2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 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"
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 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 string& fen) {
79 static const 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 == 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 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 st->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 string Position::to_fen() const {
226 static const 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 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 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.
382 Bitboard Position::attacks_to(Square s) const {
384 return (pawn_attacks(BLACK, s) & pawns(WHITE))
385 | (pawn_attacks(WHITE, s) & pawns(BLACK))
386 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
387 | (piece_attacks<ROOK>(s) & rooks_and_queens())
388 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
389 | (piece_attacks<KING>(s) & pieces_of_type(KING));
392 /// Position::piece_attacks_square() tests whether the piece on square f
393 /// attacks square t.
395 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
397 assert(square_is_ok(f));
398 assert(square_is_ok(t));
402 case WP: return pawn_attacks_square(WHITE, f, t);
403 case BP: return pawn_attacks_square(BLACK, f, t);
404 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
405 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
406 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
407 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
408 case WK: case BK: return piece_attacks_square<KING>(f, t);
415 /// Position::move_attacks_square() tests whether a move from the current
416 /// position attacks a given square.
418 bool Position::move_attacks_square(Move m, Square s) const {
420 assert(move_is_ok(m));
421 assert(square_is_ok(s));
423 Square f = move_from(m), t = move_to(m);
425 assert(square_is_occupied(f));
427 if (piece_attacks_square(piece_on(f), t, s))
430 // Move the piece and scan for X-ray attacks behind it
431 Bitboard occ = occupied_squares();
432 Color us = color_of_piece_on(f);
435 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
436 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
438 // If we have attacks we need to verify that are caused by our move
439 // and are not already existent ones.
440 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
444 /// Position::find_checkers() computes the checkersBB bitboard, which
445 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
446 /// currently works by calling Position::attacks_to, which is probably
447 /// inefficient. Consider rewriting this function to use the last move
448 /// played, like in non-bitboard versions of Glaurung.
450 void Position::find_checkers() {
452 Color us = side_to_move();
453 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
457 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
459 bool Position::pl_move_is_legal(Move m) const {
461 // If we're in check, all pseudo-legal moves are legal, because our
462 // check evasion generator only generates true legal moves.
463 return is_check() || 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()));
473 // Castling moves are checked for legality during move generation.
474 if (move_is_castle(m))
477 Color us = side_to_move();
478 Square from = move_from(m);
479 Square ksq = king_square(us);
481 assert(color_of_piece_on(from) == us);
482 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
484 // En passant captures are a tricky special case. Because they are
485 // rather uncommon, we do it simply by testing whether the king is attacked
486 // after the move is made
489 Color them = opposite_color(us);
490 Square to = move_to(m);
491 Square capsq = make_square(square_file(to), square_rank(from));
492 Bitboard b = occupied_squares();
494 assert(to == ep_square());
495 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
496 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
497 assert(piece_on(to) == EMPTY);
500 clear_bit(&b, capsq);
503 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
504 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
507 // If the moving piece is a king, check whether the destination
508 // square is attacked by the opponent.
510 return !(square_is_attacked(move_to(m), opposite_color(us)));
512 // A non-king move is legal if and only if it is not pinned or it
513 // is moving along the ray towards or away from the king.
515 || !bit_is_set(pinned, from)
516 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
520 /// Position::move_is_check() tests whether a pseudo-legal move is a check
522 bool Position::move_is_check(Move m) const {
524 Bitboard dc = discovered_check_candidates(side_to_move());
525 return move_is_check(m, dc);
528 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
531 assert(move_is_ok(m));
532 assert(dcCandidates == discovered_check_candidates(side_to_move()));
534 Color us = side_to_move();
535 Color them = opposite_color(us);
536 Square from = move_from(m);
537 Square to = move_to(m);
538 Square ksq = king_square(them);
540 assert(color_of_piece_on(from) == us);
541 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
543 // Proceed according to the type of the moving piece
544 switch (type_of_piece_on(from))
548 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
551 if ( dcCandidates // Discovered check?
552 && bit_is_set(dcCandidates, from)
553 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
556 if (move_promotion(m)) // Promotion with check?
558 Bitboard b = occupied_squares();
561 switch (move_promotion(m))
564 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
566 return bit_is_set(bishop_attacks_bb(to, b), ksq);
568 return bit_is_set(rook_attacks_bb(to, b), ksq);
570 return bit_is_set(queen_attacks_bb(to, b), ksq);
575 // En passant capture with check? We have already handled the case
576 // of direct checks and ordinary discovered check, the only case we
577 // need to handle is the unusual case of a discovered check through the
579 else if (move_is_ep(m))
581 Square capsq = make_square(square_file(to), square_rank(from));
582 Bitboard b = occupied_squares();
584 clear_bit(&b, capsq);
586 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
587 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
591 // Test discovered check and normal check according to piece type
593 return (dcCandidates && bit_is_set(dcCandidates, from))
594 || bit_is_set(piece_attacks<KNIGHT>(ksq), to);
597 return (dcCandidates && bit_is_set(dcCandidates, from))
598 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to));
601 return (dcCandidates && bit_is_set(dcCandidates, from))
602 || (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to));
605 // Discovered checks are impossible!
606 assert(!bit_is_set(dcCandidates, from));
607 return ( (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to))
608 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to)));
612 if ( bit_is_set(dcCandidates, from)
613 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
616 // Castling with check?
617 if (move_is_castle(m))
619 Square kfrom, kto, rfrom, rto;
620 Bitboard b = occupied_squares();
626 kto = relative_square(us, SQ_G1);
627 rto = relative_square(us, SQ_F1);
629 kto = relative_square(us, SQ_C1);
630 rto = relative_square(us, SQ_D1);
632 clear_bit(&b, kfrom);
633 clear_bit(&b, rfrom);
636 return bit_is_set(rook_attacks_bb(rto, b), ksq);
640 default: // NO_PIECE_TYPE
648 /// Position::update_checkers() udpates chekers info given the move. It is called
649 /// in do_move() and is faster then find_checkers().
651 template<PieceType Piece>
652 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
653 Square to, Bitboard dcCandidates) {
655 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
656 const bool Rook = (Piece == QUEEN || Piece == ROOK);
657 const bool Slider = Bishop || Rook;
660 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
661 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
662 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
663 set_bit(pCheckersBB, to);
665 else if ( Piece != KING
667 && bit_is_set(piece_attacks<Piece>(ksq), to))
668 set_bit(pCheckersBB, to);
671 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
674 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
677 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
682 /// Position::do_move() makes a move, and saves all information necessary
683 /// to a StateInfo object. The move is assumed to be legal.
684 /// Pseudo-legal moves should be filtered out before this function is called.
686 void Position::do_move(Move m, StateInfo& newSt) {
688 do_move(m, newSt, discovered_check_candidates(side_to_move()));
691 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
694 assert(move_is_ok(m));
696 // Copy some fields of old state to our new StateInfo object except the
697 // ones which are recalculated from scratch anyway, then switch our state
698 // pointer to point to the new, ready to be updated, state.
699 struct ReducedStateInfo {
700 Key key, pawnKey, materialKey;
701 int castleRights, rule50;
703 Value mgValue, egValue;
707 memcpy(&newSt, st, sizeof(ReducedStateInfo));
708 newSt.capture = NO_PIECE_TYPE;
712 // Save the current key to the history[] array, in order to be able to
713 // detect repetition draws.
714 history[gamePly] = st->key;
716 // Increment the 50 moves rule draw counter. Resetting it to zero in the
717 // case of non-reversible moves is taken care of later.
720 if (move_is_castle(m))
722 else if (move_promotion(m))
723 do_promotion_move(m);
724 else if (move_is_ep(m))
728 Color us = side_to_move();
729 Color them = opposite_color(us);
730 Square from = move_from(m);
731 Square to = move_to(m);
733 assert(color_of_piece_on(from) == us);
734 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
736 PieceType piece = type_of_piece_on(from);
738 st->capture = type_of_piece_on(to);
741 do_capture_move(st->capture, them, to);
744 clear_bit(&(byColorBB[us]), from);
745 clear_bit(&(byTypeBB[piece]), from);
746 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
747 set_bit(&(byColorBB[us]), to);
748 set_bit(&(byTypeBB[piece]), to);
749 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
750 board[to] = board[from];
754 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
756 // Update incremental scores
757 st->mgValue -= pst<MidGame>(us, piece, from);
758 st->mgValue += pst<MidGame>(us, piece, to);
759 st->egValue -= pst<EndGame>(us, piece, from);
760 st->egValue += pst<EndGame>(us, piece, to);
762 // If the moving piece was a king, update the king square
766 // Reset en passant square
767 if (st->epSquare != SQ_NONE)
769 st->key ^= zobEp[st->epSquare];
770 st->epSquare = SQ_NONE;
773 // If the moving piece was a pawn do some special extra work
776 // Reset rule 50 draw counter
779 // Update pawn hash key
780 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
782 // Set en passant square, only if moved pawn can be captured
783 if (abs(int(to) - int(from)) == 16)
785 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
786 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
788 st->epSquare = Square((int(from) + int(to)) / 2);
789 st->key ^= zobEp[st->epSquare];
794 // Update piece lists
795 pieceList[us][piece][index[from]] = to;
796 index[to] = index[from];
798 // Update castle rights
799 st->key ^= zobCastle[st->castleRights];
800 st->castleRights &= castleRightsMask[from];
801 st->castleRights &= castleRightsMask[to];
802 st->key ^= zobCastle[st->castleRights];
804 // Update checkers bitboard, piece must be already moved
805 st->checkersBB = EmptyBoardBB;
806 Square ksq = king_square(them);
809 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
810 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
811 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
812 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
813 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
814 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
815 default: assert(false); break;
820 st->key ^= zobSideToMove;
821 sideToMove = opposite_color(sideToMove);
824 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
825 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
831 /// Position::do_capture_move() is a private method used to update captured
832 /// piece info. It is called from the main Position::do_move function.
834 void Position::do_capture_move(PieceType capture, Color them, Square to) {
836 assert(capture != KING);
838 // Remove captured piece
839 clear_bit(&(byColorBB[them]), to);
840 clear_bit(&(byTypeBB[capture]), to);
843 st->key ^= zobrist[them][capture][to];
845 // If the captured piece was a pawn, update pawn hash key
847 st->pawnKey ^= zobrist[them][PAWN][to];
849 // Update incremental scores
850 st->mgValue -= pst<MidGame>(them, capture, to);
851 st->egValue -= pst<EndGame>(them, capture, to);
855 st->npMaterial[them] -= piece_value_midgame(capture);
857 // Update material hash key
858 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
860 // Update piece count
861 pieceCount[them][capture]--;
864 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
865 index[pieceList[them][capture][index[to]]] = index[to];
867 // Reset rule 50 counter
872 /// Position::do_castle_move() is a private method used to make a castling
873 /// move. It is called from the main Position::do_move function. Note that
874 /// castling moves are encoded as "king captures friendly rook" moves, for
875 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
877 void Position::do_castle_move(Move m) {
880 assert(move_is_ok(m));
881 assert(move_is_castle(m));
883 Color us = side_to_move();
884 Color them = opposite_color(us);
886 // Find source squares for king and rook
887 Square kfrom = move_from(m);
888 Square rfrom = move_to(m); // HACK: See comment at beginning of function
891 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
892 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
894 // Find destination squares for king and rook
895 if (rfrom > kfrom) // O-O
897 kto = relative_square(us, SQ_G1);
898 rto = relative_square(us, SQ_F1);
900 kto = relative_square(us, SQ_C1);
901 rto = relative_square(us, SQ_D1);
904 // Remove pieces from source squares
905 clear_bit(&(byColorBB[us]), kfrom);
906 clear_bit(&(byTypeBB[KING]), kfrom);
907 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
908 clear_bit(&(byColorBB[us]), rfrom);
909 clear_bit(&(byTypeBB[ROOK]), rfrom);
910 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
912 // Put pieces on destination squares
913 set_bit(&(byColorBB[us]), kto);
914 set_bit(&(byTypeBB[KING]), kto);
915 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
916 set_bit(&(byColorBB[us]), rto);
917 set_bit(&(byTypeBB[ROOK]), rto);
918 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
920 // Update board array
921 board[kfrom] = board[rfrom] = EMPTY;
922 board[kto] = piece_of_color_and_type(us, KING);
923 board[rto] = piece_of_color_and_type(us, ROOK);
925 // Update king square
926 kingSquare[us] = kto;
928 // Update piece lists
929 pieceList[us][KING][index[kfrom]] = kto;
930 pieceList[us][ROOK][index[rfrom]] = rto;
931 int tmp = index[rfrom];
932 index[kto] = index[kfrom];
935 // Update incremental scores
936 st->mgValue -= pst<MidGame>(us, KING, kfrom);
937 st->mgValue += pst<MidGame>(us, KING, kto);
938 st->egValue -= pst<EndGame>(us, KING, kfrom);
939 st->egValue += pst<EndGame>(us, KING, kto);
940 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
941 st->mgValue += pst<MidGame>(us, ROOK, rto);
942 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
943 st->egValue += pst<EndGame>(us, ROOK, rto);
946 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
947 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
949 // Clear en passant square
950 if (st->epSquare != SQ_NONE)
952 st->key ^= zobEp[st->epSquare];
953 st->epSquare = SQ_NONE;
956 // Update castling rights
957 st->key ^= zobCastle[st->castleRights];
958 st->castleRights &= castleRightsMask[kfrom];
959 st->key ^= zobCastle[st->castleRights];
961 // Reset rule 50 counter
964 // Update checkers BB
965 st->checkersBB = attacks_to(king_square(them), us);
969 /// Position::do_promotion_move() is a private method used to make a promotion
970 /// move. It is called from the main Position::do_move function.
972 void Position::do_promotion_move(Move m) {
979 assert(move_is_ok(m));
980 assert(move_promotion(m));
983 them = opposite_color(us);
987 assert(relative_rank(us, to) == RANK_8);
988 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
989 assert(color_of_piece_on(to) == them || square_is_empty(to));
991 st->capture = type_of_piece_on(to);
994 do_capture_move(st->capture, them, to);
997 clear_bit(&(byColorBB[us]), from);
998 clear_bit(&(byTypeBB[PAWN]), from);
999 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1000 board[from] = EMPTY;
1002 // Insert promoted piece
1003 promotion = move_promotion(m);
1004 assert(promotion >= KNIGHT && promotion <= QUEEN);
1005 set_bit(&(byColorBB[us]), to);
1006 set_bit(&(byTypeBB[promotion]), to);
1007 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1008 board[to] = piece_of_color_and_type(us, promotion);
1011 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1013 // Update pawn hash key
1014 st->pawnKey ^= zobrist[us][PAWN][from];
1016 // Update material key
1017 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1018 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1020 // Update piece counts
1021 pieceCount[us][PAWN]--;
1022 pieceCount[us][promotion]++;
1024 // Update piece lists
1025 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1026 index[pieceList[us][PAWN][index[from]]] = index[from];
1027 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1028 index[to] = pieceCount[us][promotion] - 1;
1030 // Update incremental scores
1031 st->mgValue -= pst<MidGame>(us, PAWN, from);
1032 st->mgValue += pst<MidGame>(us, promotion, to);
1033 st->egValue -= pst<EndGame>(us, PAWN, from);
1034 st->egValue += pst<EndGame>(us, promotion, to);
1037 st->npMaterial[us] += piece_value_midgame(promotion);
1039 // Clear the en passant square
1040 if (st->epSquare != SQ_NONE)
1042 st->key ^= zobEp[st->epSquare];
1043 st->epSquare = SQ_NONE;
1046 // Update castle rights
1047 st->key ^= zobCastle[st->castleRights];
1048 st->castleRights &= castleRightsMask[to];
1049 st->key ^= zobCastle[st->castleRights];
1051 // Reset rule 50 counter
1054 // Update checkers BB
1055 st->checkersBB = attacks_to(king_square(them), us);
1059 /// Position::do_ep_move() is a private method used to make an en passant
1060 /// capture. It is called from the main Position::do_move function.
1062 void Position::do_ep_move(Move m) {
1065 Square from, to, capsq;
1068 assert(move_is_ok(m));
1069 assert(move_is_ep(m));
1071 us = side_to_move();
1072 them = opposite_color(us);
1073 from = move_from(m);
1075 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1077 assert(to == st->epSquare);
1078 assert(relative_rank(us, to) == RANK_6);
1079 assert(piece_on(to) == EMPTY);
1080 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1081 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1083 // Remove captured piece
1084 clear_bit(&(byColorBB[them]), capsq);
1085 clear_bit(&(byTypeBB[PAWN]), capsq);
1086 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1087 board[capsq] = EMPTY;
1089 // Remove moving piece from source square
1090 clear_bit(&(byColorBB[us]), from);
1091 clear_bit(&(byTypeBB[PAWN]), from);
1092 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1094 // Put moving piece on destination square
1095 set_bit(&(byColorBB[us]), to);
1096 set_bit(&(byTypeBB[PAWN]), to);
1097 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1098 board[to] = board[from];
1099 board[from] = EMPTY;
1101 // Update material hash key
1102 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1104 // Update piece count
1105 pieceCount[them][PAWN]--;
1107 // Update piece list
1108 pieceList[us][PAWN][index[from]] = to;
1109 index[to] = index[from];
1110 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1111 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1114 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1115 st->key ^= zobrist[them][PAWN][capsq];
1116 st->key ^= zobEp[st->epSquare];
1118 // Update pawn hash key
1119 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1120 st->pawnKey ^= zobrist[them][PAWN][capsq];
1122 // Update incremental scores
1123 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1124 st->mgValue -= pst<MidGame>(us, PAWN, from);
1125 st->mgValue += pst<MidGame>(us, PAWN, to);
1126 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1127 st->egValue -= pst<EndGame>(us, PAWN, from);
1128 st->egValue += pst<EndGame>(us, PAWN, to);
1130 // Reset en passant square
1131 st->epSquare = SQ_NONE;
1133 // Reset rule 50 counter
1136 // Update checkers BB
1137 st->checkersBB = attacks_to(king_square(them), us);
1141 /// Position::undo_move() unmakes a move. When it returns, the position should
1142 /// be restored to exactly the same state as before the move was made.
1144 void Position::undo_move(Move m) {
1147 assert(move_is_ok(m));
1150 sideToMove = opposite_color(sideToMove);
1152 if (move_is_castle(m))
1153 undo_castle_move(m);
1154 else if (move_promotion(m))
1155 undo_promotion_move(m);
1156 else if (move_is_ep(m))
1164 us = side_to_move();
1165 them = opposite_color(us);
1166 from = move_from(m);
1169 assert(piece_on(from) == EMPTY);
1170 assert(color_of_piece_on(to) == us);
1172 // Put the piece back at the source square
1173 piece = type_of_piece_on(to);
1174 set_bit(&(byColorBB[us]), from);
1175 set_bit(&(byTypeBB[piece]), from);
1176 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1177 board[from] = piece_of_color_and_type(us, piece);
1179 // Clear the destination square
1180 clear_bit(&(byColorBB[us]), to);
1181 clear_bit(&(byTypeBB[piece]), to);
1182 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1184 // If the moving piece was a king, update the king square
1186 kingSquare[us] = from;
1188 // Update piece list
1189 pieceList[us][piece][index[to]] = from;
1190 index[from] = index[to];
1194 assert(st->capture != KING);
1196 // Replace the captured piece
1197 set_bit(&(byColorBB[them]), to);
1198 set_bit(&(byTypeBB[st->capture]), to);
1199 set_bit(&(byTypeBB[0]), to);
1200 board[to] = piece_of_color_and_type(them, st->capture);
1202 // Update piece list
1203 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1204 index[to] = pieceCount[them][st->capture];
1206 // Update piece count
1207 pieceCount[them][st->capture]++;
1212 // Finally point our state pointer back to the previous state
1219 /// Position::undo_castle_move() is a private method used to unmake a castling
1220 /// move. It is called from the main Position::undo_move function. Note that
1221 /// castling moves are encoded as "king captures friendly rook" moves, for
1222 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1224 void Position::undo_castle_move(Move m) {
1226 assert(move_is_ok(m));
1227 assert(move_is_castle(m));
1229 // When we have arrived here, some work has already been done by
1230 // Position::undo_move. In particular, the side to move has been switched,
1231 // so the code below is correct.
1232 Color us = side_to_move();
1234 // Find source squares for king and rook
1235 Square kfrom = move_from(m);
1236 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1239 // Find destination squares for king and rook
1240 if (rfrom > kfrom) // O-O
1242 kto = relative_square(us, SQ_G1);
1243 rto = relative_square(us, SQ_F1);
1245 kto = relative_square(us, SQ_C1);
1246 rto = relative_square(us, SQ_D1);
1249 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1250 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1252 // Remove pieces from destination squares
1253 clear_bit(&(byColorBB[us]), kto);
1254 clear_bit(&(byTypeBB[KING]), kto);
1255 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1256 clear_bit(&(byColorBB[us]), rto);
1257 clear_bit(&(byTypeBB[ROOK]), rto);
1258 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1260 // Put pieces on source squares
1261 set_bit(&(byColorBB[us]), kfrom);
1262 set_bit(&(byTypeBB[KING]), kfrom);
1263 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1264 set_bit(&(byColorBB[us]), rfrom);
1265 set_bit(&(byTypeBB[ROOK]), rfrom);
1266 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1269 board[rto] = board[kto] = EMPTY;
1270 board[rfrom] = piece_of_color_and_type(us, ROOK);
1271 board[kfrom] = piece_of_color_and_type(us, KING);
1273 // Update king square
1274 kingSquare[us] = kfrom;
1276 // Update piece lists
1277 pieceList[us][KING][index[kto]] = kfrom;
1278 pieceList[us][ROOK][index[rto]] = rfrom;
1279 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1280 index[kfrom] = index[kto];
1285 /// Position::undo_promotion_move() is a private method used to unmake a
1286 /// promotion move. It is called from the main Position::do_move
1289 void Position::undo_promotion_move(Move m) {
1293 PieceType promotion;
1295 assert(move_is_ok(m));
1296 assert(move_promotion(m));
1298 // When we have arrived here, some work has already been done by
1299 // Position::undo_move. In particular, the side to move has been switched,
1300 // so the code below is correct.
1301 us = side_to_move();
1302 them = opposite_color(us);
1303 from = move_from(m);
1306 assert(relative_rank(us, to) == RANK_8);
1307 assert(piece_on(from) == EMPTY);
1309 // Remove promoted piece
1310 promotion = move_promotion(m);
1311 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1312 assert(promotion >= KNIGHT && promotion <= QUEEN);
1313 clear_bit(&(byColorBB[us]), to);
1314 clear_bit(&(byTypeBB[promotion]), to);
1315 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1317 // Insert pawn at source square
1318 set_bit(&(byColorBB[us]), from);
1319 set_bit(&(byTypeBB[PAWN]), from);
1320 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1321 board[from] = piece_of_color_and_type(us, PAWN);
1323 // Update piece list
1324 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1325 index[from] = pieceCount[us][PAWN];
1326 pieceList[us][promotion][index[to]] =
1327 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1328 index[pieceList[us][promotion][index[to]]] = index[to];
1330 // Update piece counts
1331 pieceCount[us][promotion]--;
1332 pieceCount[us][PAWN]++;
1336 assert(st->capture != KING);
1338 // Insert captured piece:
1339 set_bit(&(byColorBB[them]), to);
1340 set_bit(&(byTypeBB[st->capture]), to);
1341 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1342 board[to] = piece_of_color_and_type(them, st->capture);
1344 // Update piece list
1345 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1346 index[to] = pieceCount[them][st->capture];
1348 // Update piece count
1349 pieceCount[them][st->capture]++;
1355 /// Position::undo_ep_move() is a private method used to unmake an en passant
1356 /// capture. It is called from the main Position::undo_move function.
1358 void Position::undo_ep_move(Move m) {
1360 assert(move_is_ok(m));
1361 assert(move_is_ep(m));
1363 // When we have arrived here, some work has already been done by
1364 // Position::undo_move. In particular, the side to move has been switched,
1365 // so the code below is correct.
1366 Color us = side_to_move();
1367 Color them = opposite_color(us);
1368 Square from = move_from(m);
1369 Square to = move_to(m);
1370 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1372 assert(to == st->previous->epSquare);
1373 assert(relative_rank(us, to) == RANK_6);
1374 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1375 assert(piece_on(from) == EMPTY);
1376 assert(piece_on(capsq) == EMPTY);
1378 // Replace captured piece
1379 set_bit(&(byColorBB[them]), capsq);
1380 set_bit(&(byTypeBB[PAWN]), capsq);
1381 set_bit(&(byTypeBB[0]), capsq);
1382 board[capsq] = piece_of_color_and_type(them, PAWN);
1384 // Remove moving piece from destination square
1385 clear_bit(&(byColorBB[us]), to);
1386 clear_bit(&(byTypeBB[PAWN]), to);
1387 clear_bit(&(byTypeBB[0]), to);
1390 // Replace moving piece at source square
1391 set_bit(&(byColorBB[us]), from);
1392 set_bit(&(byTypeBB[PAWN]), from);
1393 set_bit(&(byTypeBB[0]), from);
1394 board[from] = piece_of_color_and_type(us, PAWN);
1396 // Update piece list
1397 pieceList[us][PAWN][index[to]] = from;
1398 index[from] = index[to];
1399 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1400 index[capsq] = pieceCount[them][PAWN];
1402 // Update piece count
1403 pieceCount[them][PAWN]++;
1407 /// Position::do_null_move makes() a "null move": It switches the side to move
1408 /// and updates the hash key without executing any move on the board.
1410 void Position::do_null_move(StateInfo& backupSt) {
1413 assert(!is_check());
1415 // Back up the information necessary to undo the null move to the supplied
1416 // StateInfo object. In the case of a null move, the only thing we need to
1417 // remember is the en passant square.
1418 // Note that differently from normal case here backupSt is actually used as
1419 // a backup storage not as a new state to be used.
1420 backupSt.epSquare = st->epSquare;
1421 backupSt.previous = st->previous;
1422 st->previous = &backupSt;
1424 // Save the current key to the history[] array, in order to be able to
1425 // detect repetition draws.
1426 history[gamePly] = st->key;
1428 // Update the necessary information
1429 sideToMove = opposite_color(sideToMove);
1430 if (st->epSquare != SQ_NONE)
1431 st->key ^= zobEp[st->epSquare];
1433 st->epSquare = SQ_NONE;
1436 st->key ^= zobSideToMove;
1438 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1439 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1445 /// Position::undo_null_move() unmakes a "null move".
1447 void Position::undo_null_move() {
1450 assert(!is_check());
1452 // Restore information from the our backup StateInfo object
1453 st->epSquare = st->previous->epSquare;
1454 st->previous = st->previous->previous;
1456 if (st->epSquare != SQ_NONE)
1457 st->key ^= zobEp[st->epSquare];
1459 // Update the necessary information
1460 sideToMove = opposite_color(sideToMove);
1463 st->key ^= zobSideToMove;
1465 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1466 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1472 /// Position::see() is a static exchange evaluator: It tries to estimate the
1473 /// material gain or loss resulting from a move. There are three versions of
1474 /// this function: One which takes a destination square as input, one takes a
1475 /// move, and one which takes a 'from' and a 'to' square. The function does
1476 /// not yet understand promotions captures.
1478 int Position::see(Square to) const {
1480 assert(square_is_ok(to));
1481 return see(SQ_NONE, to);
1484 int Position::see(Move m) const {
1486 assert(move_is_ok(m));
1487 return see(move_from(m), move_to(m));
1490 int Position::see(Square from, Square to) const {
1493 static const int seeValues[18] = {
1494 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1495 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1496 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1497 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1501 Bitboard attackers, stmAttackers, occ, b;
1503 assert(square_is_ok(from) || from == SQ_NONE);
1504 assert(square_is_ok(to));
1506 // Initialize colors
1507 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1508 Color them = opposite_color(us);
1510 // Initialize pieces
1511 Piece piece = piece_on(from);
1512 Piece capture = piece_on(to);
1514 // Find all attackers to the destination square, with the moving piece
1515 // removed, but possibly an X-ray attacker added behind it.
1516 occ = occupied_squares();
1518 // Handle en passant moves
1519 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1521 assert(capture == EMPTY);
1523 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1524 capture = piece_on(capQq);
1525 assert(type_of_piece_on(capQq) == PAWN);
1527 // Remove the captured pawn
1528 clear_bit(&occ, capQq);
1533 clear_bit(&occ, from);
1534 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1535 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1536 | (piece_attacks<KNIGHT>(to) & knights())
1537 | (piece_attacks<KING>(to) & kings())
1538 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1539 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1541 if (from != SQ_NONE)
1544 // If we don't have any attacker we are finished
1545 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1548 // Locate the least valuable attacker to the destination square
1549 // and use it to initialize from square.
1551 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1554 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1555 piece = piece_on(from);
1558 // If the opponent has no attackers we are finished
1559 stmAttackers = attackers & pieces_of_color(them);
1561 return seeValues[capture];
1563 attackers &= occ; // Remove the moving piece
1565 // The destination square is defended, which makes things rather more
1566 // difficult to compute. We proceed by building up a "swap list" containing
1567 // the material gain or loss at each stop in a sequence of captures to the
1568 // destination square, where the sides alternately capture, and always
1569 // capture with the least valuable piece. After each capture, we look for
1570 // new X-ray attacks from behind the capturing piece.
1571 int lastCapturingPieceValue = seeValues[piece];
1572 int swapList[32], n = 1;
1576 swapList[0] = seeValues[capture];
1579 // Locate the least valuable attacker for the side to move. The loop
1580 // below looks like it is potentially infinite, but it isn't. We know
1581 // that the side to move still has at least one attacker left.
1582 for (pt = PAWN; !(stmAttackers & pieces_of_type(pt)); pt++)
1585 // Remove the attacker we just found from the 'attackers' bitboard,
1586 // and scan for new X-ray attacks behind the attacker.
1587 b = stmAttackers & pieces_of_type(pt);
1588 occ ^= (b & (~b + 1));
1589 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1590 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1594 // Add the new entry to the swap list
1596 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1599 // Remember the value of the capturing piece, and change the side to move
1600 // before beginning the next iteration
1601 lastCapturingPieceValue = seeValues[pt];
1602 c = opposite_color(c);
1603 stmAttackers = attackers & pieces_of_color(c);
1605 // Stop after a king capture
1606 if (pt == KING && stmAttackers)
1609 swapList[n++] = 100;
1612 } while (stmAttackers);
1614 // Having built the swap list, we negamax through it to find the best
1615 // achievable score from the point of view of the side to move
1617 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1623 /// Position::setStartState() copies the content of the argument
1624 /// inside startState and makes st point to it. This is needed
1625 /// when the st pointee could become stale, as example because
1626 /// the caller is about to going out of scope.
1628 void Position::setStartState(const StateInfo& s) {
1635 /// Position::clear() erases the position object to a pristine state, with an
1636 /// empty board, white to move, and no castling rights.
1638 void Position::clear() {
1641 memset(st, 0, sizeof(StateInfo));
1642 st->epSquare = SQ_NONE;
1644 memset(index, 0, sizeof(int) * 64);
1645 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1647 for (int i = 0; i < 64; i++)
1650 for (int i = 0; i < 7; i++)
1652 byTypeBB[i] = EmptyBoardBB;
1653 pieceCount[0][i] = pieceCount[1][i] = 0;
1654 for (int j = 0; j < 8; j++)
1655 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1660 initialKFile = FILE_E;
1661 initialKRFile = FILE_H;
1662 initialQRFile = FILE_A;
1666 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1667 /// UCI interface code, whenever a non-reversible move is made in a
1668 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1669 /// for the program to handle games of arbitrary length, as long as the GUI
1670 /// handles draws by the 50 move rule correctly.
1672 void Position::reset_game_ply() {
1678 /// Position::put_piece() puts a piece on the given square of the board,
1679 /// updating the board array, bitboards, and piece counts.
1681 void Position::put_piece(Piece p, Square s) {
1683 Color c = color_of_piece(p);
1684 PieceType pt = type_of_piece(p);
1687 index[s] = pieceCount[c][pt];
1688 pieceList[c][pt][index[s]] = s;
1690 set_bit(&(byTypeBB[pt]), s);
1691 set_bit(&(byColorBB[c]), s);
1692 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1694 pieceCount[c][pt]++;
1701 /// Position::allow_oo() gives the given side the right to castle kingside.
1702 /// Used when setting castling rights during parsing of FEN strings.
1704 void Position::allow_oo(Color c) {
1706 st->castleRights |= (1 + int(c));
1710 /// Position::allow_ooo() gives the given side the right to castle queenside.
1711 /// Used when setting castling rights during parsing of FEN strings.
1713 void Position::allow_ooo(Color c) {
1715 st->castleRights |= (4 + 4*int(c));
1719 /// Position::compute_key() computes the hash key of the position. The hash
1720 /// key is usually updated incrementally as moves are made and unmade, the
1721 /// compute_key() function is only used when a new position is set up, and
1722 /// to verify the correctness of the hash key when running in debug mode.
1724 Key Position::compute_key() const {
1726 Key result = Key(0ULL);
1728 for (Square s = SQ_A1; s <= SQ_H8; s++)
1729 if (square_is_occupied(s))
1730 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1732 if (ep_square() != SQ_NONE)
1733 result ^= zobEp[ep_square()];
1735 result ^= zobCastle[st->castleRights];
1736 if (side_to_move() == BLACK)
1737 result ^= zobSideToMove;
1743 /// Position::compute_pawn_key() computes the hash key of the position. The
1744 /// hash key is usually updated incrementally as moves are made and unmade,
1745 /// the compute_pawn_key() function is only used when a new position is set
1746 /// up, and to verify the correctness of the pawn hash key when running in
1749 Key Position::compute_pawn_key() const {
1751 Key result = Key(0ULL);
1755 for (Color c = WHITE; c <= BLACK; c++)
1760 s = pop_1st_bit(&b);
1761 result ^= zobrist[c][PAWN][s];
1768 /// Position::compute_material_key() computes the hash key of the position.
1769 /// The hash key is usually updated incrementally as moves are made and unmade,
1770 /// the compute_material_key() function is only used when a new position is set
1771 /// up, and to verify the correctness of the material hash key when running in
1774 Key Position::compute_material_key() const {
1776 Key result = Key(0ULL);
1777 for (Color c = WHITE; c <= BLACK; c++)
1778 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1780 int count = piece_count(c, pt);
1781 for (int i = 0; i <= count; i++)
1782 result ^= zobMaterial[c][pt][i];
1788 /// Position::compute_value() compute the incremental scores for the middle
1789 /// game and the endgame. These functions are used to initialize the incremental
1790 /// scores when a new position is set up, and to verify that the scores are correctly
1791 /// updated by do_move and undo_move when the program is running in debug mode.
1792 template<Position::GamePhase Phase>
1793 Value Position::compute_value() const {
1795 Value result = Value(0);
1799 for (Color c = WHITE; c <= BLACK; c++)
1800 for (PieceType pt = PAWN; pt <= KING; pt++)
1802 b = pieces_of_color_and_type(c, pt);
1805 s = pop_1st_bit(&b);
1806 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1807 result += pst<Phase>(c, pt, s);
1811 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1812 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1817 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1818 /// game material score for the given side. Material scores are updated
1819 /// incrementally during the search, this function is only used while
1820 /// initializing a new Position object.
1822 Value Position::compute_non_pawn_material(Color c) const {
1824 Value result = Value(0);
1826 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1828 Bitboard b = pieces_of_color_and_type(c, pt);
1831 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1833 result += piece_value_midgame(pt);
1840 /// Position::is_draw() tests whether the position is drawn by material,
1841 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1842 /// must be done by the search.
1844 bool Position::is_draw() const {
1846 // Draw by material?
1848 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1851 // Draw by the 50 moves rule?
1852 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1855 // Draw by repetition?
1856 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1857 if (history[gamePly - i] == st->key)
1864 /// Position::is_mate() returns true or false depending on whether the
1865 /// side to move is checkmated.
1867 bool Position::is_mate() const {
1869 MoveStack moves[256];
1871 return is_check() && !generate_evasions(*this, moves, pinned_pieces(sideToMove));
1875 /// Position::has_mate_threat() tests whether a given color has a mate in one
1876 /// from the current position.
1878 bool Position::has_mate_threat(Color c) {
1881 Color stm = side_to_move();
1886 // If the input color is not equal to the side to move, do a null move
1890 MoveStack mlist[120];
1892 bool result = false;
1893 Bitboard dc = discovered_check_candidates(sideToMove);
1894 Bitboard pinned = pinned_pieces(sideToMove);
1896 // Generate pseudo-legal non-capture and capture check moves
1897 count = generate_non_capture_checks(*this, mlist, dc);
1898 count += generate_captures(*this, mlist + count);
1900 // Loop through the moves, and see if one of them is mate
1901 for (int i = 0; i < count; i++)
1903 Move move = mlist[i].move;
1905 if (!pl_move_is_legal(move, pinned))
1915 // Undo null move, if necessary
1923 /// Position::init_zobrist() is a static member function which initializes the
1924 /// various arrays used to compute hash keys.
1926 void Position::init_zobrist() {
1928 for (int i = 0; i < 2; i++)
1929 for (int j = 0; j < 8; j++)
1930 for (int k = 0; k < 64; k++)
1931 zobrist[i][j][k] = Key(genrand_int64());
1933 for (int i = 0; i < 64; i++)
1934 zobEp[i] = Key(genrand_int64());
1936 for (int i = 0; i < 16; i++)
1937 zobCastle[i] = genrand_int64();
1939 zobSideToMove = genrand_int64();
1941 for (int i = 0; i < 2; i++)
1942 for (int j = 0; j < 8; j++)
1943 for (int k = 0; k < 16; k++)
1944 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1946 for (int i = 0; i < 16; i++)
1947 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1951 /// Position::init_piece_square_tables() initializes the piece square tables.
1952 /// This is a two-step operation: First, the white halves of the tables are
1953 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1954 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1955 /// Second, the black halves of the tables are initialized by mirroring
1956 /// and changing the sign of the corresponding white scores.
1958 void Position::init_piece_square_tables() {
1960 int r = get_option_value_int("Randomness"), i;
1961 for (Square s = SQ_A1; s <= SQ_H8; s++)
1962 for (Piece p = WP; p <= WK; p++)
1964 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1965 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1966 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1969 for (Square s = SQ_A1; s <= SQ_H8; s++)
1970 for (Piece p = BP; p <= BK; p++)
1972 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1973 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1978 /// Position::flipped_copy() makes a copy of the input position, but with
1979 /// the white and black sides reversed. This is only useful for debugging,
1980 /// especially for finding evaluation symmetry bugs.
1982 void Position::flipped_copy(const Position &pos) {
1984 assert(pos.is_ok());
1989 for (Square s = SQ_A1; s <= SQ_H8; s++)
1990 if (!pos.square_is_empty(s))
1991 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1994 sideToMove = opposite_color(pos.side_to_move());
1997 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1998 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1999 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2000 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2002 initialKFile = pos.initialKFile;
2003 initialKRFile = pos.initialKRFile;
2004 initialQRFile = pos.initialQRFile;
2006 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2007 castleRightsMask[sq] = ALL_CASTLES;
2009 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2010 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2011 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2012 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2013 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2014 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2016 // En passant square
2017 if (pos.st->epSquare != SQ_NONE)
2018 st->epSquare = flip_square(pos.st->epSquare);
2024 st->key = compute_key();
2025 st->pawnKey = compute_pawn_key();
2026 st->materialKey = compute_material_key();
2028 // Incremental scores
2029 st->mgValue = compute_value<MidGame>();
2030 st->egValue = compute_value<EndGame>();
2033 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2034 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2040 /// Position::is_ok() performs some consitency checks for the position object.
2041 /// This is meant to be helpful when debugging.
2043 bool Position::is_ok(int* failedStep) const {
2045 // What features of the position should be verified?
2046 static const bool debugBitboards = false;
2047 static const bool debugKingCount = false;
2048 static const bool debugKingCapture = false;
2049 static const bool debugCheckerCount = false;
2050 static const bool debugKey = false;
2051 static const bool debugMaterialKey = false;
2052 static const bool debugPawnKey = false;
2053 static const bool debugIncrementalEval = false;
2054 static const bool debugNonPawnMaterial = false;
2055 static const bool debugPieceCounts = false;
2056 static const bool debugPieceList = false;
2058 if (failedStep) *failedStep = 1;
2061 if (!color_is_ok(side_to_move()))
2064 // Are the king squares in the position correct?
2065 if (failedStep) (*failedStep)++;
2066 if (piece_on(king_square(WHITE)) != WK)
2069 if (failedStep) (*failedStep)++;
2070 if (piece_on(king_square(BLACK)) != BK)
2074 if (failedStep) (*failedStep)++;
2075 if (!file_is_ok(initialKRFile))
2078 if (!file_is_ok(initialQRFile))
2081 // Do both sides have exactly one king?
2082 if (failedStep) (*failedStep)++;
2085 int kingCount[2] = {0, 0};
2086 for (Square s = SQ_A1; s <= SQ_H8; s++)
2087 if (type_of_piece_on(s) == KING)
2088 kingCount[color_of_piece_on(s)]++;
2090 if (kingCount[0] != 1 || kingCount[1] != 1)
2094 // Can the side to move capture the opponent's king?
2095 if (failedStep) (*failedStep)++;
2096 if (debugKingCapture)
2098 Color us = side_to_move();
2099 Color them = opposite_color(us);
2100 Square ksq = king_square(them);
2101 if (square_is_attacked(ksq, us))
2105 // Is there more than 2 checkers?
2106 if (failedStep) (*failedStep)++;
2107 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2111 if (failedStep) (*failedStep)++;
2114 // The intersection of the white and black pieces must be empty
2115 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2118 // The union of the white and black pieces must be equal to all
2120 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2123 // Separate piece type bitboards must have empty intersections
2124 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2125 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2126 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2130 // En passant square OK?
2131 if (failedStep) (*failedStep)++;
2132 if (ep_square() != SQ_NONE)
2134 // The en passant square must be on rank 6, from the point of view of the
2136 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2141 if (failedStep) (*failedStep)++;
2142 if (debugKey && st->key != compute_key())
2145 // Pawn hash key OK?
2146 if (failedStep) (*failedStep)++;
2147 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2150 // Material hash key OK?
2151 if (failedStep) (*failedStep)++;
2152 if (debugMaterialKey && st->materialKey != compute_material_key())
2155 // Incremental eval OK?
2156 if (failedStep) (*failedStep)++;
2157 if (debugIncrementalEval)
2159 if (st->mgValue != compute_value<MidGame>())
2162 if (st->egValue != compute_value<EndGame>())
2166 // Non-pawn material OK?
2167 if (failedStep) (*failedStep)++;
2168 if (debugNonPawnMaterial)
2170 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2173 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2178 if (failedStep) (*failedStep)++;
2179 if (debugPieceCounts)
2180 for (Color c = WHITE; c <= BLACK; c++)
2181 for (PieceType pt = PAWN; pt <= KING; pt++)
2182 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2185 if (failedStep) (*failedStep)++;
2188 for(Color c = WHITE; c <= BLACK; c++)
2189 for(PieceType pt = PAWN; pt <= KING; pt++)
2190 for(int i = 0; i < pieceCount[c][pt]; i++)
2192 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2195 if (index[piece_list(c, pt, i)] != i)
2199 if (failedStep) *failedStep = 0;