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/>.
33 #include "ucioption.h"
39 Key Position::zobrist[2][8][64];
40 Key Position::zobEp[64];
41 Key Position::zobCastle[16];
42 Key Position::zobSideToMove;
43 Key Position::zobExclusion;
45 Score Position::PieceSquareTable[16][64];
47 // Material values arrays, indexed by Piece
48 const Value Position::PieceValueMidgame[17] = {
50 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
51 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
52 VALUE_ZERO, VALUE_ZERO,
53 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
54 RookValueMidgame, QueenValueMidgame
57 const Value Position::PieceValueEndgame[17] = {
59 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
60 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
61 VALUE_ZERO, VALUE_ZERO,
62 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
63 RookValueEndgame, QueenValueEndgame
66 // Material values array used by SEE, indexed by PieceType
67 const Value Position::seeValues[] = {
69 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
70 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
76 // Bonus for having the side to move (modified by Joona Kiiski)
77 const Score TempoValue = make_score(48, 22);
79 struct PieceLetters : public std::map<char, Piece> {
83 operator[]('K') = WK; operator[]('k') = BK;
84 operator[]('Q') = WQ; operator[]('q') = BQ;
85 operator[]('R') = WR; operator[]('r') = BR;
86 operator[]('B') = WB; operator[]('b') = BB;
87 operator[]('N') = WN; operator[]('n') = BN;
88 operator[]('P') = WP; operator[]('p') = BP;
89 operator[](' ') = PIECE_NONE;
90 operator[]('.') = PIECE_NONE_DARK_SQ;
93 char from_piece(Piece p) const {
95 std::map<char, Piece>::const_iterator it;
96 for (it = begin(); it != end(); ++it)
105 PieceLetters pieceLetters;
111 CheckInfo::CheckInfo(const Position& pos) {
113 Color us = pos.side_to_move();
114 Color them = opposite_color(us);
116 ksq = pos.king_square(them);
117 dcCandidates = pos.discovered_check_candidates(us);
119 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
120 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
121 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
122 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
123 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
124 checkSq[KING] = EmptyBoardBB;
128 /// Position c'tors. Here we always create a copy of the original position
129 /// or the FEN string, we want the new born Position object do not depend
130 /// on any external data so we detach state pointer from the source one.
132 Position::Position(const Position& pos, int th) {
134 memcpy(this, &pos, sizeof(Position));
135 detach(); // Always detach() in copy c'tor to avoid surprises
140 Position::Position(const string& fen, bool isChess960, int th) {
142 from_fen(fen, isChess960);
147 /// Position::detach() copies the content of the current state and castling
148 /// masks inside the position itself. This is needed when the st pointee could
149 /// become stale, as example because the caller is about to going out of scope.
151 void Position::detach() {
155 st->previous = NULL; // as a safe guard
159 /// Position::from_fen() initializes the position object with the given FEN
160 /// string. This function is not very robust - make sure that input FENs are
161 /// correct (this is assumed to be the responsibility of the GUI).
163 void Position::from_fen(const string& fen, bool isChess960) {
165 A FEN string defines a particular position using only the ASCII character set.
167 A FEN string contains six fields. The separator between fields is a space. The fields are:
169 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
170 with rank 1; within each rank, the contents of each square are described from file A through file H.
171 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
172 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
173 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
174 of blank squares), and "/" separate ranks.
176 2) Active color. "w" means white moves next, "b" means black.
178 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
179 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
180 kingside), and/or "q" (Black can castle queenside).
182 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
183 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
184 regardless of whether there is a pawn in position to make an en passant capture.
186 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
187 to determine if a draw can be claimed under the fifty-move rule.
189 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
194 std::istringstream ss(fen);
199 // 1. Piece placement field
200 while (ss.get(token) && token != ' ')
202 if (pieceLetters.find(token) != pieceLetters.end())
204 put_piece(pieceLetters[token], sq);
207 else if (isdigit(token))
208 sq += Square(token - '0'); // Skip the given number of files
209 else if (token == '/')
210 sq -= SQ_A3; // Jump back of 2 rows
216 if (!ss.get(token) || (token != 'w' && token != 'b'))
219 sideToMove = (token == 'w' ? WHITE : BLACK);
221 if (!ss.get(token) || token != ' ')
224 // 3. Castling availability
225 while (ss.get(token) && token != ' ')
226 if (!set_castling_rights(token))
229 // 4. En passant square
231 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
232 && (ss.get(row) && (row == '3' || row == '6')))
234 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
236 // Ignore if no capture is possible
237 Color them = opposite_color(sideToMove);
238 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
239 st->epSquare = SQ_NONE;
246 // 6. Fullmove number
248 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
250 // Various initialisations
251 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
252 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
253 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
254 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
255 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
256 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
258 chess960 = isChess960;
261 st->key = compute_key();
262 st->pawnKey = compute_pawn_key();
263 st->materialKey = compute_material_key();
264 st->value = compute_value();
265 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
266 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
270 cout << "Error in FEN string: " << fen << endl;
274 /// Position::set_castling_rights() sets castling parameters castling avaiability.
275 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
276 /// that uses the letters of the columns on which the rooks began the game instead
277 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
278 /// associated with the castling right, the traditional castling tag will be replaced
279 /// by the file letter of the involved rook as for the Shredder-FEN.
281 bool Position::set_castling_rights(char token) {
283 Color c = token >= 'a' ? BLACK : WHITE;
284 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
285 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
286 Piece rook = (c == WHITE ? WR : BR);
288 initialKFile = square_file(king_square(c));
289 token = char(toupper(token));
293 for (Square sq = sqH; sq >= sqA; sq--)
294 if (piece_on(sq) == rook)
297 initialKRFile = square_file(sq);
301 else if (token == 'Q')
303 for (Square sq = sqA; sq <= sqH; sq++)
304 if (piece_on(sq) == rook)
307 initialQRFile = square_file(sq);
311 else if (token >= 'A' && token <= 'H')
313 File rookFile = File(token - 'A') + FILE_A;
314 if (rookFile < initialKFile)
317 initialQRFile = rookFile;
322 initialKRFile = rookFile;
332 /// Position::to_fen() returns a FEN representation of the position. In case
333 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
335 const string Position::to_fen() const {
341 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
343 for (File file = FILE_A; file <= FILE_H; file++)
345 sq = make_square(file, rank);
347 if (square_is_occupied(sq))
354 fen += pieceLetters.from_piece(piece_on(sq));
366 fen += (sideToMove == WHITE ? " w " : " b ");
368 if (st->castleRights != CASTLES_NONE)
370 if (can_castle_kingside(WHITE))
371 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
373 if (can_castle_queenside(WHITE))
374 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
376 if (can_castle_kingside(BLACK))
377 fen += chess960 ? file_to_char(initialKRFile) : 'k';
379 if (can_castle_queenside(BLACK))
380 fen += chess960 ? file_to_char(initialQRFile) : 'q';
384 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
389 /// Position::print() prints an ASCII representation of the position to
390 /// the standard output. If a move is given then also the san is printed.
392 void Position::print(Move move) const {
394 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
398 Position p(*this, thread());
399 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
400 cout << "\nMove is: " << dd << move_to_san(p, move);
403 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
405 cout << dottedLine << '|';
406 for (File file = FILE_A; file <= FILE_H; file++)
408 Square sq = make_square(file, rank);
409 Piece piece = piece_on(sq);
411 if (piece == PIECE_NONE && square_color(sq) == DARK)
412 piece = PIECE_NONE_DARK_SQ;
414 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
415 cout << c << pieceLetters.from_piece(piece) << c << '|';
418 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
422 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
423 /// king) pieces for the given color and for the given pinner type. Or, when
424 /// template parameter FindPinned is false, the pieces of the given color
425 /// candidate for a discovery check against the enemy king.
426 /// Bitboard checkersBB must be already updated when looking for pinners.
428 template<bool FindPinned>
429 Bitboard Position::hidden_checkers(Color c) const {
431 Bitboard result = EmptyBoardBB;
432 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
434 // Pinned pieces protect our king, dicovery checks attack
436 Square ksq = king_square(FindPinned ? c : opposite_color(c));
438 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
439 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
441 if (FindPinned && pinners)
442 pinners &= ~st->checkersBB;
446 Square s = pop_1st_bit(&pinners);
447 Bitboard b = squares_between(s, ksq) & occupied_squares();
451 if ( !(b & (b - 1)) // Only one bit set?
452 && (b & pieces_of_color(c))) // Is an our piece?
459 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
460 /// king) pieces for the given color. Note that checkersBB bitboard must
461 /// be already updated.
463 Bitboard Position::pinned_pieces(Color c) const {
465 return hidden_checkers<true>(c);
469 /// Position:discovered_check_candidates() returns a bitboard containing all
470 /// pieces for the given side which are candidates for giving a discovered
471 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
472 /// to be already updated.
474 Bitboard Position::discovered_check_candidates(Color c) const {
476 return hidden_checkers<false>(c);
479 /// Position::attackers_to() computes a bitboard containing all pieces which
480 /// attacks a given square.
482 Bitboard Position::attackers_to(Square s) const {
484 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
485 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
486 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
487 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
488 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
489 | (attacks_from<KING>(s) & pieces(KING));
492 /// Position::attacks_from() computes a bitboard of all attacks
493 /// of a given piece put in a given square.
495 Bitboard Position::attacks_from(Piece p, Square s) const {
497 assert(square_is_ok(s));
501 case WB: case BB: return attacks_from<BISHOP>(s);
502 case WR: case BR: return attacks_from<ROOK>(s);
503 case WQ: case BQ: return attacks_from<QUEEN>(s);
504 default: return StepAttacksBB[p][s];
508 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
510 assert(square_is_ok(s));
514 case WB: case BB: return bishop_attacks_bb(s, occ);
515 case WR: case BR: return rook_attacks_bb(s, occ);
516 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
517 default: return StepAttacksBB[p][s];
522 /// Position::move_attacks_square() tests whether a move from the current
523 /// position attacks a given square.
525 bool Position::move_attacks_square(Move m, Square s) const {
527 assert(move_is_ok(m));
528 assert(square_is_ok(s));
531 Square f = move_from(m), t = move_to(m);
533 assert(square_is_occupied(f));
535 if (bit_is_set(attacks_from(piece_on(f), t), s))
538 // Move the piece and scan for X-ray attacks behind it
539 occ = occupied_squares();
540 do_move_bb(&occ, make_move_bb(f, t));
541 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
542 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
543 & pieces_of_color(color_of_piece_on(f));
545 // If we have attacks we need to verify that are caused by our move
546 // and are not already existent ones.
547 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
551 /// Position::find_checkers() computes the checkersBB bitboard, which
552 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
553 /// currently works by calling Position::attackers_to, which is probably
554 /// inefficient. Consider rewriting this function to use the last move
555 /// played, like in non-bitboard versions of Glaurung.
557 void Position::find_checkers() {
559 Color us = side_to_move();
560 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
564 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
566 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
569 assert(move_is_ok(m));
570 assert(pinned == pinned_pieces(side_to_move()));
572 // Castling moves are checked for legality during move generation.
573 if (move_is_castle(m))
576 // En passant captures are a tricky special case. Because they are
577 // rather uncommon, we do it simply by testing whether the king is attacked
578 // after the move is made
581 Color us = side_to_move();
582 Color them = opposite_color(us);
583 Square from = move_from(m);
584 Square to = move_to(m);
585 Square capsq = make_square(square_file(to), square_rank(from));
586 Square ksq = king_square(us);
587 Bitboard b = occupied_squares();
589 assert(to == ep_square());
590 assert(piece_on(from) == make_piece(us, PAWN));
591 assert(piece_on(capsq) == make_piece(them, PAWN));
592 assert(piece_on(to) == PIECE_NONE);
595 clear_bit(&b, capsq);
598 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
599 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
602 Color us = side_to_move();
603 Square from = move_from(m);
605 assert(color_of_piece_on(from) == us);
606 assert(piece_on(king_square(us)) == make_piece(us, KING));
608 // If the moving piece is a king, check whether the destination
609 // square is attacked by the opponent.
610 if (type_of_piece_on(from) == KING)
611 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
613 // A non-king move is legal if and only if it is not pinned or it
614 // is moving along the ray towards or away from the king.
616 || !bit_is_set(pinned, from)
617 || squares_aligned(from, move_to(m), king_square(us));
621 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
623 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
627 Color us = side_to_move();
628 Square from = move_from(m);
629 Square to = move_to(m);
631 // King moves and en-passant captures are verified in pl_move_is_legal()
632 if (type_of_piece_on(from) == KING || move_is_ep(m))
633 return pl_move_is_legal(m, pinned);
635 Bitboard target = checkers();
636 Square checksq = pop_1st_bit(&target);
638 if (target) // double check ?
641 // Our move must be a blocking evasion or a capture of the checking piece
642 target = squares_between(checksq, king_square(us)) | checkers();
643 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
646 /// Position::move_is_legal() takes a position and a (not necessarily pseudo-legal)
647 /// move and tests whether the move is legal. This version is not very fast and
648 /// should be used only in non time-critical paths.
650 bool Position::move_is_legal(const Move m) const {
652 MoveStack mlist[MOVES_MAX];
653 MoveStack *cur, *last = generate<MV_PSEUDO_LEGAL>(*this, mlist);
655 for (cur = mlist; cur != last; cur++)
657 return pl_move_is_legal(m, pinned_pieces(sideToMove));
663 /// Fast version of Position::move_is_legal() that takes a position a move and
664 /// a bitboard of pinned pieces as input, and tests whether the move is legal.
666 bool Position::move_is_legal(const Move m, Bitboard pinned) const {
669 assert(pinned == pinned_pieces(sideToMove));
671 Color us = sideToMove;
672 Color them = opposite_color(sideToMove);
673 Square from = move_from(m);
674 Square to = move_to(m);
675 Piece pc = piece_on(from);
677 // Use a slower but simpler function for uncommon cases
678 if (move_is_special(m))
679 return move_is_legal(m);
681 // If the from square is not occupied by a piece belonging to the side to
682 // move, the move is obviously not legal.
683 if (color_of_piece(pc) != us)
686 // The destination square cannot be occupied by a friendly piece
687 if (color_of_piece_on(to) == us)
690 // Handle the special case of a pawn move
691 if (type_of_piece(pc) == PAWN)
693 // Move direction must be compatible with pawn color
694 int direction = to - from;
695 if ((us == WHITE) != (direction > 0))
698 // We have already handled promotion moves, so destination
699 // cannot be on the 8/1th rank.
700 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
703 // Proceed according to the square delta between the origin and
704 // destination squares.
711 // Capture. The destination square must be occupied by an enemy
712 // piece (en passant captures was handled earlier).
713 if (color_of_piece_on(to) != them)
719 // Pawn push. The destination square must be empty.
720 if (!square_is_empty(to))
725 // Double white pawn push. The destination square must be on the fourth
726 // rank, and both the destination square and the square between the
727 // source and destination squares must be empty.
728 if ( square_rank(to) != RANK_4
729 || !square_is_empty(to)
730 || !square_is_empty(from + DELTA_N))
735 // Double black pawn push. The destination square must be on the fifth
736 // rank, and both the destination square and the square between the
737 // source and destination squares must be empty.
738 if ( square_rank(to) != RANK_5
739 || !square_is_empty(to)
740 || !square_is_empty(from + DELTA_S))
748 else if (!bit_is_set(attacks_from(pc, from), to))
751 // The move is pseudo-legal, check if it is also legal
752 return is_check() ? pl_move_is_evasion(m, pinned) : pl_move_is_legal(m, pinned);
756 /// Position::move_is_check() tests whether a pseudo-legal move is a check
758 bool Position::move_is_check(Move m) const {
760 return move_is_check(m, CheckInfo(*this));
763 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
766 assert(move_is_ok(m));
767 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
768 assert(color_of_piece_on(move_from(m)) == side_to_move());
769 assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
771 Square from = move_from(m);
772 Square to = move_to(m);
773 PieceType pt = type_of_piece_on(from);
776 if (bit_is_set(ci.checkSq[pt], to))
780 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
782 // For pawn and king moves we need to verify also direction
783 if ( (pt != PAWN && pt != KING)
784 || !squares_aligned(from, to, ci.ksq))
788 // Can we skip the ugly special cases ?
789 if (!move_is_special(m))
792 Color us = side_to_move();
793 Bitboard b = occupied_squares();
795 // Promotion with check ?
796 if (move_is_promotion(m))
800 switch (move_promotion_piece(m))
803 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
805 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
807 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
809 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
815 // En passant capture with check ? We have already handled the case
816 // of direct checks and ordinary discovered check, the only case we
817 // need to handle is the unusual case of a discovered check through
818 // the captured pawn.
821 Square capsq = make_square(square_file(to), square_rank(from));
823 clear_bit(&b, capsq);
825 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
826 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
829 // Castling with check ?
830 if (move_is_castle(m))
832 Square kfrom, kto, rfrom, rto;
838 kto = relative_square(us, SQ_G1);
839 rto = relative_square(us, SQ_F1);
841 kto = relative_square(us, SQ_C1);
842 rto = relative_square(us, SQ_D1);
844 clear_bit(&b, kfrom);
845 clear_bit(&b, rfrom);
848 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
855 /// Position::do_setup_move() makes a permanent move on the board.
856 /// It should be used when setting up a position on board.
857 /// You can't undo the move.
859 void Position::do_setup_move(Move m) {
865 // Reset "game ply" in case we made a non-reversible move.
866 // "game ply" is used for repetition detection.
870 // Update the number of plies played from the starting position
871 startPosPlyCounter++;
873 // Our StateInfo newSt is about going out of scope so copy
874 // its content inside pos before it disappears.
878 /// Position::do_move() makes a move, and saves all information necessary
879 /// to a StateInfo object. The move is assumed to be legal.
880 /// Pseudo-legal moves should be filtered out before this function is called.
882 void Position::do_move(Move m, StateInfo& newSt) {
885 do_move(m, newSt, ci, move_is_check(m, ci));
888 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
891 assert(move_is_ok(m));
892 assert(&newSt != st);
897 // Copy some fields of old state to our new StateInfo object except the
898 // ones which are recalculated from scratch anyway, then switch our state
899 // pointer to point to the new, ready to be updated, state.
900 struct ReducedStateInfo {
901 Key pawnKey, materialKey;
902 int castleRights, rule50, gamePly, pliesFromNull;
908 memcpy(&newSt, st, sizeof(ReducedStateInfo));
913 // Save the current key to the history[] array, in order to be able to
914 // detect repetition draws.
915 history[st->gamePly++] = key;
917 // Update side to move
918 key ^= zobSideToMove;
920 // Increment the 50 moves rule draw counter. Resetting it to zero in the
921 // case of non-reversible moves is taken care of later.
925 if (move_is_castle(m))
932 Color us = side_to_move();
933 Color them = opposite_color(us);
934 Square from = move_from(m);
935 Square to = move_to(m);
936 bool ep = move_is_ep(m);
937 bool pm = move_is_promotion(m);
939 Piece piece = piece_on(from);
940 PieceType pt = type_of_piece(piece);
941 PieceType capture = ep ? PAWN : type_of_piece_on(to);
943 assert(color_of_piece_on(from) == us);
944 assert(color_of_piece_on(to) == them || square_is_empty(to));
945 assert(!(ep || pm) || piece == make_piece(us, PAWN));
946 assert(!pm || relative_rank(us, to) == RANK_8);
949 do_capture_move(key, capture, them, to, ep);
952 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
954 // Reset en passant square
955 if (st->epSquare != SQ_NONE)
957 key ^= zobEp[st->epSquare];
958 st->epSquare = SQ_NONE;
961 // Update castle rights, try to shortcut a common case
962 int cm = castleRightsMask[from] & castleRightsMask[to];
963 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
965 key ^= zobCastle[st->castleRights];
966 st->castleRights &= castleRightsMask[from];
967 st->castleRights &= castleRightsMask[to];
968 key ^= zobCastle[st->castleRights];
971 // Prefetch TT access as soon as we know key is updated
972 prefetch((char*)TT.first_entry(key));
975 Bitboard move_bb = make_move_bb(from, to);
976 do_move_bb(&(byColorBB[us]), move_bb);
977 do_move_bb(&(byTypeBB[pt]), move_bb);
978 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
980 board[to] = board[from];
981 board[from] = PIECE_NONE;
983 // Update piece lists, note that index[from] is not updated and
984 // becomes stale. This works as long as index[] is accessed just
985 // by known occupied squares.
986 index[to] = index[from];
987 pieceList[us][pt][index[to]] = to;
989 // If the moving piece was a pawn do some special extra work
992 // Reset rule 50 draw counter
995 // Update pawn hash key and prefetch in L1/L2 cache
996 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
998 // Set en passant square, only if moved pawn can be captured
999 if ((to ^ from) == 16)
1001 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
1003 st->epSquare = Square((int(from) + int(to)) / 2);
1004 key ^= zobEp[st->epSquare];
1008 if (pm) // promotion ?
1010 PieceType promotion = move_promotion_piece(m);
1012 assert(promotion >= KNIGHT && promotion <= QUEEN);
1014 // Insert promoted piece instead of pawn
1015 clear_bit(&(byTypeBB[PAWN]), to);
1016 set_bit(&(byTypeBB[promotion]), to);
1017 board[to] = make_piece(us, promotion);
1019 // Update piece counts
1020 pieceCount[us][promotion]++;
1021 pieceCount[us][PAWN]--;
1023 // Update material key
1024 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
1025 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
1027 // Update piece lists, move the last pawn at index[to] position
1028 // and shrink the list. Add a new promotion piece to the list.
1029 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
1030 index[lastPawnSquare] = index[to];
1031 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
1032 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
1033 index[to] = pieceCount[us][promotion] - 1;
1034 pieceList[us][promotion][index[to]] = to;
1036 // Partially revert hash keys update
1037 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
1038 st->pawnKey ^= zobrist[us][PAWN][to];
1040 // Partially revert and update incremental scores
1041 st->value -= pst(us, PAWN, to);
1042 st->value += pst(us, promotion, to);
1045 st->npMaterial[us] += PieceValueMidgame[promotion];
1049 // Prefetch pawn and material hash tables
1050 prefetchTables(st->pawnKey, st->materialKey, threadID);
1052 // Update incremental scores
1053 st->value += pst_delta(piece, from, to);
1055 // Set capture piece
1056 st->capturedType = capture;
1058 // Update the key with the final value
1061 // Update checkers bitboard, piece must be already moved
1062 st->checkersBB = EmptyBoardBB;
1067 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1071 if (bit_is_set(ci.checkSq[pt], to))
1072 st->checkersBB = SetMaskBB[to];
1075 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1078 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
1081 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
1087 sideToMove = opposite_color(sideToMove);
1088 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1094 /// Position::do_capture_move() is a private method used to update captured
1095 /// piece info. It is called from the main Position::do_move function.
1097 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1099 assert(capture != KING);
1103 // If the captured piece was a pawn, update pawn hash key,
1104 // otherwise update non-pawn material.
1105 if (capture == PAWN)
1107 if (ep) // en passant ?
1109 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1111 assert(to == st->epSquare);
1112 assert(relative_rank(opposite_color(them), to) == RANK_6);
1113 assert(piece_on(to) == PIECE_NONE);
1114 assert(piece_on(capsq) == make_piece(them, PAWN));
1116 board[capsq] = PIECE_NONE;
1118 st->pawnKey ^= zobrist[them][PAWN][capsq];
1121 st->npMaterial[them] -= PieceValueMidgame[capture];
1123 // Remove captured piece
1124 clear_bit(&(byColorBB[them]), capsq);
1125 clear_bit(&(byTypeBB[capture]), capsq);
1126 clear_bit(&(byTypeBB[0]), capsq);
1129 key ^= zobrist[them][capture][capsq];
1131 // Update incremental scores
1132 st->value -= pst(them, capture, capsq);
1134 // Update piece count
1135 pieceCount[them][capture]--;
1137 // Update material hash key
1138 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1140 // Update piece list, move the last piece at index[capsq] position
1142 // WARNING: This is a not perfectly revresible operation. When we
1143 // will reinsert the captured piece in undo_move() we will put it
1144 // at the end of the list and not in its original place, it means
1145 // index[] and pieceList[] are not guaranteed to be invariant to a
1146 // do_move() + undo_move() sequence.
1147 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1148 index[lastPieceSquare] = index[capsq];
1149 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1150 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1152 // Reset rule 50 counter
1157 /// Position::do_castle_move() is a private method used to make a castling
1158 /// move. It is called from the main Position::do_move function. Note that
1159 /// castling moves are encoded as "king captures friendly rook" moves, for
1160 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1162 void Position::do_castle_move(Move m) {
1164 assert(move_is_ok(m));
1165 assert(move_is_castle(m));
1167 Color us = side_to_move();
1168 Color them = opposite_color(us);
1170 // Reset capture field
1171 st->capturedType = PIECE_TYPE_NONE;
1173 // Find source squares for king and rook
1174 Square kfrom = move_from(m);
1175 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1178 assert(piece_on(kfrom) == make_piece(us, KING));
1179 assert(piece_on(rfrom) == make_piece(us, ROOK));
1181 // Find destination squares for king and rook
1182 if (rfrom > kfrom) // O-O
1184 kto = relative_square(us, SQ_G1);
1185 rto = relative_square(us, SQ_F1);
1187 kto = relative_square(us, SQ_C1);
1188 rto = relative_square(us, SQ_D1);
1191 // Remove pieces from source squares:
1192 clear_bit(&(byColorBB[us]), kfrom);
1193 clear_bit(&(byTypeBB[KING]), kfrom);
1194 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1195 clear_bit(&(byColorBB[us]), rfrom);
1196 clear_bit(&(byTypeBB[ROOK]), rfrom);
1197 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1199 // Put pieces on destination squares:
1200 set_bit(&(byColorBB[us]), kto);
1201 set_bit(&(byTypeBB[KING]), kto);
1202 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1203 set_bit(&(byColorBB[us]), rto);
1204 set_bit(&(byTypeBB[ROOK]), rto);
1205 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1207 // Update board array
1208 Piece king = make_piece(us, KING);
1209 Piece rook = make_piece(us, ROOK);
1210 board[kfrom] = board[rfrom] = PIECE_NONE;
1214 // Update piece lists
1215 pieceList[us][KING][index[kfrom]] = kto;
1216 pieceList[us][ROOK][index[rfrom]] = rto;
1217 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1218 index[kto] = index[kfrom];
1221 // Update incremental scores
1222 st->value += pst_delta(king, kfrom, kto);
1223 st->value += pst_delta(rook, rfrom, rto);
1226 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1227 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1229 // Clear en passant square
1230 if (st->epSquare != SQ_NONE)
1232 st->key ^= zobEp[st->epSquare];
1233 st->epSquare = SQ_NONE;
1236 // Update castling rights
1237 st->key ^= zobCastle[st->castleRights];
1238 st->castleRights &= castleRightsMask[kfrom];
1239 st->key ^= zobCastle[st->castleRights];
1241 // Reset rule 50 counter
1244 // Update checkers BB
1245 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1248 sideToMove = opposite_color(sideToMove);
1249 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1255 /// Position::undo_move() unmakes a move. When it returns, the position should
1256 /// be restored to exactly the same state as before the move was made.
1258 void Position::undo_move(Move m) {
1261 assert(move_is_ok(m));
1263 sideToMove = opposite_color(sideToMove);
1265 if (move_is_castle(m))
1267 undo_castle_move(m);
1271 Color us = side_to_move();
1272 Color them = opposite_color(us);
1273 Square from = move_from(m);
1274 Square to = move_to(m);
1275 bool ep = move_is_ep(m);
1276 bool pm = move_is_promotion(m);
1278 PieceType pt = type_of_piece_on(to);
1280 assert(square_is_empty(from));
1281 assert(color_of_piece_on(to) == us);
1282 assert(!pm || relative_rank(us, to) == RANK_8);
1283 assert(!ep || to == st->previous->epSquare);
1284 assert(!ep || relative_rank(us, to) == RANK_6);
1285 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1287 if (pm) // promotion ?
1289 PieceType promotion = move_promotion_piece(m);
1292 assert(promotion >= KNIGHT && promotion <= QUEEN);
1293 assert(piece_on(to) == make_piece(us, promotion));
1295 // Replace promoted piece with a pawn
1296 clear_bit(&(byTypeBB[promotion]), to);
1297 set_bit(&(byTypeBB[PAWN]), to);
1299 // Update piece counts
1300 pieceCount[us][promotion]--;
1301 pieceCount[us][PAWN]++;
1303 // Update piece list replacing promotion piece with a pawn
1304 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1305 index[lastPromotionSquare] = index[to];
1306 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1307 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1308 index[to] = pieceCount[us][PAWN] - 1;
1309 pieceList[us][PAWN][index[to]] = to;
1312 // Put the piece back at the source square
1313 Bitboard move_bb = make_move_bb(to, from);
1314 do_move_bb(&(byColorBB[us]), move_bb);
1315 do_move_bb(&(byTypeBB[pt]), move_bb);
1316 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1318 board[from] = make_piece(us, pt);
1319 board[to] = PIECE_NONE;
1321 // Update piece list
1322 index[from] = index[to];
1323 pieceList[us][pt][index[from]] = from;
1325 if (st->capturedType)
1330 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1332 assert(st->capturedType != KING);
1333 assert(!ep || square_is_empty(capsq));
1335 // Restore the captured piece
1336 set_bit(&(byColorBB[them]), capsq);
1337 set_bit(&(byTypeBB[st->capturedType]), capsq);
1338 set_bit(&(byTypeBB[0]), capsq);
1340 board[capsq] = make_piece(them, st->capturedType);
1342 // Update piece count
1343 pieceCount[them][st->capturedType]++;
1345 // Update piece list, add a new captured piece in capsq square
1346 index[capsq] = pieceCount[them][st->capturedType] - 1;
1347 pieceList[them][st->capturedType][index[capsq]] = capsq;
1350 // Finally point our state pointer back to the previous state
1357 /// Position::undo_castle_move() is a private method used to unmake a castling
1358 /// move. It is called from the main Position::undo_move function. Note that
1359 /// castling moves are encoded as "king captures friendly rook" moves, for
1360 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1362 void Position::undo_castle_move(Move m) {
1364 assert(move_is_ok(m));
1365 assert(move_is_castle(m));
1367 // When we have arrived here, some work has already been done by
1368 // Position::undo_move. In particular, the side to move has been switched,
1369 // so the code below is correct.
1370 Color us = side_to_move();
1372 // Find source squares for king and rook
1373 Square kfrom = move_from(m);
1374 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1377 // Find destination squares for king and rook
1378 if (rfrom > kfrom) // O-O
1380 kto = relative_square(us, SQ_G1);
1381 rto = relative_square(us, SQ_F1);
1383 kto = relative_square(us, SQ_C1);
1384 rto = relative_square(us, SQ_D1);
1387 assert(piece_on(kto) == make_piece(us, KING));
1388 assert(piece_on(rto) == make_piece(us, ROOK));
1390 // Remove pieces from destination squares:
1391 clear_bit(&(byColorBB[us]), kto);
1392 clear_bit(&(byTypeBB[KING]), kto);
1393 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1394 clear_bit(&(byColorBB[us]), rto);
1395 clear_bit(&(byTypeBB[ROOK]), rto);
1396 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1398 // Put pieces on source squares:
1399 set_bit(&(byColorBB[us]), kfrom);
1400 set_bit(&(byTypeBB[KING]), kfrom);
1401 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1402 set_bit(&(byColorBB[us]), rfrom);
1403 set_bit(&(byTypeBB[ROOK]), rfrom);
1404 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1407 board[rto] = board[kto] = PIECE_NONE;
1408 board[rfrom] = make_piece(us, ROOK);
1409 board[kfrom] = make_piece(us, KING);
1411 // Update piece lists
1412 pieceList[us][KING][index[kto]] = kfrom;
1413 pieceList[us][ROOK][index[rto]] = rfrom;
1414 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1415 index[kfrom] = index[kto];
1418 // Finally point our state pointer back to the previous state
1425 /// Position::do_null_move makes() a "null move": It switches the side to move
1426 /// and updates the hash key without executing any move on the board.
1428 void Position::do_null_move(StateInfo& backupSt) {
1431 assert(!is_check());
1433 // Back up the information necessary to undo the null move to the supplied
1434 // StateInfo object.
1435 // Note that differently from normal case here backupSt is actually used as
1436 // a backup storage not as a new state to be used.
1437 backupSt.key = st->key;
1438 backupSt.epSquare = st->epSquare;
1439 backupSt.value = st->value;
1440 backupSt.previous = st->previous;
1441 backupSt.pliesFromNull = st->pliesFromNull;
1442 st->previous = &backupSt;
1444 // Save the current key to the history[] array, in order to be able to
1445 // detect repetition draws.
1446 history[st->gamePly++] = st->key;
1448 // Update the necessary information
1449 if (st->epSquare != SQ_NONE)
1450 st->key ^= zobEp[st->epSquare];
1452 st->key ^= zobSideToMove;
1453 prefetch((char*)TT.first_entry(st->key));
1455 sideToMove = opposite_color(sideToMove);
1456 st->epSquare = SQ_NONE;
1458 st->pliesFromNull = 0;
1459 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1463 /// Position::undo_null_move() unmakes a "null move".
1465 void Position::undo_null_move() {
1468 assert(!is_check());
1470 // Restore information from the our backup StateInfo object
1471 StateInfo* backupSt = st->previous;
1472 st->key = backupSt->key;
1473 st->epSquare = backupSt->epSquare;
1474 st->value = backupSt->value;
1475 st->previous = backupSt->previous;
1476 st->pliesFromNull = backupSt->pliesFromNull;
1478 // Update the necessary information
1479 sideToMove = opposite_color(sideToMove);
1485 /// Position::see() is a static exchange evaluator: It tries to estimate the
1486 /// material gain or loss resulting from a move. There are three versions of
1487 /// this function: One which takes a destination square as input, one takes a
1488 /// move, and one which takes a 'from' and a 'to' square. The function does
1489 /// not yet understand promotions captures.
1491 int Position::see(Move m) const {
1493 assert(move_is_ok(m));
1494 return see(move_from(m), move_to(m));
1497 int Position::see_sign(Move m) const {
1499 assert(move_is_ok(m));
1501 Square from = move_from(m);
1502 Square to = move_to(m);
1504 // Early return if SEE cannot be negative because captured piece value
1505 // is not less then capturing one. Note that king moves always return
1506 // here because king midgame value is set to 0.
1507 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1510 return see(from, to);
1513 int Position::see(Square from, Square to) const {
1515 Bitboard occupied, attackers, stmAttackers, b;
1516 int swapList[32], slIndex = 1;
1517 PieceType capturedType, pt;
1520 assert(square_is_ok(from));
1521 assert(square_is_ok(to));
1523 capturedType = type_of_piece_on(to);
1525 // King cannot be recaptured
1526 if (capturedType == KING)
1527 return seeValues[capturedType];
1529 occupied = occupied_squares();
1531 // Handle en passant moves
1532 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1534 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1536 assert(capturedType == PIECE_TYPE_NONE);
1537 assert(type_of_piece_on(capQq) == PAWN);
1539 // Remove the captured pawn
1540 clear_bit(&occupied, capQq);
1541 capturedType = PAWN;
1544 // Find all attackers to the destination square, with the moving piece
1545 // removed, but possibly an X-ray attacker added behind it.
1546 clear_bit(&occupied, from);
1547 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1548 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1549 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1550 | (attacks_from<KING>(to) & pieces(KING))
1551 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1552 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1554 // If the opponent has no attackers we are finished
1555 stm = opposite_color(color_of_piece_on(from));
1556 stmAttackers = attackers & pieces_of_color(stm);
1558 return seeValues[capturedType];
1560 // The destination square is defended, which makes things rather more
1561 // difficult to compute. We proceed by building up a "swap list" containing
1562 // the material gain or loss at each stop in a sequence of captures to the
1563 // destination square, where the sides alternately capture, and always
1564 // capture with the least valuable piece. After each capture, we look for
1565 // new X-ray attacks from behind the capturing piece.
1566 swapList[0] = seeValues[capturedType];
1567 capturedType = type_of_piece_on(from);
1570 // Locate the least valuable attacker for the side to move. The loop
1571 // below looks like it is potentially infinite, but it isn't. We know
1572 // that the side to move still has at least one attacker left.
1573 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1576 // Remove the attacker we just found from the 'occupied' bitboard,
1577 // and scan for new X-ray attacks behind the attacker.
1578 b = stmAttackers & pieces(pt);
1579 occupied ^= (b & (~b + 1));
1580 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1581 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1583 attackers &= occupied; // Cut out pieces we've already done
1585 // Add the new entry to the swap list
1586 assert(slIndex < 32);
1587 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1590 // Remember the value of the capturing piece, and change the side to
1591 // move before beginning the next iteration.
1593 stm = opposite_color(stm);
1594 stmAttackers = attackers & pieces_of_color(stm);
1596 // Stop before processing a king capture
1597 if (capturedType == KING && stmAttackers)
1599 assert(slIndex < 32);
1600 swapList[slIndex++] = QueenValueMidgame*10;
1603 } while (stmAttackers);
1605 // Having built the swap list, we negamax through it to find the best
1606 // achievable score from the point of view of the side to move.
1608 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1614 /// Position::clear() erases the position object to a pristine state, with an
1615 /// empty board, white to move, and no castling rights.
1617 void Position::clear() {
1620 memset(st, 0, sizeof(StateInfo));
1621 st->epSquare = SQ_NONE;
1622 startPosPlyCounter = 0;
1625 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1626 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1627 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1628 memset(index, 0, sizeof(int) * 64);
1630 for (int i = 0; i < 64; i++)
1631 board[i] = PIECE_NONE;
1633 for (int i = 0; i < 8; i++)
1634 for (int j = 0; j < 16; j++)
1635 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1637 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1638 castleRightsMask[sq] = ALL_CASTLES;
1641 initialKFile = FILE_E;
1642 initialKRFile = FILE_H;
1643 initialQRFile = FILE_A;
1647 /// Position::put_piece() puts a piece on the given square of the board,
1648 /// updating the board array, pieces list, bitboards, and piece counts.
1650 void Position::put_piece(Piece p, Square s) {
1652 Color c = color_of_piece(p);
1653 PieceType pt = type_of_piece(p);
1656 index[s] = pieceCount[c][pt]++;
1657 pieceList[c][pt][index[s]] = s;
1659 set_bit(&(byTypeBB[pt]), s);
1660 set_bit(&(byColorBB[c]), s);
1661 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1665 /// Position::compute_key() computes the hash key of the position. The hash
1666 /// key is usually updated incrementally as moves are made and unmade, the
1667 /// compute_key() function is only used when a new position is set up, and
1668 /// to verify the correctness of the hash key when running in debug mode.
1670 Key Position::compute_key() const {
1672 Key result = zobCastle[st->castleRights];
1674 for (Square s = SQ_A1; s <= SQ_H8; s++)
1675 if (square_is_occupied(s))
1676 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1678 if (ep_square() != SQ_NONE)
1679 result ^= zobEp[ep_square()];
1681 if (side_to_move() == BLACK)
1682 result ^= zobSideToMove;
1688 /// Position::compute_pawn_key() computes the hash key of the position. The
1689 /// hash key is usually updated incrementally as moves are made and unmade,
1690 /// the compute_pawn_key() function is only used when a new position is set
1691 /// up, and to verify the correctness of the pawn hash key when running in
1694 Key Position::compute_pawn_key() const {
1699 for (Color c = WHITE; c <= BLACK; c++)
1701 b = pieces(PAWN, c);
1703 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1709 /// Position::compute_material_key() computes the hash key of the position.
1710 /// The hash key is usually updated incrementally as moves are made and unmade,
1711 /// the compute_material_key() function is only used when a new position is set
1712 /// up, and to verify the correctness of the material hash key when running in
1715 Key Position::compute_material_key() const {
1720 for (Color c = WHITE; c <= BLACK; c++)
1721 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1723 count = piece_count(c, pt);
1724 for (int i = 0; i < count; i++)
1725 result ^= zobrist[c][pt][i];
1731 /// Position::compute_value() compute the incremental scores for the middle
1732 /// game and the endgame. These functions are used to initialize the incremental
1733 /// scores when a new position is set up, and to verify that the scores are correctly
1734 /// updated by do_move and undo_move when the program is running in debug mode.
1735 Score Position::compute_value() const {
1738 Score result = SCORE_ZERO;
1740 for (Color c = WHITE; c <= BLACK; c++)
1741 for (PieceType pt = PAWN; pt <= KING; pt++)
1745 result += pst(c, pt, pop_1st_bit(&b));
1748 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1753 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1754 /// game material value for the given side. Material values are updated
1755 /// incrementally during the search, this function is only used while
1756 /// initializing a new Position object.
1758 Value Position::compute_non_pawn_material(Color c) const {
1760 Value result = VALUE_ZERO;
1762 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1763 result += piece_count(c, pt) * PieceValueMidgame[pt];
1769 /// Position::is_draw() tests whether the position is drawn by material,
1770 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1771 /// must be done by the search.
1773 bool Position::is_draw() const {
1775 // Draw by material?
1777 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1780 // Draw by the 50 moves rule?
1781 if (st->rule50 > 99 && !is_mate())
1784 // Draw by repetition?
1785 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1786 if (history[st->gamePly - i] == st->key)
1793 /// Position::is_mate() returns true or false depending on whether the
1794 /// side to move is checkmated.
1796 bool Position::is_mate() const {
1798 MoveStack moves[MOVES_MAX];
1799 return is_check() && generate<MV_LEGAL>(*this, moves) == moves;
1803 /// Position::init_zobrist() is a static member function which initializes at
1804 /// startup the various arrays used to compute hash keys.
1806 void Position::init_zobrist() {
1811 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1812 zobrist[i][j][k] = rk.rand<Key>();
1814 for (i = 0; i < 64; i++)
1815 zobEp[i] = rk.rand<Key>();
1817 for (i = 0; i < 16; i++)
1818 zobCastle[i] = rk.rand<Key>();
1820 zobSideToMove = rk.rand<Key>();
1821 zobExclusion = rk.rand<Key>();
1825 /// Position::init_piece_square_tables() initializes the piece square tables.
1826 /// This is a two-step operation: First, the white halves of the tables are
1827 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1828 /// of the tables are initialized by mirroring and changing the sign of the
1829 /// corresponding white scores.
1831 void Position::init_piece_square_tables() {
1833 for (Square s = SQ_A1; s <= SQ_H8; s++)
1834 for (Piece p = WP; p <= WK; p++)
1835 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1837 for (Square s = SQ_A1; s <= SQ_H8; s++)
1838 for (Piece p = BP; p <= BK; p++)
1839 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1843 /// Position::flipped_copy() makes a copy of the input position, but with
1844 /// the white and black sides reversed. This is only useful for debugging,
1845 /// especially for finding evaluation symmetry bugs.
1847 void Position::flipped_copy(const Position& pos) {
1849 assert(pos.is_ok());
1852 threadID = pos.thread();
1855 for (Square s = SQ_A1; s <= SQ_H8; s++)
1856 if (!pos.square_is_empty(s))
1857 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1860 sideToMove = opposite_color(pos.side_to_move());
1863 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1864 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1865 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1866 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1868 initialKFile = pos.initialKFile;
1869 initialKRFile = pos.initialKRFile;
1870 initialQRFile = pos.initialQRFile;
1872 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1873 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1874 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1875 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1876 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1877 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1879 // En passant square
1880 if (pos.st->epSquare != SQ_NONE)
1881 st->epSquare = flip_square(pos.st->epSquare);
1887 st->key = compute_key();
1888 st->pawnKey = compute_pawn_key();
1889 st->materialKey = compute_material_key();
1891 // Incremental scores
1892 st->value = compute_value();
1895 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1896 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1902 /// Position::is_ok() performs some consitency checks for the position object.
1903 /// This is meant to be helpful when debugging.
1905 bool Position::is_ok(int* failedStep) const {
1907 // What features of the position should be verified?
1908 const bool debugAll = false;
1910 const bool debugBitboards = debugAll || false;
1911 const bool debugKingCount = debugAll || false;
1912 const bool debugKingCapture = debugAll || false;
1913 const bool debugCheckerCount = debugAll || false;
1914 const bool debugKey = debugAll || false;
1915 const bool debugMaterialKey = debugAll || false;
1916 const bool debugPawnKey = debugAll || false;
1917 const bool debugIncrementalEval = debugAll || false;
1918 const bool debugNonPawnMaterial = debugAll || false;
1919 const bool debugPieceCounts = debugAll || false;
1920 const bool debugPieceList = debugAll || false;
1921 const bool debugCastleSquares = debugAll || false;
1923 if (failedStep) *failedStep = 1;
1926 if (!color_is_ok(side_to_move()))
1929 // Are the king squares in the position correct?
1930 if (failedStep) (*failedStep)++;
1931 if (piece_on(king_square(WHITE)) != WK)
1934 if (failedStep) (*failedStep)++;
1935 if (piece_on(king_square(BLACK)) != BK)
1939 if (failedStep) (*failedStep)++;
1940 if (!file_is_ok(initialKRFile))
1943 if (!file_is_ok(initialQRFile))
1946 // Do both sides have exactly one king?
1947 if (failedStep) (*failedStep)++;
1950 int kingCount[2] = {0, 0};
1951 for (Square s = SQ_A1; s <= SQ_H8; s++)
1952 if (type_of_piece_on(s) == KING)
1953 kingCount[color_of_piece_on(s)]++;
1955 if (kingCount[0] != 1 || kingCount[1] != 1)
1959 // Can the side to move capture the opponent's king?
1960 if (failedStep) (*failedStep)++;
1961 if (debugKingCapture)
1963 Color us = side_to_move();
1964 Color them = opposite_color(us);
1965 Square ksq = king_square(them);
1966 if (attackers_to(ksq) & pieces_of_color(us))
1970 // Is there more than 2 checkers?
1971 if (failedStep) (*failedStep)++;
1972 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1976 if (failedStep) (*failedStep)++;
1979 // The intersection of the white and black pieces must be empty
1980 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1983 // The union of the white and black pieces must be equal to all
1985 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1988 // Separate piece type bitboards must have empty intersections
1989 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1990 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1991 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1995 // En passant square OK?
1996 if (failedStep) (*failedStep)++;
1997 if (ep_square() != SQ_NONE)
1999 // The en passant square must be on rank 6, from the point of view of the
2001 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2006 if (failedStep) (*failedStep)++;
2007 if (debugKey && st->key != compute_key())
2010 // Pawn hash key OK?
2011 if (failedStep) (*failedStep)++;
2012 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2015 // Material hash key OK?
2016 if (failedStep) (*failedStep)++;
2017 if (debugMaterialKey && st->materialKey != compute_material_key())
2020 // Incremental eval OK?
2021 if (failedStep) (*failedStep)++;
2022 if (debugIncrementalEval && st->value != compute_value())
2025 // Non-pawn material OK?
2026 if (failedStep) (*failedStep)++;
2027 if (debugNonPawnMaterial)
2029 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2032 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2037 if (failedStep) (*failedStep)++;
2038 if (debugPieceCounts)
2039 for (Color c = WHITE; c <= BLACK; c++)
2040 for (PieceType pt = PAWN; pt <= KING; pt++)
2041 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
2044 if (failedStep) (*failedStep)++;
2046 for (Color c = WHITE; c <= BLACK; c++)
2047 for (PieceType pt = PAWN; pt <= KING; pt++)
2048 for (int i = 0; i < pieceCount[c][pt]; i++)
2050 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
2053 if (index[piece_list(c, pt, i)] != i)
2057 if (failedStep) (*failedStep)++;
2058 if (debugCastleSquares)
2060 for (Color c = WHITE; c <= BLACK; c++)
2062 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
2065 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
2068 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2070 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2072 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2074 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2078 if (failedStep) *failedStep = 0;