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;
211 st->key = compute_key();
212 st->pawnKey = compute_pawn_key();
213 st->materialKey = compute_material_key();
214 st->mgValue = compute_value<MidGame>();
215 st->egValue = compute_value<EndGame>();
216 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
221 /// Position::to_fen() converts the position object to a FEN string. This is
222 /// probably only useful for debugging.
224 const std::string Position::to_fen() const {
226 static const std::string pieceLetters = " PNBRQK pnbrqk";
230 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
233 for (File file = FILE_A; file <= FILE_H; file++)
235 Square sq = make_square(file, rank);
236 if (!square_is_occupied(sq))
242 fen += (char)skip + '0';
245 fen += pieceLetters[piece_on(sq)];
248 fen += (char)skip + '0';
250 fen += (rank > RANK_1 ? '/' : ' ');
252 fen += (sideToMove == WHITE ? "w " : "b ");
253 if (st->castleRights != NO_CASTLES)
255 if (can_castle_kingside(WHITE)) fen += 'K';
256 if (can_castle_queenside(WHITE)) fen += 'Q';
257 if (can_castle_kingside(BLACK)) fen += 'k';
258 if (can_castle_queenside(BLACK)) fen += 'q';
263 if (ep_square() != SQ_NONE)
264 fen += square_to_string(ep_square());
272 /// Position::print() prints an ASCII representation of the position to
273 /// the standard output. If a move is given then also the san is print.
275 void Position::print(Move m) const {
277 static const std::string pieceLetters = " PNBRQK PNBRQK .";
279 // Check for reentrancy, as example when called from inside
280 // MovePicker that is used also here in move_to_san()
284 RequestPending = true;
286 std::cout << std::endl;
289 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
290 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
292 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
294 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
295 for (File file = FILE_A; file <= FILE_H; file++)
297 Square sq = make_square(file, rank);
298 Piece piece = piece_on(sq);
299 if (piece == EMPTY && square_color(sq) == WHITE)
302 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
303 std::cout << '|' << col << pieceLetters[piece] << col;
305 std::cout << '|' << std::endl;
307 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
308 << "Fen is: " << to_fen() << std::endl
309 << "Key is: " << st->key << std::endl;
311 RequestPending = false;
315 /// Position::copy() creates a copy of the input position.
317 void Position::copy(const Position &pos) {
319 memcpy(this, &pos, sizeof(Position));
323 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
324 /// king) pieces for the given color and for the given pinner type. Or, when
325 /// template parameter FindPinned is false, the pieces of the given color
326 /// candidate for a discovery check against the enemy king.
327 /// Note that checkersBB bitboard must be already updated.
329 template<bool FindPinned>
330 Bitboard Position::hidden_checkers(Color c) const {
332 Bitboard pinners, result = EmptyBoardBB;
334 // Pinned pieces protect our king, dicovery checks attack
336 Square ksq = king_square(FindPinned ? c : opposite_color(c));
338 // Pinners are sliders, not checkers, that give check when
339 // candidate pinned is removed.
340 pinners = (rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
341 | (bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
343 if (FindPinned && pinners)
344 pinners &= ~st->checkersBB;
348 Square s = pop_1st_bit(&pinners);
349 Bitboard b = squares_between(s, ksq) & occupied_squares();
353 if ( !(b & (b - 1)) // Only one bit set?
354 && (b & pieces_of_color(c))) // Is an our piece?
361 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
362 /// king) pieces for the given color.
364 Bitboard Position::pinned_pieces(Color c) const {
366 return hidden_checkers<true>(c);
370 /// Position:discovered_check_candidates() returns a bitboard containing all
371 /// pieces for the given side which are candidates for giving a discovered
374 Bitboard Position::discovered_check_candidates(Color c) const {
376 return hidden_checkers<false>(c);
379 /// Position::attacks_to() computes a bitboard containing all pieces which
380 /// attacks a given square. There are two versions of this function: One
381 /// which finds attackers of both colors, and one which only finds the
382 /// attackers for one side.
384 Bitboard Position::attacks_to(Square s) const {
386 return (pawn_attacks(BLACK, s) & pawns(WHITE))
387 | (pawn_attacks(WHITE, s) & pawns(BLACK))
388 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
389 | (piece_attacks<ROOK>(s) & rooks_and_queens())
390 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
391 | (piece_attacks<KING>(s) & pieces_of_type(KING));
394 /// Position::piece_attacks_square() tests whether the piece on square f
395 /// attacks square t.
397 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
399 assert(square_is_ok(f));
400 assert(square_is_ok(t));
404 case WP: return pawn_attacks_square(WHITE, f, t);
405 case BP: return pawn_attacks_square(BLACK, f, t);
406 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
407 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
408 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
409 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
410 case WK: case BK: return piece_attacks_square<KING>(f, t);
417 /// Position::move_attacks_square() tests whether a move from the current
418 /// position attacks a given square.
420 bool Position::move_attacks_square(Move m, Square s) const {
422 assert(move_is_ok(m));
423 assert(square_is_ok(s));
425 Square f = move_from(m), t = move_to(m);
427 assert(square_is_occupied(f));
429 if (piece_attacks_square(piece_on(f), t, s))
432 // Move the piece and scan for X-ray attacks behind it
433 Bitboard occ = occupied_squares();
434 Color us = color_of_piece_on(f);
437 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
438 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
440 // If we have attacks we need to verify that are caused by our move
441 // and are not already existent ones.
442 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
446 /// Position::find_checkers() computes the checkersBB bitboard, which
447 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
448 /// currently works by calling Position::attacks_to, which is probably
449 /// inefficient. Consider rewriting this function to use the last move
450 /// played, like in non-bitboard versions of Glaurung.
452 void Position::find_checkers() {
454 Color us = side_to_move();
455 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
459 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
461 bool Position::pl_move_is_legal(Move m) const {
463 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
466 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
469 assert(move_is_ok(m));
470 assert(pinned == pinned_pieces(side_to_move()));
472 // If we're in check, all pseudo-legal moves are legal, because our
473 // check evasion generator only generates true legal moves.
477 // Castling moves are checked for legality during move generation.
478 if (move_is_castle(m))
481 Color us = side_to_move();
482 Square from = move_from(m);
483 Square ksq = king_square(us);
485 assert(color_of_piece_on(from) == us);
486 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
488 // En passant captures are a tricky special case. Because they are
489 // rather uncommon, we do it simply by testing whether the king is attacked
490 // after the move is made
493 Color them = opposite_color(us);
494 Square to = move_to(m);
495 Square capsq = make_square(square_file(to), square_rank(from));
496 Bitboard b = occupied_squares();
498 assert(to == ep_square());
499 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
500 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
501 assert(piece_on(to) == EMPTY);
504 clear_bit(&b, capsq);
507 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
508 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
511 // If the moving piece is a king, check whether the destination
512 // square is attacked by the opponent.
514 return !(square_is_attacked(move_to(m), opposite_color(us)));
516 // A non-king move is legal if and only if it is not pinned or it
517 // is moving along the ray towards or away from the king.
519 || !bit_is_set(pinned, from)
520 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
524 /// Position::move_is_check() tests whether a pseudo-legal move is a check
526 bool Position::move_is_check(Move m) const {
528 Bitboard dc = discovered_check_candidates(side_to_move());
529 return move_is_check(m, dc);
532 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
535 assert(move_is_ok(m));
536 assert(dcCandidates == discovered_check_candidates(side_to_move()));
538 Color us = side_to_move();
539 Color them = opposite_color(us);
540 Square from = move_from(m);
541 Square to = move_to(m);
542 Square ksq = king_square(them);
544 assert(color_of_piece_on(from) == us);
545 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
547 // Proceed according to the type of the moving piece
548 switch (type_of_piece_on(from))
552 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
555 if ( dcCandidates // Discovered check?
556 && bit_is_set(dcCandidates, from)
557 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
560 if (move_promotion(m)) // Promotion with check?
562 Bitboard b = occupied_squares();
565 switch (move_promotion(m))
568 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
570 return bit_is_set(bishop_attacks_bb(to, b), ksq);
572 return bit_is_set(rook_attacks_bb(to, b), ksq);
574 return bit_is_set(queen_attacks_bb(to, b), ksq);
579 // En passant capture with check? We have already handled the case
580 // of direct checks and ordinary discovered check, the only case we
581 // need to handle is the unusual case of a discovered check through the
583 else if (move_is_ep(m))
585 Square capsq = make_square(square_file(to), square_rank(from));
586 Bitboard b = occupied_squares();
588 clear_bit(&b, capsq);
590 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
591 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
595 // Test discovered check and normal check according to piece type
597 return (dcCandidates && bit_is_set(dcCandidates, from))
598 || bit_is_set(piece_attacks<KNIGHT>(ksq), to);
601 return (dcCandidates && bit_is_set(dcCandidates, from))
602 || ( direction_between_squares(ksq, to) != DIR_NONE
603 && bit_is_set(piece_attacks<BISHOP>(ksq), to));
606 return (dcCandidates && bit_is_set(dcCandidates, from))
607 || ( direction_between_squares(ksq, to) != DIR_NONE
608 && bit_is_set(piece_attacks<ROOK>(ksq), to));
611 // Discovered checks are impossible!
612 assert(!bit_is_set(dcCandidates, from));
613 return ( direction_between_squares(ksq, to) != DIR_NONE
614 && bit_is_set(piece_attacks<QUEEN>(ksq), to));
618 if ( bit_is_set(dcCandidates, from)
619 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
622 // Castling with check?
623 if (move_is_castle(m))
625 Square kfrom, kto, rfrom, rto;
626 Bitboard b = occupied_squares();
632 kto = relative_square(us, SQ_G1);
633 rto = relative_square(us, SQ_F1);
635 kto = relative_square(us, SQ_C1);
636 rto = relative_square(us, SQ_D1);
638 clear_bit(&b, kfrom);
639 clear_bit(&b, rfrom);
642 return bit_is_set(rook_attacks_bb(rto, b), ksq);
646 default: // NO_PIECE_TYPE
654 /// Position::move_is_capture() tests whether a move from the current
655 /// position is a capture. Move must not be MOVE_NONE.
657 bool Position::move_is_capture(Move m) const {
659 assert(m != MOVE_NONE);
661 return ( !square_is_empty(move_to(m))
662 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
668 /// Position::update_checkers() udpates chekers info given the move. It is called
669 /// in do_move() and is faster then find_checkers().
671 template<PieceType Piece>
672 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
673 Square to, Bitboard dcCandidates) {
675 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
676 const bool Rook = (Piece == QUEEN || Piece == ROOK);
677 const bool Slider = Bishop || Rook;
679 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
680 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
681 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
682 set_bit(pCheckersBB, to);
684 else if ( Piece != KING
686 && bit_is_set(piece_attacks<Piece>(ksq), to))
687 set_bit(pCheckersBB, to);
689 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
692 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
695 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
700 /// Position::do_move() makes a move, and saves all information necessary
701 /// to a StateInfo object. The move is assumed to be legal.
702 /// Pseudo-legal moves should be filtered out before this function is called.
704 void Position::do_move(Move m, StateInfo& newSt) {
706 do_move(m, newSt, discovered_check_candidates(side_to_move()));
709 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
712 assert(move_is_ok(m));
714 // Copy some fields of old state to our new StateInfo object except the
715 // ones which are recalculated from scratch anyway, then switch our state
716 // pointer to point to the new, ready to be updated, state.
717 struct ReducedStateInfo {
718 Key key, pawnKey, materialKey;
719 int castleRights, rule50;
721 Value mgValue, egValue;
724 memcpy(&newSt, st, sizeof(ReducedStateInfo));
725 newSt.capture = NO_PIECE_TYPE;
729 // Save the current key to the history[] array, in order to be able to
730 // detect repetition draws.
731 history[gamePly] = st->key;
733 // Increment the 50 moves rule draw counter. Resetting it to zero in the
734 // case of non-reversible moves is taken care of later.
737 if (move_is_castle(m))
739 else if (move_promotion(m))
740 do_promotion_move(m);
741 else if (move_is_ep(m))
745 Color us = side_to_move();
746 Color them = opposite_color(us);
747 Square from = move_from(m);
748 Square to = move_to(m);
750 assert(color_of_piece_on(from) == us);
751 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
753 PieceType piece = type_of_piece_on(from);
755 st->capture = type_of_piece_on(to);
758 do_capture_move(m, st->capture, them, to);
761 clear_bit(&(byColorBB[us]), from);
762 clear_bit(&(byTypeBB[piece]), from);
763 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
764 set_bit(&(byColorBB[us]), to);
765 set_bit(&(byTypeBB[piece]), to);
766 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
767 board[to] = board[from];
771 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
773 // Update incremental scores
774 st->mgValue -= pst<MidGame>(us, piece, from);
775 st->mgValue += pst<MidGame>(us, piece, to);
776 st->egValue -= pst<EndGame>(us, piece, from);
777 st->egValue += pst<EndGame>(us, piece, to);
779 // If the moving piece was a king, update the king square
783 // Reset en passant square
784 if (st->epSquare != SQ_NONE)
786 st->key ^= zobEp[st->epSquare];
787 st->epSquare = SQ_NONE;
790 // If the moving piece was a pawn do some special extra work
793 // Reset rule 50 draw counter
796 // Update pawn hash key
797 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
799 // Set en passant square, only if moved pawn can be captured
800 if (abs(int(to) - int(from)) == 16)
802 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
803 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
805 st->epSquare = Square((int(from) + int(to)) / 2);
806 st->key ^= zobEp[st->epSquare];
811 // Update piece lists
812 pieceList[us][piece][index[from]] = to;
813 index[to] = index[from];
815 // Update castle rights
816 st->key ^= zobCastle[st->castleRights];
817 st->castleRights &= castleRightsMask[from];
818 st->castleRights &= castleRightsMask[to];
819 st->key ^= zobCastle[st->castleRights];
821 // Update checkers bitboard, piece must be already moved
822 st->checkersBB = EmptyBoardBB;
823 Square ksq = king_square(them);
826 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
827 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
828 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
829 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
830 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
831 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
832 default: assert(false); break;
837 st->key ^= zobSideToMove;
838 sideToMove = opposite_color(sideToMove);
841 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
842 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
848 /// Position::do_capture_move() is a private method used to update captured
849 /// piece info. It is called from the main Position::do_move function.
851 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
853 assert(capture != KING);
855 // Remove captured piece
856 clear_bit(&(byColorBB[them]), to);
857 clear_bit(&(byTypeBB[capture]), to);
860 st->key ^= zobrist[them][capture][to];
862 // If the captured piece was a pawn, update pawn hash key
864 st->pawnKey ^= zobrist[them][PAWN][to];
866 // Update incremental scores
867 st->mgValue -= pst<MidGame>(them, capture, to);
868 st->egValue -= pst<EndGame>(them, capture, to);
870 assert(!move_promotion(m) || capture != PAWN);
874 npMaterial[them] -= piece_value_midgame(capture);
876 // Update material hash key
877 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
879 // Update piece count
880 pieceCount[them][capture]--;
883 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
884 index[pieceList[them][capture][index[to]]] = index[to];
886 // Reset rule 50 counter
891 /// Position::do_castle_move() is a private method used to make a castling
892 /// move. It is called from the main Position::do_move function. Note that
893 /// castling moves are encoded as "king captures friendly rook" moves, for
894 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
896 void Position::do_castle_move(Move m) {
899 assert(move_is_ok(m));
900 assert(move_is_castle(m));
902 Color us = side_to_move();
903 Color them = opposite_color(us);
905 // Find source squares for king and rook
906 Square kfrom = move_from(m);
907 Square rfrom = move_to(m); // HACK: See comment at beginning of function
910 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
911 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
913 // Find destination squares for king and rook
914 if (rfrom > kfrom) // O-O
916 kto = relative_square(us, SQ_G1);
917 rto = relative_square(us, SQ_F1);
919 kto = relative_square(us, SQ_C1);
920 rto = relative_square(us, SQ_D1);
923 // Remove pieces from source squares
924 clear_bit(&(byColorBB[us]), kfrom);
925 clear_bit(&(byTypeBB[KING]), kfrom);
926 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
927 clear_bit(&(byColorBB[us]), rfrom);
928 clear_bit(&(byTypeBB[ROOK]), rfrom);
929 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
931 // Put pieces on destination squares
932 set_bit(&(byColorBB[us]), kto);
933 set_bit(&(byTypeBB[KING]), kto);
934 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
935 set_bit(&(byColorBB[us]), rto);
936 set_bit(&(byTypeBB[ROOK]), rto);
937 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
939 // Update board array
940 board[kfrom] = board[rfrom] = EMPTY;
941 board[kto] = piece_of_color_and_type(us, KING);
942 board[rto] = piece_of_color_and_type(us, ROOK);
944 // Update king square
945 kingSquare[us] = kto;
947 // Update piece lists
948 pieceList[us][KING][index[kfrom]] = kto;
949 pieceList[us][ROOK][index[rfrom]] = rto;
950 int tmp = index[rfrom];
951 index[kto] = index[kfrom];
954 // Update incremental scores
955 st->mgValue -= pst<MidGame>(us, KING, kfrom);
956 st->mgValue += pst<MidGame>(us, KING, kto);
957 st->egValue -= pst<EndGame>(us, KING, kfrom);
958 st->egValue += pst<EndGame>(us, KING, kto);
959 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
960 st->mgValue += pst<MidGame>(us, ROOK, rto);
961 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
962 st->egValue += pst<EndGame>(us, ROOK, rto);
965 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
966 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
968 // Clear en passant square
969 if (st->epSquare != SQ_NONE)
971 st->key ^= zobEp[st->epSquare];
972 st->epSquare = SQ_NONE;
975 // Update castling rights
976 st->key ^= zobCastle[st->castleRights];
977 st->castleRights &= castleRightsMask[kfrom];
978 st->key ^= zobCastle[st->castleRights];
980 // Reset rule 50 counter
983 // Update checkers BB
984 st->checkersBB = attacks_to(king_square(them), us);
988 /// Position::do_promotion_move() is a private method used to make a promotion
989 /// move. It is called from the main Position::do_move function.
991 void Position::do_promotion_move(Move m) {
998 assert(move_is_ok(m));
999 assert(move_promotion(m));
1001 us = side_to_move();
1002 them = opposite_color(us);
1003 from = move_from(m);
1006 assert(relative_rank(us, to) == RANK_8);
1007 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1008 assert(color_of_piece_on(to) == them || square_is_empty(to));
1010 st->capture = type_of_piece_on(to);
1013 do_capture_move(m, st->capture, them, to);
1016 clear_bit(&(byColorBB[us]), from);
1017 clear_bit(&(byTypeBB[PAWN]), from);
1018 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1019 board[from] = EMPTY;
1021 // Insert promoted piece
1022 promotion = move_promotion(m);
1023 assert(promotion >= KNIGHT && promotion <= QUEEN);
1024 set_bit(&(byColorBB[us]), to);
1025 set_bit(&(byTypeBB[promotion]), to);
1026 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1027 board[to] = piece_of_color_and_type(us, promotion);
1030 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1032 // Update pawn hash key
1033 st->pawnKey ^= zobrist[us][PAWN][from];
1035 // Update material key
1036 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1037 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1039 // Update piece counts
1040 pieceCount[us][PAWN]--;
1041 pieceCount[us][promotion]++;
1043 // Update piece lists
1044 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1045 index[pieceList[us][PAWN][index[from]]] = index[from];
1046 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1047 index[to] = pieceCount[us][promotion] - 1;
1049 // Update incremental scores
1050 st->mgValue -= pst<MidGame>(us, PAWN, from);
1051 st->mgValue += pst<MidGame>(us, promotion, to);
1052 st->egValue -= pst<EndGame>(us, PAWN, from);
1053 st->egValue += pst<EndGame>(us, promotion, to);
1056 npMaterial[us] += piece_value_midgame(promotion);
1058 // Clear the en passant square
1059 if (st->epSquare != SQ_NONE)
1061 st->key ^= zobEp[st->epSquare];
1062 st->epSquare = SQ_NONE;
1065 // Update castle rights
1066 st->key ^= zobCastle[st->castleRights];
1067 st->castleRights &= castleRightsMask[to];
1068 st->key ^= zobCastle[st->castleRights];
1070 // Reset rule 50 counter
1073 // Update checkers BB
1074 st->checkersBB = attacks_to(king_square(them), us);
1078 /// Position::do_ep_move() is a private method used to make an en passant
1079 /// capture. It is called from the main Position::do_move function.
1081 void Position::do_ep_move(Move m) {
1084 Square from, to, capsq;
1087 assert(move_is_ok(m));
1088 assert(move_is_ep(m));
1090 us = side_to_move();
1091 them = opposite_color(us);
1092 from = move_from(m);
1094 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1096 assert(to == st->epSquare);
1097 assert(relative_rank(us, to) == RANK_6);
1098 assert(piece_on(to) == EMPTY);
1099 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1100 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1102 // Remove captured piece
1103 clear_bit(&(byColorBB[them]), capsq);
1104 clear_bit(&(byTypeBB[PAWN]), capsq);
1105 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1106 board[capsq] = EMPTY;
1108 // Remove moving piece from source square
1109 clear_bit(&(byColorBB[us]), from);
1110 clear_bit(&(byTypeBB[PAWN]), from);
1111 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1113 // Put moving piece on destination square
1114 set_bit(&(byColorBB[us]), to);
1115 set_bit(&(byTypeBB[PAWN]), to);
1116 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1117 board[to] = board[from];
1118 board[from] = EMPTY;
1120 // Update material hash key
1121 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1123 // Update piece count
1124 pieceCount[them][PAWN]--;
1126 // Update piece list
1127 pieceList[us][PAWN][index[from]] = to;
1128 index[to] = index[from];
1129 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1130 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1133 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1134 st->key ^= zobrist[them][PAWN][capsq];
1135 st->key ^= zobEp[st->epSquare];
1137 // Update pawn hash key
1138 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1139 st->pawnKey ^= zobrist[them][PAWN][capsq];
1141 // Update incremental scores
1142 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1143 st->mgValue -= pst<MidGame>(us, PAWN, from);
1144 st->mgValue += pst<MidGame>(us, PAWN, to);
1145 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1146 st->egValue -= pst<EndGame>(us, PAWN, from);
1147 st->egValue += pst<EndGame>(us, PAWN, to);
1149 // Reset en passant square
1150 st->epSquare = SQ_NONE;
1152 // Reset rule 50 counter
1155 // Update checkers BB
1156 st->checkersBB = attacks_to(king_square(them), us);
1160 /// Position::undo_move() unmakes a move. When it returns, the position should
1161 /// be restored to exactly the same state as before the move was made.
1163 void Position::undo_move(Move m) {
1166 assert(move_is_ok(m));
1169 sideToMove = opposite_color(sideToMove);
1171 if (move_is_castle(m))
1172 undo_castle_move(m);
1173 else if (move_promotion(m))
1174 undo_promotion_move(m);
1175 else if (move_is_ep(m))
1183 us = side_to_move();
1184 them = opposite_color(us);
1185 from = move_from(m);
1188 assert(piece_on(from) == EMPTY);
1189 assert(color_of_piece_on(to) == us);
1191 // Put the piece back at the source square
1192 piece = type_of_piece_on(to);
1193 set_bit(&(byColorBB[us]), from);
1194 set_bit(&(byTypeBB[piece]), from);
1195 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1196 board[from] = piece_of_color_and_type(us, piece);
1198 // Clear the destination square
1199 clear_bit(&(byColorBB[us]), to);
1200 clear_bit(&(byTypeBB[piece]), to);
1201 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1203 // If the moving piece was a king, update the king square
1205 kingSquare[us] = from;
1207 // Update piece list
1208 pieceList[us][piece][index[to]] = from;
1209 index[from] = index[to];
1213 assert(st->capture != KING);
1215 // Replace the captured piece
1216 set_bit(&(byColorBB[them]), to);
1217 set_bit(&(byTypeBB[st->capture]), to);
1218 set_bit(&(byTypeBB[0]), to);
1219 board[to] = piece_of_color_and_type(them, st->capture);
1222 if (st->capture != PAWN)
1223 npMaterial[them] += piece_value_midgame(st->capture);
1225 // Update piece list
1226 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1227 index[to] = pieceCount[them][st->capture];
1229 // Update piece count
1230 pieceCount[them][st->capture]++;
1235 // Finally point our state pointer back to the previous state
1242 /// Position::undo_castle_move() is a private method used to unmake a castling
1243 /// move. It is called from the main Position::undo_move function. Note that
1244 /// castling moves are encoded as "king captures friendly rook" moves, for
1245 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1247 void Position::undo_castle_move(Move m) {
1249 assert(move_is_ok(m));
1250 assert(move_is_castle(m));
1252 // When we have arrived here, some work has already been done by
1253 // Position::undo_move. In particular, the side to move has been switched,
1254 // so the code below is correct.
1255 Color us = side_to_move();
1257 // Find source squares for king and rook
1258 Square kfrom = move_from(m);
1259 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1262 // Find destination squares for king and rook
1263 if (rfrom > kfrom) // O-O
1265 kto = relative_square(us, SQ_G1);
1266 rto = relative_square(us, SQ_F1);
1268 kto = relative_square(us, SQ_C1);
1269 rto = relative_square(us, SQ_D1);
1272 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1273 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1275 // Remove pieces from destination squares
1276 clear_bit(&(byColorBB[us]), kto);
1277 clear_bit(&(byTypeBB[KING]), kto);
1278 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1279 clear_bit(&(byColorBB[us]), rto);
1280 clear_bit(&(byTypeBB[ROOK]), rto);
1281 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1283 // Put pieces on source squares
1284 set_bit(&(byColorBB[us]), kfrom);
1285 set_bit(&(byTypeBB[KING]), kfrom);
1286 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1287 set_bit(&(byColorBB[us]), rfrom);
1288 set_bit(&(byTypeBB[ROOK]), rfrom);
1289 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1292 board[rto] = board[kto] = EMPTY;
1293 board[rfrom] = piece_of_color_and_type(us, ROOK);
1294 board[kfrom] = piece_of_color_and_type(us, KING);
1296 // Update king square
1297 kingSquare[us] = kfrom;
1299 // Update piece lists
1300 pieceList[us][KING][index[kto]] = kfrom;
1301 pieceList[us][ROOK][index[rto]] = rfrom;
1302 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1303 index[kfrom] = index[kto];
1308 /// Position::undo_promotion_move() is a private method used to unmake a
1309 /// promotion move. It is called from the main Position::do_move
1312 void Position::undo_promotion_move(Move m) {
1316 PieceType promotion;
1318 assert(move_is_ok(m));
1319 assert(move_promotion(m));
1321 // When we have arrived here, some work has already been done by
1322 // Position::undo_move. In particular, the side to move has been switched,
1323 // so the code below is correct.
1324 us = side_to_move();
1325 them = opposite_color(us);
1326 from = move_from(m);
1329 assert(relative_rank(us, to) == RANK_8);
1330 assert(piece_on(from) == EMPTY);
1332 // Remove promoted piece
1333 promotion = move_promotion(m);
1334 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1335 assert(promotion >= KNIGHT && promotion <= QUEEN);
1336 clear_bit(&(byColorBB[us]), to);
1337 clear_bit(&(byTypeBB[promotion]), to);
1338 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1340 // Insert pawn at source square
1341 set_bit(&(byColorBB[us]), from);
1342 set_bit(&(byTypeBB[PAWN]), from);
1343 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1344 board[from] = piece_of_color_and_type(us, PAWN);
1347 npMaterial[us] -= piece_value_midgame(promotion);
1349 // Update piece list
1350 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1351 index[from] = pieceCount[us][PAWN];
1352 pieceList[us][promotion][index[to]] =
1353 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1354 index[pieceList[us][promotion][index[to]]] = index[to];
1356 // Update piece counts
1357 pieceCount[us][promotion]--;
1358 pieceCount[us][PAWN]++;
1362 assert(st->capture != KING);
1364 // Insert captured piece:
1365 set_bit(&(byColorBB[them]), to);
1366 set_bit(&(byTypeBB[st->capture]), to);
1367 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1368 board[to] = piece_of_color_and_type(them, st->capture);
1370 // Update material. Because the move is a promotion move, we know
1371 // that the captured piece cannot be a pawn.
1372 assert(st->capture != PAWN);
1373 npMaterial[them] += piece_value_midgame(st->capture);
1375 // Update piece list
1376 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1377 index[to] = pieceCount[them][st->capture];
1379 // Update piece count
1380 pieceCount[them][st->capture]++;
1386 /// Position::undo_ep_move() is a private method used to unmake an en passant
1387 /// capture. It is called from the main Position::undo_move function.
1389 void Position::undo_ep_move(Move m) {
1391 assert(move_is_ok(m));
1392 assert(move_is_ep(m));
1394 // When we have arrived here, some work has already been done by
1395 // Position::undo_move. In particular, the side to move has been switched,
1396 // so the code below is correct.
1397 Color us = side_to_move();
1398 Color them = opposite_color(us);
1399 Square from = move_from(m);
1400 Square to = move_to(m);
1401 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1403 assert(to == st->previous->epSquare);
1404 assert(relative_rank(us, to) == RANK_6);
1405 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1406 assert(piece_on(from) == EMPTY);
1407 assert(piece_on(capsq) == EMPTY);
1409 // Replace captured piece
1410 set_bit(&(byColorBB[them]), capsq);
1411 set_bit(&(byTypeBB[PAWN]), capsq);
1412 set_bit(&(byTypeBB[0]), capsq);
1413 board[capsq] = piece_of_color_and_type(them, PAWN);
1415 // Remove moving piece from destination square
1416 clear_bit(&(byColorBB[us]), to);
1417 clear_bit(&(byTypeBB[PAWN]), to);
1418 clear_bit(&(byTypeBB[0]), to);
1421 // Replace moving piece at source square
1422 set_bit(&(byColorBB[us]), from);
1423 set_bit(&(byTypeBB[PAWN]), from);
1424 set_bit(&(byTypeBB[0]), from);
1425 board[from] = piece_of_color_and_type(us, PAWN);
1427 // Update piece list:
1428 pieceList[us][PAWN][index[to]] = from;
1429 index[from] = index[to];
1430 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1431 index[capsq] = pieceCount[them][PAWN];
1433 // Update piece count:
1434 pieceCount[them][PAWN]++;
1438 /// Position::do_null_move makes() a "null move": It switches the side to move
1439 /// and updates the hash key without executing any move on the board.
1441 void Position::do_null_move(StateInfo& backupSt) {
1444 assert(!is_check());
1446 // Back up the information necessary to undo the null move to the supplied
1447 // StateInfo object. In the case of a null move, the only thing we need to
1448 // remember is the last move made and the en passant square.
1449 // Note that differently from normal case here backupSt is actually used as
1450 // a backup storage not as a new state to be used.
1451 backupSt.lastMove = st->lastMove;
1452 backupSt.epSquare = st->epSquare;
1453 backupSt.previous = st->previous;
1454 st->previous = &backupSt;
1456 // Save the current key to the history[] array, in order to be able to
1457 // detect repetition draws.
1458 history[gamePly] = st->key;
1460 // Update the necessary information
1461 sideToMove = opposite_color(sideToMove);
1462 if (st->epSquare != SQ_NONE)
1463 st->key ^= zobEp[st->epSquare];
1465 st->epSquare = SQ_NONE;
1468 st->key ^= zobSideToMove;
1470 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1471 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1477 /// Position::undo_null_move() unmakes a "null move".
1479 void Position::undo_null_move() {
1482 assert(!is_check());
1484 // Restore information from the our backup StateInfo object
1485 st->lastMove = st->previous->lastMove;
1486 st->epSquare = st->previous->epSquare;
1487 st->previous = st->previous->previous;
1489 if (st->epSquare != SQ_NONE)
1490 st->key ^= zobEp[st->epSquare];
1492 // Update the necessary information
1493 sideToMove = opposite_color(sideToMove);
1496 st->key ^= zobSideToMove;
1498 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1499 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1505 /// Position::see() is a static exchange evaluator: It tries to estimate the
1506 /// material gain or loss resulting from a move. There are three versions of
1507 /// this function: One which takes a destination square as input, one takes a
1508 /// move, and one which takes a 'from' and a 'to' square. The function does
1509 /// not yet understand promotions captures.
1511 int Position::see(Square to) const {
1513 assert(square_is_ok(to));
1514 return see(SQ_NONE, to);
1517 int Position::see(Move m) const {
1519 assert(move_is_ok(m));
1520 return see(move_from(m), move_to(m));
1523 int Position::see(Square from, Square to) const {
1526 static const int seeValues[18] = {
1527 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1528 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1529 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1530 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1534 Bitboard attackers, occ, b;
1536 assert(square_is_ok(from) || from == SQ_NONE);
1537 assert(square_is_ok(to));
1539 // Initialize colors
1540 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1541 Color them = opposite_color(us);
1543 // Initialize pieces
1544 Piece piece = piece_on(from);
1545 Piece capture = piece_on(to);
1547 // Find all attackers to the destination square, with the moving piece
1548 // removed, but possibly an X-ray attacker added behind it.
1549 occ = occupied_squares();
1551 // Handle en passant moves
1552 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1554 assert(capture == EMPTY);
1556 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1557 capture = piece_on(capQq);
1559 assert(type_of_piece_on(capQq) == PAWN);
1561 // Remove the captured pawn
1562 clear_bit(&occ, capQq);
1567 clear_bit(&occ, from);
1568 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1569 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1570 | (piece_attacks<KNIGHT>(to) & knights())
1571 | (piece_attacks<KING>(to) & kings())
1572 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1573 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1575 if (from != SQ_NONE)
1578 // If we don't have any attacker we are finished
1579 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1582 // Locate the least valuable attacker to the destination square
1583 // and use it to initialize from square.
1585 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1588 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1589 piece = piece_on(from);
1592 // If the opponent has no attackers we are finished
1593 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1594 return seeValues[capture];
1596 attackers &= occ; // Remove the moving piece
1598 // The destination square is defended, which makes things rather more
1599 // difficult to compute. We proceed by building up a "swap list" containing
1600 // the material gain or loss at each stop in a sequence of captures to the
1601 // destination square, where the sides alternately capture, and always
1602 // capture with the least valuable piece. After each capture, we look for
1603 // new X-ray attacks from behind the capturing piece.
1604 int lastCapturingPieceValue = seeValues[piece];
1605 int swapList[32], n = 1;
1609 swapList[0] = seeValues[capture];
1612 // Locate the least valuable attacker for the side to move. The loop
1613 // below looks like it is potentially infinite, but it isn't. We know
1614 // that the side to move still has at least one attacker left.
1615 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1618 // Remove the attacker we just found from the 'attackers' bitboard,
1619 // and scan for new X-ray attacks behind the attacker.
1620 b = attackers & pieces_of_color_and_type(c, pt);
1622 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1623 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1627 // Add the new entry to the swap list
1629 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1632 // Remember the value of the capturing piece, and change the side to move
1633 // before beginning the next iteration
1634 lastCapturingPieceValue = seeValues[pt];
1635 c = opposite_color(c);
1637 // Stop after a king capture
1638 if (pt == KING && (attackers & pieces_of_color(c)))
1641 swapList[n++] = 100;
1644 } while (attackers & pieces_of_color(c));
1646 // Having built the swap list, we negamax through it to find the best
1647 // achievable score from the point of view of the side to move
1649 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1655 /// Position::setStartState() copies the content of the argument
1656 /// inside startState and makes st point to it. This is needed
1657 /// when the st pointee could become stale, as example because
1658 /// the caller is about to going out of scope.
1660 void Position::setStartState(const StateInfo& s) {
1667 /// Position::clear() erases the position object to a pristine state, with an
1668 /// empty board, white to move, and no castling rights.
1670 void Position::clear() {
1673 memset(st, 0, sizeof(StateInfo));
1674 st->epSquare = SQ_NONE;
1676 memset(index, 0, sizeof(int) * 64);
1677 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1679 for (int i = 0; i < 64; i++)
1682 for (int i = 0; i < 7; i++)
1684 byTypeBB[i] = EmptyBoardBB;
1685 pieceCount[0][i] = pieceCount[1][i] = 0;
1686 for (int j = 0; j < 8; j++)
1687 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1692 initialKFile = FILE_E;
1693 initialKRFile = FILE_H;
1694 initialQRFile = FILE_A;
1698 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1699 /// UCI interface code, whenever a non-reversible move is made in a
1700 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1701 /// for the program to handle games of arbitrary length, as long as the GUI
1702 /// handles draws by the 50 move rule correctly.
1704 void Position::reset_game_ply() {
1710 /// Position::put_piece() puts a piece on the given square of the board,
1711 /// updating the board array, bitboards, and piece counts.
1713 void Position::put_piece(Piece p, Square s) {
1715 Color c = color_of_piece(p);
1716 PieceType pt = type_of_piece(p);
1719 index[s] = pieceCount[c][pt];
1720 pieceList[c][pt][index[s]] = s;
1722 set_bit(&(byTypeBB[pt]), s);
1723 set_bit(&(byColorBB[c]), s);
1724 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1726 pieceCount[c][pt]++;
1733 /// Position::allow_oo() gives the given side the right to castle kingside.
1734 /// Used when setting castling rights during parsing of FEN strings.
1736 void Position::allow_oo(Color c) {
1738 st->castleRights |= (1 + int(c));
1742 /// Position::allow_ooo() gives the given side the right to castle queenside.
1743 /// Used when setting castling rights during parsing of FEN strings.
1745 void Position::allow_ooo(Color c) {
1747 st->castleRights |= (4 + 4*int(c));
1751 /// Position::compute_key() computes the hash key of the position. The hash
1752 /// key is usually updated incrementally as moves are made and unmade, the
1753 /// compute_key() function is only used when a new position is set up, and
1754 /// to verify the correctness of the hash key when running in debug mode.
1756 Key Position::compute_key() const {
1758 Key result = Key(0ULL);
1760 for (Square s = SQ_A1; s <= SQ_H8; s++)
1761 if (square_is_occupied(s))
1762 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1764 if (ep_square() != SQ_NONE)
1765 result ^= zobEp[ep_square()];
1767 result ^= zobCastle[st->castleRights];
1768 if (side_to_move() == BLACK)
1769 result ^= zobSideToMove;
1775 /// Position::compute_pawn_key() computes the hash key of the position. The
1776 /// hash key is usually updated incrementally as moves are made and unmade,
1777 /// the compute_pawn_key() function is only used when a new position is set
1778 /// up, and to verify the correctness of the pawn hash key when running in
1781 Key Position::compute_pawn_key() const {
1783 Key result = Key(0ULL);
1787 for (Color c = WHITE; c <= BLACK; c++)
1792 s = pop_1st_bit(&b);
1793 result ^= zobrist[c][PAWN][s];
1800 /// Position::compute_material_key() computes the hash key of the position.
1801 /// The hash key is usually updated incrementally as moves are made and unmade,
1802 /// the compute_material_key() function is only used when a new position is set
1803 /// up, and to verify the correctness of the material hash key when running in
1806 Key Position::compute_material_key() const {
1808 Key result = Key(0ULL);
1809 for (Color c = WHITE; c <= BLACK; c++)
1810 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1812 int count = piece_count(c, pt);
1813 for (int i = 0; i <= count; i++)
1814 result ^= zobMaterial[c][pt][i];
1820 /// Position::compute_value() compute the incremental scores for the middle
1821 /// game and the endgame. These functions are used to initialize the incremental
1822 /// scores when a new position is set up, and to verify that the scores are correctly
1823 /// updated by do_move and undo_move when the program is running in debug mode.
1824 template<Position::GamePhase Phase>
1825 Value Position::compute_value() const {
1827 Value result = Value(0);
1831 for (Color c = WHITE; c <= BLACK; c++)
1832 for (PieceType pt = PAWN; pt <= KING; pt++)
1834 b = pieces_of_color_and_type(c, pt);
1837 s = pop_1st_bit(&b);
1838 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1839 result += pst<Phase>(c, pt, s);
1843 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1844 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1849 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1850 /// game material score for the given side. Material scores are updated
1851 /// incrementally during the search, this function is only used while
1852 /// initializing a new Position object.
1854 Value Position::compute_non_pawn_material(Color c) const {
1856 Value result = Value(0);
1859 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1861 Bitboard b = pieces_of_color_and_type(c, pt);
1864 s = pop_1st_bit(&b);
1865 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1866 result += piece_value_midgame(pt);
1873 /// Position::is_mate() returns true or false depending on whether the
1874 /// side to move is checkmated. Note that this function is currently very
1875 /// slow, and shouldn't be used frequently inside the search.
1877 bool Position::is_mate() const {
1881 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1882 return mp.get_next_move() == MOVE_NONE;
1888 /// Position::is_draw() tests whether the position is drawn by material,
1889 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1890 /// must be done by the search.
1892 bool Position::is_draw() const {
1894 // Draw by material?
1896 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1899 // Draw by the 50 moves rule?
1900 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1903 // Draw by repetition?
1904 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1905 if (history[gamePly - i] == st->key)
1912 /// Position::has_mate_threat() tests whether a given color has a mate in one
1913 /// from the current position. This function is quite slow, but it doesn't
1914 /// matter, because it is currently only called from PV nodes, which are rare.
1916 bool Position::has_mate_threat(Color c) {
1919 Color stm = side_to_move();
1921 // The following lines are useless and silly, but prevents gcc from
1922 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1923 // be used uninitialized.
1924 st1.lastMove = st->lastMove;
1925 st1.epSquare = st->epSquare;
1930 // If the input color is not equal to the side to move, do a null move
1934 MoveStack mlist[120];
1936 bool result = false;
1938 // Generate legal moves
1939 count = generate_legal_moves(*this, mlist);
1941 // Loop through the moves, and see if one of them is mate
1942 for (int i = 0; i < count; i++)
1944 do_move(mlist[i].move, st2);
1948 undo_move(mlist[i].move);
1951 // Undo null move, if necessary
1959 /// Position::init_zobrist() is a static member function which initializes the
1960 /// various arrays used to compute hash keys.
1962 void Position::init_zobrist() {
1964 for (int i = 0; i < 2; i++)
1965 for (int j = 0; j < 8; j++)
1966 for (int k = 0; k < 64; k++)
1967 zobrist[i][j][k] = Key(genrand_int64());
1969 for (int i = 0; i < 64; i++)
1970 zobEp[i] = Key(genrand_int64());
1972 for (int i = 0; i < 16; i++)
1973 zobCastle[i] = genrand_int64();
1975 zobSideToMove = genrand_int64();
1977 for (int i = 0; i < 2; i++)
1978 for (int j = 0; j < 8; j++)
1979 for (int k = 0; k < 16; k++)
1980 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1982 for (int i = 0; i < 16; i++)
1983 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1987 /// Position::init_piece_square_tables() initializes the piece square tables.
1988 /// This is a two-step operation: First, the white halves of the tables are
1989 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1990 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1991 /// Second, the black halves of the tables are initialized by mirroring
1992 /// and changing the sign of the corresponding white scores.
1994 void Position::init_piece_square_tables() {
1996 int r = get_option_value_int("Randomness"), i;
1997 for (Square s = SQ_A1; s <= SQ_H8; s++)
1998 for (Piece p = WP; p <= WK; p++)
2000 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2001 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2002 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2005 for (Square s = SQ_A1; s <= SQ_H8; s++)
2006 for (Piece p = BP; p <= BK; p++)
2008 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2009 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2014 /// Position::flipped_copy() makes a copy of the input position, but with
2015 /// the white and black sides reversed. This is only useful for debugging,
2016 /// especially for finding evaluation symmetry bugs.
2018 void Position::flipped_copy(const Position &pos) {
2020 assert(pos.is_ok());
2025 for (Square s = SQ_A1; s <= SQ_H8; s++)
2026 if (!pos.square_is_empty(s))
2027 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2030 sideToMove = opposite_color(pos.side_to_move());
2033 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2034 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2035 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2036 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2038 initialKFile = pos.initialKFile;
2039 initialKRFile = pos.initialKRFile;
2040 initialQRFile = pos.initialQRFile;
2042 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2043 castleRightsMask[sq] = ALL_CASTLES;
2045 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2046 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2047 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2048 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2049 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2050 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2052 // En passant square
2053 if (pos.st->epSquare != SQ_NONE)
2054 st->epSquare = flip_square(pos.st->epSquare);
2060 st->key = compute_key();
2061 st->pawnKey = compute_pawn_key();
2062 st->materialKey = compute_material_key();
2064 // Incremental scores
2065 st->mgValue = compute_value<MidGame>();
2066 st->egValue = compute_value<EndGame>();
2069 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2070 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2076 /// Position::is_ok() performs some consitency checks for the position object.
2077 /// This is meant to be helpful when debugging.
2079 bool Position::is_ok(int* failedStep) const {
2081 // What features of the position should be verified?
2082 static const bool debugBitboards = false;
2083 static const bool debugKingCount = false;
2084 static const bool debugKingCapture = false;
2085 static const bool debugCheckerCount = false;
2086 static const bool debugKey = false;
2087 static const bool debugMaterialKey = false;
2088 static const bool debugPawnKey = false;
2089 static const bool debugIncrementalEval = false;
2090 static const bool debugNonPawnMaterial = false;
2091 static const bool debugPieceCounts = false;
2092 static const bool debugPieceList = false;
2094 if (failedStep) *failedStep = 1;
2097 if (!color_is_ok(side_to_move()))
2100 // Are the king squares in the position correct?
2101 if (failedStep) (*failedStep)++;
2102 if (piece_on(king_square(WHITE)) != WK)
2105 if (failedStep) (*failedStep)++;
2106 if (piece_on(king_square(BLACK)) != BK)
2110 if (failedStep) (*failedStep)++;
2111 if (!file_is_ok(initialKRFile))
2114 if (!file_is_ok(initialQRFile))
2117 // Do both sides have exactly one king?
2118 if (failedStep) (*failedStep)++;
2121 int kingCount[2] = {0, 0};
2122 for (Square s = SQ_A1; s <= SQ_H8; s++)
2123 if (type_of_piece_on(s) == KING)
2124 kingCount[color_of_piece_on(s)]++;
2126 if (kingCount[0] != 1 || kingCount[1] != 1)
2130 // Can the side to move capture the opponent's king?
2131 if (failedStep) (*failedStep)++;
2132 if (debugKingCapture)
2134 Color us = side_to_move();
2135 Color them = opposite_color(us);
2136 Square ksq = king_square(them);
2137 if (square_is_attacked(ksq, us))
2141 // Is there more than 2 checkers?
2142 if (failedStep) (*failedStep)++;
2143 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2147 if (failedStep) (*failedStep)++;
2150 // The intersection of the white and black pieces must be empty
2151 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2154 // The union of the white and black pieces must be equal to all
2156 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2159 // Separate piece type bitboards must have empty intersections
2160 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2161 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2162 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2166 // En passant square OK?
2167 if (failedStep) (*failedStep)++;
2168 if (ep_square() != SQ_NONE)
2170 // The en passant square must be on rank 6, from the point of view of the
2172 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2177 if (failedStep) (*failedStep)++;
2178 if (debugKey && st->key != compute_key())
2181 // Pawn hash key OK?
2182 if (failedStep) (*failedStep)++;
2183 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2186 // Material hash key OK?
2187 if (failedStep) (*failedStep)++;
2188 if (debugMaterialKey && st->materialKey != compute_material_key())
2191 // Incremental eval OK?
2192 if (failedStep) (*failedStep)++;
2193 if (debugIncrementalEval)
2195 if (st->mgValue != compute_value<MidGame>())
2198 if (st->egValue != compute_value<EndGame>())
2202 // Non-pawn material OK?
2203 if (failedStep) (*failedStep)++;
2204 if (debugNonPawnMaterial)
2206 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2209 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2214 if (failedStep) (*failedStep)++;
2215 if (debugPieceCounts)
2216 for (Color c = WHITE; c <= BLACK; c++)
2217 for (PieceType pt = PAWN; pt <= KING; pt++)
2218 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2221 if (failedStep) (*failedStep)++;
2224 for(Color c = WHITE; c <= BLACK; c++)
2225 for(PieceType pt = PAWN; pt <= KING; pt++)
2226 for(int i = 0; i < pieceCount[c][pt]; i++)
2228 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2231 if (index[piece_list(c, pt, i)] != i)
2235 if (failedStep) *failedStep = 0;