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/>.
38 Key Position::zobrist[2][8][64];
39 Key Position::zobEp[64];
40 Key Position::zobCastle[16];
41 Key Position::zobSideToMove;
42 Key Position::zobExclusion;
44 Score Position::pieceSquareTable[16][64];
46 // Material values arrays, indexed by Piece
47 const Value PieceValueMidgame[17] = {
49 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
50 RookValueMidgame, QueenValueMidgame,
51 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
52 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
53 RookValueMidgame, QueenValueMidgame
56 const Value PieceValueEndgame[17] = {
58 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
59 RookValueEndgame, QueenValueEndgame,
60 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
61 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
62 RookValueEndgame, QueenValueEndgame
68 // Bonus for having the side to move (modified by Joona Kiiski)
69 const Score TempoValue = make_score(48, 22);
71 // To convert a Piece to and from a FEN char
72 const string PieceToChar(".PNBRQK pnbrqk ");
78 CheckInfo::CheckInfo(const Position& pos) {
80 Color them = opposite_color(pos.side_to_move());
81 Square ksq = pos.king_square(them);
83 pinned = pos.pinned_pieces();
84 dcCandidates = pos.discovered_check_candidates();
86 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
87 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
88 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
89 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
90 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
91 checkSq[KING] = EmptyBoardBB;
95 /// Position c'tors. Here we always create a copy of the original position
96 /// or the FEN string, we want the new born Position object do not depend
97 /// on any external data so we detach state pointer from the source one.
99 Position::Position(const Position& pos, int th) {
101 memcpy(this, &pos, sizeof(Position));
108 Position::Position(const string& fen, bool isChess960, int th) {
110 from_fen(fen, isChess960);
115 /// Position::from_fen() initializes the position object with the given FEN
116 /// string. This function is not very robust - make sure that input FENs are
117 /// correct (this is assumed to be the responsibility of the GUI).
119 void Position::from_fen(const string& fenStr, bool isChess960) {
121 A FEN string defines a particular position using only the ASCII character set.
123 A FEN string contains six fields. The separator between fields is a space. The fields are:
125 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
126 with rank 1; within each rank, the contents of each square are described from file A through file H.
127 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
128 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
129 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
130 of blank squares), and "/" separate ranks.
132 2) Active color. "w" means white moves next, "b" means black.
134 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
135 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
136 kingside), and/or "q" (Black can castle queenside).
138 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
139 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
140 regardless of whether there is a pawn in position to make an en passant capture.
142 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
143 to determine if a draw can be claimed under the fifty-move rule.
145 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
148 char col, row, token;
151 std::istringstream fen(fenStr);
154 fen >> std::noskipws;
156 // 1. Piece placement
157 while ((fen >> token) && !isspace(token))
160 sq -= Square(16); // Jump back of 2 rows
162 else if (isdigit(token))
163 sq += Square(token - '0'); // Skip the given number of files
165 else if ((p = PieceToChar.find(token)) != string::npos)
167 put_piece(Piece(p), sq);
174 sideToMove = (token == 'w' ? WHITE : BLACK);
177 // 3. Castling availability
178 while ((fen >> token) && !isspace(token))
179 set_castling_rights(token);
181 // 4. En passant square. Ignore if no pawn capture is possible
182 if ( ((fen >> col) && (col >= 'a' && col <= 'h'))
183 && ((fen >> row) && (row == '3' || row == '6')))
185 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
186 Color them = opposite_color(sideToMove);
188 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
189 st->epSquare = SQ_NONE;
192 // 5-6. Halfmove clock and fullmove number
193 fen >> std::skipws >> st->rule50 >> fullMoves;
195 // Various initialisations
196 chess960 = isChess960;
197 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
199 st->key = compute_key();
200 st->pawnKey = compute_pawn_key();
201 st->materialKey = compute_material_key();
202 st->value = compute_value();
203 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
204 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
210 /// Position::set_castle() is an helper function used to set
211 /// correct castling related flags.
213 void Position::set_castle(int f, Square ksq, Square rsq) {
215 st->castleRights |= f;
216 castleRightsMask[ksq] ^= f;
217 castleRightsMask[rsq] ^= f;
218 castleRookSquare[f] = rsq;
222 /// Position::set_castling_rights() sets castling parameters castling avaiability.
223 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
224 /// that uses the letters of the columns on which the rooks began the game instead
225 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
226 /// associated with the castling right, the traditional castling tag will be replaced
227 /// by the file letter of the involved rook as for the Shredder-FEN.
229 void Position::set_castling_rights(char token) {
231 Color c = islower(token) ? BLACK : WHITE;
233 Square sqA = relative_square(c, SQ_A1);
234 Square sqH = relative_square(c, SQ_H1);
235 Square rsq, ksq = king_square(c);
237 token = char(toupper(token));
240 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
242 else if (token == 'Q')
243 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
245 else if (token >= 'A' && token <= 'H')
246 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
250 if (square_file(rsq) < square_file(ksq))
251 set_castle(WHITE_OOO << c, ksq, rsq);
253 set_castle(WHITE_OO << c, ksq, rsq);
257 /// Position::to_fen() returns a FEN representation of the position. In case
258 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
260 const string Position::to_fen() const {
262 std::ostringstream fen;
266 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
270 for (File file = FILE_A; file <= FILE_H; file++)
272 sq = make_square(file, rank);
274 if (!square_is_empty(sq))
281 fen << PieceToChar[piece_on(sq)];
294 fen << (sideToMove == WHITE ? " w " : " b ");
296 if (st->castleRights != CASTLES_NONE)
298 if (can_castle(WHITE_OO))
299 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K');
301 if (can_castle(WHITE_OOO))
302 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q');
304 if (can_castle(BLACK_OO))
305 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k');
307 if (can_castle(BLACK_OOO))
308 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q');
312 fen << (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()))
313 << " " << st->rule50 << " " << fullMoves;
319 /// Position::print() prints an ASCII representation of the position to
320 /// the standard output. If a move is given then also the san is printed.
322 void Position::print(Move move) const {
324 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
328 Position p(*this, thread());
329 string dd = (sideToMove == BLACK ? ".." : "");
330 cout << "\nMove is: " << dd << move_to_san(p, move);
333 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
335 cout << dottedLine << '|';
336 for (File file = FILE_A; file <= FILE_H; file++)
338 Square sq = make_square(file, rank);
339 Piece piece = piece_on(sq);
341 if (piece == PIECE_NONE && square_color(sq) == DARK)
342 piece = PIECE_NONE_DARK_SQ;
344 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
345 cout << c << PieceToChar[piece] << c << '|';
348 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
352 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
353 /// king) pieces for the given color. Or, when template parameter FindPinned is
354 /// false, the function return the pieces of the given color candidate for a
355 /// discovery check against the enemy king.
357 template<bool FindPinned>
358 Bitboard Position::hidden_checkers() const {
360 // Pinned pieces protect our king, dicovery checks attack the enemy king
361 Bitboard b, result = EmptyBoardBB;
362 Bitboard pinners = pieces(FindPinned ? opposite_color(sideToMove) : sideToMove);
363 Square ksq = king_square(FindPinned ? sideToMove : opposite_color(sideToMove));
365 // Pinners are sliders, that give check when candidate pinned is removed
366 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq])
367 | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
371 b = squares_between(ksq, pop_1st_bit(&pinners)) & occupied_squares();
373 // Only one bit set and is an our piece?
374 if (b && !(b & (b - 1)) && (b & pieces(sideToMove)))
381 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
382 /// king) pieces for the side to move.
384 Bitboard Position::pinned_pieces() const {
386 return hidden_checkers<true>();
390 /// Position:discovered_check_candidates() returns a bitboard containing all
391 /// pieces for the side to move which are candidates for giving a discovered
394 Bitboard Position::discovered_check_candidates() const {
396 return hidden_checkers<false>();
399 /// Position::attackers_to() computes a bitboard containing all pieces which
400 /// attacks a given square.
402 Bitboard Position::attackers_to(Square s) const {
404 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
405 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
406 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
407 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
408 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
409 | (attacks_from<KING>(s) & pieces(KING));
412 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
414 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
415 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
416 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
417 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
418 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
419 | (attacks_from<KING>(s) & pieces(KING));
422 /// Position::attacks_from() computes a bitboard of all attacks
423 /// of a given piece put in a given square.
425 Bitboard Position::attacks_from(Piece p, Square s) const {
427 assert(square_is_ok(s));
431 case WB: case BB: return attacks_from<BISHOP>(s);
432 case WR: case BR: return attacks_from<ROOK>(s);
433 case WQ: case BQ: return attacks_from<QUEEN>(s);
434 default: return StepAttacksBB[p][s];
438 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
440 assert(square_is_ok(s));
444 case WB: case BB: return bishop_attacks_bb(s, occ);
445 case WR: case BR: return rook_attacks_bb(s, occ);
446 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
447 default: return StepAttacksBB[p][s];
452 /// Position::move_attacks_square() tests whether a move from the current
453 /// position attacks a given square.
455 bool Position::move_attacks_square(Move m, Square s) const {
457 assert(move_is_ok(m));
458 assert(square_is_ok(s));
461 Square f = move_from(m), t = move_to(m);
463 assert(!square_is_empty(f));
465 if (bit_is_set(attacks_from(piece_on(f), t), s))
468 // Move the piece and scan for X-ray attacks behind it
469 occ = occupied_squares();
470 do_move_bb(&occ, make_move_bb(f, t));
471 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
472 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
473 & pieces(piece_color(piece_on(f)));
475 // If we have attacks we need to verify that are caused by our move
476 // and are not already existent ones.
477 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
481 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
483 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
485 assert(move_is_ok(m));
486 assert(pinned == pinned_pieces());
488 Color us = side_to_move();
489 Square from = move_from(m);
491 assert(piece_color(piece_on(from)) == us);
492 assert(piece_on(king_square(us)) == make_piece(us, KING));
494 // En passant captures are a tricky special case. Because they are rather
495 // uncommon, we do it simply by testing whether the king is attacked after
499 Color them = opposite_color(us);
500 Square to = move_to(m);
501 Square capsq = to + pawn_push(them);
502 Square ksq = king_square(us);
503 Bitboard b = occupied_squares();
505 assert(to == ep_square());
506 assert(piece_on(from) == make_piece(us, PAWN));
507 assert(piece_on(capsq) == make_piece(them, PAWN));
508 assert(piece_on(to) == PIECE_NONE);
511 clear_bit(&b, capsq);
514 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
515 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
518 // If the moving piece is a king, check whether the destination
519 // square is attacked by the opponent. Castling moves are checked
520 // for legality during move generation.
521 if (piece_type(piece_on(from)) == KING)
522 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces(opposite_color(us)));
524 // A non-king move is legal if and only if it is not pinned or it
525 // is moving along the ray towards or away from the king.
527 || !bit_is_set(pinned, from)
528 || squares_aligned(from, move_to(m), king_square(us));
532 /// Position::move_is_legal() takes a move and tests whether the move
533 /// is legal. This version is not very fast and should be used only
534 /// in non time-critical paths.
536 bool Position::move_is_legal(const Move m) const {
538 for (MoveList<MV_LEGAL> ml(*this); !ml.end(); ++ml)
546 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
547 /// of pinned pieces as input, and tests whether the move is pseudo legal.
549 bool Position::move_is_pl(const Move m) const {
551 Color us = sideToMove;
552 Color them = opposite_color(sideToMove);
553 Square from = move_from(m);
554 Square to = move_to(m);
555 Piece pc = piece_on(from);
557 // Use a slower but simpler function for uncommon cases
558 if (move_is_special(m))
559 return move_is_legal(m);
561 // Is not a promotion, so promotion piece must be empty
562 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
565 // If the from square is not occupied by a piece belonging to the side to
566 // move, the move is obviously not legal.
567 if (pc == PIECE_NONE || piece_color(pc) != us)
570 // The destination square cannot be occupied by a friendly piece
571 if (piece_color(piece_on(to)) == us)
574 // Handle the special case of a pawn move
575 if (piece_type(pc) == PAWN)
577 // Move direction must be compatible with pawn color
578 int direction = to - from;
579 if ((us == WHITE) != (direction > 0))
582 // We have already handled promotion moves, so destination
583 // cannot be on the 8/1th rank.
584 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
587 // Proceed according to the square delta between the origin and
588 // destination squares.
595 // Capture. The destination square must be occupied by an enemy
596 // piece (en passant captures was handled earlier).
597 if (piece_color(piece_on(to)) != them)
600 // From and to files must be one file apart, avoids a7h5
601 if (abs(square_file(from) - square_file(to)) != 1)
607 // Pawn push. The destination square must be empty.
608 if (!square_is_empty(to))
613 // Double white pawn push. The destination square must be on the fourth
614 // rank, and both the destination square and the square between the
615 // source and destination squares must be empty.
616 if ( square_rank(to) != RANK_4
617 || !square_is_empty(to)
618 || !square_is_empty(from + DELTA_N))
623 // Double black pawn push. The destination square must be on the fifth
624 // rank, and both the destination square and the square between the
625 // source and destination squares must be empty.
626 if ( square_rank(to) != RANK_5
627 || !square_is_empty(to)
628 || !square_is_empty(from + DELTA_S))
636 else if (!bit_is_set(attacks_from(pc, from), to))
641 // In case of king moves under check we have to remove king so to catch
642 // as invalid moves like b1a1 when opposite queen is on c1.
643 if (piece_type(piece_on(from)) == KING)
645 Bitboard b = occupied_squares();
647 if (attackers_to(move_to(m), b) & pieces(opposite_color(us)))
652 Bitboard target = checkers();
653 Square checksq = pop_1st_bit(&target);
655 if (target) // double check ? In this case a king move is required
658 // Our move must be a blocking evasion or a capture of the checking piece
659 target = squares_between(checksq, king_square(us)) | checkers();
660 if (!bit_is_set(target, move_to(m)))
669 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
671 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
673 assert(move_is_ok(m));
674 assert(ci.dcCandidates == discovered_check_candidates());
675 assert(piece_color(piece_on(move_from(m))) == side_to_move());
677 Square from = move_from(m);
678 Square to = move_to(m);
679 PieceType pt = piece_type(piece_on(from));
682 if (bit_is_set(ci.checkSq[pt], to))
686 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
688 // For pawn and king moves we need to verify also direction
689 if ( (pt != PAWN && pt != KING)
690 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
694 // Can we skip the ugly special cases ?
695 if (!move_is_special(m))
698 Color us = side_to_move();
699 Bitboard b = occupied_squares();
700 Square ksq = king_square(opposite_color(us));
702 // Promotion with check ?
703 if (move_is_promotion(m))
707 switch (promotion_piece_type(m))
710 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
712 return bit_is_set(bishop_attacks_bb(to, b), ksq);
714 return bit_is_set(rook_attacks_bb(to, b), ksq);
716 return bit_is_set(queen_attacks_bb(to, b), ksq);
722 // En passant capture with check ? We have already handled the case
723 // of direct checks and ordinary discovered check, the only case we
724 // need to handle is the unusual case of a discovered check through
725 // the captured pawn.
728 Square capsq = make_square(square_file(to), square_rank(from));
730 clear_bit(&b, capsq);
732 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
733 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
736 // Castling with check ?
737 if (move_is_castle(m))
739 Square kfrom, kto, rfrom, rto;
745 kto = relative_square(us, SQ_G1);
746 rto = relative_square(us, SQ_F1);
748 kto = relative_square(us, SQ_C1);
749 rto = relative_square(us, SQ_D1);
751 clear_bit(&b, kfrom);
752 clear_bit(&b, rfrom);
755 return bit_is_set(rook_attacks_bb(rto, b), ksq);
762 /// Position::do_setup_move() makes a permanent move on the board. It should
763 /// be used when setting up a position on board. You can't undo the move.
765 void Position::do_setup_move(Move m, StateInfo& newSt) {
767 assert(move_is_ok(m));
769 // Update the number of full moves after black's move
770 if (sideToMove == BLACK)
779 /// Position::do_move() makes a move, and saves all information necessary
780 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
781 /// moves should be filtered out before this function is called.
783 void Position::do_move(Move m, StateInfo& newSt) {
786 do_move(m, newSt, ci, move_gives_check(m, ci));
789 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
791 assert(move_is_ok(m));
792 assert(&newSt != st);
797 // Copy some fields of old state to our new StateInfo object except the
798 // ones which are recalculated from scratch anyway, then switch our state
799 // pointer to point to the new, ready to be updated, state.
800 struct ReducedStateInfo {
801 Key pawnKey, materialKey;
802 int castleRights, rule50, gamePly, pliesFromNull;
808 memcpy(&newSt, st, sizeof(ReducedStateInfo));
813 // Update side to move
814 key ^= zobSideToMove;
816 // Increment the 50 moves rule draw counter. Resetting it to zero in the
817 // case of non-reversible moves is taken care of later.
822 if (move_is_castle(m))
829 Color us = side_to_move();
830 Color them = opposite_color(us);
831 Square from = move_from(m);
832 Square to = move_to(m);
833 bool ep = move_is_ep(m);
834 bool pm = move_is_promotion(m);
836 Piece piece = piece_on(from);
837 PieceType pt = piece_type(piece);
838 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
840 assert(piece_color(piece_on(from)) == us);
841 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
842 assert(!(ep || pm) || piece == make_piece(us, PAWN));
843 assert(!pm || relative_rank(us, to) == RANK_8);
846 do_capture_move(key, capture, them, to, ep);
849 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
851 // Reset en passant square
852 if (st->epSquare != SQ_NONE)
854 key ^= zobEp[st->epSquare];
855 st->epSquare = SQ_NONE;
858 // Update castle rights if needed
859 if ( st->castleRights != CASTLES_NONE
860 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
862 key ^= zobCastle[st->castleRights];
863 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
864 key ^= zobCastle[st->castleRights];
867 // Prefetch TT access as soon as we know key is updated
868 prefetch((char*)TT.first_entry(key));
871 Bitboard move_bb = make_move_bb(from, to);
872 do_move_bb(&byColorBB[us], move_bb);
873 do_move_bb(&byTypeBB[pt], move_bb);
874 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
876 board[to] = board[from];
877 board[from] = PIECE_NONE;
879 // Update piece lists, note that index[from] is not updated and
880 // becomes stale. This works as long as index[] is accessed just
881 // by known occupied squares.
882 index[to] = index[from];
883 pieceList[us][pt][index[to]] = to;
885 // If the moving piece was a pawn do some special extra work
888 // Reset rule 50 draw counter
891 // Update pawn hash key and prefetch in L1/L2 cache
892 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
894 // Set en passant square, only if moved pawn can be captured
895 if ((to ^ from) == 16)
897 if (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(PAWN, them))
899 st->epSquare = Square((int(from) + int(to)) / 2);
900 key ^= zobEp[st->epSquare];
904 if (pm) // promotion ?
906 PieceType promotion = promotion_piece_type(m);
908 assert(promotion >= KNIGHT && promotion <= QUEEN);
910 // Insert promoted piece instead of pawn
911 clear_bit(&byTypeBB[PAWN], to);
912 set_bit(&byTypeBB[promotion], to);
913 board[to] = make_piece(us, promotion);
915 // Update piece counts
916 pieceCount[us][promotion]++;
917 pieceCount[us][PAWN]--;
919 // Update material key
920 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
921 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
923 // Update piece lists, move the last pawn at index[to] position
924 // and shrink the list. Add a new promotion piece to the list.
925 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
926 index[lastPawnSquare] = index[to];
927 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
928 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
929 index[to] = pieceCount[us][promotion] - 1;
930 pieceList[us][promotion][index[to]] = to;
932 // Partially revert hash keys update
933 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
934 st->pawnKey ^= zobrist[us][PAWN][to];
936 // Partially revert and update incremental scores
937 st->value -= pst(make_piece(us, PAWN), to);
938 st->value += pst(make_piece(us, promotion), to);
941 st->npMaterial[us] += PieceValueMidgame[promotion];
945 // Prefetch pawn and material hash tables
946 Threads[threadID].pawnTable.prefetch(st->pawnKey);
947 Threads[threadID].materialTable.prefetch(st->materialKey);
949 // Update incremental scores
950 st->value += pst_delta(piece, from, to);
953 st->capturedType = capture;
955 // Update the key with the final value
958 // Update checkers bitboard, piece must be already moved
959 st->checkersBB = EmptyBoardBB;
964 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
968 if (bit_is_set(ci.checkSq[pt], to))
969 st->checkersBB = SetMaskBB[to];
972 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
975 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
978 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
984 sideToMove = opposite_color(sideToMove);
985 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
991 /// Position::do_capture_move() is a private method used to update captured
992 /// piece info. It is called from the main Position::do_move function.
994 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
996 assert(capture != KING);
1000 // If the captured piece was a pawn, update pawn hash key,
1001 // otherwise update non-pawn material.
1002 if (capture == PAWN)
1004 if (ep) // en passant ?
1006 capsq = to + pawn_push(them);
1008 assert(to == st->epSquare);
1009 assert(relative_rank(opposite_color(them), to) == RANK_6);
1010 assert(piece_on(to) == PIECE_NONE);
1011 assert(piece_on(capsq) == make_piece(them, PAWN));
1013 board[capsq] = PIECE_NONE;
1015 st->pawnKey ^= zobrist[them][PAWN][capsq];
1018 st->npMaterial[them] -= PieceValueMidgame[capture];
1020 // Remove captured piece
1021 clear_bit(&byColorBB[them], capsq);
1022 clear_bit(&byTypeBB[capture], capsq);
1023 clear_bit(&byTypeBB[0], capsq);
1026 key ^= zobrist[them][capture][capsq];
1028 // Update incremental scores
1029 st->value -= pst(make_piece(them, capture), capsq);
1031 // Update piece count
1032 pieceCount[them][capture]--;
1034 // Update material hash key
1035 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1037 // Update piece list, move the last piece at index[capsq] position
1039 // WARNING: This is a not perfectly revresible operation. When we
1040 // will reinsert the captured piece in undo_move() we will put it
1041 // at the end of the list and not in its original place, it means
1042 // index[] and pieceList[] are not guaranteed to be invariant to a
1043 // do_move() + undo_move() sequence.
1044 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1045 index[lastPieceSquare] = index[capsq];
1046 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1047 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1049 // Reset rule 50 counter
1054 /// Position::do_castle_move() is a private method used to make a castling
1055 /// move. It is called from the main Position::do_move function. Note that
1056 /// castling moves are encoded as "king captures friendly rook" moves, for
1057 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1059 void Position::do_castle_move(Move m) {
1061 assert(move_is_ok(m));
1062 assert(move_is_castle(m));
1064 Color us = side_to_move();
1065 Color them = opposite_color(us);
1067 // Find source squares for king and rook
1068 Square kfrom = move_from(m);
1069 Square rfrom = move_to(m);
1072 assert(piece_on(kfrom) == make_piece(us, KING));
1073 assert(piece_on(rfrom) == make_piece(us, ROOK));
1075 // Find destination squares for king and rook
1076 if (rfrom > kfrom) // O-O
1078 kto = relative_square(us, SQ_G1);
1079 rto = relative_square(us, SQ_F1);
1083 kto = relative_square(us, SQ_C1);
1084 rto = relative_square(us, SQ_D1);
1087 // Remove pieces from source squares
1088 clear_bit(&byColorBB[us], kfrom);
1089 clear_bit(&byTypeBB[KING], kfrom);
1090 clear_bit(&byTypeBB[0], kfrom);
1091 clear_bit(&byColorBB[us], rfrom);
1092 clear_bit(&byTypeBB[ROOK], rfrom);
1093 clear_bit(&byTypeBB[0], rfrom);
1095 // Put pieces on destination squares
1096 set_bit(&byColorBB[us], kto);
1097 set_bit(&byTypeBB[KING], kto);
1098 set_bit(&byTypeBB[0], kto);
1099 set_bit(&byColorBB[us], rto);
1100 set_bit(&byTypeBB[ROOK], rto);
1101 set_bit(&byTypeBB[0], rto);
1104 Piece king = make_piece(us, KING);
1105 Piece rook = make_piece(us, ROOK);
1106 board[kfrom] = board[rfrom] = PIECE_NONE;
1110 // Update piece lists
1111 pieceList[us][KING][index[kfrom]] = kto;
1112 pieceList[us][ROOK][index[rfrom]] = rto;
1113 int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
1114 index[kto] = index[kfrom];
1117 // Reset capture field
1118 st->capturedType = PIECE_TYPE_NONE;
1120 // Update incremental scores
1121 st->value += pst_delta(king, kfrom, kto);
1122 st->value += pst_delta(rook, rfrom, rto);
1125 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1126 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1128 // Clear en passant square
1129 if (st->epSquare != SQ_NONE)
1131 st->key ^= zobEp[st->epSquare];
1132 st->epSquare = SQ_NONE;
1135 // Update castling rights
1136 st->key ^= zobCastle[st->castleRights];
1137 st->castleRights &= castleRightsMask[kfrom];
1138 st->key ^= zobCastle[st->castleRights];
1140 // Reset rule 50 counter
1143 // Update checkers BB
1144 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1147 sideToMove = opposite_color(sideToMove);
1148 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1154 /// Position::undo_move() unmakes a move. When it returns, the position should
1155 /// be restored to exactly the same state as before the move was made.
1157 void Position::undo_move(Move m) {
1159 assert(move_is_ok(m));
1161 sideToMove = opposite_color(sideToMove);
1163 if (move_is_castle(m))
1165 undo_castle_move(m);
1169 Color us = side_to_move();
1170 Color them = opposite_color(us);
1171 Square from = move_from(m);
1172 Square to = move_to(m);
1173 bool ep = move_is_ep(m);
1174 bool pm = move_is_promotion(m);
1176 PieceType pt = piece_type(piece_on(to));
1178 assert(square_is_empty(from));
1179 assert(piece_color(piece_on(to)) == us);
1180 assert(!pm || relative_rank(us, to) == RANK_8);
1181 assert(!ep || to == st->previous->epSquare);
1182 assert(!ep || relative_rank(us, to) == RANK_6);
1183 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1185 if (pm) // promotion ?
1187 PieceType promotion = promotion_piece_type(m);
1190 assert(promotion >= KNIGHT && promotion <= QUEEN);
1191 assert(piece_on(to) == make_piece(us, promotion));
1193 // Replace promoted piece with a pawn
1194 clear_bit(&byTypeBB[promotion], to);
1195 set_bit(&byTypeBB[PAWN], to);
1197 // Update piece counts
1198 pieceCount[us][promotion]--;
1199 pieceCount[us][PAWN]++;
1201 // Update piece list replacing promotion piece with a pawn
1202 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1203 index[lastPromotionSquare] = index[to];
1204 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1205 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1206 index[to] = pieceCount[us][PAWN] - 1;
1207 pieceList[us][PAWN][index[to]] = to;
1210 // Put the piece back at the source square
1211 Bitboard move_bb = make_move_bb(to, from);
1212 do_move_bb(&byColorBB[us], move_bb);
1213 do_move_bb(&byTypeBB[pt], move_bb);
1214 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
1216 board[from] = make_piece(us, pt);
1217 board[to] = PIECE_NONE;
1219 // Update piece list
1220 index[from] = index[to];
1221 pieceList[us][pt][index[from]] = from;
1223 if (st->capturedType)
1228 capsq = to - pawn_push(us);
1230 assert(st->capturedType != KING);
1231 assert(!ep || square_is_empty(capsq));
1233 // Restore the captured piece
1234 set_bit(&byColorBB[them], capsq);
1235 set_bit(&byTypeBB[st->capturedType], capsq);
1236 set_bit(&byTypeBB[0], capsq);
1238 board[capsq] = make_piece(them, st->capturedType);
1240 // Update piece count
1241 pieceCount[them][st->capturedType]++;
1243 // Update piece list, add a new captured piece in capsq square
1244 index[capsq] = pieceCount[them][st->capturedType] - 1;
1245 pieceList[them][st->capturedType][index[capsq]] = capsq;
1248 // Finally point our state pointer back to the previous state
1255 /// Position::undo_castle_move() is a private method used to unmake a castling
1256 /// move. It is called from the main Position::undo_move function. Note that
1257 /// castling moves are encoded as "king captures friendly rook" moves, for
1258 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1260 void Position::undo_castle_move(Move m) {
1262 assert(move_is_ok(m));
1263 assert(move_is_castle(m));
1265 // When we have arrived here, some work has already been done by
1266 // Position::undo_move. In particular, the side to move has been switched,
1267 // so the code below is correct.
1268 Color us = side_to_move();
1270 // Find source squares for king and rook
1271 Square kfrom = move_from(m);
1272 Square rfrom = move_to(m);
1275 // Find destination squares for king and rook
1276 if (rfrom > kfrom) // O-O
1278 kto = relative_square(us, SQ_G1);
1279 rto = relative_square(us, SQ_F1);
1283 kto = relative_square(us, SQ_C1);
1284 rto = relative_square(us, SQ_D1);
1287 assert(piece_on(kto) == make_piece(us, KING));
1288 assert(piece_on(rto) == make_piece(us, ROOK));
1290 // Remove pieces from destination squares
1291 clear_bit(&byColorBB[us], kto);
1292 clear_bit(&byTypeBB[KING], kto);
1293 clear_bit(&byTypeBB[0], kto);
1294 clear_bit(&byColorBB[us], rto);
1295 clear_bit(&byTypeBB[ROOK], rto);
1296 clear_bit(&byTypeBB[0], rto);
1298 // Put pieces on source squares
1299 set_bit(&byColorBB[us], kfrom);
1300 set_bit(&byTypeBB[KING], kfrom);
1301 set_bit(&byTypeBB[0], kfrom);
1302 set_bit(&byColorBB[us], rfrom);
1303 set_bit(&byTypeBB[ROOK], rfrom);
1304 set_bit(&byTypeBB[0], rfrom);
1307 Piece king = make_piece(us, KING);
1308 Piece rook = make_piece(us, ROOK);
1309 board[kto] = board[rto] = PIECE_NONE;
1310 board[kfrom] = king;
1311 board[rfrom] = rook;
1313 // Update piece lists
1314 pieceList[us][KING][index[kto]] = kfrom;
1315 pieceList[us][ROOK][index[rto]] = rfrom;
1316 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1317 index[kfrom] = index[kto];
1320 // Finally point our state pointer back to the previous state
1327 /// Position::do_null_move makes() a "null move": It switches the side to move
1328 /// and updates the hash key without executing any move on the board.
1330 void Position::do_null_move(StateInfo& backupSt) {
1332 assert(!in_check());
1334 // Back up the information necessary to undo the null move to the supplied
1335 // StateInfo object.
1336 // Note that differently from normal case here backupSt is actually used as
1337 // a backup storage not as a new state to be used.
1338 backupSt.key = st->key;
1339 backupSt.epSquare = st->epSquare;
1340 backupSt.value = st->value;
1341 backupSt.previous = st->previous;
1342 backupSt.pliesFromNull = st->pliesFromNull;
1343 st->previous = &backupSt;
1345 // Update the necessary information
1346 if (st->epSquare != SQ_NONE)
1347 st->key ^= zobEp[st->epSquare];
1349 st->key ^= zobSideToMove;
1350 prefetch((char*)TT.first_entry(st->key));
1352 sideToMove = opposite_color(sideToMove);
1353 st->epSquare = SQ_NONE;
1356 st->pliesFromNull = 0;
1357 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1363 /// Position::undo_null_move() unmakes a "null move".
1365 void Position::undo_null_move() {
1367 assert(!in_check());
1369 // Restore information from the our backup StateInfo object
1370 StateInfo* backupSt = st->previous;
1371 st->key = backupSt->key;
1372 st->epSquare = backupSt->epSquare;
1373 st->value = backupSt->value;
1374 st->previous = backupSt->previous;
1375 st->pliesFromNull = backupSt->pliesFromNull;
1377 // Update the necessary information
1378 sideToMove = opposite_color(sideToMove);
1386 /// Position::see() is a static exchange evaluator: It tries to estimate the
1387 /// material gain or loss resulting from a move. There are three versions of
1388 /// this function: One which takes a destination square as input, one takes a
1389 /// move, and one which takes a 'from' and a 'to' square. The function does
1390 /// not yet understand promotions captures.
1392 int Position::see_sign(Move m) const {
1394 assert(move_is_ok(m));
1396 Square from = move_from(m);
1397 Square to = move_to(m);
1399 // Early return if SEE cannot be negative because captured piece value
1400 // is not less then capturing one. Note that king moves always return
1401 // here because king midgame value is set to 0.
1402 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1408 int Position::see(Move m) const {
1411 Bitboard occupied, attackers, stmAttackers, b;
1412 int swapList[32], slIndex = 1;
1413 PieceType capturedType, pt;
1416 assert(move_is_ok(m));
1418 // As castle moves are implemented as capturing the rook, they have
1419 // SEE == RookValueMidgame most of the times (unless the rook is under
1421 if (move_is_castle(m))
1424 from = move_from(m);
1426 capturedType = piece_type(piece_on(to));
1427 occupied = occupied_squares();
1429 // Handle en passant moves
1430 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1432 Square capQq = to - pawn_push(side_to_move());
1434 assert(capturedType == PIECE_TYPE_NONE);
1435 assert(piece_type(piece_on(capQq)) == PAWN);
1437 // Remove the captured pawn
1438 clear_bit(&occupied, capQq);
1439 capturedType = PAWN;
1442 // Find all attackers to the destination square, with the moving piece
1443 // removed, but possibly an X-ray attacker added behind it.
1444 clear_bit(&occupied, from);
1445 attackers = attackers_to(to, occupied);
1447 // If the opponent has no attackers we are finished
1448 stm = opposite_color(piece_color(piece_on(from)));
1449 stmAttackers = attackers & pieces(stm);
1451 return PieceValueMidgame[capturedType];
1453 // The destination square is defended, which makes things rather more
1454 // difficult to compute. We proceed by building up a "swap list" containing
1455 // the material gain or loss at each stop in a sequence of captures to the
1456 // destination square, where the sides alternately capture, and always
1457 // capture with the least valuable piece. After each capture, we look for
1458 // new X-ray attacks from behind the capturing piece.
1459 swapList[0] = PieceValueMidgame[capturedType];
1460 capturedType = piece_type(piece_on(from));
1463 // Locate the least valuable attacker for the side to move. The loop
1464 // below looks like it is potentially infinite, but it isn't. We know
1465 // that the side to move still has at least one attacker left.
1466 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1469 // Remove the attacker we just found from the 'occupied' bitboard,
1470 // and scan for new X-ray attacks behind the attacker.
1471 b = stmAttackers & pieces(pt);
1472 occupied ^= (b & (~b + 1));
1473 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1474 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1476 attackers &= occupied; // Cut out pieces we've already done
1478 // Add the new entry to the swap list
1479 assert(slIndex < 32);
1480 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1483 // Remember the value of the capturing piece, and change the side to
1484 // move before beginning the next iteration.
1486 stm = opposite_color(stm);
1487 stmAttackers = attackers & pieces(stm);
1489 // Stop before processing a king capture
1490 if (capturedType == KING && stmAttackers)
1492 assert(slIndex < 32);
1493 swapList[slIndex++] = QueenValueMidgame*10;
1496 } while (stmAttackers);
1498 // Having built the swap list, we negamax through it to find the best
1499 // achievable score from the point of view of the side to move.
1501 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1507 /// Position::clear() erases the position object to a pristine state, with an
1508 /// empty board, white to move, and no castling rights.
1510 void Position::clear() {
1513 memset(st, 0, sizeof(StateInfo));
1514 st->epSquare = SQ_NONE;
1516 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1517 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1518 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1519 memset(index, 0, sizeof(int) * 64);
1521 for (int i = 0; i < 8; i++)
1522 for (int j = 0; j < 16; j++)
1523 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1525 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1527 board[sq] = PIECE_NONE;
1528 castleRightsMask[sq] = ALL_CASTLES;
1536 /// Position::put_piece() puts a piece on the given square of the board,
1537 /// updating the board array, pieces list, bitboards, and piece counts.
1539 void Position::put_piece(Piece p, Square s) {
1541 Color c = piece_color(p);
1542 PieceType pt = piece_type(p);
1545 index[s] = pieceCount[c][pt]++;
1546 pieceList[c][pt][index[s]] = s;
1548 set_bit(&byTypeBB[pt], s);
1549 set_bit(&byColorBB[c], s);
1550 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1554 /// Position::compute_key() computes the hash key of the position. The hash
1555 /// key is usually updated incrementally as moves are made and unmade, the
1556 /// compute_key() function is only used when a new position is set up, and
1557 /// to verify the correctness of the hash key when running in debug mode.
1559 Key Position::compute_key() const {
1561 Key result = zobCastle[st->castleRights];
1563 for (Square s = SQ_A1; s <= SQ_H8; s++)
1564 if (!square_is_empty(s))
1565 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1567 if (ep_square() != SQ_NONE)
1568 result ^= zobEp[ep_square()];
1570 if (side_to_move() == BLACK)
1571 result ^= zobSideToMove;
1577 /// Position::compute_pawn_key() computes the hash key of the position. The
1578 /// hash key is usually updated incrementally as moves are made and unmade,
1579 /// the compute_pawn_key() function is only used when a new position is set
1580 /// up, and to verify the correctness of the pawn hash key when running in
1583 Key Position::compute_pawn_key() const {
1588 for (Color c = WHITE; c <= BLACK; c++)
1590 b = pieces(PAWN, c);
1592 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1598 /// Position::compute_material_key() computes the hash key of the position.
1599 /// The hash key is usually updated incrementally as moves are made and unmade,
1600 /// the compute_material_key() function is only used when a new position is set
1601 /// up, and to verify the correctness of the material hash key when running in
1604 Key Position::compute_material_key() const {
1608 for (Color c = WHITE; c <= BLACK; c++)
1609 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1610 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1611 result ^= zobrist[c][pt][i];
1617 /// Position::compute_value() compute the incremental scores for the middle
1618 /// game and the endgame. These functions are used to initialize the incremental
1619 /// scores when a new position is set up, and to verify that the scores are correctly
1620 /// updated by do_move and undo_move when the program is running in debug mode.
1621 Score Position::compute_value() const {
1624 Score result = SCORE_ZERO;
1626 for (Color c = WHITE; c <= BLACK; c++)
1627 for (PieceType pt = PAWN; pt <= KING; pt++)
1631 result += pst(make_piece(c, pt), pop_1st_bit(&b));
1634 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1639 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1640 /// game material value for the given side. Material values are updated
1641 /// incrementally during the search, this function is only used while
1642 /// initializing a new Position object.
1644 Value Position::compute_non_pawn_material(Color c) const {
1646 Value result = VALUE_ZERO;
1648 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1649 result += piece_count(c, pt) * PieceValueMidgame[pt];
1655 /// Position::is_draw() tests whether the position is drawn by material,
1656 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1657 /// must be done by the search.
1658 template<bool SkipRepetition>
1659 bool Position::is_draw() const {
1661 // Draw by material?
1663 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1666 // Draw by the 50 moves rule?
1667 if (st->rule50 > 99 && !is_mate())
1670 // Draw by repetition?
1671 if (!SkipRepetition)
1673 int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull);
1677 StateInfo* stp = st->previous->previous;
1680 stp = stp->previous->previous;
1682 if (stp->key == st->key)
1694 // Explicit template instantiations
1695 template bool Position::is_draw<false>() const;
1696 template bool Position::is_draw<true>() const;
1699 /// Position::is_mate() returns true or false depending on whether the
1700 /// side to move is checkmated.
1702 bool Position::is_mate() const {
1704 return in_check() && !MoveList<MV_LEGAL>(*this).size();
1708 /// Position::init() is a static member function which initializes at
1709 /// startup the various arrays used to compute hash keys and the piece
1710 /// square tables. The latter is a two-step operation: First, the white
1711 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1712 /// Second, the black halves of the tables are initialized by mirroring
1713 /// and changing the sign of the corresponding white scores.
1715 void Position::init() {
1719 for (Color c = WHITE; c <= BLACK; c++)
1720 for (PieceType pt = PAWN; pt <= KING; pt++)
1721 for (Square s = SQ_A1; s <= SQ_H8; s++)
1722 zobrist[c][pt][s] = rk.rand<Key>();
1724 for (Square s = SQ_A1; s <= SQ_H8; s++)
1725 zobEp[s] = rk.rand<Key>();
1727 for (int i = 0; i < 16; i++)
1728 zobCastle[i] = rk.rand<Key>();
1730 zobSideToMove = rk.rand<Key>();
1731 zobExclusion = rk.rand<Key>();
1733 for (Square s = SQ_A1; s <= SQ_H8; s++)
1734 for (Piece p = WP; p <= WK; p++)
1735 pieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1737 for (Square s = SQ_A1; s <= SQ_H8; s++)
1738 for (Piece p = BP; p <= BK; p++)
1739 pieceSquareTable[p][s] = -pieceSquareTable[p-8][flip_square(s)];
1743 /// Position::flip() flips position with the white and black sides reversed. This
1744 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1746 void Position::flip() {
1748 // Make a copy of current position before to start changing
1749 const Position pos(*this, threadID);
1752 threadID = pos.thread();
1755 for (Square s = SQ_A1; s <= SQ_H8; s++)
1756 if (!pos.square_is_empty(s))
1757 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1760 sideToMove = opposite_color(pos.side_to_move());
1763 if (pos.can_castle(WHITE_OO))
1764 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1765 if (pos.can_castle(WHITE_OOO))
1766 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1767 if (pos.can_castle(BLACK_OO))
1768 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1769 if (pos.can_castle(BLACK_OOO))
1770 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1772 // En passant square
1773 if (pos.st->epSquare != SQ_NONE)
1774 st->epSquare = flip_square(pos.st->epSquare);
1777 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
1780 st->key = compute_key();
1781 st->pawnKey = compute_pawn_key();
1782 st->materialKey = compute_material_key();
1784 // Incremental scores
1785 st->value = compute_value();
1788 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1789 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1795 /// Position::is_ok() performs some consitency checks for the position object.
1796 /// This is meant to be helpful when debugging.
1798 bool Position::is_ok(int* failedStep) const {
1800 // What features of the position should be verified?
1801 const bool debugAll = false;
1803 const bool debugBitboards = debugAll || false;
1804 const bool debugKingCount = debugAll || false;
1805 const bool debugKingCapture = debugAll || false;
1806 const bool debugCheckerCount = debugAll || false;
1807 const bool debugKey = debugAll || false;
1808 const bool debugMaterialKey = debugAll || false;
1809 const bool debugPawnKey = debugAll || false;
1810 const bool debugIncrementalEval = debugAll || false;
1811 const bool debugNonPawnMaterial = debugAll || false;
1812 const bool debugPieceCounts = debugAll || false;
1813 const bool debugPieceList = debugAll || false;
1814 const bool debugCastleSquares = debugAll || false;
1816 if (failedStep) *failedStep = 1;
1819 if (side_to_move() != WHITE && side_to_move() != BLACK)
1822 // Are the king squares in the position correct?
1823 if (failedStep) (*failedStep)++;
1824 if (piece_on(king_square(WHITE)) != WK)
1827 if (failedStep) (*failedStep)++;
1828 if (piece_on(king_square(BLACK)) != BK)
1831 // Do both sides have exactly one king?
1832 if (failedStep) (*failedStep)++;
1835 int kingCount[2] = {0, 0};
1836 for (Square s = SQ_A1; s <= SQ_H8; s++)
1837 if (piece_type(piece_on(s)) == KING)
1838 kingCount[piece_color(piece_on(s))]++;
1840 if (kingCount[0] != 1 || kingCount[1] != 1)
1844 // Can the side to move capture the opponent's king?
1845 if (failedStep) (*failedStep)++;
1846 if (debugKingCapture)
1848 Color us = side_to_move();
1849 Color them = opposite_color(us);
1850 Square ksq = king_square(them);
1851 if (attackers_to(ksq) & pieces(us))
1855 // Is there more than 2 checkers?
1856 if (failedStep) (*failedStep)++;
1857 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1861 if (failedStep) (*failedStep)++;
1864 // The intersection of the white and black pieces must be empty
1865 if ((pieces(WHITE) & pieces(BLACK)) != EmptyBoardBB)
1868 // The union of the white and black pieces must be equal to all
1870 if ((pieces(WHITE) | pieces(BLACK)) != occupied_squares())
1873 // Separate piece type bitboards must have empty intersections
1874 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1875 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1876 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1880 // En passant square OK?
1881 if (failedStep) (*failedStep)++;
1882 if (ep_square() != SQ_NONE)
1884 // The en passant square must be on rank 6, from the point of view of the
1886 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1891 if (failedStep) (*failedStep)++;
1892 if (debugKey && st->key != compute_key())
1895 // Pawn hash key OK?
1896 if (failedStep) (*failedStep)++;
1897 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1900 // Material hash key OK?
1901 if (failedStep) (*failedStep)++;
1902 if (debugMaterialKey && st->materialKey != compute_material_key())
1905 // Incremental eval OK?
1906 if (failedStep) (*failedStep)++;
1907 if (debugIncrementalEval && st->value != compute_value())
1910 // Non-pawn material OK?
1911 if (failedStep) (*failedStep)++;
1912 if (debugNonPawnMaterial)
1914 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1917 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1922 if (failedStep) (*failedStep)++;
1923 if (debugPieceCounts)
1924 for (Color c = WHITE; c <= BLACK; c++)
1925 for (PieceType pt = PAWN; pt <= KING; pt++)
1926 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1929 if (failedStep) (*failedStep)++;
1931 for (Color c = WHITE; c <= BLACK; c++)
1932 for (PieceType pt = PAWN; pt <= KING; pt++)
1933 for (int i = 0; i < pieceCount[c][pt]; i++)
1935 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1938 if (index[piece_list(c, pt)[i]] != i)
1942 if (failedStep) (*failedStep)++;
1943 if (debugCastleSquares)
1944 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1949 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1951 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1952 || piece_on(castleRookSquare[f]) != rook)
1956 if (failedStep) *failedStep = 0;