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/>.
36 #include "ucioption.h"
43 extern SearchStack EmptySearchStack;
45 int Position::castleRightsMask[64];
47 Key Position::zobrist[2][8][64];
48 Key Position::zobEp[64];
49 Key Position::zobCastle[16];
50 Key Position::zobMaterial[2][8][16];
51 Key Position::zobSideToMove;
53 Value Position::MgPieceSquareTable[16][64];
54 Value Position::EgPieceSquareTable[16][64];
56 static bool RequestPending = false;
64 Position::Position(const Position& pos) {
68 Position::Position(const std::string& fen) {
73 /// Position::from_fen() initializes the position object with the given FEN
74 /// string. This function is not very robust - make sure that input FENs are
75 /// correct (this is assumed to be the responsibility of the GUI).
77 void Position::from_fen(const std::string& fen) {
79 static const std::string pieceLetters = "KQRBNPkqrbnp";
80 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
88 for ( ; fen[i] != ' '; i++)
92 // Skip the given number of files
93 file += (fen[i] - '1' + 1);
96 else if (fen[i] == '/')
102 size_t idx = pieceLetters.find(fen[i]);
103 if (idx == std::string::npos)
105 std::cout << "Error in FEN at character " << i << std::endl;
108 Square square = make_square(file, rank);
109 put_piece(pieces[idx], square);
115 if (fen[i] != 'w' && fen[i] != 'b')
117 std::cout << "Error in FEN at character " << i << std::endl;
120 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
126 std::cout << "Error in FEN at character " << i << std::endl;
131 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
137 else if(fen[i] == 'K') allow_oo(WHITE);
138 else if(fen[i] == 'Q') allow_ooo(WHITE);
139 else if(fen[i] == 'k') allow_oo(BLACK);
140 else if(fen[i] == 'q') allow_ooo(BLACK);
141 else if(fen[i] >= 'A' && fen[i] <= 'H') {
142 File rookFile, kingFile = FILE_NONE;
143 for(Square square = SQ_B1; square <= SQ_G1; square++)
144 if(piece_on(square) == WK)
145 kingFile = square_file(square);
146 if(kingFile == FILE_NONE) {
147 std::cout << "Error in FEN at character " << i << std::endl;
150 initialKFile = kingFile;
151 rookFile = File(fen[i] - 'A') + FILE_A;
152 if(rookFile < initialKFile) {
154 initialQRFile = rookFile;
158 initialKRFile = rookFile;
161 else if(fen[i] >= 'a' && fen[i] <= 'h') {
162 File rookFile, kingFile = FILE_NONE;
163 for(Square square = SQ_B8; square <= SQ_G8; square++)
164 if(piece_on(square) == BK)
165 kingFile = square_file(square);
166 if(kingFile == FILE_NONE) {
167 std::cout << "Error in FEN at character " << i << std::endl;
170 initialKFile = kingFile;
171 rookFile = File(fen[i] - 'a') + FILE_A;
172 if(rookFile < initialKFile) {
174 initialQRFile = rookFile;
178 initialKRFile = rookFile;
182 std::cout << "Error in FEN at character " << i << std::endl;
189 while (fen[i] == ' ')
193 if ( i < fen.length() - 2
194 && (fen[i] >= 'a' && fen[i] <= 'h')
195 && (fen[i+1] == '3' || fen[i+1] == '6'))
196 st->epSquare = square_from_string(fen.substr(i, 2));
198 // Various initialisation
199 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
200 castleRightsMask[sq] = ALL_CASTLES;
202 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
203 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
204 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
205 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
206 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
207 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
210 find_hidden_checks();
212 st->key = compute_key();
213 st->pawnKey = compute_pawn_key();
214 st->materialKey = compute_material_key();
215 st->mgValue = compute_value<MidGame>();
216 st->egValue = compute_value<EndGame>();
217 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
218 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
222 /// Position::to_fen() converts the position object to a FEN string. This is
223 /// probably only useful for debugging.
225 const std::string Position::to_fen() const {
227 static const std::string pieceLetters = " PNBRQK pnbrqk";
231 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
234 for (File file = FILE_A; file <= FILE_H; file++)
236 Square sq = make_square(file, rank);
237 if (!square_is_occupied(sq))
243 fen += (char)skip + '0';
246 fen += pieceLetters[piece_on(sq)];
249 fen += (char)skip + '0';
251 fen += (rank > RANK_1 ? '/' : ' ');
253 fen += (sideToMove == WHITE ? "w " : "b ");
254 if (st->castleRights != NO_CASTLES)
256 if (can_castle_kingside(WHITE)) fen += 'K';
257 if (can_castle_queenside(WHITE)) fen += 'Q';
258 if (can_castle_kingside(BLACK)) fen += 'k';
259 if (can_castle_queenside(BLACK)) fen += 'q';
264 if (ep_square() != SQ_NONE)
265 fen += square_to_string(ep_square());
273 /// Position::print() prints an ASCII representation of the position to
274 /// the standard output. If a move is given then also the san is print.
276 void Position::print(Move m) const {
278 static const std::string pieceLetters = " PNBRQK PNBRQK .";
280 // Check for reentrancy, as example when called from inside
281 // MovePicker that is used also here in move_to_san()
285 RequestPending = true;
287 std::cout << std::endl;
290 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
291 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
293 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
295 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
296 for (File file = FILE_A; file <= FILE_H; file++)
298 Square sq = make_square(file, rank);
299 Piece piece = piece_on(sq);
300 if (piece == EMPTY && square_color(sq) == WHITE)
303 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
304 std::cout << '|' << col << pieceLetters[piece] << col;
306 std::cout << '|' << std::endl;
308 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
309 << "Fen is: " << to_fen() << std::endl
310 << "Key is: " << st->key << std::endl;
312 RequestPending = false;
316 /// Position::copy() creates a copy of the input position.
318 void Position::copy(const Position &pos) {
320 memcpy(this, &pos, sizeof(Position));
324 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
325 /// king) pieces for the given color and for the given pinner type. Or, when
326 /// template parameter FindPinned is false, the pinned pieces of opposite color
327 /// that are, indeed, the pieces candidate for a discovery check.
328 /// Note that checkersBB bitboard must be already updated.
329 template<PieceType Piece, bool FindPinned>
330 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
333 Bitboard sliders, result = EmptyBoardBB;
335 if (Piece == ROOK) // Resolved at compile time
336 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
338 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
340 if (sliders && (!FindPinned || (sliders & ~st->checkersBB)))
342 // King blockers are candidate pinned pieces
343 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
345 // Pinners are sliders, not checkers, that give check when
346 // candidate pinned are removed.
347 pinners = (FindPinned ? sliders & ~st->checkersBB : sliders);
350 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
352 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
354 // Finally for each pinner find the corresponding pinned piece (if same color of king)
355 // or discovery checker (if opposite color) among the candidates.
356 Bitboard p = pinners;
360 result |= (squares_between(s, ksq) & candidate_pinned);
364 pinners = EmptyBoardBB;
370 /// Position::attacks_to() computes a bitboard containing all pieces which
371 /// attacks a given square. There are two versions of this function: One
372 /// which finds attackers of both colors, and one which only finds the
373 /// attackers for one side.
375 Bitboard Position::attacks_to(Square s) const {
377 return (pawn_attacks(BLACK, s) & pawns(WHITE))
378 | (pawn_attacks(WHITE, s) & pawns(BLACK))
379 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
380 | (piece_attacks<ROOK>(s) & rooks_and_queens())
381 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
382 | (piece_attacks<KING>(s) & pieces_of_type(KING));
385 /// Position::piece_attacks_square() tests whether the piece on square f
386 /// attacks square t.
388 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
390 assert(square_is_ok(f));
391 assert(square_is_ok(t));
395 case WP: return pawn_attacks_square(WHITE, f, t);
396 case BP: return pawn_attacks_square(BLACK, f, t);
397 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
398 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
399 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
400 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
401 case WK: case BK: return piece_attacks_square<KING>(f, t);
408 /// Position::move_attacks_square() tests whether a move from the current
409 /// position attacks a given square.
411 bool Position::move_attacks_square(Move m, Square s) const {
413 assert(move_is_ok(m));
414 assert(square_is_ok(s));
416 Square f = move_from(m), t = move_to(m);
418 assert(square_is_occupied(f));
420 if (piece_attacks_square(piece_on(f), t, s))
423 // Move the piece and scan for X-ray attacks behind it
424 Bitboard occ = occupied_squares();
425 Color us = color_of_piece_on(f);
428 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
429 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
431 // If we have attacks we need to verify that are caused by our move
432 // and are not already existent ones.
433 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
437 /// Position::find_checkers() computes the checkersBB bitboard, which
438 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
439 /// currently works by calling Position::attacks_to, which is probably
440 /// inefficient. Consider rewriting this function to use the last move
441 /// played, like in non-bitboard versions of Glaurung.
443 void Position::find_checkers() {
445 Color us = side_to_move();
446 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
449 /// Position:find_hidden_checks() computes the pinned, pinners and dcCandidates
450 /// bitboards. There are two versions of this function. One takes a color and
451 /// computes bitboards relative to that color only, the other computes both
452 /// colors. Bitboard checkersBB must be already updated.
454 void Position::find_hidden_checks(Color us, unsigned int types) {
457 Color them = opposite_color(us);
458 Square ksq = king_square(them);
461 st->pinned[them] = hidden_checks<ROOK, true>(them, ksq, p1) | hidden_checks<BISHOP, true>(them, ksq, p2);
462 st->pinners[them] = p1 | p2;
464 if (types & DcCandidates)
465 st->dcCandidates[us] = hidden_checks<ROOK, false>(us, ksq, p1) | hidden_checks<BISHOP, false>(us, ksq, p2);
468 void Position::find_hidden_checks() {
470 for (Color c = WHITE; c <= BLACK; c++)
471 find_hidden_checks(c, Pinned | DcCandidates);
475 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
477 bool Position::pl_move_is_legal(Move m) const {
480 assert(move_is_ok(m));
482 // If we're in check, all pseudo-legal moves are legal, because our
483 // check evasion generator only generates true legal moves.
487 // Castling moves are checked for legality during move generation.
488 if (move_is_castle(m))
491 Color us = side_to_move();
492 Color them = opposite_color(us);
493 Square from = move_from(m);
494 Square ksq = king_square(us);
496 assert(color_of_piece_on(from) == us);
497 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
499 // En passant captures are a tricky special case. Because they are
500 // rather uncommon, we do it simply by testing whether the king is attacked
501 // after the move is made
504 Square to = move_to(m);
505 Square capsq = make_square(square_file(to), square_rank(from));
506 Bitboard b = occupied_squares();
508 assert(to == ep_square());
509 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
510 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
511 assert(piece_on(to) == EMPTY);
514 clear_bit(&b, capsq);
517 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
518 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
521 // If the moving piece is a king, check whether the destination
522 // square is attacked by the opponent.
524 return !(square_is_attacked(move_to(m), them));
526 // A non-king move is legal if and only if it is not pinned or it
527 // is moving along the ray towards or away from the king.
528 return ( !bit_is_set(pinned_pieces(us), from)
529 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
533 /// Position::move_is_check() tests whether a pseudo-legal move is a check
535 bool Position::move_is_check(Move m) const {
538 assert(move_is_ok(m));
540 Color us = side_to_move();
541 Color them = opposite_color(us);
542 Square from = move_from(m);
543 Square to = move_to(m);
544 Square ksq = king_square(them);
545 Bitboard dcCandidates = discovered_check_candidates(us);
547 assert(color_of_piece_on(from) == us);
548 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
550 // Proceed according to the type of the moving piece
551 switch (type_of_piece_on(from))
555 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
558 if ( bit_is_set(dcCandidates, from) // Discovered check?
559 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
562 if (move_promotion(m)) // Promotion with check?
564 Bitboard b = occupied_squares();
567 switch (move_promotion(m))
570 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
572 return bit_is_set(bishop_attacks_bb(to, b), ksq);
574 return bit_is_set(rook_attacks_bb(to, b), ksq);
576 return bit_is_set(queen_attacks_bb(to, b), ksq);
581 // En passant capture with check? We have already handled the case
582 // of direct checks and ordinary discovered check, the only case we
583 // need to handle is the unusual case of a discovered check through the
585 else if (move_is_ep(m))
587 Square capsq = make_square(square_file(to), square_rank(from));
588 Bitboard b = occupied_squares();
590 clear_bit(&b, capsq);
592 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
593 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
598 return bit_is_set(dcCandidates, from) // Discovered check?
599 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
602 return bit_is_set(dcCandidates, from) // Discovered check?
603 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
606 return bit_is_set(dcCandidates, from) // Discovered check?
607 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
610 // Discovered checks are impossible!
611 assert(!bit_is_set(dcCandidates, from));
612 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
616 if ( bit_is_set(dcCandidates, from)
617 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
620 // Castling with check?
621 if (move_is_castle(m))
623 Square kfrom, kto, rfrom, rto;
624 Bitboard b = occupied_squares();
630 kto = relative_square(us, SQ_G1);
631 rto = relative_square(us, SQ_F1);
633 kto = relative_square(us, SQ_C1);
634 rto = relative_square(us, SQ_D1);
636 clear_bit(&b, kfrom);
637 clear_bit(&b, rfrom);
640 return bit_is_set(rook_attacks_bb(rto, b), ksq);
644 default: // NO_PIECE_TYPE
652 /// Position::move_is_capture() tests whether a move from the current
653 /// position is a capture. Move must not be MOVE_NONE.
655 bool Position::move_is_capture(Move m) const {
657 assert(m != MOVE_NONE);
659 return ( !square_is_empty(move_to(m))
660 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
666 /// Position::update_checkers() udpates chekers info given the move. It is called
667 /// in do_move() and is faster then find_checkers().
669 template<PieceType Piece>
670 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
671 Square to, Bitboard dcCandidates) {
673 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
674 set_bit(pCheckersBB, to);
676 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
679 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
682 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
687 /// Position::update_hidden_checks() udpates pinned, pinners and dcCandidates
688 /// bitboards incrementally, given the move. It is called in do_move and is
689 /// faster then find_hidden_checks().
691 void Position::update_hidden_checks(Square from, Square to) {
693 Color us = sideToMove;
694 Color them = opposite_color(us);
695 Square ksq = king_square(opposite_color(us));
697 Bitboard moveSquares = EmptyBoardBB;
698 set_bit(&moveSquares, from);
699 set_bit(&moveSquares, to);
701 // Our moving piece could have been a possible pinner or hidden checker behind a dcCandidates?
702 bool checkerMoved = (st->dcCandidates[us] || bit_is_set(st->pinners[them], from)) && (moveSquares & sliders());
704 // If we are moving from/to an opponent king attack direction and we was a possible hidden checker
705 // or there exsist some possible hidden checker on that line then recalculate the position
706 // otherwise skip because our dcCandidates and opponent pinned pieces are not changed.
707 if ( (moveSquares & RookPseudoAttacks[ksq]) && (checkerMoved || (rooks_and_queens(us) & RookPseudoAttacks[ksq]))
708 || (moveSquares & BishopPseudoAttacks[ksq]) && (checkerMoved || (bishops_and_queens(us) & BishopPseudoAttacks[ksq])))
710 // If the move gives direct check and we don't have pinners/dc cadidates
711 // then we can be sure that we won't have them also after the move if
712 // we are not moving from a possible king attack direction.
713 bool outsideChecker = false;
715 if ( bit_is_set(st->checkersBB, to)
716 && !(bit_is_set(RookPseudoAttacks[ksq], from) && (checkerMoved || (rooks_and_queens(us) & RookPseudoAttacks[ksq])))
717 && !(bit_is_set(BishopPseudoAttacks[ksq], from) && (checkerMoved || (bishops_and_queens(us) & BishopPseudoAttacks[ksq]))))
718 outsideChecker = true;
720 if (!outsideChecker || st->pinned[them])
721 find_hidden_checks(us, Pinned);
723 if (!outsideChecker || st->dcCandidates[us] || bit_is_set(st->pinned[them], to))
724 find_hidden_checks(us, DcCandidates);
727 ksq = king_square(us);
731 find_hidden_checks(them, Pinned | DcCandidates);
735 // It is possible that we have captured an opponent hidden checker?
736 Bitboard checkerCaptured = st->capture && (st->dcCandidates[them] || bit_is_set(st->pinners[us], to));
738 // If we are moving from/to an our king attack direction and there was/is some possible
739 // opponent hidden checker then calculate the position otherwise skip because opponent
740 // dcCandidates and our pinned pieces are not changed.
741 if ( (moveSquares & RookPseudoAttacks[ksq]) && (checkerCaptured || (rooks_and_queens(them) & RookPseudoAttacks[ksq]))
742 || (moveSquares & BishopPseudoAttacks[ksq]) && (checkerCaptured || (bishops_and_queens(them) & BishopPseudoAttacks[ksq])))
744 find_hidden_checks(them, Pinned);
746 // If we don't have opponent dc candidates and we are moving in the
747 // attack line then won't be any dc candidates also after the move.
748 if ( st->dcCandidates[them]
749 || (bit_is_set(RookPseudoAttacks[ksq], from) && (rooks_and_queens(them) & RookPseudoAttacks[ksq]))
750 || (bit_is_set(BishopPseudoAttacks[ksq], from) && (bishops_and_queens(them) & BishopPseudoAttacks[ksq])))
751 find_hidden_checks(them, DcCandidates);
756 /// Position::do_move() makes a move, and saves all information necessary
757 /// to a StateInfo object. The move is assumed to be legal.
758 /// Pseudo-legal moves should be filtered out before this function is called.
760 void Position::do_move(Move m, StateInfo& newSt) {
763 assert(move_is_ok(m));
765 // Get now the current (before to move) dc candidates that we will use
766 // in update_checkers().
767 Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
769 // Copy some fields of old state to our new StateInfo object (except the
770 // captured piece, which is taken care of later) and switch state pointer
771 // to point to the new, ready to be updated, state.
773 newSt.capture = NO_PIECE_TYPE;
777 // Save the current key to the history[] array, in order to be able to
778 // detect repetition draws.
779 history[gamePly] = st->key;
781 // Increment the 50 moves rule draw counter. Resetting it to zero in the
782 // case of non-reversible moves is taken care of later.
785 if (move_is_castle(m))
787 else if (move_promotion(m))
788 do_promotion_move(m);
789 else if (move_is_ep(m))
793 Color us = side_to_move();
794 Color them = opposite_color(us);
795 Square from = move_from(m);
796 Square to = move_to(m);
798 assert(color_of_piece_on(from) == us);
799 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
801 PieceType piece = type_of_piece_on(from);
803 st->capture = type_of_piece_on(to);
806 do_capture_move(m, st->capture, them, to);
809 clear_bit(&(byColorBB[us]), from);
810 clear_bit(&(byTypeBB[piece]), from);
811 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
812 set_bit(&(byColorBB[us]), to);
813 set_bit(&(byTypeBB[piece]), to);
814 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
815 board[to] = board[from];
819 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
821 // Update incremental scores
822 st->mgValue -= pst<MidGame>(us, piece, from);
823 st->mgValue += pst<MidGame>(us, piece, to);
824 st->egValue -= pst<EndGame>(us, piece, from);
825 st->egValue += pst<EndGame>(us, piece, to);
827 // If the moving piece was a king, update the king square
831 // Reset en passant square
832 if (st->epSquare != SQ_NONE)
834 st->key ^= zobEp[st->epSquare];
835 st->epSquare = SQ_NONE;
838 // If the moving piece was a pawn do some special extra work
841 // Reset rule 50 draw counter
844 // Update pawn hash key
845 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
847 // Set en passant square, only if moved pawn can be captured
848 if (abs(int(to) - int(from)) == 16)
850 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
851 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
853 st->epSquare = Square((int(from) + int(to)) / 2);
854 st->key ^= zobEp[st->epSquare];
859 // Update piece lists
860 pieceList[us][piece][index[from]] = to;
861 index[to] = index[from];
863 // Update castle rights
864 st->key ^= zobCastle[st->castleRights];
865 st->castleRights &= castleRightsMask[from];
866 st->castleRights &= castleRightsMask[to];
867 st->key ^= zobCastle[st->castleRights];
869 // Update checkers bitboard, piece must be already moved
870 st->checkersBB = EmptyBoardBB;
871 Square ksq = king_square(them);
874 case PAWN: update_checkers<PAWN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
875 case KNIGHT: update_checkers<KNIGHT>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
876 case BISHOP: update_checkers<BISHOP>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
877 case ROOK: update_checkers<ROOK>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
878 case QUEEN: update_checkers<QUEEN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
879 case KING: update_checkers<KING>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
880 default: assert(false); break;
883 update_hidden_checks(from, to);
887 st->key ^= zobSideToMove;
888 sideToMove = opposite_color(sideToMove);
891 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
892 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
898 /// Position::do_capture_move() is a private method used to update captured
899 /// piece info. It is called from the main Position::do_move function.
901 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
903 assert(capture != KING);
905 // Remove captured piece
906 clear_bit(&(byColorBB[them]), to);
907 clear_bit(&(byTypeBB[capture]), to);
910 st->key ^= zobrist[them][capture][to];
912 // If the captured piece was a pawn, update pawn hash key
914 st->pawnKey ^= zobrist[them][PAWN][to];
916 // Update incremental scores
917 st->mgValue -= pst<MidGame>(them, capture, to);
918 st->egValue -= pst<EndGame>(them, capture, to);
920 assert(!move_promotion(m) || capture != PAWN);
924 npMaterial[them] -= piece_value_midgame(capture);
926 // Update material hash key
927 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
929 // Update piece count
930 pieceCount[them][capture]--;
933 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
934 index[pieceList[them][capture][index[to]]] = index[to];
936 // Reset rule 50 counter
941 /// Position::do_castle_move() is a private method used to make a castling
942 /// move. It is called from the main Position::do_move function. Note that
943 /// castling moves are encoded as "king captures friendly rook" moves, for
944 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
946 void Position::do_castle_move(Move m) {
949 assert(move_is_ok(m));
950 assert(move_is_castle(m));
952 Color us = side_to_move();
953 Color them = opposite_color(us);
955 // Find source squares for king and rook
956 Square kfrom = move_from(m);
957 Square rfrom = move_to(m); // HACK: See comment at beginning of function
960 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
961 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
963 // Find destination squares for king and rook
964 if (rfrom > kfrom) // O-O
966 kto = relative_square(us, SQ_G1);
967 rto = relative_square(us, SQ_F1);
969 kto = relative_square(us, SQ_C1);
970 rto = relative_square(us, SQ_D1);
973 // Remove pieces from source squares
974 clear_bit(&(byColorBB[us]), kfrom);
975 clear_bit(&(byTypeBB[KING]), kfrom);
976 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
977 clear_bit(&(byColorBB[us]), rfrom);
978 clear_bit(&(byTypeBB[ROOK]), rfrom);
979 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
981 // Put pieces on destination squares
982 set_bit(&(byColorBB[us]), kto);
983 set_bit(&(byTypeBB[KING]), kto);
984 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
985 set_bit(&(byColorBB[us]), rto);
986 set_bit(&(byTypeBB[ROOK]), rto);
987 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
989 // Update board array
990 board[kfrom] = board[rfrom] = EMPTY;
991 board[kto] = piece_of_color_and_type(us, KING);
992 board[rto] = piece_of_color_and_type(us, ROOK);
994 // Update king square
995 kingSquare[us] = kto;
997 // Update piece lists
998 pieceList[us][KING][index[kfrom]] = kto;
999 pieceList[us][ROOK][index[rfrom]] = rto;
1000 int tmp = index[rfrom];
1001 index[kto] = index[kfrom];
1004 // Update incremental scores
1005 st->mgValue -= pst<MidGame>(us, KING, kfrom);
1006 st->mgValue += pst<MidGame>(us, KING, kto);
1007 st->egValue -= pst<EndGame>(us, KING, kfrom);
1008 st->egValue += pst<EndGame>(us, KING, kto);
1009 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
1010 st->mgValue += pst<MidGame>(us, ROOK, rto);
1011 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
1012 st->egValue += pst<EndGame>(us, ROOK, rto);
1015 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1016 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1018 // Clear en passant square
1019 if (st->epSquare != SQ_NONE)
1021 st->key ^= zobEp[st->epSquare];
1022 st->epSquare = SQ_NONE;
1025 // Update castling rights
1026 st->key ^= zobCastle[st->castleRights];
1027 st->castleRights &= castleRightsMask[kfrom];
1028 st->key ^= zobCastle[st->castleRights];
1030 // Reset rule 50 counter
1033 // Update checkers BB
1034 st->checkersBB = attacks_to(king_square(them), us);
1036 // Update hidden checks
1037 find_hidden_checks();
1041 /// Position::do_promotion_move() is a private method used to make a promotion
1042 /// move. It is called from the main Position::do_move function.
1044 void Position::do_promotion_move(Move m) {
1048 PieceType promotion;
1051 assert(move_is_ok(m));
1052 assert(move_promotion(m));
1054 us = side_to_move();
1055 them = opposite_color(us);
1056 from = move_from(m);
1059 assert(relative_rank(us, to) == RANK_8);
1060 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1061 assert(color_of_piece_on(to) == them || square_is_empty(to));
1063 st->capture = type_of_piece_on(to);
1066 do_capture_move(m, st->capture, them, to);
1069 clear_bit(&(byColorBB[us]), from);
1070 clear_bit(&(byTypeBB[PAWN]), from);
1071 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1072 board[from] = EMPTY;
1074 // Insert promoted piece
1075 promotion = move_promotion(m);
1076 assert(promotion >= KNIGHT && promotion <= QUEEN);
1077 set_bit(&(byColorBB[us]), to);
1078 set_bit(&(byTypeBB[promotion]), to);
1079 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1080 board[to] = piece_of_color_and_type(us, promotion);
1083 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1085 // Update pawn hash key
1086 st->pawnKey ^= zobrist[us][PAWN][from];
1088 // Update material key
1089 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1090 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1092 // Update piece counts
1093 pieceCount[us][PAWN]--;
1094 pieceCount[us][promotion]++;
1096 // Update piece lists
1097 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1098 index[pieceList[us][PAWN][index[from]]] = index[from];
1099 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1100 index[to] = pieceCount[us][promotion] - 1;
1102 // Update incremental scores
1103 st->mgValue -= pst<MidGame>(us, PAWN, from);
1104 st->mgValue += pst<MidGame>(us, promotion, to);
1105 st->egValue -= pst<EndGame>(us, PAWN, from);
1106 st->egValue += pst<EndGame>(us, promotion, to);
1109 npMaterial[us] += piece_value_midgame(promotion);
1111 // Clear the en passant square
1112 if (st->epSquare != SQ_NONE)
1114 st->key ^= zobEp[st->epSquare];
1115 st->epSquare = SQ_NONE;
1118 // Update castle rights
1119 st->key ^= zobCastle[st->castleRights];
1120 st->castleRights &= castleRightsMask[to];
1121 st->key ^= zobCastle[st->castleRights];
1123 // Reset rule 50 counter
1126 // Update checkers BB
1127 st->checkersBB = attacks_to(king_square(them), us);
1129 // Update hidden checks
1130 find_hidden_checks();
1134 /// Position::do_ep_move() is a private method used to make an en passant
1135 /// capture. It is called from the main Position::do_move function.
1137 void Position::do_ep_move(Move m) {
1140 Square from, to, capsq;
1143 assert(move_is_ok(m));
1144 assert(move_is_ep(m));
1146 us = side_to_move();
1147 them = opposite_color(us);
1148 from = move_from(m);
1150 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1152 assert(to == st->epSquare);
1153 assert(relative_rank(us, to) == RANK_6);
1154 assert(piece_on(to) == EMPTY);
1155 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1156 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1158 // Remove captured piece
1159 clear_bit(&(byColorBB[them]), capsq);
1160 clear_bit(&(byTypeBB[PAWN]), capsq);
1161 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1162 board[capsq] = EMPTY;
1164 // Remove moving piece from source square
1165 clear_bit(&(byColorBB[us]), from);
1166 clear_bit(&(byTypeBB[PAWN]), from);
1167 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1169 // Put moving piece on destination square
1170 set_bit(&(byColorBB[us]), to);
1171 set_bit(&(byTypeBB[PAWN]), to);
1172 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1173 board[to] = board[from];
1174 board[from] = EMPTY;
1176 // Update material hash key
1177 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1179 // Update piece count
1180 pieceCount[them][PAWN]--;
1182 // Update piece list
1183 pieceList[us][PAWN][index[from]] = to;
1184 index[to] = index[from];
1185 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1186 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1189 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1190 st->key ^= zobrist[them][PAWN][capsq];
1191 st->key ^= zobEp[st->epSquare];
1193 // Update pawn hash key
1194 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1195 st->pawnKey ^= zobrist[them][PAWN][capsq];
1197 // Update incremental scores
1198 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1199 st->mgValue -= pst<MidGame>(us, PAWN, from);
1200 st->mgValue += pst<MidGame>(us, PAWN, to);
1201 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1202 st->egValue -= pst<EndGame>(us, PAWN, from);
1203 st->egValue += pst<EndGame>(us, PAWN, to);
1205 // Reset en passant square
1206 st->epSquare = SQ_NONE;
1208 // Reset rule 50 counter
1211 // Update checkers BB
1212 st->checkersBB = attacks_to(king_square(them), us);
1214 // Update hidden checks
1215 find_hidden_checks();
1219 /// Position::undo_move() unmakes a move. When it returns, the position should
1220 /// be restored to exactly the same state as before the move was made.
1222 void Position::undo_move(Move m) {
1225 assert(move_is_ok(m));
1228 sideToMove = opposite_color(sideToMove);
1230 if (move_is_castle(m))
1231 undo_castle_move(m);
1232 else if (move_promotion(m))
1233 undo_promotion_move(m);
1234 else if (move_is_ep(m))
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];
1272 assert(st->capture != KING);
1274 // Replace the captured piece
1275 set_bit(&(byColorBB[them]), to);
1276 set_bit(&(byTypeBB[st->capture]), to);
1277 set_bit(&(byTypeBB[0]), to);
1278 board[to] = piece_of_color_and_type(them, st->capture);
1281 if (st->capture != PAWN)
1282 npMaterial[them] += piece_value_midgame(st->capture);
1284 // Update piece list
1285 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1286 index[to] = pieceCount[them][st->capture];
1288 // Update piece count
1289 pieceCount[them][st->capture]++;
1294 // Finally point out state pointer back to the previous state
1301 /// Position::undo_castle_move() is a private method used to unmake a castling
1302 /// move. It is called from the main Position::undo_move function. Note that
1303 /// castling moves are encoded as "king captures friendly rook" moves, for
1304 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1306 void Position::undo_castle_move(Move m) {
1308 assert(move_is_ok(m));
1309 assert(move_is_castle(m));
1311 // When we have arrived here, some work has already been done by
1312 // Position::undo_move. In particular, the side to move has been switched,
1313 // so the code below is correct.
1314 Color us = side_to_move();
1316 // Find source squares for king and rook
1317 Square kfrom = move_from(m);
1318 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1321 // Find destination squares for king and rook
1322 if (rfrom > kfrom) // O-O
1324 kto = relative_square(us, SQ_G1);
1325 rto = relative_square(us, SQ_F1);
1327 kto = relative_square(us, SQ_C1);
1328 rto = relative_square(us, SQ_D1);
1331 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1332 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1334 // Remove pieces from destination squares
1335 clear_bit(&(byColorBB[us]), kto);
1336 clear_bit(&(byTypeBB[KING]), kto);
1337 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1338 clear_bit(&(byColorBB[us]), rto);
1339 clear_bit(&(byTypeBB[ROOK]), rto);
1340 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1342 // Put pieces on source squares
1343 set_bit(&(byColorBB[us]), kfrom);
1344 set_bit(&(byTypeBB[KING]), kfrom);
1345 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1346 set_bit(&(byColorBB[us]), rfrom);
1347 set_bit(&(byTypeBB[ROOK]), rfrom);
1348 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1351 board[rto] = board[kto] = EMPTY;
1352 board[rfrom] = piece_of_color_and_type(us, ROOK);
1353 board[kfrom] = piece_of_color_and_type(us, KING);
1355 // Update king square
1356 kingSquare[us] = kfrom;
1358 // Update piece lists
1359 pieceList[us][KING][index[kto]] = kfrom;
1360 pieceList[us][ROOK][index[rto]] = rfrom;
1361 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1362 index[kfrom] = index[kto];
1367 /// Position::undo_promotion_move() is a private method used to unmake a
1368 /// promotion move. It is called from the main Position::do_move
1371 void Position::undo_promotion_move(Move m) {
1375 PieceType 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] = piece_of_color_and_type(us, PAWN);
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]++;
1421 assert(st->capture != KING);
1423 // Insert captured piece:
1424 set_bit(&(byColorBB[them]), to);
1425 set_bit(&(byTypeBB[st->capture]), to);
1426 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1427 board[to] = piece_of_color_and_type(them, st->capture);
1429 // Update material. Because the move is a promotion move, we know
1430 // that the captured piece cannot be a pawn.
1431 assert(st->capture != PAWN);
1432 npMaterial[them] += piece_value_midgame(st->capture);
1434 // Update piece list
1435 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1436 index[to] = pieceCount[them][st->capture];
1438 // Update piece count
1439 pieceCount[them][st->capture]++;
1445 /// Position::undo_ep_move() is a private method used to unmake an en passant
1446 /// capture. It is called from the main Position::undo_move function.
1448 void Position::undo_ep_move(Move m) {
1450 assert(move_is_ok(m));
1451 assert(move_is_ep(m));
1453 // When we have arrived here, some work has already been done by
1454 // Position::undo_move. In particular, the side to move has been switched,
1455 // so the code below is correct.
1456 Color us = side_to_move();
1457 Color them = opposite_color(us);
1458 Square from = move_from(m);
1459 Square to = move_to(m);
1460 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1462 assert(to == st->previous->epSquare);
1463 assert(relative_rank(us, to) == RANK_6);
1464 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1465 assert(piece_on(from) == EMPTY);
1466 assert(piece_on(capsq) == EMPTY);
1468 // Replace captured piece
1469 set_bit(&(byColorBB[them]), capsq);
1470 set_bit(&(byTypeBB[PAWN]), capsq);
1471 set_bit(&(byTypeBB[0]), capsq);
1472 board[capsq] = piece_of_color_and_type(them, PAWN);
1474 // Remove moving piece from destination square
1475 clear_bit(&(byColorBB[us]), to);
1476 clear_bit(&(byTypeBB[PAWN]), to);
1477 clear_bit(&(byTypeBB[0]), to);
1480 // Replace moving piece at source square
1481 set_bit(&(byColorBB[us]), from);
1482 set_bit(&(byTypeBB[PAWN]), from);
1483 set_bit(&(byTypeBB[0]), from);
1484 board[from] = piece_of_color_and_type(us, PAWN);
1486 // Update piece list:
1487 pieceList[us][PAWN][index[to]] = from;
1488 index[from] = index[to];
1489 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1490 index[capsq] = pieceCount[them][PAWN];
1492 // Update piece count:
1493 pieceCount[them][PAWN]++;
1497 /// Position::do_null_move makes() a "null move": It switches the side to move
1498 /// and updates the hash key without executing any move on the board.
1500 void Position::do_null_move(StateInfo& newSt) {
1503 assert(!is_check());
1505 // Back up the information necessary to undo the null move to the supplied
1506 // StateInfo object. In the case of a null move, the only thing we need to
1507 // remember is the last move made and the en passant square.
1508 newSt.lastMove = st->lastMove;
1509 newSt.epSquare = st->epSquare;
1510 newSt.previous = st->previous;
1511 st->previous = &newSt;
1513 // Save the current key to the history[] array, in order to be able to
1514 // detect repetition draws.
1515 history[gamePly] = st->key;
1517 // Update the necessary information
1518 sideToMove = opposite_color(sideToMove);
1519 if (st->epSquare != SQ_NONE)
1520 st->key ^= zobEp[st->epSquare];
1522 st->epSquare = SQ_NONE;
1525 st->key ^= zobSideToMove;
1527 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1528 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1534 /// Position::undo_null_move() unmakes a "null move".
1536 void Position::undo_null_move() {
1539 assert(!is_check());
1541 // Restore information from the our StateInfo object
1542 st->lastMove = st->previous->lastMove;
1543 st->epSquare = st->previous->epSquare;
1544 st->previous = st->previous->previous;
1546 if (st->epSquare != SQ_NONE)
1547 st->key ^= zobEp[st->epSquare];
1549 // Update the necessary information
1550 sideToMove = opposite_color(sideToMove);
1553 st->key ^= zobSideToMove;
1555 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1556 st->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 three versions of
1564 /// this function: One which takes a destination square as input, one takes a
1565 /// move, and one which takes a 'from' and a 'to' square. The function does
1566 /// not yet understand promotions captures.
1568 int Position::see(Square to) const {
1570 assert(square_is_ok(to));
1571 return see(SQ_NONE, to);
1574 int Position::see(Move m) const {
1576 assert(move_is_ok(m));
1577 return see(move_from(m), move_to(m));
1580 int Position::see(Square from, Square to) const {
1583 static const int seeValues[18] = {
1584 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1585 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1586 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1587 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1591 Bitboard attackers, occ, b;
1593 assert(square_is_ok(from) || from == SQ_NONE);
1594 assert(square_is_ok(to));
1596 // Initialize colors
1597 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1598 Color them = opposite_color(us);
1600 // Initialize pinned and pinners bitboards
1601 Bitboard pinned[2], pinners[2];
1602 pinned[us] = pinned_pieces(us, pinners[us]);
1603 pinned[them] = pinned_pieces(them, pinners[them]);
1605 // Initialize pieces
1606 Piece piece = piece_on(from);
1607 Piece capture = piece_on(to);
1609 // Find all attackers to the destination square, with the moving piece
1610 // removed, but possibly an X-ray attacker added behind it.
1611 occ = occupied_squares();
1613 // Handle en passant moves
1614 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1616 assert(capture == EMPTY);
1618 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1619 capture = piece_on(capQq);
1621 assert(type_of_piece_on(capQq) == PAWN);
1623 // Remove the captured pawn
1624 clear_bit(&occ, capQq);
1629 clear_bit(&occ, from);
1630 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1631 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1632 | (piece_attacks<KNIGHT>(to) & knights())
1633 | (piece_attacks<KING>(to) & kings())
1634 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1635 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1637 // Remove our pinned pieces from attacks if the captured piece is not
1638 // a pinner, otherwise we could remove a valid "capture the pinner" attack.
1639 if (pinned[us] != EmptyBoardBB && !bit_is_set(pinners[us], to))
1640 attackers &= ~pinned[us];
1642 // Remove opponent pinned pieces from attacks if the moving piece is not
1643 // a pinner, otherwise we could remove a piece that is no more pinned
1644 // due to our pinner piece is moving away.
1645 if (pinned[them] != EmptyBoardBB && !bit_is_set(pinners[them], from))
1646 attackers &= ~pinned[them];
1648 if (from != SQ_NONE)
1651 // If we don't have any attacker we are finished
1652 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1655 // Locate the least valuable attacker to the destination square
1656 // and use it to initialize from square.
1658 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1661 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1662 piece = piece_on(from);
1665 // If the opponent has no attackers we are finished
1666 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1667 return seeValues[capture];
1669 attackers &= occ; // Remove the moving piece
1671 // The destination square is defended, which makes things rather more
1672 // difficult to compute. We proceed by building up a "swap list" containing
1673 // the material gain or loss at each stop in a sequence of captures to the
1674 // destination square, where the sides alternately capture, and always
1675 // capture with the least valuable piece. After each capture, we look for
1676 // new X-ray attacks from behind the capturing piece.
1677 int lastCapturingPieceValue = seeValues[piece];
1678 int swapList[32], n = 1;
1682 swapList[0] = seeValues[capture];
1685 // Locate the least valuable attacker for the side to move. The loop
1686 // below looks like it is potentially infinite, but it isn't. We know
1687 // that the side to move still has at least one attacker left.
1688 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1691 // Remove the attacker we just found from the 'attackers' bitboard,
1692 // and scan for new X-ray attacks behind the attacker.
1693 b = attackers & pieces_of_color_and_type(c, pt);
1695 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1696 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1700 // Add the new entry to the swap list
1702 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1705 // Remember the value of the capturing piece, and change the side to move
1706 // before beginning the next iteration
1707 lastCapturingPieceValue = seeValues[pt];
1708 c = opposite_color(c);
1710 // Remove pinned pieces from attackers
1711 if ( pinned[c] != EmptyBoardBB
1712 && !bit_is_set(pinners[c], to)
1713 && !(pinners[c] & attackers))
1714 attackers &= ~pinned[c];
1716 // Stop after a king capture
1717 if (pt == KING && (attackers & pieces_of_color(c)))
1720 swapList[n++] = 100;
1723 } while (attackers & pieces_of_color(c));
1725 // Having built the swap list, we negamax through it to find the best
1726 // achievable score from the point of view of the side to move
1728 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1734 /// Position::setStartState() copies the content of the argument
1735 /// inside startState and makes st point to it. This is needed
1736 /// when the st pointee could become stale, as example because
1737 /// the caller is about to going out of scope.
1739 void Position::setStartState(const StateInfo& s) {
1746 /// Position::clear() erases the position object to a pristine state, with an
1747 /// empty board, white to move, and no castling rights.
1749 void Position::clear() {
1752 memset(st, 0, sizeof(StateInfo));
1753 st->epSquare = SQ_NONE;
1755 memset(index, 0, sizeof(int) * 64);
1756 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1758 for (int i = 0; i < 64; i++)
1761 for (int i = 0; i < 7; i++)
1763 byTypeBB[i] = EmptyBoardBB;
1764 pieceCount[0][i] = pieceCount[1][i] = 0;
1765 for (int j = 0; j < 8; j++)
1766 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1771 initialKFile = FILE_E;
1772 initialKRFile = FILE_H;
1773 initialQRFile = FILE_A;
1777 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1778 /// UCI interface code, whenever a non-reversible move is made in a
1779 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1780 /// for the program to handle games of arbitrary length, as long as the GUI
1781 /// handles draws by the 50 move rule correctly.
1783 void Position::reset_game_ply() {
1789 /// Position::put_piece() puts a piece on the given square of the board,
1790 /// updating the board array, bitboards, and piece counts.
1792 void Position::put_piece(Piece p, Square s) {
1794 Color c = color_of_piece(p);
1795 PieceType pt = type_of_piece(p);
1798 index[s] = pieceCount[c][pt];
1799 pieceList[c][pt][index[s]] = s;
1801 set_bit(&(byTypeBB[pt]), s);
1802 set_bit(&(byColorBB[c]), s);
1803 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1805 pieceCount[c][pt]++;
1812 /// Position::allow_oo() gives the given side the right to castle kingside.
1813 /// Used when setting castling rights during parsing of FEN strings.
1815 void Position::allow_oo(Color c) {
1817 st->castleRights |= (1 + int(c));
1821 /// Position::allow_ooo() gives the given side the right to castle queenside.
1822 /// Used when setting castling rights during parsing of FEN strings.
1824 void Position::allow_ooo(Color c) {
1826 st->castleRights |= (4 + 4*int(c));
1830 /// Position::compute_key() computes the hash key of the position. The hash
1831 /// key is usually updated incrementally as moves are made and unmade, the
1832 /// compute_key() function is only used when a new position is set up, and
1833 /// to verify the correctness of the hash key when running in debug mode.
1835 Key Position::compute_key() const {
1837 Key result = Key(0ULL);
1839 for (Square s = SQ_A1; s <= SQ_H8; s++)
1840 if (square_is_occupied(s))
1841 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1843 if (ep_square() != SQ_NONE)
1844 result ^= zobEp[ep_square()];
1846 result ^= zobCastle[st->castleRights];
1847 if (side_to_move() == BLACK)
1848 result ^= zobSideToMove;
1854 /// Position::compute_pawn_key() computes the hash key of the position. The
1855 /// hash key is usually updated incrementally as moves are made and unmade,
1856 /// the compute_pawn_key() function is only used when a new position is set
1857 /// up, and to verify the correctness of the pawn hash key when running in
1860 Key Position::compute_pawn_key() const {
1862 Key result = Key(0ULL);
1866 for (Color c = WHITE; c <= BLACK; c++)
1871 s = pop_1st_bit(&b);
1872 result ^= zobrist[c][PAWN][s];
1879 /// Position::compute_material_key() computes the hash key of the position.
1880 /// The hash key is usually updated incrementally as moves are made and unmade,
1881 /// the compute_material_key() function is only used when a new position is set
1882 /// up, and to verify the correctness of the material hash key when running in
1885 Key Position::compute_material_key() const {
1887 Key result = Key(0ULL);
1888 for (Color c = WHITE; c <= BLACK; c++)
1889 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1891 int count = piece_count(c, pt);
1892 for (int i = 0; i <= count; i++)
1893 result ^= zobMaterial[c][pt][i];
1899 /// Position::compute_value() compute the incremental scores for the middle
1900 /// game and the endgame. These functions are used to initialize the incremental
1901 /// scores when a new position is set up, and to verify that the scores are correctly
1902 /// updated by do_move and undo_move when the program is running in debug mode.
1903 template<Position::GamePhase Phase>
1904 Value Position::compute_value() const {
1906 Value result = Value(0);
1910 for (Color c = WHITE; c <= BLACK; c++)
1911 for (PieceType pt = PAWN; pt <= KING; pt++)
1913 b = pieces_of_color_and_type(c, pt);
1916 s = pop_1st_bit(&b);
1917 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1918 result += pst<Phase>(c, pt, s);
1922 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1923 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1928 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1929 /// game material score for the given side. Material scores are updated
1930 /// incrementally during the search, this function is only used while
1931 /// initializing a new Position object.
1933 Value Position::compute_non_pawn_material(Color c) const {
1935 Value result = Value(0);
1938 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1940 Bitboard b = pieces_of_color_and_type(c, pt);
1943 s = pop_1st_bit(&b);
1944 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1945 result += piece_value_midgame(pt);
1952 /// Position::is_mate() returns true or false depending on whether the
1953 /// side to move is checkmated. Note that this function is currently very
1954 /// slow, and shouldn't be used frequently inside the search.
1956 bool Position::is_mate() const {
1960 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1961 return mp.get_next_move() == MOVE_NONE;
1967 /// Position::is_draw() tests whether the position is drawn by material,
1968 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1969 /// must be done by the search.
1971 bool Position::is_draw() const {
1973 // Draw by material?
1975 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1978 // Draw by the 50 moves rule?
1979 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1982 // Draw by repetition?
1983 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1984 if (history[gamePly - i] == st->key)
1991 /// Position::has_mate_threat() tests whether a given color has a mate in one
1992 /// from the current position. This function is quite slow, but it doesn't
1993 /// matter, because it is currently only called from PV nodes, which are rare.
1995 bool Position::has_mate_threat(Color c) {
1998 Color stm = side_to_move();
2000 // The following lines are useless and silly, but prevents gcc from
2001 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
2002 // be used uninitialized.
2003 st1.lastMove = st->lastMove;
2004 st1.epSquare = st->epSquare;
2009 // If the input color is not equal to the side to move, do a null move
2013 MoveStack mlist[120];
2015 bool result = false;
2017 // Generate legal moves
2018 count = generate_legal_moves(*this, mlist);
2020 // Loop through the moves, and see if one of them is mate
2021 for (int i = 0; i < count; i++)
2023 do_move(mlist[i].move, st2);
2027 undo_move(mlist[i].move);
2030 // Undo null move, if necessary
2038 /// Position::init_zobrist() is a static member function which initializes the
2039 /// various arrays used to compute hash keys.
2041 void Position::init_zobrist() {
2043 for (int i = 0; i < 2; i++)
2044 for (int j = 0; j < 8; j++)
2045 for (int k = 0; k < 64; k++)
2046 zobrist[i][j][k] = Key(genrand_int64());
2048 for (int i = 0; i < 64; i++)
2049 zobEp[i] = Key(genrand_int64());
2051 for (int i = 0; i < 16; i++)
2052 zobCastle[i] = genrand_int64();
2054 zobSideToMove = genrand_int64();
2056 for (int i = 0; i < 2; i++)
2057 for (int j = 0; j < 8; j++)
2058 for (int k = 0; k < 16; k++)
2059 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2061 for (int i = 0; i < 16; i++)
2062 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2066 /// Position::init_piece_square_tables() initializes the piece square tables.
2067 /// This is a two-step operation: First, the white halves of the tables are
2068 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2069 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2070 /// Second, the black halves of the tables are initialized by mirroring
2071 /// and changing the sign of the corresponding white scores.
2073 void Position::init_piece_square_tables() {
2075 int r = get_option_value_int("Randomness"), i;
2076 for (Square s = SQ_A1; s <= SQ_H8; s++)
2077 for (Piece p = WP; p <= WK; p++)
2079 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2080 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2081 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2084 for (Square s = SQ_A1; s <= SQ_H8; s++)
2085 for (Piece p = BP; p <= BK; p++)
2087 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2088 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2093 /// Position::flipped_copy() makes a copy of the input position, but with
2094 /// the white and black sides reversed. This is only useful for debugging,
2095 /// especially for finding evaluation symmetry bugs.
2097 void Position::flipped_copy(const Position &pos) {
2099 assert(pos.is_ok());
2104 for (Square s = SQ_A1; s <= SQ_H8; s++)
2105 if (!pos.square_is_empty(s))
2106 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2109 sideToMove = opposite_color(pos.side_to_move());
2112 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2113 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2114 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2115 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2117 initialKFile = pos.initialKFile;
2118 initialKRFile = pos.initialKRFile;
2119 initialQRFile = pos.initialQRFile;
2121 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2122 castleRightsMask[sq] = ALL_CASTLES;
2124 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2125 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2126 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2127 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2128 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2129 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2131 // En passant square
2132 if (pos.st->epSquare != SQ_NONE)
2133 st->epSquare = flip_square(pos.st->epSquare);
2139 st->key = compute_key();
2140 st->pawnKey = compute_pawn_key();
2141 st->materialKey = compute_material_key();
2143 // Incremental scores
2144 st->mgValue = compute_value<MidGame>();
2145 st->egValue = compute_value<EndGame>();
2148 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2149 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2155 /// Position::is_ok() performs some consitency checks for the position object.
2156 /// This is meant to be helpful when debugging.
2158 bool Position::is_ok(int* failedStep) const {
2160 // What features of the position should be verified?
2161 static const bool debugBitboards = false;
2162 static const bool debugKingCount = false;
2163 static const bool debugKingCapture = false;
2164 static const bool debugCheckerCount = false;
2165 static const bool debugKey = false;
2166 static const bool debugMaterialKey = false;
2167 static const bool debugPawnKey = false;
2168 static const bool debugIncrementalEval = false;
2169 static const bool debugNonPawnMaterial = false;
2170 static const bool debugPieceCounts = false;
2171 static const bool debugPieceList = false;
2173 if (failedStep) *failedStep = 1;
2176 if (!color_is_ok(side_to_move()))
2179 // Are the king squares in the position correct?
2180 if (failedStep) (*failedStep)++;
2181 if (piece_on(king_square(WHITE)) != WK)
2184 if (failedStep) (*failedStep)++;
2185 if (piece_on(king_square(BLACK)) != BK)
2189 if (failedStep) (*failedStep)++;
2190 if (!file_is_ok(initialKRFile))
2193 if (!file_is_ok(initialQRFile))
2196 // Do both sides have exactly one king?
2197 if (failedStep) (*failedStep)++;
2200 int kingCount[2] = {0, 0};
2201 for (Square s = SQ_A1; s <= SQ_H8; s++)
2202 if (type_of_piece_on(s) == KING)
2203 kingCount[color_of_piece_on(s)]++;
2205 if (kingCount[0] != 1 || kingCount[1] != 1)
2209 // Can the side to move capture the opponent's king?
2210 if (failedStep) (*failedStep)++;
2211 if (debugKingCapture)
2213 Color us = side_to_move();
2214 Color them = opposite_color(us);
2215 Square ksq = king_square(them);
2216 if (square_is_attacked(ksq, us))
2220 // Is there more than 2 checkers?
2221 if (failedStep) (*failedStep)++;
2222 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2226 if (failedStep) (*failedStep)++;
2229 // The intersection of the white and black pieces must be empty
2230 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2233 // The union of the white and black pieces must be equal to all
2235 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2238 // Separate piece type bitboards must have empty intersections
2239 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2240 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2241 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2245 // En passant square OK?
2246 if (failedStep) (*failedStep)++;
2247 if (ep_square() != SQ_NONE)
2249 // The en passant square must be on rank 6, from the point of view of the
2251 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2256 if (failedStep) (*failedStep)++;
2257 if (debugKey && st->key != compute_key())
2260 // Pawn hash key OK?
2261 if (failedStep) (*failedStep)++;
2262 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2265 // Material hash key OK?
2266 if (failedStep) (*failedStep)++;
2267 if (debugMaterialKey && st->materialKey != compute_material_key())
2270 // Incremental eval OK?
2271 if (failedStep) (*failedStep)++;
2272 if (debugIncrementalEval)
2274 if (st->mgValue != compute_value<MidGame>())
2277 if (st->egValue != compute_value<EndGame>())
2281 // Non-pawn material OK?
2282 if (failedStep) (*failedStep)++;
2283 if (debugNonPawnMaterial)
2285 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2288 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2293 if (failedStep) (*failedStep)++;
2294 if (debugPieceCounts)
2295 for (Color c = WHITE; c <= BLACK; c++)
2296 for (PieceType pt = PAWN; pt <= KING; pt++)
2297 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2300 if (failedStep) (*failedStep)++;
2303 for(Color c = WHITE; c <= BLACK; c++)
2304 for(PieceType pt = PAWN; pt <= KING; pt++)
2305 for(int i = 0; i < pieceCount[c][pt]; i++)
2307 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2310 if (index[piece_list(c, pt, i)] != i)
2314 if (failedStep) *failedStep = 0;