2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
33 #include "ucioption.h"
39 Key Position::zobrist[2][8][64];
40 Key Position::zobEp[64];
41 Key Position::zobCastle[16];
42 Key Position::zobSideToMove;
43 Key Position::zobExclusion;
45 Score Position::PieceSquareTable[16][64];
47 // Material values arrays, indexed by Piece
48 const Value Position::PieceValueMidgame[17] = {
50 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
51 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
52 VALUE_ZERO, VALUE_ZERO,
53 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
54 RookValueMidgame, QueenValueMidgame
57 const Value Position::PieceValueEndgame[17] = {
59 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
60 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
61 VALUE_ZERO, VALUE_ZERO,
62 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
63 RookValueEndgame, QueenValueEndgame
66 // Material values array used by SEE, indexed by PieceType
67 const Value Position::seeValues[] = {
69 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
70 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
76 // Bonus for having the side to move (modified by Joona Kiiski)
77 const Score TempoValue = make_score(48, 22);
79 struct PieceLetters : public std::map<char, Piece> {
83 operator[]('K') = WK; operator[]('k') = BK;
84 operator[]('Q') = WQ; operator[]('q') = BQ;
85 operator[]('R') = WR; operator[]('r') = BR;
86 operator[]('B') = WB; operator[]('b') = BB;
87 operator[]('N') = WN; operator[]('n') = BN;
88 operator[]('P') = WP; operator[]('p') = BP;
89 operator[](' ') = PIECE_NONE;
90 operator[]('.') = PIECE_NONE_DARK_SQ;
93 char from_piece(Piece p) const {
95 std::map<char, Piece>::const_iterator it;
96 for (it = begin(); it != end(); ++it)
105 PieceLetters pieceLetters;
111 CheckInfo::CheckInfo(const Position& pos) {
113 Color us = pos.side_to_move();
114 Color them = opposite_color(us);
116 ksq = pos.king_square(them);
117 dcCandidates = pos.discovered_check_candidates(us);
119 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
120 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
121 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
122 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
123 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
124 checkSq[KING] = EmptyBoardBB;
128 /// Position c'tors. Here we always create a copy of the original position
129 /// or the FEN string, we want the new born Position object do not depend
130 /// on any external data so we detach state pointer from the source one.
132 Position::Position(const Position& pos, int th) {
134 memcpy(this, &pos, sizeof(Position));
135 detach(); // Always detach() in copy c'tor to avoid surprises
140 Position::Position(const string& fen, bool isChess960, int th) {
142 from_fen(fen, isChess960);
147 /// Position::detach() copies the content of the current state and castling
148 /// masks inside the position itself. This is needed when the st pointee could
149 /// become stale, as example because the caller is about to going out of scope.
151 void Position::detach() {
155 st->previous = NULL; // as a safe guard
159 /// Position::from_fen() initializes the position object with the given FEN
160 /// string. This function is not very robust - make sure that input FENs are
161 /// correct (this is assumed to be the responsibility of the GUI).
163 void Position::from_fen(const string& fen, bool isChess960) {
165 A FEN string defines a particular position using only the ASCII character set.
167 A FEN string contains six fields. The separator between fields is a space. The fields are:
169 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
170 with rank 1; within each rank, the contents of each square are described from file A through file H.
171 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
172 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
173 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
174 of blank squares), and "/" separate ranks.
176 2) Active color. "w" means white moves next, "b" means black.
178 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
179 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
180 kingside), and/or "q" (Black can castle queenside).
182 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
183 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
184 regardless of whether there is a pawn in position to make an en passant capture.
186 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
187 to determine if a draw can be claimed under the fifty-move rule.
189 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
194 std::istringstream ss(fen);
199 // 1. Piece placement field
200 while (ss.get(token) && token != ' ')
202 if (pieceLetters.find(token) != pieceLetters.end())
204 put_piece(pieceLetters[token], sq);
207 else if (isdigit(token))
208 sq += Square(token - '0'); // Skip the given number of files
209 else if (token == '/')
210 sq -= SQ_A3; // Jump back of 2 rows
216 if (!ss.get(token) || (token != 'w' && token != 'b'))
219 sideToMove = (token == 'w' ? WHITE : BLACK);
221 if (!ss.get(token) || token != ' ')
224 // 3. Castling availability
225 while (ss.get(token) && token != ' ')
226 if (!set_castling_rights(token))
229 // 4. En passant square
231 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
232 && (ss.get(row) && (row == '3' || row == '6')))
234 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
236 // Ignore if no capture is possible
237 Color them = opposite_color(sideToMove);
238 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
239 st->epSquare = SQ_NONE;
246 // 6. Fullmove number
248 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
250 // Various initialisations
251 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
252 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
253 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
254 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
255 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
256 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
258 chess960 = isChess960;
261 st->key = compute_key();
262 st->pawnKey = compute_pawn_key();
263 st->materialKey = compute_material_key();
264 st->value = compute_value();
265 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
266 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
270 cout << "Error in FEN string: " << fen << endl;
274 /// Position::set_castling_rights() sets castling parameters castling avaiability.
275 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
276 /// that uses the letters of the columns on which the rooks began the game instead
277 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
278 /// associated with the castling right, the traditional castling tag will be replaced
279 /// by the file letter of the involved rook as for the Shredder-FEN.
281 bool Position::set_castling_rights(char token) {
283 Color c = token >= 'a' ? BLACK : WHITE;
284 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
285 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
286 Piece rook = (c == WHITE ? WR : BR);
288 initialKFile = square_file(king_square(c));
289 token = char(toupper(token));
293 for (Square sq = sqH; sq >= sqA; sq--)
294 if (piece_on(sq) == rook)
297 initialKRFile = square_file(sq);
301 else if (token == 'Q')
303 for (Square sq = sqA; sq <= sqH; sq++)
304 if (piece_on(sq) == rook)
307 initialQRFile = square_file(sq);
311 else if (token >= 'A' && token <= 'H')
313 File rookFile = File(token - 'A') + FILE_A;
314 if (rookFile < initialKFile)
317 initialQRFile = rookFile;
322 initialKRFile = rookFile;
332 /// Position::to_fen() returns a FEN representation of the position. In case
333 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
335 const string Position::to_fen() const {
341 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
343 for (File file = FILE_A; file <= FILE_H; file++)
345 sq = make_square(file, rank);
347 if (square_is_occupied(sq))
354 fen += pieceLetters.from_piece(piece_on(sq));
366 fen += (sideToMove == WHITE ? " w " : " b ");
368 if (st->castleRights != CASTLES_NONE)
370 if (can_castle_kingside(WHITE))
371 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
373 if (can_castle_queenside(WHITE))
374 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
376 if (can_castle_kingside(BLACK))
377 fen += chess960 ? file_to_char(initialKRFile) : 'k';
379 if (can_castle_queenside(BLACK))
380 fen += chess960 ? file_to_char(initialQRFile) : 'q';
384 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
389 /// Position::print() prints an ASCII representation of the position to
390 /// the standard output. If a move is given then also the san is printed.
392 void Position::print(Move move) const {
394 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
398 Position p(*this, thread());
399 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
400 cout << "\nMove is: " << dd << move_to_san(p, move);
403 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
405 cout << dottedLine << '|';
406 for (File file = FILE_A; file <= FILE_H; file++)
408 Square sq = make_square(file, rank);
409 Piece piece = piece_on(sq);
411 if (piece == PIECE_NONE && square_color(sq) == DARK)
412 piece = PIECE_NONE_DARK_SQ;
414 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
415 cout << c << pieceLetters.from_piece(piece) << c << '|';
418 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
422 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
423 /// king) pieces for the given color and for the given pinner type. Or, when
424 /// template parameter FindPinned is false, the pieces of the given color
425 /// candidate for a discovery check against the enemy king.
426 /// Bitboard checkersBB must be already updated when looking for pinners.
428 template<bool FindPinned>
429 Bitboard Position::hidden_checkers(Color c) const {
431 Bitboard result = EmptyBoardBB;
432 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
434 // Pinned pieces protect our king, dicovery checks attack
436 Square ksq = king_square(FindPinned ? c : opposite_color(c));
438 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
439 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
441 if (FindPinned && pinners)
442 pinners &= ~st->checkersBB;
446 Square s = pop_1st_bit(&pinners);
447 Bitboard b = squares_between(s, ksq) & occupied_squares();
451 if ( !(b & (b - 1)) // Only one bit set?
452 && (b & pieces_of_color(c))) // Is an our piece?
459 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
460 /// king) pieces for the given color. Note that checkersBB bitboard must
461 /// be already updated.
463 Bitboard Position::pinned_pieces(Color c) const {
465 return hidden_checkers<true>(c);
469 /// Position:discovered_check_candidates() returns a bitboard containing all
470 /// pieces for the given side which are candidates for giving a discovered
471 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
472 /// to be already updated.
474 Bitboard Position::discovered_check_candidates(Color c) const {
476 return hidden_checkers<false>(c);
479 /// Position::attackers_to() computes a bitboard containing all pieces which
480 /// attacks a given square.
482 Bitboard Position::attackers_to(Square s) const {
484 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
485 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
486 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
487 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
488 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
489 | (attacks_from<KING>(s) & pieces(KING));
492 /// Position::attacks_from() computes a bitboard of all attacks
493 /// of a given piece put in a given square.
495 Bitboard Position::attacks_from(Piece p, Square s) const {
497 assert(square_is_ok(s));
501 case WB: case BB: return attacks_from<BISHOP>(s);
502 case WR: case BR: return attacks_from<ROOK>(s);
503 case WQ: case BQ: return attacks_from<QUEEN>(s);
504 default: return StepAttacksBB[p][s];
508 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
510 assert(square_is_ok(s));
514 case WB: case BB: return bishop_attacks_bb(s, occ);
515 case WR: case BR: return rook_attacks_bb(s, occ);
516 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
517 default: return StepAttacksBB[p][s];
522 /// Position::move_attacks_square() tests whether a move from the current
523 /// position attacks a given square.
525 bool Position::move_attacks_square(Move m, Square s) const {
527 assert(move_is_ok(m));
528 assert(square_is_ok(s));
531 Square f = move_from(m), t = move_to(m);
533 assert(square_is_occupied(f));
535 if (bit_is_set(attacks_from(piece_on(f), t), s))
538 // Move the piece and scan for X-ray attacks behind it
539 occ = occupied_squares();
540 do_move_bb(&occ, make_move_bb(f, t));
541 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
542 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
543 & pieces_of_color(color_of_piece_on(f));
545 // If we have attacks we need to verify that are caused by our move
546 // and are not already existent ones.
547 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
551 /// Position::find_checkers() computes the checkersBB bitboard, which
552 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
553 /// currently works by calling Position::attackers_to, which is probably
554 /// inefficient. Consider rewriting this function to use the last move
555 /// played, like in non-bitboard versions of Glaurung.
557 void Position::find_checkers() {
559 Color us = side_to_move();
560 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
564 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
566 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
569 assert(move_is_ok(m));
570 assert(pinned == pinned_pieces(side_to_move()));
572 // Castling moves are checked for legality during move generation.
573 if (move_is_castle(m))
576 // En passant captures are a tricky special case. Because they are
577 // rather uncommon, we do it simply by testing whether the king is attacked
578 // after the move is made
581 Color us = side_to_move();
582 Color them = opposite_color(us);
583 Square from = move_from(m);
584 Square to = move_to(m);
585 Square capsq = make_square(square_file(to), square_rank(from));
586 Square ksq = king_square(us);
587 Bitboard b = occupied_squares();
589 assert(to == ep_square());
590 assert(piece_on(from) == make_piece(us, PAWN));
591 assert(piece_on(capsq) == make_piece(them, PAWN));
592 assert(piece_on(to) == PIECE_NONE);
595 clear_bit(&b, capsq);
598 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
599 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
602 Color us = side_to_move();
603 Square from = move_from(m);
605 assert(color_of_piece_on(from) == us);
606 assert(piece_on(king_square(us)) == make_piece(us, KING));
608 // If the moving piece is a king, check whether the destination
609 // square is attacked by the opponent.
610 if (type_of_piece_on(from) == KING)
611 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
613 // A non-king move is legal if and only if it is not pinned or it
614 // is moving along the ray towards or away from the king.
616 || !bit_is_set(pinned, from)
617 || squares_aligned(from, move_to(m), king_square(us));
621 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
623 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
627 Color us = side_to_move();
628 Square from = move_from(m);
629 Square to = move_to(m);
631 // King moves and en-passant captures are verified in pl_move_is_legal()
632 if (type_of_piece_on(from) == KING || move_is_ep(m))
633 return pl_move_is_legal(m, pinned);
635 Bitboard target = checkers();
636 Square checksq = pop_1st_bit(&target);
638 if (target) // double check ?
641 // Our move must be a blocking evasion or a capture of the checking piece
642 target = squares_between(checksq, king_square(us)) | checkers();
643 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
647 /// Position::move_is_check() tests whether a pseudo-legal move is a check
649 bool Position::move_is_check(Move m) const {
651 return move_is_check(m, CheckInfo(*this));
654 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
657 assert(move_is_ok(m));
658 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
659 assert(color_of_piece_on(move_from(m)) == side_to_move());
660 assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
662 Square from = move_from(m);
663 Square to = move_to(m);
664 PieceType pt = type_of_piece_on(from);
667 if (bit_is_set(ci.checkSq[pt], to))
671 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
673 // For pawn and king moves we need to verify also direction
674 if ( (pt != PAWN && pt != KING)
675 || !squares_aligned(from, to, ci.ksq))
679 // Can we skip the ugly special cases ?
680 if (!move_is_special(m))
683 Color us = side_to_move();
684 Bitboard b = occupied_squares();
686 // Promotion with check ?
687 if (move_is_promotion(m))
691 switch (move_promotion_piece(m))
694 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
696 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
698 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
700 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
706 // En passant capture with check ? We have already handled the case
707 // of direct checks and ordinary discovered check, the only case we
708 // need to handle is the unusual case of a discovered check through
709 // the captured pawn.
712 Square capsq = make_square(square_file(to), square_rank(from));
714 clear_bit(&b, capsq);
716 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
717 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
720 // Castling with check ?
721 if (move_is_castle(m))
723 Square kfrom, kto, rfrom, rto;
729 kto = relative_square(us, SQ_G1);
730 rto = relative_square(us, SQ_F1);
732 kto = relative_square(us, SQ_C1);
733 rto = relative_square(us, SQ_D1);
735 clear_bit(&b, kfrom);
736 clear_bit(&b, rfrom);
739 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
746 /// Position::do_setup_move() makes a permanent move on the board.
747 /// It should be used when setting up a position on board.
748 /// You can't undo the move.
750 void Position::do_setup_move(Move m) {
756 // Reset "game ply" in case we made a non-reversible move.
757 // "game ply" is used for repetition detection.
761 // Update the number of plies played from the starting position
762 startPosPlyCounter++;
764 // Our StateInfo newSt is about going out of scope so copy
765 // its content inside pos before it disappears.
769 /// Position::do_move() makes a move, and saves all information necessary
770 /// to a StateInfo object. The move is assumed to be legal.
771 /// Pseudo-legal moves should be filtered out before this function is called.
773 void Position::do_move(Move m, StateInfo& newSt) {
776 do_move(m, newSt, ci, move_is_check(m, ci));
779 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
782 assert(move_is_ok(m));
783 assert(&newSt != st);
788 // Copy some fields of old state to our new StateInfo object except the
789 // ones which are recalculated from scratch anyway, then switch our state
790 // pointer to point to the new, ready to be updated, state.
791 struct ReducedStateInfo {
792 Key pawnKey, materialKey;
793 int castleRights, rule50, gamePly, pliesFromNull;
799 memcpy(&newSt, st, sizeof(ReducedStateInfo));
804 // Save the current key to the history[] array, in order to be able to
805 // detect repetition draws.
806 history[st->gamePly++] = key;
808 // Update side to move
809 key ^= zobSideToMove;
811 // Increment the 50 moves rule draw counter. Resetting it to zero in the
812 // case of non-reversible moves is taken care of later.
816 if (move_is_castle(m))
823 Color us = side_to_move();
824 Color them = opposite_color(us);
825 Square from = move_from(m);
826 Square to = move_to(m);
827 bool ep = move_is_ep(m);
828 bool pm = move_is_promotion(m);
830 Piece piece = piece_on(from);
831 PieceType pt = type_of_piece(piece);
832 PieceType capture = ep ? PAWN : type_of_piece_on(to);
834 assert(color_of_piece_on(from) == us);
835 assert(color_of_piece_on(to) == them || square_is_empty(to));
836 assert(!(ep || pm) || piece == make_piece(us, PAWN));
837 assert(!pm || relative_rank(us, to) == RANK_8);
840 do_capture_move(key, capture, them, to, ep);
843 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
845 // Reset en passant square
846 if (st->epSquare != SQ_NONE)
848 key ^= zobEp[st->epSquare];
849 st->epSquare = SQ_NONE;
852 // Update castle rights, try to shortcut a common case
853 int cm = castleRightsMask[from] & castleRightsMask[to];
854 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
856 key ^= zobCastle[st->castleRights];
857 st->castleRights &= castleRightsMask[from];
858 st->castleRights &= castleRightsMask[to];
859 key ^= zobCastle[st->castleRights];
862 // Prefetch TT access as soon as we know key is updated
863 prefetch((char*)TT.first_entry(key));
866 Bitboard move_bb = make_move_bb(from, to);
867 do_move_bb(&(byColorBB[us]), move_bb);
868 do_move_bb(&(byTypeBB[pt]), move_bb);
869 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
871 board[to] = board[from];
872 board[from] = PIECE_NONE;
874 // Update piece lists, note that index[from] is not updated and
875 // becomes stale. This works as long as index[] is accessed just
876 // by known occupied squares.
877 index[to] = index[from];
878 pieceList[us][pt][index[to]] = to;
880 // If the moving piece was a pawn do some special extra work
883 // Reset rule 50 draw counter
886 // Update pawn hash key and prefetch in L1/L2 cache
887 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
889 // Set en passant square, only if moved pawn can be captured
890 if ((to ^ from) == 16)
892 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
894 st->epSquare = Square((int(from) + int(to)) / 2);
895 key ^= zobEp[st->epSquare];
899 if (pm) // promotion ?
901 PieceType promotion = move_promotion_piece(m);
903 assert(promotion >= KNIGHT && promotion <= QUEEN);
905 // Insert promoted piece instead of pawn
906 clear_bit(&(byTypeBB[PAWN]), to);
907 set_bit(&(byTypeBB[promotion]), to);
908 board[to] = make_piece(us, promotion);
910 // Update piece counts
911 pieceCount[us][promotion]++;
912 pieceCount[us][PAWN]--;
914 // Update material key
915 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
916 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
918 // Update piece lists, move the last pawn at index[to] position
919 // and shrink the list. Add a new promotion piece to the list.
920 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
921 index[lastPawnSquare] = index[to];
922 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
923 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
924 index[to] = pieceCount[us][promotion] - 1;
925 pieceList[us][promotion][index[to]] = to;
927 // Partially revert hash keys update
928 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
929 st->pawnKey ^= zobrist[us][PAWN][to];
931 // Partially revert and update incremental scores
932 st->value -= pst(us, PAWN, to);
933 st->value += pst(us, promotion, to);
936 st->npMaterial[us] += PieceValueMidgame[promotion];
940 // Prefetch pawn and material hash tables
941 prefetchTables(st->pawnKey, st->materialKey, threadID);
943 // Update incremental scores
944 st->value += pst_delta(piece, from, to);
947 st->capturedType = capture;
949 // Update the key with the final value
952 // Update checkers bitboard, piece must be already moved
953 st->checkersBB = EmptyBoardBB;
958 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
962 if (bit_is_set(ci.checkSq[pt], to))
963 st->checkersBB = SetMaskBB[to];
966 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
969 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
972 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
978 sideToMove = opposite_color(sideToMove);
979 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
985 /// Position::do_capture_move() is a private method used to update captured
986 /// piece info. It is called from the main Position::do_move function.
988 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
990 assert(capture != KING);
994 // If the captured piece was a pawn, update pawn hash key,
995 // otherwise update non-pawn material.
998 if (ep) // en passant ?
1000 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1002 assert(to == st->epSquare);
1003 assert(relative_rank(opposite_color(them), to) == RANK_6);
1004 assert(piece_on(to) == PIECE_NONE);
1005 assert(piece_on(capsq) == make_piece(them, PAWN));
1007 board[capsq] = PIECE_NONE;
1009 st->pawnKey ^= zobrist[them][PAWN][capsq];
1012 st->npMaterial[them] -= PieceValueMidgame[capture];
1014 // Remove captured piece
1015 clear_bit(&(byColorBB[them]), capsq);
1016 clear_bit(&(byTypeBB[capture]), capsq);
1017 clear_bit(&(byTypeBB[0]), capsq);
1020 key ^= zobrist[them][capture][capsq];
1022 // Update incremental scores
1023 st->value -= pst(them, capture, capsq);
1025 // Update piece count
1026 pieceCount[them][capture]--;
1028 // Update material hash key
1029 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1031 // Update piece list, move the last piece at index[capsq] position
1033 // WARNING: This is a not perfectly revresible operation. When we
1034 // will reinsert the captured piece in undo_move() we will put it
1035 // at the end of the list and not in its original place, it means
1036 // index[] and pieceList[] are not guaranteed to be invariant to a
1037 // do_move() + undo_move() sequence.
1038 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1039 index[lastPieceSquare] = index[capsq];
1040 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1041 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1043 // Reset rule 50 counter
1048 /// Position::do_castle_move() is a private method used to make a castling
1049 /// move. It is called from the main Position::do_move function. Note that
1050 /// castling moves are encoded as "king captures friendly rook" moves, for
1051 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1053 void Position::do_castle_move(Move m) {
1055 assert(move_is_ok(m));
1056 assert(move_is_castle(m));
1058 Color us = side_to_move();
1059 Color them = opposite_color(us);
1061 // Reset capture field
1062 st->capturedType = PIECE_TYPE_NONE;
1064 // Find source squares for king and rook
1065 Square kfrom = move_from(m);
1066 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1069 assert(piece_on(kfrom) == make_piece(us, KING));
1070 assert(piece_on(rfrom) == make_piece(us, ROOK));
1072 // Find destination squares for king and rook
1073 if (rfrom > kfrom) // O-O
1075 kto = relative_square(us, SQ_G1);
1076 rto = relative_square(us, SQ_F1);
1078 kto = relative_square(us, SQ_C1);
1079 rto = relative_square(us, SQ_D1);
1082 // Remove pieces from source squares:
1083 clear_bit(&(byColorBB[us]), kfrom);
1084 clear_bit(&(byTypeBB[KING]), kfrom);
1085 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1086 clear_bit(&(byColorBB[us]), rfrom);
1087 clear_bit(&(byTypeBB[ROOK]), rfrom);
1088 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1090 // Put pieces on destination squares:
1091 set_bit(&(byColorBB[us]), kto);
1092 set_bit(&(byTypeBB[KING]), kto);
1093 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1094 set_bit(&(byColorBB[us]), rto);
1095 set_bit(&(byTypeBB[ROOK]), rto);
1096 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1098 // Update board array
1099 Piece king = make_piece(us, KING);
1100 Piece rook = make_piece(us, ROOK);
1101 board[kfrom] = board[rfrom] = PIECE_NONE;
1105 // Update piece lists
1106 pieceList[us][KING][index[kfrom]] = kto;
1107 pieceList[us][ROOK][index[rfrom]] = rto;
1108 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1109 index[kto] = index[kfrom];
1112 // Update incremental scores
1113 st->value += pst_delta(king, kfrom, kto);
1114 st->value += pst_delta(rook, rfrom, rto);
1117 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1118 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1120 // Clear en passant square
1121 if (st->epSquare != SQ_NONE)
1123 st->key ^= zobEp[st->epSquare];
1124 st->epSquare = SQ_NONE;
1127 // Update castling rights
1128 st->key ^= zobCastle[st->castleRights];
1129 st->castleRights &= castleRightsMask[kfrom];
1130 st->key ^= zobCastle[st->castleRights];
1132 // Reset rule 50 counter
1135 // Update checkers BB
1136 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1139 sideToMove = opposite_color(sideToMove);
1140 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1146 /// Position::undo_move() unmakes a move. When it returns, the position should
1147 /// be restored to exactly the same state as before the move was made.
1149 void Position::undo_move(Move m) {
1152 assert(move_is_ok(m));
1154 sideToMove = opposite_color(sideToMove);
1156 if (move_is_castle(m))
1158 undo_castle_move(m);
1162 Color us = side_to_move();
1163 Color them = opposite_color(us);
1164 Square from = move_from(m);
1165 Square to = move_to(m);
1166 bool ep = move_is_ep(m);
1167 bool pm = move_is_promotion(m);
1169 PieceType pt = type_of_piece_on(to);
1171 assert(square_is_empty(from));
1172 assert(color_of_piece_on(to) == us);
1173 assert(!pm || relative_rank(us, to) == RANK_8);
1174 assert(!ep || to == st->previous->epSquare);
1175 assert(!ep || relative_rank(us, to) == RANK_6);
1176 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1178 if (pm) // promotion ?
1180 PieceType promotion = move_promotion_piece(m);
1183 assert(promotion >= KNIGHT && promotion <= QUEEN);
1184 assert(piece_on(to) == make_piece(us, promotion));
1186 // Replace promoted piece with a pawn
1187 clear_bit(&(byTypeBB[promotion]), to);
1188 set_bit(&(byTypeBB[PAWN]), to);
1190 // Update piece counts
1191 pieceCount[us][promotion]--;
1192 pieceCount[us][PAWN]++;
1194 // Update piece list replacing promotion piece with a pawn
1195 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1196 index[lastPromotionSquare] = index[to];
1197 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1198 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1199 index[to] = pieceCount[us][PAWN] - 1;
1200 pieceList[us][PAWN][index[to]] = to;
1203 // Put the piece back at the source square
1204 Bitboard move_bb = make_move_bb(to, from);
1205 do_move_bb(&(byColorBB[us]), move_bb);
1206 do_move_bb(&(byTypeBB[pt]), move_bb);
1207 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1209 board[from] = make_piece(us, pt);
1210 board[to] = PIECE_NONE;
1212 // Update piece list
1213 index[from] = index[to];
1214 pieceList[us][pt][index[from]] = from;
1216 if (st->capturedType)
1221 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1223 assert(st->capturedType != KING);
1224 assert(!ep || square_is_empty(capsq));
1226 // Restore the captured piece
1227 set_bit(&(byColorBB[them]), capsq);
1228 set_bit(&(byTypeBB[st->capturedType]), capsq);
1229 set_bit(&(byTypeBB[0]), capsq);
1231 board[capsq] = make_piece(them, st->capturedType);
1233 // Update piece count
1234 pieceCount[them][st->capturedType]++;
1236 // Update piece list, add a new captured piece in capsq square
1237 index[capsq] = pieceCount[them][st->capturedType] - 1;
1238 pieceList[them][st->capturedType][index[capsq]] = capsq;
1241 // Finally point our state pointer back to the previous state
1248 /// Position::undo_castle_move() is a private method used to unmake a castling
1249 /// move. It is called from the main Position::undo_move function. Note that
1250 /// castling moves are encoded as "king captures friendly rook" moves, for
1251 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1253 void Position::undo_castle_move(Move m) {
1255 assert(move_is_ok(m));
1256 assert(move_is_castle(m));
1258 // When we have arrived here, some work has already been done by
1259 // Position::undo_move. In particular, the side to move has been switched,
1260 // so the code below is correct.
1261 Color us = side_to_move();
1263 // Find source squares for king and rook
1264 Square kfrom = move_from(m);
1265 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1268 // Find destination squares for king and rook
1269 if (rfrom > kfrom) // O-O
1271 kto = relative_square(us, SQ_G1);
1272 rto = relative_square(us, SQ_F1);
1274 kto = relative_square(us, SQ_C1);
1275 rto = relative_square(us, SQ_D1);
1278 assert(piece_on(kto) == make_piece(us, KING));
1279 assert(piece_on(rto) == make_piece(us, ROOK));
1281 // Remove pieces from destination squares:
1282 clear_bit(&(byColorBB[us]), kto);
1283 clear_bit(&(byTypeBB[KING]), kto);
1284 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1285 clear_bit(&(byColorBB[us]), rto);
1286 clear_bit(&(byTypeBB[ROOK]), rto);
1287 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1289 // Put pieces on source squares:
1290 set_bit(&(byColorBB[us]), kfrom);
1291 set_bit(&(byTypeBB[KING]), kfrom);
1292 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1293 set_bit(&(byColorBB[us]), rfrom);
1294 set_bit(&(byTypeBB[ROOK]), rfrom);
1295 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1298 board[rto] = board[kto] = PIECE_NONE;
1299 board[rfrom] = make_piece(us, ROOK);
1300 board[kfrom] = make_piece(us, KING);
1302 // Update piece lists
1303 pieceList[us][KING][index[kto]] = kfrom;
1304 pieceList[us][ROOK][index[rto]] = rfrom;
1305 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1306 index[kfrom] = index[kto];
1309 // Finally point our state pointer back to the previous state
1316 /// Position::do_null_move makes() a "null move": It switches the side to move
1317 /// and updates the hash key without executing any move on the board.
1319 void Position::do_null_move(StateInfo& backupSt) {
1322 assert(!is_check());
1324 // Back up the information necessary to undo the null move to the supplied
1325 // StateInfo object.
1326 // Note that differently from normal case here backupSt is actually used as
1327 // a backup storage not as a new state to be used.
1328 backupSt.key = st->key;
1329 backupSt.epSquare = st->epSquare;
1330 backupSt.value = st->value;
1331 backupSt.previous = st->previous;
1332 backupSt.pliesFromNull = st->pliesFromNull;
1333 st->previous = &backupSt;
1335 // Save the current key to the history[] array, in order to be able to
1336 // detect repetition draws.
1337 history[st->gamePly++] = st->key;
1339 // Update the necessary information
1340 if (st->epSquare != SQ_NONE)
1341 st->key ^= zobEp[st->epSquare];
1343 st->key ^= zobSideToMove;
1344 prefetch((char*)TT.first_entry(st->key));
1346 sideToMove = opposite_color(sideToMove);
1347 st->epSquare = SQ_NONE;
1349 st->pliesFromNull = 0;
1350 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1354 /// Position::undo_null_move() unmakes a "null move".
1356 void Position::undo_null_move() {
1359 assert(!is_check());
1361 // Restore information from the our backup StateInfo object
1362 StateInfo* backupSt = st->previous;
1363 st->key = backupSt->key;
1364 st->epSquare = backupSt->epSquare;
1365 st->value = backupSt->value;
1366 st->previous = backupSt->previous;
1367 st->pliesFromNull = backupSt->pliesFromNull;
1369 // Update the necessary information
1370 sideToMove = opposite_color(sideToMove);
1376 /// Position::see() is a static exchange evaluator: It tries to estimate the
1377 /// material gain or loss resulting from a move. There are three versions of
1378 /// this function: One which takes a destination square as input, one takes a
1379 /// move, and one which takes a 'from' and a 'to' square. The function does
1380 /// not yet understand promotions captures.
1382 int Position::see(Move m) const {
1384 assert(move_is_ok(m));
1385 return see(move_from(m), move_to(m));
1388 int Position::see_sign(Move m) const {
1390 assert(move_is_ok(m));
1392 Square from = move_from(m);
1393 Square to = move_to(m);
1395 // Early return if SEE cannot be negative because captured piece value
1396 // is not less then capturing one. Note that king moves always return
1397 // here because king midgame value is set to 0.
1398 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1401 return see(from, to);
1404 int Position::see(Square from, Square to) const {
1406 Bitboard occupied, attackers, stmAttackers, b;
1407 int swapList[32], slIndex = 1;
1408 PieceType capturedType, pt;
1411 assert(square_is_ok(from));
1412 assert(square_is_ok(to));
1414 capturedType = type_of_piece_on(to);
1416 // King cannot be recaptured
1417 if (capturedType == KING)
1418 return seeValues[capturedType];
1420 occupied = occupied_squares();
1422 // Handle en passant moves
1423 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1425 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1427 assert(capturedType == PIECE_TYPE_NONE);
1428 assert(type_of_piece_on(capQq) == PAWN);
1430 // Remove the captured pawn
1431 clear_bit(&occupied, capQq);
1432 capturedType = PAWN;
1435 // Find all attackers to the destination square, with the moving piece
1436 // removed, but possibly an X-ray attacker added behind it.
1437 clear_bit(&occupied, from);
1438 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1439 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1440 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1441 | (attacks_from<KING>(to) & pieces(KING))
1442 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1443 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1445 // If the opponent has no attackers we are finished
1446 stm = opposite_color(color_of_piece_on(from));
1447 stmAttackers = attackers & pieces_of_color(stm);
1449 return seeValues[capturedType];
1451 // The destination square is defended, which makes things rather more
1452 // difficult to compute. We proceed by building up a "swap list" containing
1453 // the material gain or loss at each stop in a sequence of captures to the
1454 // destination square, where the sides alternately capture, and always
1455 // capture with the least valuable piece. After each capture, we look for
1456 // new X-ray attacks from behind the capturing piece.
1457 swapList[0] = seeValues[capturedType];
1458 capturedType = type_of_piece_on(from);
1461 // Locate the least valuable attacker for the side to move. The loop
1462 // below looks like it is potentially infinite, but it isn't. We know
1463 // that the side to move still has at least one attacker left.
1464 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1467 // Remove the attacker we just found from the 'occupied' bitboard,
1468 // and scan for new X-ray attacks behind the attacker.
1469 b = stmAttackers & pieces(pt);
1470 occupied ^= (b & (~b + 1));
1471 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1472 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1474 attackers &= occupied; // Cut out pieces we've already done
1476 // Add the new entry to the swap list
1477 assert(slIndex < 32);
1478 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1481 // Remember the value of the capturing piece, and change the side to
1482 // move before beginning the next iteration.
1484 stm = opposite_color(stm);
1485 stmAttackers = attackers & pieces_of_color(stm);
1487 // Stop before processing a king capture
1488 if (capturedType == KING && stmAttackers)
1490 assert(slIndex < 32);
1491 swapList[slIndex++] = QueenValueMidgame*10;
1494 } while (stmAttackers);
1496 // Having built the swap list, we negamax through it to find the best
1497 // achievable score from the point of view of the side to move.
1499 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1505 /// Position::clear() erases the position object to a pristine state, with an
1506 /// empty board, white to move, and no castling rights.
1508 void Position::clear() {
1511 memset(st, 0, sizeof(StateInfo));
1512 st->epSquare = SQ_NONE;
1513 startPosPlyCounter = 0;
1516 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1517 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1518 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1519 memset(index, 0, sizeof(int) * 64);
1521 for (int i = 0; i < 64; i++)
1522 board[i] = PIECE_NONE;
1524 for (int i = 0; i < 8; i++)
1525 for (int j = 0; j < 16; j++)
1526 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1528 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1529 castleRightsMask[sq] = ALL_CASTLES;
1532 initialKFile = FILE_E;
1533 initialKRFile = FILE_H;
1534 initialQRFile = FILE_A;
1538 /// Position::put_piece() puts a piece on the given square of the board,
1539 /// updating the board array, pieces list, bitboards, and piece counts.
1541 void Position::put_piece(Piece p, Square s) {
1543 Color c = color_of_piece(p);
1544 PieceType pt = type_of_piece(p);
1547 index[s] = pieceCount[c][pt]++;
1548 pieceList[c][pt][index[s]] = s;
1550 set_bit(&(byTypeBB[pt]), s);
1551 set_bit(&(byColorBB[c]), s);
1552 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1556 /// Position::compute_key() computes the hash key of the position. The hash
1557 /// key is usually updated incrementally as moves are made and unmade, the
1558 /// compute_key() function is only used when a new position is set up, and
1559 /// to verify the correctness of the hash key when running in debug mode.
1561 Key Position::compute_key() const {
1563 Key result = zobCastle[st->castleRights];
1565 for (Square s = SQ_A1; s <= SQ_H8; s++)
1566 if (square_is_occupied(s))
1567 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1569 if (ep_square() != SQ_NONE)
1570 result ^= zobEp[ep_square()];
1572 if (side_to_move() == BLACK)
1573 result ^= zobSideToMove;
1579 /// Position::compute_pawn_key() computes the hash key of the position. The
1580 /// hash key is usually updated incrementally as moves are made and unmade,
1581 /// the compute_pawn_key() function is only used when a new position is set
1582 /// up, and to verify the correctness of the pawn hash key when running in
1585 Key Position::compute_pawn_key() const {
1590 for (Color c = WHITE; c <= BLACK; c++)
1592 b = pieces(PAWN, c);
1594 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1600 /// Position::compute_material_key() computes the hash key of the position.
1601 /// The hash key is usually updated incrementally as moves are made and unmade,
1602 /// the compute_material_key() function is only used when a new position is set
1603 /// up, and to verify the correctness of the material hash key when running in
1606 Key Position::compute_material_key() const {
1611 for (Color c = WHITE; c <= BLACK; c++)
1612 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1614 count = piece_count(c, pt);
1615 for (int i = 0; i < count; i++)
1616 result ^= zobrist[c][pt][i];
1622 /// Position::compute_value() compute the incremental scores for the middle
1623 /// game and the endgame. These functions are used to initialize the incremental
1624 /// scores when a new position is set up, and to verify that the scores are correctly
1625 /// updated by do_move and undo_move when the program is running in debug mode.
1626 Score Position::compute_value() const {
1629 Score result = SCORE_ZERO;
1631 for (Color c = WHITE; c <= BLACK; c++)
1632 for (PieceType pt = PAWN; pt <= KING; pt++)
1636 result += pst(c, pt, pop_1st_bit(&b));
1639 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1644 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1645 /// game material value for the given side. Material values are updated
1646 /// incrementally during the search, this function is only used while
1647 /// initializing a new Position object.
1649 Value Position::compute_non_pawn_material(Color c) const {
1651 Value result = VALUE_ZERO;
1653 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1654 result += piece_count(c, pt) * PieceValueMidgame[pt];
1660 /// Position::is_draw() tests whether the position is drawn by material,
1661 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1662 /// must be done by the search.
1664 bool Position::is_draw() const {
1666 // Draw by material?
1668 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1671 // Draw by the 50 moves rule?
1672 if (st->rule50 > 99 && !is_mate())
1675 // Draw by repetition?
1676 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1677 if (history[st->gamePly - i] == st->key)
1684 /// Position::is_mate() returns true or false depending on whether the
1685 /// side to move is checkmated.
1687 bool Position::is_mate() const {
1689 MoveStack moves[MOVES_MAX];
1690 return is_check() && generate<MV_LEGAL>(*this, moves) == moves;
1694 /// Position::init_zobrist() is a static member function which initializes at
1695 /// startup the various arrays used to compute hash keys.
1697 void Position::init_zobrist() {
1702 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1703 zobrist[i][j][k] = rk.rand<Key>();
1705 for (i = 0; i < 64; i++)
1706 zobEp[i] = rk.rand<Key>();
1708 for (i = 0; i < 16; i++)
1709 zobCastle[i] = rk.rand<Key>();
1711 zobSideToMove = rk.rand<Key>();
1712 zobExclusion = rk.rand<Key>();
1716 /// Position::init_piece_square_tables() initializes the piece square tables.
1717 /// This is a two-step operation: First, the white halves of the tables are
1718 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1719 /// of the tables are initialized by mirroring and changing the sign of the
1720 /// corresponding white scores.
1722 void Position::init_piece_square_tables() {
1724 for (Square s = SQ_A1; s <= SQ_H8; s++)
1725 for (Piece p = WP; p <= WK; p++)
1726 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1728 for (Square s = SQ_A1; s <= SQ_H8; s++)
1729 for (Piece p = BP; p <= BK; p++)
1730 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1734 /// Position::flipped_copy() makes a copy of the input position, but with
1735 /// the white and black sides reversed. This is only useful for debugging,
1736 /// especially for finding evaluation symmetry bugs.
1738 void Position::flipped_copy(const Position& pos) {
1740 assert(pos.is_ok());
1743 threadID = pos.thread();
1746 for (Square s = SQ_A1; s <= SQ_H8; s++)
1747 if (!pos.square_is_empty(s))
1748 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1751 sideToMove = opposite_color(pos.side_to_move());
1754 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1755 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1756 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1757 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1759 initialKFile = pos.initialKFile;
1760 initialKRFile = pos.initialKRFile;
1761 initialQRFile = pos.initialQRFile;
1763 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1764 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1765 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1766 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1767 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1768 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1770 // En passant square
1771 if (pos.st->epSquare != SQ_NONE)
1772 st->epSquare = flip_square(pos.st->epSquare);
1778 st->key = compute_key();
1779 st->pawnKey = compute_pawn_key();
1780 st->materialKey = compute_material_key();
1782 // Incremental scores
1783 st->value = compute_value();
1786 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1787 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1793 /// Position::is_ok() performs some consitency checks for the position object.
1794 /// This is meant to be helpful when debugging.
1796 bool Position::is_ok(int* failedStep) const {
1798 // What features of the position should be verified?
1799 const bool debugAll = false;
1801 const bool debugBitboards = debugAll || false;
1802 const bool debugKingCount = debugAll || false;
1803 const bool debugKingCapture = debugAll || false;
1804 const bool debugCheckerCount = debugAll || false;
1805 const bool debugKey = debugAll || false;
1806 const bool debugMaterialKey = debugAll || false;
1807 const bool debugPawnKey = debugAll || false;
1808 const bool debugIncrementalEval = debugAll || false;
1809 const bool debugNonPawnMaterial = debugAll || false;
1810 const bool debugPieceCounts = debugAll || false;
1811 const bool debugPieceList = debugAll || false;
1812 const bool debugCastleSquares = debugAll || false;
1814 if (failedStep) *failedStep = 1;
1817 if (!color_is_ok(side_to_move()))
1820 // Are the king squares in the position correct?
1821 if (failedStep) (*failedStep)++;
1822 if (piece_on(king_square(WHITE)) != WK)
1825 if (failedStep) (*failedStep)++;
1826 if (piece_on(king_square(BLACK)) != BK)
1830 if (failedStep) (*failedStep)++;
1831 if (!file_is_ok(initialKRFile))
1834 if (!file_is_ok(initialQRFile))
1837 // Do both sides have exactly one king?
1838 if (failedStep) (*failedStep)++;
1841 int kingCount[2] = {0, 0};
1842 for (Square s = SQ_A1; s <= SQ_H8; s++)
1843 if (type_of_piece_on(s) == KING)
1844 kingCount[color_of_piece_on(s)]++;
1846 if (kingCount[0] != 1 || kingCount[1] != 1)
1850 // Can the side to move capture the opponent's king?
1851 if (failedStep) (*failedStep)++;
1852 if (debugKingCapture)
1854 Color us = side_to_move();
1855 Color them = opposite_color(us);
1856 Square ksq = king_square(them);
1857 if (attackers_to(ksq) & pieces_of_color(us))
1861 // Is there more than 2 checkers?
1862 if (failedStep) (*failedStep)++;
1863 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1867 if (failedStep) (*failedStep)++;
1870 // The intersection of the white and black pieces must be empty
1871 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1874 // The union of the white and black pieces must be equal to all
1876 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1879 // Separate piece type bitboards must have empty intersections
1880 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1881 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1882 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1886 // En passant square OK?
1887 if (failedStep) (*failedStep)++;
1888 if (ep_square() != SQ_NONE)
1890 // The en passant square must be on rank 6, from the point of view of the
1892 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1897 if (failedStep) (*failedStep)++;
1898 if (debugKey && st->key != compute_key())
1901 // Pawn hash key OK?
1902 if (failedStep) (*failedStep)++;
1903 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1906 // Material hash key OK?
1907 if (failedStep) (*failedStep)++;
1908 if (debugMaterialKey && st->materialKey != compute_material_key())
1911 // Incremental eval OK?
1912 if (failedStep) (*failedStep)++;
1913 if (debugIncrementalEval && st->value != compute_value())
1916 // Non-pawn material OK?
1917 if (failedStep) (*failedStep)++;
1918 if (debugNonPawnMaterial)
1920 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1923 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1928 if (failedStep) (*failedStep)++;
1929 if (debugPieceCounts)
1930 for (Color c = WHITE; c <= BLACK; c++)
1931 for (PieceType pt = PAWN; pt <= KING; pt++)
1932 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1935 if (failedStep) (*failedStep)++;
1937 for (Color c = WHITE; c <= BLACK; c++)
1938 for (PieceType pt = PAWN; pt <= KING; pt++)
1939 for (int i = 0; i < pieceCount[c][pt]; i++)
1941 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
1944 if (index[piece_list(c, pt, i)] != i)
1948 if (failedStep) (*failedStep)++;
1949 if (debugCastleSquares)
1951 for (Color c = WHITE; c <= BLACK; c++)
1953 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
1956 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
1959 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
1961 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
1963 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
1965 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
1969 if (failedStep) *failedStep = 0;