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/>.
40 #include "ucioption.h"
48 //// Position's static data definitions
51 Key Position::zobrist[2][8][64];
52 Key Position::zobEp[64];
53 Key Position::zobCastle[16];
54 Key Position::zobSideToMove;
55 Key Position::zobExclusion;
57 Score Position::PieceSquareTable[16][64];
59 // Material values arrays, indexed by Piece
60 const Value Position::PieceValueMidgame[17] = {
62 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
63 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
64 VALUE_ZERO, VALUE_ZERO,
65 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
66 RookValueMidgame, QueenValueMidgame
69 const Value Position::PieceValueEndgame[17] = {
71 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
72 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
73 VALUE_ZERO, VALUE_ZERO,
74 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
75 RookValueEndgame, QueenValueEndgame
78 // Material values array used by SEE, indexed by PieceType
79 const Value Position::seeValues[] = {
81 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
82 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
88 // Bonus for having the side to move (modified by Joona Kiiski)
89 const Score TempoValue = make_score(48, 22);
91 bool isZero(char c) { return c == '0'; }
93 struct PieceLetters : public std::map<char, Piece> {
97 operator[]('K') = WK; operator[]('k') = BK;
98 operator[]('Q') = WQ; operator[]('q') = BQ;
99 operator[]('R') = WR; operator[]('r') = BR;
100 operator[]('B') = WB; operator[]('b') = BB;
101 operator[]('N') = WN; operator[]('n') = BN;
102 operator[]('P') = WP; operator[]('p') = BP;
103 operator[](' ') = PIECE_NONE;
104 operator[]('.') = PIECE_NONE_DARK_SQ;
107 char from_piece(Piece p) const {
109 std::map<char, Piece>::const_iterator it;
110 for (it = begin(); it != end(); ++it)
119 PieceLetters pieceLetters;
125 CheckInfo::CheckInfo(const Position& pos) {
127 Color us = pos.side_to_move();
128 Color them = opposite_color(us);
130 ksq = pos.king_square(them);
131 dcCandidates = pos.discovered_check_candidates(us);
133 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
134 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
135 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
136 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
137 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
138 checkSq[KING] = EmptyBoardBB;
142 /// Position c'tors. Here we always create a copy of the original position
143 /// or the FEN string, we want the new born Position object do not depend
144 /// on any external data so we detach state pointer from the source one.
146 Position::Position(const Position& pos, int th) {
148 memcpy(this, &pos, sizeof(Position));
149 detach(); // Always detach() in copy c'tor to avoid surprises
154 Position::Position(const string& fen, bool isChess960, int th) {
156 from_fen(fen, isChess960);
161 /// Position::detach() copies the content of the current state and castling
162 /// masks inside the position itself. This is needed when the st pointee could
163 /// become stale, as example because the caller is about to going out of scope.
165 void Position::detach() {
169 st->previous = NULL; // as a safe guard
173 /// Position::from_fen() initializes the position object with the given FEN
174 /// string. This function is not very robust - make sure that input FENs are
175 /// correct (this is assumed to be the responsibility of the GUI).
177 void Position::from_fen(const string& fen, bool c960) {
179 A FEN string defines a particular position using only the ASCII character set.
181 A FEN string contains six fields. The separator between fields is a space. The fields are:
183 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
184 with rank 1; within each rank, the contents of each square are described from file A through file H.
185 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
186 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
187 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
188 of blank squares), and "/" separate ranks.
190 2) Active color. "w" means white moves next, "b" means black.
192 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
193 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
194 kingside), and/or "q" (Black can castle queenside).
196 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
197 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
198 regardless of whether there is a pawn in position to make an en passant capture.
200 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
201 to determine if a draw can be claimed under the fifty-move rule.
203 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
208 std::istringstream ss(fen);
213 // 1. Piece placement field
214 while (ss.get(token) && token != ' ')
216 if (pieceLetters.find(token) != pieceLetters.end())
218 put_piece(pieceLetters[token], sq);
221 else if (isdigit(token))
222 sq += Square(token - '0'); // Skip the given number of files
223 else if (token == '/')
224 sq -= SQ_A3; // Jump back of 2 rows
230 if (!ss.get(token) || (token != 'w' && token != 'b'))
233 sideToMove = (token == 'w' ? WHITE : BLACK);
235 if (!ss.get(token) || token != ' ')
238 // 3. Castling availability
239 while (ss.get(token) && token != ' ')
240 if (!set_castling_rights(token))
243 // 4. En passant square
245 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
246 && (ss.get(row) && (row == '3' || row == '6')))
248 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
250 // Ignore if no capture is possible
251 Color them = opposite_color(sideToMove);
252 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
253 st->epSquare = SQ_NONE;
260 // 6. Fullmove number
262 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
264 // Various initialisations
265 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
266 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
267 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
268 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
269 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
270 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
275 st->key = compute_key();
276 st->pawnKey = compute_pawn_key();
277 st->materialKey = compute_material_key();
278 st->value = compute_value();
279 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
280 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
284 cout << "Error in FEN string: " << fen << endl;
288 /// Position::set_castling_rights() sets castling parameters castling avaiability.
289 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
290 /// that uses the letters of the columns on which the rooks began the game instead
291 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
292 /// associated with the castling right, the traditional castling tag will be replaced
293 /// by the file letter of the involved rook as for the Shredder-FEN.
295 bool Position::set_castling_rights(char token) {
297 Color c = token >= 'a' ? BLACK : WHITE;
298 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
299 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
300 Piece rook = (c == WHITE ? WR : BR);
302 initialKFile = square_file(king_square(c));
303 token = char(toupper(token));
307 for (Square sq = sqH; sq >= sqA; sq--)
308 if (piece_on(sq) == rook)
311 initialKRFile = square_file(sq);
315 else if (token == 'Q')
317 for (Square sq = sqA; sq <= sqH; sq++)
318 if (piece_on(sq) == rook)
321 initialQRFile = square_file(sq);
325 else if (token >= 'A' && token <= 'H')
327 File rookFile = File(token - 'A') + FILE_A;
328 if (rookFile < initialKFile)
331 initialQRFile = rookFile;
336 initialKRFile = rookFile;
346 /// Position::to_fen() returns a FEN representation of the position. In case
347 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
349 const string Position::to_fen() const {
355 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
357 for (File file = FILE_A; file <= FILE_H; file++)
359 sq = make_square(file, rank);
361 if (square_is_occupied(sq))
364 fen += pieceLetters.from_piece(piece_on(sq));
374 fen.erase(std::remove_if(fen.begin(), fen.end(), isZero), fen.end());
375 fen.erase(--fen.end());
376 fen += (sideToMove == WHITE ? " w " : " b ");
378 if (st->castleRights != CASTLES_NONE)
380 if (can_castle_kingside(WHITE))
381 fen += isChess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
383 if (can_castle_queenside(WHITE))
384 fen += isChess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
386 if (can_castle_kingside(BLACK))
387 fen += isChess960 ? file_to_char(initialKRFile) : 'k';
389 if (can_castle_queenside(BLACK))
390 fen += isChess960 ? file_to_char(initialQRFile) : 'q';
394 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
399 /// Position::print() prints an ASCII representation of the position to
400 /// the standard output. If a move is given then also the san is printed.
402 void Position::print(Move move) const {
404 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
405 static bool requestPending = false;
407 // Check for reentrancy, as example when called from inside
408 // MovePicker that is used also here in move_to_san()
412 requestPending = true;
416 Position p(*this, thread());
417 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
418 cout << "\nMove is: " << dd << move_to_san(p, move);
421 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
423 cout << dottedLine << '|';
424 for (File file = FILE_A; file <= FILE_H; file++)
426 Square sq = make_square(file, rank);
427 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
428 Piece piece = piece_on(sq);
430 if (piece == PIECE_NONE && square_color(sq) == DARK)
431 piece = PIECE_NONE_DARK_SQ;
433 cout << c << pieceLetters.from_piece(piece) << c << '|';
436 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
437 requestPending = false;
441 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
442 /// king) pieces for the given color and for the given pinner type. Or, when
443 /// template parameter FindPinned is false, the pieces of the given color
444 /// candidate for a discovery check against the enemy king.
445 /// Bitboard checkersBB must be already updated when looking for pinners.
447 template<bool FindPinned>
448 Bitboard Position::hidden_checkers(Color c) const {
450 Bitboard result = EmptyBoardBB;
451 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
453 // Pinned pieces protect our king, dicovery checks attack
455 Square ksq = king_square(FindPinned ? c : opposite_color(c));
457 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
458 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
460 if (FindPinned && pinners)
461 pinners &= ~st->checkersBB;
465 Square s = pop_1st_bit(&pinners);
466 Bitboard b = squares_between(s, ksq) & occupied_squares();
470 if ( !(b & (b - 1)) // Only one bit set?
471 && (b & pieces_of_color(c))) // Is an our piece?
478 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
479 /// king) pieces for the given color. Note that checkersBB bitboard must
480 /// be already updated.
482 Bitboard Position::pinned_pieces(Color c) const {
484 return hidden_checkers<true>(c);
488 /// Position:discovered_check_candidates() returns a bitboard containing all
489 /// pieces for the given side which are candidates for giving a discovered
490 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
491 /// to be already updated.
493 Bitboard Position::discovered_check_candidates(Color c) const {
495 return hidden_checkers<false>(c);
498 /// Position::attackers_to() computes a bitboard containing all pieces which
499 /// attacks a given square.
501 Bitboard Position::attackers_to(Square s) const {
503 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
504 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
505 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
506 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
507 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
508 | (attacks_from<KING>(s) & pieces(KING));
511 /// Position::attacks_from() computes a bitboard of all attacks
512 /// of a given piece put in a given square.
514 Bitboard Position::attacks_from(Piece p, Square s) const {
516 assert(square_is_ok(s));
520 case WB: case BB: return attacks_from<BISHOP>(s);
521 case WR: case BR: return attacks_from<ROOK>(s);
522 case WQ: case BQ: return attacks_from<QUEEN>(s);
523 default: return NonSlidingAttacksBB[p][s];
527 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
529 assert(square_is_ok(s));
533 case WB: case BB: return bishop_attacks_bb(s, occ);
534 case WR: case BR: return rook_attacks_bb(s, occ);
535 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
536 default: return NonSlidingAttacksBB[p][s];
541 /// Position::move_attacks_square() tests whether a move from the current
542 /// position attacks a given square.
544 bool Position::move_attacks_square(Move m, Square s) const {
546 assert(move_is_ok(m));
547 assert(square_is_ok(s));
550 Square f = move_from(m), t = move_to(m);
552 assert(square_is_occupied(f));
554 if (bit_is_set(attacks_from(piece_on(f), t), s))
557 // Move the piece and scan for X-ray attacks behind it
558 occ = occupied_squares();
559 do_move_bb(&occ, make_move_bb(f, t));
560 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
561 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
562 & pieces_of_color(color_of_piece_on(f));
564 // If we have attacks we need to verify that are caused by our move
565 // and are not already existent ones.
566 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
570 /// Position::find_checkers() computes the checkersBB bitboard, which
571 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
572 /// currently works by calling Position::attackers_to, which is probably
573 /// inefficient. Consider rewriting this function to use the last move
574 /// played, like in non-bitboard versions of Glaurung.
576 void Position::find_checkers() {
578 Color us = side_to_move();
579 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
583 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
585 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
588 assert(move_is_ok(m));
589 assert(pinned == pinned_pieces(side_to_move()));
591 // Castling moves are checked for legality during move generation.
592 if (move_is_castle(m))
595 // En passant captures are a tricky special case. Because they are
596 // rather uncommon, we do it simply by testing whether the king is attacked
597 // after the move is made
600 Color us = side_to_move();
601 Color them = opposite_color(us);
602 Square from = move_from(m);
603 Square to = move_to(m);
604 Square capsq = make_square(square_file(to), square_rank(from));
605 Square ksq = king_square(us);
606 Bitboard b = occupied_squares();
608 assert(to == ep_square());
609 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
610 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
611 assert(piece_on(to) == PIECE_NONE);
614 clear_bit(&b, capsq);
617 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
618 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
621 Color us = side_to_move();
622 Square from = move_from(m);
624 assert(color_of_piece_on(from) == us);
625 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
627 // If the moving piece is a king, check whether the destination
628 // square is attacked by the opponent.
629 if (type_of_piece_on(from) == KING)
630 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
632 // A non-king move is legal if and only if it is not pinned or it
633 // is moving along the ray towards or away from the king.
635 || !bit_is_set(pinned, from)
636 || squares_aligned(from, move_to(m), king_square(us));
640 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
642 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
646 Color us = side_to_move();
647 Square from = move_from(m);
648 Square to = move_to(m);
650 // King moves and en-passant captures are verified in pl_move_is_legal()
651 if (type_of_piece_on(from) == KING || move_is_ep(m))
652 return pl_move_is_legal(m, pinned);
654 Bitboard target = checkers();
655 Square checksq = pop_1st_bit(&target);
657 if (target) // double check ?
660 // Our move must be a blocking evasion or a capture of the checking piece
661 target = squares_between(checksq, king_square(us)) | checkers();
662 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
666 /// Position::move_is_check() tests whether a pseudo-legal move is a check
668 bool Position::move_is_check(Move m) const {
670 return move_is_check(m, CheckInfo(*this));
673 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
676 assert(move_is_ok(m));
677 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
678 assert(color_of_piece_on(move_from(m)) == side_to_move());
679 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
681 Square from = move_from(m);
682 Square to = move_to(m);
683 PieceType pt = type_of_piece_on(from);
686 if (bit_is_set(ci.checkSq[pt], to))
690 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
692 // For pawn and king moves we need to verify also direction
693 if ( (pt != PAWN && pt != KING)
694 || !squares_aligned(from, to, ci.ksq))
698 // Can we skip the ugly special cases ?
699 if (!move_is_special(m))
702 Color us = side_to_move();
703 Bitboard b = occupied_squares();
705 // Promotion with check ?
706 if (move_is_promotion(m))
710 switch (move_promotion_piece(m))
713 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
715 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
717 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
719 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
725 // En passant capture with check ? We have already handled the case
726 // of direct checks and ordinary discovered check, the only case we
727 // need to handle is the unusual case of a discovered check through
728 // the captured pawn.
731 Square capsq = make_square(square_file(to), square_rank(from));
733 clear_bit(&b, capsq);
735 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
736 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
739 // Castling with check ?
740 if (move_is_castle(m))
742 Square kfrom, kto, rfrom, rto;
748 kto = relative_square(us, SQ_G1);
749 rto = relative_square(us, SQ_F1);
751 kto = relative_square(us, SQ_C1);
752 rto = relative_square(us, SQ_D1);
754 clear_bit(&b, kfrom);
755 clear_bit(&b, rfrom);
758 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
765 /// Position::do_setup_move() makes a permanent move on the board.
766 /// It should be used when setting up a position on board.
767 /// You can't undo the move.
769 void Position::do_setup_move(Move m) {
775 // Reset "game ply" in case we made a non-reversible move.
776 // "game ply" is used for repetition detection.
780 // Update the number of plies played from the starting position
781 startPosPlyCounter++;
783 // Our StateInfo newSt is about going out of scope so copy
784 // its content inside pos before it disappears.
788 /// Position::do_move() makes a move, and saves all information necessary
789 /// to a StateInfo object. The move is assumed to be legal.
790 /// Pseudo-legal moves should be filtered out before this function is called.
792 void Position::do_move(Move m, StateInfo& newSt) {
795 do_move(m, newSt, ci, move_is_check(m, ci));
798 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
801 assert(move_is_ok(m));
802 assert(&newSt != st);
807 // Copy some fields of old state to our new StateInfo object except the
808 // ones which are recalculated from scratch anyway, then switch our state
809 // pointer to point to the new, ready to be updated, state.
810 struct ReducedStateInfo {
811 Key pawnKey, materialKey;
812 int castleRights, rule50, gamePly, pliesFromNull;
818 memcpy(&newSt, st, sizeof(ReducedStateInfo));
823 // Save the current key to the history[] array, in order to be able to
824 // detect repetition draws.
825 history[st->gamePly++] = key;
827 // Update side to move
828 key ^= zobSideToMove;
830 // Increment the 50 moves rule draw counter. Resetting it to zero in the
831 // case of non-reversible moves is taken care of later.
835 if (move_is_castle(m))
842 Color us = side_to_move();
843 Color them = opposite_color(us);
844 Square from = move_from(m);
845 Square to = move_to(m);
846 bool ep = move_is_ep(m);
847 bool pm = move_is_promotion(m);
849 Piece piece = piece_on(from);
850 PieceType pt = type_of_piece(piece);
851 PieceType capture = ep ? PAWN : type_of_piece_on(to);
853 assert(color_of_piece_on(from) == us);
854 assert(color_of_piece_on(to) == them || square_is_empty(to));
855 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
856 assert(!pm || relative_rank(us, to) == RANK_8);
859 do_capture_move(key, capture, them, to, ep);
862 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
864 // Reset en passant square
865 if (st->epSquare != SQ_NONE)
867 key ^= zobEp[st->epSquare];
868 st->epSquare = SQ_NONE;
871 // Update castle rights, try to shortcut a common case
872 int cm = castleRightsMask[from] & castleRightsMask[to];
873 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
875 key ^= zobCastle[st->castleRights];
876 st->castleRights &= castleRightsMask[from];
877 st->castleRights &= castleRightsMask[to];
878 key ^= zobCastle[st->castleRights];
881 // Prefetch TT access as soon as we know key is updated
882 prefetch((char*)TT.first_entry(key));
885 Bitboard move_bb = make_move_bb(from, to);
886 do_move_bb(&(byColorBB[us]), move_bb);
887 do_move_bb(&(byTypeBB[pt]), move_bb);
888 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
890 board[to] = board[from];
891 board[from] = PIECE_NONE;
893 // Update piece lists, note that index[from] is not updated and
894 // becomes stale. This works as long as index[] is accessed just
895 // by known occupied squares.
896 index[to] = index[from];
897 pieceList[us][pt][index[to]] = to;
899 // If the moving piece was a pawn do some special extra work
902 // Reset rule 50 draw counter
905 // Update pawn hash key and prefetch in L1/L2 cache
906 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
907 prefetchPawn(st->pawnKey, threadID);
909 // Set en passant square, only if moved pawn can be captured
910 if ((to ^ from) == 16)
912 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
914 st->epSquare = Square((int(from) + int(to)) / 2);
915 key ^= zobEp[st->epSquare];
919 if (pm) // promotion ?
921 PieceType promotion = move_promotion_piece(m);
923 assert(promotion >= KNIGHT && promotion <= QUEEN);
925 // Insert promoted piece instead of pawn
926 clear_bit(&(byTypeBB[PAWN]), to);
927 set_bit(&(byTypeBB[promotion]), to);
928 board[to] = piece_of_color_and_type(us, promotion);
930 // Update piece counts
931 pieceCount[us][promotion]++;
932 pieceCount[us][PAWN]--;
934 // Update material key
935 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
936 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
938 // Update piece lists, move the last pawn at index[to] position
939 // and shrink the list. Add a new promotion piece to the list.
940 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
941 index[lastPawnSquare] = index[to];
942 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
943 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
944 index[to] = pieceCount[us][promotion] - 1;
945 pieceList[us][promotion][index[to]] = to;
947 // Partially revert hash keys update
948 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
949 st->pawnKey ^= zobrist[us][PAWN][to];
951 // Partially revert and update incremental scores
952 st->value -= pst(us, PAWN, to);
953 st->value += pst(us, promotion, to);
956 st->npMaterial[us] += PieceValueMidgame[promotion];
960 // Update incremental scores
961 st->value += pst_delta(piece, from, to);
964 st->capturedType = capture;
966 // Update the key with the final value
969 // Update checkers bitboard, piece must be already moved
970 st->checkersBB = EmptyBoardBB;
975 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
979 if (bit_is_set(ci.checkSq[pt], to))
980 st->checkersBB = SetMaskBB[to];
983 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
986 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
989 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
995 sideToMove = opposite_color(sideToMove);
996 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1002 /// Position::do_capture_move() is a private method used to update captured
1003 /// piece info. It is called from the main Position::do_move function.
1005 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1007 assert(capture != KING);
1011 // If the captured piece was a pawn, update pawn hash key,
1012 // otherwise update non-pawn material.
1013 if (capture == PAWN)
1015 if (ep) // en passant ?
1017 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1019 assert(to == st->epSquare);
1020 assert(relative_rank(opposite_color(them), to) == RANK_6);
1021 assert(piece_on(to) == PIECE_NONE);
1022 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1024 board[capsq] = PIECE_NONE;
1026 st->pawnKey ^= zobrist[them][PAWN][capsq];
1029 st->npMaterial[them] -= PieceValueMidgame[capture];
1031 // Remove captured piece
1032 clear_bit(&(byColorBB[them]), capsq);
1033 clear_bit(&(byTypeBB[capture]), capsq);
1034 clear_bit(&(byTypeBB[0]), capsq);
1037 key ^= zobrist[them][capture][capsq];
1039 // Update incremental scores
1040 st->value -= pst(them, capture, capsq);
1042 // Update piece count
1043 pieceCount[them][capture]--;
1045 // Update material hash key
1046 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1048 // Update piece list, move the last piece at index[capsq] position
1050 // WARNING: This is a not perfectly revresible operation. When we
1051 // will reinsert the captured piece in undo_move() we will put it
1052 // at the end of the list and not in its original place, it means
1053 // index[] and pieceList[] are not guaranteed to be invariant to a
1054 // do_move() + undo_move() sequence.
1055 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1056 index[lastPieceSquare] = index[capsq];
1057 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1058 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1060 // Reset rule 50 counter
1065 /// Position::do_castle_move() is a private method used to make a castling
1066 /// move. It is called from the main Position::do_move function. Note that
1067 /// castling moves are encoded as "king captures friendly rook" moves, for
1068 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1070 void Position::do_castle_move(Move m) {
1072 assert(move_is_ok(m));
1073 assert(move_is_castle(m));
1075 Color us = side_to_move();
1076 Color them = opposite_color(us);
1078 // Reset capture field
1079 st->capturedType = PIECE_TYPE_NONE;
1081 // Find source squares for king and rook
1082 Square kfrom = move_from(m);
1083 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1086 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1087 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1089 // Find destination squares for king and rook
1090 if (rfrom > kfrom) // O-O
1092 kto = relative_square(us, SQ_G1);
1093 rto = relative_square(us, SQ_F1);
1095 kto = relative_square(us, SQ_C1);
1096 rto = relative_square(us, SQ_D1);
1099 // Remove pieces from source squares:
1100 clear_bit(&(byColorBB[us]), kfrom);
1101 clear_bit(&(byTypeBB[KING]), kfrom);
1102 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1103 clear_bit(&(byColorBB[us]), rfrom);
1104 clear_bit(&(byTypeBB[ROOK]), rfrom);
1105 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1107 // Put pieces on destination squares:
1108 set_bit(&(byColorBB[us]), kto);
1109 set_bit(&(byTypeBB[KING]), kto);
1110 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1111 set_bit(&(byColorBB[us]), rto);
1112 set_bit(&(byTypeBB[ROOK]), rto);
1113 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1115 // Update board array
1116 Piece king = piece_of_color_and_type(us, KING);
1117 Piece rook = piece_of_color_and_type(us, ROOK);
1118 board[kfrom] = board[rfrom] = PIECE_NONE;
1122 // Update piece lists
1123 pieceList[us][KING][index[kfrom]] = kto;
1124 pieceList[us][ROOK][index[rfrom]] = rto;
1125 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1126 index[kto] = index[kfrom];
1129 // Update incremental scores
1130 st->value += pst_delta(king, kfrom, kto);
1131 st->value += pst_delta(rook, rfrom, rto);
1134 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1135 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1137 // Clear en passant square
1138 if (st->epSquare != SQ_NONE)
1140 st->key ^= zobEp[st->epSquare];
1141 st->epSquare = SQ_NONE;
1144 // Update castling rights
1145 st->key ^= zobCastle[st->castleRights];
1146 st->castleRights &= castleRightsMask[kfrom];
1147 st->key ^= zobCastle[st->castleRights];
1149 // Reset rule 50 counter
1152 // Update checkers BB
1153 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1156 sideToMove = opposite_color(sideToMove);
1157 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1163 /// Position::undo_move() unmakes a move. When it returns, the position should
1164 /// be restored to exactly the same state as before the move was made.
1166 void Position::undo_move(Move m) {
1169 assert(move_is_ok(m));
1171 sideToMove = opposite_color(sideToMove);
1173 if (move_is_castle(m))
1175 undo_castle_move(m);
1179 Color us = side_to_move();
1180 Color them = opposite_color(us);
1181 Square from = move_from(m);
1182 Square to = move_to(m);
1183 bool ep = move_is_ep(m);
1184 bool pm = move_is_promotion(m);
1186 PieceType pt = type_of_piece_on(to);
1188 assert(square_is_empty(from));
1189 assert(color_of_piece_on(to) == us);
1190 assert(!pm || relative_rank(us, to) == RANK_8);
1191 assert(!ep || to == st->previous->epSquare);
1192 assert(!ep || relative_rank(us, to) == RANK_6);
1193 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1195 if (pm) // promotion ?
1197 PieceType promotion = move_promotion_piece(m);
1200 assert(promotion >= KNIGHT && promotion <= QUEEN);
1201 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1203 // Replace promoted piece with a pawn
1204 clear_bit(&(byTypeBB[promotion]), to);
1205 set_bit(&(byTypeBB[PAWN]), to);
1207 // Update piece counts
1208 pieceCount[us][promotion]--;
1209 pieceCount[us][PAWN]++;
1211 // Update piece list replacing promotion piece with a pawn
1212 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1213 index[lastPromotionSquare] = index[to];
1214 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1215 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1216 index[to] = pieceCount[us][PAWN] - 1;
1217 pieceList[us][PAWN][index[to]] = to;
1220 // Put the piece back at the source square
1221 Bitboard move_bb = make_move_bb(to, from);
1222 do_move_bb(&(byColorBB[us]), move_bb);
1223 do_move_bb(&(byTypeBB[pt]), move_bb);
1224 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1226 board[from] = piece_of_color_and_type(us, pt);
1227 board[to] = PIECE_NONE;
1229 // Update piece list
1230 index[from] = index[to];
1231 pieceList[us][pt][index[from]] = from;
1233 if (st->capturedType)
1238 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1240 assert(st->capturedType != KING);
1241 assert(!ep || square_is_empty(capsq));
1243 // Restore the captured piece
1244 set_bit(&(byColorBB[them]), capsq);
1245 set_bit(&(byTypeBB[st->capturedType]), capsq);
1246 set_bit(&(byTypeBB[0]), capsq);
1248 board[capsq] = piece_of_color_and_type(them, st->capturedType);
1250 // Update piece count
1251 pieceCount[them][st->capturedType]++;
1253 // Update piece list, add a new captured piece in capsq square
1254 index[capsq] = pieceCount[them][st->capturedType] - 1;
1255 pieceList[them][st->capturedType][index[capsq]] = capsq;
1258 // Finally point our state pointer back to the previous state
1265 /// Position::undo_castle_move() is a private method used to unmake a castling
1266 /// move. It is called from the main Position::undo_move function. Note that
1267 /// castling moves are encoded as "king captures friendly rook" moves, for
1268 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1270 void Position::undo_castle_move(Move m) {
1272 assert(move_is_ok(m));
1273 assert(move_is_castle(m));
1275 // When we have arrived here, some work has already been done by
1276 // Position::undo_move. In particular, the side to move has been switched,
1277 // so the code below is correct.
1278 Color us = side_to_move();
1280 // Find source squares for king and rook
1281 Square kfrom = move_from(m);
1282 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1285 // Find destination squares for king and rook
1286 if (rfrom > kfrom) // O-O
1288 kto = relative_square(us, SQ_G1);
1289 rto = relative_square(us, SQ_F1);
1291 kto = relative_square(us, SQ_C1);
1292 rto = relative_square(us, SQ_D1);
1295 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1296 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1298 // Remove pieces from destination squares:
1299 clear_bit(&(byColorBB[us]), kto);
1300 clear_bit(&(byTypeBB[KING]), kto);
1301 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1302 clear_bit(&(byColorBB[us]), rto);
1303 clear_bit(&(byTypeBB[ROOK]), rto);
1304 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1306 // Put pieces on source squares:
1307 set_bit(&(byColorBB[us]), kfrom);
1308 set_bit(&(byTypeBB[KING]), kfrom);
1309 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1310 set_bit(&(byColorBB[us]), rfrom);
1311 set_bit(&(byTypeBB[ROOK]), rfrom);
1312 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1315 board[rto] = board[kto] = PIECE_NONE;
1316 board[rfrom] = piece_of_color_and_type(us, ROOK);
1317 board[kfrom] = piece_of_color_and_type(us, KING);
1319 // Update piece lists
1320 pieceList[us][KING][index[kto]] = kfrom;
1321 pieceList[us][ROOK][index[rto]] = rfrom;
1322 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1323 index[kfrom] = index[kto];
1326 // Finally point our state pointer back to the previous state
1333 /// Position::do_null_move makes() a "null move": It switches the side to move
1334 /// and updates the hash key without executing any move on the board.
1336 void Position::do_null_move(StateInfo& backupSt) {
1339 assert(!is_check());
1341 // Back up the information necessary to undo the null move to the supplied
1342 // StateInfo object.
1343 // Note that differently from normal case here backupSt is actually used as
1344 // a backup storage not as a new state to be used.
1345 backupSt.key = st->key;
1346 backupSt.epSquare = st->epSquare;
1347 backupSt.value = st->value;
1348 backupSt.previous = st->previous;
1349 backupSt.pliesFromNull = st->pliesFromNull;
1350 st->previous = &backupSt;
1352 // Save the current key to the history[] array, in order to be able to
1353 // detect repetition draws.
1354 history[st->gamePly++] = st->key;
1356 // Update the necessary information
1357 if (st->epSquare != SQ_NONE)
1358 st->key ^= zobEp[st->epSquare];
1360 st->key ^= zobSideToMove;
1361 prefetch((char*)TT.first_entry(st->key));
1363 sideToMove = opposite_color(sideToMove);
1364 st->epSquare = SQ_NONE;
1366 st->pliesFromNull = 0;
1367 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1371 /// Position::undo_null_move() unmakes a "null move".
1373 void Position::undo_null_move() {
1376 assert(!is_check());
1378 // Restore information from the our backup StateInfo object
1379 StateInfo* backupSt = st->previous;
1380 st->key = backupSt->key;
1381 st->epSquare = backupSt->epSquare;
1382 st->value = backupSt->value;
1383 st->previous = backupSt->previous;
1384 st->pliesFromNull = backupSt->pliesFromNull;
1386 // Update the necessary information
1387 sideToMove = opposite_color(sideToMove);
1393 /// Position::see() is a static exchange evaluator: It tries to estimate the
1394 /// material gain or loss resulting from a move. There are three versions of
1395 /// this function: One which takes a destination square as input, one takes a
1396 /// move, and one which takes a 'from' and a 'to' square. The function does
1397 /// not yet understand promotions captures.
1399 int Position::see(Move m) const {
1401 assert(move_is_ok(m));
1402 return see(move_from(m), move_to(m));
1405 int Position::see_sign(Move m) const {
1407 assert(move_is_ok(m));
1409 Square from = move_from(m);
1410 Square to = move_to(m);
1412 // Early return if SEE cannot be negative because captured piece value
1413 // is not less then capturing one. Note that king moves always return
1414 // here because king midgame value is set to 0.
1415 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1418 return see(from, to);
1421 int Position::see(Square from, Square to) const {
1423 Bitboard occupied, attackers, stmAttackers, b;
1424 int swapList[32], slIndex = 1;
1425 PieceType capturedType, pt;
1428 assert(square_is_ok(from));
1429 assert(square_is_ok(to));
1431 capturedType = type_of_piece_on(to);
1433 // King cannot be recaptured
1434 if (capturedType == KING)
1435 return seeValues[capturedType];
1437 occupied = occupied_squares();
1439 // Handle en passant moves
1440 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1442 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1444 assert(capturedType == PIECE_TYPE_NONE);
1445 assert(type_of_piece_on(capQq) == PAWN);
1447 // Remove the captured pawn
1448 clear_bit(&occupied, capQq);
1449 capturedType = PAWN;
1452 // Find all attackers to the destination square, with the moving piece
1453 // removed, but possibly an X-ray attacker added behind it.
1454 clear_bit(&occupied, from);
1455 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1456 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1457 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1458 | (attacks_from<KING>(to) & pieces(KING))
1459 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1460 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1462 // If the opponent has no attackers we are finished
1463 stm = opposite_color(color_of_piece_on(from));
1464 stmAttackers = attackers & pieces_of_color(stm);
1466 return seeValues[capturedType];
1468 // The destination square is defended, which makes things rather more
1469 // difficult to compute. We proceed by building up a "swap list" containing
1470 // the material gain or loss at each stop in a sequence of captures to the
1471 // destination square, where the sides alternately capture, and always
1472 // capture with the least valuable piece. After each capture, we look for
1473 // new X-ray attacks from behind the capturing piece.
1474 swapList[0] = seeValues[capturedType];
1475 capturedType = type_of_piece_on(from);
1478 // Locate the least valuable attacker for the side to move. The loop
1479 // below looks like it is potentially infinite, but it isn't. We know
1480 // that the side to move still has at least one attacker left.
1481 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1484 // Remove the attacker we just found from the 'occupied' bitboard,
1485 // and scan for new X-ray attacks behind the attacker.
1486 b = stmAttackers & pieces(pt);
1487 occupied ^= (b & (~b + 1));
1488 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1489 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1491 attackers &= occupied; // Cut out pieces we've already done
1493 // Add the new entry to the swap list
1494 assert(slIndex < 32);
1495 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1498 // Remember the value of the capturing piece, and change the side to
1499 // move before beginning the next iteration.
1501 stm = opposite_color(stm);
1502 stmAttackers = attackers & pieces_of_color(stm);
1504 // Stop before processing a king capture
1505 if (capturedType == KING && stmAttackers)
1507 assert(slIndex < 32);
1508 swapList[slIndex++] = QueenValueMidgame*10;
1511 } while (stmAttackers);
1513 // Having built the swap list, we negamax through it to find the best
1514 // achievable score from the point of view of the side to move.
1516 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1522 /// Position::clear() erases the position object to a pristine state, with an
1523 /// empty board, white to move, and no castling rights.
1525 void Position::clear() {
1528 memset(st, 0, sizeof(StateInfo));
1529 st->epSquare = SQ_NONE;
1530 startPosPlyCounter = 0;
1533 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1534 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1535 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1536 memset(index, 0, sizeof(int) * 64);
1538 for (int i = 0; i < 64; i++)
1539 board[i] = PIECE_NONE;
1541 for (int i = 0; i < 8; i++)
1542 for (int j = 0; j < 16; j++)
1543 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1545 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1546 castleRightsMask[sq] = ALL_CASTLES;
1549 initialKFile = FILE_E;
1550 initialKRFile = FILE_H;
1551 initialQRFile = FILE_A;
1555 /// Position::put_piece() puts a piece on the given square of the board,
1556 /// updating the board array, pieces list, bitboards, and piece counts.
1558 void Position::put_piece(Piece p, Square s) {
1560 Color c = color_of_piece(p);
1561 PieceType pt = type_of_piece(p);
1564 index[s] = pieceCount[c][pt]++;
1565 pieceList[c][pt][index[s]] = s;
1567 set_bit(&(byTypeBB[pt]), s);
1568 set_bit(&(byColorBB[c]), s);
1569 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1573 /// Position::compute_key() computes the hash key of the position. The hash
1574 /// key is usually updated incrementally as moves are made and unmade, the
1575 /// compute_key() function is only used when a new position is set up, and
1576 /// to verify the correctness of the hash key when running in debug mode.
1578 Key Position::compute_key() const {
1580 Key result = zobCastle[st->castleRights];
1582 for (Square s = SQ_A1; s <= SQ_H8; s++)
1583 if (square_is_occupied(s))
1584 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1586 if (ep_square() != SQ_NONE)
1587 result ^= zobEp[ep_square()];
1589 if (side_to_move() == BLACK)
1590 result ^= zobSideToMove;
1596 /// Position::compute_pawn_key() computes the hash key of the position. The
1597 /// hash key is usually updated incrementally as moves are made and unmade,
1598 /// the compute_pawn_key() function is only used when a new position is set
1599 /// up, and to verify the correctness of the pawn hash key when running in
1602 Key Position::compute_pawn_key() const {
1607 for (Color c = WHITE; c <= BLACK; c++)
1609 b = pieces(PAWN, c);
1611 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1617 /// Position::compute_material_key() computes the hash key of the position.
1618 /// The hash key is usually updated incrementally as moves are made and unmade,
1619 /// the compute_material_key() function is only used when a new position is set
1620 /// up, and to verify the correctness of the material hash key when running in
1623 Key Position::compute_material_key() const {
1628 for (Color c = WHITE; c <= BLACK; c++)
1629 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1631 count = piece_count(c, pt);
1632 for (int i = 0; i < count; i++)
1633 result ^= zobrist[c][pt][i];
1639 /// Position::compute_value() compute the incremental scores for the middle
1640 /// game and the endgame. These functions are used to initialize the incremental
1641 /// scores when a new position is set up, and to verify that the scores are correctly
1642 /// updated by do_move and undo_move when the program is running in debug mode.
1643 Score Position::compute_value() const {
1646 Score result = SCORE_ZERO;
1648 for (Color c = WHITE; c <= BLACK; c++)
1649 for (PieceType pt = PAWN; pt <= KING; pt++)
1653 result += pst(c, pt, pop_1st_bit(&b));
1656 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1661 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1662 /// game material value for the given side. Material values are updated
1663 /// incrementally during the search, this function is only used while
1664 /// initializing a new Position object.
1666 Value Position::compute_non_pawn_material(Color c) const {
1668 Value result = VALUE_ZERO;
1670 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1671 result += piece_count(c, pt) * PieceValueMidgame[pt];
1677 /// Position::is_draw() tests whether the position is drawn by material,
1678 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1679 /// must be done by the search.
1681 bool Position::is_draw() const {
1683 // Draw by material?
1685 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1688 // Draw by the 50 moves rule?
1689 if (st->rule50 > 99 && !is_mate())
1692 // Draw by repetition?
1693 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1694 if (history[st->gamePly - i] == st->key)
1701 /// Position::is_mate() returns true or false depending on whether the
1702 /// side to move is checkmated.
1704 bool Position::is_mate() const {
1706 MoveStack moves[MOVES_MAX];
1707 return is_check() && generate<MV_LEGAL>(*this, moves) == moves;
1711 /// Position::has_mate_threat() tests whether the side to move is under
1712 /// a threat of being mated in one from the current position.
1714 bool Position::has_mate_threat() {
1716 MoveStack mlist[MOVES_MAX], *last, *cur;
1718 bool mateFound = false;
1720 // If we are under check it's up to evasions to do the job
1724 // First pass the move to our opponent doing a null move
1727 // Then generate pseudo-legal moves that could give check
1728 last = generate<MV_NON_CAPTURE_CHECK>(*this, mlist);
1729 last = generate<MV_CAPTURE>(*this, last);
1731 // Loop through the moves, and see if one of them gives mate
1732 Bitboard pinned = pinned_pieces(sideToMove);
1733 CheckInfo ci(*this);
1734 for (cur = mlist; cur != last && !mateFound; cur++)
1736 Move move = cur->move;
1737 if ( !pl_move_is_legal(move, pinned)
1738 || !move_is_check(move, ci))
1741 do_move(move, st2, ci, true);
1754 /// Position::init_zobrist() is a static member function which initializes at
1755 /// startup the various arrays used to compute hash keys.
1757 void Position::init_zobrist() {
1762 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1763 zobrist[i][j][k] = rk.rand<Key>();
1765 for (i = 0; i < 64; i++)
1766 zobEp[i] = rk.rand<Key>();
1768 for (i = 0; i < 16; i++)
1769 zobCastle[i] = rk.rand<Key>();
1771 zobSideToMove = rk.rand<Key>();
1772 zobExclusion = rk.rand<Key>();
1776 /// Position::init_piece_square_tables() initializes the piece square tables.
1777 /// This is a two-step operation: First, the white halves of the tables are
1778 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1779 /// of the tables are initialized by mirroring and changing the sign of the
1780 /// corresponding white scores.
1782 void Position::init_piece_square_tables() {
1784 for (Square s = SQ_A1; s <= SQ_H8; s++)
1785 for (Piece p = WP; p <= WK; p++)
1786 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1788 for (Square s = SQ_A1; s <= SQ_H8; s++)
1789 for (Piece p = BP; p <= BK; p++)
1790 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1794 /// Position::flipped_copy() makes a copy of the input position, but with
1795 /// the white and black sides reversed. This is only useful for debugging,
1796 /// especially for finding evaluation symmetry bugs.
1798 void Position::flipped_copy(const Position& pos) {
1800 assert(pos.is_ok());
1803 threadID = pos.thread();
1806 for (Square s = SQ_A1; s <= SQ_H8; s++)
1807 if (!pos.square_is_empty(s))
1808 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1811 sideToMove = opposite_color(pos.side_to_move());
1814 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1815 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1816 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1817 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1819 initialKFile = pos.initialKFile;
1820 initialKRFile = pos.initialKRFile;
1821 initialQRFile = pos.initialQRFile;
1823 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1824 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1825 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1826 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1827 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1828 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1830 // En passant square
1831 if (pos.st->epSquare != SQ_NONE)
1832 st->epSquare = flip_square(pos.st->epSquare);
1838 st->key = compute_key();
1839 st->pawnKey = compute_pawn_key();
1840 st->materialKey = compute_material_key();
1842 // Incremental scores
1843 st->value = compute_value();
1846 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1847 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1853 /// Position::is_ok() performs some consitency checks for the position object.
1854 /// This is meant to be helpful when debugging.
1856 bool Position::is_ok(int* failedStep) const {
1858 // What features of the position should be verified?
1859 const bool debugAll = false;
1861 const bool debugBitboards = debugAll || false;
1862 const bool debugKingCount = debugAll || false;
1863 const bool debugKingCapture = debugAll || false;
1864 const bool debugCheckerCount = debugAll || false;
1865 const bool debugKey = debugAll || false;
1866 const bool debugMaterialKey = debugAll || false;
1867 const bool debugPawnKey = debugAll || false;
1868 const bool debugIncrementalEval = debugAll || false;
1869 const bool debugNonPawnMaterial = debugAll || false;
1870 const bool debugPieceCounts = debugAll || false;
1871 const bool debugPieceList = debugAll || false;
1872 const bool debugCastleSquares = debugAll || false;
1874 if (failedStep) *failedStep = 1;
1877 if (!color_is_ok(side_to_move()))
1880 // Are the king squares in the position correct?
1881 if (failedStep) (*failedStep)++;
1882 if (piece_on(king_square(WHITE)) != WK)
1885 if (failedStep) (*failedStep)++;
1886 if (piece_on(king_square(BLACK)) != BK)
1890 if (failedStep) (*failedStep)++;
1891 if (!file_is_ok(initialKRFile))
1894 if (!file_is_ok(initialQRFile))
1897 // Do both sides have exactly one king?
1898 if (failedStep) (*failedStep)++;
1901 int kingCount[2] = {0, 0};
1902 for (Square s = SQ_A1; s <= SQ_H8; s++)
1903 if (type_of_piece_on(s) == KING)
1904 kingCount[color_of_piece_on(s)]++;
1906 if (kingCount[0] != 1 || kingCount[1] != 1)
1910 // Can the side to move capture the opponent's king?
1911 if (failedStep) (*failedStep)++;
1912 if (debugKingCapture)
1914 Color us = side_to_move();
1915 Color them = opposite_color(us);
1916 Square ksq = king_square(them);
1917 if (attackers_to(ksq) & pieces_of_color(us))
1921 // Is there more than 2 checkers?
1922 if (failedStep) (*failedStep)++;
1923 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1927 if (failedStep) (*failedStep)++;
1930 // The intersection of the white and black pieces must be empty
1931 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1934 // The union of the white and black pieces must be equal to all
1936 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1939 // Separate piece type bitboards must have empty intersections
1940 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1941 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1942 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1946 // En passant square OK?
1947 if (failedStep) (*failedStep)++;
1948 if (ep_square() != SQ_NONE)
1950 // The en passant square must be on rank 6, from the point of view of the
1952 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1957 if (failedStep) (*failedStep)++;
1958 if (debugKey && st->key != compute_key())
1961 // Pawn hash key OK?
1962 if (failedStep) (*failedStep)++;
1963 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1966 // Material hash key OK?
1967 if (failedStep) (*failedStep)++;
1968 if (debugMaterialKey && st->materialKey != compute_material_key())
1971 // Incremental eval OK?
1972 if (failedStep) (*failedStep)++;
1973 if (debugIncrementalEval && st->value != compute_value())
1976 // Non-pawn material OK?
1977 if (failedStep) (*failedStep)++;
1978 if (debugNonPawnMaterial)
1980 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1983 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1988 if (failedStep) (*failedStep)++;
1989 if (debugPieceCounts)
1990 for (Color c = WHITE; c <= BLACK; c++)
1991 for (PieceType pt = PAWN; pt <= KING; pt++)
1992 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1995 if (failedStep) (*failedStep)++;
1998 for (Color c = WHITE; c <= BLACK; c++)
1999 for (PieceType pt = PAWN; pt <= KING; pt++)
2000 for (int i = 0; i < pieceCount[c][pt]; i++)
2002 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2005 if (index[piece_list(c, pt, i)] != i)
2010 if (failedStep) (*failedStep)++;
2011 if (debugCastleSquares) {
2012 for (Color c = WHITE; c <= BLACK; c++) {
2013 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2015 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2018 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2020 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2022 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2024 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2028 if (failedStep) *failedStep = 0;