is_set(ei.attackedBy[Them][PAWN], s))
536 bonus -= ThreatedByPawnPenalty[Piece];
538 // Bishop and knight outposts squares
539 if ((Piece == BISHOP || Piece == KNIGHT) && pos.square_is_weak(s, Us))
540 bonus += evaluate_outposts<Piece, Us>(pos, ei, s);
542 // Queen or rook on 7th rank
543 if ( (Piece == ROOK || Piece == QUEEN)
544 && relative_rank(Us, s) == RANK_7
545 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
547 bonus += (Piece == ROOK ? RookOn7thBonus : QueenOn7thBonus);
550 // Special extra evaluation for rooks
553 // Open and half-open files
555 if (ei.pi->file_is_half_open(Us, f))
557 if (ei.pi->file_is_half_open(Them, f))
558 bonus += RookOpenFileBonus;
560 bonus += RookHalfOpenFileBonus;
563 // Penalize rooks which are trapped inside a king. Penalize more if
564 // king has lost right to castle.
565 if (mob > 6 || ei.pi->file_is_half_open(Us, f))
568 ksq = pos.king_square(Us);
570 if ( square_file(ksq) >= FILE_E
571 && square_file(s) > square_file(ksq)
572 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
574 // Is there a half-open file between the king and the edge of the board?
575 if (!ei.pi->has_open_file_to_right(Us, square_file(ksq)))
576 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
577 : (TrappedRookPenalty - mob * 16), 0);
579 else if ( square_file(ksq) <= FILE_D
580 && square_file(s) < square_file(ksq)
581 && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
583 // Is there a half-open file between the king and the edge of the board?
584 if (!ei.pi->has_open_file_to_left(Us, square_file(ksq)))
585 bonus -= make_score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
586 : (TrappedRookPenalty - mob * 16), 0);
594 // evaluate_threats<>() assigns bonuses according to the type of attacking piece
595 // and the type of attacked one.
598 Score evaluate_threats(const Position& pos, EvalInfo& ei) {
600 const Color Them = (Us == WHITE ? BLACK : WHITE);
603 Score bonus = SCORE_ZERO;
605 // Enemy pieces not defended by a pawn and under our attack
606 Bitboard weakEnemies = pos.pieces_of_color(Them)
607 & ~ei.attackedBy[Them][PAWN]
608 & ei.attackedBy[Us][0];
612 // Add bonus according to type of attacked enemy piece and to the
613 // type of attacking piece, from knights to queens. Kings are not
614 // considered because are already handled in king evaluation.
615 for (PieceType pt1 = KNIGHT; pt1 < KING; pt1++)
617 b = ei.attackedBy[Us][pt1] & weakEnemies;
619 for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
620 if (b & pos.pieces(pt2))
621 bonus += ThreatBonus[pt1][pt2];
627 // evaluate_pieces_of_color<>() assigns bonuses and penalties to all the
628 // pieces of a given color.
630 template<Color Us, bool HasPopCnt>
631 Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score& mobility) {
633 const Color Them = (Us == WHITE ? BLACK : WHITE);
635 Score bonus = mobility = SCORE_ZERO;
637 // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
638 const Bitboard no_mob_area = ~(ei.attackedBy[Them][PAWN] | pos.pieces_of_color(Us));
640 bonus += evaluate_pieces<KNIGHT, Us, HasPopCnt>(pos, ei, mobility, no_mob_area);
641 bonus += evaluate_pieces<BISHOP, Us, HasPopCnt>(pos, ei, mobility, no_mob_area);
642 bonus += evaluate_pieces<ROOK, Us, HasPopCnt>(pos, ei, mobility, no_mob_area);
643 bonus += evaluate_pieces<QUEEN, Us, HasPopCnt>(pos, ei, mobility, no_mob_area);
645 // Sum up all attacked squares
646 ei.attackedBy[Us][0] = ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
647 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
648 | ei.attackedBy[Us][QUEEN] | ei.attackedBy[Us][KING];
653 // evaluate_king<>() assigns bonuses and penalties to a king of a given color
655 template<Color Us, bool HasPopCnt>
656 Score evaluate_king(const Position& pos, EvalInfo& ei, Value margins[]) {
658 const Color Them = (Us == WHITE ? BLACK : WHITE);
660 Bitboard undefended, b, b1, b2, safe;
662 const Square ksq = pos.king_square(Us);
665 Score bonus = ei.pi->king_shelter<Us>(pos, ksq);
667 // King safety. This is quite complicated, and is almost certainly far
668 // from optimally tuned.
669 if ( ei.kingAttackersCount[Them] >= 2
670 && pos.non_pawn_material(Them) >= QueenValueMidgame + RookValueMidgame
671 && pos.piece_count(Them, QUEEN) >= 1
672 && ei.kingAdjacentZoneAttacksCount[Them])
674 // Find the attacked squares around the king which has no defenders
675 // apart from the king itself
676 undefended = ei.attackedBy[Them][0] & ei.attackedBy[Us][KING];
677 undefended &= ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
678 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
679 | ei.attackedBy[Us][QUEEN]);
681 // Initialize the 'attackUnits' variable, which is used later on as an
682 // index to the KingDangerTable[] array. The initial value is based on
683 // the number and types of the enemy's attacking pieces, the number of
684 // attacked and undefended squares around our king, the square of the
685 // king, and the quality of the pawn shelter.
686 attackUnits = Min(25, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
687 + 3 * (ei.kingAdjacentZoneAttacksCount[Them] + count_1s_max_15<HasPopCnt>(undefended))
688 + InitKingDanger[relative_square(Us, ksq)]
689 - mg_value(ei.pi->king_shelter<Us>(pos, ksq)) / 32;
691 // Analyse enemy's safe queen contact checks. First find undefended
692 // squares around the king attacked by enemy queen...
693 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces_of_color(Them);
696 // ...then remove squares not supported by another enemy piece
697 b &= ( ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
698 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]);
700 attackUnits += QueenContactCheckBonus
701 * count_1s_max_15<HasPopCnt>(b)
702 * (Them == pos.side_to_move() ? 2 : 1);
705 // Analyse enemy's safe distance checks for sliders and knights
706 safe = ~(pos.pieces_of_color(Them) | ei.attackedBy[Us][0]);
708 b1 = pos.attacks_from<ROOK>(ksq) & safe;
709 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
711 // Enemy queen safe checks
712 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
714 attackUnits += QueenCheckBonus * count_1s_max_15<HasPopCnt>(b);
716 // Enemy rooks safe checks
717 b = b1 & ei.attackedBy[Them][ROOK];
719 attackUnits += RookCheckBonus * count_1s_max_15<HasPopCnt>(b);
721 // Enemy bishops safe checks
722 b = b2 & ei.attackedBy[Them][BISHOP];
724 attackUnits += BishopCheckBonus * count_1s_max_15<HasPopCnt>(b);
726 // Enemy knights safe checks
727 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
729 attackUnits += KnightCheckBonus * count_1s_max_15<HasPopCnt>(b);
731 // To index KingDangerTable[] attackUnits must be in [0, 99] range
732 attackUnits = Min(99, Max(0, attackUnits));
734 // Finally, extract the king danger score from the KingDangerTable[]
735 // array and subtract the score from evaluation. Set also margins[]
736 // value that will be used for pruning because this value can sometimes
737 // be very big, and so capturing a single attacking piece can therefore
738 // result in a score change far bigger than the value of the captured piece.
739 bonus -= KingDangerTable[Us][attackUnits];
740 margins[Us] += mg_value(KingDangerTable[Us][attackUnits]);
746 // evaluate_passed_pawns<>() evaluates the passed pawns of the given color
749 Score evaluate_passed_pawns(const Position& pos, EvalInfo& ei) {
751 const Color Them = (Us == WHITE ? BLACK : WHITE);
753 Score bonus = SCORE_ZERO;
754 Bitboard squaresToQueen, defendedSquares, unsafeSquares, supportingPawns;
755 Bitboard b = ei.pi->passed_pawns(Us);
761 Square s = pop_1st_bit(&b);
763 assert(pos.pawn_is_passed(Us, s));
765 int r = int(relative_rank(Us, s) - RANK_2);
766 int rr = r * (r - 1);
768 // Base bonus based on rank
769 Value mbonus = Value(20 * rr);
770 Value ebonus = Value(10 * (rr + r + 1));
774 Square blockSq = s + pawn_push(Us);
776 // Adjust bonus based on kings proximity
777 ebonus -= Value(square_distance(pos.king_square(Us), blockSq) * 3 * rr);
778 ebonus -= Value(square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * rr);
779 ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 6 * rr);
781 // If the pawn is free to advance, increase bonus
782 if (pos.square_is_empty(blockSq))
784 squaresToQueen = squares_in_front_of(Us, s);
785 defendedSquares = squaresToQueen & ei.attackedBy[Us][0];
787 // If there is an enemy rook or queen attacking the pawn from behind,
788 // add all X-ray attacks by the rook or queen. Otherwise consider only
789 // the squares in the pawn's path attacked or occupied by the enemy.
790 if ( (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them))
791 && (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<ROOK>(s)))
792 unsafeSquares = squaresToQueen;
794 unsafeSquares = squaresToQueen & (ei.attackedBy[Them][0] | pos.pieces_of_color(Them));
796 // If there aren't enemy attacks or pieces along the path to queen give
797 // huge bonus. Even bigger if we protect the pawn's path.
799 ebonus += Value(rr * (squaresToQueen == defendedSquares ? 17 : 15));
801 // OK, there are enemy attacks or pieces (but not pawns). Are those
802 // squares which are attacked by the enemy also attacked by us ?
803 // If yes, big bonus (but smaller than when there are no enemy attacks),
804 // if no, somewhat smaller bonus.
805 ebonus += Value(rr * ((unsafeSquares & defendedSquares) == unsafeSquares ? 13 : 8));
807 // At last, add a small bonus when there are no *friendly* pieces
808 // in the pawn's path.
809 if (!(squaresToQueen & pos.pieces_of_color(Us)))
814 // Increase the bonus if the passed pawn is supported by a friendly pawn
815 // on the same rank and a bit smaller if it's on the previous rank.
816 supportingPawns = pos.pieces(PAWN, Us) & neighboring_files_bb(s);
817 if (supportingPawns & rank_bb(s))
818 ebonus += Value(r * 20);
819 else if (supportingPawns & rank_bb(s - pawn_push(Us)))
820 ebonus += Value(r * 12);
822 // Rook pawns are a special case: They are sometimes worse, and
823 // sometimes better than other passed pawns. It is difficult to find
824 // good rules for determining whether they are good or bad. For now,
825 // we try the following: Increase the value for rook pawns if the
826 // other side has no pieces apart from a knight, and decrease the
827 // value if the other side has a rook or queen.
828 if (square_file(s) == FILE_A || square_file(s) == FILE_H)
830 if (pos.non_pawn_material(Them) <= KnightValueMidgame)
831 ebonus += ebonus / 4;
832 else if (pos.pieces(ROOK, QUEEN, Them))
833 ebonus -= ebonus / 4;
835 bonus += make_score(mbonus, ebonus);
839 // Add the scores to the middle game and endgame eval
840 return apply_weight(bonus, Weights[PassedPawns]);
844 // evaluate_space() computes the space evaluation for a given side. The
845 // space evaluation is a simple bonus based on the number of safe squares
846 // available for minor pieces on the central four files on ranks 2--4. Safe
847 // squares one, two or three squares behind a friendly pawn are counted
848 // twice. Finally, the space bonus is scaled by a weight taken from the
849 // material hash table. The aim is to improve play on game opening.
850 template<Color Us, bool HasPopCnt>
851 int evaluate_space(const Position& pos, EvalInfo& ei) {
853 const Color Them = (Us == WHITE ? BLACK : WHITE);
855 // Find the safe squares for our pieces inside the area defined by
856 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
857 // pawn, or if it is undefended and attacked by an enemy piece.
858 Bitboard safe = SpaceMask[Us]
859 & ~pos.pieces(PAWN, Us)
860 & ~ei.attackedBy[Them][PAWN]
861 & (ei.attackedBy[Us][0] | ~ei.attackedBy[Them][0]);
863 // Find all squares which are at most three squares behind some friendly pawn
864 Bitboard behind = pos.pieces(PAWN, Us);
865 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
866 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
868 return count_1s_max_15<HasPopCnt>(safe) + count_1s_max_15<HasPopCnt>(behind & safe);
872 // apply_weight() applies an evaluation weight to a value trying to prevent overflow
874 inline Score apply_weight(Score v, Score w) {
875 return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
876 (int(eg_value(v)) * eg_value(w)) / 0x100);
880 // scale_by_game_phase() interpolates between a middle game and an endgame score,
881 // based on game phase. It also scales the return value by a ScaleFactor array.
883 Value scale_by_game_phase(const Score& v, Phase ph, const ScaleFactor sf[]) {
885 assert(mg_value(v) > -VALUE_INFINITE && mg_value(v) < VALUE_INFINITE);
886 assert(eg_value(v) > -VALUE_INFINITE && eg_value(v) < VALUE_INFINITE);
887 assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
889 Value eg = eg_value(v);
890 ScaleFactor f = sf[eg > VALUE_ZERO ? WHITE : BLACK];
891 Value ev = Value((eg * int(f)) / SCALE_FACTOR_NORMAL);
893 int result = (mg_value(v) * int(ph) + ev * int(128 - ph)) / 128;
894 return Value(result & ~(GrainSize - 1));
898 // weight_option() computes the value of an evaluation weight, by combining
899 // two UCI-configurable weights (midgame and endgame) with an internal weight.
901 Score weight_option(const std::string& mgOpt, const std::string& egOpt, Score internalWeight) {
903 // Scale option value from 100 to 256
904 int mg = get_option_value_int(mgOpt) * 256 / 100;
905 int eg = get_option_value_int(egOpt) * 256 / 100;
907 return apply_weight(make_score(mg, eg), internalWeight);
911 // init_safety() initizes the king safety evaluation, based on UCI
912 // parameters. It is called from read_weights().
916 const Value MaxSlope = Value(30);
917 const Value Peak = Value(1280);
920 // First setup the base table
921 for (int i = 0; i < 100; i++)
923 t[i] = Value(int(0.4 * i * i));
926 t[i] = Min(t[i], t[i - 1] + MaxSlope);
928 t[i] = Min(t[i], Peak);
931 // Then apply the weights and get the final KingDangerTable[] array
932 for (Color c = WHITE; c <= BLACK; c++)
933 for (int i = 0; i < 100; i++)
934 KingDangerTable[c][i] = apply_weight(make_score(t[i], 0), Weights[KingDangerUs + c]);