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;
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));
450 /// Position:find_pinned() computes the pinned, pinners and dcCandidates
451 /// bitboards for both colors. Bitboard checkersBB must be already updated.
453 void Position::find_pinned() {
458 for (Color c = WHITE; c <= BLACK; c++)
460 ksq = king_square(c);
461 st->pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
462 st->pinners[c] = p1 | p2;
463 ksq = king_square(opposite_color(c));
464 st->dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, p1) | hidden_checks<BISHOP, false>(c, ksq, p2);
469 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
471 bool Position::pl_move_is_legal(Move m) const {
474 assert(move_is_ok(m));
476 // If we're in check, all pseudo-legal moves are legal, because our
477 // check evasion generator only generates true legal moves.
481 // Castling moves are checked for legality during move generation.
482 if (move_is_castle(m))
485 Color us = side_to_move();
486 Color them = opposite_color(us);
487 Square from = move_from(m);
488 Square ksq = king_square(us);
490 assert(color_of_piece_on(from) == us);
491 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
493 // En passant captures are a tricky special case. Because they are
494 // rather uncommon, we do it simply by testing whether the king is attacked
495 // after the move is made
498 Square to = move_to(m);
499 Square capsq = make_square(square_file(to), square_rank(from));
500 Bitboard b = occupied_squares();
502 assert(to == ep_square());
503 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
504 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
505 assert(piece_on(to) == EMPTY);
508 clear_bit(&b, capsq);
511 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
512 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
515 // If the moving piece is a king, check whether the destination
516 // square is attacked by the opponent.
518 return !(square_is_attacked(move_to(m), them));
520 // A non-king move is legal if and only if it is not pinned or it
521 // is moving along the ray towards or away from the king.
522 return ( !bit_is_set(pinned_pieces(us), from)
523 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
527 /// Position::move_is_check() tests whether a pseudo-legal move is a check
529 bool Position::move_is_check(Move m) const {
532 assert(move_is_ok(m));
534 Color us = side_to_move();
535 Color them = opposite_color(us);
536 Square from = move_from(m);
537 Square to = move_to(m);
538 Square ksq = king_square(them);
539 Bitboard dcCandidates = discovered_check_candidates(us);
541 assert(color_of_piece_on(from) == us);
542 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
544 // Proceed according to the type of the moving piece
545 switch (type_of_piece_on(from))
549 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
552 if ( bit_is_set(dcCandidates, from) // Discovered check?
553 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
556 if (move_promotion(m)) // Promotion with check?
558 Bitboard b = occupied_squares();
561 switch (move_promotion(m))
564 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
566 return bit_is_set(bishop_attacks_bb(to, b), ksq);
568 return bit_is_set(rook_attacks_bb(to, b), ksq);
570 return bit_is_set(queen_attacks_bb(to, b), ksq);
575 // En passant capture with check? We have already handled the case
576 // of direct checks and ordinary discovered check, the only case we
577 // need to handle is the unusual case of a discovered check through the
579 else if (move_is_ep(m))
581 Square capsq = make_square(square_file(to), square_rank(from));
582 Bitboard b = occupied_squares();
584 clear_bit(&b, capsq);
586 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
587 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
592 return bit_is_set(dcCandidates, from) // Discovered check?
593 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
596 return bit_is_set(dcCandidates, from) // Discovered check?
597 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
600 return bit_is_set(dcCandidates, from) // Discovered check?
601 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
604 // Discovered checks are impossible!
605 assert(!bit_is_set(dcCandidates, from));
606 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
610 if ( bit_is_set(dcCandidates, from)
611 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
614 // Castling with check?
615 if (move_is_castle(m))
617 Square kfrom, kto, rfrom, rto;
618 Bitboard b = occupied_squares();
624 kto = relative_square(us, SQ_G1);
625 rto = relative_square(us, SQ_F1);
627 kto = relative_square(us, SQ_C1);
628 rto = relative_square(us, SQ_D1);
630 clear_bit(&b, kfrom);
631 clear_bit(&b, rfrom);
634 return bit_is_set(rook_attacks_bb(rto, b), ksq);
638 default: // NO_PIECE_TYPE
646 /// Position::move_is_capture() tests whether a move from the current
647 /// position is a capture. Move must not be MOVE_NONE.
649 bool Position::move_is_capture(Move m) const {
651 assert(m != MOVE_NONE);
653 return ( !square_is_empty(move_to(m))
654 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
660 /// Position::update_checkers() is a private method to udpate chekers info
662 template<PieceType Piece>
663 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
664 Square to, Bitboard dcCandidates) {
666 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
667 set_bit(pCheckersBB, to);
669 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
672 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
675 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
680 /// Position::init_new_state() copies from the current state the fields
681 /// that will be updated incrementally, skips the fields, like bitboards
682 /// that will be recalculated form scratch anyway.
684 void Position::init_new_state(StateInfo& newSt) {
687 newSt.pawnKey = st->pawnKey;
688 newSt.materialKey = st->materialKey;
689 newSt.castleRights = st->castleRights;
690 newSt.rule50 = st->rule50;
691 newSt.epSquare = st->epSquare;
692 newSt.mgValue = st->mgValue;
693 newSt.egValue = st->egValue;
694 newSt.capture = NO_PIECE_TYPE;
699 /// Position::do_move() makes a move, and saves all information necessary
700 /// to a StateInfo object. The move is assumed to be legal.
701 /// Pseudo-legal moves should be filtered out before this function is called.
703 void Position::do_move(Move m, StateInfo& newSt) {
706 assert(move_is_ok(m));
708 // Get now the current (before to move) dc candidates that we will use
709 // in update_checkers().
710 Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
712 // Copy some fields of old state to our new StateInfo object (except the
713 // captured piece, which is taken care of later) and switch state pointer
714 // to point to the new, ready to be updated, state.
715 init_new_state(newSt);
718 // Save the current key to the history[] array, in order to be able to
719 // detect repetition draws.
720 history[gamePly] = st->key;
722 // Increment the 50 moves rule draw counter. Resetting it to zero in the
723 // case of non-reversible moves is taken care of later.
726 if (move_is_castle(m))
728 else if (move_promotion(m))
729 do_promotion_move(m);
730 else if (move_is_ep(m))
734 Color us = side_to_move();
735 Color them = opposite_color(us);
736 Square from = move_from(m);
737 Square to = move_to(m);
739 assert(color_of_piece_on(from) == us);
740 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
742 PieceType piece = type_of_piece_on(from);
744 st->capture = type_of_piece_on(to);
747 do_capture_move(m, st->capture, them, to);
750 clear_bit(&(byColorBB[us]), from);
751 clear_bit(&(byTypeBB[piece]), from);
752 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
753 set_bit(&(byColorBB[us]), to);
754 set_bit(&(byTypeBB[piece]), to);
755 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
756 board[to] = board[from];
760 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
762 // Update incremental scores
763 st->mgValue -= pst<MidGame>(us, piece, from);
764 st->mgValue += pst<MidGame>(us, piece, to);
765 st->egValue -= pst<EndGame>(us, piece, from);
766 st->egValue += pst<EndGame>(us, piece, to);
768 // If the moving piece was a king, update the king square
772 // Reset en passant square
773 if (st->epSquare != SQ_NONE)
775 st->key ^= zobEp[st->epSquare];
776 st->epSquare = SQ_NONE;
779 // If the moving piece was a pawn do some special extra work
782 // Reset rule 50 draw counter
785 // Update pawn hash key
786 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
788 // Set en passant square, only if moved pawn can be captured
789 if (abs(int(to) - int(from)) == 16)
791 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
792 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
794 st->epSquare = Square((int(from) + int(to)) / 2);
795 st->key ^= zobEp[st->epSquare];
800 // Update piece lists
801 pieceList[us][piece][index[from]] = to;
802 index[to] = index[from];
804 // Update castle rights
805 st->key ^= zobCastle[st->castleRights];
806 st->castleRights &= castleRightsMask[from];
807 st->castleRights &= castleRightsMask[to];
808 st->key ^= zobCastle[st->castleRights];
810 // Update checkers bitboard, piece must be already moved
811 st->checkersBB = EmptyBoardBB;
812 Square ksq = king_square(them);
815 case PAWN: update_checkers<PAWN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
816 case KNIGHT: update_checkers<KNIGHT>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
817 case BISHOP: update_checkers<BISHOP>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
818 case ROOK: update_checkers<ROOK>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
819 case QUEEN: update_checkers<QUEEN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
820 case KING: update_checkers<KING>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
821 default: assert(false); break;
827 st->key ^= zobSideToMove;
828 sideToMove = opposite_color(sideToMove);
831 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
832 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
838 /// Position::do_capture_move() is a private method used to update captured
839 /// piece info. It is called from the main Position::do_move function.
841 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
843 assert(capture != KING);
845 // Remove captured piece
846 clear_bit(&(byColorBB[them]), to);
847 clear_bit(&(byTypeBB[capture]), to);
850 st->key ^= zobrist[them][capture][to];
852 // If the captured piece was a pawn, update pawn hash key
854 st->pawnKey ^= zobrist[them][PAWN][to];
856 // Update incremental scores
857 st->mgValue -= pst<MidGame>(them, capture, to);
858 st->egValue -= pst<EndGame>(them, capture, to);
860 assert(!move_promotion(m) || capture != PAWN);
864 npMaterial[them] -= piece_value_midgame(capture);
866 // Update material hash key
867 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
869 // Update piece count
870 pieceCount[them][capture]--;
873 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
874 index[pieceList[them][capture][index[to]]] = index[to];
876 // Reset rule 50 counter
881 /// Position::do_castle_move() is a private method used to make a castling
882 /// move. It is called from the main Position::do_move function. Note that
883 /// castling moves are encoded as "king captures friendly rook" moves, for
884 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
886 void Position::do_castle_move(Move m) {
889 assert(move_is_ok(m));
890 assert(move_is_castle(m));
892 Color us = side_to_move();
893 Color them = opposite_color(us);
895 // Find source squares for king and rook
896 Square kfrom = move_from(m);
897 Square rfrom = move_to(m); // HACK: See comment at beginning of function
900 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
901 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
903 // Find destination squares for king and rook
904 if (rfrom > kfrom) // O-O
906 kto = relative_square(us, SQ_G1);
907 rto = relative_square(us, SQ_F1);
909 kto = relative_square(us, SQ_C1);
910 rto = relative_square(us, SQ_D1);
913 // Remove pieces from source squares
914 clear_bit(&(byColorBB[us]), kfrom);
915 clear_bit(&(byTypeBB[KING]), kfrom);
916 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
917 clear_bit(&(byColorBB[us]), rfrom);
918 clear_bit(&(byTypeBB[ROOK]), rfrom);
919 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
921 // Put pieces on destination squares
922 set_bit(&(byColorBB[us]), kto);
923 set_bit(&(byTypeBB[KING]), kto);
924 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
925 set_bit(&(byColorBB[us]), rto);
926 set_bit(&(byTypeBB[ROOK]), rto);
927 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
929 // Update board array
930 board[kfrom] = board[rfrom] = EMPTY;
931 board[kto] = piece_of_color_and_type(us, KING);
932 board[rto] = piece_of_color_and_type(us, ROOK);
934 // Update king square
935 kingSquare[us] = kto;
937 // Update piece lists
938 pieceList[us][KING][index[kfrom]] = kto;
939 pieceList[us][ROOK][index[rfrom]] = rto;
940 int tmp = index[rfrom];
941 index[kto] = index[kfrom];
944 // Update incremental scores
945 st->mgValue -= pst<MidGame>(us, KING, kfrom);
946 st->mgValue += pst<MidGame>(us, KING, kto);
947 st->egValue -= pst<EndGame>(us, KING, kfrom);
948 st->egValue += pst<EndGame>(us, KING, kto);
949 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
950 st->mgValue += pst<MidGame>(us, ROOK, rto);
951 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
952 st->egValue += pst<EndGame>(us, ROOK, rto);
955 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
956 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
958 // Clear en passant square
959 if (st->epSquare != SQ_NONE)
961 st->key ^= zobEp[st->epSquare];
962 st->epSquare = SQ_NONE;
965 // Update castling rights
966 st->key ^= zobCastle[st->castleRights];
967 st->castleRights &= castleRightsMask[kfrom];
968 st->key ^= zobCastle[st->castleRights];
970 // Reset rule 50 counter
973 // Update checkers BB
974 st->checkersBB = attacks_to(king_square(them), us);
978 /// Position::do_promotion_move() is a private method used to make a promotion
979 /// move. It is called from the main Position::do_move function.
981 void Position::do_promotion_move(Move m) {
988 assert(move_is_ok(m));
989 assert(move_promotion(m));
992 them = opposite_color(us);
996 assert(relative_rank(us, to) == RANK_8);
997 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
998 assert(color_of_piece_on(to) == them || square_is_empty(to));
1000 st->capture = type_of_piece_on(to);
1003 do_capture_move(m, st->capture, them, to);
1006 clear_bit(&(byColorBB[us]), from);
1007 clear_bit(&(byTypeBB[PAWN]), from);
1008 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1009 board[from] = EMPTY;
1011 // Insert promoted piece
1012 promotion = move_promotion(m);
1013 assert(promotion >= KNIGHT && promotion <= QUEEN);
1014 set_bit(&(byColorBB[us]), to);
1015 set_bit(&(byTypeBB[promotion]), to);
1016 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1017 board[to] = piece_of_color_and_type(us, promotion);
1020 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1022 // Update pawn hash key
1023 st->pawnKey ^= zobrist[us][PAWN][from];
1025 // Update material key
1026 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1027 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1029 // Update piece counts
1030 pieceCount[us][PAWN]--;
1031 pieceCount[us][promotion]++;
1033 // Update piece lists
1034 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1035 index[pieceList[us][PAWN][index[from]]] = index[from];
1036 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1037 index[to] = pieceCount[us][promotion] - 1;
1039 // Update incremental scores
1040 st->mgValue -= pst<MidGame>(us, PAWN, from);
1041 st->mgValue += pst<MidGame>(us, promotion, to);
1042 st->egValue -= pst<EndGame>(us, PAWN, from);
1043 st->egValue += pst<EndGame>(us, promotion, to);
1046 npMaterial[us] += piece_value_midgame(promotion);
1048 // Clear the en passant square
1049 if (st->epSquare != SQ_NONE)
1051 st->key ^= zobEp[st->epSquare];
1052 st->epSquare = SQ_NONE;
1055 // Update castle rights
1056 st->key ^= zobCastle[st->castleRights];
1057 st->castleRights &= castleRightsMask[to];
1058 st->key ^= zobCastle[st->castleRights];
1060 // Reset rule 50 counter
1063 // Update checkers BB
1064 st->checkersBB = attacks_to(king_square(them), us);
1068 /// Position::do_ep_move() is a private method used to make an en passant
1069 /// capture. It is called from the main Position::do_move function.
1071 void Position::do_ep_move(Move m) {
1074 Square from, to, capsq;
1077 assert(move_is_ok(m));
1078 assert(move_is_ep(m));
1080 us = side_to_move();
1081 them = opposite_color(us);
1082 from = move_from(m);
1084 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1086 assert(to == st->epSquare);
1087 assert(relative_rank(us, to) == RANK_6);
1088 assert(piece_on(to) == EMPTY);
1089 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1090 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1092 // Remove captured piece
1093 clear_bit(&(byColorBB[them]), capsq);
1094 clear_bit(&(byTypeBB[PAWN]), capsq);
1095 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1096 board[capsq] = EMPTY;
1098 // Remove moving piece from source square
1099 clear_bit(&(byColorBB[us]), from);
1100 clear_bit(&(byTypeBB[PAWN]), from);
1101 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1103 // Put moving piece on destination square
1104 set_bit(&(byColorBB[us]), to);
1105 set_bit(&(byTypeBB[PAWN]), to);
1106 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1107 board[to] = board[from];
1108 board[from] = EMPTY;
1110 // Update material hash key
1111 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1113 // Update piece count
1114 pieceCount[them][PAWN]--;
1116 // Update piece list
1117 pieceList[us][PAWN][index[from]] = to;
1118 index[to] = index[from];
1119 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1120 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1123 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1124 st->key ^= zobrist[them][PAWN][capsq];
1125 st->key ^= zobEp[st->epSquare];
1127 // Update pawn hash key
1128 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1129 st->pawnKey ^= zobrist[them][PAWN][capsq];
1131 // Update incremental scores
1132 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1133 st->mgValue -= pst<MidGame>(us, PAWN, from);
1134 st->mgValue += pst<MidGame>(us, PAWN, to);
1135 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1136 st->egValue -= pst<EndGame>(us, PAWN, from);
1137 st->egValue += pst<EndGame>(us, PAWN, to);
1139 // Reset en passant square
1140 st->epSquare = SQ_NONE;
1142 // Reset rule 50 counter
1145 // Update checkers BB
1146 st->checkersBB = attacks_to(king_square(them), us);
1150 /// Position::undo_move() unmakes a move. When it returns, the position should
1151 /// be restored to exactly the same state as before the move was made.
1153 void Position::undo_move(Move m) {
1156 assert(move_is_ok(m));
1159 sideToMove = opposite_color(sideToMove);
1161 if (move_is_castle(m))
1162 undo_castle_move(m);
1163 else if (move_promotion(m))
1164 undo_promotion_move(m);
1165 else if (move_is_ep(m))
1173 us = side_to_move();
1174 them = opposite_color(us);
1175 from = move_from(m);
1178 assert(piece_on(from) == EMPTY);
1179 assert(color_of_piece_on(to) == us);
1181 // Put the piece back at the source square
1182 piece = type_of_piece_on(to);
1183 set_bit(&(byColorBB[us]), from);
1184 set_bit(&(byTypeBB[piece]), from);
1185 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1186 board[from] = piece_of_color_and_type(us, piece);
1188 // Clear the destination square
1189 clear_bit(&(byColorBB[us]), to);
1190 clear_bit(&(byTypeBB[piece]), to);
1191 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1193 // If the moving piece was a king, update the king square
1195 kingSquare[us] = from;
1197 // Update piece list
1198 pieceList[us][piece][index[to]] = from;
1199 index[from] = index[to];
1203 assert(st->capture != KING);
1205 // Replace the captured piece
1206 set_bit(&(byColorBB[them]), to);
1207 set_bit(&(byTypeBB[st->capture]), to);
1208 set_bit(&(byTypeBB[0]), to);
1209 board[to] = piece_of_color_and_type(them, st->capture);
1212 if (st->capture != PAWN)
1213 npMaterial[them] += piece_value_midgame(st->capture);
1215 // Update piece list
1216 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1217 index[to] = pieceCount[them][st->capture];
1219 // Update piece count
1220 pieceCount[them][st->capture]++;
1225 // Finally point out state pointer back to the previous state
1232 /// Position::undo_castle_move() is a private method used to unmake a castling
1233 /// move. It is called from the main Position::undo_move function. Note that
1234 /// castling moves are encoded as "king captures friendly rook" moves, for
1235 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1237 void Position::undo_castle_move(Move m) {
1239 assert(move_is_ok(m));
1240 assert(move_is_castle(m));
1242 // When we have arrived here, some work has already been done by
1243 // Position::undo_move. In particular, the side to move has been switched,
1244 // so the code below is correct.
1245 Color us = side_to_move();
1247 // Find source squares for king and rook
1248 Square kfrom = move_from(m);
1249 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1252 // Find destination squares for king and rook
1253 if (rfrom > kfrom) // O-O
1255 kto = relative_square(us, SQ_G1);
1256 rto = relative_square(us, SQ_F1);
1258 kto = relative_square(us, SQ_C1);
1259 rto = relative_square(us, SQ_D1);
1262 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1263 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1265 // Remove pieces from destination squares
1266 clear_bit(&(byColorBB[us]), kto);
1267 clear_bit(&(byTypeBB[KING]), kto);
1268 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1269 clear_bit(&(byColorBB[us]), rto);
1270 clear_bit(&(byTypeBB[ROOK]), rto);
1271 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1273 // Put pieces on source squares
1274 set_bit(&(byColorBB[us]), kfrom);
1275 set_bit(&(byTypeBB[KING]), kfrom);
1276 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1277 set_bit(&(byColorBB[us]), rfrom);
1278 set_bit(&(byTypeBB[ROOK]), rfrom);
1279 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1282 board[rto] = board[kto] = EMPTY;
1283 board[rfrom] = piece_of_color_and_type(us, ROOK);
1284 board[kfrom] = piece_of_color_and_type(us, KING);
1286 // Update king square
1287 kingSquare[us] = kfrom;
1289 // Update piece lists
1290 pieceList[us][KING][index[kto]] = kfrom;
1291 pieceList[us][ROOK][index[rto]] = rfrom;
1292 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1293 index[kfrom] = index[kto];
1298 /// Position::undo_promotion_move() is a private method used to unmake a
1299 /// promotion move. It is called from the main Position::do_move
1302 void Position::undo_promotion_move(Move m) {
1306 PieceType promotion;
1308 assert(move_is_ok(m));
1309 assert(move_promotion(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 us = side_to_move();
1315 them = opposite_color(us);
1316 from = move_from(m);
1319 assert(relative_rank(us, to) == RANK_8);
1320 assert(piece_on(from) == EMPTY);
1322 // Remove promoted piece
1323 promotion = move_promotion(m);
1324 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1325 assert(promotion >= KNIGHT && promotion <= QUEEN);
1326 clear_bit(&(byColorBB[us]), to);
1327 clear_bit(&(byTypeBB[promotion]), to);
1328 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1330 // Insert pawn at source square
1331 set_bit(&(byColorBB[us]), from);
1332 set_bit(&(byTypeBB[PAWN]), from);
1333 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1334 board[from] = piece_of_color_and_type(us, PAWN);
1337 npMaterial[us] -= piece_value_midgame(promotion);
1339 // Update piece list
1340 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1341 index[from] = pieceCount[us][PAWN];
1342 pieceList[us][promotion][index[to]] =
1343 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1344 index[pieceList[us][promotion][index[to]]] = index[to];
1346 // Update piece counts
1347 pieceCount[us][promotion]--;
1348 pieceCount[us][PAWN]++;
1352 assert(st->capture != KING);
1354 // Insert captured piece:
1355 set_bit(&(byColorBB[them]), to);
1356 set_bit(&(byTypeBB[st->capture]), to);
1357 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1358 board[to] = piece_of_color_and_type(them, st->capture);
1360 // Update material. Because the move is a promotion move, we know
1361 // that the captured piece cannot be a pawn.
1362 assert(st->capture != PAWN);
1363 npMaterial[them] += piece_value_midgame(st->capture);
1365 // Update piece list
1366 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1367 index[to] = pieceCount[them][st->capture];
1369 // Update piece count
1370 pieceCount[them][st->capture]++;
1376 /// Position::undo_ep_move() is a private method used to unmake an en passant
1377 /// capture. It is called from the main Position::undo_move function.
1379 void Position::undo_ep_move(Move m) {
1381 assert(move_is_ok(m));
1382 assert(move_is_ep(m));
1384 // When we have arrived here, some work has already been done by
1385 // Position::undo_move. In particular, the side to move has been switched,
1386 // so the code below is correct.
1387 Color us = side_to_move();
1388 Color them = opposite_color(us);
1389 Square from = move_from(m);
1390 Square to = move_to(m);
1391 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1393 assert(to == st->previous->epSquare);
1394 assert(relative_rank(us, to) == RANK_6);
1395 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1396 assert(piece_on(from) == EMPTY);
1397 assert(piece_on(capsq) == EMPTY);
1399 // Replace captured piece
1400 set_bit(&(byColorBB[them]), capsq);
1401 set_bit(&(byTypeBB[PAWN]), capsq);
1402 set_bit(&(byTypeBB[0]), capsq);
1403 board[capsq] = piece_of_color_and_type(them, PAWN);
1405 // Remove moving piece from destination square
1406 clear_bit(&(byColorBB[us]), to);
1407 clear_bit(&(byTypeBB[PAWN]), to);
1408 clear_bit(&(byTypeBB[0]), to);
1411 // Replace moving piece at source square
1412 set_bit(&(byColorBB[us]), from);
1413 set_bit(&(byTypeBB[PAWN]), from);
1414 set_bit(&(byTypeBB[0]), from);
1415 board[from] = piece_of_color_and_type(us, PAWN);
1417 // Update piece list:
1418 pieceList[us][PAWN][index[to]] = from;
1419 index[from] = index[to];
1420 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1421 index[capsq] = pieceCount[them][PAWN];
1423 // Update piece count:
1424 pieceCount[them][PAWN]++;
1428 /// Position::do_null_move makes() a "null move": It switches the side to move
1429 /// and updates the hash key without executing any move on the board.
1431 void Position::do_null_move(StateInfo& newSt) {
1434 assert(!is_check());
1436 // Back up the information necessary to undo the null move to the supplied
1437 // StateInfo object. In the case of a null move, the only thing we need to
1438 // remember is the last move made and the en passant square.
1439 newSt.lastMove = st->lastMove;
1440 newSt.epSquare = st->epSquare;
1441 newSt.previous = st->previous;
1442 st->previous = &newSt;
1444 // Save the current key to the history[] array, in order to be able to
1445 // detect repetition draws.
1446 history[gamePly] = st->key;
1448 // Update the necessary information
1449 sideToMove = opposite_color(sideToMove);
1450 if (st->epSquare != SQ_NONE)
1451 st->key ^= zobEp[st->epSquare];
1453 st->epSquare = SQ_NONE;
1456 st->key ^= zobSideToMove;
1458 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1459 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1465 /// Position::undo_null_move() unmakes a "null move".
1467 void Position::undo_null_move() {
1470 assert(!is_check());
1472 // Restore information from the our StateInfo object
1473 st->lastMove = st->previous->lastMove;
1474 st->epSquare = st->previous->epSquare;
1475 st->previous = st->previous->previous;
1477 if (st->epSquare != SQ_NONE)
1478 st->key ^= zobEp[st->epSquare];
1480 // Update the necessary information
1481 sideToMove = opposite_color(sideToMove);
1484 st->key ^= zobSideToMove;
1486 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1487 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1493 /// Position::see() is a static exchange evaluator: It tries to estimate the
1494 /// material gain or loss resulting from a move. There are three versions of
1495 /// this function: One which takes a destination square as input, one takes a
1496 /// move, and one which takes a 'from' and a 'to' square. The function does
1497 /// not yet understand promotions captures.
1499 int Position::see(Square to) const {
1501 assert(square_is_ok(to));
1502 return see(SQ_NONE, to);
1505 int Position::see(Move m) const {
1507 assert(move_is_ok(m));
1508 return see(move_from(m), move_to(m));
1511 int Position::see(Square from, Square to) const {
1514 static const int seeValues[18] = {
1515 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1516 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1517 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1518 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1522 Bitboard attackers, occ, b;
1524 assert(square_is_ok(from) || from == SQ_NONE);
1525 assert(square_is_ok(to));
1527 // Initialize colors
1528 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1529 Color them = opposite_color(us);
1531 // Initialize pinned and pinners bitboards
1532 Bitboard pinned[2], pinners[2];
1533 pinned[us] = pinned_pieces(us, pinners[us]);
1534 pinned[them] = pinned_pieces(them, pinners[them]);
1536 // Initialize pieces
1537 Piece piece = piece_on(from);
1538 Piece capture = piece_on(to);
1540 // Find all attackers to the destination square, with the moving piece
1541 // removed, but possibly an X-ray attacker added behind it.
1542 occ = occupied_squares();
1544 // Handle en passant moves
1545 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1547 assert(capture == EMPTY);
1549 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1550 capture = piece_on(capQq);
1552 assert(type_of_piece_on(capQq) == PAWN);
1554 // Remove the captured pawn
1555 clear_bit(&occ, capQq);
1560 clear_bit(&occ, from);
1561 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1562 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1563 | (piece_attacks<KNIGHT>(to) & knights())
1564 | (piece_attacks<KING>(to) & kings())
1565 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1566 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1568 // Remove our pinned pieces from attacks if the captured piece is not
1569 // a pinner, otherwise we could remove a valid "capture the pinner" attack.
1570 if (pinned[us] != EmptyBoardBB && !bit_is_set(pinners[us], to))
1571 attackers &= ~pinned[us];
1573 // Remove opponent pinned pieces from attacks if the moving piece is not
1574 // a pinner, otherwise we could remove a piece that is no more pinned
1575 // due to our pinner piece is moving away.
1576 if (pinned[them] != EmptyBoardBB && !bit_is_set(pinners[them], from))
1577 attackers &= ~pinned[them];
1579 if (from != SQ_NONE)
1582 // If we don't have any attacker we are finished
1583 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1586 // Locate the least valuable attacker to the destination square
1587 // and use it to initialize from square.
1589 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1592 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1593 piece = piece_on(from);
1596 // If the opponent has no attackers we are finished
1597 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1598 return seeValues[capture];
1600 attackers &= occ; // Remove the moving piece
1602 // The destination square is defended, which makes things rather more
1603 // difficult to compute. We proceed by building up a "swap list" containing
1604 // the material gain or loss at each stop in a sequence of captures to the
1605 // destination square, where the sides alternately capture, and always
1606 // capture with the least valuable piece. After each capture, we look for
1607 // new X-ray attacks from behind the capturing piece.
1608 int lastCapturingPieceValue = seeValues[piece];
1609 int swapList[32], n = 1;
1613 swapList[0] = seeValues[capture];
1616 // Locate the least valuable attacker for the side to move. The loop
1617 // below looks like it is potentially infinite, but it isn't. We know
1618 // that the side to move still has at least one attacker left.
1619 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1622 // Remove the attacker we just found from the 'attackers' bitboard,
1623 // and scan for new X-ray attacks behind the attacker.
1624 b = attackers & pieces_of_color_and_type(c, pt);
1626 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1627 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1631 // Add the new entry to the swap list
1633 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1636 // Remember the value of the capturing piece, and change the side to move
1637 // before beginning the next iteration
1638 lastCapturingPieceValue = seeValues[pt];
1639 c = opposite_color(c);
1641 // Remove pinned pieces from attackers
1642 if ( pinned[c] != EmptyBoardBB
1643 && !bit_is_set(pinners[c], to)
1644 && !(pinners[c] & attackers))
1645 attackers &= ~pinned[c];
1647 // Stop after a king capture
1648 if (pt == KING && (attackers & pieces_of_color(c)))
1651 swapList[n++] = 100;
1654 } while (attackers & pieces_of_color(c));
1656 // Having built the swap list, we negamax through it to find the best
1657 // achievable score from the point of view of the side to move
1659 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1665 /// Position::clear() erases the position object to a pristine state, with an
1666 /// empty board, white to move, and no castling rights.
1668 void Position::clear() {
1671 memset(st, 0, sizeof(StateInfo));
1672 st->epSquare = SQ_NONE;
1674 memset(index, 0, sizeof(int) * 64);
1675 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1677 for (int i = 0; i < 64; i++)
1680 for (int i = 0; i < 7; i++)
1682 byTypeBB[i] = EmptyBoardBB;
1683 pieceCount[0][i] = pieceCount[1][i] = 0;
1684 for (int j = 0; j < 8; j++)
1685 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1690 initialKFile = FILE_E;
1691 initialKRFile = FILE_H;
1692 initialQRFile = FILE_A;
1696 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1697 /// UCI interface code, whenever a non-reversible move is made in a
1698 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1699 /// for the program to handle games of arbitrary length, as long as the GUI
1700 /// handles draws by the 50 move rule correctly.
1702 void Position::reset_game_ply() {
1708 /// Position::put_piece() puts a piece on the given square of the board,
1709 /// updating the board array, bitboards, and piece counts.
1711 void Position::put_piece(Piece p, Square s) {
1713 Color c = color_of_piece(p);
1714 PieceType pt = type_of_piece(p);
1717 index[s] = pieceCount[c][pt];
1718 pieceList[c][pt][index[s]] = s;
1720 set_bit(&(byTypeBB[pt]), s);
1721 set_bit(&(byColorBB[c]), s);
1722 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1724 pieceCount[c][pt]++;
1731 /// Position::allow_oo() gives the given side the right to castle kingside.
1732 /// Used when setting castling rights during parsing of FEN strings.
1734 void Position::allow_oo(Color c) {
1736 st->castleRights |= (1 + int(c));
1740 /// Position::allow_ooo() gives the given side the right to castle queenside.
1741 /// Used when setting castling rights during parsing of FEN strings.
1743 void Position::allow_ooo(Color c) {
1745 st->castleRights |= (4 + 4*int(c));
1749 /// Position::compute_key() computes the hash key of the position. The hash
1750 /// key is usually updated incrementally as moves are made and unmade, the
1751 /// compute_key() function is only used when a new position is set up, and
1752 /// to verify the correctness of the hash key when running in debug mode.
1754 Key Position::compute_key() const {
1756 Key result = Key(0ULL);
1758 for (Square s = SQ_A1; s <= SQ_H8; s++)
1759 if (square_is_occupied(s))
1760 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1762 if (ep_square() != SQ_NONE)
1763 result ^= zobEp[ep_square()];
1765 result ^= zobCastle[st->castleRights];
1766 if (side_to_move() == BLACK)
1767 result ^= zobSideToMove;
1773 /// Position::compute_pawn_key() computes the hash key of the position. The
1774 /// hash key is usually updated incrementally as moves are made and unmade,
1775 /// the compute_pawn_key() function is only used when a new position is set
1776 /// up, and to verify the correctness of the pawn hash key when running in
1779 Key Position::compute_pawn_key() const {
1781 Key result = Key(0ULL);
1785 for (Color c = WHITE; c <= BLACK; c++)
1790 s = pop_1st_bit(&b);
1791 result ^= zobrist[c][PAWN][s];
1798 /// Position::compute_material_key() computes the hash key of the position.
1799 /// The hash key is usually updated incrementally as moves are made and unmade,
1800 /// the compute_material_key() function is only used when a new position is set
1801 /// up, and to verify the correctness of the material hash key when running in
1804 Key Position::compute_material_key() const {
1806 Key result = Key(0ULL);
1807 for (Color c = WHITE; c <= BLACK; c++)
1808 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1810 int count = piece_count(c, pt);
1811 for (int i = 0; i <= count; i++)
1812 result ^= zobMaterial[c][pt][i];
1818 /// Position::compute_value() compute the incremental scores for the middle
1819 /// game and the endgame. These functions are used to initialize the incremental
1820 /// scores when a new position is set up, and to verify that the scores are correctly
1821 /// updated by do_move and undo_move when the program is running in debug mode.
1822 template<Position::GamePhase Phase>
1823 Value Position::compute_value() const {
1825 Value result = Value(0);
1829 for (Color c = WHITE; c <= BLACK; c++)
1830 for (PieceType pt = PAWN; pt <= KING; pt++)
1832 b = pieces_of_color_and_type(c, pt);
1835 s = pop_1st_bit(&b);
1836 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1837 result += pst<Phase>(c, pt, s);
1841 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1842 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1847 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1848 /// game material score for the given side. Material scores are updated
1849 /// incrementally during the search, this function is only used while
1850 /// initializing a new Position object.
1852 Value Position::compute_non_pawn_material(Color c) const {
1854 Value result = Value(0);
1857 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1859 Bitboard b = pieces_of_color_and_type(c, pt);
1862 s = pop_1st_bit(&b);
1863 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1864 result += piece_value_midgame(pt);
1871 /// Position::is_mate() returns true or false depending on whether the
1872 /// side to move is checkmated. Note that this function is currently very
1873 /// slow, and shouldn't be used frequently inside the search.
1875 bool Position::is_mate() const {
1879 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1880 return mp.get_next_move() == MOVE_NONE;
1886 /// Position::is_draw() tests whether the position is drawn by material,
1887 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1888 /// must be done by the search.
1890 bool Position::is_draw() const {
1892 // Draw by material?
1894 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1897 // Draw by the 50 moves rule?
1898 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1901 // Draw by repetition?
1902 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1903 if (history[gamePly - i] == st->key)
1910 /// Position::has_mate_threat() tests whether a given color has a mate in one
1911 /// from the current position. This function is quite slow, but it doesn't
1912 /// matter, because it is currently only called from PV nodes, which are rare.
1914 bool Position::has_mate_threat(Color c) {
1917 Color stm = side_to_move();
1919 // The following lines are useless and silly, but prevents gcc from
1920 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1921 // be used uninitialized.
1922 st1.lastMove = st->lastMove;
1923 st1.epSquare = st->epSquare;
1928 // If the input color is not equal to the side to move, do a null move
1932 MoveStack mlist[120];
1934 bool result = false;
1936 // Generate legal moves
1937 count = generate_legal_moves(*this, mlist);
1939 // Loop through the moves, and see if one of them is mate
1940 for (int i = 0; i < count; i++)
1942 do_move(mlist[i].move, st2);
1946 undo_move(mlist[i].move);
1949 // Undo null move, if necessary
1957 /// Position::init_zobrist() is a static member function which initializes the
1958 /// various arrays used to compute hash keys.
1960 void Position::init_zobrist() {
1962 for (int i = 0; i < 2; i++)
1963 for (int j = 0; j < 8; j++)
1964 for (int k = 0; k < 64; k++)
1965 zobrist[i][j][k] = Key(genrand_int64());
1967 for (int i = 0; i < 64; i++)
1968 zobEp[i] = Key(genrand_int64());
1970 for (int i = 0; i < 16; i++)
1971 zobCastle[i] = genrand_int64();
1973 zobSideToMove = genrand_int64();
1975 for (int i = 0; i < 2; i++)
1976 for (int j = 0; j < 8; j++)
1977 for (int k = 0; k < 16; k++)
1978 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1980 for (int i = 0; i < 16; i++)
1981 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1985 /// Position::init_piece_square_tables() initializes the piece square tables.
1986 /// This is a two-step operation: First, the white halves of the tables are
1987 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1988 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1989 /// Second, the black halves of the tables are initialized by mirroring
1990 /// and changing the sign of the corresponding white scores.
1992 void Position::init_piece_square_tables() {
1994 int r = get_option_value_int("Randomness"), i;
1995 for (Square s = SQ_A1; s <= SQ_H8; s++)
1996 for (Piece p = WP; p <= WK; p++)
1998 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1999 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2000 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2003 for (Square s = SQ_A1; s <= SQ_H8; s++)
2004 for (Piece p = BP; p <= BK; p++)
2006 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2007 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2012 /// Position::flipped_copy() makes a copy of the input position, but with
2013 /// the white and black sides reversed. This is only useful for debugging,
2014 /// especially for finding evaluation symmetry bugs.
2016 void Position::flipped_copy(const Position &pos) {
2018 assert(pos.is_ok());
2023 for (Square s = SQ_A1; s <= SQ_H8; s++)
2024 if (!pos.square_is_empty(s))
2025 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2028 sideToMove = opposite_color(pos.side_to_move());
2031 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2032 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2033 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2034 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2036 initialKFile = pos.initialKFile;
2037 initialKRFile = pos.initialKRFile;
2038 initialQRFile = pos.initialQRFile;
2040 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2041 castleRightsMask[sq] = ALL_CASTLES;
2043 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2044 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2045 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2046 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2047 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2048 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2050 // En passant square
2051 if (pos.st->epSquare != SQ_NONE)
2052 st->epSquare = flip_square(pos.st->epSquare);
2058 st->key = compute_key();
2059 st->pawnKey = compute_pawn_key();
2060 st->materialKey = compute_material_key();
2062 // Incremental scores
2063 st->mgValue = compute_value<MidGame>();
2064 st->egValue = compute_value<EndGame>();
2067 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2068 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2074 /// Position::is_ok() performs some consitency checks for the position object.
2075 /// This is meant to be helpful when debugging.
2077 bool Position::is_ok(int* failedStep) const {
2079 // What features of the position should be verified?
2080 static const bool debugBitboards = false;
2081 static const bool debugKingCount = false;
2082 static const bool debugKingCapture = false;
2083 static const bool debugCheckerCount = false;
2084 static const bool debugKey = false;
2085 static const bool debugMaterialKey = false;
2086 static const bool debugPawnKey = false;
2087 static const bool debugIncrementalEval = false;
2088 static const bool debugNonPawnMaterial = false;
2089 static const bool debugPieceCounts = false;
2090 static const bool debugPieceList = false;
2092 if (failedStep) *failedStep = 1;
2095 if (!color_is_ok(side_to_move()))
2098 // Are the king squares in the position correct?
2099 if (failedStep) (*failedStep)++;
2100 if (piece_on(king_square(WHITE)) != WK)
2103 if (failedStep) (*failedStep)++;
2104 if (piece_on(king_square(BLACK)) != BK)
2108 if (failedStep) (*failedStep)++;
2109 if (!file_is_ok(initialKRFile))
2112 if (!file_is_ok(initialQRFile))
2115 // Do both sides have exactly one king?
2116 if (failedStep) (*failedStep)++;
2119 int kingCount[2] = {0, 0};
2120 for (Square s = SQ_A1; s <= SQ_H8; s++)
2121 if (type_of_piece_on(s) == KING)
2122 kingCount[color_of_piece_on(s)]++;
2124 if (kingCount[0] != 1 || kingCount[1] != 1)
2128 // Can the side to move capture the opponent's king?
2129 if (failedStep) (*failedStep)++;
2130 if (debugKingCapture)
2132 Color us = side_to_move();
2133 Color them = opposite_color(us);
2134 Square ksq = king_square(them);
2135 if (square_is_attacked(ksq, us))
2139 // Is there more than 2 checkers?
2140 if (failedStep) (*failedStep)++;
2141 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2145 if (failedStep) (*failedStep)++;
2148 // The intersection of the white and black pieces must be empty
2149 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2152 // The union of the white and black pieces must be equal to all
2154 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2157 // Separate piece type bitboards must have empty intersections
2158 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2159 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2160 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2164 // En passant square OK?
2165 if (failedStep) (*failedStep)++;
2166 if (ep_square() != SQ_NONE)
2168 // The en passant square must be on rank 6, from the point of view of the
2170 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2175 if (failedStep) (*failedStep)++;
2176 if (debugKey && st->key != compute_key())
2179 // Pawn hash key OK?
2180 if (failedStep) (*failedStep)++;
2181 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2184 // Material hash key OK?
2185 if (failedStep) (*failedStep)++;
2186 if (debugMaterialKey && st->materialKey != compute_material_key())
2189 // Incremental eval OK?
2190 if (failedStep) (*failedStep)++;
2191 if (debugIncrementalEval)
2193 if (st->mgValue != compute_value<MidGame>())
2196 if (st->egValue != compute_value<EndGame>())
2200 // Non-pawn material OK?
2201 if (failedStep) (*failedStep)++;
2202 if (debugNonPawnMaterial)
2204 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2207 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2212 if (failedStep) (*failedStep)++;
2213 if (debugPieceCounts)
2214 for (Color c = WHITE; c <= BLACK; c++)
2215 for (PieceType pt = PAWN; pt <= KING; pt++)
2216 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2219 if (failedStep) (*failedStep)++;
2222 for(Color c = WHITE; c <= BLACK; c++)
2223 for(PieceType pt = PAWN; pt <= KING; pt++)
2224 for(int i = 0; i < pieceCount[c][pt]; i++)
2226 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2229 if (index[piece_list(c, pt, i)] != i)
2233 if (failedStep) *failedStep = 0;