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/>.
34 #include "ucioption.h"
40 Key Position::zobrist[2][8][64];
41 Key Position::zobEp[64];
42 Key Position::zobCastle[16];
43 Key Position::zobSideToMove;
44 Key Position::zobExclusion;
46 Score Position::PieceSquareTable[16][64];
48 // Material values arrays, indexed by Piece
49 const Value Position::PieceValueMidgame[17] = {
51 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
52 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
53 VALUE_ZERO, VALUE_ZERO,
54 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
55 RookValueMidgame, QueenValueMidgame
58 const Value Position::PieceValueEndgame[17] = {
60 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
61 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
62 VALUE_ZERO, VALUE_ZERO,
63 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
64 RookValueEndgame, QueenValueEndgame
67 // Material values array used by SEE, indexed by PieceType
68 const Value Position::seeValues[] = {
70 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
71 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
77 // Bonus for having the side to move (modified by Joona Kiiski)
78 const Score TempoValue = make_score(48, 22);
80 struct PieceLetters : public std::map<char, Piece> {
84 operator[]('K') = WK; operator[]('k') = BK;
85 operator[]('Q') = WQ; operator[]('q') = BQ;
86 operator[]('R') = WR; operator[]('r') = BR;
87 operator[]('B') = WB; operator[]('b') = BB;
88 operator[]('N') = WN; operator[]('n') = BN;
89 operator[]('P') = WP; operator[]('p') = BP;
90 operator[](' ') = PIECE_NONE;
91 operator[]('.') = PIECE_NONE_DARK_SQ;
94 char from_piece(Piece p) const {
96 std::map<char, Piece>::const_iterator it;
97 for (it = begin(); it != end(); ++it)
106 PieceLetters pieceLetters;
112 CheckInfo::CheckInfo(const Position& pos) {
114 Color us = pos.side_to_move();
115 Color them = opposite_color(us);
117 ksq = pos.king_square(them);
118 dcCandidates = pos.discovered_check_candidates(us);
120 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
121 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
122 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
123 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
124 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
125 checkSq[KING] = EmptyBoardBB;
129 /// Position c'tors. Here we always create a copy of the original position
130 /// or the FEN string, we want the new born Position object do not depend
131 /// on any external data so we detach state pointer from the source one.
133 Position::Position(const Position& pos, int th) {
135 memcpy(this, &pos, sizeof(Position));
136 detach(); // Always detach() in copy c'tor to avoid surprises
141 Position::Position(const string& fen, bool isChess960, int th) {
143 from_fen(fen, isChess960);
148 /// Position::detach() copies the content of the current state and castling
149 /// masks inside the position itself. This is needed when the st pointee could
150 /// become stale, as example because the caller is about to going out of scope.
152 void Position::detach() {
156 st->previous = NULL; // as a safe guard
160 /// Position::from_fen() initializes the position object with the given FEN
161 /// string. This function is not very robust - make sure that input FENs are
162 /// correct (this is assumed to be the responsibility of the GUI).
164 void Position::from_fen(const string& fen, bool isChess960) {
166 A FEN string defines a particular position using only the ASCII character set.
168 A FEN string contains six fields. The separator between fields is a space. The fields are:
170 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
171 with rank 1; within each rank, the contents of each square are described from file A through file H.
172 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
173 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
174 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
175 of blank squares), and "/" separate ranks.
177 2) Active color. "w" means white moves next, "b" means black.
179 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
180 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
181 kingside), and/or "q" (Black can castle queenside).
183 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
184 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
185 regardless of whether there is a pawn in position to make an en passant capture.
187 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
188 to determine if a draw can be claimed under the fifty-move rule.
190 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
195 std::istringstream ss(fen);
200 // 1. Piece placement field
201 while (ss.get(token) && token != ' ')
203 if (pieceLetters.find(token) != pieceLetters.end())
205 put_piece(pieceLetters[token], sq);
208 else if (isdigit(token))
209 sq += Square(token - '0'); // Skip the given number of files
210 else if (token == '/')
211 sq -= SQ_A3; // Jump back of 2 rows
217 if (!ss.get(token) || (token != 'w' && token != 'b'))
220 sideToMove = (token == 'w' ? WHITE : BLACK);
222 if (!ss.get(token) || token != ' ')
225 // 3. Castling availability
226 while (ss.get(token) && token != ' ')
227 if (!set_castling_rights(token))
230 // 4. En passant square
232 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
233 && (ss.get(row) && (row == '3' || row == '6')))
235 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
237 // Ignore if no capture is possible
238 Color them = opposite_color(sideToMove);
239 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
240 st->epSquare = SQ_NONE;
247 // 6. Fullmove number
249 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
251 // Various initialisations
252 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
253 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
254 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
255 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
256 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
257 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
259 chess960 = isChess960;
262 st->key = compute_key();
263 st->pawnKey = compute_pawn_key();
264 st->materialKey = compute_material_key();
265 st->value = compute_value();
266 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
267 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
271 cout << "Error in FEN string: " << fen << endl;
275 /// Position::set_castling_rights() sets castling parameters castling avaiability.
276 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
277 /// that uses the letters of the columns on which the rooks began the game instead
278 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
279 /// associated with the castling right, the traditional castling tag will be replaced
280 /// by the file letter of the involved rook as for the Shredder-FEN.
282 bool Position::set_castling_rights(char token) {
284 Color c = token >= 'a' ? BLACK : WHITE;
285 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
286 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
287 Piece rook = (c == WHITE ? WR : BR);
289 initialKFile = square_file(king_square(c));
290 token = char(toupper(token));
294 for (Square sq = sqH; sq >= sqA; sq--)
295 if (piece_on(sq) == rook)
298 initialKRFile = square_file(sq);
302 else if (token == 'Q')
304 for (Square sq = sqA; sq <= sqH; sq++)
305 if (piece_on(sq) == rook)
308 initialQRFile = square_file(sq);
312 else if (token >= 'A' && token <= 'H')
314 File rookFile = File(token - 'A') + FILE_A;
315 if (rookFile < initialKFile)
318 initialQRFile = rookFile;
323 initialKRFile = rookFile;
333 /// Position::to_fen() returns a FEN representation of the position. In case
334 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
336 const string Position::to_fen() const {
342 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
344 for (File file = FILE_A; file <= FILE_H; file++)
346 sq = make_square(file, rank);
348 if (square_is_occupied(sq))
355 fen += pieceLetters.from_piece(piece_on(sq));
367 fen += (sideToMove == WHITE ? " w " : " b ");
369 if (st->castleRights != CASTLES_NONE)
371 if (can_castle_kingside(WHITE))
372 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
374 if (can_castle_queenside(WHITE))
375 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
377 if (can_castle_kingside(BLACK))
378 fen += chess960 ? file_to_char(initialKRFile) : 'k';
380 if (can_castle_queenside(BLACK))
381 fen += chess960 ? file_to_char(initialQRFile) : 'q';
385 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
390 /// Position::print() prints an ASCII representation of the position to
391 /// the standard output. If a move is given then also the san is printed.
393 void Position::print(Move move) const {
395 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
399 Position p(*this, thread());
400 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
401 cout << "\nMove is: " << dd << move_to_san(p, move);
404 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
406 cout << dottedLine << '|';
407 for (File file = FILE_A; file <= FILE_H; file++)
409 Square sq = make_square(file, rank);
410 Piece piece = piece_on(sq);
412 if (piece == PIECE_NONE && square_color(sq) == DARK)
413 piece = PIECE_NONE_DARK_SQ;
415 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
416 cout << c << pieceLetters.from_piece(piece) << c << '|';
419 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
423 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
424 /// king) pieces for the given color and for the given pinner type. Or, when
425 /// template parameter FindPinned is false, the pieces of the given color
426 /// candidate for a discovery check against the enemy king.
427 /// Bitboard checkersBB must be already updated when looking for pinners.
429 template<bool FindPinned>
430 Bitboard Position::hidden_checkers(Color c) const {
432 Bitboard result = EmptyBoardBB;
433 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
435 // Pinned pieces protect our king, dicovery checks attack
437 Square ksq = king_square(FindPinned ? c : opposite_color(c));
439 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
440 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
442 if (FindPinned && pinners)
443 pinners &= ~st->checkersBB;
447 Square s = pop_1st_bit(&pinners);
448 Bitboard b = squares_between(s, ksq) & occupied_squares();
452 if ( !(b & (b - 1)) // Only one bit set?
453 && (b & pieces_of_color(c))) // Is an our piece?
460 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
461 /// king) pieces for the given color. Note that checkersBB bitboard must
462 /// be already updated.
464 Bitboard Position::pinned_pieces(Color c) const {
466 return hidden_checkers<true>(c);
470 /// Position:discovered_check_candidates() returns a bitboard containing all
471 /// pieces for the given side which are candidates for giving a discovered
472 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
473 /// to be already updated.
475 Bitboard Position::discovered_check_candidates(Color c) const {
477 return hidden_checkers<false>(c);
480 /// Position::attackers_to() computes a bitboard containing all pieces which
481 /// attacks a given square.
483 Bitboard Position::attackers_to(Square s) const {
485 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
486 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
487 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
488 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
489 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
490 | (attacks_from<KING>(s) & pieces(KING));
493 /// Position::attacks_from() computes a bitboard of all attacks
494 /// of a given piece put in a given square.
496 Bitboard Position::attacks_from(Piece p, Square s) const {
498 assert(square_is_ok(s));
502 case WB: case BB: return attacks_from<BISHOP>(s);
503 case WR: case BR: return attacks_from<ROOK>(s);
504 case WQ: case BQ: return attacks_from<QUEEN>(s);
505 default: return StepAttacksBB[p][s];
509 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
511 assert(square_is_ok(s));
515 case WB: case BB: return bishop_attacks_bb(s, occ);
516 case WR: case BR: return rook_attacks_bb(s, occ);
517 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
518 default: return StepAttacksBB[p][s];
523 /// Position::move_attacks_square() tests whether a move from the current
524 /// position attacks a given square.
526 bool Position::move_attacks_square(Move m, Square s) const {
528 assert(move_is_ok(m));
529 assert(square_is_ok(s));
532 Square f = move_from(m), t = move_to(m);
534 assert(square_is_occupied(f));
536 if (bit_is_set(attacks_from(piece_on(f), t), s))
539 // Move the piece and scan for X-ray attacks behind it
540 occ = occupied_squares();
541 do_move_bb(&occ, make_move_bb(f, t));
542 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
543 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
544 & pieces_of_color(color_of_piece_on(f));
546 // If we have attacks we need to verify that are caused by our move
547 // and are not already existent ones.
548 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
552 /// Position::find_checkers() computes the checkersBB bitboard, which
553 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
554 /// currently works by calling Position::attackers_to, which is probably
555 /// inefficient. Consider rewriting this function to use the last move
556 /// played, like in non-bitboard versions of Glaurung.
558 void Position::find_checkers() {
560 Color us = side_to_move();
561 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
565 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
567 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
570 assert(move_is_ok(m));
571 assert(pinned == pinned_pieces(side_to_move()));
573 // En passant captures are a tricky special case. Because they are
574 // rather uncommon, we do it simply by testing whether the king is attacked
575 // after the move is made
578 Color us = side_to_move();
579 Color them = opposite_color(us);
580 Square from = move_from(m);
581 Square to = move_to(m);
582 Square capsq = make_square(square_file(to), square_rank(from));
583 Square ksq = king_square(us);
584 Bitboard b = occupied_squares();
586 assert(to == ep_square());
587 assert(piece_on(from) == make_piece(us, PAWN));
588 assert(piece_on(capsq) == make_piece(them, PAWN));
589 assert(piece_on(to) == PIECE_NONE);
592 clear_bit(&b, capsq);
595 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
596 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
599 Color us = side_to_move();
600 Square from = move_from(m);
602 assert(color_of_piece_on(from) == us);
603 assert(piece_on(king_square(us)) == make_piece(us, KING));
605 // If the moving piece is a king, check whether the destination
606 // square is attacked by the opponent. Castling moves are checked
607 // for legality during move generation.
608 if (type_of_piece_on(from) == KING)
609 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
611 // A non-king move is legal if and only if it is not pinned or it
612 // is moving along the ray towards or away from the king.
614 || !bit_is_set(pinned, from)
615 || squares_aligned(from, move_to(m), king_square(us));
619 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
621 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
625 Color us = side_to_move();
626 Square from = move_from(m);
627 Square to = move_to(m);
629 // King moves and en-passant captures are verified in pl_move_is_legal()
630 if (type_of_piece_on(from) == KING || move_is_ep(m))
631 return pl_move_is_legal(m, pinned);
633 Bitboard target = checkers();
634 Square checksq = pop_1st_bit(&target);
636 if (target) // double check ?
639 // Our move must be a blocking evasion or a capture of the checking piece
640 target = squares_between(checksq, king_square(us)) | checkers();
641 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
644 /// Position::move_is_legal() takes a position and a (not necessarily pseudo-legal)
645 /// move and tests whether the move is legal. This version is not very fast and
646 /// should be used only in non time-critical paths.
648 bool Position::move_is_legal(const Move m) const {
650 MoveStack mlist[MAX_MOVES];
651 MoveStack *cur, *last = generate<MV_PSEUDO_LEGAL>(*this, mlist);
653 for (cur = mlist; cur != last; cur++)
655 return pl_move_is_legal(m, pinned_pieces(sideToMove));
661 /// Fast version of Position::move_is_legal() that takes a position a move and
662 /// a bitboard of pinned pieces as input, and tests whether the move is legal.
664 bool Position::move_is_legal(const Move m, Bitboard pinned) const {
667 assert(pinned == pinned_pieces(sideToMove));
669 Color us = sideToMove;
670 Color them = opposite_color(sideToMove);
671 Square from = move_from(m);
672 Square to = move_to(m);
673 Piece pc = piece_on(from);
675 // Use a slower but simpler function for uncommon cases
676 if (move_is_special(m))
677 return move_is_legal(m);
679 // If the from square is not occupied by a piece belonging to the side to
680 // move, the move is obviously not legal.
681 if (color_of_piece(pc) != us)
684 // The destination square cannot be occupied by a friendly piece
685 if (color_of_piece_on(to) == us)
688 // Handle the special case of a pawn move
689 if (type_of_piece(pc) == PAWN)
691 // Move direction must be compatible with pawn color
692 int direction = to - from;
693 if ((us == WHITE) != (direction > 0))
696 // We have already handled promotion moves, so destination
697 // cannot be on the 8/1th rank.
698 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
701 // Proceed according to the square delta between the origin and
702 // destination squares.
709 // Capture. The destination square must be occupied by an enemy
710 // piece (en passant captures was handled earlier).
711 if (color_of_piece_on(to) != them)
717 // Pawn push. The destination square must be empty.
718 if (!square_is_empty(to))
723 // Double white pawn push. The destination square must be on the fourth
724 // rank, and both the destination square and the square between the
725 // source and destination squares must be empty.
726 if ( square_rank(to) != RANK_4
727 || !square_is_empty(to)
728 || !square_is_empty(from + DELTA_N))
733 // Double black pawn push. The destination square must be on the fifth
734 // rank, and both the destination square and the square between the
735 // source and destination squares must be empty.
736 if ( square_rank(to) != RANK_5
737 || !square_is_empty(to)
738 || !square_is_empty(from + DELTA_S))
746 else if (!bit_is_set(attacks_from(pc, from), to))
749 // The move is pseudo-legal, check if it is also legal
750 return in_check() ? pl_move_is_evasion(m, pinned) : pl_move_is_legal(m, pinned);
754 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
756 bool Position::move_gives_check(Move m) const {
758 return move_gives_check(m, CheckInfo(*this));
761 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
764 assert(move_is_ok(m));
765 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
766 assert(color_of_piece_on(move_from(m)) == side_to_move());
767 assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
769 Square from = move_from(m);
770 Square to = move_to(m);
771 PieceType pt = type_of_piece_on(from);
774 if (bit_is_set(ci.checkSq[pt], to))
778 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
780 // For pawn and king moves we need to verify also direction
781 if ( (pt != PAWN && pt != KING)
782 || !squares_aligned(from, to, ci.ksq))
786 // Can we skip the ugly special cases ?
787 if (!move_is_special(m))
790 Color us = side_to_move();
791 Bitboard b = occupied_squares();
793 // Promotion with check ?
794 if (move_is_promotion(m))
798 switch (move_promotion_piece(m))
801 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
803 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
805 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
807 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
813 // En passant capture with check ? We have already handled the case
814 // of direct checks and ordinary discovered check, the only case we
815 // need to handle is the unusual case of a discovered check through
816 // the captured pawn.
819 Square capsq = make_square(square_file(to), square_rank(from));
821 clear_bit(&b, capsq);
823 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
824 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
827 // Castling with check ?
828 if (move_is_castle(m))
830 Square kfrom, kto, rfrom, rto;
836 kto = relative_square(us, SQ_G1);
837 rto = relative_square(us, SQ_F1);
839 kto = relative_square(us, SQ_C1);
840 rto = relative_square(us, SQ_D1);
842 clear_bit(&b, kfrom);
843 clear_bit(&b, rfrom);
846 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
853 /// Position::do_setup_move() makes a permanent move on the board. It should
854 /// be used when setting up a position on board. You can't undo the move.
856 void Position::do_setup_move(Move m) {
862 // Reset "game ply" in case we made a non-reversible move.
863 // "game ply" is used for repetition detection.
867 // Update the number of plies played from the starting position
868 startPosPlyCounter++;
870 // Our StateInfo newSt is about going out of scope so copy
871 // its content before it disappears.
876 /// Position::do_move() makes a move, and saves all information necessary
877 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
878 /// moves should be filtered out before this function is called.
880 void Position::do_move(Move m, StateInfo& newSt) {
883 do_move(m, newSt, ci, move_gives_check(m, ci));
886 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
889 assert(move_is_ok(m));
890 assert(&newSt != st);
895 // Copy some fields of old state to our new StateInfo object except the
896 // ones which are recalculated from scratch anyway, then switch our state
897 // pointer to point to the new, ready to be updated, state.
898 struct ReducedStateInfo {
899 Key pawnKey, materialKey;
900 int castleRights, rule50, gamePly, pliesFromNull;
906 memcpy(&newSt, st, sizeof(ReducedStateInfo));
911 // Save the current key to the history[] array, in order to be able to
912 // detect repetition draws.
913 history[st->gamePly++] = key;
915 // Update side to move
916 key ^= zobSideToMove;
918 // Increment the 50 moves rule draw counter. Resetting it to zero in the
919 // case of non-reversible moves is taken care of later.
923 if (move_is_castle(m))
930 Color us = side_to_move();
931 Color them = opposite_color(us);
932 Square from = move_from(m);
933 Square to = move_to(m);
934 bool ep = move_is_ep(m);
935 bool pm = move_is_promotion(m);
937 Piece piece = piece_on(from);
938 PieceType pt = type_of_piece(piece);
939 PieceType capture = ep ? PAWN : type_of_piece_on(to);
941 assert(color_of_piece_on(from) == us);
942 assert(color_of_piece_on(to) == them || square_is_empty(to));
943 assert(!(ep || pm) || piece == make_piece(us, PAWN));
944 assert(!pm || relative_rank(us, to) == RANK_8);
947 do_capture_move(key, capture, them, to, ep);
950 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
952 // Reset en passant square
953 if (st->epSquare != SQ_NONE)
955 key ^= zobEp[st->epSquare];
956 st->epSquare = SQ_NONE;
959 // Update castle rights, try to shortcut a common case
960 int cm = castleRightsMask[from] & castleRightsMask[to];
961 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
963 key ^= zobCastle[st->castleRights];
964 st->castleRights &= castleRightsMask[from];
965 st->castleRights &= castleRightsMask[to];
966 key ^= zobCastle[st->castleRights];
969 // Prefetch TT access as soon as we know key is updated
970 prefetch((char*)TT.first_entry(key));
973 Bitboard move_bb = make_move_bb(from, to);
974 do_move_bb(&(byColorBB[us]), move_bb);
975 do_move_bb(&(byTypeBB[pt]), move_bb);
976 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
978 board[to] = board[from];
979 board[from] = PIECE_NONE;
981 // Update piece lists, note that index[from] is not updated and
982 // becomes stale. This works as long as index[] is accessed just
983 // by known occupied squares.
984 index[to] = index[from];
985 pieceList[us][pt][index[to]] = to;
987 // If the moving piece was a pawn do some special extra work
990 // Reset rule 50 draw counter
993 // Update pawn hash key and prefetch in L1/L2 cache
994 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
996 // Set en passant square, only if moved pawn can be captured
997 if ((to ^ from) == 16)
999 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
1001 st->epSquare = Square((int(from) + int(to)) / 2);
1002 key ^= zobEp[st->epSquare];
1006 if (pm) // promotion ?
1008 PieceType promotion = move_promotion_piece(m);
1010 assert(promotion >= KNIGHT && promotion <= QUEEN);
1012 // Insert promoted piece instead of pawn
1013 clear_bit(&(byTypeBB[PAWN]), to);
1014 set_bit(&(byTypeBB[promotion]), to);
1015 board[to] = make_piece(us, promotion);
1017 // Update piece counts
1018 pieceCount[us][promotion]++;
1019 pieceCount[us][PAWN]--;
1021 // Update material key
1022 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
1023 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
1025 // Update piece lists, move the last pawn at index[to] position
1026 // and shrink the list. Add a new promotion piece to the list.
1027 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
1028 index[lastPawnSquare] = index[to];
1029 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
1030 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
1031 index[to] = pieceCount[us][promotion] - 1;
1032 pieceList[us][promotion][index[to]] = to;
1034 // Partially revert hash keys update
1035 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
1036 st->pawnKey ^= zobrist[us][PAWN][to];
1038 // Partially revert and update incremental scores
1039 st->value -= pst(us, PAWN, to);
1040 st->value += pst(us, promotion, to);
1043 st->npMaterial[us] += PieceValueMidgame[promotion];
1047 // Prefetch pawn and material hash tables
1048 Threads[threadID].pawnTable.prefetch(st->pawnKey);
1049 Threads[threadID].materialTable.prefetch(st->materialKey);
1051 // Update incremental scores
1052 st->value += pst_delta(piece, from, to);
1054 // Set capture piece
1055 st->capturedType = capture;
1057 // Update the key with the final value
1060 // Update checkers bitboard, piece must be already moved
1061 st->checkersBB = EmptyBoardBB;
1066 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1070 if (bit_is_set(ci.checkSq[pt], to))
1071 st->checkersBB = SetMaskBB[to];
1074 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1077 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
1080 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
1086 sideToMove = opposite_color(sideToMove);
1087 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1093 /// Position::do_capture_move() is a private method used to update captured
1094 /// piece info. It is called from the main Position::do_move function.
1096 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1098 assert(capture != KING);
1102 // If the captured piece was a pawn, update pawn hash key,
1103 // otherwise update non-pawn material.
1104 if (capture == PAWN)
1106 if (ep) // en passant ?
1108 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1110 assert(to == st->epSquare);
1111 assert(relative_rank(opposite_color(them), to) == RANK_6);
1112 assert(piece_on(to) == PIECE_NONE);
1113 assert(piece_on(capsq) == make_piece(them, PAWN));
1115 board[capsq] = PIECE_NONE;
1117 st->pawnKey ^= zobrist[them][PAWN][capsq];
1120 st->npMaterial[them] -= PieceValueMidgame[capture];
1122 // Remove captured piece
1123 clear_bit(&(byColorBB[them]), capsq);
1124 clear_bit(&(byTypeBB[capture]), capsq);
1125 clear_bit(&(byTypeBB[0]), capsq);
1128 key ^= zobrist[them][capture][capsq];
1130 // Update incremental scores
1131 st->value -= pst(them, capture, capsq);
1133 // Update piece count
1134 pieceCount[them][capture]--;
1136 // Update material hash key
1137 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1139 // Update piece list, move the last piece at index[capsq] position
1141 // WARNING: This is a not perfectly revresible operation. When we
1142 // will reinsert the captured piece in undo_move() we will put it
1143 // at the end of the list and not in its original place, it means
1144 // index[] and pieceList[] are not guaranteed to be invariant to a
1145 // do_move() + undo_move() sequence.
1146 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1147 index[lastPieceSquare] = index[capsq];
1148 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1149 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1151 // Reset rule 50 counter
1156 /// Position::do_castle_move() is a private method used to make a castling
1157 /// move. It is called from the main Position::do_move function. Note that
1158 /// castling moves are encoded as "king captures friendly rook" moves, for
1159 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1161 void Position::do_castle_move(Move m) {
1163 assert(move_is_ok(m));
1164 assert(move_is_castle(m));
1166 Color us = side_to_move();
1167 Color them = opposite_color(us);
1169 // Reset capture field
1170 st->capturedType = PIECE_TYPE_NONE;
1172 // Find source squares for king and rook
1173 Square kfrom = move_from(m);
1174 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1177 assert(piece_on(kfrom) == make_piece(us, KING));
1178 assert(piece_on(rfrom) == make_piece(us, ROOK));
1180 // Find destination squares for king and rook
1181 if (rfrom > kfrom) // O-O
1183 kto = relative_square(us, SQ_G1);
1184 rto = relative_square(us, SQ_F1);
1186 kto = relative_square(us, SQ_C1);
1187 rto = relative_square(us, SQ_D1);
1190 // Remove pieces from source squares:
1191 clear_bit(&(byColorBB[us]), kfrom);
1192 clear_bit(&(byTypeBB[KING]), kfrom);
1193 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1194 clear_bit(&(byColorBB[us]), rfrom);
1195 clear_bit(&(byTypeBB[ROOK]), rfrom);
1196 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1198 // Put pieces on destination squares:
1199 set_bit(&(byColorBB[us]), kto);
1200 set_bit(&(byTypeBB[KING]), kto);
1201 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1202 set_bit(&(byColorBB[us]), rto);
1203 set_bit(&(byTypeBB[ROOK]), rto);
1204 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1206 // Update board array
1207 Piece king = make_piece(us, KING);
1208 Piece rook = make_piece(us, ROOK);
1209 board[kfrom] = board[rfrom] = PIECE_NONE;
1213 // Update piece lists
1214 pieceList[us][KING][index[kfrom]] = kto;
1215 pieceList[us][ROOK][index[rfrom]] = rto;
1216 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1217 index[kto] = index[kfrom];
1220 // Update incremental scores
1221 st->value += pst_delta(king, kfrom, kto);
1222 st->value += pst_delta(rook, rfrom, rto);
1225 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1226 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1228 // Clear en passant square
1229 if (st->epSquare != SQ_NONE)
1231 st->key ^= zobEp[st->epSquare];
1232 st->epSquare = SQ_NONE;
1235 // Update castling rights
1236 st->key ^= zobCastle[st->castleRights];
1237 st->castleRights &= castleRightsMask[kfrom];
1238 st->key ^= zobCastle[st->castleRights];
1240 // Reset rule 50 counter
1243 // Update checkers BB
1244 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1247 sideToMove = opposite_color(sideToMove);
1248 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1254 /// Position::undo_move() unmakes a move. When it returns, the position should
1255 /// be restored to exactly the same state as before the move was made.
1257 void Position::undo_move(Move m) {
1260 assert(move_is_ok(m));
1262 sideToMove = opposite_color(sideToMove);
1264 if (move_is_castle(m))
1266 undo_castle_move(m);
1270 Color us = side_to_move();
1271 Color them = opposite_color(us);
1272 Square from = move_from(m);
1273 Square to = move_to(m);
1274 bool ep = move_is_ep(m);
1275 bool pm = move_is_promotion(m);
1277 PieceType pt = type_of_piece_on(to);
1279 assert(square_is_empty(from));
1280 assert(color_of_piece_on(to) == us);
1281 assert(!pm || relative_rank(us, to) == RANK_8);
1282 assert(!ep || to == st->previous->epSquare);
1283 assert(!ep || relative_rank(us, to) == RANK_6);
1284 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1286 if (pm) // promotion ?
1288 PieceType promotion = move_promotion_piece(m);
1291 assert(promotion >= KNIGHT && promotion <= QUEEN);
1292 assert(piece_on(to) == make_piece(us, promotion));
1294 // Replace promoted piece with a pawn
1295 clear_bit(&(byTypeBB[promotion]), to);
1296 set_bit(&(byTypeBB[PAWN]), to);
1298 // Update piece counts
1299 pieceCount[us][promotion]--;
1300 pieceCount[us][PAWN]++;
1302 // Update piece list replacing promotion piece with a pawn
1303 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1304 index[lastPromotionSquare] = index[to];
1305 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1306 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1307 index[to] = pieceCount[us][PAWN] - 1;
1308 pieceList[us][PAWN][index[to]] = to;
1311 // Put the piece back at the source square
1312 Bitboard move_bb = make_move_bb(to, from);
1313 do_move_bb(&(byColorBB[us]), move_bb);
1314 do_move_bb(&(byTypeBB[pt]), move_bb);
1315 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1317 board[from] = make_piece(us, pt);
1318 board[to] = PIECE_NONE;
1320 // Update piece list
1321 index[from] = index[to];
1322 pieceList[us][pt][index[from]] = from;
1324 if (st->capturedType)
1329 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1331 assert(st->capturedType != KING);
1332 assert(!ep || square_is_empty(capsq));
1334 // Restore the captured piece
1335 set_bit(&(byColorBB[them]), capsq);
1336 set_bit(&(byTypeBB[st->capturedType]), capsq);
1337 set_bit(&(byTypeBB[0]), capsq);
1339 board[capsq] = make_piece(them, st->capturedType);
1341 // Update piece count
1342 pieceCount[them][st->capturedType]++;
1344 // Update piece list, add a new captured piece in capsq square
1345 index[capsq] = pieceCount[them][st->capturedType] - 1;
1346 pieceList[them][st->capturedType][index[capsq]] = capsq;
1349 // Finally point our state pointer back to the previous state
1356 /// Position::undo_castle_move() is a private method used to unmake a castling
1357 /// move. It is called from the main Position::undo_move function. Note that
1358 /// castling moves are encoded as "king captures friendly rook" moves, for
1359 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1361 void Position::undo_castle_move(Move m) {
1363 assert(move_is_ok(m));
1364 assert(move_is_castle(m));
1366 // When we have arrived here, some work has already been done by
1367 // Position::undo_move. In particular, the side to move has been switched,
1368 // so the code below is correct.
1369 Color us = side_to_move();
1371 // Find source squares for king and rook
1372 Square kfrom = move_from(m);
1373 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1376 // Find destination squares for king and rook
1377 if (rfrom > kfrom) // O-O
1379 kto = relative_square(us, SQ_G1);
1380 rto = relative_square(us, SQ_F1);
1382 kto = relative_square(us, SQ_C1);
1383 rto = relative_square(us, SQ_D1);
1386 assert(piece_on(kto) == make_piece(us, KING));
1387 assert(piece_on(rto) == make_piece(us, ROOK));
1389 // Remove pieces from destination squares:
1390 clear_bit(&(byColorBB[us]), kto);
1391 clear_bit(&(byTypeBB[KING]), kto);
1392 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1393 clear_bit(&(byColorBB[us]), rto);
1394 clear_bit(&(byTypeBB[ROOK]), rto);
1395 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1397 // Put pieces on source squares:
1398 set_bit(&(byColorBB[us]), kfrom);
1399 set_bit(&(byTypeBB[KING]), kfrom);
1400 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1401 set_bit(&(byColorBB[us]), rfrom);
1402 set_bit(&(byTypeBB[ROOK]), rfrom);
1403 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1406 board[rto] = board[kto] = PIECE_NONE;
1407 board[rfrom] = make_piece(us, ROOK);
1408 board[kfrom] = make_piece(us, KING);
1410 // Update piece lists
1411 pieceList[us][KING][index[kto]] = kfrom;
1412 pieceList[us][ROOK][index[rto]] = rfrom;
1413 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1414 index[kfrom] = index[kto];
1417 // Finally point our state pointer back to the previous state
1424 /// Position::do_null_move makes() a "null move": It switches the side to move
1425 /// and updates the hash key without executing any move on the board.
1427 void Position::do_null_move(StateInfo& backupSt) {
1430 assert(!in_check());
1432 // Back up the information necessary to undo the null move to the supplied
1433 // StateInfo object.
1434 // Note that differently from normal case here backupSt is actually used as
1435 // a backup storage not as a new state to be used.
1436 backupSt.key = st->key;
1437 backupSt.epSquare = st->epSquare;
1438 backupSt.value = st->value;
1439 backupSt.previous = st->previous;
1440 backupSt.pliesFromNull = st->pliesFromNull;
1441 st->previous = &backupSt;
1443 // Save the current key to the history[] array, in order to be able to
1444 // detect repetition draws.
1445 history[st->gamePly++] = st->key;
1447 // Update the necessary information
1448 if (st->epSquare != SQ_NONE)
1449 st->key ^= zobEp[st->epSquare];
1451 st->key ^= zobSideToMove;
1452 prefetch((char*)TT.first_entry(st->key));
1454 sideToMove = opposite_color(sideToMove);
1455 st->epSquare = SQ_NONE;
1457 st->pliesFromNull = 0;
1458 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1462 /// Position::undo_null_move() unmakes a "null move".
1464 void Position::undo_null_move() {
1467 assert(!in_check());
1469 // Restore information from the our backup StateInfo object
1470 StateInfo* backupSt = st->previous;
1471 st->key = backupSt->key;
1472 st->epSquare = backupSt->epSquare;
1473 st->value = backupSt->value;
1474 st->previous = backupSt->previous;
1475 st->pliesFromNull = backupSt->pliesFromNull;
1477 // Update the necessary information
1478 sideToMove = opposite_color(sideToMove);
1484 /// Position::see() is a static exchange evaluator: It tries to estimate the
1485 /// material gain or loss resulting from a move. There are three versions of
1486 /// this function: One which takes a destination square as input, one takes a
1487 /// move, and one which takes a 'from' and a 'to' square. The function does
1488 /// not yet understand promotions captures.
1490 int Position::see_sign(Move m) const {
1492 assert(move_is_ok(m));
1494 Square from = move_from(m);
1495 Square to = move_to(m);
1497 // Early return if SEE cannot be negative because captured piece value
1498 // is not less then capturing one. Note that king moves always return
1499 // here because king midgame value is set to 0.
1500 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1506 int Position::see(Move m) const {
1509 Bitboard occupied, attackers, stmAttackers, b;
1510 int swapList[32], slIndex = 1;
1511 PieceType capturedType, pt;
1514 assert(move_is_ok(m));
1516 // As castle moves are implemented as capturing the rook, they have
1517 // SEE == RookValueMidgame most of the times (unless the rook is under
1519 if (move_is_castle(m))
1522 from = move_from(m);
1524 capturedType = type_of_piece_on(to);
1525 occupied = occupied_squares();
1527 // Handle en passant moves
1528 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1530 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1532 assert(capturedType == PIECE_TYPE_NONE);
1533 assert(type_of_piece_on(capQq) == PAWN);
1535 // Remove the captured pawn
1536 clear_bit(&occupied, capQq);
1537 capturedType = PAWN;
1540 // Find all attackers to the destination square, with the moving piece
1541 // removed, but possibly an X-ray attacker added behind it.
1542 clear_bit(&occupied, from);
1543 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1544 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1545 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1546 | (attacks_from<KING>(to) & pieces(KING))
1547 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1548 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1550 // If the opponent has no attackers we are finished
1551 stm = opposite_color(color_of_piece_on(from));
1552 stmAttackers = attackers & pieces_of_color(stm);
1554 return seeValues[capturedType];
1556 // The destination square is defended, which makes things rather more
1557 // difficult to compute. We proceed by building up a "swap list" containing
1558 // the material gain or loss at each stop in a sequence of captures to the
1559 // destination square, where the sides alternately capture, and always
1560 // capture with the least valuable piece. After each capture, we look for
1561 // new X-ray attacks from behind the capturing piece.
1562 swapList[0] = seeValues[capturedType];
1563 capturedType = type_of_piece_on(from);
1566 // Locate the least valuable attacker for the side to move. The loop
1567 // below looks like it is potentially infinite, but it isn't. We know
1568 // that the side to move still has at least one attacker left.
1569 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1572 // Remove the attacker we just found from the 'occupied' bitboard,
1573 // and scan for new X-ray attacks behind the attacker.
1574 b = stmAttackers & pieces(pt);
1575 occupied ^= (b & (~b + 1));
1576 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1577 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1579 attackers &= occupied; // Cut out pieces we've already done
1581 // Add the new entry to the swap list
1582 assert(slIndex < 32);
1583 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1586 // Remember the value of the capturing piece, and change the side to
1587 // move before beginning the next iteration.
1589 stm = opposite_color(stm);
1590 stmAttackers = attackers & pieces_of_color(stm);
1592 // Stop before processing a king capture
1593 if (capturedType == KING && stmAttackers)
1595 assert(slIndex < 32);
1596 swapList[slIndex++] = QueenValueMidgame*10;
1599 } while (stmAttackers);
1601 // Having built the swap list, we negamax through it to find the best
1602 // achievable score from the point of view of the side to move.
1604 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1610 /// Position::clear() erases the position object to a pristine state, with an
1611 /// empty board, white to move, and no castling rights.
1613 void Position::clear() {
1616 memset(st, 0, sizeof(StateInfo));
1617 st->epSquare = SQ_NONE;
1618 startPosPlyCounter = 0;
1621 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1622 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1623 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1624 memset(index, 0, sizeof(int) * 64);
1626 for (int i = 0; i < 64; i++)
1627 board[i] = PIECE_NONE;
1629 for (int i = 0; i < 8; i++)
1630 for (int j = 0; j < 16; j++)
1631 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1633 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1634 castleRightsMask[sq] = ALL_CASTLES;
1637 initialKFile = FILE_E;
1638 initialKRFile = FILE_H;
1639 initialQRFile = FILE_A;
1643 /// Position::put_piece() puts a piece on the given square of the board,
1644 /// updating the board array, pieces list, bitboards, and piece counts.
1646 void Position::put_piece(Piece p, Square s) {
1648 Color c = color_of_piece(p);
1649 PieceType pt = type_of_piece(p);
1652 index[s] = pieceCount[c][pt]++;
1653 pieceList[c][pt][index[s]] = s;
1655 set_bit(&(byTypeBB[pt]), s);
1656 set_bit(&(byColorBB[c]), s);
1657 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1661 /// Position::compute_key() computes the hash key of the position. The hash
1662 /// key is usually updated incrementally as moves are made and unmade, the
1663 /// compute_key() function is only used when a new position is set up, and
1664 /// to verify the correctness of the hash key when running in debug mode.
1666 Key Position::compute_key() const {
1668 Key result = zobCastle[st->castleRights];
1670 for (Square s = SQ_A1; s <= SQ_H8; s++)
1671 if (square_is_occupied(s))
1672 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1674 if (ep_square() != SQ_NONE)
1675 result ^= zobEp[ep_square()];
1677 if (side_to_move() == BLACK)
1678 result ^= zobSideToMove;
1684 /// Position::compute_pawn_key() computes the hash key of the position. The
1685 /// hash key is usually updated incrementally as moves are made and unmade,
1686 /// the compute_pawn_key() function is only used when a new position is set
1687 /// up, and to verify the correctness of the pawn hash key when running in
1690 Key Position::compute_pawn_key() const {
1695 for (Color c = WHITE; c <= BLACK; c++)
1697 b = pieces(PAWN, c);
1699 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1705 /// Position::compute_material_key() computes the hash key of the position.
1706 /// The hash key is usually updated incrementally as moves are made and unmade,
1707 /// the compute_material_key() function is only used when a new position is set
1708 /// up, and to verify the correctness of the material hash key when running in
1711 Key Position::compute_material_key() const {
1716 for (Color c = WHITE; c <= BLACK; c++)
1717 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1719 count = piece_count(c, pt);
1720 for (int i = 0; i < count; i++)
1721 result ^= zobrist[c][pt][i];
1727 /// Position::compute_value() compute the incremental scores for the middle
1728 /// game and the endgame. These functions are used to initialize the incremental
1729 /// scores when a new position is set up, and to verify that the scores are correctly
1730 /// updated by do_move and undo_move when the program is running in debug mode.
1731 Score Position::compute_value() const {
1734 Score result = SCORE_ZERO;
1736 for (Color c = WHITE; c <= BLACK; c++)
1737 for (PieceType pt = PAWN; pt <= KING; pt++)
1741 result += pst(c, pt, pop_1st_bit(&b));
1744 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1749 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1750 /// game material value for the given side. Material values are updated
1751 /// incrementally during the search, this function is only used while
1752 /// initializing a new Position object.
1754 Value Position::compute_non_pawn_material(Color c) const {
1756 Value result = VALUE_ZERO;
1758 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1759 result += piece_count(c, pt) * PieceValueMidgame[pt];
1765 /// Position::is_draw() tests whether the position is drawn by material,
1766 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1767 /// must be done by the search.
1769 bool Position::is_draw() const {
1771 // Draw by material?
1773 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1776 // Draw by the 50 moves rule?
1777 if (st->rule50 > 99 && !is_mate())
1780 // Draw by repetition?
1781 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1782 if (history[st->gamePly - i] == st->key)
1789 /// Position::is_mate() returns true or false depending on whether the
1790 /// side to move is checkmated.
1792 bool Position::is_mate() const {
1794 MoveStack moves[MAX_MOVES];
1795 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1799 /// Position::init_zobrist() is a static member function which initializes at
1800 /// startup the various arrays used to compute hash keys.
1802 void Position::init_zobrist() {
1807 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1808 zobrist[i][j][k] = rk.rand<Key>();
1810 for (i = 0; i < 64; i++)
1811 zobEp[i] = rk.rand<Key>();
1813 for (i = 0; i < 16; i++)
1814 zobCastle[i] = rk.rand<Key>();
1816 zobSideToMove = rk.rand<Key>();
1817 zobExclusion = rk.rand<Key>();
1821 /// Position::init_piece_square_tables() initializes the piece square tables.
1822 /// This is a two-step operation: First, the white halves of the tables are
1823 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1824 /// of the tables are initialized by mirroring and changing the sign of the
1825 /// corresponding white scores.
1827 void Position::init_piece_square_tables() {
1829 for (Square s = SQ_A1; s <= SQ_H8; s++)
1830 for (Piece p = WP; p <= WK; p++)
1831 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1833 for (Square s = SQ_A1; s <= SQ_H8; s++)
1834 for (Piece p = BP; p <= BK; p++)
1835 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1839 /// Position::flip() flips position with the white and black sides reversed. This
1840 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1842 void Position::flip() {
1846 // Make a copy of current position before to start changing
1847 const Position pos(*this, threadID);
1850 threadID = pos.thread();
1853 for (Square s = SQ_A1; s <= SQ_H8; s++)
1854 if (!pos.square_is_empty(s))
1855 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1858 sideToMove = opposite_color(pos.side_to_move());
1861 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1862 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1863 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1864 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1866 initialKFile = pos.initialKFile;
1867 initialKRFile = pos.initialKRFile;
1868 initialQRFile = pos.initialQRFile;
1870 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1871 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1872 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1873 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1874 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1875 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1877 // En passant square
1878 if (pos.st->epSquare != SQ_NONE)
1879 st->epSquare = flip_square(pos.st->epSquare);
1885 st->key = compute_key();
1886 st->pawnKey = compute_pawn_key();
1887 st->materialKey = compute_material_key();
1889 // Incremental scores
1890 st->value = compute_value();
1893 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1894 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1900 /// Position::is_ok() performs some consitency checks for the position object.
1901 /// This is meant to be helpful when debugging.
1903 bool Position::is_ok(int* failedStep) const {
1905 // What features of the position should be verified?
1906 const bool debugAll = false;
1908 const bool debugBitboards = debugAll || false;
1909 const bool debugKingCount = debugAll || false;
1910 const bool debugKingCapture = debugAll || false;
1911 const bool debugCheckerCount = debugAll || false;
1912 const bool debugKey = debugAll || false;
1913 const bool debugMaterialKey = debugAll || false;
1914 const bool debugPawnKey = debugAll || false;
1915 const bool debugIncrementalEval = debugAll || false;
1916 const bool debugNonPawnMaterial = debugAll || false;
1917 const bool debugPieceCounts = debugAll || false;
1918 const bool debugPieceList = debugAll || false;
1919 const bool debugCastleSquares = debugAll || false;
1921 if (failedStep) *failedStep = 1;
1924 if (!color_is_ok(side_to_move()))
1927 // Are the king squares in the position correct?
1928 if (failedStep) (*failedStep)++;
1929 if (piece_on(king_square(WHITE)) != WK)
1932 if (failedStep) (*failedStep)++;
1933 if (piece_on(king_square(BLACK)) != BK)
1937 if (failedStep) (*failedStep)++;
1938 if (!file_is_ok(initialKRFile))
1941 if (!file_is_ok(initialQRFile))
1944 // Do both sides have exactly one king?
1945 if (failedStep) (*failedStep)++;
1948 int kingCount[2] = {0, 0};
1949 for (Square s = SQ_A1; s <= SQ_H8; s++)
1950 if (type_of_piece_on(s) == KING)
1951 kingCount[color_of_piece_on(s)]++;
1953 if (kingCount[0] != 1 || kingCount[1] != 1)
1957 // Can the side to move capture the opponent's king?
1958 if (failedStep) (*failedStep)++;
1959 if (debugKingCapture)
1961 Color us = side_to_move();
1962 Color them = opposite_color(us);
1963 Square ksq = king_square(them);
1964 if (attackers_to(ksq) & pieces_of_color(us))
1968 // Is there more than 2 checkers?
1969 if (failedStep) (*failedStep)++;
1970 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1974 if (failedStep) (*failedStep)++;
1977 // The intersection of the white and black pieces must be empty
1978 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1981 // The union of the white and black pieces must be equal to all
1983 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1986 // Separate piece type bitboards must have empty intersections
1987 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1988 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1989 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1993 // En passant square OK?
1994 if (failedStep) (*failedStep)++;
1995 if (ep_square() != SQ_NONE)
1997 // The en passant square must be on rank 6, from the point of view of the
1999 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2004 if (failedStep) (*failedStep)++;
2005 if (debugKey && st->key != compute_key())
2008 // Pawn hash key OK?
2009 if (failedStep) (*failedStep)++;
2010 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2013 // Material hash key OK?
2014 if (failedStep) (*failedStep)++;
2015 if (debugMaterialKey && st->materialKey != compute_material_key())
2018 // Incremental eval OK?
2019 if (failedStep) (*failedStep)++;
2020 if (debugIncrementalEval && st->value != compute_value())
2023 // Non-pawn material OK?
2024 if (failedStep) (*failedStep)++;
2025 if (debugNonPawnMaterial)
2027 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2030 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2035 if (failedStep) (*failedStep)++;
2036 if (debugPieceCounts)
2037 for (Color c = WHITE; c <= BLACK; c++)
2038 for (PieceType pt = PAWN; pt <= KING; pt++)
2039 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
2042 if (failedStep) (*failedStep)++;
2044 for (Color c = WHITE; c <= BLACK; c++)
2045 for (PieceType pt = PAWN; pt <= KING; pt++)
2046 for (int i = 0; i < pieceCount[c][pt]; i++)
2048 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
2051 if (index[piece_list(c, pt, i)] != i)
2055 if (failedStep) (*failedStep)++;
2056 if (debugCastleSquares)
2058 for (Color c = WHITE; c <= BLACK; c++)
2060 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
2063 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
2066 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2068 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2070 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2072 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2076 if (failedStep) *failedStep = 0;