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/>.
34 #include "ucioption.h"
41 int Position::castleRightsMask[64];
43 Key Position::zobrist[2][8][64];
44 Key Position::zobEp[64];
45 Key Position::zobCastle[16];
46 Key Position::zobMaterial[2][8][16];
47 Key Position::zobSideToMove;
49 Value Position::MgPieceSquareTable[16][64];
50 Value Position::EgPieceSquareTable[16][64];
59 Position::Position(const Position &pos) {
63 Position::Position(const std::string &fen) {
68 /// Position::from_fen() initializes the position object with the given FEN
69 /// string. This function is not very robust - make sure that input FENs are
70 /// correct (this is assumed to be the responsibility of the GUI).
72 void Position::from_fen(const std::string &fen) {
74 static const std::string pieceLetters = "KQRBNPkqrbnp";
75 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
83 for ( ; fen[i] != ' '; i++)
87 // Skip the given number of files
88 file += (fen[i] - '1' + 1);
91 else if (fen[i] == '/')
97 size_t idx = pieceLetters.find(fen[i]);
98 if (idx == std::string::npos)
100 std::cout << "Error in FEN at character " << i << std::endl;
103 Square square = make_square(file, rank);
104 put_piece(pieces[idx], square);
110 if (fen[i] != 'w' && fen[i] != 'b')
112 std::cout << "Error in FEN at character " << i << std::endl;
115 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
121 std::cout << "Error in FEN at character " << i << std::endl;
126 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
130 else if(fen[i] == 'K') allow_oo(WHITE);
131 else if(fen[i] == 'Q') allow_ooo(WHITE);
132 else if(fen[i] == 'k') allow_oo(BLACK);
133 else if(fen[i] == 'q') allow_ooo(BLACK);
134 else if(fen[i] >= 'A' && fen[i] <= 'H') {
135 File rookFile, kingFile = FILE_NONE;
136 for(Square square = SQ_B1; square <= SQ_G1; square++)
137 if(piece_on(square) == WK)
138 kingFile = square_file(square);
139 if(kingFile == FILE_NONE) {
140 std::cout << "Error in FEN at character " << i << std::endl;
143 initialKFile = kingFile;
144 rookFile = File(fen[i] - 'A') + FILE_A;
145 if(rookFile < initialKFile) {
147 initialQRFile = rookFile;
151 initialKRFile = rookFile;
154 else if(fen[i] >= 'a' && fen[i] <= 'h') {
155 File rookFile, kingFile = FILE_NONE;
156 for(Square square = SQ_B8; square <= SQ_G8; square++)
157 if(piece_on(square) == BK)
158 kingFile = square_file(square);
159 if(kingFile == FILE_NONE) {
160 std::cout << "Error in FEN at character " << i << std::endl;
163 initialKFile = kingFile;
164 rookFile = File(fen[i] - 'a') + FILE_A;
165 if(rookFile < initialKFile) {
167 initialQRFile = rookFile;
171 initialKRFile = rookFile;
175 std::cout << "Error in FEN at character " << i << std::endl;
182 while (fen[i] == ' ')
186 if ( i < fen.length() - 2
187 && (fen[i] >= 'a' && fen[i] <= 'h')
188 && (fen[i+1] == '3' || fen[i+1] == '6'))
189 epSquare = square_from_string(fen.substr(i, 2));
191 // Various initialisation
192 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
193 castleRightsMask[sq] = ALL_CASTLES;
195 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
196 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
197 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
198 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
199 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
200 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
205 pawnKey = compute_pawn_key();
206 materialKey = compute_material_key();
207 mgValue = compute_mg_value();
208 egValue = compute_eg_value();
209 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
210 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
214 /// Position::to_fen() converts the position object to a FEN string. This is
215 /// probably only useful for debugging.
217 const std::string Position::to_fen() const {
219 static const std::string pieceLetters = " PNBRQK pnbrqk";
223 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
226 for (File file = FILE_A; file <= FILE_H; file++)
228 Square sq = make_square(file, rank);
229 if (!square_is_occupied(sq))
235 fen += (char)skip + '0';
238 fen += pieceLetters[piece_on(sq)];
241 fen += (char)skip + '0';
243 fen += (rank > RANK_1 ? '/' : ' ');
245 fen += (sideToMove == WHITE ? 'w' : 'b') + ' ';
246 if (castleRights != NO_CASTLES)
248 if (can_castle_kingside(WHITE)) fen += 'K';
249 if (can_castle_queenside(WHITE)) fen += 'Q';
250 if (can_castle_kingside(BLACK)) fen += 'k';
251 if (can_castle_queenside(BLACK)) fen += 'q';
256 if (ep_square() != SQ_NONE)
257 fen += square_to_string(ep_square());
265 /// Position::print() prints an ASCII representation of the position to
266 /// the standard output.
268 void Position::print() const {
269 char pieceStrings[][8] =
270 {"| ? ", "| P ", "| N ", "| B ", "| R ", "| Q ", "| K ", "| ? ",
271 "| ? ", "|=P=", "|=N=", "|=B=", "|=R=", "|=Q=", "|=K="
274 for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
275 std::cout << "+---+---+---+---+---+---+---+---+\n";
276 for(File file = FILE_A; file <= FILE_H; file++) {
277 Square sq = make_square(file, rank);
278 Piece piece = piece_on(sq);
280 std::cout << ((square_color(sq) == WHITE)? "| " : "| . ");
282 std::cout << pieceStrings[piece];
286 std::cout << "+---+---+---+---+---+---+---+---+\n";
287 std::cout << to_fen() << std::endl;
288 std::cout << key << std::endl;
292 /// Position::copy() creates a copy of the input position.
294 void Position::copy(const Position &pos) {
296 memcpy(this, &pos, sizeof(Position));
300 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
301 /// king) pieces for the given color.
302 Bitboard Position::pinned_pieces(Color c) const {
304 Square ksq = king_square(c);
305 return hidden_checks<ROOK, true>(c, ksq) | hidden_checks<BISHOP, true>(c, ksq);
309 /// Position:discovered_check_candidates() returns a bitboard containing all
310 /// pieces for the given side which are candidates for giving a discovered
311 /// check. The code is almost the same as the function for finding pinned
314 Bitboard Position::discovered_check_candidates(Color c) const {
316 Square ksq = king_square(opposite_color(c));
317 return hidden_checks<ROOK, false>(c, ksq) | hidden_checks<BISHOP, false>(c, ksq);
321 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
322 /// king) pieces for the given color and for the given pinner type. Or, when
323 /// template parameter FindPinned is false, the pinned pieces of opposite color
324 /// that are, indeed, the pieces candidate for a discovery check.
325 template<PieceType Piece, bool FindPinned>
326 Bitboard Position::hidden_checks(Color c, Square ksq) const {
329 Bitboard sliders, result = EmptyBoardBB;
331 if (Piece == ROOK) // Resolved at compile time
332 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
334 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
336 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
338 // King blockers are candidate pinned pieces
339 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
341 // Pinners are sliders, not checkers, that give check when
342 // candidate pinned are removed.
343 Bitboard pinners = (FindPinned ? sliders & ~checkersBB : sliders);
346 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
348 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
350 // Finally for each pinner find the corresponding pinned piece (if same color of king)
351 // or discovery checker (if opposite color) among the candidates.
354 s = pop_1st_bit(&pinners);
355 result |= (squares_between(s, ksq) & candidate_pinned);
362 /// Position::square_is_attacked() checks whether the given side attacks the
365 bool Position::square_is_attacked(Square s, Color c) const {
367 return (pawn_attacks(opposite_color(c), s) & pawns(c))
368 || (piece_attacks<KNIGHT>(s) & knights(c))
369 || (piece_attacks<KING>(s) & kings(c))
370 || (piece_attacks<ROOK>(s) & rooks_and_queens(c))
371 || (piece_attacks<BISHOP>(s) & bishops_and_queens(c));
375 /// Position::attacks_to() computes a bitboard containing all pieces which
376 /// attacks a given square. There are two versions of this function: One
377 /// which finds attackers of both colors, and one which only finds the
378 /// attackers for one side.
380 Bitboard Position::attacks_to(Square s) const {
382 return (pawn_attacks(BLACK, s) & pawns(WHITE))
383 | (pawn_attacks(WHITE, s) & pawns(BLACK))
384 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
385 | (piece_attacks<ROOK>(s) & rooks_and_queens())
386 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
387 | (piece_attacks<KING>(s) & pieces_of_type(KING));
390 Bitboard Position::attacks_to(Square s, Color c) const {
392 return attacks_to(s) & pieces_of_color(c);
396 /// Position::piece_attacks_square() tests whether the piece on square f
397 /// attacks square t.
399 bool Position::piece_attacks_square(Square f, Square t) const {
401 assert(square_is_ok(f));
402 assert(square_is_ok(t));
406 case WP: return pawn_attacks_square(WHITE, f, t);
407 case BP: return pawn_attacks_square(BLACK, f, t);
408 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
409 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
410 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
411 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
412 case WK: case BK: return piece_attacks_square<KING>(f, t);
419 /// Position::move_attacks_square() tests whether a move from the current
420 /// position attacks a given square. Only attacks by the moving piece are
421 /// considered; the function does not handle X-ray attacks.
423 bool Position::move_attacks_square(Move m, Square s) const {
425 assert(move_is_ok(m));
426 assert(square_is_ok(s));
428 Square f = move_from(m), t = move_to(m);
430 assert(square_is_occupied(f));
434 case WP: return pawn_attacks_square(WHITE, t, s);
435 case BP: return pawn_attacks_square(BLACK, t, s);
436 case WN: case BN: return piece_attacks_square<KNIGHT>(t, s);
437 case WB: case BB: return piece_attacks_square<BISHOP>(t, s);
438 case WR: case BR: return piece_attacks_square<ROOK>(t, s);
439 case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s);
440 case WK: case BK: return piece_attacks_square<KING>(t, s);
447 /// Position::find_checkers() computes the checkersBB bitboard, which
448 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
449 /// currently works by calling Position::attacks_to, which is probably
450 /// inefficient. Consider rewriting this function to use the last move
451 /// played, like in non-bitboard versions of Glaurung.
453 void Position::find_checkers() {
455 Color us = side_to_move();
456 checkersBB = attacks_to(king_square(us), opposite_color(us));
460 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal.
461 /// There are two versions of this function: One which takes only a
462 /// move as input, and one which takes a move and a bitboard of pinned
463 /// pieces. The latter function is faster, and should always be preferred
464 /// when a pinned piece bitboard has already been computed.
466 bool Position::pl_move_is_legal(Move m) const {
468 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
471 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
474 assert(move_is_ok(m));
475 assert(pinned == pinned_pieces(side_to_move()));
477 // If we're in check, all pseudo-legal moves are legal, because our
478 // check evasion generator only generates true legal moves.
482 // Castling moves are checked for legality during move generation.
483 if (move_is_castle(m))
486 Color us = side_to_move();
487 Color them = opposite_color(us);
488 Square from = move_from(m);
489 Square ksq = king_square(us);
491 assert(color_of_piece_on(from) == us);
492 assert(piece_on(ksq) == king_of_color(us));
494 // En passant captures are a tricky special case. Because they are
495 // rather uncommon, we do it simply by testing whether the king is attacked
496 // after the move is made
499 Square to = move_to(m);
500 Square capsq = make_square(square_file(to), square_rank(from));
501 Bitboard b = occupied_squares();
503 assert(to == ep_square());
504 assert(piece_on(from) == pawn_of_color(us));
505 assert(piece_on(capsq) == pawn_of_color(them));
506 assert(piece_on(to) == EMPTY);
509 clear_bit(&b, capsq);
512 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
513 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
516 // If the moving piece is a king, check whether the destination
517 // square is attacked by the opponent.
519 return !(square_is_attacked(move_to(m), them));
521 // A non-king move is legal if and only if it is not pinned or it
522 // is moving along the ray towards or away from the king.
523 return ( !bit_is_set(pinned, from)
524 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
528 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
529 /// There are two versions of this function: One which takes only a move as
530 /// input, and one which takes a move and a bitboard of discovered check
531 /// candidates. The latter function is faster, and should always be preferred
532 /// when a discovered check candidates bitboard has already been computed.
534 bool Position::move_is_check(Move m) const {
536 Bitboard dc = discovered_check_candidates(side_to_move());
537 return move_is_check(m, dc);
540 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
543 assert(move_is_ok(m));
544 assert(dcCandidates == discovered_check_candidates(side_to_move()));
546 Color us = side_to_move();
547 Color them = opposite_color(us);
548 Square from = move_from(m);
549 Square to = move_to(m);
550 Square ksq = king_square(them);
552 assert(color_of_piece_on(from) == us);
553 assert(piece_on(ksq) == king_of_color(them));
555 // Proceed according to the type of the moving piece
556 switch (type_of_piece_on(from))
560 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
563 if ( bit_is_set(dcCandidates, from) // Discovered check?
564 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
567 if (move_promotion(m)) // Promotion with check?
569 Bitboard b = occupied_squares();
572 switch (move_promotion(m))
575 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
577 return bit_is_set(bishop_attacks_bb(to, b), ksq);
579 return bit_is_set(rook_attacks_bb(to, b), ksq);
581 return bit_is_set(queen_attacks_bb(to, b), ksq);
586 // En passant capture with check? We have already handled the case
587 // of direct checks and ordinary discovered check, the only case we
588 // need to handle is the unusual case of a discovered check through the
590 else if (move_is_ep(m))
592 Square capsq = make_square(square_file(to), square_rank(from));
593 Bitboard b = occupied_squares();
595 clear_bit(&b, capsq);
597 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
598 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
603 return bit_is_set(dcCandidates, from) // Discovered check?
604 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
607 return bit_is_set(dcCandidates, from) // Discovered check?
608 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
611 return bit_is_set(dcCandidates, from) // Discovered check?
612 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
615 // Discovered checks are impossible!
616 assert(!bit_is_set(dcCandidates, from));
617 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
621 if ( bit_is_set(dcCandidates, from)
622 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
625 // Castling with check?
626 if (move_is_castle(m))
628 Square kfrom, kto, rfrom, rto;
629 Bitboard b = occupied_squares();
635 kto = relative_square(us, SQ_G1);
636 rto = relative_square(us, SQ_F1);
638 kto = relative_square(us, SQ_C1);
639 rto = relative_square(us, SQ_D1);
641 clear_bit(&b, kfrom);
642 clear_bit(&b, rfrom);
645 return bit_is_set(rook_attacks_bb(rto, b), ksq);
649 default: // NO_PIECE_TYPE
657 /// Position::move_is_capture() tests whether a move from the current
658 /// position is a capture.
660 bool Position::move_is_capture(Move m) const {
662 return ( !square_is_empty(move_to(m))
663 && (color_of_piece_on(move_to(m)) == opposite_color(side_to_move()))
669 /// Position::backup() is called when making a move. All information
670 /// necessary to restore the position when the move is later unmade
671 /// is saved to an UndoInfo object. The function Position::restore
672 /// does the reverse operation: When one does a backup followed by
673 /// a restore with the same UndoInfo object, the position is restored
674 /// to the state before backup was called.
676 void Position::backup(UndoInfo& u) const {
678 u.castleRights = castleRights;
679 u.epSquare = epSquare;
680 u.checkersBB = checkersBB;
683 u.materialKey = materialKey;
685 u.lastMove = lastMove;
688 u.capture = NO_PIECE_TYPE;
692 /// Position::restore() is called when unmaking a move. It copies back
693 /// the information backed up during a previous call to Position::backup.
695 void Position::restore(const UndoInfo& u) {
697 castleRights = u.castleRights;
698 epSquare = u.epSquare;
699 checkersBB = u.checkersBB;
702 materialKey = u.materialKey;
704 lastMove = u.lastMove;
707 // u.capture is restored in undo_move()
710 /// Position::do_move() makes a move, and backs up all information necessary
711 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
712 /// Pseudo-legal moves should be filtered out before this function is called.
713 /// There are two versions of this function, one which takes only the move and
714 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
715 /// discovered check candidates. The second version is faster, because knowing
716 /// the discovered check candidates makes it easier to update the checkersBB
717 /// member variable in the position object.
719 void Position::do_move(Move m, UndoInfo& u) {
721 do_move(m, u, discovered_check_candidates(side_to_move()));
724 void Position::do_move(Move m, UndoInfo& u, Bitboard dcCandidates) {
727 assert(move_is_ok(m));
729 // Back up the necessary information to our UndoInfo object (except the
730 // captured piece, which is taken care of later.
733 // Save the current key to the history[] array, in order to be able to
734 // detect repetition draws.
735 history[gamePly] = key;
737 // Increment the 50 moves rule draw counter. Resetting it to zero in the
738 // case of non-reversible moves is taken care of later.
741 if (move_is_castle(m))
743 else if (move_promotion(m))
744 do_promotion_move(m, u);
745 else if (move_is_ep(m))
749 Color us = side_to_move();
750 Color them = opposite_color(us);
751 Square from = move_from(m);
752 Square to = move_to(m);
754 assert(color_of_piece_on(from) == us);
755 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
757 PieceType piece = type_of_piece_on(from);
758 PieceType capture = type_of_piece_on(to);
763 do_capture_move(m, capture, them, to);
767 clear_bit(&(byColorBB[us]), from);
768 clear_bit(&(byTypeBB[piece]), from);
769 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
770 set_bit(&(byColorBB[us]), to);
771 set_bit(&(byTypeBB[piece]), to);
772 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
773 board[to] = board[from];
777 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
779 // Update incremental scores
780 mgValue -= mg_pst(us, piece, from);
781 mgValue += mg_pst(us, piece, to);
782 egValue -= eg_pst(us, piece, from);
783 egValue += eg_pst(us, piece, to);
785 // If the moving piece was a king, update the king square
789 // If the move was a double pawn push, set the en passant square.
790 // This code is a bit ugly right now, and should be cleaned up later.
792 if (epSquare != SQ_NONE)
794 key ^= zobEp[epSquare];
799 if (abs(int(to) - int(from)) == 16)
802 && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
804 && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
806 epSquare = Square((int(from) + int(to)) / 2);
807 key ^= zobEp[epSquare];
810 // Reset rule 50 draw counter
813 // Update pawn hash key
814 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
816 // Update piece lists
817 pieceList[us][piece][index[from]] = to;
818 index[to] = index[from];
820 // Update castle rights
821 key ^= zobCastle[castleRights];
822 castleRights &= castleRightsMask[from];
823 castleRights &= castleRightsMask[to];
824 key ^= zobCastle[castleRights];
826 // Update checkers bitboard
827 checkersBB = EmptyBoardBB;
828 Square ksq = king_square(them);
832 if (bit_is_set(pawn_attacks(them, ksq), to))
833 set_bit(&checkersBB, to);
835 if (bit_is_set(dcCandidates, from))
836 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
837 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
841 if (bit_is_set(piece_attacks<KNIGHT>(ksq), to))
842 set_bit(&checkersBB, to);
844 if (bit_is_set(dcCandidates, from))
845 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
846 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
850 if (bit_is_set(piece_attacks<BISHOP>(ksq), to))
851 set_bit(&checkersBB, to);
853 if (bit_is_set(dcCandidates, from))
854 checkersBB |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(us));
858 if (bit_is_set(piece_attacks<ROOK>(ksq), to))
859 set_bit(&checkersBB, to);
861 if (bit_is_set(dcCandidates, from))
862 checkersBB |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us));
866 if (bit_is_set(piece_attacks<QUEEN>(ksq), to))
867 set_bit(&checkersBB, to);
871 if (bit_is_set(dcCandidates, from))
872 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
873 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
883 key ^= zobSideToMove;
884 sideToMove = opposite_color(sideToMove);
887 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
888 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
894 /// Position::do_capture_move() is a private method used to update captured
895 /// piece info. It is called from the main Position::do_move function.
897 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
899 assert(capture != KING);
901 // Remove captured piece
902 clear_bit(&(byColorBB[them]), to);
903 clear_bit(&(byTypeBB[capture]), to);
906 key ^= zobrist[them][capture][to];
908 // If the captured piece was a pawn, update pawn hash key
910 pawnKey ^= zobrist[them][PAWN][to];
912 // Update incremental scores
913 mgValue -= mg_pst(them, capture, to);
914 egValue -= eg_pst(them, capture, to);
916 assert(!move_promotion(m) || capture != PAWN);
920 npMaterial[them] -= piece_value_midgame(capture);
922 // Update material hash key
923 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
925 // Update piece count
926 pieceCount[them][capture]--;
929 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
930 index[pieceList[them][capture][index[to]]] = index[to];
932 // Reset rule 50 counter
937 /// Position::do_castle_move() is a private method used to make a castling
938 /// move. It is called from the main Position::do_move function. Note that
939 /// castling moves are encoded as "king captures friendly rook" moves, for
940 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
942 void Position::do_castle_move(Move m) {
945 assert(move_is_ok(m));
946 assert(move_is_castle(m));
948 Color us = side_to_move();
949 Color them = opposite_color(us);
951 // Find source squares for king and rook
952 Square kfrom = move_from(m);
953 Square rfrom = move_to(m); // HACK: See comment at beginning of function
956 assert(piece_on(kfrom) == king_of_color(us));
957 assert(piece_on(rfrom) == rook_of_color(us));
959 // Find destination squares for king and rook
960 if (rfrom > kfrom) // O-O
962 kto = relative_square(us, SQ_G1);
963 rto = relative_square(us, SQ_F1);
965 kto = relative_square(us, SQ_C1);
966 rto = relative_square(us, SQ_D1);
969 // Remove pieces from source squares
970 clear_bit(&(byColorBB[us]), kfrom);
971 clear_bit(&(byTypeBB[KING]), kfrom);
972 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
973 clear_bit(&(byColorBB[us]), rfrom);
974 clear_bit(&(byTypeBB[ROOK]), rfrom);
975 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
977 // Put pieces on destination squares
978 set_bit(&(byColorBB[us]), kto);
979 set_bit(&(byTypeBB[KING]), kto);
980 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
981 set_bit(&(byColorBB[us]), rto);
982 set_bit(&(byTypeBB[ROOK]), rto);
983 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
985 // Update board array
986 board[kfrom] = board[rfrom] = EMPTY;
987 board[kto] = king_of_color(us);
988 board[rto] = rook_of_color(us);
990 // Update king square
991 kingSquare[us] = kto;
993 // Update piece lists
994 pieceList[us][KING][index[kfrom]] = kto;
995 pieceList[us][ROOK][index[rfrom]] = rto;
996 int tmp = index[rfrom];
997 index[kto] = index[kfrom];
1000 // Update incremental scores
1001 mgValue -= mg_pst(us, KING, kfrom);
1002 mgValue += mg_pst(us, KING, kto);
1003 egValue -= eg_pst(us, KING, kfrom);
1004 egValue += eg_pst(us, KING, kto);
1005 mgValue -= mg_pst(us, ROOK, rfrom);
1006 mgValue += mg_pst(us, ROOK, rto);
1007 egValue -= eg_pst(us, ROOK, rfrom);
1008 egValue += eg_pst(us, ROOK, rto);
1011 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1012 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1014 // Clear en passant square
1015 if(epSquare != SQ_NONE)
1017 key ^= zobEp[epSquare];
1021 // Update castling rights
1022 key ^= zobCastle[castleRights];
1023 castleRights &= castleRightsMask[kfrom];
1024 key ^= zobCastle[castleRights];
1026 // Reset rule 50 counter
1029 // Update checkers BB
1030 checkersBB = attacks_to(king_square(them), us);
1034 /// Position::do_promotion_move() is a private method used to make a promotion
1035 /// move. It is called from the main Position::do_move function. The
1036 /// UndoInfo object, which has been initialized in Position::do_move, is
1037 /// used to store the captured piece (if any).
1039 void Position::do_promotion_move(Move m, UndoInfo &u) {
1043 PieceType capture, promotion;
1046 assert(move_is_ok(m));
1047 assert(move_promotion(m));
1049 us = side_to_move();
1050 them = opposite_color(us);
1051 from = move_from(m);
1054 assert(relative_rank(us, to) == RANK_8);
1055 assert(piece_on(from) == pawn_of_color(us));
1056 assert(color_of_piece_on(to) == them || square_is_empty(to));
1058 capture = type_of_piece_on(to);
1062 u.capture = capture;
1063 do_capture_move(m, capture, them, to);
1067 clear_bit(&(byColorBB[us]), from);
1068 clear_bit(&(byTypeBB[PAWN]), from);
1069 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1070 board[from] = EMPTY;
1072 // Insert promoted piece
1073 promotion = move_promotion(m);
1074 assert(promotion >= KNIGHT && promotion <= QUEEN);
1075 set_bit(&(byColorBB[us]), to);
1076 set_bit(&(byTypeBB[promotion]), to);
1077 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1078 board[to] = piece_of_color_and_type(us, promotion);
1081 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1083 // Update pawn hash key
1084 pawnKey ^= zobrist[us][PAWN][from];
1086 // Update material key
1087 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1088 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1090 // Update piece counts
1091 pieceCount[us][PAWN]--;
1092 pieceCount[us][promotion]++;
1094 // Update piece lists
1095 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1096 index[pieceList[us][PAWN][index[from]]] = index[from];
1097 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1098 index[to] = pieceCount[us][promotion] - 1;
1100 // Update incremental scores
1101 mgValue -= mg_pst(us, PAWN, from);
1102 mgValue += mg_pst(us, promotion, to);
1103 egValue -= eg_pst(us, PAWN, from);
1104 egValue += eg_pst(us, promotion, to);
1107 npMaterial[us] += piece_value_midgame(promotion);
1109 // Clear the en passant square
1110 if (epSquare != SQ_NONE)
1112 key ^= zobEp[epSquare];
1116 // Update castle rights
1117 key ^= zobCastle[castleRights];
1118 castleRights &= castleRightsMask[to];
1119 key ^= zobCastle[castleRights];
1121 // Reset rule 50 counter
1124 // Update checkers BB
1125 checkersBB = attacks_to(king_square(them), us);
1129 /// Position::do_ep_move() is a private method used to make an en passant
1130 /// capture. It is called from the main Position::do_move function. Because
1131 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1132 /// object in which to store the captured piece.
1134 void Position::do_ep_move(Move m) {
1137 Square from, to, capsq;
1140 assert(move_is_ok(m));
1141 assert(move_is_ep(m));
1143 us = side_to_move();
1144 them = opposite_color(us);
1145 from = move_from(m);
1147 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1149 assert(to == epSquare);
1150 assert(relative_rank(us, to) == RANK_6);
1151 assert(piece_on(to) == EMPTY);
1152 assert(piece_on(from) == pawn_of_color(us));
1153 assert(piece_on(capsq) == pawn_of_color(them));
1155 // Remove captured piece
1156 clear_bit(&(byColorBB[them]), capsq);
1157 clear_bit(&(byTypeBB[PAWN]), capsq);
1158 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1159 board[capsq] = EMPTY;
1161 // Remove moving piece from source square
1162 clear_bit(&(byColorBB[us]), from);
1163 clear_bit(&(byTypeBB[PAWN]), from);
1164 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1166 // Put moving piece on destination square
1167 set_bit(&(byColorBB[us]), to);
1168 set_bit(&(byTypeBB[PAWN]), to);
1169 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1170 board[to] = board[from];
1171 board[from] = EMPTY;
1173 // Update material hash key
1174 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1176 // Update piece count
1177 pieceCount[them][PAWN]--;
1179 // Update piece list
1180 pieceList[us][PAWN][index[from]] = to;
1181 index[to] = index[from];
1182 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1183 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1186 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1187 key ^= zobrist[them][PAWN][capsq];
1188 key ^= zobEp[epSquare];
1190 // Update pawn hash key
1191 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1192 pawnKey ^= zobrist[them][PAWN][capsq];
1194 // Update incremental scores
1195 mgValue -= mg_pst(them, PAWN, capsq);
1196 mgValue -= mg_pst(us, PAWN, from);
1197 mgValue += mg_pst(us, PAWN, to);
1198 egValue -= eg_pst(them, PAWN, capsq);
1199 egValue -= eg_pst(us, PAWN, from);
1200 egValue += eg_pst(us, PAWN, to);
1202 // Reset en passant square
1205 // Reset rule 50 counter
1208 // Update checkers BB
1209 checkersBB = attacks_to(king_square(them), us);
1213 /// Position::undo_move() unmakes a move. When it returns, the position should
1214 /// be restored to exactly the same state as before the move was made. It is
1215 /// important that Position::undo_move is called with the same move and UndoInfo
1216 /// object as the earlier call to Position::do_move.
1218 void Position::undo_move(Move m, const UndoInfo &u) {
1221 assert(move_is_ok(m));
1224 sideToMove = opposite_color(sideToMove);
1226 // Restore information from our UndoInfo object (except the captured piece,
1227 // which is taken care of later)
1230 if (move_is_castle(m))
1231 undo_castle_move(m);
1232 else if (move_promotion(m))
1233 undo_promotion_move(m, u);
1234 else if (move_is_ep(m))
1240 PieceType piece, capture;
1242 us = side_to_move();
1243 them = opposite_color(us);
1244 from = move_from(m);
1247 assert(piece_on(from) == EMPTY);
1248 assert(color_of_piece_on(to) == us);
1250 // Put the piece back at the source square
1251 piece = type_of_piece_on(to);
1252 set_bit(&(byColorBB[us]), from);
1253 set_bit(&(byTypeBB[piece]), from);
1254 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1255 board[from] = piece_of_color_and_type(us, piece);
1257 // Clear the destination square
1258 clear_bit(&(byColorBB[us]), to);
1259 clear_bit(&(byTypeBB[piece]), to);
1260 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1262 // If the moving piece was a king, update the king square
1264 kingSquare[us] = from;
1266 // Update piece list
1267 pieceList[us][piece][index[to]] = from;
1268 index[from] = index[to];
1270 capture = u.capture;
1274 assert(capture != KING);
1276 // Replace the captured piece
1277 set_bit(&(byColorBB[them]), to);
1278 set_bit(&(byTypeBB[capture]), to);
1279 set_bit(&(byTypeBB[0]), to);
1280 board[to] = piece_of_color_and_type(them, capture);
1283 if (capture != PAWN)
1284 npMaterial[them] += piece_value_midgame(capture);
1286 // Update piece list
1287 pieceList[them][capture][pieceCount[them][capture]] = to;
1288 index[to] = pieceCount[them][capture];
1290 // Update piece count
1291 pieceCount[them][capture]++;
1300 /// Position::undo_castle_move() is a private method used to unmake a castling
1301 /// move. It is called from the main Position::undo_move function. Note that
1302 /// castling moves are encoded as "king captures friendly rook" moves, for
1303 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1305 void Position::undo_castle_move(Move m) {
1307 assert(move_is_ok(m));
1308 assert(move_is_castle(m));
1310 // When we have arrived here, some work has already been done by
1311 // Position::undo_move. In particular, the side to move has been switched,
1312 // so the code below is correct.
1313 Color us = side_to_move();
1315 // Find source squares for king and rook
1316 Square kfrom = move_from(m);
1317 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1320 // Find destination squares for king and rook
1321 if (rfrom > kfrom) // O-O
1323 kto = relative_square(us, SQ_G1);
1324 rto = relative_square(us, SQ_F1);
1326 kto = relative_square(us, SQ_C1);
1327 rto = relative_square(us, SQ_D1);
1330 assert(piece_on(kto) == king_of_color(us));
1331 assert(piece_on(rto) == rook_of_color(us));
1333 // Remove pieces from destination squares
1334 clear_bit(&(byColorBB[us]), kto);
1335 clear_bit(&(byTypeBB[KING]), kto);
1336 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1337 clear_bit(&(byColorBB[us]), rto);
1338 clear_bit(&(byTypeBB[ROOK]), rto);
1339 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1341 // Put pieces on source squares
1342 set_bit(&(byColorBB[us]), kfrom);
1343 set_bit(&(byTypeBB[KING]), kfrom);
1344 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1345 set_bit(&(byColorBB[us]), rfrom);
1346 set_bit(&(byTypeBB[ROOK]), rfrom);
1347 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1350 board[rto] = board[kto] = EMPTY;
1351 board[rfrom] = rook_of_color(us);
1352 board[kfrom] = king_of_color(us);
1354 // Update king square
1355 kingSquare[us] = kfrom;
1357 // Update piece lists
1358 pieceList[us][KING][index[kto]] = kfrom;
1359 pieceList[us][ROOK][index[rto]] = rfrom;
1360 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1361 index[kfrom] = index[kto];
1366 /// Position::undo_promotion_move() is a private method used to unmake a
1367 /// promotion move. It is called from the main Position::do_move
1368 /// function. The UndoInfo object, which has been initialized in
1369 /// Position::do_move, is used to put back the captured piece (if any).
1371 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1375 PieceType capture, promotion;
1377 assert(move_is_ok(m));
1378 assert(move_promotion(m));
1380 // When we have arrived here, some work has already been done by
1381 // Position::undo_move. In particular, the side to move has been switched,
1382 // so the code below is correct.
1383 us = side_to_move();
1384 them = opposite_color(us);
1385 from = move_from(m);
1388 assert(relative_rank(us, to) == RANK_8);
1389 assert(piece_on(from) == EMPTY);
1391 // Remove promoted piece
1392 promotion = move_promotion(m);
1393 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1394 assert(promotion >= KNIGHT && promotion <= QUEEN);
1395 clear_bit(&(byColorBB[us]), to);
1396 clear_bit(&(byTypeBB[promotion]), to);
1397 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1399 // Insert pawn at source square
1400 set_bit(&(byColorBB[us]), from);
1401 set_bit(&(byTypeBB[PAWN]), from);
1402 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1403 board[from] = pawn_of_color(us);
1406 npMaterial[us] -= piece_value_midgame(promotion);
1408 // Update piece list
1409 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1410 index[from] = pieceCount[us][PAWN];
1411 pieceList[us][promotion][index[to]] =
1412 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1413 index[pieceList[us][promotion][index[to]]] = index[to];
1415 // Update piece counts
1416 pieceCount[us][promotion]--;
1417 pieceCount[us][PAWN]++;
1419 capture = u.capture;
1423 assert(capture != KING);
1425 // Insert captured piece:
1426 set_bit(&(byColorBB[them]), to);
1427 set_bit(&(byTypeBB[capture]), to);
1428 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1429 board[to] = piece_of_color_and_type(them, capture);
1431 // Update material. Because the move is a promotion move, we know
1432 // that the captured piece cannot be a pawn.
1433 assert(capture != PAWN);
1434 npMaterial[them] += piece_value_midgame(capture);
1436 // Update piece list
1437 pieceList[them][capture][pieceCount[them][capture]] = to;
1438 index[to] = pieceCount[them][capture];
1440 // Update piece count
1441 pieceCount[them][capture]++;
1447 /// Position::undo_ep_move() is a private method used to unmake an en passant
1448 /// capture. It is called from the main Position::undo_move function. Because
1449 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1450 /// object from which to retrieve the captured piece.
1452 void Position::undo_ep_move(Move m) {
1454 assert(move_is_ok(m));
1455 assert(move_is_ep(m));
1457 // When we have arrived here, some work has already been done by
1458 // Position::undo_move. In particular, the side to move has been switched,
1459 // so the code below is correct.
1460 Color us = side_to_move();
1461 Color them = opposite_color(us);
1462 Square from = move_from(m);
1463 Square to = move_to(m);
1464 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1466 assert(to == ep_square());
1467 assert(relative_rank(us, to) == RANK_6);
1468 assert(piece_on(to) == pawn_of_color(us));
1469 assert(piece_on(from) == EMPTY);
1470 assert(piece_on(capsq) == EMPTY);
1472 // Replace captured piece
1473 set_bit(&(byColorBB[them]), capsq);
1474 set_bit(&(byTypeBB[PAWN]), capsq);
1475 set_bit(&(byTypeBB[0]), capsq);
1476 board[capsq] = pawn_of_color(them);
1478 // Remove moving piece from destination square
1479 clear_bit(&(byColorBB[us]), to);
1480 clear_bit(&(byTypeBB[PAWN]), to);
1481 clear_bit(&(byTypeBB[0]), to);
1484 // Replace moving piece at source square
1485 set_bit(&(byColorBB[us]), from);
1486 set_bit(&(byTypeBB[PAWN]), from);
1487 set_bit(&(byTypeBB[0]), from);
1488 board[from] = pawn_of_color(us);
1490 // Update piece list:
1491 pieceList[us][PAWN][index[to]] = from;
1492 index[from] = index[to];
1493 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1494 index[capsq] = pieceCount[them][PAWN];
1496 // Update piece count:
1497 pieceCount[them][PAWN]++;
1501 /// Position::do_null_move makes() a "null move": It switches the side to move
1502 /// and updates the hash key without executing any move on the board.
1504 void Position::do_null_move(UndoInfo &u) {
1507 assert(!is_check());
1509 // Back up the information necessary to undo the null move to the supplied
1510 // UndoInfo object. In the case of a null move, the only thing we need to
1511 // remember is the last move made and the en passant square.
1512 u.lastMove = lastMove;
1513 u.epSquare = epSquare;
1515 // Save the current key to the history[] array, in order to be able to
1516 // detect repetition draws.
1517 history[gamePly] = key;
1519 // Update the necessary information
1520 sideToMove = opposite_color(sideToMove);
1521 if (epSquare != SQ_NONE)
1522 key ^= zobEp[epSquare];
1527 key ^= zobSideToMove;
1529 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1530 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1536 /// Position::undo_null_move() unmakes a "null move".
1538 void Position::undo_null_move(const UndoInfo &u) {
1541 assert(!is_check());
1543 // Restore information from the supplied UndoInfo object:
1544 lastMove = u.lastMove;
1545 epSquare = u.epSquare;
1546 if (epSquare != SQ_NONE)
1547 key ^= zobEp[epSquare];
1549 // Update the necessary information.
1550 sideToMove = opposite_color(sideToMove);
1553 key ^= zobSideToMove;
1555 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1556 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1562 /// Position::see() is a static exchange evaluator: It tries to estimate the
1563 /// material gain or loss resulting from a move. There are two versions of
1564 /// this function: One which takes a move as input, and one which takes a
1565 /// 'from' and a 'to' square. The function does not yet understand promotions
1566 /// or en passant captures.
1568 int Position::see(Move m) const {
1570 assert(move_is_ok(m));
1571 return see(move_from(m), move_to(m));
1574 int Position::see(Square from, Square to) const {
1576 // Approximate material values, with pawn = 1
1577 static const int seeValues[18] = {
1578 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1581 Bitboard attackers, occ, b;
1583 assert(square_is_ok(from));
1584 assert(square_is_ok(to));
1586 // Initialize colors
1587 Color us = color_of_piece_on(from);
1588 Color them = opposite_color(us);
1590 // Initialize pieces
1591 Piece piece = piece_on(from);
1592 Piece capture = piece_on(to);
1594 // Find all attackers to the destination square, with the moving piece
1595 // removed, but possibly an X-ray attacker added behind it.
1596 occ = occupied_squares();
1597 clear_bit(&occ, from);
1598 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1599 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1600 | (piece_attacks<KNIGHT>(to) & knights())
1601 | (piece_attacks<KING>(to) & kings())
1602 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1603 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1605 // If the opponent has no attackers, we are finished
1606 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1607 return seeValues[capture];
1609 attackers &= occ; // Remove the moving piece
1611 // The destination square is defended, which makes things rather more
1612 // difficult to compute. We proceed by building up a "swap list" containing
1613 // the material gain or loss at each stop in a sequence of captures to the
1614 // destination square, where the sides alternately capture, and always
1615 // capture with the least valuable piece. After each capture, we look for
1616 // new X-ray attacks from behind the capturing piece.
1617 int lastCapturingPieceValue = seeValues[piece];
1618 int swapList[32], n = 1;
1622 swapList[0] = seeValues[capture];
1625 // Locate the least valuable attacker for the side to move. The loop
1626 // below looks like it is potentially infinite, but it isn't. We know
1627 // that the side to move still has at least one attacker left.
1628 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1631 // Remove the attacker we just found from the 'attackers' bitboard,
1632 // and scan for new X-ray attacks behind the attacker.
1633 b = attackers & pieces_of_color_and_type(c, pt);
1635 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1636 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1640 // Add the new entry to the swap list
1642 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1645 // Remember the value of the capturing piece, and change the side to move
1646 // before beginning the next iteration
1647 lastCapturingPieceValue = seeValues[pt];
1648 c = opposite_color(c);
1650 // Stop after a king capture
1651 if (pt == KING && (attackers & pieces_of_color(c)))
1654 swapList[n++] = 100;
1657 } while (attackers & pieces_of_color(c));
1659 // Having built the swap list, we negamax through it to find the best
1660 // achievable score from the point of view of the side to move
1662 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1668 /// Position::clear() erases the position object to a pristine state, with an
1669 /// empty board, white to move, and no castling rights.
1671 void Position::clear() {
1673 for (int i = 0; i < 64; i++)
1679 for (int i = 0; i < 2; i++)
1680 byColorBB[i] = EmptyBoardBB;
1682 for (int i = 0; i < 7; i++)
1684 byTypeBB[i] = EmptyBoardBB;
1685 pieceCount[0][i] = pieceCount[1][i] = 0;
1686 for (int j = 0; j < 8; j++)
1687 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1690 checkersBB = EmptyBoardBB;
1692 lastMove = MOVE_NONE;
1695 castleRights = NO_CASTLES;
1696 initialKFile = FILE_E;
1697 initialKRFile = FILE_H;
1698 initialQRFile = FILE_A;
1705 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1706 /// UCI interface code, whenever a non-reversible move is made in a
1707 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1708 /// for the program to handle games of arbitrary length, as long as the GUI
1709 /// handles draws by the 50 move rule correctly.
1711 void Position::reset_game_ply() {
1717 /// Position::put_piece() puts a piece on the given square of the board,
1718 /// updating the board array, bitboards, and piece counts.
1720 void Position::put_piece(Piece p, Square s) {
1722 Color c = color_of_piece(p);
1723 PieceType pt = type_of_piece(p);
1726 index[s] = pieceCount[c][pt];
1727 pieceList[c][pt][index[s]] = s;
1729 set_bit(&(byTypeBB[pt]), s);
1730 set_bit(&(byColorBB[c]), s);
1731 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1733 pieceCount[c][pt]++;
1740 /// Position::allow_oo() gives the given side the right to castle kingside.
1741 /// Used when setting castling rights during parsing of FEN strings.
1743 void Position::allow_oo(Color c) {
1745 castleRights |= (1 + int(c));
1749 /// Position::allow_ooo() gives the given side the right to castle queenside.
1750 /// Used when setting castling rights during parsing of FEN strings.
1752 void Position::allow_ooo(Color c) {
1754 castleRights |= (4 + 4*int(c));
1758 /// Position::compute_key() computes the hash key of the position. The hash
1759 /// key is usually updated incrementally as moves are made and unmade, the
1760 /// compute_key() function is only used when a new position is set up, and
1761 /// to verify the correctness of the hash key when running in debug mode.
1763 Key Position::compute_key() const {
1765 Key result = Key(0ULL);
1767 for (Square s = SQ_A1; s <= SQ_H8; s++)
1768 if (square_is_occupied(s))
1769 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1771 if (ep_square() != SQ_NONE)
1772 result ^= zobEp[ep_square()];
1774 result ^= zobCastle[castleRights];
1775 if (side_to_move() == BLACK)
1776 result ^= zobSideToMove;
1782 /// Position::compute_pawn_key() computes the hash key of the position. The
1783 /// hash key is usually updated incrementally as moves are made and unmade,
1784 /// the compute_pawn_key() function is only used when a new position is set
1785 /// up, and to verify the correctness of the pawn hash key when running in
1788 Key Position::compute_pawn_key() const {
1790 Key result = Key(0ULL);
1794 for (Color c = WHITE; c <= BLACK; c++)
1799 s = pop_1st_bit(&b);
1800 result ^= zobrist[c][PAWN][s];
1807 /// Position::compute_material_key() computes the hash key of the position.
1808 /// The hash key is usually updated incrementally as moves are made and unmade,
1809 /// the compute_material_key() function is only used when a new position is set
1810 /// up, and to verify the correctness of the material hash key when running in
1813 Key Position::compute_material_key() const {
1815 Key result = Key(0ULL);
1816 for (Color c = WHITE; c <= BLACK; c++)
1817 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1819 int count = piece_count(c, pt);
1820 for (int i = 0; i <= count; i++)
1821 result ^= zobMaterial[c][pt][i];
1827 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1828 /// incremental scores for the middle game and the endgame. These functions
1829 /// are used to initialize the incremental scores when a new position is set
1830 /// up, and to verify that the scores are correctly updated by do_move
1831 /// and undo_move when the program is running in debug mode.
1833 Value Position::compute_mg_value() const {
1835 Value result = Value(0);
1839 for (Color c = WHITE; c <= BLACK; c++)
1840 for (PieceType pt = PAWN; pt <= KING; pt++)
1842 b = pieces_of_color_and_type(c, pt);
1845 s = pop_1st_bit(&b);
1846 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1847 result += mg_pst(c, pt, s);
1850 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1854 Value Position::compute_eg_value() const {
1856 Value result = Value(0);
1860 for (Color c = WHITE; c <= BLACK; c++)
1861 for (PieceType pt = PAWN; pt <= KING; pt++)
1863 b = pieces_of_color_and_type(c, pt);
1866 s = pop_1st_bit(&b);
1867 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1868 result += eg_pst(c, pt, s);
1871 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1876 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1877 /// game material score for the given side. Material scores are updated
1878 /// incrementally during the search, this function is only used while
1879 /// initializing a new Position object.
1881 Value Position::compute_non_pawn_material(Color c) const {
1883 Value result = Value(0);
1886 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1888 Bitboard b = pieces_of_color_and_type(c, pt);
1891 s = pop_1st_bit(&b);
1892 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1893 result += piece_value_midgame(pt);
1900 /// Position::is_mate() returns true or false depending on whether the
1901 /// side to move is checkmated. Note that this function is currently very
1902 /// slow, and shouldn't be used frequently inside the search.
1904 bool Position::is_mate() {
1908 MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE,
1909 MOVE_NONE, MOVE_NONE, Depth(0));
1910 return mp.get_next_move() == MOVE_NONE;
1916 /// Position::is_draw() tests whether the position is drawn by material,
1917 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1918 /// must be done by the search.
1920 bool Position::is_draw() const {
1922 // Draw by material?
1924 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1927 // Draw by the 50 moves rule?
1928 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1931 // Draw by repetition?
1932 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1933 if (history[gamePly - i] == key)
1940 /// Position::has_mate_threat() tests whether a given color has a mate in one
1941 /// from the current position. This function is quite slow, but it doesn't
1942 /// matter, because it is currently only called from PV nodes, which are rare.
1944 bool Position::has_mate_threat(Color c) {
1947 Color stm = side_to_move();
1949 // The following lines are useless and silly, but prevents gcc from
1950 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1951 // be used uninitialized.
1952 u1.lastMove = lastMove;
1953 u1.epSquare = epSquare;
1958 // If the input color is not equal to the side to move, do a null move
1962 MoveStack mlist[120];
1964 bool result = false;
1966 // Generate legal moves
1967 count = generate_legal_moves(*this, mlist);
1969 // Loop through the moves, and see if one of them is mate
1970 for (int i = 0; i < count; i++)
1972 do_move(mlist[i].move, u2);
1976 undo_move(mlist[i].move, u2);
1979 // Undo null move, if necessary
1987 /// Position::init_zobrist() is a static member function which initializes the
1988 /// various arrays used to compute hash keys.
1990 void Position::init_zobrist() {
1992 for (int i = 0; i < 2; i++)
1993 for (int j = 0; j < 8; j++)
1994 for (int k = 0; k < 64; k++)
1995 zobrist[i][j][k] = Key(genrand_int64());
1997 for (int i = 0; i < 64; i++)
1998 zobEp[i] = Key(genrand_int64());
2000 for (int i = 0; i < 16; i++)
2001 zobCastle[i] = genrand_int64();
2003 zobSideToMove = genrand_int64();
2005 for (int i = 0; i < 2; i++)
2006 for (int j = 0; j < 8; j++)
2007 for (int k = 0; k < 16; k++)
2008 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2010 for (int i = 0; i < 16; i++)
2011 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2015 /// Position::init_piece_square_tables() initializes the piece square tables.
2016 /// This is a two-step operation: First, the white halves of the tables are
2017 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2018 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2019 /// Second, the black halves of the tables are initialized by mirroring
2020 /// and changing the sign of the corresponding white scores.
2022 void Position::init_piece_square_tables() {
2024 int r = get_option_value_int("Randomness"), i;
2025 for (Square s = SQ_A1; s <= SQ_H8; s++)
2026 for (Piece p = WP; p <= WK; p++)
2028 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2029 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2030 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2033 for (Square s = SQ_A1; s <= SQ_H8; s++)
2034 for (Piece p = BP; p <= BK; p++)
2036 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2037 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2042 /// Position::flipped_copy() makes a copy of the input position, but with
2043 /// the white and black sides reversed. This is only useful for debugging,
2044 /// especially for finding evaluation symmetry bugs.
2046 void Position::flipped_copy(const Position &pos) {
2048 assert(pos.is_ok());
2053 for (Square s = SQ_A1; s <= SQ_H8; s++)
2054 if (!pos.square_is_empty(s))
2055 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2058 sideToMove = opposite_color(pos.side_to_move());
2061 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2062 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2063 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2064 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2066 initialKFile = pos.initialKFile;
2067 initialKRFile = pos.initialKRFile;
2068 initialQRFile = pos.initialQRFile;
2070 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2071 castleRightsMask[sq] = ALL_CASTLES;
2073 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2074 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2075 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2076 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2077 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2078 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2080 // En passant square
2081 if (pos.epSquare != SQ_NONE)
2082 epSquare = flip_square(pos.epSquare);
2088 key = compute_key();
2089 pawnKey = compute_pawn_key();
2090 materialKey = compute_material_key();
2092 // Incremental scores
2093 mgValue = compute_mg_value();
2094 egValue = compute_eg_value();
2097 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2098 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2104 /// Position::is_ok() performs some consitency checks for the position object.
2105 /// This is meant to be helpful when debugging.
2107 bool Position::is_ok(int* failedStep) const {
2109 // What features of the position should be verified?
2110 static const bool debugBitboards = false;
2111 static const bool debugKingCount = false;
2112 static const bool debugKingCapture = false;
2113 static const bool debugCheckerCount = false;
2114 static const bool debugKey = false;
2115 static const bool debugMaterialKey = false;
2116 static const bool debugPawnKey = false;
2117 static const bool debugIncrementalEval = false;
2118 static const bool debugNonPawnMaterial = false;
2119 static const bool debugPieceCounts = false;
2120 static const bool debugPieceList = false;
2122 if (failedStep) *failedStep = 1;
2125 if (!color_is_ok(side_to_move()))
2128 // Are the king squares in the position correct?
2129 if (failedStep) (*failedStep)++;
2130 if (piece_on(king_square(WHITE)) != WK)
2133 if (failedStep) (*failedStep)++;
2134 if (piece_on(king_square(BLACK)) != BK)
2138 if (failedStep) (*failedStep)++;
2139 if (!file_is_ok(initialKRFile))
2142 if (!file_is_ok(initialQRFile))
2145 // Do both sides have exactly one king?
2146 if (failedStep) (*failedStep)++;
2149 int kingCount[2] = {0, 0};
2150 for (Square s = SQ_A1; s <= SQ_H8; s++)
2151 if (type_of_piece_on(s) == KING)
2152 kingCount[color_of_piece_on(s)]++;
2154 if(kingCount[0] != 1 || kingCount[1] != 1)
2158 // Can the side to move capture the opponent's king?
2159 if (failedStep) (*failedStep)++;
2160 if (debugKingCapture)
2162 Color us = side_to_move();
2163 Color them = opposite_color(us);
2164 Square ksq = king_square(them);
2165 if (square_is_attacked(ksq, us))
2169 // Is there more than 2 checkers?
2170 if (failedStep) (*failedStep)++;
2171 if (debugCheckerCount && count_1s(checkersBB) > 2)
2175 if (failedStep) (*failedStep)++;
2178 // The intersection of the white and black pieces must be empty
2179 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2182 // The union of the white and black pieces must be equal to all
2184 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2187 // Separate piece type bitboards must have empty intersections
2188 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2189 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2190 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2194 // En passant square OK?
2195 if (failedStep) (*failedStep)++;
2196 if (ep_square() != SQ_NONE)
2198 // The en passant square must be on rank 6, from the point of view of the
2200 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2205 if (failedStep) (*failedStep)++;
2206 if (debugKey && key != compute_key())
2209 // Pawn hash key OK?
2210 if (failedStep) (*failedStep)++;
2211 if (debugPawnKey && pawnKey != compute_pawn_key())
2214 // Material hash key OK?
2215 if (failedStep) (*failedStep)++;
2216 if (debugMaterialKey && materialKey != compute_material_key())
2219 // Incremental eval OK?
2220 if (failedStep) (*failedStep)++;
2221 if (debugIncrementalEval)
2223 if (mgValue != compute_mg_value())
2226 if (egValue != compute_eg_value())
2230 // Non-pawn material OK?
2231 if (failedStep) (*failedStep)++;
2232 if (debugNonPawnMaterial)
2234 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2237 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2242 if (failedStep) (*failedStep)++;
2243 if (debugPieceCounts)
2244 for (Color c = WHITE; c <= BLACK; c++)
2245 for (PieceType pt = PAWN; pt <= KING; pt++)
2246 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2249 if (failedStep) (*failedStep)++;
2252 for(Color c = WHITE; c <= BLACK; c++)
2253 for(PieceType pt = PAWN; pt <= KING; pt++)
2254 for(int i = 0; i < pieceCount[c][pt]; i++)
2256 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2259 if (index[piece_list(c, pt, i)] != i)
2263 if (failedStep) *failedStep = 0;