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 Marco Costalba
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/>.
35 #include "ucioption.h"
42 extern SearchStack EmptySearchStack;
44 int Position::castleRightsMask[64];
46 Key Position::zobrist[2][8][64];
47 Key Position::zobEp[64];
48 Key Position::zobCastle[16];
49 Key Position::zobMaterial[2][8][16];
50 Key Position::zobSideToMove;
52 Value Position::MgPieceSquareTable[16][64];
53 Value Position::EgPieceSquareTable[16][64];
55 static bool RequestPending = false;
63 Position::Position(const Position& pos) {
67 Position::Position(const std::string& fen) {
72 /// Position::from_fen() initializes the position object with the given FEN
73 /// string. This function is not very robust - make sure that input FENs are
74 /// correct (this is assumed to be the responsibility of the GUI).
76 void Position::from_fen(const std::string& fen) {
78 static const std::string pieceLetters = "KQRBNPkqrbnp";
79 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
87 for ( ; fen[i] != ' '; i++)
91 // Skip the given number of files
92 file += (fen[i] - '1' + 1);
95 else if (fen[i] == '/')
101 size_t idx = pieceLetters.find(fen[i]);
102 if (idx == std::string::npos)
104 std::cout << "Error in FEN at character " << i << std::endl;
107 Square square = make_square(file, rank);
108 put_piece(pieces[idx], square);
114 if (fen[i] != 'w' && fen[i] != 'b')
116 std::cout << "Error in FEN at character " << i << std::endl;
119 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
125 std::cout << "Error in FEN at character " << i << std::endl;
130 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
136 else if(fen[i] == 'K') allow_oo(WHITE);
137 else if(fen[i] == 'Q') allow_ooo(WHITE);
138 else if(fen[i] == 'k') allow_oo(BLACK);
139 else if(fen[i] == 'q') allow_ooo(BLACK);
140 else if(fen[i] >= 'A' && fen[i] <= 'H') {
141 File rookFile, kingFile = FILE_NONE;
142 for(Square square = SQ_B1; square <= SQ_G1; square++)
143 if(piece_on(square) == WK)
144 kingFile = square_file(square);
145 if(kingFile == FILE_NONE) {
146 std::cout << "Error in FEN at character " << i << std::endl;
149 initialKFile = kingFile;
150 rookFile = File(fen[i] - 'A') + FILE_A;
151 if(rookFile < initialKFile) {
153 initialQRFile = rookFile;
157 initialKRFile = rookFile;
160 else if(fen[i] >= 'a' && fen[i] <= 'h') {
161 File rookFile, kingFile = FILE_NONE;
162 for(Square square = SQ_B8; square <= SQ_G8; square++)
163 if(piece_on(square) == BK)
164 kingFile = square_file(square);
165 if(kingFile == FILE_NONE) {
166 std::cout << "Error in FEN at character " << i << std::endl;
169 initialKFile = kingFile;
170 rookFile = File(fen[i] - 'a') + FILE_A;
171 if(rookFile < initialKFile) {
173 initialQRFile = rookFile;
177 initialKRFile = rookFile;
181 std::cout << "Error in FEN at character " << i << std::endl;
188 while (fen[i] == ' ')
192 if ( i < fen.length() - 2
193 && (fen[i] >= 'a' && fen[i] <= 'h')
194 && (fen[i+1] == '3' || fen[i+1] == '6'))
195 epSquare = square_from_string(fen.substr(i, 2));
197 // Various initialisation
198 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
199 castleRightsMask[sq] = ALL_CASTLES;
201 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
202 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
203 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
204 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
205 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
206 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
211 pawnKey = compute_pawn_key();
212 materialKey = compute_material_key();
213 mgValue = compute_mg_value();
214 egValue = compute_eg_value();
215 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
216 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
220 /// Position::to_fen() converts the position object to a FEN string. This is
221 /// probably only useful for debugging.
223 const std::string Position::to_fen() const {
225 static const std::string pieceLetters = " PNBRQK pnbrqk";
229 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
232 for (File file = FILE_A; file <= FILE_H; file++)
234 Square sq = make_square(file, rank);
235 if (!square_is_occupied(sq))
241 fen += (char)skip + '0';
244 fen += pieceLetters[piece_on(sq)];
247 fen += (char)skip + '0';
249 fen += (rank > RANK_1 ? '/' : ' ');
251 fen += (sideToMove == WHITE ? "w " : "b ");
252 if (castleRights != NO_CASTLES)
254 if (can_castle_kingside(WHITE)) fen += 'K';
255 if (can_castle_queenside(WHITE)) fen += 'Q';
256 if (can_castle_kingside(BLACK)) fen += 'k';
257 if (can_castle_queenside(BLACK)) fen += 'q';
262 if (ep_square() != SQ_NONE)
263 fen += square_to_string(ep_square());
271 /// Position::print() prints an ASCII representation of the position to
272 /// the standard output. If a move is given then also the san is print.
274 void Position::print(Move m) const {
276 static const std::string pieceLetters = " PNBRQK PNBRQK .";
278 // Check for reentrancy, as example when called from inside
279 // MovePicker that is used also here in move_to_san()
283 RequestPending = true;
285 std::cout << std::endl;
288 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
289 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
291 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
293 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
294 for (File file = FILE_A; file <= FILE_H; file++)
296 Square sq = make_square(file, rank);
297 Piece piece = piece_on(sq);
298 if (piece == EMPTY && square_color(sq) == WHITE)
301 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
302 std::cout << '|' << col << pieceLetters[piece] << col;
304 std::cout << '|' << std::endl;
306 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
307 << "Fen is: " << to_fen() << std::endl
308 << "Key is: " << key << std::endl;
310 RequestPending = false;
314 /// Position::copy() creates a copy of the input position.
316 void Position::copy(const Position &pos) {
318 memcpy(this, &pos, sizeof(Position));
322 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
323 /// king) pieces for the given color.
324 Bitboard Position::pinned_pieces(Color c) const {
326 if (pinned[c] != ~EmptyBoardBB)
330 Square ksq = king_square(c);
331 pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
332 pinners[c] = p1 | p2;
336 Bitboard Position::pinned_pieces(Color c, Bitboard& p) const {
338 if (pinned[c] == ~EmptyBoardBB)
345 Bitboard Position::discovered_check_candidates(Color c) const {
347 if (dcCandidates[c] != ~EmptyBoardBB)
348 return dcCandidates[c];
351 Square ksq = king_square(opposite_color(c));
352 dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, dummy) | hidden_checks<BISHOP, false>(c, ksq, dummy);
353 return dcCandidates[c];
356 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
357 /// king) pieces for the given color and for the given pinner type. Or, when
358 /// template parameter FindPinned is false, the pinned pieces of opposite color
359 /// that are, indeed, the pieces candidate for a discovery check.
360 template<PieceType Piece, bool FindPinned>
361 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
364 Bitboard sliders, result = EmptyBoardBB;
366 if (Piece == ROOK) // Resolved at compile time
367 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
369 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
371 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
373 // King blockers are candidate pinned pieces
374 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
376 // Pinners are sliders, not checkers, that give check when
377 // candidate pinned are removed.
378 pinners = (FindPinned ? sliders & ~checkersBB : sliders);
381 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
383 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
385 // Finally for each pinner find the corresponding pinned piece (if same color of king)
386 // or discovery checker (if opposite color) among the candidates.
387 Bitboard p = pinners;
391 result |= (squares_between(s, ksq) & candidate_pinned);
395 pinners = EmptyBoardBB;
401 /// Position::attacks_to() computes a bitboard containing all pieces which
402 /// attacks a given square. There are two versions of this function: One
403 /// which finds attackers of both colors, and one which only finds the
404 /// attackers for one side.
406 Bitboard Position::attacks_to(Square s) const {
408 return (pawn_attacks(BLACK, s) & pawns(WHITE))
409 | (pawn_attacks(WHITE, s) & pawns(BLACK))
410 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
411 | (piece_attacks<ROOK>(s) & rooks_and_queens())
412 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
413 | (piece_attacks<KING>(s) & pieces_of_type(KING));
416 /// Position::piece_attacks_square() tests whether the piece on square f
417 /// attacks square t.
419 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
421 assert(square_is_ok(f));
422 assert(square_is_ok(t));
426 case WP: return pawn_attacks_square(WHITE, f, t);
427 case BP: return pawn_attacks_square(BLACK, f, t);
428 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
429 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
430 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
431 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
432 case WK: case BK: return piece_attacks_square<KING>(f, t);
439 /// Position::move_attacks_square() tests whether a move from the current
440 /// position attacks a given square.
442 bool Position::move_attacks_square(Move m, Square s) const {
444 assert(move_is_ok(m));
445 assert(square_is_ok(s));
447 Square f = move_from(m), t = move_to(m);
449 assert(square_is_occupied(f));
451 if (piece_attacks_square(piece_on(f), t, s))
454 // Move the piece and scan for X-ray attacks behind it
455 Bitboard occ = occupied_squares();
456 Color us = color_of_piece_on(f);
459 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
460 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
462 // If we have attacks we need to verify that are caused by our move
463 // and are not already existent ones.
464 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
468 /// Position::find_checkers() computes the checkersBB bitboard, which
469 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
470 /// currently works by calling Position::attacks_to, which is probably
471 /// inefficient. Consider rewriting this function to use the last move
472 /// played, like in non-bitboard versions of Glaurung.
474 void Position::find_checkers() {
476 Color us = side_to_move();
477 checkersBB = attacks_to(king_square(us), opposite_color(us));
481 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
483 bool Position::pl_move_is_legal(Move m) const {
486 assert(move_is_ok(m));
488 // If we're in check, all pseudo-legal moves are legal, because our
489 // check evasion generator only generates true legal moves.
493 // Castling moves are checked for legality during move generation.
494 if (move_is_castle(m))
497 Color us = side_to_move();
498 Color them = opposite_color(us);
499 Square from = move_from(m);
500 Square ksq = king_square(us);
502 assert(color_of_piece_on(from) == us);
503 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
505 // En passant captures are a tricky special case. Because they are
506 // rather uncommon, we do it simply by testing whether the king is attacked
507 // after the move is made
510 Square to = move_to(m);
511 Square capsq = make_square(square_file(to), square_rank(from));
512 Bitboard b = occupied_squares();
514 assert(to == ep_square());
515 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
516 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
517 assert(piece_on(to) == EMPTY);
520 clear_bit(&b, capsq);
523 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
524 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
527 // If the moving piece is a king, check whether the destination
528 // square is attacked by the opponent.
530 return !(square_is_attacked(move_to(m), them));
532 // A non-king move is legal if and only if it is not pinned or it
533 // is moving along the ray towards or away from the king.
534 return ( !bit_is_set(pinned_pieces(us), from)
535 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
539 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
540 /// There are two versions of this function: One which takes only a move as
541 /// input, and one which takes a move and a bitboard of discovered check
542 /// candidates. The latter function is faster, and should always be preferred
543 /// when a discovered check candidates bitboard has already been computed.
545 bool Position::move_is_check(Move m) const {
547 Bitboard dc = discovered_check_candidates(side_to_move());
548 return move_is_check(m, dc);
551 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
554 assert(move_is_ok(m));
555 assert(dcCandidates == discovered_check_candidates(side_to_move()));
557 Color us = side_to_move();
558 Color them = opposite_color(us);
559 Square from = move_from(m);
560 Square to = move_to(m);
561 Square ksq = king_square(them);
563 assert(color_of_piece_on(from) == us);
564 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
566 // Proceed according to the type of the moving piece
567 switch (type_of_piece_on(from))
571 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
574 if ( bit_is_set(dcCandidates, from) // Discovered check?
575 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
578 if (move_promotion(m)) // Promotion with check?
580 Bitboard b = occupied_squares();
583 switch (move_promotion(m))
586 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
588 return bit_is_set(bishop_attacks_bb(to, b), ksq);
590 return bit_is_set(rook_attacks_bb(to, b), ksq);
592 return bit_is_set(queen_attacks_bb(to, b), ksq);
597 // En passant capture with check? We have already handled the case
598 // of direct checks and ordinary discovered check, the only case we
599 // need to handle is the unusual case of a discovered check through the
601 else if (move_is_ep(m))
603 Square capsq = make_square(square_file(to), square_rank(from));
604 Bitboard b = occupied_squares();
606 clear_bit(&b, capsq);
608 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
609 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
614 return bit_is_set(dcCandidates, from) // Discovered check?
615 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
618 return bit_is_set(dcCandidates, from) // Discovered check?
619 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
622 return bit_is_set(dcCandidates, from) // Discovered check?
623 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
626 // Discovered checks are impossible!
627 assert(!bit_is_set(dcCandidates, from));
628 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
632 if ( bit_is_set(dcCandidates, from)
633 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
636 // Castling with check?
637 if (move_is_castle(m))
639 Square kfrom, kto, rfrom, rto;
640 Bitboard b = occupied_squares();
646 kto = relative_square(us, SQ_G1);
647 rto = relative_square(us, SQ_F1);
649 kto = relative_square(us, SQ_C1);
650 rto = relative_square(us, SQ_D1);
652 clear_bit(&b, kfrom);
653 clear_bit(&b, rfrom);
656 return bit_is_set(rook_attacks_bb(rto, b), ksq);
660 default: // NO_PIECE_TYPE
668 /// Position::move_is_capture() tests whether a move from the current
669 /// position is a capture. Move must not be MOVE_NONE.
671 bool Position::move_is_capture(Move m) const {
673 assert(m != MOVE_NONE);
675 return ( !square_is_empty(move_to(m))
676 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
682 /// Position::backup() is called when making a move. All information
683 /// necessary to restore the position when the move is later unmade
684 /// is saved to an UndoInfo object. The function Position::restore
685 /// does the reverse operation: When one does a backup followed by
686 /// a restore with the same UndoInfo object, the position is restored
687 /// to the state before backup was called.
689 void Position::backup(UndoInfo& u) const {
691 u.castleRights = castleRights;
692 u.epSquare = epSquare;
693 u.checkersBB = checkersBB;
696 u.materialKey = materialKey;
698 u.lastMove = lastMove;
701 u.capture = NO_PIECE_TYPE;
703 for (Color c = WHITE; c <= BLACK; c++)
705 u.pinners[c] = pinners[c];
706 u.pinned[c] = pinned[c];
707 u.dcCandidates[c] = dcCandidates[c];
712 /// Position::restore() is called when unmaking a move. It copies back
713 /// the information backed up during a previous call to Position::backup.
715 void Position::restore(const UndoInfo& u) {
717 castleRights = u.castleRights;
718 epSquare = u.epSquare;
719 checkersBB = u.checkersBB;
722 materialKey = u.materialKey;
724 lastMove = u.lastMove;
727 // u.capture is restored in undo_move()
729 for (Color c = WHITE; c <= BLACK; c++)
731 pinners[c] = u.pinners[c];
732 pinned[c] = u.pinned[c];
733 dcCandidates[c] = u.dcCandidates[c];
738 /// Position::update_checkers() is a private method to udpate chekers info
740 template<PieceType Piece>
741 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
742 Square to, Bitboard dcCandidates) {
744 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
745 set_bit(pCheckersBB, to);
747 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
750 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
753 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
758 /// Position::do_move() makes a move, and backs up all information necessary
759 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
760 /// Pseudo-legal moves should be filtered out before this function is called.
761 /// There are two versions of this function, one which takes only the move and
762 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
763 /// discovered check candidates. The second version is faster, because knowing
764 /// the discovered check candidates makes it easier to update the checkersBB
765 /// member variable in the position object.
767 void Position::do_move(Move m, UndoInfo& u) {
769 do_move(m, u, discovered_check_candidates(side_to_move()));
772 void Position::do_move(Move m, UndoInfo& u, Bitboard dc) {
775 assert(move_is_ok(m));
777 // Back up the necessary information to our UndoInfo object (except the
778 // captured piece, which is taken care of later.
781 // Save the current key to the history[] array, in order to be able to
782 // detect repetition draws.
783 history[gamePly] = key;
785 // Increment the 50 moves rule draw counter. Resetting it to zero in the
786 // case of non-reversible moves is taken care of later.
789 // Reset pinned bitboard and its friends
790 for (Color c = WHITE; c <= BLACK; c++)
791 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
793 if (move_is_castle(m))
795 else if (move_promotion(m))
796 do_promotion_move(m, u);
797 else if (move_is_ep(m))
801 Color us = side_to_move();
802 Color them = opposite_color(us);
803 Square from = move_from(m);
804 Square to = move_to(m);
806 assert(color_of_piece_on(from) == us);
807 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
809 PieceType piece = type_of_piece_on(from);
810 PieceType capture = type_of_piece_on(to);
815 do_capture_move(m, capture, them, to);
819 clear_bit(&(byColorBB[us]), from);
820 clear_bit(&(byTypeBB[piece]), from);
821 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
822 set_bit(&(byColorBB[us]), to);
823 set_bit(&(byTypeBB[piece]), to);
824 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
825 board[to] = board[from];
829 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
831 // Update incremental scores
832 mgValue -= mg_pst(us, piece, from);
833 mgValue += mg_pst(us, piece, to);
834 egValue -= eg_pst(us, piece, from);
835 egValue += eg_pst(us, piece, to);
837 // If the moving piece was a king, update the king square
841 // Reset en passant square
842 if (epSquare != SQ_NONE)
844 key ^= zobEp[epSquare];
848 // If the moving piece was a pawn do some special extra work
851 // Reset rule 50 draw counter
854 // Update pawn hash key
855 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
857 // Set en passant square, only if moved pawn can be captured
858 if (abs(int(to) - int(from)) == 16)
860 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
861 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
863 epSquare = Square((int(from) + int(to)) / 2);
864 key ^= zobEp[epSquare];
869 // Update piece lists
870 pieceList[us][piece][index[from]] = to;
871 index[to] = index[from];
873 // Update castle rights
874 key ^= zobCastle[castleRights];
875 castleRights &= castleRightsMask[from];
876 castleRights &= castleRightsMask[to];
877 key ^= zobCastle[castleRights];
879 // Update checkers bitboard, piece must be already moved
880 checkersBB = EmptyBoardBB;
881 Square ksq = king_square(them);
884 case PAWN: update_checkers<PAWN>(&checkersBB, ksq, from, to, dc); break;
885 case KNIGHT: update_checkers<KNIGHT>(&checkersBB, ksq, from, to, dc); break;
886 case BISHOP: update_checkers<BISHOP>(&checkersBB, ksq, from, to, dc); break;
887 case ROOK: update_checkers<ROOK>(&checkersBB, ksq, from, to, dc); break;
888 case QUEEN: update_checkers<QUEEN>(&checkersBB, ksq, from, to, dc); break;
889 case KING: update_checkers<KING>(&checkersBB, ksq, from, to, dc); break;
890 default: assert(false); break;
895 key ^= zobSideToMove;
896 sideToMove = opposite_color(sideToMove);
899 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
900 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
906 /// Position::do_capture_move() is a private method used to update captured
907 /// piece info. It is called from the main Position::do_move function.
909 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
911 assert(capture != KING);
913 // Remove captured piece
914 clear_bit(&(byColorBB[them]), to);
915 clear_bit(&(byTypeBB[capture]), to);
918 key ^= zobrist[them][capture][to];
920 // If the captured piece was a pawn, update pawn hash key
922 pawnKey ^= zobrist[them][PAWN][to];
924 // Update incremental scores
925 mgValue -= mg_pst(them, capture, to);
926 egValue -= eg_pst(them, capture, to);
928 assert(!move_promotion(m) || capture != PAWN);
932 npMaterial[them] -= piece_value_midgame(capture);
934 // Update material hash key
935 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
937 // Update piece count
938 pieceCount[them][capture]--;
941 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
942 index[pieceList[them][capture][index[to]]] = index[to];
944 // Reset rule 50 counter
949 /// Position::do_castle_move() is a private method used to make a castling
950 /// move. It is called from the main Position::do_move function. Note that
951 /// castling moves are encoded as "king captures friendly rook" moves, for
952 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
954 void Position::do_castle_move(Move m) {
957 assert(move_is_ok(m));
958 assert(move_is_castle(m));
960 Color us = side_to_move();
961 Color them = opposite_color(us);
963 // Find source squares for king and rook
964 Square kfrom = move_from(m);
965 Square rfrom = move_to(m); // HACK: See comment at beginning of function
968 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
969 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
971 // Find destination squares for king and rook
972 if (rfrom > kfrom) // O-O
974 kto = relative_square(us, SQ_G1);
975 rto = relative_square(us, SQ_F1);
977 kto = relative_square(us, SQ_C1);
978 rto = relative_square(us, SQ_D1);
981 // Remove pieces from source squares
982 clear_bit(&(byColorBB[us]), kfrom);
983 clear_bit(&(byTypeBB[KING]), kfrom);
984 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
985 clear_bit(&(byColorBB[us]), rfrom);
986 clear_bit(&(byTypeBB[ROOK]), rfrom);
987 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
989 // Put pieces on destination squares
990 set_bit(&(byColorBB[us]), kto);
991 set_bit(&(byTypeBB[KING]), kto);
992 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
993 set_bit(&(byColorBB[us]), rto);
994 set_bit(&(byTypeBB[ROOK]), rto);
995 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
997 // Update board array
998 board[kfrom] = board[rfrom] = EMPTY;
999 board[kto] = piece_of_color_and_type(us, KING);
1000 board[rto] = piece_of_color_and_type(us, ROOK);
1002 // Update king square
1003 kingSquare[us] = kto;
1005 // Update piece lists
1006 pieceList[us][KING][index[kfrom]] = kto;
1007 pieceList[us][ROOK][index[rfrom]] = rto;
1008 int tmp = index[rfrom];
1009 index[kto] = index[kfrom];
1012 // Update incremental scores
1013 mgValue -= mg_pst(us, KING, kfrom);
1014 mgValue += mg_pst(us, KING, kto);
1015 egValue -= eg_pst(us, KING, kfrom);
1016 egValue += eg_pst(us, KING, kto);
1017 mgValue -= mg_pst(us, ROOK, rfrom);
1018 mgValue += mg_pst(us, ROOK, rto);
1019 egValue -= eg_pst(us, ROOK, rfrom);
1020 egValue += eg_pst(us, ROOK, rto);
1023 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1024 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1026 // Clear en passant square
1027 if (epSquare != SQ_NONE)
1029 key ^= zobEp[epSquare];
1033 // Update castling rights
1034 key ^= zobCastle[castleRights];
1035 castleRights &= castleRightsMask[kfrom];
1036 key ^= zobCastle[castleRights];
1038 // Reset rule 50 counter
1041 // Update checkers BB
1042 checkersBB = attacks_to(king_square(them), us);
1046 /// Position::do_promotion_move() is a private method used to make a promotion
1047 /// move. It is called from the main Position::do_move function. The
1048 /// UndoInfo object, which has been initialized in Position::do_move, is
1049 /// used to store the captured piece (if any).
1051 void Position::do_promotion_move(Move m, UndoInfo &u) {
1055 PieceType capture, promotion;
1058 assert(move_is_ok(m));
1059 assert(move_promotion(m));
1061 us = side_to_move();
1062 them = opposite_color(us);
1063 from = move_from(m);
1066 assert(relative_rank(us, to) == RANK_8);
1067 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1068 assert(color_of_piece_on(to) == them || square_is_empty(to));
1070 capture = type_of_piece_on(to);
1074 u.capture = capture;
1075 do_capture_move(m, capture, them, to);
1079 clear_bit(&(byColorBB[us]), from);
1080 clear_bit(&(byTypeBB[PAWN]), from);
1081 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1082 board[from] = EMPTY;
1084 // Insert promoted piece
1085 promotion = move_promotion(m);
1086 assert(promotion >= KNIGHT && promotion <= QUEEN);
1087 set_bit(&(byColorBB[us]), to);
1088 set_bit(&(byTypeBB[promotion]), to);
1089 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1090 board[to] = piece_of_color_and_type(us, promotion);
1093 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1095 // Update pawn hash key
1096 pawnKey ^= zobrist[us][PAWN][from];
1098 // Update material key
1099 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1100 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1102 // Update piece counts
1103 pieceCount[us][PAWN]--;
1104 pieceCount[us][promotion]++;
1106 // Update piece lists
1107 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1108 index[pieceList[us][PAWN][index[from]]] = index[from];
1109 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1110 index[to] = pieceCount[us][promotion] - 1;
1112 // Update incremental scores
1113 mgValue -= mg_pst(us, PAWN, from);
1114 mgValue += mg_pst(us, promotion, to);
1115 egValue -= eg_pst(us, PAWN, from);
1116 egValue += eg_pst(us, promotion, to);
1119 npMaterial[us] += piece_value_midgame(promotion);
1121 // Clear the en passant square
1122 if (epSquare != SQ_NONE)
1124 key ^= zobEp[epSquare];
1128 // Update castle rights
1129 key ^= zobCastle[castleRights];
1130 castleRights &= castleRightsMask[to];
1131 key ^= zobCastle[castleRights];
1133 // Reset rule 50 counter
1136 // Update checkers BB
1137 checkersBB = attacks_to(king_square(them), us);
1141 /// Position::do_ep_move() is a private method used to make an en passant
1142 /// capture. It is called from the main Position::do_move function. Because
1143 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1144 /// object in which to store the captured piece.
1146 void Position::do_ep_move(Move m) {
1149 Square from, to, capsq;
1152 assert(move_is_ok(m));
1153 assert(move_is_ep(m));
1155 us = side_to_move();
1156 them = opposite_color(us);
1157 from = move_from(m);
1159 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1161 assert(to == epSquare);
1162 assert(relative_rank(us, to) == RANK_6);
1163 assert(piece_on(to) == EMPTY);
1164 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1165 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1167 // Remove captured piece
1168 clear_bit(&(byColorBB[them]), capsq);
1169 clear_bit(&(byTypeBB[PAWN]), capsq);
1170 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1171 board[capsq] = EMPTY;
1173 // Remove moving piece from source square
1174 clear_bit(&(byColorBB[us]), from);
1175 clear_bit(&(byTypeBB[PAWN]), from);
1176 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1178 // Put moving piece on destination square
1179 set_bit(&(byColorBB[us]), to);
1180 set_bit(&(byTypeBB[PAWN]), to);
1181 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1182 board[to] = board[from];
1183 board[from] = EMPTY;
1185 // Update material hash key
1186 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1188 // Update piece count
1189 pieceCount[them][PAWN]--;
1191 // Update piece list
1192 pieceList[us][PAWN][index[from]] = to;
1193 index[to] = index[from];
1194 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1195 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1198 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1199 key ^= zobrist[them][PAWN][capsq];
1200 key ^= zobEp[epSquare];
1202 // Update pawn hash key
1203 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1204 pawnKey ^= zobrist[them][PAWN][capsq];
1206 // Update incremental scores
1207 mgValue -= mg_pst(them, PAWN, capsq);
1208 mgValue -= mg_pst(us, PAWN, from);
1209 mgValue += mg_pst(us, PAWN, to);
1210 egValue -= eg_pst(them, PAWN, capsq);
1211 egValue -= eg_pst(us, PAWN, from);
1212 egValue += eg_pst(us, PAWN, to);
1214 // Reset en passant square
1217 // Reset rule 50 counter
1220 // Update checkers BB
1221 checkersBB = attacks_to(king_square(them), us);
1225 /// Position::undo_move() unmakes a move. When it returns, the position should
1226 /// be restored to exactly the same state as before the move was made. It is
1227 /// important that Position::undo_move is called with the same move and UndoInfo
1228 /// object as the earlier call to Position::do_move.
1230 void Position::undo_move(Move m, const UndoInfo &u) {
1233 assert(move_is_ok(m));
1236 sideToMove = opposite_color(sideToMove);
1238 // Restore information from our UndoInfo object (except the captured piece,
1239 // which is taken care of later)
1242 if (move_is_castle(m))
1243 undo_castle_move(m);
1244 else if (move_promotion(m))
1245 undo_promotion_move(m, u);
1246 else if (move_is_ep(m))
1252 PieceType piece, capture;
1254 us = side_to_move();
1255 them = opposite_color(us);
1256 from = move_from(m);
1259 assert(piece_on(from) == EMPTY);
1260 assert(color_of_piece_on(to) == us);
1262 // Put the piece back at the source square
1263 piece = type_of_piece_on(to);
1264 set_bit(&(byColorBB[us]), from);
1265 set_bit(&(byTypeBB[piece]), from);
1266 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1267 board[from] = piece_of_color_and_type(us, piece);
1269 // Clear the destination square
1270 clear_bit(&(byColorBB[us]), to);
1271 clear_bit(&(byTypeBB[piece]), to);
1272 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1274 // If the moving piece was a king, update the king square
1276 kingSquare[us] = from;
1278 // Update piece list
1279 pieceList[us][piece][index[to]] = from;
1280 index[from] = index[to];
1282 capture = u.capture;
1286 assert(capture != KING);
1288 // Replace the captured piece
1289 set_bit(&(byColorBB[them]), to);
1290 set_bit(&(byTypeBB[capture]), to);
1291 set_bit(&(byTypeBB[0]), to);
1292 board[to] = piece_of_color_and_type(them, capture);
1295 if (capture != PAWN)
1296 npMaterial[them] += piece_value_midgame(capture);
1298 // Update piece list
1299 pieceList[them][capture][pieceCount[them][capture]] = to;
1300 index[to] = pieceCount[them][capture];
1302 // Update piece count
1303 pieceCount[them][capture]++;
1312 /// Position::undo_castle_move() is a private method used to unmake a castling
1313 /// move. It is called from the main Position::undo_move function. Note that
1314 /// castling moves are encoded as "king captures friendly rook" moves, for
1315 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1317 void Position::undo_castle_move(Move m) {
1319 assert(move_is_ok(m));
1320 assert(move_is_castle(m));
1322 // When we have arrived here, some work has already been done by
1323 // Position::undo_move. In particular, the side to move has been switched,
1324 // so the code below is correct.
1325 Color us = side_to_move();
1327 // Find source squares for king and rook
1328 Square kfrom = move_from(m);
1329 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1332 // Find destination squares for king and rook
1333 if (rfrom > kfrom) // O-O
1335 kto = relative_square(us, SQ_G1);
1336 rto = relative_square(us, SQ_F1);
1338 kto = relative_square(us, SQ_C1);
1339 rto = relative_square(us, SQ_D1);
1342 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1343 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1345 // Remove pieces from destination squares
1346 clear_bit(&(byColorBB[us]), kto);
1347 clear_bit(&(byTypeBB[KING]), kto);
1348 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1349 clear_bit(&(byColorBB[us]), rto);
1350 clear_bit(&(byTypeBB[ROOK]), rto);
1351 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1353 // Put pieces on source squares
1354 set_bit(&(byColorBB[us]), kfrom);
1355 set_bit(&(byTypeBB[KING]), kfrom);
1356 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1357 set_bit(&(byColorBB[us]), rfrom);
1358 set_bit(&(byTypeBB[ROOK]), rfrom);
1359 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1362 board[rto] = board[kto] = EMPTY;
1363 board[rfrom] = piece_of_color_and_type(us, ROOK);
1364 board[kfrom] = piece_of_color_and_type(us, KING);
1366 // Update king square
1367 kingSquare[us] = kfrom;
1369 // Update piece lists
1370 pieceList[us][KING][index[kto]] = kfrom;
1371 pieceList[us][ROOK][index[rto]] = rfrom;
1372 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1373 index[kfrom] = index[kto];
1378 /// Position::undo_promotion_move() is a private method used to unmake a
1379 /// promotion move. It is called from the main Position::do_move
1380 /// function. The UndoInfo object, which has been initialized in
1381 /// Position::do_move, is used to put back the captured piece (if any).
1383 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1387 PieceType capture, promotion;
1389 assert(move_is_ok(m));
1390 assert(move_promotion(m));
1392 // When we have arrived here, some work has already been done by
1393 // Position::undo_move. In particular, the side to move has been switched,
1394 // so the code below is correct.
1395 us = side_to_move();
1396 them = opposite_color(us);
1397 from = move_from(m);
1400 assert(relative_rank(us, to) == RANK_8);
1401 assert(piece_on(from) == EMPTY);
1403 // Remove promoted piece
1404 promotion = move_promotion(m);
1405 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1406 assert(promotion >= KNIGHT && promotion <= QUEEN);
1407 clear_bit(&(byColorBB[us]), to);
1408 clear_bit(&(byTypeBB[promotion]), to);
1409 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1411 // Insert pawn at source square
1412 set_bit(&(byColorBB[us]), from);
1413 set_bit(&(byTypeBB[PAWN]), from);
1414 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1415 board[from] = piece_of_color_and_type(us, PAWN);
1418 npMaterial[us] -= piece_value_midgame(promotion);
1420 // Update piece list
1421 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1422 index[from] = pieceCount[us][PAWN];
1423 pieceList[us][promotion][index[to]] =
1424 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1425 index[pieceList[us][promotion][index[to]]] = index[to];
1427 // Update piece counts
1428 pieceCount[us][promotion]--;
1429 pieceCount[us][PAWN]++;
1431 capture = u.capture;
1435 assert(capture != KING);
1437 // Insert captured piece:
1438 set_bit(&(byColorBB[them]), to);
1439 set_bit(&(byTypeBB[capture]), to);
1440 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1441 board[to] = piece_of_color_and_type(them, capture);
1443 // Update material. Because the move is a promotion move, we know
1444 // that the captured piece cannot be a pawn.
1445 assert(capture != PAWN);
1446 npMaterial[them] += piece_value_midgame(capture);
1448 // Update piece list
1449 pieceList[them][capture][pieceCount[them][capture]] = to;
1450 index[to] = pieceCount[them][capture];
1452 // Update piece count
1453 pieceCount[them][capture]++;
1459 /// Position::undo_ep_move() is a private method used to unmake an en passant
1460 /// capture. It is called from the main Position::undo_move function. Because
1461 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1462 /// object from which to retrieve the captured piece.
1464 void Position::undo_ep_move(Move m) {
1466 assert(move_is_ok(m));
1467 assert(move_is_ep(m));
1469 // When we have arrived here, some work has already been done by
1470 // Position::undo_move. In particular, the side to move has been switched,
1471 // so the code below is correct.
1472 Color us = side_to_move();
1473 Color them = opposite_color(us);
1474 Square from = move_from(m);
1475 Square to = move_to(m);
1476 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1478 assert(to == ep_square());
1479 assert(relative_rank(us, to) == RANK_6);
1480 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1481 assert(piece_on(from) == EMPTY);
1482 assert(piece_on(capsq) == EMPTY);
1484 // Replace captured piece
1485 set_bit(&(byColorBB[them]), capsq);
1486 set_bit(&(byTypeBB[PAWN]), capsq);
1487 set_bit(&(byTypeBB[0]), capsq);
1488 board[capsq] = piece_of_color_and_type(them, PAWN);
1490 // Remove moving piece from destination square
1491 clear_bit(&(byColorBB[us]), to);
1492 clear_bit(&(byTypeBB[PAWN]), to);
1493 clear_bit(&(byTypeBB[0]), to);
1496 // Replace moving piece at source square
1497 set_bit(&(byColorBB[us]), from);
1498 set_bit(&(byTypeBB[PAWN]), from);
1499 set_bit(&(byTypeBB[0]), from);
1500 board[from] = piece_of_color_and_type(us, PAWN);
1502 // Update piece list:
1503 pieceList[us][PAWN][index[to]] = from;
1504 index[from] = index[to];
1505 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1506 index[capsq] = pieceCount[them][PAWN];
1508 // Update piece count:
1509 pieceCount[them][PAWN]++;
1513 /// Position::do_null_move makes() a "null move": It switches the side to move
1514 /// and updates the hash key without executing any move on the board.
1516 void Position::do_null_move(UndoInfo& u) {
1519 assert(!is_check());
1521 // Back up the information necessary to undo the null move to the supplied
1522 // UndoInfo object. In the case of a null move, the only thing we need to
1523 // remember is the last move made and the en passant square.
1524 u.lastMove = lastMove;
1525 u.epSquare = epSquare;
1527 // Save the current key to the history[] array, in order to be able to
1528 // detect repetition draws.
1529 history[gamePly] = key;
1531 // Update the necessary information
1532 sideToMove = opposite_color(sideToMove);
1533 if (epSquare != SQ_NONE)
1534 key ^= zobEp[epSquare];
1539 key ^= zobSideToMove;
1541 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1542 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1548 /// Position::undo_null_move() unmakes a "null move".
1550 void Position::undo_null_move(const UndoInfo &u) {
1553 assert(!is_check());
1555 // Restore information from the supplied UndoInfo object:
1556 lastMove = u.lastMove;
1557 epSquare = u.epSquare;
1558 if (epSquare != SQ_NONE)
1559 key ^= zobEp[epSquare];
1561 // Update the necessary information.
1562 sideToMove = opposite_color(sideToMove);
1565 key ^= zobSideToMove;
1567 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1568 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1574 /// Position::see() is a static exchange evaluator: It tries to estimate the
1575 /// material gain or loss resulting from a move. There are three versions of
1576 /// this function: One which takes a destination square as input, one takes a
1577 /// move, and one which takes a 'from' and a 'to' square. The function does
1578 /// not yet understand promotions captures.
1580 int Position::see(Square to) const {
1582 assert(square_is_ok(to));
1583 return see(SQ_NONE, to);
1586 int Position::see(Move m) const {
1588 assert(move_is_ok(m));
1589 return see(move_from(m), move_to(m));
1592 int Position::see(Square from, Square to) const {
1595 static const int seeValues[18] = {
1596 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1597 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1598 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1599 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1603 Bitboard attackers, occ, b;
1605 assert(square_is_ok(from) || from == SQ_NONE);
1606 assert(square_is_ok(to));
1608 // Initialize colors
1609 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1610 Color them = opposite_color(us);
1612 // Initialize pieces
1613 Piece piece = piece_on(from);
1614 Piece capture = piece_on(to);
1616 // Find all attackers to the destination square, with the moving piece
1617 // removed, but possibly an X-ray attacker added behind it.
1618 occ = occupied_squares();
1620 // Handle en passant moves
1621 if (epSquare == to && type_of_piece_on(from) == PAWN)
1623 assert(capture == EMPTY);
1625 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1626 capture = piece_on(capQq);
1628 assert(type_of_piece_on(capQq) == PAWN);
1630 // Remove the captured pawn
1631 clear_bit(&occ, capQq);
1636 clear_bit(&occ, from);
1637 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1638 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1639 | (piece_attacks<KNIGHT>(to) & knights())
1640 | (piece_attacks<KING>(to) & kings())
1641 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1642 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1644 if (from != SQ_NONE)
1647 // If we don't have any attacker we are finished
1648 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1651 // Locate the least valuable attacker to the destination square
1652 // and use it to initialize from square.
1654 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1657 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1658 piece = piece_on(from);
1661 // If the opponent has no attackers we are finished
1662 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1663 return seeValues[capture];
1665 attackers &= occ; // Remove the moving piece
1667 // The destination square is defended, which makes things rather more
1668 // difficult to compute. We proceed by building up a "swap list" containing
1669 // the material gain or loss at each stop in a sequence of captures to the
1670 // destination square, where the sides alternately capture, and always
1671 // capture with the least valuable piece. After each capture, we look for
1672 // new X-ray attacks from behind the capturing piece.
1673 int lastCapturingPieceValue = seeValues[piece];
1674 int swapList[32], n = 1;
1678 swapList[0] = seeValues[capture];
1681 // Locate the least valuable attacker for the side to move. The loop
1682 // below looks like it is potentially infinite, but it isn't. We know
1683 // that the side to move still has at least one attacker left.
1684 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1687 // Remove the attacker we just found from the 'attackers' bitboard,
1688 // and scan for new X-ray attacks behind the attacker.
1689 b = attackers & pieces_of_color_and_type(c, pt);
1691 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1692 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1696 // Add the new entry to the swap list
1698 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1701 // Remember the value of the capturing piece, and change the side to move
1702 // before beginning the next iteration
1703 lastCapturingPieceValue = seeValues[pt];
1704 c = opposite_color(c);
1706 // Stop after a king capture
1707 if (pt == KING && (attackers & pieces_of_color(c)))
1710 swapList[n++] = 100;
1713 } while (attackers & pieces_of_color(c));
1715 // Having built the swap list, we negamax through it to find the best
1716 // achievable score from the point of view of the side to move
1718 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1724 /// Position::clear() erases the position object to a pristine state, with an
1725 /// empty board, white to move, and no castling rights.
1727 void Position::clear() {
1729 for (int i = 0; i < 64; i++)
1735 for (int i = 0; i < 2; i++)
1736 byColorBB[i] = EmptyBoardBB;
1738 for (int i = 0; i < 7; i++)
1740 byTypeBB[i] = EmptyBoardBB;
1741 pieceCount[0][i] = pieceCount[1][i] = 0;
1742 for (int j = 0; j < 8; j++)
1743 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1746 checkersBB = EmptyBoardBB;
1747 for (Color c = WHITE; c <= BLACK; c++)
1748 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
1750 lastMove = MOVE_NONE;
1753 castleRights = NO_CASTLES;
1754 initialKFile = FILE_E;
1755 initialKRFile = FILE_H;
1756 initialQRFile = FILE_A;
1763 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1764 /// UCI interface code, whenever a non-reversible move is made in a
1765 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1766 /// for the program to handle games of arbitrary length, as long as the GUI
1767 /// handles draws by the 50 move rule correctly.
1769 void Position::reset_game_ply() {
1775 /// Position::put_piece() puts a piece on the given square of the board,
1776 /// updating the board array, bitboards, and piece counts.
1778 void Position::put_piece(Piece p, Square s) {
1780 Color c = color_of_piece(p);
1781 PieceType pt = type_of_piece(p);
1784 index[s] = pieceCount[c][pt];
1785 pieceList[c][pt][index[s]] = s;
1787 set_bit(&(byTypeBB[pt]), s);
1788 set_bit(&(byColorBB[c]), s);
1789 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1791 pieceCount[c][pt]++;
1798 /// Position::allow_oo() gives the given side the right to castle kingside.
1799 /// Used when setting castling rights during parsing of FEN strings.
1801 void Position::allow_oo(Color c) {
1803 castleRights |= (1 + int(c));
1807 /// Position::allow_ooo() gives the given side the right to castle queenside.
1808 /// Used when setting castling rights during parsing of FEN strings.
1810 void Position::allow_ooo(Color c) {
1812 castleRights |= (4 + 4*int(c));
1816 /// Position::compute_key() computes the hash key of the position. The hash
1817 /// key is usually updated incrementally as moves are made and unmade, the
1818 /// compute_key() function is only used when a new position is set up, and
1819 /// to verify the correctness of the hash key when running in debug mode.
1821 Key Position::compute_key() const {
1823 Key result = Key(0ULL);
1825 for (Square s = SQ_A1; s <= SQ_H8; s++)
1826 if (square_is_occupied(s))
1827 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1829 if (ep_square() != SQ_NONE)
1830 result ^= zobEp[ep_square()];
1832 result ^= zobCastle[castleRights];
1833 if (side_to_move() == BLACK)
1834 result ^= zobSideToMove;
1840 /// Position::compute_pawn_key() computes the hash key of the position. The
1841 /// hash key is usually updated incrementally as moves are made and unmade,
1842 /// the compute_pawn_key() function is only used when a new position is set
1843 /// up, and to verify the correctness of the pawn hash key when running in
1846 Key Position::compute_pawn_key() const {
1848 Key result = Key(0ULL);
1852 for (Color c = WHITE; c <= BLACK; c++)
1857 s = pop_1st_bit(&b);
1858 result ^= zobrist[c][PAWN][s];
1865 /// Position::compute_material_key() computes the hash key of the position.
1866 /// The hash key is usually updated incrementally as moves are made and unmade,
1867 /// the compute_material_key() function is only used when a new position is set
1868 /// up, and to verify the correctness of the material hash key when running in
1871 Key Position::compute_material_key() const {
1873 Key result = Key(0ULL);
1874 for (Color c = WHITE; c <= BLACK; c++)
1875 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1877 int count = piece_count(c, pt);
1878 for (int i = 0; i <= count; i++)
1879 result ^= zobMaterial[c][pt][i];
1885 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1886 /// incremental scores for the middle game and the endgame. These functions
1887 /// are used to initialize the incremental scores when a new position is set
1888 /// up, and to verify that the scores are correctly updated by do_move
1889 /// and undo_move when the program is running in debug mode.
1891 Value Position::compute_mg_value() const {
1893 Value result = Value(0);
1897 for (Color c = WHITE; c <= BLACK; c++)
1898 for (PieceType pt = PAWN; pt <= KING; pt++)
1900 b = pieces_of_color_and_type(c, pt);
1903 s = pop_1st_bit(&b);
1904 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1905 result += mg_pst(c, pt, s);
1908 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1912 Value Position::compute_eg_value() const {
1914 Value result = Value(0);
1918 for (Color c = WHITE; c <= BLACK; c++)
1919 for (PieceType pt = PAWN; pt <= KING; pt++)
1921 b = pieces_of_color_and_type(c, pt);
1924 s = pop_1st_bit(&b);
1925 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1926 result += eg_pst(c, pt, s);
1929 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1934 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1935 /// game material score for the given side. Material scores are updated
1936 /// incrementally during the search, this function is only used while
1937 /// initializing a new Position object.
1939 Value Position::compute_non_pawn_material(Color c) const {
1941 Value result = Value(0);
1944 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1946 Bitboard b = pieces_of_color_and_type(c, pt);
1949 s = pop_1st_bit(&b);
1950 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1951 result += piece_value_midgame(pt);
1958 /// Position::is_mate() returns true or false depending on whether the
1959 /// side to move is checkmated. Note that this function is currently very
1960 /// slow, and shouldn't be used frequently inside the search.
1962 bool Position::is_mate() const {
1966 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1967 return mp.get_next_move() == MOVE_NONE;
1973 /// Position::is_draw() tests whether the position is drawn by material,
1974 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1975 /// must be done by the search.
1977 bool Position::is_draw() const {
1979 // Draw by material?
1981 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1984 // Draw by the 50 moves rule?
1985 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1988 // Draw by repetition?
1989 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1990 if (history[gamePly - i] == key)
1997 /// Position::has_mate_threat() tests whether a given color has a mate in one
1998 /// from the current position. This function is quite slow, but it doesn't
1999 /// matter, because it is currently only called from PV nodes, which are rare.
2001 bool Position::has_mate_threat(Color c) {
2004 Color stm = side_to_move();
2006 // The following lines are useless and silly, but prevents gcc from
2007 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
2008 // be used uninitialized.
2009 u1.lastMove = lastMove;
2010 u1.epSquare = epSquare;
2015 // If the input color is not equal to the side to move, do a null move
2019 MoveStack mlist[120];
2021 bool result = false;
2023 // Generate legal moves
2024 count = generate_legal_moves(*this, mlist);
2026 // Loop through the moves, and see if one of them is mate
2027 for (int i = 0; i < count; i++)
2029 do_move(mlist[i].move, u2);
2033 undo_move(mlist[i].move, u2);
2036 // Undo null move, if necessary
2044 /// Position::init_zobrist() is a static member function which initializes the
2045 /// various arrays used to compute hash keys.
2047 void Position::init_zobrist() {
2049 for (int i = 0; i < 2; i++)
2050 for (int j = 0; j < 8; j++)
2051 for (int k = 0; k < 64; k++)
2052 zobrist[i][j][k] = Key(genrand_int64());
2054 for (int i = 0; i < 64; i++)
2055 zobEp[i] = Key(genrand_int64());
2057 for (int i = 0; i < 16; i++)
2058 zobCastle[i] = genrand_int64();
2060 zobSideToMove = genrand_int64();
2062 for (int i = 0; i < 2; i++)
2063 for (int j = 0; j < 8; j++)
2064 for (int k = 0; k < 16; k++)
2065 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2067 for (int i = 0; i < 16; i++)
2068 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2072 /// Position::init_piece_square_tables() initializes the piece square tables.
2073 /// This is a two-step operation: First, the white halves of the tables are
2074 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2075 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2076 /// Second, the black halves of the tables are initialized by mirroring
2077 /// and changing the sign of the corresponding white scores.
2079 void Position::init_piece_square_tables() {
2081 int r = get_option_value_int("Randomness"), i;
2082 for (Square s = SQ_A1; s <= SQ_H8; s++)
2083 for (Piece p = WP; p <= WK; p++)
2085 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2086 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2087 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2090 for (Square s = SQ_A1; s <= SQ_H8; s++)
2091 for (Piece p = BP; p <= BK; p++)
2093 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2094 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2099 /// Position::flipped_copy() makes a copy of the input position, but with
2100 /// the white and black sides reversed. This is only useful for debugging,
2101 /// especially for finding evaluation symmetry bugs.
2103 void Position::flipped_copy(const Position &pos) {
2105 assert(pos.is_ok());
2110 for (Square s = SQ_A1; s <= SQ_H8; s++)
2111 if (!pos.square_is_empty(s))
2112 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2115 sideToMove = opposite_color(pos.side_to_move());
2118 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2119 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2120 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2121 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2123 initialKFile = pos.initialKFile;
2124 initialKRFile = pos.initialKRFile;
2125 initialQRFile = pos.initialQRFile;
2127 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2128 castleRightsMask[sq] = ALL_CASTLES;
2130 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2131 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2132 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2133 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2134 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2135 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2137 // En passant square
2138 if (pos.epSquare != SQ_NONE)
2139 epSquare = flip_square(pos.epSquare);
2145 key = compute_key();
2146 pawnKey = compute_pawn_key();
2147 materialKey = compute_material_key();
2149 // Incremental scores
2150 mgValue = compute_mg_value();
2151 egValue = compute_eg_value();
2154 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2155 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2161 /// Position::is_ok() performs some consitency checks for the position object.
2162 /// This is meant to be helpful when debugging.
2164 bool Position::is_ok(int* failedStep) const {
2166 // What features of the position should be verified?
2167 static const bool debugBitboards = false;
2168 static const bool debugKingCount = false;
2169 static const bool debugKingCapture = false;
2170 static const bool debugCheckerCount = false;
2171 static const bool debugKey = false;
2172 static const bool debugMaterialKey = false;
2173 static const bool debugPawnKey = false;
2174 static const bool debugIncrementalEval = false;
2175 static const bool debugNonPawnMaterial = false;
2176 static const bool debugPieceCounts = false;
2177 static const bool debugPieceList = false;
2179 if (failedStep) *failedStep = 1;
2182 if (!color_is_ok(side_to_move()))
2185 // Are the king squares in the position correct?
2186 if (failedStep) (*failedStep)++;
2187 if (piece_on(king_square(WHITE)) != WK)
2190 if (failedStep) (*failedStep)++;
2191 if (piece_on(king_square(BLACK)) != BK)
2195 if (failedStep) (*failedStep)++;
2196 if (!file_is_ok(initialKRFile))
2199 if (!file_is_ok(initialQRFile))
2202 // Do both sides have exactly one king?
2203 if (failedStep) (*failedStep)++;
2206 int kingCount[2] = {0, 0};
2207 for (Square s = SQ_A1; s <= SQ_H8; s++)
2208 if (type_of_piece_on(s) == KING)
2209 kingCount[color_of_piece_on(s)]++;
2211 if (kingCount[0] != 1 || kingCount[1] != 1)
2215 // Can the side to move capture the opponent's king?
2216 if (failedStep) (*failedStep)++;
2217 if (debugKingCapture)
2219 Color us = side_to_move();
2220 Color them = opposite_color(us);
2221 Square ksq = king_square(them);
2222 if (square_is_attacked(ksq, us))
2226 // Is there more than 2 checkers?
2227 if (failedStep) (*failedStep)++;
2228 if (debugCheckerCount && count_1s(checkersBB) > 2)
2232 if (failedStep) (*failedStep)++;
2235 // The intersection of the white and black pieces must be empty
2236 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2239 // The union of the white and black pieces must be equal to all
2241 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2244 // Separate piece type bitboards must have empty intersections
2245 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2246 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2247 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2251 // En passant square OK?
2252 if (failedStep) (*failedStep)++;
2253 if (ep_square() != SQ_NONE)
2255 // The en passant square must be on rank 6, from the point of view of the
2257 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2262 if (failedStep) (*failedStep)++;
2263 if (debugKey && key != compute_key())
2266 // Pawn hash key OK?
2267 if (failedStep) (*failedStep)++;
2268 if (debugPawnKey && pawnKey != compute_pawn_key())
2271 // Material hash key OK?
2272 if (failedStep) (*failedStep)++;
2273 if (debugMaterialKey && materialKey != compute_material_key())
2276 // Incremental eval OK?
2277 if (failedStep) (*failedStep)++;
2278 if (debugIncrementalEval)
2280 if (mgValue != compute_mg_value())
2283 if (egValue != compute_eg_value())
2287 // Non-pawn material OK?
2288 if (failedStep) (*failedStep)++;
2289 if (debugNonPawnMaterial)
2291 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2294 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2299 if (failedStep) (*failedStep)++;
2300 if (debugPieceCounts)
2301 for (Color c = WHITE; c <= BLACK; c++)
2302 for (PieceType pt = PAWN; pt <= KING; pt++)
2303 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2306 if (failedStep) (*failedStep)++;
2309 for(Color c = WHITE; c <= BLACK; c++)
2310 for(PieceType pt = PAWN; pt <= KING; pt++)
2311 for(int i = 0; i < pieceCount[c][pt]; i++)
2313 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2316 if (index[piece_list(c, pt, i)] != i)
2320 if (failedStep) *failedStep = 0;