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) {
295 memcpy(this, &pos, sizeof(Position));
299 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
300 /// king) pieces for the given color.
301 Bitboard Position::pinned_pieces(Color c) const {
303 Square ksq = king_square(c);
304 return hidden_checks<ROOK, true>(c, ksq) | hidden_checks<BISHOP, true>(c, ksq);
308 /// Position:discovered_check_candidates() returns a bitboard containing all
309 /// pieces for the given side which are candidates for giving a discovered
310 /// check. The code is almost the same as the function for finding pinned
313 Bitboard Position::discovered_check_candidates(Color c) const {
315 Square ksq = king_square(opposite_color(c));
316 return hidden_checks<ROOK, false>(c, ksq) | hidden_checks<BISHOP, false>(c, ksq);
320 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
321 /// king) pieces for the given color and for the given pinner type. Or, when
322 /// template parameter FindPinned is false, the pinned pieces of opposite color
323 /// that are, indeed, the pieces candidate for a discovery check.
324 template<PieceType Piece, bool FindPinned>
325 Bitboard Position::hidden_checks(Color c, Square ksq) const {
328 Bitboard sliders, result = EmptyBoardBB;
330 if (Piece == ROOK) // Resolved at compile time
331 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
333 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
335 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
337 // King blockers are candidate pinned pieces
338 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
340 // Pinners are sliders, not checkers, that give check when
341 // candidate pinned are removed.
342 Bitboard pinners = (FindPinned ? sliders & ~checkersBB : sliders);
345 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
347 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 (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 (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 {
391 return attacks_to(s) & pieces_of_color(c);
395 /// Position::piece_attacks_square() tests whether the piece on square f
396 /// attacks square t.
398 bool Position::piece_attacks_square(Square f, Square t) const {
399 assert(square_is_ok(f));
400 assert(square_is_ok(t));
402 switch(piece_on(f)) {
403 case WP: return pawn_attacks_square(WHITE, f, t);
404 case BP: return pawn_attacks_square(BLACK, f, t);
405 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
406 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
407 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
408 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
409 case WK: case BK: return piece_attacks_square<KING>(f, t);
410 default: return false;
417 /// Position::find_checkers() computes the checkersBB bitboard, which
418 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
419 /// currently works by calling Position::attacks_to, which is probably
420 /// inefficient. Consider rewriting this function to use the last move
421 /// played, like in non-bitboard versions of Glaurung.
423 void Position::find_checkers() {
424 checkersBB = attacks_to(king_square(side_to_move()),
425 opposite_color(side_to_move()));
429 /// Position::move_is_legal() tests whether a pseudo-legal move is legal.
430 /// There are two versions of this function: One which takes only a
431 /// move as input, and one which takes a move and a bitboard of pinned
432 /// pieces. The latter function is faster, and should always be preferred
433 /// when a pinned piece bitboard has already been computed.
435 bool Position::move_is_legal(Move m) const {
436 return move_is_legal(m, pinned_pieces(side_to_move()));
440 bool Position::move_is_legal(Move m, Bitboard pinned) const {
445 assert(move_is_ok(m));
446 assert(pinned == pinned_pieces(side_to_move()));
448 // If we're in check, all pseudo-legal moves are legal, because our
449 // check evasion generator only generates true legal moves.
450 if(is_check()) return true;
452 // Castling moves are checked for legality during move generation.
453 if(move_is_castle(m)) return true;
456 them = opposite_color(us);
459 ksq = king_square(us);
461 assert(color_of_piece_on(from) == us);
462 assert(piece_on(ksq) == king_of_color(us));
464 // En passant captures are a tricky special case. Because they are
465 // rather uncommon, we do it simply by testing whether the king is attacked
466 // after the move is made:
468 Square to = move_to(m);
469 Square capsq = make_square(square_file(to), square_rank(from));
470 Bitboard b = occupied_squares();
472 assert(to == ep_square());
473 assert(piece_on(from) == pawn_of_color(us));
474 assert(piece_on(capsq) == pawn_of_color(them));
475 assert(piece_on(to) == EMPTY);
477 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
479 (!(rook_attacks_bb(ksq, b) & rooks_and_queens(them)) &&
480 !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them)));
483 // If the moving piece is a king, check whether the destination
484 // square is attacked by the opponent.
485 if(from == ksq) return !(square_is_attacked(move_to(m), them));
487 // A non-king move is legal if and only if it is not pinned or it
488 // is moving along the ray towards or away from the king.
489 if(!bit_is_set(pinned, from)) return true;
490 if(direction_between_squares(from, ksq) ==
491 direction_between_squares(move_to(m), ksq))
498 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
499 /// There are two versions of this function: One which takes only a move as
500 /// input, and one which takes a move and a bitboard of discovered check
501 /// candidates. The latter function is faster, and should always be preferred
502 /// when a discovered check candidates bitboard has already been computed.
504 bool Position::move_is_check(Move m) const {
505 Bitboard dc = discovered_check_candidates(side_to_move());
506 return move_is_check(m, dc);
510 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
512 Square ksq, from, to;
515 assert(move_is_ok(m));
516 assert(dcCandidates ==
517 discovered_check_candidates(side_to_move()));
520 them = opposite_color(us);
524 ksq = king_square(them);
525 assert(color_of_piece_on(from) == us);
526 assert(piece_on(ksq) == king_of_color(them));
528 // Proceed according to the type of the moving piece:
529 switch(type_of_piece_on(from)) {
532 if(bit_is_set(pawn_attacks(them, ksq), to))
535 else if(bit_is_set(dcCandidates, from) &&
536 direction_between_squares(from, ksq) !=
537 direction_between_squares(to, ksq))
539 // Promotion with check?
540 else if(move_promotion(m)) {
541 Bitboard b = occupied_squares();
544 switch(move_promotion(m)) {
546 return piece_attacks_square<KNIGHT>(to, ksq);
548 return bit_is_set(bishop_attacks_bb(to, b), ksq);
550 return bit_is_set(rook_attacks_bb(to, b), ksq);
552 return bit_is_set(queen_attacks_bb(to, b), ksq);
557 // En passant capture with check? We have already handled the case
558 // of direct checks and ordinary discovered check, the only case we
559 // need to handle is the unusual case of a discovered check through the
561 else if(move_is_ep(m)) {
562 Square capsq = make_square(square_file(to), square_rank(from));
563 Bitboard b = occupied_squares();
565 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
567 ((rook_attacks_bb(ksq, b) & rooks_and_queens(us)) ||
568 (bishop_attacks_bb(ksq, b) & bishops_and_queens(us)));
574 if(bit_is_set(dcCandidates, from))
578 return bit_is_set(piece_attacks<KNIGHT>(ksq), to);
582 if(bit_is_set(dcCandidates, from))
586 return bit_is_set(piece_attacks<BISHOP>(ksq), to);
590 if(bit_is_set(dcCandidates, from))
594 return bit_is_set(piece_attacks<ROOK>(ksq), to);
597 // Discovered checks are impossible!
598 assert(!bit_is_set(dcCandidates, from));
600 return bit_is_set(piece_attacks<QUEEN>(ksq), to);
604 if(bit_is_set(dcCandidates, from) &&
605 direction_between_squares(from, ksq) !=
606 direction_between_squares(to, ksq))
608 // Castling with check?
609 if(move_is_castle(m)) {
610 Square kfrom, kto, rfrom, rto;
611 Bitboard b = occupied_squares();
616 kto = relative_square(us, SQ_G1);
617 rto = relative_square(us, SQ_F1);
620 kto = relative_square(us, SQ_C1);
621 rto = relative_square(us, SQ_D1);
624 clear_bit(&b, kfrom); clear_bit(&b, rfrom);
625 set_bit(&b, rto); set_bit(&b, kto);
627 return bit_is_set(rook_attacks_bb(rto, b), ksq);
642 /// Position::move_is_capture() tests whether a move from the current
643 /// position is a capture.
645 bool Position::move_is_capture(Move m) const {
647 color_of_piece_on(move_to(m)) == opposite_color(side_to_move())
652 /// Position::move_attacks_square() tests whether a move from the current
653 /// position attacks a given square. Only attacks by the moving piece are
654 /// considered; the function does not handle X-ray attacks.
656 bool Position::move_attacks_square(Move m, Square s) const {
657 assert(move_is_ok(m));
658 assert(square_is_ok(s));
660 Square f = move_from(m), t = move_to(m);
662 assert(square_is_occupied(f));
664 switch(piece_on(f)) {
665 case WP: return pawn_attacks_square(WHITE, t, s);
666 case BP: return pawn_attacks_square(BLACK, t, s);
667 case WN: case BN: return piece_attacks_square<KNIGHT>(t, s);
668 case WB: case BB: return piece_attacks_square<BISHOP>(t, s);
669 case WR: case BR: return piece_attacks_square<ROOK>(t, s);
670 case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s);
671 case WK: case BK: return piece_attacks_square<KING>(t, s);
672 default: assert(false);
680 /// Position::backup() is called when making a move. All information
681 /// necessary to restore the position when the move is later unmade
682 /// is saved to an UndoInfo object. The function Position::restore
683 /// does the reverse operation: When one does a backup followed by
684 /// a restore with the same UndoInfo object, the position is restored
685 /// to the state before backup was called.
687 void Position::backup(UndoInfo &u) const {
688 u.castleRights = castleRights;
689 u.epSquare = epSquare;
690 u.checkersBB = checkersBB;
693 u.materialKey = materialKey;
695 u.lastMove = lastMove;
696 u.capture = NO_PIECE_TYPE;
702 /// Position::restore() is called when unmaking a move. It copies back
703 /// the information backed up during a previous call to Position::backup.
705 void Position::restore(const UndoInfo &u) {
706 castleRights = u.castleRights;
707 epSquare = u.epSquare;
708 checkersBB = u.checkersBB;
711 materialKey = u.materialKey;
713 lastMove = u.lastMove;
719 /// Position::do_move() makes a move, and backs up all information necessary
720 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
721 /// Pseudo-legal moves should be filtered out before this function is called.
722 /// There are two versions of this function, one which takes only the move and
723 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
724 /// discovered check candidates. The second version is faster, because knowing
725 /// the discovered check candidates makes it easier to update the checkersBB
726 /// member variable in the position object.
728 void Position::do_move(Move m, UndoInfo &u) {
729 do_move(m, u, discovered_check_candidates(side_to_move()));
732 void Position::do_move(Move m, UndoInfo &u, Bitboard dcCandidates) {
734 assert(move_is_ok(m));
736 // Back up the necessary information to our UndoInfo object (except the
737 // captured piece, which is taken care of later:
740 // Save the current key to the history[] array, in order to be able to
741 // detect repetition draws:
742 history[gamePly] = key;
744 // Increment the 50 moves rule draw counter. Resetting it to zero in the
745 // case of non-reversible moves is taken care of later.
748 if(move_is_castle(m))
750 else if(move_promotion(m))
751 do_promotion_move(m, u);
752 else if(move_is_ep(m))
757 PieceType piece, capture;
760 them = opposite_color(us);
765 assert(color_of_piece_on(from) == us);
766 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
768 piece = type_of_piece_on(from);
769 capture = type_of_piece_on(to);
772 assert(capture != KING);
774 // Remove captured piece:
775 clear_bit(&(byColorBB[them]), to);
776 clear_bit(&(byTypeBB[capture]), to);
779 key ^= zobrist[them][capture][to];
781 // If the captured piece was a pawn, update pawn hash key:
783 pawnKey ^= zobrist[them][PAWN][to];
785 // Update incremental scores:
786 mgValue -= mg_pst(them, capture, to);
787 egValue -= eg_pst(them, capture, to);
791 npMaterial[them] -= piece_value_midgame(capture);
793 // Update material hash key:
794 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
796 // Update piece count:
797 pieceCount[them][capture]--;
799 // Update piece list:
800 pieceList[them][capture][index[to]] =
801 pieceList[them][capture][pieceCount[them][capture]];
802 index[pieceList[them][capture][index[to]]] = index[to];
804 // Remember the captured piece, in order to be able to undo the move
808 // Reset rule 50 counter:
813 clear_bit(&(byColorBB[us]), from);
814 clear_bit(&(byTypeBB[piece]), from);
815 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
816 set_bit(&(byColorBB[us]), to);
817 set_bit(&(byTypeBB[piece]), to);
818 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
819 board[to] = board[from];
823 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
825 // Update incremental scores:
826 mgValue -= mg_pst(us, piece, from);
827 mgValue += mg_pst(us, piece, to);
828 egValue -= eg_pst(us, piece, from);
829 egValue += eg_pst(us, piece, to);
831 // If the moving piece was a king, update the king square:
835 // If the move was a double pawn push, set the en passant square.
836 // This code is a bit ugly right now, and should be cleaned up later.
838 if(epSquare != SQ_NONE) {
839 key ^= zobEp[epSquare];
843 if(abs(int(to) - int(from)) == 16) {
844 if((us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) &
846 (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) &
848 epSquare = Square((int(from) + int(to)) / 2);
849 key ^= zobEp[epSquare];
852 // Reset rule 50 draw counter.
854 // Update pawn hash key:
855 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
858 // Update piece lists:
859 pieceList[us][piece][index[from]] = to;
860 index[to] = index[from];
862 // Update castle rights:
863 key ^= zobCastle[castleRights];
864 castleRights &= castleRightsMask[from];
865 castleRights &= castleRightsMask[to];
866 key ^= zobCastle[castleRights];
868 // Update checkers bitboard:
869 checkersBB = EmptyBoardBB;
870 Square ksq = king_square(them);
875 if(bit_is_set(pawn_attacks(them, ksq), to))
876 set_bit(&checkersBB, to);
877 if(bit_is_set(dcCandidates, from))
879 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
880 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
884 if(bit_is_set(piece_attacks<KNIGHT>(ksq), to))
885 set_bit(&checkersBB, to);
886 if(bit_is_set(dcCandidates, from))
888 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
889 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
893 if(bit_is_set(piece_attacks<BISHOP>(ksq), to))
894 set_bit(&checkersBB, to);
895 if(bit_is_set(dcCandidates, from))
897 (piece_attacks<ROOK>(ksq) & rooks_and_queens(us));
901 if(bit_is_set(piece_attacks<ROOK>(ksq), to))
902 set_bit(&checkersBB, to);
903 if(bit_is_set(dcCandidates, from))
905 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us));
909 if(bit_is_set(piece_attacks<QUEEN>(ksq), to))
910 set_bit(&checkersBB, to);
914 if(bit_is_set(dcCandidates, from))
916 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
917 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
927 key ^= zobSideToMove;
928 sideToMove = opposite_color(sideToMove);
931 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
932 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
938 /// Position::do_castle_move() is a private method used to make a castling
939 /// move. It is called from the main Position::do_move function. Note that
940 /// castling moves are encoded as "king captures friendly rook" moves, for
941 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
943 void Position::do_castle_move(Move m) {
945 Square kfrom, kto, rfrom, rto;
948 assert(move_is_ok(m));
949 assert(move_is_castle(m));
952 them = opposite_color(us);
954 // Find source squares for king and rook:
955 kfrom = move_from(m);
956 rfrom = move_to(m); // HACK: See comment at beginning of function.
958 assert(piece_on(kfrom) == king_of_color(us));
959 assert(piece_on(rfrom) == rook_of_color(us));
961 // Find destination squares for king and rook:
962 if(rfrom > kfrom) { // O-O
963 kto = relative_square(us, SQ_G1);
964 rto = relative_square(us, SQ_F1);
967 kto = relative_square(us, SQ_C1);
968 rto = relative_square(us, SQ_D1);
971 // Remove pieces from source squares:
972 clear_bit(&(byColorBB[us]), kfrom);
973 clear_bit(&(byTypeBB[KING]), kfrom);
974 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
975 clear_bit(&(byColorBB[us]), rfrom);
976 clear_bit(&(byTypeBB[ROOK]), rfrom);
977 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
979 // Put pieces on destination squares:
980 set_bit(&(byColorBB[us]), kto);
981 set_bit(&(byTypeBB[KING]), kto);
982 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
983 set_bit(&(byColorBB[us]), rto);
984 set_bit(&(byTypeBB[ROOK]), rto);
985 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
987 // Update board array:
988 board[kfrom] = board[rfrom] = EMPTY;
989 board[kto] = king_of_color(us);
990 board[rto] = rook_of_color(us);
992 // Update king square:
993 kingSquare[us] = kto;
995 // Update piece lists:
996 pieceList[us][KING][index[kfrom]] = kto;
997 pieceList[us][ROOK][index[rfrom]] = rto;
998 int tmp = index[rfrom];
999 index[kto] = index[kfrom];
1002 // Update incremental scores:
1003 mgValue -= mg_pst(us, KING, kfrom);
1004 mgValue += mg_pst(us, KING, kto);
1005 egValue -= eg_pst(us, KING, kfrom);
1006 egValue += eg_pst(us, KING, kto);
1007 mgValue -= mg_pst(us, ROOK, rfrom);
1008 mgValue += mg_pst(us, ROOK, rto);
1009 egValue -= eg_pst(us, ROOK, rfrom);
1010 egValue += eg_pst(us, ROOK, rto);
1013 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1014 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1016 // Clear en passant square:
1017 if(epSquare != SQ_NONE) {
1018 key ^= zobEp[epSquare];
1022 // Update castling rights:
1023 key ^= zobCastle[castleRights];
1024 castleRights &= castleRightsMask[kfrom];
1025 key ^= zobCastle[castleRights];
1027 // Reset rule 50 counter:
1030 // Update checkers BB:
1031 checkersBB = attacks_to(king_square(them), us);
1035 /// Position::do_promotion_move() is a private method used to make a promotion
1036 /// move. It is called from the main Position::do_move function. The
1037 /// UndoInfo object, which has been initialized in Position::do_move, is
1038 /// used to store the captured piece (if any).
1040 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);
1052 from = move_from(m);
1055 assert(relative_rank(us, to) == RANK_8);
1056 assert(piece_on(from) == pawn_of_color(us));
1057 assert(color_of_piece_on(to) == them || square_is_empty(to));
1059 capture = type_of_piece_on(to);
1062 assert(capture != KING);
1064 // Remove captured piece:
1065 clear_bit(&(byColorBB[them]), to);
1066 clear_bit(&(byTypeBB[capture]), to);
1069 key ^= zobrist[them][capture][to];
1071 // Update incremental scores:
1072 mgValue -= mg_pst(them, capture, to);
1073 egValue -= eg_pst(them, capture, to);
1075 // Update material. Because our move is a promotion, we know that the
1076 // captured piece is not a pawn.
1077 assert(capture != PAWN);
1078 npMaterial[them] -= piece_value_midgame(capture);
1080 // Update material hash key:
1081 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
1083 // Update piece count:
1084 pieceCount[them][capture]--;
1086 // Update piece list:
1087 pieceList[them][capture][index[to]] =
1088 pieceList[them][capture][pieceCount[them][capture]];
1089 index[pieceList[them][capture][index[to]]] = index[to];
1091 // Remember the captured piece, in order to be able to undo the move
1093 u.capture = capture;
1097 clear_bit(&(byColorBB[us]), from);
1098 clear_bit(&(byTypeBB[PAWN]), from);
1099 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1100 board[from] = EMPTY;
1102 // Insert promoted piece:
1103 promotion = move_promotion(m);
1104 assert(promotion >= KNIGHT && promotion <= QUEEN);
1105 set_bit(&(byColorBB[us]), to);
1106 set_bit(&(byTypeBB[promotion]), to);
1107 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1108 board[to] = piece_of_color_and_type(us, promotion);
1111 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1113 // Update pawn hash key:
1114 pawnKey ^= zobrist[us][PAWN][from];
1116 // Update material key:
1117 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1118 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1120 // Update piece counts:
1121 pieceCount[us][PAWN]--;
1122 pieceCount[us][promotion]++;
1124 // Update piece lists:
1125 pieceList[us][PAWN][index[from]] =
1126 pieceList[us][PAWN][pieceCount[us][PAWN]];
1127 index[pieceList[us][PAWN][index[from]]] = index[from];
1128 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1129 index[to] = pieceCount[us][promotion] - 1;
1131 // Update incremental scores:
1132 mgValue -= mg_pst(us, PAWN, from);
1133 mgValue += mg_pst(us, promotion, to);
1134 egValue -= eg_pst(us, PAWN, from);
1135 egValue += eg_pst(us, promotion, to);
1138 npMaterial[us] += piece_value_midgame(promotion);
1140 // Clear the en passant square:
1141 if(epSquare != SQ_NONE) {
1142 key ^= zobEp[epSquare];
1146 // Update castle rights:
1147 key ^= zobCastle[castleRights];
1148 castleRights &= castleRightsMask[to];
1149 key ^= zobCastle[castleRights];
1151 // Reset rule 50 counter:
1154 // Update checkers BB:
1155 checkersBB = attacks_to(king_square(them), us);
1159 /// Position::do_ep_move() is a private method used to make an en passant
1160 /// capture. It is called from the main Position::do_move function. Because
1161 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1162 /// object in which to store the captured piece.
1164 void Position::do_ep_move(Move m) {
1166 Square from, to, capsq;
1169 assert(move_is_ok(m));
1170 assert(move_is_ep(m));
1172 us = side_to_move();
1173 them = opposite_color(us);
1175 // Find from, to and capture squares:
1176 from = move_from(m);
1178 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1180 assert(to == epSquare);
1181 assert(relative_rank(us, to) == RANK_6);
1182 assert(piece_on(to) == EMPTY);
1183 assert(piece_on(from) == pawn_of_color(us));
1184 assert(piece_on(capsq) == pawn_of_color(them));
1186 // Remove captured piece:
1187 clear_bit(&(byColorBB[them]), capsq);
1188 clear_bit(&(byTypeBB[PAWN]), capsq);
1189 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1190 board[capsq] = EMPTY;
1192 // Remove moving piece from source square:
1193 clear_bit(&(byColorBB[us]), from);
1194 clear_bit(&(byTypeBB[PAWN]), from);
1195 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1197 // Put moving piece on destination square:
1198 set_bit(&(byColorBB[us]), to);
1199 set_bit(&(byTypeBB[PAWN]), to);
1200 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1201 board[to] = board[from];
1202 board[from] = EMPTY;
1204 // Update material hash key:
1205 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1207 // Update piece count:
1208 pieceCount[them][PAWN]--;
1210 // Update piece list:
1211 pieceList[us][PAWN][index[from]] = to;
1212 index[to] = index[from];
1213 pieceList[them][PAWN][index[capsq]] =
1214 pieceList[them][PAWN][pieceCount[them][PAWN]];
1215 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1218 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1219 key ^= zobrist[them][PAWN][capsq];
1220 key ^= zobEp[epSquare];
1222 // Update pawn hash key:
1223 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1224 pawnKey ^= zobrist[them][PAWN][capsq];
1226 // Update incremental scores:
1227 mgValue -= mg_pst(them, PAWN, capsq);
1228 mgValue -= mg_pst(us, PAWN, from);
1229 mgValue += mg_pst(us, PAWN, to);
1230 egValue -= eg_pst(them, PAWN, capsq);
1231 egValue -= eg_pst(us, PAWN, from);
1232 egValue += eg_pst(us, PAWN, to);
1234 // Reset en passant square:
1237 // Reset rule 50 counter:
1240 // Update checkers BB:
1241 checkersBB = attacks_to(king_square(them), us);
1245 /// Position::undo_move() unmakes a move. When it returns, the position should
1246 /// be restored to exactly the same state as before the move was made. It is
1247 /// important that Position::undo_move is called with the same move and UndoInfo
1248 /// object as the earlier call to Position::do_move.
1250 void Position::undo_move(Move m, const UndoInfo &u) {
1252 assert(move_is_ok(m));
1255 sideToMove = opposite_color(sideToMove);
1257 // Restore information from our UndoInfo object (except the captured piece,
1258 // which is taken care of later):
1261 if(move_is_castle(m))
1262 undo_castle_move(m);
1263 else if(move_promotion(m))
1264 undo_promotion_move(m, u);
1265 else if(move_is_ep(m))
1270 PieceType piece, capture;
1272 us = side_to_move();
1273 them = opposite_color(us);
1275 from = move_from(m);
1278 assert(piece_on(from) == EMPTY);
1279 assert(color_of_piece_on(to) == us);
1281 // Put the piece back at the source square:
1282 piece = type_of_piece_on(to);
1283 set_bit(&(byColorBB[us]), from);
1284 set_bit(&(byTypeBB[piece]), from);
1285 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1286 board[from] = piece_of_color_and_type(us, piece);
1288 // Clear the destination square
1289 clear_bit(&(byColorBB[us]), to);
1290 clear_bit(&(byTypeBB[piece]), to);
1291 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1293 // If the moving piece was a king, update the king square:
1295 kingSquare[us] = from;
1297 // Update piece list:
1298 pieceList[us][piece][index[to]] = from;
1299 index[from] = index[to];
1301 capture = u.capture;
1304 assert(capture != KING);
1305 // Replace the captured piece:
1306 set_bit(&(byColorBB[them]), to);
1307 set_bit(&(byTypeBB[capture]), to);
1308 set_bit(&(byTypeBB[0]), to);
1309 board[to] = piece_of_color_and_type(them, capture);
1313 npMaterial[them] += piece_value_midgame(capture);
1315 // Update piece list:
1316 pieceList[them][capture][pieceCount[them][capture]] = to;
1317 index[to] = pieceCount[them][capture];
1319 // Update piece count:
1320 pieceCount[them][capture]++;
1330 /// Position::undo_castle_move() is a private method used to unmake a castling
1331 /// move. It is called from the main Position::undo_move function. Note that
1332 /// castling moves are encoded as "king captures friendly rook" moves, for
1333 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1335 void Position::undo_castle_move(Move m) {
1337 Square kfrom, kto, rfrom, rto;
1339 assert(move_is_ok(m));
1340 assert(move_is_castle(m));
1342 // When we have arrived here, some work has already been done by
1343 // Position::undo_move. In particular, the side to move has been switched,
1344 // so the code below is correct.
1345 us = side_to_move();
1346 them = opposite_color(us);
1348 // Find source squares for king and rook:
1349 kfrom = move_from(m);
1350 rfrom = move_to(m); // HACK: See comment at beginning of function.
1352 // Find destination squares for king and rook:
1353 if(rfrom > kfrom) { // O-O
1354 kto = relative_square(us, SQ_G1);
1355 rto = relative_square(us, SQ_F1);
1358 kto = relative_square(us, SQ_C1);
1359 rto = relative_square(us, SQ_D1);
1362 assert(piece_on(kto) == king_of_color(us));
1363 assert(piece_on(rto) == rook_of_color(us));
1365 // Remove pieces from destination squares:
1366 clear_bit(&(byColorBB[us]), kto);
1367 clear_bit(&(byTypeBB[KING]), kto);
1368 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1369 clear_bit(&(byColorBB[us]), rto);
1370 clear_bit(&(byTypeBB[ROOK]), rto);
1371 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1373 // Put pieces on source squares:
1374 set_bit(&(byColorBB[us]), kfrom);
1375 set_bit(&(byTypeBB[KING]), kfrom);
1376 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1377 set_bit(&(byColorBB[us]), rfrom);
1378 set_bit(&(byTypeBB[ROOK]), rfrom);
1379 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1382 board[rto] = board[kto] = EMPTY;
1383 board[rfrom] = rook_of_color(us);
1384 board[kfrom] = king_of_color(us);
1386 // Update king square:
1387 kingSquare[us] = kfrom;
1389 // Update piece lists:
1390 pieceList[us][KING][index[kto]] = kfrom;
1391 pieceList[us][ROOK][index[rto]] = rfrom;
1392 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1393 index[kfrom] = index[kto];
1398 /// Position::undo_promotion_move() is a private method used to unmake a
1399 /// promotion move. It is called from the main Position::do_move
1400 /// function. The UndoInfo object, which has been initialized in
1401 /// Position::do_move, is used to put back the captured piece (if any).
1403 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1406 PieceType capture, promotion;
1408 assert(move_is_ok(m));
1409 assert(move_promotion(m));
1411 // When we have arrived here, some work has already been done by
1412 // Position::undo_move. In particular, the side to move has been switched,
1413 // so the code below is correct.
1414 us = side_to_move();
1415 them = opposite_color(us);
1417 from = move_from(m);
1420 assert(relative_rank(us, to) == RANK_8);
1421 assert(piece_on(from) == EMPTY);
1423 // Remove promoted piece:
1424 promotion = move_promotion(m);
1425 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1426 assert(promotion >= KNIGHT && promotion <= QUEEN);
1427 clear_bit(&(byColorBB[us]), to);
1428 clear_bit(&(byTypeBB[promotion]), to);
1429 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1431 // Insert pawn at source square:
1432 set_bit(&(byColorBB[us]), from);
1433 set_bit(&(byTypeBB[PAWN]), from);
1434 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1435 board[from] = pawn_of_color(us);
1438 npMaterial[us] -= piece_value_midgame(promotion);
1440 // Update piece list:
1441 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1442 index[from] = pieceCount[us][PAWN];
1443 pieceList[us][promotion][index[to]] =
1444 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1445 index[pieceList[us][promotion][index[to]]] = index[to];
1447 // Update piece counts:
1448 pieceCount[us][promotion]--;
1449 pieceCount[us][PAWN]++;
1451 capture = u.capture;
1453 assert(capture != KING);
1455 // Insert captured piece:
1456 set_bit(&(byColorBB[them]), to);
1457 set_bit(&(byTypeBB[capture]), to);
1458 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1459 board[to] = piece_of_color_and_type(them, capture);
1461 // Update material. Because the move is a promotion move, we know
1462 // that the captured piece cannot be a pawn.
1463 assert(capture != PAWN);
1464 npMaterial[them] += piece_value_midgame(capture);
1466 // Update piece list:
1467 pieceList[them][capture][pieceCount[them][capture]] = to;
1468 index[to] = pieceCount[them][capture];
1470 // Update piece count:
1471 pieceCount[them][capture]++;
1478 /// Position::undo_ep_move() is a private method used to unmake an en passant
1479 /// capture. It is called from the main Position::undo_move function. Because
1480 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1481 /// object from which to retrieve the captured piece.
1483 void Position::undo_ep_move(Move m) {
1485 Square from, to, capsq;
1487 assert(move_is_ok(m));
1488 assert(move_is_ep(m));
1490 // When we have arrived here, some work has already been done by
1491 // Position::undo_move. In particular, the side to move has been switched,
1492 // so the code below is correct.
1493 us = side_to_move();
1494 them = opposite_color(us);
1496 // Find from, to and captures squares:
1497 from = move_from(m);
1499 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1501 assert(to == ep_square());
1502 assert(relative_rank(us, to) == RANK_6);
1503 assert(piece_on(to) == pawn_of_color(us));
1504 assert(piece_on(from) == EMPTY);
1505 assert(piece_on(capsq) == EMPTY);
1507 // Replace captured piece:
1508 set_bit(&(byColorBB[them]), capsq);
1509 set_bit(&(byTypeBB[PAWN]), capsq);
1510 set_bit(&(byTypeBB[0]), capsq);
1511 board[capsq] = pawn_of_color(them);
1513 // Remove moving piece from destination square:
1514 clear_bit(&(byColorBB[us]), to);
1515 clear_bit(&(byTypeBB[PAWN]), to);
1516 clear_bit(&(byTypeBB[0]), to);
1519 // Replace moving piece at source square:
1520 set_bit(&(byColorBB[us]), from);
1521 set_bit(&(byTypeBB[PAWN]), from);
1522 set_bit(&(byTypeBB[0]), from);
1523 board[from] = pawn_of_color(us);
1525 // Update piece list:
1526 pieceList[us][PAWN][index[to]] = from;
1527 index[from] = index[to];
1528 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1529 index[capsq] = pieceCount[them][PAWN];
1531 // Update piece count:
1532 pieceCount[them][PAWN]++;
1536 /// Position::do_null_move makes() a "null move": It switches the side to move
1537 /// and updates the hash key without executing any move on the board.
1539 void Position::do_null_move(UndoInfo &u) {
1541 assert(!is_check());
1543 // Back up the information necessary to undo the null move to the supplied
1544 // UndoInfo object. In the case of a null move, the only thing we need to
1545 // remember is the last move made and the en passant square.
1546 u.lastMove = lastMove;
1547 u.epSquare = epSquare;
1549 // Save the current key to the history[] array, in order to be able to
1550 // detect repetition draws:
1551 history[gamePly] = key;
1553 // Update the necessary information.
1554 sideToMove = opposite_color(sideToMove);
1555 if(epSquare != SQ_NONE)
1556 key ^= zobEp[epSquare];
1560 key ^= zobSideToMove;
1562 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1563 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1569 /// Position::undo_null_move() unmakes a "null move".
1571 void Position::undo_null_move(const UndoInfo &u) {
1573 assert(!is_check());
1575 // Restore information from the supplied UndoInfo object:
1576 lastMove = u.lastMove;
1577 epSquare = u.epSquare;
1578 if(epSquare != SQ_NONE)
1579 key ^= zobEp[epSquare];
1581 // Update the necessary information.
1582 sideToMove = opposite_color(sideToMove);
1585 key ^= zobSideToMove;
1587 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1588 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1594 /// Position::see() is a static exchange evaluator: It tries to estimate the
1595 /// material gain or loss resulting from a move. There are two versions of
1596 /// this function: One which takes a move as input, and one which takes a
1597 /// 'from' and a 'to' square. The function does not yet understand promotions
1598 /// or en passant captures.
1600 int Position::see(Square from, Square to) const {
1601 // Approximate material values, with pawn = 1:
1602 static const int seeValues[18] = {
1603 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1606 Piece piece, capture;
1607 Bitboard attackers, occ, b;
1609 assert(square_is_ok(from));
1610 assert(square_is_ok(to));
1612 // Initialize colors:
1613 us = color_of_piece_on(from);
1614 them = opposite_color(us);
1616 // Initialize pieces:
1617 piece = piece_on(from);
1618 capture = piece_on(to);
1620 // Find all attackers to the destination square, with the moving piece
1621 // removed, but possibly an X-ray attacker added behind it:
1622 occ = occupied_squares();
1623 clear_bit(&occ, from);
1625 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1626 (bishop_attacks_bb(to, occ) & bishops_and_queens()) |
1627 (piece_attacks<KNIGHT>(to) & knights()) |
1628 (piece_attacks<KING>(to) & kings()) |
1629 (pawn_attacks(WHITE, to) & pawns(BLACK)) |
1630 (pawn_attacks(BLACK, to) & pawns(WHITE));
1633 // If the opponent has no attackers, we are finished:
1634 if((attackers & pieces_of_color(them)) == EmptyBoardBB)
1635 return seeValues[capture];
1637 // The destination square is defended, which makes things rather more
1638 // difficult to compute. We proceed by building up a "swap list" containing
1639 // the material gain or loss at each stop in a sequence of captures to the
1640 // destianation square, where the sides alternately capture, and always
1641 // capture with the least valuable piece. After each capture, we look for
1642 // new X-ray attacks from behind the capturing piece.
1643 int lastCapturingPieceValue = seeValues[piece];
1644 int swapList[32], n = 1;
1648 swapList[0] = seeValues[capture];
1651 // Locate the least valuable attacker for the side to move. The loop
1652 // below looks like it is potentially infinite, but it isn't. We know
1653 // that the side to move still has at least one attacker left.
1654 for(pt = PAWN; !(attackers&pieces_of_color_and_type(c, pt)); pt++)
1657 // Remove the attacker we just found from the 'attackers' bitboard,
1658 // and scan for new X-ray attacks behind the attacker:
1659 b = attackers & pieces_of_color_and_type(c, pt);
1662 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1663 (bishop_attacks_bb(to, occ) & bishops_and_queens());
1666 // Add the new entry to the swap list:
1668 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1671 // Remember the value of the capturing piece, and change the side to move
1672 // before beginning the next iteration:
1673 lastCapturingPieceValue = seeValues[pt];
1674 c = opposite_color(c);
1676 // Stop after a king capture:
1677 if(pt == KING && (attackers & pieces_of_color(c))) {
1679 swapList[n++] = 100;
1682 } while(attackers & pieces_of_color(c));
1684 // Having built the swap list, we negamax through it to find the best
1685 // achievable score from the point of view of the side to move:
1686 while(--n) swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1692 int Position::see(Move m) const {
1693 assert(move_is_ok(m));
1694 return see(move_from(m), move_to(m));
1698 /// Position::clear() erases the position object to a pristine state, with an
1699 /// empty board, white to move, and no castling rights.
1701 void Position::clear() {
1704 for(i = 0; i < 64; i++) {
1709 for(i = 0; i < 2; i++)
1710 byColorBB[i] = EmptyBoardBB;
1712 for(i = 0; i < 7; i++) {
1713 byTypeBB[i] = EmptyBoardBB;
1714 pieceCount[0][i] = pieceCount[1][i] = 0;
1715 for(j = 0; j < 8; j++)
1716 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1719 checkersBB = EmptyBoardBB;
1721 lastMove = MOVE_NONE;
1724 castleRights = NO_CASTLES;
1725 initialKFile = FILE_E;
1726 initialKRFile = FILE_H;
1727 initialQRFile = FILE_A;
1734 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1735 /// UCI interface code, whenever a non-reversible move is made in a
1736 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1737 /// for the program to handle games of arbitrary length, as long as the GUI
1738 /// handles draws by the 50 move rule correctly.
1740 void Position::reset_game_ply() {
1745 /// Position::put_piece() puts a piece on the given square of the board,
1746 /// updating the board array, bitboards, and piece counts.
1748 void Position::put_piece(Piece p, Square s) {
1749 Color c = color_of_piece(p);
1750 PieceType pt = type_of_piece(p);
1753 index[s] = pieceCount[c][pt];
1754 pieceList[c][pt][index[s]] = s;
1756 set_bit(&(byTypeBB[pt]), s);
1757 set_bit(&(byColorBB[c]), s);
1758 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1760 pieceCount[c][pt]++;
1767 /// Position::allow_oo() gives the given side the right to castle kingside.
1768 /// Used when setting castling rights during parsing of FEN strings.
1770 void Position::allow_oo(Color c) {
1771 castleRights |= (1 + int(c));
1775 /// Position::allow_ooo() gives the given side the right to castle queenside.
1776 /// Used when setting castling rights during parsing of FEN strings.
1778 void Position::allow_ooo(Color c) {
1779 castleRights |= (4 + 4*int(c));
1783 /// Position::compute_key() computes the hash key of the position. The hash
1784 /// key is usually updated incrementally as moves are made and unmade, the
1785 /// compute_key() function is only used when a new position is set up, and
1786 /// to verify the correctness of the hash key when running in debug mode.
1788 Key Position::compute_key() const {
1789 Key result = Key(0ULL);
1791 for(Square s = SQ_A1; s <= SQ_H8; s++)
1792 if(square_is_occupied(s))
1794 zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1796 if(ep_square() != SQ_NONE)
1797 result ^= zobEp[ep_square()];
1798 result ^= zobCastle[castleRights];
1799 if(side_to_move() == BLACK) result ^= zobSideToMove;
1805 /// Position::compute_pawn_key() computes the hash key of the position. The
1806 /// hash key is usually updated incrementally as moves are made and unmade,
1807 /// the compute_pawn_key() function is only used when a new position is set
1808 /// up, and to verify the correctness of the pawn hash key when running in
1811 Key Position::compute_pawn_key() const {
1812 Key result = Key(0ULL);
1816 for(Color c = WHITE; c <= BLACK; c++) {
1819 s = pop_1st_bit(&b);
1820 result ^= zobrist[c][PAWN][s];
1827 /// Position::compute_material_key() computes the hash key of the position.
1828 /// The hash key is usually updated incrementally as moves are made and unmade,
1829 /// the compute_material_key() function is only used when a new position is set
1830 /// up, and to verify the correctness of the material hash key when running in
1833 Key Position::compute_material_key() const {
1834 Key result = Key(0ULL);
1835 for(Color c = WHITE; c <= BLACK; c++)
1836 for(PieceType pt = PAWN; pt <= QUEEN; pt++) {
1837 int count = piece_count(c, pt);
1838 for(int i = 0; i <= count; i++)
1839 result ^= zobMaterial[c][pt][i];
1845 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1846 /// incremental scores for the middle game and the endgame. These functions
1847 /// are used to initialize the incremental scores when a new position is set
1848 /// up, and to verify that the scores are correctly updated by do_move
1849 /// and undo_move when the program is running in debug mode.
1851 Value Position::compute_mg_value() const {
1852 Value result = Value(0);
1856 for(Color c = WHITE; c <= BLACK; c++)
1857 for(PieceType pt = PAWN; pt <= KING; pt++) {
1858 b = pieces_of_color_and_type(c, pt);
1860 s = pop_1st_bit(&b);
1861 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1862 result += mg_pst(c, pt, s);
1865 result += (side_to_move() == WHITE)?
1866 (TempoValueMidgame / 2) : -(TempoValueMidgame / 2);
1870 Value Position::compute_eg_value() const {
1871 Value result = Value(0);
1875 for(Color c = WHITE; c <= BLACK; c++)
1876 for(PieceType pt = PAWN; pt <= KING; pt++) {
1877 b = pieces_of_color_and_type(c, pt);
1879 s = pop_1st_bit(&b);
1880 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1881 result += eg_pst(c, pt, s);
1884 result += (side_to_move() == WHITE)?
1885 (TempoValueEndgame / 2) : -(TempoValueEndgame / 2);
1890 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1891 /// game material score for the given side. Material scores are updated
1892 /// incrementally during the search, this function is only used while
1893 /// initializing a new Position object.
1895 Value Position::compute_non_pawn_material(Color c) const {
1896 Value result = Value(0);
1899 for(PieceType pt = KNIGHT; pt <= QUEEN; pt++) {
1900 Bitboard b = pieces_of_color_and_type(c, pt);
1902 s = pop_1st_bit(&b);
1903 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1904 result += piece_value_midgame(pt);
1911 /// Position::is_mate() returns true or false depending on whether the
1912 /// side to move is checkmated. Note that this function is currently very
1913 /// slow, and shouldn't be used frequently inside the search.
1915 bool Position::is_mate() {
1917 MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
1918 MOVE_NONE, Depth(0));
1919 return mp.get_next_move() == MOVE_NONE;
1926 /// Position::is_draw() tests whether the position is drawn by material,
1927 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1928 /// must be done by the search.
1930 bool Position::is_draw() const {
1931 // Draw by material?
1933 non_pawn_material(WHITE) + non_pawn_material(BLACK)
1934 <= BishopValueMidgame)
1937 // Draw by the 50 moves rule?
1938 if(rule50 > 100 || (rule50 == 100 && !is_check()))
1941 // Draw by repetition?
1942 for(int i = 2; i < Min(gamePly, rule50); i += 2)
1943 if(history[gamePly - i] == key)
1950 /// Position::has_mate_threat() tests whether a given color has a mate in one
1951 /// from the current position. This function is quite slow, but it doesn't
1952 /// matter, because it is currently only called from PV nodes, which are rare.
1954 bool Position::has_mate_threat(Color c) {
1956 Color stm = side_to_move();
1958 // The following lines are useless and silly, but prevents gcc from
1959 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1960 // be used uninitialized.
1961 u1.lastMove = lastMove;
1962 u1.epSquare = epSquare;
1967 // If the input color is not equal to the side to move, do a null move
1968 if(c != stm) do_null_move(u1);
1970 MoveStack mlist[120];
1972 bool result = false;
1974 // Generate legal moves
1975 count = generate_legal_moves(*this, mlist);
1977 // Loop through the moves, and see if one of them is mate.
1978 for(int i = 0; i < count; i++) {
1979 do_move(mlist[i].move, u2);
1980 if(is_mate()) result = true;
1981 undo_move(mlist[i].move, u2);
1984 // Undo null move, if necessary
1985 if(c != stm) undo_null_move(u1);
1991 /// Position::init_zobrist() is a static member function which initializes the
1992 /// various arrays used to compute hash keys.
1994 void Position::init_zobrist() {
1996 for(int i = 0; i < 2; i++)
1997 for(int j = 0; j < 8; j++)
1998 for(int k = 0; k < 64; k++)
1999 zobrist[i][j][k] = Key(genrand_int64());
2001 for(int i = 0; i < 64; i++)
2002 zobEp[i] = Key(genrand_int64());
2004 for(int i = 0; i < 16; i++)
2005 zobCastle[i] = genrand_int64();
2007 zobSideToMove = genrand_int64();
2009 for(int i = 0; i < 2; i++)
2010 for(int j = 0; j < 8; j++)
2011 for(int k = 0; k < 16; k++)
2012 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2014 for(int i = 0; i < 16; i++)
2015 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2019 /// Position::init_piece_square_tables() initializes the piece square tables.
2020 /// This is a two-step operation: First, the white halves of the tables are
2021 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2022 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2023 /// Second, the black halves of the tables are initialized by mirroring
2024 /// and changing the sign of the corresponding white scores.
2026 void Position::init_piece_square_tables() {
2027 int r = get_option_value_int("Randomness"), i;
2028 for(Square s = SQ_A1; s <= SQ_H8; s++) {
2029 for(Piece p = WP; p <= WK; p++) {
2030 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2031 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2032 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2035 for(Square s = SQ_A1; s <= SQ_H8; s++)
2036 for(Piece p = BP; p <= BK; p++) {
2037 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2038 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2043 /// Position::flipped_copy() makes a copy of the input position, but with
2044 /// the white and black sides reversed. This is only useful for debugging,
2045 /// especially for finding evaluation symmetry bugs.
2047 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;
2072 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
2073 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
2074 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2075 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2076 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2077 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2079 // En passant square
2080 if(pos.epSquare != SQ_NONE)
2081 epSquare = flip_square(pos.epSquare);
2087 key = compute_key();
2088 pawnKey = compute_pawn_key();
2089 materialKey = compute_material_key();
2091 // Incremental scores
2092 mgValue = compute_mg_value();
2093 egValue = compute_eg_value();
2096 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2097 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2103 /// Position::is_ok() performs some consitency checks for the position object.
2104 /// This is meant to be helpful when debugging.
2106 bool Position::is_ok(int* failedStep) const {
2108 // What features of the position should be verified?
2109 static const bool debugBitboards = false;
2110 static const bool debugKingCount = false;
2111 static const bool debugKingCapture = false;
2112 static const bool debugCheckerCount = false;
2113 static const bool debugKey = false;
2114 static const bool debugMaterialKey = false;
2115 static const bool debugPawnKey = false;
2116 static const bool debugIncrementalEval = false;
2117 static const bool debugNonPawnMaterial = false;
2118 static const bool debugPieceCounts = false;
2119 static const bool debugPieceList = false;
2121 if (failedStep) *failedStep = 1;
2124 if(!color_is_ok(side_to_move()))
2127 // Are the king squares in the position correct?
2128 if (failedStep) (*failedStep)++;
2129 if(piece_on(king_square(WHITE)) != WK)
2132 if (failedStep) (*failedStep)++;
2133 if(piece_on(king_square(BLACK)) != BK)
2137 if (failedStep) (*failedStep)++;
2138 if(!file_is_ok(initialKRFile))
2140 if(!file_is_ok(initialQRFile))
2143 // Do both sides have exactly one king?
2144 if (failedStep) (*failedStep)++;
2145 if(debugKingCount) {
2146 int kingCount[2] = {0, 0};
2147 for(Square s = SQ_A1; s <= SQ_H8; s++)
2148 if(type_of_piece_on(s) == KING)
2149 kingCount[color_of_piece_on(s)]++;
2150 if(kingCount[0] != 1 || kingCount[1] != 1)
2154 // Can the side to move capture the opponent's king?
2155 if (failedStep) (*failedStep)++;
2156 if(debugKingCapture) {
2157 Color us = side_to_move();
2158 Color them = opposite_color(us);
2159 Square ksq = king_square(them);
2160 if(square_is_attacked(ksq, us))
2164 // Is there more than 2 checkers?
2165 if (failedStep) (*failedStep)++;
2166 if(debugCheckerCount && count_1s(checkersBB) > 2)
2170 if (failedStep) (*failedStep)++;
2171 if(debugBitboards) {
2172 // The intersection of the white and black pieces must be empty:
2173 if((pieces_of_color(WHITE) & pieces_of_color(BLACK))
2177 // The union of the white and black pieces must be equal to all
2178 // occupied squares:
2179 if((pieces_of_color(WHITE) | pieces_of_color(BLACK))
2180 != occupied_squares())
2183 // Separate piece type bitboards must have empty intersections:
2184 for(PieceType p1 = PAWN; p1 <= KING; p1++)
2185 for(PieceType p2 = PAWN; p2 <= KING; p2++)
2186 if(p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2190 // En passant square OK?
2191 if (failedStep) (*failedStep)++;
2192 if(ep_square() != SQ_NONE) {
2193 // The en passant square must be on rank 6, from the point of view of the
2195 if(relative_rank(side_to_move(), ep_square()) != RANK_6)
2200 if (failedStep) (*failedStep)++;
2201 if(debugKey && key != compute_key())
2204 // Pawn hash key OK?
2205 if (failedStep) (*failedStep)++;
2206 if(debugPawnKey && pawnKey != compute_pawn_key())
2209 // Material hash key OK?
2210 if (failedStep) (*failedStep)++;
2211 if(debugMaterialKey && materialKey != compute_material_key())
2214 // Incremental eval OK?
2215 if (failedStep) (*failedStep)++;
2216 if(debugIncrementalEval) {
2217 if(mgValue != compute_mg_value())
2219 if(egValue != compute_eg_value())
2223 // Non-pawn material OK?
2224 if (failedStep) (*failedStep)++;
2225 if(debugNonPawnMaterial) {
2226 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2228 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2233 if (failedStep) (*failedStep)++;
2234 if(debugPieceCounts)
2235 for(Color c = WHITE; c <= BLACK; c++)
2236 for(PieceType pt = PAWN; pt <= KING; pt++)
2237 if(pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2240 if (failedStep) (*failedStep)++;
2241 if(debugPieceList) {
2242 for(Color c = WHITE; c <= BLACK; c++)
2243 for(PieceType pt = PAWN; pt <= KING; pt++)
2244 for(int i = 0; i < pieceCount[c][pt]; i++) {
2245 if(piece_on(piece_list(c, pt, i)) !=
2246 piece_of_color_and_type(c, pt))
2248 if(index[piece_list(c, pt, i)] != i)
2252 if (failedStep) *failedStep = 0;