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 // If we're in check, all pseudo-legal moves are legal, because our
464 // check evasion generator only generates true legal moves.
465 return is_check() || pl_move_is_legal(m, pinned_pieces(side_to_move()));
468 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
471 assert(move_is_ok(m));
472 assert(pinned == pinned_pieces(side_to_move()));
475 // Castling moves are checked for legality during move generation.
476 if (move_is_castle(m))
479 Color us = side_to_move();
480 Square from = move_from(m);
481 Square ksq = king_square(us);
483 assert(color_of_piece_on(from) == us);
484 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
486 // En passant captures are a tricky special case. Because they are
487 // rather uncommon, we do it simply by testing whether the king is attacked
488 // after the move is made
491 Color them = opposite_color(us);
492 Square to = move_to(m);
493 Square capsq = make_square(square_file(to), square_rank(from));
494 Bitboard b = occupied_squares();
496 assert(to == ep_square());
497 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
498 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
499 assert(piece_on(to) == EMPTY);
502 clear_bit(&b, capsq);
505 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
506 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
509 // If the moving piece is a king, check whether the destination
510 // square is attacked by the opponent.
512 return !(square_is_attacked(move_to(m), opposite_color(us)));
514 // A non-king move is legal if and only if it is not pinned or it
515 // is moving along the ray towards or away from the king.
517 || !bit_is_set(pinned, from)
518 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
522 /// Position::move_is_check() tests whether a pseudo-legal move is a check
524 bool Position::move_is_check(Move m) const {
526 Bitboard dc = discovered_check_candidates(side_to_move());
527 return move_is_check(m, dc);
530 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
533 assert(move_is_ok(m));
534 assert(dcCandidates == discovered_check_candidates(side_to_move()));
536 Color us = side_to_move();
537 Color them = opposite_color(us);
538 Square from = move_from(m);
539 Square to = move_to(m);
540 Square ksq = king_square(them);
542 assert(color_of_piece_on(from) == us);
543 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
545 // Proceed according to the type of the moving piece
546 switch (type_of_piece_on(from))
550 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
553 if ( dcCandidates // Discovered check?
554 && bit_is_set(dcCandidates, from)
555 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
558 if (move_promotion(m)) // Promotion with check?
560 Bitboard b = occupied_squares();
563 switch (move_promotion(m))
566 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
568 return bit_is_set(bishop_attacks_bb(to, b), ksq);
570 return bit_is_set(rook_attacks_bb(to, b), ksq);
572 return bit_is_set(queen_attacks_bb(to, b), ksq);
577 // En passant capture with check? We have already handled the case
578 // of direct checks and ordinary discovered check, the only case we
579 // need to handle is the unusual case of a discovered check through the
581 else if (move_is_ep(m))
583 Square capsq = make_square(square_file(to), square_rank(from));
584 Bitboard b = occupied_squares();
586 clear_bit(&b, capsq);
588 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
589 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
593 // Test discovered check and normal check according to piece type
595 return (dcCandidates && bit_is_set(dcCandidates, from))
596 || bit_is_set(piece_attacks<KNIGHT>(ksq), to);
599 return (dcCandidates && bit_is_set(dcCandidates, from))
600 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to));
603 return (dcCandidates && bit_is_set(dcCandidates, from))
604 || (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to));
607 // Discovered checks are impossible!
608 assert(!bit_is_set(dcCandidates, from));
609 return ( (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to))
610 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to)));
614 if ( bit_is_set(dcCandidates, from)
615 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
618 // Castling with check?
619 if (move_is_castle(m))
621 Square kfrom, kto, rfrom, rto;
622 Bitboard b = occupied_squares();
628 kto = relative_square(us, SQ_G1);
629 rto = relative_square(us, SQ_F1);
631 kto = relative_square(us, SQ_C1);
632 rto = relative_square(us, SQ_D1);
634 clear_bit(&b, kfrom);
635 clear_bit(&b, rfrom);
638 return bit_is_set(rook_attacks_bb(rto, b), ksq);
642 default: // NO_PIECE_TYPE
650 /// Position::update_checkers() udpates chekers info given the move. It is called
651 /// in do_move() and is faster then find_checkers().
653 template<PieceType Piece>
654 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
655 Square to, Bitboard dcCandidates) {
657 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
658 const bool Rook = (Piece == QUEEN || Piece == ROOK);
659 const bool Slider = Bishop || Rook;
661 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
662 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
663 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
664 set_bit(pCheckersBB, to);
666 else if ( Piece != KING
668 && bit_is_set(piece_attacks<Piece>(ksq), to))
669 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;
706 memcpy(&newSt, st, sizeof(ReducedStateInfo));
707 newSt.capture = NO_PIECE_TYPE;
711 // Save the current key to the history[] array, in order to be able to
712 // detect repetition draws.
713 history[gamePly] = st->key;
715 // Increment the 50 moves rule draw counter. Resetting it to zero in the
716 // case of non-reversible moves is taken care of later.
719 if (move_is_castle(m))
721 else if (move_promotion(m))
722 do_promotion_move(m);
723 else if (move_is_ep(m))
727 Color us = side_to_move();
728 Color them = opposite_color(us);
729 Square from = move_from(m);
730 Square to = move_to(m);
732 assert(color_of_piece_on(from) == us);
733 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
735 PieceType piece = type_of_piece_on(from);
737 st->capture = type_of_piece_on(to);
740 do_capture_move(st->capture, them, to);
743 clear_bit(&(byColorBB[us]), from);
744 clear_bit(&(byTypeBB[piece]), from);
745 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
746 set_bit(&(byColorBB[us]), to);
747 set_bit(&(byTypeBB[piece]), to);
748 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
749 board[to] = board[from];
753 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
755 // Update incremental scores
756 st->mgValue -= pst<MidGame>(us, piece, from);
757 st->mgValue += pst<MidGame>(us, piece, to);
758 st->egValue -= pst<EndGame>(us, piece, from);
759 st->egValue += pst<EndGame>(us, piece, to);
761 // If the moving piece was a king, update the king square
765 // Reset en passant square
766 if (st->epSquare != SQ_NONE)
768 st->key ^= zobEp[st->epSquare];
769 st->epSquare = SQ_NONE;
772 // If the moving piece was a pawn do some special extra work
775 // Reset rule 50 draw counter
778 // Update pawn hash key
779 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
781 // Set en passant square, only if moved pawn can be captured
782 if (abs(int(to) - int(from)) == 16)
784 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
785 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
787 st->epSquare = Square((int(from) + int(to)) / 2);
788 st->key ^= zobEp[st->epSquare];
793 // Update piece lists
794 pieceList[us][piece][index[from]] = to;
795 index[to] = index[from];
797 // Update castle rights
798 st->key ^= zobCastle[st->castleRights];
799 st->castleRights &= castleRightsMask[from];
800 st->castleRights &= castleRightsMask[to];
801 st->key ^= zobCastle[st->castleRights];
803 // Update checkers bitboard, piece must be already moved
804 st->checkersBB = EmptyBoardBB;
805 Square ksq = king_square(them);
808 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
809 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
810 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
811 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
812 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
813 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
814 default: assert(false); break;
819 st->key ^= zobSideToMove;
820 sideToMove = opposite_color(sideToMove);
823 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
824 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
830 /// Position::do_capture_move() is a private method used to update captured
831 /// piece info. It is called from the main Position::do_move function.
833 void Position::do_capture_move(PieceType capture, Color them, Square to) {
835 assert(capture != KING);
837 // Remove captured piece
838 clear_bit(&(byColorBB[them]), to);
839 clear_bit(&(byTypeBB[capture]), to);
842 st->key ^= zobrist[them][capture][to];
844 // If the captured piece was a pawn, update pawn hash key
846 st->pawnKey ^= zobrist[them][PAWN][to];
848 // Update incremental scores
849 st->mgValue -= pst<MidGame>(them, capture, to);
850 st->egValue -= pst<EndGame>(them, capture, to);
854 npMaterial[them] -= piece_value_midgame(capture);
856 // Update material hash key
857 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
859 // Update piece count
860 pieceCount[them][capture]--;
863 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
864 index[pieceList[them][capture][index[to]]] = index[to];
866 // Reset rule 50 counter
871 /// Position::do_castle_move() is a private method used to make a castling
872 /// move. It is called from the main Position::do_move function. Note that
873 /// castling moves are encoded as "king captures friendly rook" moves, for
874 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
876 void Position::do_castle_move(Move m) {
879 assert(move_is_ok(m));
880 assert(move_is_castle(m));
882 Color us = side_to_move();
883 Color them = opposite_color(us);
885 // Find source squares for king and rook
886 Square kfrom = move_from(m);
887 Square rfrom = move_to(m); // HACK: See comment at beginning of function
890 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
891 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
893 // Find destination squares for king and rook
894 if (rfrom > kfrom) // O-O
896 kto = relative_square(us, SQ_G1);
897 rto = relative_square(us, SQ_F1);
899 kto = relative_square(us, SQ_C1);
900 rto = relative_square(us, SQ_D1);
903 // Remove pieces from source squares
904 clear_bit(&(byColorBB[us]), kfrom);
905 clear_bit(&(byTypeBB[KING]), kfrom);
906 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
907 clear_bit(&(byColorBB[us]), rfrom);
908 clear_bit(&(byTypeBB[ROOK]), rfrom);
909 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
911 // Put pieces on destination squares
912 set_bit(&(byColorBB[us]), kto);
913 set_bit(&(byTypeBB[KING]), kto);
914 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
915 set_bit(&(byColorBB[us]), rto);
916 set_bit(&(byTypeBB[ROOK]), rto);
917 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
919 // Update board array
920 board[kfrom] = board[rfrom] = EMPTY;
921 board[kto] = piece_of_color_and_type(us, KING);
922 board[rto] = piece_of_color_and_type(us, ROOK);
924 // Update king square
925 kingSquare[us] = kto;
927 // Update piece lists
928 pieceList[us][KING][index[kfrom]] = kto;
929 pieceList[us][ROOK][index[rfrom]] = rto;
930 int tmp = index[rfrom];
931 index[kto] = index[kfrom];
934 // Update incremental scores
935 st->mgValue -= pst<MidGame>(us, KING, kfrom);
936 st->mgValue += pst<MidGame>(us, KING, kto);
937 st->egValue -= pst<EndGame>(us, KING, kfrom);
938 st->egValue += pst<EndGame>(us, KING, kto);
939 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
940 st->mgValue += pst<MidGame>(us, ROOK, rto);
941 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
942 st->egValue += pst<EndGame>(us, ROOK, rto);
945 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
946 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
948 // Clear en passant square
949 if (st->epSquare != SQ_NONE)
951 st->key ^= zobEp[st->epSquare];
952 st->epSquare = SQ_NONE;
955 // Update castling rights
956 st->key ^= zobCastle[st->castleRights];
957 st->castleRights &= castleRightsMask[kfrom];
958 st->key ^= zobCastle[st->castleRights];
960 // Reset rule 50 counter
963 // Update checkers BB
964 st->checkersBB = attacks_to(king_square(them), us);
968 /// Position::do_promotion_move() is a private method used to make a promotion
969 /// move. It is called from the main Position::do_move function.
971 void Position::do_promotion_move(Move m) {
978 assert(move_is_ok(m));
979 assert(move_promotion(m));
982 them = opposite_color(us);
986 assert(relative_rank(us, to) == RANK_8);
987 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
988 assert(color_of_piece_on(to) == them || square_is_empty(to));
990 st->capture = type_of_piece_on(to);
993 do_capture_move(st->capture, them, to);
996 clear_bit(&(byColorBB[us]), from);
997 clear_bit(&(byTypeBB[PAWN]), from);
998 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1001 // Insert promoted piece
1002 promotion = move_promotion(m);
1003 assert(promotion >= KNIGHT && promotion <= QUEEN);
1004 set_bit(&(byColorBB[us]), to);
1005 set_bit(&(byTypeBB[promotion]), to);
1006 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1007 board[to] = piece_of_color_and_type(us, promotion);
1010 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1012 // Update pawn hash key
1013 st->pawnKey ^= zobrist[us][PAWN][from];
1015 // Update material key
1016 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1017 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1019 // Update piece counts
1020 pieceCount[us][PAWN]--;
1021 pieceCount[us][promotion]++;
1023 // Update piece lists
1024 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1025 index[pieceList[us][PAWN][index[from]]] = index[from];
1026 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1027 index[to] = pieceCount[us][promotion] - 1;
1029 // Update incremental scores
1030 st->mgValue -= pst<MidGame>(us, PAWN, from);
1031 st->mgValue += pst<MidGame>(us, promotion, to);
1032 st->egValue -= pst<EndGame>(us, PAWN, from);
1033 st->egValue += pst<EndGame>(us, promotion, to);
1036 npMaterial[us] += piece_value_midgame(promotion);
1038 // Clear the en passant square
1039 if (st->epSquare != SQ_NONE)
1041 st->key ^= zobEp[st->epSquare];
1042 st->epSquare = SQ_NONE;
1045 // Update castle rights
1046 st->key ^= zobCastle[st->castleRights];
1047 st->castleRights &= castleRightsMask[to];
1048 st->key ^= zobCastle[st->castleRights];
1050 // Reset rule 50 counter
1053 // Update checkers BB
1054 st->checkersBB = attacks_to(king_square(them), us);
1058 /// Position::do_ep_move() is a private method used to make an en passant
1059 /// capture. It is called from the main Position::do_move function.
1061 void Position::do_ep_move(Move m) {
1064 Square from, to, capsq;
1067 assert(move_is_ok(m));
1068 assert(move_is_ep(m));
1070 us = side_to_move();
1071 them = opposite_color(us);
1072 from = move_from(m);
1074 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1076 assert(to == st->epSquare);
1077 assert(relative_rank(us, to) == RANK_6);
1078 assert(piece_on(to) == EMPTY);
1079 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1080 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1082 // Remove captured piece
1083 clear_bit(&(byColorBB[them]), capsq);
1084 clear_bit(&(byTypeBB[PAWN]), capsq);
1085 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1086 board[capsq] = EMPTY;
1088 // Remove moving piece from source square
1089 clear_bit(&(byColorBB[us]), from);
1090 clear_bit(&(byTypeBB[PAWN]), from);
1091 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1093 // Put moving piece on destination square
1094 set_bit(&(byColorBB[us]), to);
1095 set_bit(&(byTypeBB[PAWN]), to);
1096 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1097 board[to] = board[from];
1098 board[from] = EMPTY;
1100 // Update material hash key
1101 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1103 // Update piece count
1104 pieceCount[them][PAWN]--;
1106 // Update piece list
1107 pieceList[us][PAWN][index[from]] = to;
1108 index[to] = index[from];
1109 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1110 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1113 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1114 st->key ^= zobrist[them][PAWN][capsq];
1115 st->key ^= zobEp[st->epSquare];
1117 // Update pawn hash key
1118 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1119 st->pawnKey ^= zobrist[them][PAWN][capsq];
1121 // Update incremental scores
1122 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1123 st->mgValue -= pst<MidGame>(us, PAWN, from);
1124 st->mgValue += pst<MidGame>(us, PAWN, to);
1125 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1126 st->egValue -= pst<EndGame>(us, PAWN, from);
1127 st->egValue += pst<EndGame>(us, PAWN, to);
1129 // Reset en passant square
1130 st->epSquare = SQ_NONE;
1132 // Reset rule 50 counter
1135 // Update checkers BB
1136 st->checkersBB = attacks_to(king_square(them), us);
1140 /// Position::undo_move() unmakes a move. When it returns, the position should
1141 /// be restored to exactly the same state as before the move was made.
1143 void Position::undo_move(Move m) {
1146 assert(move_is_ok(m));
1149 sideToMove = opposite_color(sideToMove);
1151 if (move_is_castle(m))
1152 undo_castle_move(m);
1153 else if (move_promotion(m))
1154 undo_promotion_move(m);
1155 else if (move_is_ep(m))
1163 us = side_to_move();
1164 them = opposite_color(us);
1165 from = move_from(m);
1168 assert(piece_on(from) == EMPTY);
1169 assert(color_of_piece_on(to) == us);
1171 // Put the piece back at the source square
1172 piece = type_of_piece_on(to);
1173 set_bit(&(byColorBB[us]), from);
1174 set_bit(&(byTypeBB[piece]), from);
1175 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1176 board[from] = piece_of_color_and_type(us, piece);
1178 // Clear the destination square
1179 clear_bit(&(byColorBB[us]), to);
1180 clear_bit(&(byTypeBB[piece]), to);
1181 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1183 // If the moving piece was a king, update the king square
1185 kingSquare[us] = from;
1187 // Update piece list
1188 pieceList[us][piece][index[to]] = from;
1189 index[from] = index[to];
1193 assert(st->capture != KING);
1195 // Replace the captured piece
1196 set_bit(&(byColorBB[them]), to);
1197 set_bit(&(byTypeBB[st->capture]), to);
1198 set_bit(&(byTypeBB[0]), to);
1199 board[to] = piece_of_color_and_type(them, st->capture);
1202 if (st->capture != PAWN)
1203 npMaterial[them] += piece_value_midgame(st->capture);
1205 // Update piece list
1206 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1207 index[to] = pieceCount[them][st->capture];
1209 // Update piece count
1210 pieceCount[them][st->capture]++;
1215 // Finally point our state pointer back to the previous state
1222 /// Position::undo_castle_move() is a private method used to unmake a castling
1223 /// move. It is called from the main Position::undo_move function. Note that
1224 /// castling moves are encoded as "king captures friendly rook" moves, for
1225 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1227 void Position::undo_castle_move(Move m) {
1229 assert(move_is_ok(m));
1230 assert(move_is_castle(m));
1232 // When we have arrived here, some work has already been done by
1233 // Position::undo_move. In particular, the side to move has been switched,
1234 // so the code below is correct.
1235 Color us = side_to_move();
1237 // Find source squares for king and rook
1238 Square kfrom = move_from(m);
1239 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1242 // Find destination squares for king and rook
1243 if (rfrom > kfrom) // O-O
1245 kto = relative_square(us, SQ_G1);
1246 rto = relative_square(us, SQ_F1);
1248 kto = relative_square(us, SQ_C1);
1249 rto = relative_square(us, SQ_D1);
1252 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1253 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1255 // Remove pieces from destination squares
1256 clear_bit(&(byColorBB[us]), kto);
1257 clear_bit(&(byTypeBB[KING]), kto);
1258 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1259 clear_bit(&(byColorBB[us]), rto);
1260 clear_bit(&(byTypeBB[ROOK]), rto);
1261 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1263 // Put pieces on source squares
1264 set_bit(&(byColorBB[us]), kfrom);
1265 set_bit(&(byTypeBB[KING]), kfrom);
1266 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1267 set_bit(&(byColorBB[us]), rfrom);
1268 set_bit(&(byTypeBB[ROOK]), rfrom);
1269 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1272 board[rto] = board[kto] = EMPTY;
1273 board[rfrom] = piece_of_color_and_type(us, ROOK);
1274 board[kfrom] = piece_of_color_and_type(us, KING);
1276 // Update king square
1277 kingSquare[us] = kfrom;
1279 // Update piece lists
1280 pieceList[us][KING][index[kto]] = kfrom;
1281 pieceList[us][ROOK][index[rto]] = rfrom;
1282 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1283 index[kfrom] = index[kto];
1288 /// Position::undo_promotion_move() is a private method used to unmake a
1289 /// promotion move. It is called from the main Position::do_move
1292 void Position::undo_promotion_move(Move m) {
1296 PieceType promotion;
1298 assert(move_is_ok(m));
1299 assert(move_promotion(m));
1301 // When we have arrived here, some work has already been done by
1302 // Position::undo_move. In particular, the side to move has been switched,
1303 // so the code below is correct.
1304 us = side_to_move();
1305 them = opposite_color(us);
1306 from = move_from(m);
1309 assert(relative_rank(us, to) == RANK_8);
1310 assert(piece_on(from) == EMPTY);
1312 // Remove promoted piece
1313 promotion = move_promotion(m);
1314 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1315 assert(promotion >= KNIGHT && promotion <= QUEEN);
1316 clear_bit(&(byColorBB[us]), to);
1317 clear_bit(&(byTypeBB[promotion]), to);
1318 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1320 // Insert pawn at source square
1321 set_bit(&(byColorBB[us]), from);
1322 set_bit(&(byTypeBB[PAWN]), from);
1323 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1324 board[from] = piece_of_color_and_type(us, PAWN);
1327 npMaterial[us] -= piece_value_midgame(promotion);
1329 // Update piece list
1330 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1331 index[from] = pieceCount[us][PAWN];
1332 pieceList[us][promotion][index[to]] =
1333 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1334 index[pieceList[us][promotion][index[to]]] = index[to];
1336 // Update piece counts
1337 pieceCount[us][promotion]--;
1338 pieceCount[us][PAWN]++;
1342 assert(st->capture != KING);
1344 // Insert captured piece:
1345 set_bit(&(byColorBB[them]), to);
1346 set_bit(&(byTypeBB[st->capture]), to);
1347 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1348 board[to] = piece_of_color_and_type(them, st->capture);
1350 // Update material. Because the move is a promotion move, we know
1351 // that the captured piece cannot be a pawn.
1352 assert(st->capture != PAWN);
1353 npMaterial[them] += piece_value_midgame(st->capture);
1355 // Update piece list
1356 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1357 index[to] = pieceCount[them][st->capture];
1359 // Update piece count
1360 pieceCount[them][st->capture]++;
1366 /// Position::undo_ep_move() is a private method used to unmake an en passant
1367 /// capture. It is called from the main Position::undo_move function.
1369 void Position::undo_ep_move(Move m) {
1371 assert(move_is_ok(m));
1372 assert(move_is_ep(m));
1374 // When we have arrived here, some work has already been done by
1375 // Position::undo_move. In particular, the side to move has been switched,
1376 // so the code below is correct.
1377 Color us = side_to_move();
1378 Color them = opposite_color(us);
1379 Square from = move_from(m);
1380 Square to = move_to(m);
1381 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1383 assert(to == st->previous->epSquare);
1384 assert(relative_rank(us, to) == RANK_6);
1385 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1386 assert(piece_on(from) == EMPTY);
1387 assert(piece_on(capsq) == EMPTY);
1389 // Replace captured piece
1390 set_bit(&(byColorBB[them]), capsq);
1391 set_bit(&(byTypeBB[PAWN]), capsq);
1392 set_bit(&(byTypeBB[0]), capsq);
1393 board[capsq] = piece_of_color_and_type(them, PAWN);
1395 // Remove moving piece from destination square
1396 clear_bit(&(byColorBB[us]), to);
1397 clear_bit(&(byTypeBB[PAWN]), to);
1398 clear_bit(&(byTypeBB[0]), to);
1401 // Replace moving piece at source square
1402 set_bit(&(byColorBB[us]), from);
1403 set_bit(&(byTypeBB[PAWN]), from);
1404 set_bit(&(byTypeBB[0]), from);
1405 board[from] = piece_of_color_and_type(us, PAWN);
1407 // Update piece list:
1408 pieceList[us][PAWN][index[to]] = from;
1409 index[from] = index[to];
1410 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1411 index[capsq] = pieceCount[them][PAWN];
1413 // Update piece count:
1414 pieceCount[them][PAWN]++;
1418 /// Position::do_null_move makes() a "null move": It switches the side to move
1419 /// and updates the hash key without executing any move on the board.
1421 void Position::do_null_move(StateInfo& backupSt) {
1424 assert(!is_check());
1426 // Back up the information necessary to undo the null move to the supplied
1427 // StateInfo object. In the case of a null move, the only thing we need to
1428 // remember is the last move made and the en passant square.
1429 // Note that differently from normal case here backupSt is actually used as
1430 // a backup storage not as a new state to be used.
1431 backupSt.lastMove = st->lastMove;
1432 backupSt.epSquare = st->epSquare;
1433 backupSt.previous = st->previous;
1434 st->previous = &backupSt;
1436 // Save the current key to the history[] array, in order to be able to
1437 // detect repetition draws.
1438 history[gamePly] = st->key;
1440 // Update the necessary information
1441 sideToMove = opposite_color(sideToMove);
1442 if (st->epSquare != SQ_NONE)
1443 st->key ^= zobEp[st->epSquare];
1445 st->epSquare = SQ_NONE;
1448 st->key ^= zobSideToMove;
1450 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1451 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1457 /// Position::undo_null_move() unmakes a "null move".
1459 void Position::undo_null_move() {
1462 assert(!is_check());
1464 // Restore information from the our backup StateInfo object
1465 st->lastMove = st->previous->lastMove;
1466 st->epSquare = st->previous->epSquare;
1467 st->previous = st->previous->previous;
1469 if (st->epSquare != SQ_NONE)
1470 st->key ^= zobEp[st->epSquare];
1472 // Update the necessary information
1473 sideToMove = opposite_color(sideToMove);
1476 st->key ^= zobSideToMove;
1478 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1479 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1485 /// Position::see() is a static exchange evaluator: It tries to estimate the
1486 /// material gain or loss resulting from a move. There are three versions of
1487 /// this function: One which takes a destination square as input, one takes a
1488 /// move, and one which takes a 'from' and a 'to' square. The function does
1489 /// not yet understand promotions captures.
1491 int Position::see(Square to) const {
1493 assert(square_is_ok(to));
1494 return see(SQ_NONE, to);
1497 int Position::see(Move m) const {
1499 assert(move_is_ok(m));
1500 return see(move_from(m), move_to(m));
1503 int Position::see(Square from, Square to) const {
1506 static const int seeValues[18] = {
1507 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1508 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1509 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1510 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1514 Bitboard attackers, stmAttackers, occ, b;
1516 assert(square_is_ok(from) || from == SQ_NONE);
1517 assert(square_is_ok(to));
1519 // Initialize colors
1520 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1521 Color them = opposite_color(us);
1523 // Initialize pieces
1524 Piece piece = piece_on(from);
1525 Piece capture = piece_on(to);
1527 // Find all attackers to the destination square, with the moving piece
1528 // removed, but possibly an X-ray attacker added behind it.
1529 occ = occupied_squares();
1531 // Handle en passant moves
1532 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1534 assert(capture == EMPTY);
1536 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1537 capture = piece_on(capQq);
1538 assert(type_of_piece_on(capQq) == PAWN);
1540 // Remove the captured pawn
1541 clear_bit(&occ, capQq);
1546 clear_bit(&occ, from);
1547 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1548 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1549 | (piece_attacks<KNIGHT>(to) & knights())
1550 | (piece_attacks<KING>(to) & kings())
1551 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1552 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1554 if (from != SQ_NONE)
1557 // If we don't have any attacker we are finished
1558 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1561 // Locate the least valuable attacker to the destination square
1562 // and use it to initialize from square.
1564 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1567 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1568 piece = piece_on(from);
1571 // If the opponent has no attackers we are finished
1572 stmAttackers = attackers & pieces_of_color(them);
1574 return seeValues[capture];
1576 attackers &= occ; // Remove the moving piece
1578 // The destination square is defended, which makes things rather more
1579 // difficult to compute. We proceed by building up a "swap list" containing
1580 // the material gain or loss at each stop in a sequence of captures to the
1581 // destination square, where the sides alternately capture, and always
1582 // capture with the least valuable piece. After each capture, we look for
1583 // new X-ray attacks from behind the capturing piece.
1584 int lastCapturingPieceValue = seeValues[piece];
1585 int swapList[32], n = 1;
1589 swapList[0] = seeValues[capture];
1592 // Locate the least valuable attacker for the side to move. The loop
1593 // below looks like it is potentially infinite, but it isn't. We know
1594 // that the side to move still has at least one attacker left.
1595 for (pt = PAWN; !(stmAttackers & pieces_of_type(pt)); pt++)
1598 // Remove the attacker we just found from the 'attackers' bitboard,
1599 // and scan for new X-ray attacks behind the attacker.
1600 b = stmAttackers & pieces_of_type(pt);
1601 occ ^= (b & (~b + 1));
1602 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1603 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1607 // Add the new entry to the swap list
1609 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1612 // Remember the value of the capturing piece, and change the side to move
1613 // before beginning the next iteration
1614 lastCapturingPieceValue = seeValues[pt];
1615 c = opposite_color(c);
1616 stmAttackers = attackers & pieces_of_color(c);
1618 // Stop after a king capture
1619 if (pt == KING && stmAttackers)
1622 swapList[n++] = 100;
1625 } while (stmAttackers);
1627 // Having built the swap list, we negamax through it to find the best
1628 // achievable score from the point of view of the side to move
1630 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1636 /// Position::setStartState() copies the content of the argument
1637 /// inside startState and makes st point to it. This is needed
1638 /// when the st pointee could become stale, as example because
1639 /// the caller is about to going out of scope.
1641 void Position::setStartState(const StateInfo& s) {
1648 /// Position::clear() erases the position object to a pristine state, with an
1649 /// empty board, white to move, and no castling rights.
1651 void Position::clear() {
1654 memset(st, 0, sizeof(StateInfo));
1655 st->epSquare = SQ_NONE;
1657 memset(index, 0, sizeof(int) * 64);
1658 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1660 for (int i = 0; i < 64; i++)
1663 for (int i = 0; i < 7; i++)
1665 byTypeBB[i] = EmptyBoardBB;
1666 pieceCount[0][i] = pieceCount[1][i] = 0;
1667 for (int j = 0; j < 8; j++)
1668 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1673 initialKFile = FILE_E;
1674 initialKRFile = FILE_H;
1675 initialQRFile = FILE_A;
1679 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1680 /// UCI interface code, whenever a non-reversible move is made in a
1681 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1682 /// for the program to handle games of arbitrary length, as long as the GUI
1683 /// handles draws by the 50 move rule correctly.
1685 void Position::reset_game_ply() {
1691 /// Position::put_piece() puts a piece on the given square of the board,
1692 /// updating the board array, bitboards, and piece counts.
1694 void Position::put_piece(Piece p, Square s) {
1696 Color c = color_of_piece(p);
1697 PieceType pt = type_of_piece(p);
1700 index[s] = pieceCount[c][pt];
1701 pieceList[c][pt][index[s]] = s;
1703 set_bit(&(byTypeBB[pt]), s);
1704 set_bit(&(byColorBB[c]), s);
1705 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1707 pieceCount[c][pt]++;
1714 /// Position::allow_oo() gives the given side the right to castle kingside.
1715 /// Used when setting castling rights during parsing of FEN strings.
1717 void Position::allow_oo(Color c) {
1719 st->castleRights |= (1 + int(c));
1723 /// Position::allow_ooo() gives the given side the right to castle queenside.
1724 /// Used when setting castling rights during parsing of FEN strings.
1726 void Position::allow_ooo(Color c) {
1728 st->castleRights |= (4 + 4*int(c));
1732 /// Position::compute_key() computes the hash key of the position. The hash
1733 /// key is usually updated incrementally as moves are made and unmade, the
1734 /// compute_key() function is only used when a new position is set up, and
1735 /// to verify the correctness of the hash key when running in debug mode.
1737 Key Position::compute_key() const {
1739 Key result = Key(0ULL);
1741 for (Square s = SQ_A1; s <= SQ_H8; s++)
1742 if (square_is_occupied(s))
1743 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1745 if (ep_square() != SQ_NONE)
1746 result ^= zobEp[ep_square()];
1748 result ^= zobCastle[st->castleRights];
1749 if (side_to_move() == BLACK)
1750 result ^= zobSideToMove;
1756 /// Position::compute_pawn_key() computes the hash key of the position. The
1757 /// hash key is usually updated incrementally as moves are made and unmade,
1758 /// the compute_pawn_key() function is only used when a new position is set
1759 /// up, and to verify the correctness of the pawn hash key when running in
1762 Key Position::compute_pawn_key() const {
1764 Key result = Key(0ULL);
1768 for (Color c = WHITE; c <= BLACK; c++)
1773 s = pop_1st_bit(&b);
1774 result ^= zobrist[c][PAWN][s];
1781 /// Position::compute_material_key() computes the hash key of the position.
1782 /// The hash key is usually updated incrementally as moves are made and unmade,
1783 /// the compute_material_key() function is only used when a new position is set
1784 /// up, and to verify the correctness of the material hash key when running in
1787 Key Position::compute_material_key() const {
1789 Key result = Key(0ULL);
1790 for (Color c = WHITE; c <= BLACK; c++)
1791 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1793 int count = piece_count(c, pt);
1794 for (int i = 0; i <= count; i++)
1795 result ^= zobMaterial[c][pt][i];
1801 /// Position::compute_value() compute the incremental scores for the middle
1802 /// game and the endgame. These functions are used to initialize the incremental
1803 /// scores when a new position is set up, and to verify that the scores are correctly
1804 /// updated by do_move and undo_move when the program is running in debug mode.
1805 template<Position::GamePhase Phase>
1806 Value Position::compute_value() const {
1808 Value result = Value(0);
1812 for (Color c = WHITE; c <= BLACK; c++)
1813 for (PieceType pt = PAWN; pt <= KING; pt++)
1815 b = pieces_of_color_and_type(c, pt);
1818 s = pop_1st_bit(&b);
1819 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1820 result += pst<Phase>(c, pt, s);
1824 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1825 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1830 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1831 /// game material score for the given side. Material scores are updated
1832 /// incrementally during the search, this function is only used while
1833 /// initializing a new Position object.
1835 Value Position::compute_non_pawn_material(Color c) const {
1837 Value result = Value(0);
1839 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1841 Bitboard b = pieces_of_color_and_type(c, pt);
1844 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1846 result += piece_value_midgame(pt);
1853 /// Position::is_draw() tests whether the position is drawn by material,
1854 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1855 /// must be done by the search.
1857 bool Position::is_draw() const {
1859 // Draw by material?
1861 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1864 // Draw by the 50 moves rule?
1865 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1868 // Draw by repetition?
1869 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1870 if (history[gamePly - i] == st->key)
1877 /// Position::is_mate() returns true or false depending on whether the
1878 /// side to move is checkmated.
1880 bool Position::is_mate() const {
1882 MoveStack moves[256];
1884 return is_check() && !generate_evasions(*this, moves, pinned_pieces(sideToMove));
1888 /// Position::has_mate_threat() tests whether a given color has a mate in one
1889 /// from the current position.
1891 bool Position::has_mate_threat(Color c) {
1894 Color stm = side_to_move();
1899 // If the input color is not equal to the side to move, do a null move
1903 MoveStack mlist[120];
1905 bool result = false;
1906 Bitboard dc = discovered_check_candidates(sideToMove);
1907 Bitboard pinned = pinned_pieces(sideToMove);
1909 // Generate pseudo-legal non-capture and capture check moves
1910 count = generate_non_capture_checks(*this, mlist, dc);
1911 count += generate_captures(*this, mlist + count);
1913 // Loop through the moves, and see if one of them is mate
1914 for (int i = 0; i < count; i++)
1916 Move move = mlist[i].move;
1918 if (!pl_move_is_legal(move, pinned))
1928 // Undo null move, if necessary
1936 /// Position::init_zobrist() is a static member function which initializes the
1937 /// various arrays used to compute hash keys.
1939 void Position::init_zobrist() {
1941 for (int i = 0; i < 2; i++)
1942 for (int j = 0; j < 8; j++)
1943 for (int k = 0; k < 64; k++)
1944 zobrist[i][j][k] = Key(genrand_int64());
1946 for (int i = 0; i < 64; i++)
1947 zobEp[i] = Key(genrand_int64());
1949 for (int i = 0; i < 16; i++)
1950 zobCastle[i] = genrand_int64();
1952 zobSideToMove = genrand_int64();
1954 for (int i = 0; i < 2; i++)
1955 for (int j = 0; j < 8; j++)
1956 for (int k = 0; k < 16; k++)
1957 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1959 for (int i = 0; i < 16; i++)
1960 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1964 /// Position::init_piece_square_tables() initializes the piece square tables.
1965 /// This is a two-step operation: First, the white halves of the tables are
1966 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1967 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1968 /// Second, the black halves of the tables are initialized by mirroring
1969 /// and changing the sign of the corresponding white scores.
1971 void Position::init_piece_square_tables() {
1973 int r = get_option_value_int("Randomness"), i;
1974 for (Square s = SQ_A1; s <= SQ_H8; s++)
1975 for (Piece p = WP; p <= WK; p++)
1977 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1978 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1979 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1982 for (Square s = SQ_A1; s <= SQ_H8; s++)
1983 for (Piece p = BP; p <= BK; p++)
1985 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1986 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1991 /// Position::flipped_copy() makes a copy of the input position, but with
1992 /// the white and black sides reversed. This is only useful for debugging,
1993 /// especially for finding evaluation symmetry bugs.
1995 void Position::flipped_copy(const Position &pos) {
1997 assert(pos.is_ok());
2002 for (Square s = SQ_A1; s <= SQ_H8; s++)
2003 if (!pos.square_is_empty(s))
2004 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2007 sideToMove = opposite_color(pos.side_to_move());
2010 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2011 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2012 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2013 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2015 initialKFile = pos.initialKFile;
2016 initialKRFile = pos.initialKRFile;
2017 initialQRFile = pos.initialQRFile;
2019 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2020 castleRightsMask[sq] = ALL_CASTLES;
2022 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2023 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2024 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2025 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2026 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2027 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2029 // En passant square
2030 if (pos.st->epSquare != SQ_NONE)
2031 st->epSquare = flip_square(pos.st->epSquare);
2037 st->key = compute_key();
2038 st->pawnKey = compute_pawn_key();
2039 st->materialKey = compute_material_key();
2041 // Incremental scores
2042 st->mgValue = compute_value<MidGame>();
2043 st->egValue = compute_value<EndGame>();
2046 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2047 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2053 /// Position::is_ok() performs some consitency checks for the position object.
2054 /// This is meant to be helpful when debugging.
2056 bool Position::is_ok(int* failedStep) const {
2058 // What features of the position should be verified?
2059 static const bool debugBitboards = false;
2060 static const bool debugKingCount = false;
2061 static const bool debugKingCapture = false;
2062 static const bool debugCheckerCount = false;
2063 static const bool debugKey = false;
2064 static const bool debugMaterialKey = false;
2065 static const bool debugPawnKey = false;
2066 static const bool debugIncrementalEval = false;
2067 static const bool debugNonPawnMaterial = false;
2068 static const bool debugPieceCounts = false;
2069 static const bool debugPieceList = false;
2071 if (failedStep) *failedStep = 1;
2074 if (!color_is_ok(side_to_move()))
2077 // Are the king squares in the position correct?
2078 if (failedStep) (*failedStep)++;
2079 if (piece_on(king_square(WHITE)) != WK)
2082 if (failedStep) (*failedStep)++;
2083 if (piece_on(king_square(BLACK)) != BK)
2087 if (failedStep) (*failedStep)++;
2088 if (!file_is_ok(initialKRFile))
2091 if (!file_is_ok(initialQRFile))
2094 // Do both sides have exactly one king?
2095 if (failedStep) (*failedStep)++;
2098 int kingCount[2] = {0, 0};
2099 for (Square s = SQ_A1; s <= SQ_H8; s++)
2100 if (type_of_piece_on(s) == KING)
2101 kingCount[color_of_piece_on(s)]++;
2103 if (kingCount[0] != 1 || kingCount[1] != 1)
2107 // Can the side to move capture the opponent's king?
2108 if (failedStep) (*failedStep)++;
2109 if (debugKingCapture)
2111 Color us = side_to_move();
2112 Color them = opposite_color(us);
2113 Square ksq = king_square(them);
2114 if (square_is_attacked(ksq, us))
2118 // Is there more than 2 checkers?
2119 if (failedStep) (*failedStep)++;
2120 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2124 if (failedStep) (*failedStep)++;
2127 // The intersection of the white and black pieces must be empty
2128 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2131 // The union of the white and black pieces must be equal to all
2133 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2136 // Separate piece type bitboards must have empty intersections
2137 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2138 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2139 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2143 // En passant square OK?
2144 if (failedStep) (*failedStep)++;
2145 if (ep_square() != SQ_NONE)
2147 // The en passant square must be on rank 6, from the point of view of the
2149 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2154 if (failedStep) (*failedStep)++;
2155 if (debugKey && st->key != compute_key())
2158 // Pawn hash key OK?
2159 if (failedStep) (*failedStep)++;
2160 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2163 // Material hash key OK?
2164 if (failedStep) (*failedStep)++;
2165 if (debugMaterialKey && st->materialKey != compute_material_key())
2168 // Incremental eval OK?
2169 if (failedStep) (*failedStep)++;
2170 if (debugIncrementalEval)
2172 if (st->mgValue != compute_value<MidGame>())
2175 if (st->egValue != compute_value<EndGame>())
2179 // Non-pawn material OK?
2180 if (failedStep) (*failedStep)++;
2181 if (debugNonPawnMaterial)
2183 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2186 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2191 if (failedStep) (*failedStep)++;
2192 if (debugPieceCounts)
2193 for (Color c = WHITE; c <= BLACK; c++)
2194 for (PieceType pt = PAWN; pt <= KING; pt++)
2195 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2198 if (failedStep) (*failedStep)++;
2201 for(Color c = WHITE; c <= BLACK; c++)
2202 for(PieceType pt = PAWN; pt <= KING; pt++)
2203 for(int i = 0; i < pieceCount[c][pt]; i++)
2205 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2208 if (index[piece_list(c, pt, i)] != i)
2212 if (failedStep) *failedStep = 0;