2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
34 #include "ucioption.h"
41 int Position::castleRightsMask[64];
43 Key Position::zobrist[2][8][64];
44 Key Position::zobEp[64];
45 Key Position::zobCastle[16];
46 Key Position::zobMaterial[2][8][16];
47 Key Position::zobSideToMove;
49 Value Position::MgPieceSquareTable[16][64];
50 Value Position::EgPieceSquareTable[16][64];
59 Position::Position(const Position &pos) {
63 Position::Position(const std::string &fen) {
68 /// Position::from_fen() initializes the position object with the given FEN
69 /// string. This function is not very robust - make sure that input FENs are
70 /// correct (this is assumed to be the responsibility of the GUI).
72 void Position::from_fen(const std::string &fen) {
74 static const std::string pieceLetters = "KQRBNPkqrbnp";
75 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
83 for ( ; fen[i] != ' '; i++)
87 // Skip the given number of files
88 file += (fen[i] - '1' + 1);
91 else if (fen[i] == '/')
97 size_t idx = pieceLetters.find(fen[i]);
98 if (idx == std::string::npos)
100 std::cout << "Error in FEN at character " << i << std::endl;
103 Square square = make_square(file, rank);
104 put_piece(pieces[idx], square);
110 if (fen[i] != 'w' && fen[i] != 'b')
112 std::cout << "Error in FEN at character " << i << std::endl;
115 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
121 std::cout << "Error in FEN at character " << i << std::endl;
126 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
130 else if(fen[i] == 'K') allow_oo(WHITE);
131 else if(fen[i] == 'Q') allow_ooo(WHITE);
132 else if(fen[i] == 'k') allow_oo(BLACK);
133 else if(fen[i] == 'q') allow_ooo(BLACK);
134 else if(fen[i] >= 'A' && fen[i] <= 'H') {
135 File rookFile, kingFile = FILE_NONE;
136 for(Square square = SQ_B1; square <= SQ_G1; square++)
137 if(piece_on(square) == WK)
138 kingFile = square_file(square);
139 if(kingFile == FILE_NONE) {
140 std::cout << "Error in FEN at character " << i << std::endl;
143 initialKFile = kingFile;
144 rookFile = File(fen[i] - 'A') + FILE_A;
145 if(rookFile < initialKFile) {
147 initialQRFile = rookFile;
151 initialKRFile = rookFile;
154 else if(fen[i] >= 'a' && fen[i] <= 'h') {
155 File rookFile, kingFile = FILE_NONE;
156 for(Square square = SQ_B8; square <= SQ_G8; square++)
157 if(piece_on(square) == BK)
158 kingFile = square_file(square);
159 if(kingFile == FILE_NONE) {
160 std::cout << "Error in FEN at character " << i << std::endl;
163 initialKFile = kingFile;
164 rookFile = File(fen[i] - 'a') + FILE_A;
165 if(rookFile < initialKFile) {
167 initialQRFile = rookFile;
171 initialKRFile = rookFile;
175 std::cout << "Error in FEN at character " << i << std::endl;
182 while (fen[i] == ' ')
186 if ( i < fen.length() - 2
187 && (fen[i] >= 'a' && fen[i] <= 'h')
188 && (fen[i+1] == '3' || fen[i+1] == '6'))
189 epSquare = square_from_string(fen.substr(i, 2));
191 // Various initialisation
192 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
193 castleRightsMask[sq] = ALL_CASTLES;
195 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
196 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
197 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
198 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
199 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
200 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
205 pawnKey = compute_pawn_key();
206 materialKey = compute_material_key();
207 mgValue = compute_mg_value();
208 egValue = compute_eg_value();
209 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
210 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
214 /// Position::to_fen() converts the position object to a FEN string. This is
215 /// probably only useful for debugging.
217 const std::string Position::to_fen() const {
219 static const std::string pieceLetters = " PNBRQK pnbrqk";
223 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
226 for (File file = FILE_A; file <= FILE_H; file++)
228 Square sq = make_square(file, rank);
229 if (!square_is_occupied(sq))
235 fen += (char)skip + '0';
238 fen += pieceLetters[piece_on(sq)];
241 fen += (char)skip + '0';
243 fen += (rank > RANK_1 ? '/' : ' ');
245 fen += (sideToMove == WHITE ? 'w' : 'b') + ' ';
246 if (castleRights != NO_CASTLES)
248 if (can_castle_kingside(WHITE)) fen += 'K';
249 if (can_castle_queenside(WHITE)) fen += 'Q';
250 if (can_castle_kingside(BLACK)) fen += 'k';
251 if (can_castle_queenside(BLACK)) fen += 'q';
256 if (ep_square() != SQ_NONE)
257 fen += square_to_string(ep_square());
265 /// Position::print() prints an ASCII representation of the position to
266 /// the standard output.
268 void Position::print() const {
269 char pieceStrings[][8] =
270 {"| ? ", "| P ", "| N ", "| B ", "| R ", "| Q ", "| K ", "| ? ",
271 "| ? ", "|=P=", "|=N=", "|=B=", "|=R=", "|=Q=", "|=K="
274 for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
275 std::cout << "+---+---+---+---+---+---+---+---+\n";
276 for(File file = FILE_A; file <= FILE_H; file++) {
277 Square sq = make_square(file, rank);
278 Piece piece = piece_on(sq);
280 std::cout << ((square_color(sq) == WHITE)? "| " : "| . ");
282 std::cout << pieceStrings[piece];
286 std::cout << "+---+---+---+---+---+---+---+---+\n";
287 std::cout << to_fen() << std::endl;
288 std::cout << key << std::endl;
292 /// Position::copy() creates a copy of the input position.
294 void Position::copy(const Position &pos) {
295 memcpy(this, &pos, sizeof(Position));
299 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
300 /// king) pieces for the given color.
302 Bitboard Position::pinned_pieces(Color c) const {
303 Bitboard b1, b2, pinned, pinners, sliders;
304 Square ksq = king_square(c), s;
305 Color them = opposite_color(c);
307 pinned = EmptyBoardBB;
308 b1 = occupied_squares();
310 sliders = rooks_and_queens(them) & ~checkers();
311 if(sliders & RookPseudoAttacks[ksq]) {
312 b2 = piece_attacks<ROOK>(ksq) & pieces_of_color(c);
313 pinners = rook_attacks_bb(ksq, b1 ^ b2) & sliders;
315 s = pop_1st_bit(&pinners);
316 pinned |= (squares_between(s, ksq) & b2);
320 sliders = bishops_and_queens(them) & ~checkers();
321 if(sliders & BishopPseudoAttacks[ksq]) {
322 b2 = piece_attacks<BISHOP>(ksq) & pieces_of_color(c);
323 pinners = bishop_attacks_bb(ksq, b1 ^ b2) & sliders;
325 s = pop_1st_bit(&pinners);
326 pinned |= (squares_between(s, ksq) & b2);
333 /// Position:discovered_check_candidates() returns a bitboard containing all
334 /// pieces for the given side which are candidates for giving a discovered
335 /// check. The code is almost the same as the function for finding pinned
338 Bitboard Position::discovered_check_candidates(Color c) const {
339 Bitboard b1, b2, dc, checkers, sliders;
340 Square ksq = king_square(opposite_color(c)), s;
343 b1 = occupied_squares();
345 sliders = rooks_and_queens(c);
346 if(sliders & RookPseudoAttacks[ksq]) {
347 b2 = piece_attacks<ROOK>(ksq) & pieces_of_color(c);
348 checkers = rook_attacks_bb(ksq, b1 ^ b2) & sliders;
350 s = pop_1st_bit(&checkers);
351 dc |= (squares_between(s, ksq) & b2);
355 sliders = bishops_and_queens(c);
356 if(sliders & BishopPseudoAttacks[ksq]) {
357 b2 = piece_attacks<BISHOP>(ksq) & pieces_of_color(c);
358 checkers = bishop_attacks_bb(ksq, b1 ^ b2) & sliders;
360 s = pop_1st_bit(&checkers);
361 dc |= (squares_between(s, ksq) & b2);
369 /// Position::square_is_attacked() checks whether the given side attacks the
372 bool Position::square_is_attacked(Square s, Color c) const {
374 (pawn_attacks(opposite_color(c), s) & pawns(c)) ||
375 (piece_attacks<KNIGHT>(s) & knights(c)) ||
376 (piece_attacks<KING>(s) & kings(c)) ||
377 (piece_attacks<ROOK>(s) & rooks_and_queens(c)) ||
378 (piece_attacks<BISHOP>(s) & bishops_and_queens(c));
382 /// Position::attacks_to() computes a bitboard containing all pieces which
383 /// attacks a given square. There are two versions of this function: One
384 /// which finds attackers of both colors, and one which only finds the
385 /// attackers for one side.
387 Bitboard Position::attacks_to(Square s) const {
389 (pawn_attacks(BLACK, s) & pawns(WHITE)) |
390 (pawn_attacks(WHITE, s) & pawns(BLACK)) |
391 (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT)) |
392 (piece_attacks<ROOK>(s) & rooks_and_queens()) |
393 (piece_attacks<BISHOP>(s) & bishops_and_queens()) |
394 (piece_attacks<KING>(s) & pieces_of_type(KING));
397 Bitboard Position::attacks_to(Square s, Color c) const {
398 return attacks_to(s) & pieces_of_color(c);
402 /// Position::piece_attacks_square() tests whether the piece on square f
403 /// attacks square t.
405 bool Position::piece_attacks_square(Square f, Square t) const {
406 assert(square_is_ok(f));
407 assert(square_is_ok(t));
409 switch(piece_on(f)) {
410 case WP: return pawn_attacks_square(WHITE, f, t);
411 case BP: return pawn_attacks_square(BLACK, f, t);
412 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
413 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
414 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
415 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
416 case WK: case BK: return piece_attacks_square<KING>(f, t);
417 default: return false;
424 /// Position::find_checkers() computes the checkersBB bitboard, which
425 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
426 /// currently works by calling Position::attacks_to, which is probably
427 /// inefficient. Consider rewriting this function to use the last move
428 /// played, like in non-bitboard versions of Glaurung.
430 void Position::find_checkers() {
431 checkersBB = attacks_to(king_square(side_to_move()),
432 opposite_color(side_to_move()));
436 /// Position::move_is_legal() tests whether a pseudo-legal move is legal.
437 /// There are two versions of this function: One which takes only a
438 /// move as input, and one which takes a move and a bitboard of pinned
439 /// pieces. The latter function is faster, and should always be preferred
440 /// when a pinned piece bitboard has already been computed.
442 bool Position::move_is_legal(Move m) const {
443 return move_is_legal(m, pinned_pieces(side_to_move()));
447 bool Position::move_is_legal(Move m, Bitboard pinned) const {
452 assert(move_is_ok(m));
453 assert(pinned == pinned_pieces(side_to_move()));
455 // If we're in check, all pseudo-legal moves are legal, because our
456 // check evasion generator only generates true legal moves.
457 if(is_check()) return true;
459 // Castling moves are checked for legality during move generation.
460 if(move_is_castle(m)) return true;
463 them = opposite_color(us);
466 ksq = king_square(us);
468 assert(color_of_piece_on(from) == us);
469 assert(piece_on(ksq) == king_of_color(us));
471 // En passant captures are a tricky special case. Because they are
472 // rather uncommon, we do it simply by testing whether the king is attacked
473 // after the move is made:
475 Square to = move_to(m);
476 Square capsq = make_square(square_file(to), square_rank(from));
477 Bitboard b = occupied_squares();
479 assert(to == ep_square());
480 assert(piece_on(from) == pawn_of_color(us));
481 assert(piece_on(capsq) == pawn_of_color(them));
482 assert(piece_on(to) == EMPTY);
484 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
486 (!(rook_attacks_bb(ksq, b) & rooks_and_queens(them)) &&
487 !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them)));
490 // If the moving piece is a king, check whether the destination
491 // square is attacked by the opponent.
492 if(from == ksq) return !(square_is_attacked(move_to(m), them));
494 // A non-king move is legal if and only if it is not pinned or it
495 // is moving along the ray towards or away from the king.
496 if(!bit_is_set(pinned, from)) return true;
497 if(direction_between_squares(from, ksq) ==
498 direction_between_squares(move_to(m), ksq))
505 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
506 /// There are two versions of this function: One which takes only a move as
507 /// input, and one which takes a move and a bitboard of discovered check
508 /// candidates. The latter function is faster, and should always be preferred
509 /// when a discovered check candidates bitboard has already been computed.
511 bool Position::move_is_check(Move m) const {
512 Bitboard dc = discovered_check_candidates(side_to_move());
513 return move_is_check(m, dc);
517 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
519 Square ksq, from, to;
522 assert(move_is_ok(m));
523 assert(dcCandidates ==
524 discovered_check_candidates(side_to_move()));
527 them = opposite_color(us);
531 ksq = king_square(them);
532 assert(color_of_piece_on(from) == us);
533 assert(piece_on(ksq) == king_of_color(them));
535 // Proceed according to the type of the moving piece:
536 switch(type_of_piece_on(from)) {
539 if(bit_is_set(pawn_attacks(them, ksq), to))
542 else if(bit_is_set(dcCandidates, from) &&
543 direction_between_squares(from, ksq) !=
544 direction_between_squares(to, ksq))
546 // Promotion with check?
547 else if(move_promotion(m)) {
548 Bitboard b = occupied_squares();
551 switch(move_promotion(m)) {
553 return piece_attacks_square<KNIGHT>(to, ksq);
555 return bit_is_set(bishop_attacks_bb(to, b), ksq);
557 return bit_is_set(rook_attacks_bb(to, b), ksq);
559 return bit_is_set(queen_attacks_bb(to, b), ksq);
564 // En passant capture with check? We have already handled the case
565 // of direct checks and ordinary discovered check, the only case we
566 // need to handle is the unusual case of a discovered check through the
568 else if(move_is_ep(m)) {
569 Square capsq = make_square(square_file(to), square_rank(from));
570 Bitboard b = occupied_squares();
572 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
574 ((rook_attacks_bb(ksq, b) & rooks_and_queens(us)) ||
575 (bishop_attacks_bb(ksq, b) & bishops_and_queens(us)));
581 if(bit_is_set(dcCandidates, from))
585 return bit_is_set(piece_attacks<KNIGHT>(ksq), to);
589 if(bit_is_set(dcCandidates, from))
593 return bit_is_set(piece_attacks<BISHOP>(ksq), to);
597 if(bit_is_set(dcCandidates, from))
601 return bit_is_set(piece_attacks<ROOK>(ksq), to);
604 // Discovered checks are impossible!
605 assert(!bit_is_set(dcCandidates, from));
607 return bit_is_set(piece_attacks<QUEEN>(ksq), to);
611 if(bit_is_set(dcCandidates, from) &&
612 direction_between_squares(from, ksq) !=
613 direction_between_squares(to, ksq))
615 // Castling with check?
616 if(move_is_castle(m)) {
617 Square kfrom, kto, rfrom, rto;
618 Bitboard b = occupied_squares();
623 kto = relative_square(us, SQ_G1);
624 rto = relative_square(us, SQ_F1);
627 kto = relative_square(us, SQ_C1);
628 rto = relative_square(us, SQ_D1);
631 clear_bit(&b, kfrom); clear_bit(&b, rfrom);
632 set_bit(&b, rto); set_bit(&b, kto);
634 return bit_is_set(rook_attacks_bb(rto, b), ksq);
649 /// Position::move_is_capture() tests whether a move from the current
650 /// position is a capture.
652 bool Position::move_is_capture(Move m) const {
654 color_of_piece_on(move_to(m)) == opposite_color(side_to_move())
659 /// Position::move_attacks_square() tests whether a move from the current
660 /// position attacks a given square. Only attacks by the moving piece are
661 /// considered; the function does not handle X-ray attacks.
663 bool Position::move_attacks_square(Move m, Square s) const {
664 assert(move_is_ok(m));
665 assert(square_is_ok(s));
667 Square f = move_from(m), t = move_to(m);
669 assert(square_is_occupied(f));
671 switch(piece_on(f)) {
672 case WP: return pawn_attacks_square(WHITE, t, s);
673 case BP: return pawn_attacks_square(BLACK, t, s);
674 case WN: case BN: return piece_attacks_square<KNIGHT>(t, s);
675 case WB: case BB: return piece_attacks_square<BISHOP>(t, s);
676 case WR: case BR: return piece_attacks_square<ROOK>(t, s);
677 case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s);
678 case WK: case BK: return piece_attacks_square<KING>(t, s);
679 default: assert(false);
687 /// Position::backup() is called when making a move. All information
688 /// necessary to restore the position when the move is later unmade
689 /// is saved to an UndoInfo object. The function Position::restore
690 /// does the reverse operation: When one does a backup followed by
691 /// a restore with the same UndoInfo object, the position is restored
692 /// to the state before backup was called.
694 void Position::backup(UndoInfo &u) const {
695 u.castleRights = castleRights;
696 u.epSquare = epSquare;
697 u.checkersBB = checkersBB;
700 u.materialKey = materialKey;
702 u.lastMove = lastMove;
703 u.capture = NO_PIECE_TYPE;
709 /// Position::restore() is called when unmaking a move. It copies back
710 /// the information backed up during a previous call to Position::backup.
712 void Position::restore(const UndoInfo &u) {
713 castleRights = u.castleRights;
714 epSquare = u.epSquare;
715 checkersBB = u.checkersBB;
718 materialKey = u.materialKey;
720 lastMove = u.lastMove;
726 /// Position::do_move() makes a move, and backs up all information necessary
727 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
728 /// Pseudo-legal moves should be filtered out before this function is called.
729 /// There are two versions of this function, one which takes only the move and
730 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
731 /// discovered check candidates. The second version is faster, because knowing
732 /// the discovered check candidates makes it easier to update the checkersBB
733 /// member variable in the position object.
735 void Position::do_move(Move m, UndoInfo &u) {
736 do_move(m, u, discovered_check_candidates(side_to_move()));
739 void Position::do_move(Move m, UndoInfo &u, Bitboard dcCandidates) {
741 assert(move_is_ok(m));
743 // Back up the necessary information to our UndoInfo object (except the
744 // captured piece, which is taken care of later:
747 // Save the current key to the history[] array, in order to be able to
748 // detect repetition draws:
749 history[gamePly] = key;
751 // Increment the 50 moves rule draw counter. Resetting it to zero in the
752 // case of non-reversible moves is taken care of later.
755 if(move_is_castle(m))
757 else if(move_promotion(m))
758 do_promotion_move(m, u);
759 else if(move_is_ep(m))
764 PieceType piece, capture;
767 them = opposite_color(us);
772 assert(color_of_piece_on(from) == us);
773 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
775 piece = type_of_piece_on(from);
776 capture = type_of_piece_on(to);
779 assert(capture != KING);
781 // Remove captured piece:
782 clear_bit(&(byColorBB[them]), to);
783 clear_bit(&(byTypeBB[capture]), to);
786 key ^= zobrist[them][capture][to];
788 // If the captured piece was a pawn, update pawn hash key:
790 pawnKey ^= zobrist[them][PAWN][to];
792 // Update incremental scores:
793 mgValue -= mg_pst(them, capture, to);
794 egValue -= eg_pst(them, capture, to);
798 npMaterial[them] -= piece_value_midgame(capture);
800 // Update material hash key:
801 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
803 // Update piece count:
804 pieceCount[them][capture]--;
806 // Update piece list:
807 pieceList[them][capture][index[to]] =
808 pieceList[them][capture][pieceCount[them][capture]];
809 index[pieceList[them][capture][index[to]]] = index[to];
811 // Remember the captured piece, in order to be able to undo the move
815 // Reset rule 50 counter:
820 clear_bit(&(byColorBB[us]), from);
821 clear_bit(&(byTypeBB[piece]), from);
822 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
823 set_bit(&(byColorBB[us]), to);
824 set_bit(&(byTypeBB[piece]), to);
825 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
826 board[to] = board[from];
830 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
832 // Update incremental scores:
833 mgValue -= mg_pst(us, piece, from);
834 mgValue += mg_pst(us, piece, to);
835 egValue -= eg_pst(us, piece, from);
836 egValue += eg_pst(us, piece, to);
838 // If the moving piece was a king, update the king square:
842 // If the move was a double pawn push, set the en passant square.
843 // This code is a bit ugly right now, and should be cleaned up later.
845 if(epSquare != SQ_NONE) {
846 key ^= zobEp[epSquare];
850 if(abs(int(to) - int(from)) == 16) {
851 if((us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) &
853 (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) &
855 epSquare = Square((int(from) + int(to)) / 2);
856 key ^= zobEp[epSquare];
859 // Reset rule 50 draw counter.
861 // Update pawn hash key:
862 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
865 // Update piece lists:
866 pieceList[us][piece][index[from]] = to;
867 index[to] = index[from];
869 // Update castle rights:
870 key ^= zobCastle[castleRights];
871 castleRights &= castleRightsMask[from];
872 castleRights &= castleRightsMask[to];
873 key ^= zobCastle[castleRights];
875 // Update checkers bitboard:
876 checkersBB = EmptyBoardBB;
877 Square ksq = king_square(them);
882 if(bit_is_set(pawn_attacks(them, ksq), to))
883 set_bit(&checkersBB, to);
884 if(bit_is_set(dcCandidates, from))
886 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
887 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
891 if(bit_is_set(piece_attacks<KNIGHT>(ksq), to))
892 set_bit(&checkersBB, to);
893 if(bit_is_set(dcCandidates, from))
895 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
896 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
900 if(bit_is_set(piece_attacks<BISHOP>(ksq), to))
901 set_bit(&checkersBB, to);
902 if(bit_is_set(dcCandidates, from))
904 (piece_attacks<ROOK>(ksq) & rooks_and_queens(us));
908 if(bit_is_set(piece_attacks<ROOK>(ksq), to))
909 set_bit(&checkersBB, to);
910 if(bit_is_set(dcCandidates, from))
912 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us));
916 if(bit_is_set(piece_attacks<QUEEN>(ksq), to))
917 set_bit(&checkersBB, to);
921 if(bit_is_set(dcCandidates, from))
923 ((piece_attacks<ROOK>(ksq) & rooks_and_queens(us)) |
924 (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
934 key ^= zobSideToMove;
935 sideToMove = opposite_color(sideToMove);
938 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
939 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
945 /// Position::do_castle_move() is a private method used to make a castling
946 /// move. It is called from the main Position::do_move function. Note that
947 /// castling moves are encoded as "king captures friendly rook" moves, for
948 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
950 void Position::do_castle_move(Move m) {
952 Square kfrom, kto, rfrom, rto;
955 assert(move_is_ok(m));
956 assert(move_is_castle(m));
959 them = opposite_color(us);
961 // Find source squares for king and rook:
962 kfrom = move_from(m);
963 rfrom = move_to(m); // HACK: See comment at beginning of function.
965 assert(piece_on(kfrom) == king_of_color(us));
966 assert(piece_on(rfrom) == rook_of_color(us));
968 // Find destination squares for king and rook:
969 if(rfrom > kfrom) { // O-O
970 kto = relative_square(us, SQ_G1);
971 rto = relative_square(us, SQ_F1);
974 kto = relative_square(us, SQ_C1);
975 rto = relative_square(us, SQ_D1);
978 // Remove pieces from source squares:
979 clear_bit(&(byColorBB[us]), kfrom);
980 clear_bit(&(byTypeBB[KING]), kfrom);
981 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
982 clear_bit(&(byColorBB[us]), rfrom);
983 clear_bit(&(byTypeBB[ROOK]), rfrom);
984 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
986 // Put pieces on destination squares:
987 set_bit(&(byColorBB[us]), kto);
988 set_bit(&(byTypeBB[KING]), kto);
989 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
990 set_bit(&(byColorBB[us]), rto);
991 set_bit(&(byTypeBB[ROOK]), rto);
992 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
994 // Update board array:
995 board[kfrom] = board[rfrom] = EMPTY;
996 board[kto] = king_of_color(us);
997 board[rto] = rook_of_color(us);
999 // Update king square:
1000 kingSquare[us] = kto;
1002 // Update piece lists:
1003 pieceList[us][KING][index[kfrom]] = kto;
1004 pieceList[us][ROOK][index[rfrom]] = rto;
1005 int tmp = index[rfrom];
1006 index[kto] = index[kfrom];
1009 // Update incremental scores:
1010 mgValue -= mg_pst(us, KING, kfrom);
1011 mgValue += mg_pst(us, KING, kto);
1012 egValue -= eg_pst(us, KING, kfrom);
1013 egValue += eg_pst(us, KING, kto);
1014 mgValue -= mg_pst(us, ROOK, rfrom);
1015 mgValue += mg_pst(us, ROOK, rto);
1016 egValue -= eg_pst(us, ROOK, rfrom);
1017 egValue += eg_pst(us, ROOK, rto);
1020 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1021 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1023 // Clear en passant square:
1024 if(epSquare != SQ_NONE) {
1025 key ^= zobEp[epSquare];
1029 // Update castling rights:
1030 key ^= zobCastle[castleRights];
1031 castleRights &= castleRightsMask[kfrom];
1032 key ^= zobCastle[castleRights];
1034 // Reset rule 50 counter:
1037 // Update checkers BB:
1038 checkersBB = attacks_to(king_square(them), us);
1042 /// Position::do_promotion_move() is a private method used to make a promotion
1043 /// move. It is called from the main Position::do_move function. The
1044 /// UndoInfo object, which has been initialized in Position::do_move, is
1045 /// used to store the captured piece (if any).
1047 void Position::do_promotion_move(Move m, UndoInfo &u) {
1050 PieceType capture, promotion;
1053 assert(move_is_ok(m));
1054 assert(move_promotion(m));
1056 us = side_to_move();
1057 them = opposite_color(us);
1059 from = move_from(m);
1062 assert(relative_rank(us, to) == RANK_8);
1063 assert(piece_on(from) == pawn_of_color(us));
1064 assert(color_of_piece_on(to) == them || square_is_empty(to));
1066 capture = type_of_piece_on(to);
1069 assert(capture != KING);
1071 // Remove captured piece:
1072 clear_bit(&(byColorBB[them]), to);
1073 clear_bit(&(byTypeBB[capture]), to);
1076 key ^= zobrist[them][capture][to];
1078 // Update incremental scores:
1079 mgValue -= mg_pst(them, capture, to);
1080 egValue -= eg_pst(them, capture, to);
1082 // Update material. Because our move is a promotion, we know that the
1083 // captured piece is not a pawn.
1084 assert(capture != PAWN);
1085 npMaterial[them] -= piece_value_midgame(capture);
1087 // Update material hash key:
1088 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
1090 // Update piece count:
1091 pieceCount[them][capture]--;
1093 // Update piece list:
1094 pieceList[them][capture][index[to]] =
1095 pieceList[them][capture][pieceCount[them][capture]];
1096 index[pieceList[them][capture][index[to]]] = index[to];
1098 // Remember the captured piece, in order to be able to undo the move
1100 u.capture = capture;
1104 clear_bit(&(byColorBB[us]), from);
1105 clear_bit(&(byTypeBB[PAWN]), from);
1106 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1107 board[from] = EMPTY;
1109 // Insert promoted piece:
1110 promotion = move_promotion(m);
1111 assert(promotion >= KNIGHT && promotion <= QUEEN);
1112 set_bit(&(byColorBB[us]), to);
1113 set_bit(&(byTypeBB[promotion]), to);
1114 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1115 board[to] = piece_of_color_and_type(us, promotion);
1118 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1120 // Update pawn hash key:
1121 pawnKey ^= zobrist[us][PAWN][from];
1123 // Update material key:
1124 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1125 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1127 // Update piece counts:
1128 pieceCount[us][PAWN]--;
1129 pieceCount[us][promotion]++;
1131 // Update piece lists:
1132 pieceList[us][PAWN][index[from]] =
1133 pieceList[us][PAWN][pieceCount[us][PAWN]];
1134 index[pieceList[us][PAWN][index[from]]] = index[from];
1135 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1136 index[to] = pieceCount[us][promotion] - 1;
1138 // Update incremental scores:
1139 mgValue -= mg_pst(us, PAWN, from);
1140 mgValue += mg_pst(us, promotion, to);
1141 egValue -= eg_pst(us, PAWN, from);
1142 egValue += eg_pst(us, promotion, to);
1145 npMaterial[us] += piece_value_midgame(promotion);
1147 // Clear the en passant square:
1148 if(epSquare != SQ_NONE) {
1149 key ^= zobEp[epSquare];
1153 // Update castle rights:
1154 key ^= zobCastle[castleRights];
1155 castleRights &= castleRightsMask[to];
1156 key ^= zobCastle[castleRights];
1158 // Reset rule 50 counter:
1161 // Update checkers BB:
1162 checkersBB = attacks_to(king_square(them), us);
1166 /// Position::do_ep_move() is a private method used to make an en passant
1167 /// capture. It is called from the main Position::do_move function. Because
1168 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1169 /// object in which to store the captured piece.
1171 void Position::do_ep_move(Move m) {
1173 Square from, to, capsq;
1176 assert(move_is_ok(m));
1177 assert(move_is_ep(m));
1179 us = side_to_move();
1180 them = opposite_color(us);
1182 // Find from, to and capture squares:
1183 from = move_from(m);
1185 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1187 assert(to == epSquare);
1188 assert(relative_rank(us, to) == RANK_6);
1189 assert(piece_on(to) == EMPTY);
1190 assert(piece_on(from) == pawn_of_color(us));
1191 assert(piece_on(capsq) == pawn_of_color(them));
1193 // Remove captured piece:
1194 clear_bit(&(byColorBB[them]), capsq);
1195 clear_bit(&(byTypeBB[PAWN]), capsq);
1196 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1197 board[capsq] = EMPTY;
1199 // Remove moving piece from source square:
1200 clear_bit(&(byColorBB[us]), from);
1201 clear_bit(&(byTypeBB[PAWN]), from);
1202 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1204 // Put moving piece on destination square:
1205 set_bit(&(byColorBB[us]), to);
1206 set_bit(&(byTypeBB[PAWN]), to);
1207 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1208 board[to] = board[from];
1209 board[from] = EMPTY;
1211 // Update material hash key:
1212 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1214 // Update piece count:
1215 pieceCount[them][PAWN]--;
1217 // Update piece list:
1218 pieceList[us][PAWN][index[from]] = to;
1219 index[to] = index[from];
1220 pieceList[them][PAWN][index[capsq]] =
1221 pieceList[them][PAWN][pieceCount[them][PAWN]];
1222 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1225 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1226 key ^= zobrist[them][PAWN][capsq];
1227 key ^= zobEp[epSquare];
1229 // Update pawn hash key:
1230 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1231 pawnKey ^= zobrist[them][PAWN][capsq];
1233 // Update incremental scores:
1234 mgValue -= mg_pst(them, PAWN, capsq);
1235 mgValue -= mg_pst(us, PAWN, from);
1236 mgValue += mg_pst(us, PAWN, to);
1237 egValue -= eg_pst(them, PAWN, capsq);
1238 egValue -= eg_pst(us, PAWN, from);
1239 egValue += eg_pst(us, PAWN, to);
1241 // Reset en passant square:
1244 // Reset rule 50 counter:
1247 // Update checkers BB:
1248 checkersBB = attacks_to(king_square(them), us);
1252 /// Position::undo_move() unmakes a move. When it returns, the position should
1253 /// be restored to exactly the same state as before the move was made. It is
1254 /// important that Position::undo_move is called with the same move and UndoInfo
1255 /// object as the earlier call to Position::do_move.
1257 void Position::undo_move(Move m, const UndoInfo &u) {
1259 assert(move_is_ok(m));
1262 sideToMove = opposite_color(sideToMove);
1264 // Restore information from our UndoInfo object (except the captured piece,
1265 // which is taken care of later):
1268 if(move_is_castle(m))
1269 undo_castle_move(m);
1270 else if(move_promotion(m))
1271 undo_promotion_move(m, u);
1272 else if(move_is_ep(m))
1277 PieceType piece, capture;
1279 us = side_to_move();
1280 them = opposite_color(us);
1282 from = move_from(m);
1285 assert(piece_on(from) == EMPTY);
1286 assert(color_of_piece_on(to) == us);
1288 // Put the piece back at the source square:
1289 piece = type_of_piece_on(to);
1290 set_bit(&(byColorBB[us]), from);
1291 set_bit(&(byTypeBB[piece]), from);
1292 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1293 board[from] = piece_of_color_and_type(us, piece);
1295 // Clear the destination square
1296 clear_bit(&(byColorBB[us]), to);
1297 clear_bit(&(byTypeBB[piece]), to);
1298 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1300 // If the moving piece was a king, update the king square:
1302 kingSquare[us] = from;
1304 // Update piece list:
1305 pieceList[us][piece][index[to]] = from;
1306 index[from] = index[to];
1308 capture = u.capture;
1311 assert(capture != KING);
1312 // Replace the captured piece:
1313 set_bit(&(byColorBB[them]), to);
1314 set_bit(&(byTypeBB[capture]), to);
1315 set_bit(&(byTypeBB[0]), to);
1316 board[to] = piece_of_color_and_type(them, capture);
1320 npMaterial[them] += piece_value_midgame(capture);
1322 // Update piece list:
1323 pieceList[them][capture][pieceCount[them][capture]] = to;
1324 index[to] = pieceCount[them][capture];
1326 // Update piece count:
1327 pieceCount[them][capture]++;
1337 /// Position::undo_castle_move() is a private method used to unmake a castling
1338 /// move. It is called from the main Position::undo_move function. Note that
1339 /// castling moves are encoded as "king captures friendly rook" moves, for
1340 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1342 void Position::undo_castle_move(Move m) {
1344 Square kfrom, kto, rfrom, rto;
1346 assert(move_is_ok(m));
1347 assert(move_is_castle(m));
1349 // When we have arrived here, some work has already been done by
1350 // Position::undo_move. In particular, the side to move has been switched,
1351 // so the code below is correct.
1352 us = side_to_move();
1353 them = opposite_color(us);
1355 // Find source squares for king and rook:
1356 kfrom = move_from(m);
1357 rfrom = move_to(m); // HACK: See comment at beginning of function.
1359 // Find destination squares for king and rook:
1360 if(rfrom > kfrom) { // O-O
1361 kto = relative_square(us, SQ_G1);
1362 rto = relative_square(us, SQ_F1);
1365 kto = relative_square(us, SQ_C1);
1366 rto = relative_square(us, SQ_D1);
1369 assert(piece_on(kto) == king_of_color(us));
1370 assert(piece_on(rto) == rook_of_color(us));
1372 // Remove pieces from destination squares:
1373 clear_bit(&(byColorBB[us]), kto);
1374 clear_bit(&(byTypeBB[KING]), kto);
1375 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1376 clear_bit(&(byColorBB[us]), rto);
1377 clear_bit(&(byTypeBB[ROOK]), rto);
1378 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1380 // Put pieces on source squares:
1381 set_bit(&(byColorBB[us]), kfrom);
1382 set_bit(&(byTypeBB[KING]), kfrom);
1383 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1384 set_bit(&(byColorBB[us]), rfrom);
1385 set_bit(&(byTypeBB[ROOK]), rfrom);
1386 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1389 board[rto] = board[kto] = EMPTY;
1390 board[rfrom] = rook_of_color(us);
1391 board[kfrom] = king_of_color(us);
1393 // Update king square:
1394 kingSquare[us] = kfrom;
1396 // Update piece lists:
1397 pieceList[us][KING][index[kto]] = kfrom;
1398 pieceList[us][ROOK][index[rto]] = rfrom;
1399 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1400 index[kfrom] = index[kto];
1405 /// Position::undo_promotion_move() is a private method used to unmake a
1406 /// promotion move. It is called from the main Position::do_move
1407 /// function. The UndoInfo object, which has been initialized in
1408 /// Position::do_move, is used to put back the captured piece (if any).
1410 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1413 PieceType capture, promotion;
1415 assert(move_is_ok(m));
1416 assert(move_promotion(m));
1418 // When we have arrived here, some work has already been done by
1419 // Position::undo_move. In particular, the side to move has been switched,
1420 // so the code below is correct.
1421 us = side_to_move();
1422 them = opposite_color(us);
1424 from = move_from(m);
1427 assert(relative_rank(us, to) == RANK_8);
1428 assert(piece_on(from) == EMPTY);
1430 // Remove promoted piece:
1431 promotion = move_promotion(m);
1432 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1433 assert(promotion >= KNIGHT && promotion <= QUEEN);
1434 clear_bit(&(byColorBB[us]), to);
1435 clear_bit(&(byTypeBB[promotion]), to);
1436 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1438 // Insert pawn at source square:
1439 set_bit(&(byColorBB[us]), from);
1440 set_bit(&(byTypeBB[PAWN]), from);
1441 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1442 board[from] = pawn_of_color(us);
1445 npMaterial[us] -= piece_value_midgame(promotion);
1447 // Update piece list:
1448 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1449 index[from] = pieceCount[us][PAWN];
1450 pieceList[us][promotion][index[to]] =
1451 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1452 index[pieceList[us][promotion][index[to]]] = index[to];
1454 // Update piece counts:
1455 pieceCount[us][promotion]--;
1456 pieceCount[us][PAWN]++;
1458 capture = u.capture;
1460 assert(capture != KING);
1462 // Insert captured piece:
1463 set_bit(&(byColorBB[them]), to);
1464 set_bit(&(byTypeBB[capture]), to);
1465 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1466 board[to] = piece_of_color_and_type(them, capture);
1468 // Update material. Because the move is a promotion move, we know
1469 // that the captured piece cannot be a pawn.
1470 assert(capture != PAWN);
1471 npMaterial[them] += piece_value_midgame(capture);
1473 // Update piece list:
1474 pieceList[them][capture][pieceCount[them][capture]] = to;
1475 index[to] = pieceCount[them][capture];
1477 // Update piece count:
1478 pieceCount[them][capture]++;
1485 /// Position::undo_ep_move() is a private method used to unmake an en passant
1486 /// capture. It is called from the main Position::undo_move function. Because
1487 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1488 /// object from which to retrieve the captured piece.
1490 void Position::undo_ep_move(Move m) {
1492 Square from, to, capsq;
1494 assert(move_is_ok(m));
1495 assert(move_is_ep(m));
1497 // When we have arrived here, some work has already been done by
1498 // Position::undo_move. In particular, the side to move has been switched,
1499 // so the code below is correct.
1500 us = side_to_move();
1501 them = opposite_color(us);
1503 // Find from, to and captures squares:
1504 from = move_from(m);
1506 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1508 assert(to == ep_square());
1509 assert(relative_rank(us, to) == RANK_6);
1510 assert(piece_on(to) == pawn_of_color(us));
1511 assert(piece_on(from) == EMPTY);
1512 assert(piece_on(capsq) == EMPTY);
1514 // Replace captured piece:
1515 set_bit(&(byColorBB[them]), capsq);
1516 set_bit(&(byTypeBB[PAWN]), capsq);
1517 set_bit(&(byTypeBB[0]), capsq);
1518 board[capsq] = pawn_of_color(them);
1520 // Remove moving piece from destination square:
1521 clear_bit(&(byColorBB[us]), to);
1522 clear_bit(&(byTypeBB[PAWN]), to);
1523 clear_bit(&(byTypeBB[0]), to);
1526 // Replace moving piece at source square:
1527 set_bit(&(byColorBB[us]), from);
1528 set_bit(&(byTypeBB[PAWN]), from);
1529 set_bit(&(byTypeBB[0]), from);
1530 board[from] = pawn_of_color(us);
1532 // Update piece list:
1533 pieceList[us][PAWN][index[to]] = from;
1534 index[from] = index[to];
1535 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1536 index[capsq] = pieceCount[them][PAWN];
1538 // Update piece count:
1539 pieceCount[them][PAWN]++;
1543 /// Position::do_null_move makes() a "null move": It switches the side to move
1544 /// and updates the hash key without executing any move on the board.
1546 void Position::do_null_move(UndoInfo &u) {
1548 assert(!is_check());
1550 // Back up the information necessary to undo the null move to the supplied
1551 // UndoInfo object. In the case of a null move, the only thing we need to
1552 // remember is the last move made and the en passant square.
1553 u.lastMove = lastMove;
1554 u.epSquare = epSquare;
1556 // Save the current key to the history[] array, in order to be able to
1557 // detect repetition draws:
1558 history[gamePly] = key;
1560 // Update the necessary information.
1561 sideToMove = opposite_color(sideToMove);
1562 if(epSquare != SQ_NONE)
1563 key ^= zobEp[epSquare];
1567 key ^= zobSideToMove;
1569 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1570 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1576 /// Position::undo_null_move() unmakes a "null move".
1578 void Position::undo_null_move(const UndoInfo &u) {
1580 assert(!is_check());
1582 // Restore information from the supplied UndoInfo object:
1583 lastMove = u.lastMove;
1584 epSquare = u.epSquare;
1585 if(epSquare != SQ_NONE)
1586 key ^= zobEp[epSquare];
1588 // Update the necessary information.
1589 sideToMove = opposite_color(sideToMove);
1592 key ^= zobSideToMove;
1594 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1595 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1601 /// Position::see() is a static exchange evaluator: It tries to estimate the
1602 /// material gain or loss resulting from a move. There are two versions of
1603 /// this function: One which takes a move as input, and one which takes a
1604 /// 'from' and a 'to' square. The function does not yet understand promotions
1605 /// or en passant captures.
1607 int Position::see(Square from, Square to) const {
1608 // Approximate material values, with pawn = 1:
1609 static const int seeValues[18] = {
1610 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1613 Piece piece, capture;
1614 Bitboard attackers, occ, b;
1616 assert(square_is_ok(from));
1617 assert(square_is_ok(to));
1619 // Initialize colors:
1620 us = color_of_piece_on(from);
1621 them = opposite_color(us);
1623 // Initialize pieces:
1624 piece = piece_on(from);
1625 capture = piece_on(to);
1627 // Find all attackers to the destination square, with the moving piece
1628 // removed, but possibly an X-ray attacker added behind it:
1629 occ = occupied_squares();
1630 clear_bit(&occ, from);
1632 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1633 (bishop_attacks_bb(to, occ) & bishops_and_queens()) |
1634 (piece_attacks<KNIGHT>(to) & knights()) |
1635 (piece_attacks<KING>(to) & kings()) |
1636 (pawn_attacks(WHITE, to) & pawns(BLACK)) |
1637 (pawn_attacks(BLACK, to) & pawns(WHITE));
1640 // If the opponent has no attackers, we are finished:
1641 if((attackers & pieces_of_color(them)) == EmptyBoardBB)
1642 return seeValues[capture];
1644 // The destination square is defended, which makes things rather more
1645 // difficult to compute. We proceed by building up a "swap list" containing
1646 // the material gain or loss at each stop in a sequence of captures to the
1647 // destianation square, where the sides alternately capture, and always
1648 // capture with the least valuable piece. After each capture, we look for
1649 // new X-ray attacks from behind the capturing piece.
1650 int lastCapturingPieceValue = seeValues[piece];
1651 int swapList[32], n = 1;
1655 swapList[0] = seeValues[capture];
1658 // Locate the least valuable attacker for the side to move. The loop
1659 // below looks like it is potentially infinite, but it isn't. We know
1660 // that the side to move still has at least one attacker left.
1661 for(pt = PAWN; !(attackers&pieces_of_color_and_type(c, pt)); pt++)
1664 // Remove the attacker we just found from the 'attackers' bitboard,
1665 // and scan for new X-ray attacks behind the attacker:
1666 b = attackers & pieces_of_color_and_type(c, pt);
1669 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1670 (bishop_attacks_bb(to, occ) & bishops_and_queens());
1673 // Add the new entry to the swap list:
1675 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1678 // Remember the value of the capturing piece, and change the side to move
1679 // before beginning the next iteration:
1680 lastCapturingPieceValue = seeValues[pt];
1681 c = opposite_color(c);
1683 // Stop after a king capture:
1684 if(pt == KING && (attackers & pieces_of_color(c))) {
1686 swapList[n++] = 100;
1689 } while(attackers & pieces_of_color(c));
1691 // Having built the swap list, we negamax through it to find the best
1692 // achievable score from the point of view of the side to move:
1693 while(--n) swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1699 int Position::see(Move m) const {
1700 assert(move_is_ok(m));
1701 return see(move_from(m), move_to(m));
1705 /// Position::clear() erases the position object to a pristine state, with an
1706 /// empty board, white to move, and no castling rights.
1708 void Position::clear() {
1711 for(i = 0; i < 64; i++) {
1716 for(i = 0; i < 2; i++)
1717 byColorBB[i] = EmptyBoardBB;
1719 for(i = 0; i < 7; i++) {
1720 byTypeBB[i] = EmptyBoardBB;
1721 pieceCount[0][i] = pieceCount[1][i] = 0;
1722 for(j = 0; j < 8; j++)
1723 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1726 checkersBB = EmptyBoardBB;
1728 lastMove = MOVE_NONE;
1731 castleRights = NO_CASTLES;
1732 initialKFile = FILE_E;
1733 initialKRFile = FILE_H;
1734 initialQRFile = FILE_A;
1741 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1742 /// UCI interface code, whenever a non-reversible move is made in a
1743 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1744 /// for the program to handle games of arbitrary length, as long as the GUI
1745 /// handles draws by the 50 move rule correctly.
1747 void Position::reset_game_ply() {
1752 /// Position::put_piece() puts a piece on the given square of the board,
1753 /// updating the board array, bitboards, and piece counts.
1755 void Position::put_piece(Piece p, Square s) {
1756 Color c = color_of_piece(p);
1757 PieceType pt = type_of_piece(p);
1760 index[s] = pieceCount[c][pt];
1761 pieceList[c][pt][index[s]] = s;
1763 set_bit(&(byTypeBB[pt]), s);
1764 set_bit(&(byColorBB[c]), s);
1765 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1767 pieceCount[c][pt]++;
1774 /// Position::allow_oo() gives the given side the right to castle kingside.
1775 /// Used when setting castling rights during parsing of FEN strings.
1777 void Position::allow_oo(Color c) {
1778 castleRights |= (1 + int(c));
1782 /// Position::allow_ooo() gives the given side the right to castle queenside.
1783 /// Used when setting castling rights during parsing of FEN strings.
1785 void Position::allow_ooo(Color c) {
1786 castleRights |= (4 + 4*int(c));
1790 /// Position::compute_key() computes the hash key of the position. The hash
1791 /// key is usually updated incrementally as moves are made and unmade, the
1792 /// compute_key() function is only used when a new position is set up, and
1793 /// to verify the correctness of the hash key when running in debug mode.
1795 Key Position::compute_key() const {
1796 Key result = Key(0ULL);
1798 for(Square s = SQ_A1; s <= SQ_H8; s++)
1799 if(square_is_occupied(s))
1801 zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1803 if(ep_square() != SQ_NONE)
1804 result ^= zobEp[ep_square()];
1805 result ^= zobCastle[castleRights];
1806 if(side_to_move() == BLACK) result ^= zobSideToMove;
1812 /// Position::compute_pawn_key() computes the hash key of the position. The
1813 /// hash key is usually updated incrementally as moves are made and unmade,
1814 /// the compute_pawn_key() function is only used when a new position is set
1815 /// up, and to verify the correctness of the pawn hash key when running in
1818 Key Position::compute_pawn_key() const {
1819 Key result = Key(0ULL);
1823 for(Color c = WHITE; c <= BLACK; c++) {
1826 s = pop_1st_bit(&b);
1827 result ^= zobrist[c][PAWN][s];
1834 /// Position::compute_material_key() computes the hash key of the position.
1835 /// The hash key is usually updated incrementally as moves are made and unmade,
1836 /// the compute_material_key() function is only used when a new position is set
1837 /// up, and to verify the correctness of the material hash key when running in
1840 Key Position::compute_material_key() const {
1841 Key result = Key(0ULL);
1842 for(Color c = WHITE; c <= BLACK; c++)
1843 for(PieceType pt = PAWN; pt <= QUEEN; pt++) {
1844 int count = piece_count(c, pt);
1845 for(int i = 0; i <= count; i++)
1846 result ^= zobMaterial[c][pt][i];
1852 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1853 /// incremental scores for the middle game and the endgame. These functions
1854 /// are used to initialize the incremental scores when a new position is set
1855 /// up, and to verify that the scores are correctly updated by do_move
1856 /// and undo_move when the program is running in debug mode.
1858 Value Position::compute_mg_value() const {
1859 Value result = Value(0);
1863 for(Color c = WHITE; c <= BLACK; c++)
1864 for(PieceType pt = PAWN; pt <= KING; pt++) {
1865 b = pieces_of_color_and_type(c, pt);
1867 s = pop_1st_bit(&b);
1868 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1869 result += mg_pst(c, pt, s);
1872 result += (side_to_move() == WHITE)?
1873 (TempoValueMidgame / 2) : -(TempoValueMidgame / 2);
1877 Value Position::compute_eg_value() const {
1878 Value result = Value(0);
1882 for(Color c = WHITE; c <= BLACK; c++)
1883 for(PieceType pt = PAWN; pt <= KING; pt++) {
1884 b = pieces_of_color_and_type(c, pt);
1886 s = pop_1st_bit(&b);
1887 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1888 result += eg_pst(c, pt, s);
1891 result += (side_to_move() == WHITE)?
1892 (TempoValueEndgame / 2) : -(TempoValueEndgame / 2);
1897 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1898 /// game material score for the given side. Material scores are updated
1899 /// incrementally during the search, this function is only used while
1900 /// initializing a new Position object.
1902 Value Position::compute_non_pawn_material(Color c) const {
1903 Value result = Value(0);
1906 for(PieceType pt = KNIGHT; pt <= QUEEN; pt++) {
1907 Bitboard b = pieces_of_color_and_type(c, pt);
1909 s = pop_1st_bit(&b);
1910 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1911 result += piece_value_midgame(pt);
1918 /// Position::is_mate() returns true or false depending on whether the
1919 /// side to move is checkmated. Note that this function is currently very
1920 /// slow, and shouldn't be used frequently inside the search.
1922 bool Position::is_mate() {
1924 MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
1925 MOVE_NONE, Depth(0));
1926 return mp.get_next_move() == MOVE_NONE;
1933 /// Position::is_draw() tests whether the position is drawn by material,
1934 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1935 /// must be done by the search.
1937 bool Position::is_draw() const {
1938 // Draw by material?
1940 non_pawn_material(WHITE) + non_pawn_material(BLACK)
1941 <= BishopValueMidgame)
1944 // Draw by the 50 moves rule?
1945 if(rule50 > 100 || (rule50 == 100 && !is_check()))
1948 // Draw by repetition?
1949 for(int i = 2; i < Min(gamePly, rule50); i += 2)
1950 if(history[gamePly - i] == key)
1957 /// Position::has_mate_threat() tests whether a given color has a mate in one
1958 /// from the current position. This function is quite slow, but it doesn't
1959 /// matter, because it is currently only called from PV nodes, which are rare.
1961 bool Position::has_mate_threat(Color c) {
1963 Color stm = side_to_move();
1965 // The following lines are useless and silly, but prevents gcc from
1966 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1967 // be used uninitialized.
1968 u1.lastMove = lastMove;
1969 u1.epSquare = epSquare;
1974 // If the input color is not equal to the side to move, do a null move
1975 if(c != stm) do_null_move(u1);
1977 MoveStack mlist[120];
1979 bool result = false;
1981 // Generate legal moves
1982 count = generate_legal_moves(*this, mlist);
1984 // Loop through the moves, and see if one of them is mate.
1985 for(int i = 0; i < count; i++) {
1986 do_move(mlist[i].move, u2);
1987 if(is_mate()) result = true;
1988 undo_move(mlist[i].move, u2);
1991 // Undo null move, if necessary
1992 if(c != stm) undo_null_move(u1);
1998 /// Position::init_zobrist() is a static member function which initializes the
1999 /// various arrays used to compute hash keys.
2001 void Position::init_zobrist() {
2003 for(int i = 0; i < 2; i++)
2004 for(int j = 0; j < 8; j++)
2005 for(int k = 0; k < 64; k++)
2006 zobrist[i][j][k] = Key(genrand_int64());
2008 for(int i = 0; i < 64; i++)
2009 zobEp[i] = Key(genrand_int64());
2011 for(int i = 0; i < 16; i++)
2012 zobCastle[i] = genrand_int64();
2014 zobSideToMove = genrand_int64();
2016 for(int i = 0; i < 2; i++)
2017 for(int j = 0; j < 8; j++)
2018 for(int k = 0; k < 16; k++)
2019 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2021 for(int i = 0; i < 16; i++)
2022 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2026 /// Position::init_piece_square_tables() initializes the piece square tables.
2027 /// This is a two-step operation: First, the white halves of the tables are
2028 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2029 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2030 /// Second, the black halves of the tables are initialized by mirroring
2031 /// and changing the sign of the corresponding white scores.
2033 void Position::init_piece_square_tables() {
2034 int r = get_option_value_int("Randomness"), i;
2035 for(Square s = SQ_A1; s <= SQ_H8; s++) {
2036 for(Piece p = WP; p <= WK; p++) {
2037 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2038 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2039 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2042 for(Square s = SQ_A1; s <= SQ_H8; s++)
2043 for(Piece p = BP; p <= BK; p++) {
2044 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2045 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2050 /// Position::flipped_copy() makes a copy of the input position, but with
2051 /// the white and black sides reversed. This is only useful for debugging,
2052 /// especially for finding evaluation symmetry bugs.
2054 void Position::flipped_copy(const Position &pos) {
2055 assert(pos.is_ok());
2060 for(Square s = SQ_A1; s <= SQ_H8; s++)
2061 if(!pos.square_is_empty(s))
2062 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2065 sideToMove = opposite_color(pos.side_to_move());
2068 if(pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2069 if(pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2070 if(pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2071 if(pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2073 initialKFile = pos.initialKFile;
2074 initialKRFile = pos.initialKRFile;
2075 initialQRFile = pos.initialQRFile;
2077 for(Square sq = SQ_A1; sq <= SQ_H8; sq++)
2078 castleRightsMask[sq] = ALL_CASTLES;
2079 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
2080 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
2081 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2082 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2083 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2084 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2086 // En passant square
2087 if(pos.epSquare != SQ_NONE)
2088 epSquare = flip_square(pos.epSquare);
2094 key = compute_key();
2095 pawnKey = compute_pawn_key();
2096 materialKey = compute_material_key();
2098 // Incremental scores
2099 mgValue = compute_mg_value();
2100 egValue = compute_eg_value();
2103 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2104 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2110 /// Position::is_ok() performs some consitency checks for the position object.
2111 /// This is meant to be helpful when debugging.
2113 bool Position::is_ok(int* failedStep) const {
2115 // What features of the position should be verified?
2116 static const bool debugBitboards = false;
2117 static const bool debugKingCount = false;
2118 static const bool debugKingCapture = false;
2119 static const bool debugCheckerCount = false;
2120 static const bool debugKey = false;
2121 static const bool debugMaterialKey = false;
2122 static const bool debugPawnKey = false;
2123 static const bool debugIncrementalEval = false;
2124 static const bool debugNonPawnMaterial = false;
2125 static const bool debugPieceCounts = false;
2126 static const bool debugPieceList = false;
2128 if (failedStep) *failedStep = 1;
2131 if(!color_is_ok(side_to_move()))
2134 // Are the king squares in the position correct?
2135 if (failedStep) (*failedStep)++;
2136 if(piece_on(king_square(WHITE)) != WK)
2139 if (failedStep) (*failedStep)++;
2140 if(piece_on(king_square(BLACK)) != BK)
2144 if (failedStep) (*failedStep)++;
2145 if(!file_is_ok(initialKRFile))
2147 if(!file_is_ok(initialQRFile))
2150 // Do both sides have exactly one king?
2151 if (failedStep) (*failedStep)++;
2152 if(debugKingCount) {
2153 int kingCount[2] = {0, 0};
2154 for(Square s = SQ_A1; s <= SQ_H8; s++)
2155 if(type_of_piece_on(s) == KING)
2156 kingCount[color_of_piece_on(s)]++;
2157 if(kingCount[0] != 1 || kingCount[1] != 1)
2161 // Can the side to move capture the opponent's king?
2162 if (failedStep) (*failedStep)++;
2163 if(debugKingCapture) {
2164 Color us = side_to_move();
2165 Color them = opposite_color(us);
2166 Square ksq = king_square(them);
2167 if(square_is_attacked(ksq, us))
2171 // Is there more than 2 checkers?
2172 if (failedStep) (*failedStep)++;
2173 if(debugCheckerCount && count_1s(checkersBB) > 2)
2177 if (failedStep) (*failedStep)++;
2178 if(debugBitboards) {
2179 // The intersection of the white and black pieces must be empty:
2180 if((pieces_of_color(WHITE) & pieces_of_color(BLACK))
2184 // The union of the white and black pieces must be equal to all
2185 // occupied squares:
2186 if((pieces_of_color(WHITE) | pieces_of_color(BLACK))
2187 != occupied_squares())
2190 // Separate piece type bitboards must have empty intersections:
2191 for(PieceType p1 = PAWN; p1 <= KING; p1++)
2192 for(PieceType p2 = PAWN; p2 <= KING; p2++)
2193 if(p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2197 // En passant square OK?
2198 if (failedStep) (*failedStep)++;
2199 if(ep_square() != SQ_NONE) {
2200 // The en passant square must be on rank 6, from the point of view of the
2202 if(relative_rank(side_to_move(), ep_square()) != RANK_6)
2207 if (failedStep) (*failedStep)++;
2208 if(debugKey && key != compute_key())
2211 // Pawn hash key OK?
2212 if (failedStep) (*failedStep)++;
2213 if(debugPawnKey && pawnKey != compute_pawn_key())
2216 // Material hash key OK?
2217 if (failedStep) (*failedStep)++;
2218 if(debugMaterialKey && materialKey != compute_material_key())
2221 // Incremental eval OK?
2222 if (failedStep) (*failedStep)++;
2223 if(debugIncrementalEval) {
2224 if(mgValue != compute_mg_value())
2226 if(egValue != compute_eg_value())
2230 // Non-pawn material OK?
2231 if (failedStep) (*failedStep)++;
2232 if(debugNonPawnMaterial) {
2233 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2235 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2240 if (failedStep) (*failedStep)++;
2241 if(debugPieceCounts)
2242 for(Color c = WHITE; c <= BLACK; c++)
2243 for(PieceType pt = PAWN; pt <= KING; pt++)
2244 if(pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2247 if (failedStep) (*failedStep)++;
2248 if(debugPieceList) {
2249 for(Color c = WHITE; c <= BLACK; c++)
2250 for(PieceType pt = PAWN; pt <= KING; pt++)
2251 for(int i = 0; i < pieceCount[c][pt]; i++) {
2252 if(piece_on(piece_list(c, pt, i)) !=
2253 piece_of_color_and_type(c, pt))
2255 if(index[piece_list(c, pt, i)] != i)
2259 if (failedStep) *failedStep = 0;