2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
33 #include "ucioption.h"
39 Key Position::zobrist[2][8][64];
40 Key Position::zobEp[64];
41 Key Position::zobCastle[16];
42 Key Position::zobSideToMove;
43 Key Position::zobExclusion;
45 Score Position::PieceSquareTable[16][64];
47 // Material values arrays, indexed by Piece
48 const Value PieceValueMidgame[17] = {
50 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
51 RookValueMidgame, QueenValueMidgame,
52 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
53 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
54 RookValueMidgame, QueenValueMidgame
57 const Value PieceValueEndgame[17] = {
59 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
60 RookValueEndgame, QueenValueEndgame,
61 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
62 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
63 RookValueEndgame, QueenValueEndgame
69 // Bonus for having the side to move (modified by Joona Kiiski)
70 const Score TempoValue = make_score(48, 22);
72 // To convert a Piece to and from a FEN char
73 const string PieceToChar(".PNBRQK pnbrqk ");
79 CheckInfo::CheckInfo(const Position& pos) {
81 Color us = pos.side_to_move();
82 Color them = opposite_color(us);
83 Square ksq = pos.king_square(them);
85 dcCandidates = pos.discovered_check_candidates(us);
86 pinned = pos.pinned_pieces(us);
88 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
89 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
90 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
91 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
92 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
93 checkSq[KING] = EmptyBoardBB;
97 /// Position c'tors. Here we always create a copy of the original position
98 /// or the FEN string, we want the new born Position object do not depend
99 /// on any external data so we detach state pointer from the source one.
101 Position::Position(const Position& pos, int th) {
103 memcpy(this, &pos, sizeof(Position));
104 detach(); // Always detach() in copy c'tor to avoid surprises
109 Position::Position(const string& fen, bool isChess960, int th) {
111 from_fen(fen, isChess960);
116 /// Position::detach() copies the content of the current state and castling
117 /// masks inside the position itself. This is needed when the st pointee could
118 /// become stale, as example because the caller is about to going out of scope.
120 void Position::detach() {
124 st->previous = NULL; // As a safe guard
128 /// Position::from_fen() initializes the position object with the given FEN
129 /// string. This function is not very robust - make sure that input FENs are
130 /// correct (this is assumed to be the responsibility of the GUI).
132 void Position::from_fen(const string& fen, bool isChess960) {
134 A FEN string defines a particular position using only the ASCII character set.
136 A FEN string contains six fields. The separator between fields is a space. The fields are:
138 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
139 with rank 1; within each rank, the contents of each square are described from file A through file H.
140 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
141 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
142 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
143 of blank squares), and "/" separate ranks.
145 2) Active color. "w" means white moves next, "b" means black.
147 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
148 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
149 kingside), and/or "q" (Black can castle queenside).
151 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
152 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
153 regardless of whether there is a pawn in position to make an en passant capture.
155 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
156 to determine if a draw can be claimed under the fifty-move rule.
158 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
165 std::istringstream ss(fen);
168 ss >> std::skipws >> token >> std::noskipws;
170 // 1. Piece placement
171 while (!isspace(token))
174 sq -= Square(16); // Jump back of 2 rows
176 else if (isdigit(token))
177 sq += Square(token - '0'); // Skip the given number of files
179 else if ((p = PieceToChar.find(token)) != string::npos)
181 put_piece(Piece(p), sq);
189 ss >> std::skipws >> token;
190 sideToMove = (token == 'w' ? WHITE : BLACK);
192 // 3. Castling availability
193 ss >> token >> std::noskipws;
194 while (token != '-' && !isspace(token))
196 set_castling_rights(token);
200 // 4. En passant square. Ignore if no pawn capture is possible
201 ss >> std::skipws >> ep;
204 st->epSquare = make_square(File(ep[0] - 'a'), Rank(ep[1] - '1'));
206 if (!(attackers_to(st->epSquare) & pieces(PAWN, sideToMove)))
207 st->epSquare = SQ_NONE;
210 // 5-6. Halfmove clock and fullmove number
211 ss >> st->rule50 >> fullMoves;
213 // Various initialisations
214 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
215 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
216 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
217 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
218 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
219 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
221 chess960 = isChess960;
224 st->key = compute_key();
225 st->pawnKey = compute_pawn_key();
226 st->materialKey = compute_material_key();
227 st->value = compute_value();
228 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
229 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
233 /// Position::set_castling_rights() sets castling parameters castling avaiability.
234 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
235 /// that uses the letters of the columns on which the rooks began the game instead
236 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
237 /// associated with the castling right, the traditional castling tag will be replaced
238 /// by the file letter of the involved rook as for the Shredder-FEN.
240 void Position::set_castling_rights(char token) {
242 Color c = islower(token) ? BLACK : WHITE;
244 Square sqA = relative_square(c, SQ_A1);
245 Square sqH = relative_square(c, SQ_H1);
247 initialKFile = square_file(king_square(c));
249 if (toupper(token) == 'K')
251 for (Square sq = sqH; sq >= sqA; sq--)
252 if (piece_on(sq) == make_piece(c, ROOK))
254 set_castle_kingside(c);
255 initialKRFile = square_file(sq);
259 else if (toupper(token) == 'Q')
261 for (Square sq = sqA; sq <= sqH; sq++)
262 if (piece_on(sq) == make_piece(c, ROOK))
264 set_castle_queenside(c);
265 initialQRFile = square_file(sq);
269 else if (toupper(token) >= 'A' && toupper(token) <= 'H')
271 File rookFile = File(toupper(token) - 'A');
273 if (rookFile < initialKFile)
275 set_castle_queenside(c);
276 initialQRFile = rookFile;
280 set_castle_kingside(c);
281 initialKRFile = rookFile;
287 /// Position::to_fen() returns a FEN representation of the position. In case
288 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
290 const string Position::to_fen() const {
296 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
300 for (File file = FILE_A; file <= FILE_H; file++)
302 sq = make_square(file, rank);
304 if (square_is_occupied(sq))
311 fen += PieceToChar[piece_on(sq)];
320 fen += (sideToMove == WHITE ? " w " : " b ");
322 if (st->castleRights != CASTLES_NONE)
324 if (can_castle_kingside(WHITE))
325 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
327 if (can_castle_queenside(WHITE))
328 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
330 if (can_castle_kingside(BLACK))
331 fen += chess960 ? file_to_char(initialKRFile) : 'k';
333 if (can_castle_queenside(BLACK))
334 fen += chess960 ? file_to_char(initialQRFile) : 'q';
338 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
343 /// Position::print() prints an ASCII representation of the position to
344 /// the standard output. If a move is given then also the san is printed.
346 void Position::print(Move move) const {
348 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
352 Position p(*this, thread());
353 string dd = (piece_color(piece_on(move_from(move))) == BLACK ? ".." : "");
354 cout << "\nMove is: " << dd << move_to_san(p, move);
357 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
359 cout << dottedLine << '|';
360 for (File file = FILE_A; file <= FILE_H; file++)
362 Square sq = make_square(file, rank);
363 Piece piece = piece_on(sq);
365 if (piece == PIECE_NONE && square_color(sq) == DARK)
366 piece = PIECE_NONE_DARK_SQ;
368 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
369 cout << c << PieceToChar[piece] << c << '|';
372 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
376 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
377 /// king) pieces for the given color and for the given pinner type. Or, when
378 /// template parameter FindPinned is false, the pieces of the given color
379 /// candidate for a discovery check against the enemy king.
380 /// Bitboard checkersBB must be already updated when looking for pinners.
382 template<bool FindPinned>
383 Bitboard Position::hidden_checkers(Color c) const {
385 Bitboard result = EmptyBoardBB;
386 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
388 // Pinned pieces protect our king, dicovery checks attack
390 Square ksq = king_square(FindPinned ? c : opposite_color(c));
392 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
393 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
395 if (FindPinned && pinners)
396 pinners &= ~st->checkersBB;
400 Square s = pop_1st_bit(&pinners);
401 Bitboard b = squares_between(s, ksq) & occupied_squares();
405 if ( !(b & (b - 1)) // Only one bit set?
406 && (b & pieces_of_color(c))) // Is an our piece?
413 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
414 /// king) pieces for the given color. Note that checkersBB bitboard must
415 /// be already updated.
417 Bitboard Position::pinned_pieces(Color c) const {
419 return hidden_checkers<true>(c);
423 /// Position:discovered_check_candidates() returns a bitboard containing all
424 /// pieces for the given side which are candidates for giving a discovered
425 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
426 /// to be already updated.
428 Bitboard Position::discovered_check_candidates(Color c) const {
430 return hidden_checkers<false>(c);
433 /// Position::attackers_to() computes a bitboard containing all pieces which
434 /// attacks a given square.
436 Bitboard Position::attackers_to(Square s) const {
438 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
439 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
440 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
441 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
442 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
443 | (attacks_from<KING>(s) & pieces(KING));
446 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
448 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
449 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
450 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
451 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
452 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
453 | (attacks_from<KING>(s) & pieces(KING));
456 /// Position::attacks_from() computes a bitboard of all attacks
457 /// of a given piece put in a given square.
459 Bitboard Position::attacks_from(Piece p, Square s) const {
461 assert(square_is_ok(s));
465 case WB: case BB: return attacks_from<BISHOP>(s);
466 case WR: case BR: return attacks_from<ROOK>(s);
467 case WQ: case BQ: return attacks_from<QUEEN>(s);
468 default: return StepAttacksBB[p][s];
472 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
474 assert(square_is_ok(s));
478 case WB: case BB: return bishop_attacks_bb(s, occ);
479 case WR: case BR: return rook_attacks_bb(s, occ);
480 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
481 default: return StepAttacksBB[p][s];
486 /// Position::move_attacks_square() tests whether a move from the current
487 /// position attacks a given square.
489 bool Position::move_attacks_square(Move m, Square s) const {
491 assert(move_is_ok(m));
492 assert(square_is_ok(s));
495 Square f = move_from(m), t = move_to(m);
497 assert(square_is_occupied(f));
499 if (bit_is_set(attacks_from(piece_on(f), t), s))
502 // Move the piece and scan for X-ray attacks behind it
503 occ = occupied_squares();
504 do_move_bb(&occ, make_move_bb(f, t));
505 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
506 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
507 & pieces_of_color(piece_color(piece_on(f)));
509 // If we have attacks we need to verify that are caused by our move
510 // and are not already existent ones.
511 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
515 /// Position::find_checkers() computes the checkersBB bitboard, which
516 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
517 /// currently works by calling Position::attackers_to, which is probably
518 /// inefficient. Consider rewriting this function to use the last move
519 /// played, like in non-bitboard versions of Glaurung.
521 void Position::find_checkers() {
523 Color us = side_to_move();
524 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
528 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
530 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
533 assert(move_is_ok(m));
534 assert(pinned == pinned_pieces(side_to_move()));
536 Color us = side_to_move();
537 Square from = move_from(m);
539 assert(piece_color(piece_on(from)) == us);
540 assert(piece_on(king_square(us)) == make_piece(us, KING));
542 // En passant captures are a tricky special case. Because they are
543 // rather uncommon, we do it simply by testing whether the king is attacked
544 // after the move is made
547 Color them = opposite_color(us);
548 Square to = move_to(m);
549 Square capsq = make_square(square_file(to), square_rank(from));
550 Square ksq = king_square(us);
551 Bitboard b = occupied_squares();
553 assert(to == ep_square());
554 assert(piece_on(from) == make_piece(us, PAWN));
555 assert(piece_on(capsq) == make_piece(them, PAWN));
556 assert(piece_on(to) == PIECE_NONE);
559 clear_bit(&b, capsq);
562 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
563 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
566 // If the moving piece is a king, check whether the destination
567 // square is attacked by the opponent. Castling moves are checked
568 // for legality during move generation.
569 if (piece_type(piece_on(from)) == KING)
570 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
572 // A non-king move is legal if and only if it is not pinned or it
573 // is moving along the ray towards or away from the king.
575 || !bit_is_set(pinned, from)
576 || squares_aligned(from, move_to(m), king_square(us));
580 /// Position::move_is_pl_slow() takes a move and tests whether the move
581 /// is pseudo legal. This version is not very fast and should be used
582 /// only in non time-critical paths.
584 bool Position::move_is_pl_slow(const Move m) const {
586 MoveStack mlist[MAX_MOVES];
587 MoveStack *cur, *last;
589 last = in_check() ? generate<MV_EVASION>(*this, mlist)
590 : generate<MV_NON_EVASION>(*this, mlist);
592 for (cur = mlist; cur != last; cur++)
600 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
601 /// of pinned pieces as input, and tests whether the move is pseudo legal.
603 bool Position::move_is_pl(const Move m) const {
607 Color us = sideToMove;
608 Color them = opposite_color(sideToMove);
609 Square from = move_from(m);
610 Square to = move_to(m);
611 Piece pc = piece_on(from);
613 // Use a slower but simpler function for uncommon cases
614 if (move_is_special(m))
615 return move_is_pl_slow(m);
617 // Is not a promotion, so promotion piece must be empty
618 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
621 // If the from square is not occupied by a piece belonging to the side to
622 // move, the move is obviously not legal.
623 if (pc == PIECE_NONE || piece_color(pc) != us)
626 // The destination square cannot be occupied by a friendly piece
627 if (piece_color(piece_on(to)) == us)
630 // Handle the special case of a pawn move
631 if (piece_type(pc) == PAWN)
633 // Move direction must be compatible with pawn color
634 int direction = to - from;
635 if ((us == WHITE) != (direction > 0))
638 // We have already handled promotion moves, so destination
639 // cannot be on the 8/1th rank.
640 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
643 // Proceed according to the square delta between the origin and
644 // destination squares.
651 // Capture. The destination square must be occupied by an enemy
652 // piece (en passant captures was handled earlier).
653 if (piece_color(piece_on(to)) != them)
656 // From and to files must be one file apart, avoids a7h5
657 if (abs(square_file(from) - square_file(to)) != 1)
663 // Pawn push. The destination square must be empty.
664 if (!square_is_empty(to))
669 // Double white pawn push. The destination square must be on the fourth
670 // rank, and both the destination square and the square between the
671 // source and destination squares must be empty.
672 if ( square_rank(to) != RANK_4
673 || !square_is_empty(to)
674 || !square_is_empty(from + DELTA_N))
679 // Double black pawn push. The destination square must be on the fifth
680 // rank, and both the destination square and the square between the
681 // source and destination squares must be empty.
682 if ( square_rank(to) != RANK_5
683 || !square_is_empty(to)
684 || !square_is_empty(from + DELTA_S))
692 else if (!bit_is_set(attacks_from(pc, from), to))
697 // In case of king moves under check we have to remove king so to catch
698 // as invalid moves like b1a1 when opposite queen is on c1.
699 if (piece_type(piece_on(from)) == KING)
701 Bitboard b = occupied_squares();
703 if (attackers_to(move_to(m), b) & pieces_of_color(opposite_color(us)))
708 Bitboard target = checkers();
709 Square checksq = pop_1st_bit(&target);
711 if (target) // double check ? In this case a king move is required
714 // Our move must be a blocking evasion or a capture of the checking piece
715 target = squares_between(checksq, king_square(us)) | checkers();
716 if (!bit_is_set(target, move_to(m)))
725 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
727 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
730 assert(move_is_ok(m));
731 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
732 assert(piece_color(piece_on(move_from(m))) == side_to_move());
734 Square from = move_from(m);
735 Square to = move_to(m);
736 PieceType pt = piece_type(piece_on(from));
739 if (bit_is_set(ci.checkSq[pt], to))
743 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
745 // For pawn and king moves we need to verify also direction
746 if ( (pt != PAWN && pt != KING)
747 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
751 // Can we skip the ugly special cases ?
752 if (!move_is_special(m))
755 Color us = side_to_move();
756 Bitboard b = occupied_squares();
757 Square ksq = king_square(opposite_color(us));
759 // Promotion with check ?
760 if (move_is_promotion(m))
764 switch (promotion_piece_type(m))
767 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
769 return bit_is_set(bishop_attacks_bb(to, b), ksq);
771 return bit_is_set(rook_attacks_bb(to, b), ksq);
773 return bit_is_set(queen_attacks_bb(to, b), ksq);
779 // En passant capture with check ? We have already handled the case
780 // of direct checks and ordinary discovered check, the only case we
781 // need to handle is the unusual case of a discovered check through
782 // the captured pawn.
785 Square capsq = make_square(square_file(to), square_rank(from));
787 clear_bit(&b, capsq);
789 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
790 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
793 // Castling with check ?
794 if (move_is_castle(m))
796 Square kfrom, kto, rfrom, rto;
802 kto = relative_square(us, SQ_G1);
803 rto = relative_square(us, SQ_F1);
805 kto = relative_square(us, SQ_C1);
806 rto = relative_square(us, SQ_D1);
808 clear_bit(&b, kfrom);
809 clear_bit(&b, rfrom);
812 return bit_is_set(rook_attacks_bb(rto, b), ksq);
819 /// Position::do_setup_move() makes a permanent move on the board. It should
820 /// be used when setting up a position on board. You can't undo the move.
822 void Position::do_setup_move(Move m) {
826 // Update the number of full moves after black's move
827 if (sideToMove == BLACK)
832 // Reset "game ply" in case we made a non-reversible move.
833 // "game ply" is used for repetition detection.
837 // Our StateInfo newSt is about going out of scope so copy
838 // its content before it disappears.
843 /// Position::do_move() makes a move, and saves all information necessary
844 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
845 /// moves should be filtered out before this function is called.
847 void Position::do_move(Move m, StateInfo& newSt) {
850 do_move(m, newSt, ci, move_gives_check(m, ci));
853 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
856 assert(move_is_ok(m));
857 assert(&newSt != st);
862 // Copy some fields of old state to our new StateInfo object except the
863 // ones which are recalculated from scratch anyway, then switch our state
864 // pointer to point to the new, ready to be updated, state.
865 struct ReducedStateInfo {
866 Key pawnKey, materialKey;
867 int castleRights, rule50, gamePly, pliesFromNull;
873 memcpy(&newSt, st, sizeof(ReducedStateInfo));
878 // Save the current key to the history[] array, in order to be able to
879 // detect repetition draws.
880 history[st->gamePly++] = key;
882 // Update side to move
883 key ^= zobSideToMove;
885 // Increment the 50 moves rule draw counter. Resetting it to zero in the
886 // case of non-reversible moves is taken care of later.
890 if (move_is_castle(m))
897 Color us = side_to_move();
898 Color them = opposite_color(us);
899 Square from = move_from(m);
900 Square to = move_to(m);
901 bool ep = move_is_ep(m);
902 bool pm = move_is_promotion(m);
904 Piece piece = piece_on(from);
905 PieceType pt = piece_type(piece);
906 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
908 assert(piece_color(piece_on(from)) == us);
909 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
910 assert(!(ep || pm) || piece == make_piece(us, PAWN));
911 assert(!pm || relative_rank(us, to) == RANK_8);
914 do_capture_move(key, capture, them, to, ep);
917 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
919 // Reset en passant square
920 if (st->epSquare != SQ_NONE)
922 key ^= zobEp[st->epSquare];
923 st->epSquare = SQ_NONE;
926 // Update castle rights if needed
927 if ( st->castleRights != CASTLES_NONE
928 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
930 key ^= zobCastle[st->castleRights];
931 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
932 key ^= zobCastle[st->castleRights];
935 // Prefetch TT access as soon as we know key is updated
936 prefetch((char*)TT.first_entry(key));
939 Bitboard move_bb = make_move_bb(from, to);
940 do_move_bb(&(byColorBB[us]), move_bb);
941 do_move_bb(&(byTypeBB[pt]), move_bb);
942 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
944 board[to] = board[from];
945 board[from] = PIECE_NONE;
947 // Update piece lists, note that index[from] is not updated and
948 // becomes stale. This works as long as index[] is accessed just
949 // by known occupied squares.
950 index[to] = index[from];
951 pieceList[us][pt][index[to]] = to;
953 // If the moving piece was a pawn do some special extra work
956 // Reset rule 50 draw counter
959 // Update pawn hash key and prefetch in L1/L2 cache
960 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
962 // Set en passant square, only if moved pawn can be captured
963 if ((to ^ from) == 16)
965 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
967 st->epSquare = Square((int(from) + int(to)) / 2);
968 key ^= zobEp[st->epSquare];
972 if (pm) // promotion ?
974 PieceType promotion = promotion_piece_type(m);
976 assert(promotion >= KNIGHT && promotion <= QUEEN);
978 // Insert promoted piece instead of pawn
979 clear_bit(&(byTypeBB[PAWN]), to);
980 set_bit(&(byTypeBB[promotion]), to);
981 board[to] = make_piece(us, promotion);
983 // Update piece counts
984 pieceCount[us][promotion]++;
985 pieceCount[us][PAWN]--;
987 // Update material key
988 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
989 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
991 // Update piece lists, move the last pawn at index[to] position
992 // and shrink the list. Add a new promotion piece to the list.
993 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
994 index[lastPawnSquare] = index[to];
995 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
996 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
997 index[to] = pieceCount[us][promotion] - 1;
998 pieceList[us][promotion][index[to]] = to;
1000 // Partially revert hash keys update
1001 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
1002 st->pawnKey ^= zobrist[us][PAWN][to];
1004 // Partially revert and update incremental scores
1005 st->value -= pst(us, PAWN, to);
1006 st->value += pst(us, promotion, to);
1009 st->npMaterial[us] += PieceValueMidgame[promotion];
1013 // Prefetch pawn and material hash tables
1014 Threads[threadID].pawnTable.prefetch(st->pawnKey);
1015 Threads[threadID].materialTable.prefetch(st->materialKey);
1017 // Update incremental scores
1018 st->value += pst_delta(piece, from, to);
1020 // Set capture piece
1021 st->capturedType = capture;
1023 // Update the key with the final value
1026 // Update checkers bitboard, piece must be already moved
1027 st->checkersBB = EmptyBoardBB;
1032 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1036 if (bit_is_set(ci.checkSq[pt], to))
1037 st->checkersBB = SetMaskBB[to];
1040 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1043 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1046 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1052 sideToMove = opposite_color(sideToMove);
1053 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1059 /// Position::do_capture_move() is a private method used to update captured
1060 /// piece info. It is called from the main Position::do_move function.
1062 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1064 assert(capture != KING);
1068 // If the captured piece was a pawn, update pawn hash key,
1069 // otherwise update non-pawn material.
1070 if (capture == PAWN)
1072 if (ep) // en passant ?
1074 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1076 assert(to == st->epSquare);
1077 assert(relative_rank(opposite_color(them), to) == RANK_6);
1078 assert(piece_on(to) == PIECE_NONE);
1079 assert(piece_on(capsq) == make_piece(them, PAWN));
1081 board[capsq] = PIECE_NONE;
1083 st->pawnKey ^= zobrist[them][PAWN][capsq];
1086 st->npMaterial[them] -= PieceValueMidgame[capture];
1088 // Remove captured piece
1089 clear_bit(&(byColorBB[them]), capsq);
1090 clear_bit(&(byTypeBB[capture]), capsq);
1091 clear_bit(&(byTypeBB[0]), capsq);
1094 key ^= zobrist[them][capture][capsq];
1096 // Update incremental scores
1097 st->value -= pst(them, capture, capsq);
1099 // Update piece count
1100 pieceCount[them][capture]--;
1102 // Update material hash key
1103 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1105 // Update piece list, move the last piece at index[capsq] position
1107 // WARNING: This is a not perfectly revresible operation. When we
1108 // will reinsert the captured piece in undo_move() we will put it
1109 // at the end of the list and not in its original place, it means
1110 // index[] and pieceList[] are not guaranteed to be invariant to a
1111 // do_move() + undo_move() sequence.
1112 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1113 index[lastPieceSquare] = index[capsq];
1114 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1115 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1117 // Reset rule 50 counter
1122 /// Position::do_castle_move() is a private method used to make a castling
1123 /// move. It is called from the main Position::do_move function. Note that
1124 /// castling moves are encoded as "king captures friendly rook" moves, for
1125 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1127 void Position::do_castle_move(Move m) {
1129 assert(move_is_ok(m));
1130 assert(move_is_castle(m));
1132 Color us = side_to_move();
1133 Color them = opposite_color(us);
1135 // Reset capture field
1136 st->capturedType = PIECE_TYPE_NONE;
1138 // Find source squares for king and rook
1139 Square kfrom = move_from(m);
1140 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1143 assert(piece_on(kfrom) == make_piece(us, KING));
1144 assert(piece_on(rfrom) == make_piece(us, ROOK));
1146 // Find destination squares for king and rook
1147 if (rfrom > kfrom) // O-O
1149 kto = relative_square(us, SQ_G1);
1150 rto = relative_square(us, SQ_F1);
1152 kto = relative_square(us, SQ_C1);
1153 rto = relative_square(us, SQ_D1);
1156 // Remove pieces from source squares:
1157 clear_bit(&(byColorBB[us]), kfrom);
1158 clear_bit(&(byTypeBB[KING]), kfrom);
1159 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1160 clear_bit(&(byColorBB[us]), rfrom);
1161 clear_bit(&(byTypeBB[ROOK]), rfrom);
1162 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1164 // Put pieces on destination squares:
1165 set_bit(&(byColorBB[us]), kto);
1166 set_bit(&(byTypeBB[KING]), kto);
1167 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1168 set_bit(&(byColorBB[us]), rto);
1169 set_bit(&(byTypeBB[ROOK]), rto);
1170 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1172 // Update board array
1173 Piece king = make_piece(us, KING);
1174 Piece rook = make_piece(us, ROOK);
1175 board[kfrom] = board[rfrom] = PIECE_NONE;
1179 // Update piece lists
1180 pieceList[us][KING][index[kfrom]] = kto;
1181 pieceList[us][ROOK][index[rfrom]] = rto;
1182 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1183 index[kto] = index[kfrom];
1186 // Update incremental scores
1187 st->value += pst_delta(king, kfrom, kto);
1188 st->value += pst_delta(rook, rfrom, rto);
1191 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1192 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1194 // Clear en passant square
1195 if (st->epSquare != SQ_NONE)
1197 st->key ^= zobEp[st->epSquare];
1198 st->epSquare = SQ_NONE;
1201 // Update castling rights
1202 st->key ^= zobCastle[st->castleRights];
1203 st->castleRights &= castleRightsMask[kfrom];
1204 st->key ^= zobCastle[st->castleRights];
1206 // Reset rule 50 counter
1209 // Update checkers BB
1210 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1213 sideToMove = opposite_color(sideToMove);
1214 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1220 /// Position::undo_move() unmakes a move. When it returns, the position should
1221 /// be restored to exactly the same state as before the move was made.
1223 void Position::undo_move(Move m) {
1226 assert(move_is_ok(m));
1228 sideToMove = opposite_color(sideToMove);
1230 if (move_is_castle(m))
1232 undo_castle_move(m);
1236 Color us = side_to_move();
1237 Color them = opposite_color(us);
1238 Square from = move_from(m);
1239 Square to = move_to(m);
1240 bool ep = move_is_ep(m);
1241 bool pm = move_is_promotion(m);
1243 PieceType pt = piece_type(piece_on(to));
1245 assert(square_is_empty(from));
1246 assert(piece_color(piece_on(to)) == us);
1247 assert(!pm || relative_rank(us, to) == RANK_8);
1248 assert(!ep || to == st->previous->epSquare);
1249 assert(!ep || relative_rank(us, to) == RANK_6);
1250 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1252 if (pm) // promotion ?
1254 PieceType promotion = promotion_piece_type(m);
1257 assert(promotion >= KNIGHT && promotion <= QUEEN);
1258 assert(piece_on(to) == make_piece(us, promotion));
1260 // Replace promoted piece with a pawn
1261 clear_bit(&(byTypeBB[promotion]), to);
1262 set_bit(&(byTypeBB[PAWN]), to);
1264 // Update piece counts
1265 pieceCount[us][promotion]--;
1266 pieceCount[us][PAWN]++;
1268 // Update piece list replacing promotion piece with a pawn
1269 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1270 index[lastPromotionSquare] = index[to];
1271 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1272 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1273 index[to] = pieceCount[us][PAWN] - 1;
1274 pieceList[us][PAWN][index[to]] = to;
1277 // Put the piece back at the source square
1278 Bitboard move_bb = make_move_bb(to, from);
1279 do_move_bb(&(byColorBB[us]), move_bb);
1280 do_move_bb(&(byTypeBB[pt]), move_bb);
1281 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1283 board[from] = make_piece(us, pt);
1284 board[to] = PIECE_NONE;
1286 // Update piece list
1287 index[from] = index[to];
1288 pieceList[us][pt][index[from]] = from;
1290 if (st->capturedType)
1295 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1297 assert(st->capturedType != KING);
1298 assert(!ep || square_is_empty(capsq));
1300 // Restore the captured piece
1301 set_bit(&(byColorBB[them]), capsq);
1302 set_bit(&(byTypeBB[st->capturedType]), capsq);
1303 set_bit(&(byTypeBB[0]), capsq);
1305 board[capsq] = make_piece(them, st->capturedType);
1307 // Update piece count
1308 pieceCount[them][st->capturedType]++;
1310 // Update piece list, add a new captured piece in capsq square
1311 index[capsq] = pieceCount[them][st->capturedType] - 1;
1312 pieceList[them][st->capturedType][index[capsq]] = capsq;
1315 // Finally point our state pointer back to the previous state
1322 /// Position::undo_castle_move() is a private method used to unmake a castling
1323 /// move. It is called from the main Position::undo_move function. Note that
1324 /// castling moves are encoded as "king captures friendly rook" moves, for
1325 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1327 void Position::undo_castle_move(Move m) {
1329 assert(move_is_ok(m));
1330 assert(move_is_castle(m));
1332 // When we have arrived here, some work has already been done by
1333 // Position::undo_move. In particular, the side to move has been switched,
1334 // so the code below is correct.
1335 Color us = side_to_move();
1337 // Find source squares for king and rook
1338 Square kfrom = move_from(m);
1339 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1342 // Find destination squares for king and rook
1343 if (rfrom > kfrom) // O-O
1345 kto = relative_square(us, SQ_G1);
1346 rto = relative_square(us, SQ_F1);
1348 kto = relative_square(us, SQ_C1);
1349 rto = relative_square(us, SQ_D1);
1352 assert(piece_on(kto) == make_piece(us, KING));
1353 assert(piece_on(rto) == make_piece(us, ROOK));
1355 // Remove pieces from destination squares:
1356 clear_bit(&(byColorBB[us]), kto);
1357 clear_bit(&(byTypeBB[KING]), kto);
1358 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1359 clear_bit(&(byColorBB[us]), rto);
1360 clear_bit(&(byTypeBB[ROOK]), rto);
1361 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1363 // Put pieces on source squares:
1364 set_bit(&(byColorBB[us]), kfrom);
1365 set_bit(&(byTypeBB[KING]), kfrom);
1366 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1367 set_bit(&(byColorBB[us]), rfrom);
1368 set_bit(&(byTypeBB[ROOK]), rfrom);
1369 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1372 board[rto] = board[kto] = PIECE_NONE;
1373 board[rfrom] = make_piece(us, ROOK);
1374 board[kfrom] = make_piece(us, KING);
1376 // Update piece lists
1377 pieceList[us][KING][index[kto]] = kfrom;
1378 pieceList[us][ROOK][index[rto]] = rfrom;
1379 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1380 index[kfrom] = index[kto];
1383 // Finally point our state pointer back to the previous state
1390 /// Position::do_null_move makes() a "null move": It switches the side to move
1391 /// and updates the hash key without executing any move on the board.
1393 void Position::do_null_move(StateInfo& backupSt) {
1396 assert(!in_check());
1398 // Back up the information necessary to undo the null move to the supplied
1399 // StateInfo object.
1400 // Note that differently from normal case here backupSt is actually used as
1401 // a backup storage not as a new state to be used.
1402 backupSt.key = st->key;
1403 backupSt.epSquare = st->epSquare;
1404 backupSt.value = st->value;
1405 backupSt.previous = st->previous;
1406 backupSt.pliesFromNull = st->pliesFromNull;
1407 st->previous = &backupSt;
1409 // Save the current key to the history[] array, in order to be able to
1410 // detect repetition draws.
1411 history[st->gamePly++] = st->key;
1413 // Update the necessary information
1414 if (st->epSquare != SQ_NONE)
1415 st->key ^= zobEp[st->epSquare];
1417 st->key ^= zobSideToMove;
1418 prefetch((char*)TT.first_entry(st->key));
1420 sideToMove = opposite_color(sideToMove);
1421 st->epSquare = SQ_NONE;
1423 st->pliesFromNull = 0;
1424 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1428 /// Position::undo_null_move() unmakes a "null move".
1430 void Position::undo_null_move() {
1433 assert(!in_check());
1435 // Restore information from the our backup StateInfo object
1436 StateInfo* backupSt = st->previous;
1437 st->key = backupSt->key;
1438 st->epSquare = backupSt->epSquare;
1439 st->value = backupSt->value;
1440 st->previous = backupSt->previous;
1441 st->pliesFromNull = backupSt->pliesFromNull;
1443 // Update the necessary information
1444 sideToMove = opposite_color(sideToMove);
1450 /// Position::see() is a static exchange evaluator: It tries to estimate the
1451 /// material gain or loss resulting from a move. There are three versions of
1452 /// this function: One which takes a destination square as input, one takes a
1453 /// move, and one which takes a 'from' and a 'to' square. The function does
1454 /// not yet understand promotions captures.
1456 int Position::see_sign(Move m) const {
1458 assert(move_is_ok(m));
1460 Square from = move_from(m);
1461 Square to = move_to(m);
1463 // Early return if SEE cannot be negative because captured piece value
1464 // is not less then capturing one. Note that king moves always return
1465 // here because king midgame value is set to 0.
1466 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1472 int Position::see(Move m) const {
1475 Bitboard occupied, attackers, stmAttackers, b;
1476 int swapList[32], slIndex = 1;
1477 PieceType capturedType, pt;
1480 assert(move_is_ok(m));
1482 // As castle moves are implemented as capturing the rook, they have
1483 // SEE == RookValueMidgame most of the times (unless the rook is under
1485 if (move_is_castle(m))
1488 from = move_from(m);
1490 capturedType = piece_type(piece_on(to));
1491 occupied = occupied_squares();
1493 // Handle en passant moves
1494 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1496 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1498 assert(capturedType == PIECE_TYPE_NONE);
1499 assert(piece_type(piece_on(capQq)) == PAWN);
1501 // Remove the captured pawn
1502 clear_bit(&occupied, capQq);
1503 capturedType = PAWN;
1506 // Find all attackers to the destination square, with the moving piece
1507 // removed, but possibly an X-ray attacker added behind it.
1508 clear_bit(&occupied, from);
1509 attackers = attackers_to(to, occupied);
1511 // If the opponent has no attackers we are finished
1512 stm = opposite_color(piece_color(piece_on(from)));
1513 stmAttackers = attackers & pieces_of_color(stm);
1515 return PieceValueMidgame[capturedType];
1517 // The destination square is defended, which makes things rather more
1518 // difficult to compute. We proceed by building up a "swap list" containing
1519 // the material gain or loss at each stop in a sequence of captures to the
1520 // destination square, where the sides alternately capture, and always
1521 // capture with the least valuable piece. After each capture, we look for
1522 // new X-ray attacks from behind the capturing piece.
1523 swapList[0] = PieceValueMidgame[capturedType];
1524 capturedType = piece_type(piece_on(from));
1527 // Locate the least valuable attacker for the side to move. The loop
1528 // below looks like it is potentially infinite, but it isn't. We know
1529 // that the side to move still has at least one attacker left.
1530 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1533 // Remove the attacker we just found from the 'occupied' bitboard,
1534 // and scan for new X-ray attacks behind the attacker.
1535 b = stmAttackers & pieces(pt);
1536 occupied ^= (b & (~b + 1));
1537 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1538 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1540 attackers &= occupied; // Cut out pieces we've already done
1542 // Add the new entry to the swap list
1543 assert(slIndex < 32);
1544 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1547 // Remember the value of the capturing piece, and change the side to
1548 // move before beginning the next iteration.
1550 stm = opposite_color(stm);
1551 stmAttackers = attackers & pieces_of_color(stm);
1553 // Stop before processing a king capture
1554 if (capturedType == KING && stmAttackers)
1556 assert(slIndex < 32);
1557 swapList[slIndex++] = QueenValueMidgame*10;
1560 } while (stmAttackers);
1562 // Having built the swap list, we negamax through it to find the best
1563 // achievable score from the point of view of the side to move.
1565 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1571 /// Position::clear() erases the position object to a pristine state, with an
1572 /// empty board, white to move, and no castling rights.
1574 void Position::clear() {
1577 memset(st, 0, sizeof(StateInfo));
1578 st->epSquare = SQ_NONE;
1582 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1583 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1584 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1585 memset(index, 0, sizeof(int) * 64);
1587 for (int i = 0; i < 64; i++)
1588 board[i] = PIECE_NONE;
1590 for (int i = 0; i < 8; i++)
1591 for (int j = 0; j < 16; j++)
1592 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1594 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1595 castleRightsMask[sq] = ALL_CASTLES;
1598 initialKFile = FILE_E;
1599 initialKRFile = FILE_H;
1600 initialQRFile = FILE_A;
1604 /// Position::put_piece() puts a piece on the given square of the board,
1605 /// updating the board array, pieces list, bitboards, and piece counts.
1607 void Position::put_piece(Piece p, Square s) {
1609 Color c = piece_color(p);
1610 PieceType pt = piece_type(p);
1613 index[s] = pieceCount[c][pt]++;
1614 pieceList[c][pt][index[s]] = s;
1616 set_bit(&(byTypeBB[pt]), s);
1617 set_bit(&(byColorBB[c]), s);
1618 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1622 /// Position::compute_key() computes the hash key of the position. The hash
1623 /// key is usually updated incrementally as moves are made and unmade, the
1624 /// compute_key() function is only used when a new position is set up, and
1625 /// to verify the correctness of the hash key when running in debug mode.
1627 Key Position::compute_key() const {
1629 Key result = zobCastle[st->castleRights];
1631 for (Square s = SQ_A1; s <= SQ_H8; s++)
1632 if (square_is_occupied(s))
1633 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1635 if (ep_square() != SQ_NONE)
1636 result ^= zobEp[ep_square()];
1638 if (side_to_move() == BLACK)
1639 result ^= zobSideToMove;
1645 /// Position::compute_pawn_key() computes the hash key of the position. The
1646 /// hash key is usually updated incrementally as moves are made and unmade,
1647 /// the compute_pawn_key() function is only used when a new position is set
1648 /// up, and to verify the correctness of the pawn hash key when running in
1651 Key Position::compute_pawn_key() const {
1656 for (Color c = WHITE; c <= BLACK; c++)
1658 b = pieces(PAWN, c);
1660 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1666 /// Position::compute_material_key() computes the hash key of the position.
1667 /// The hash key is usually updated incrementally as moves are made and unmade,
1668 /// the compute_material_key() function is only used when a new position is set
1669 /// up, and to verify the correctness of the material hash key when running in
1672 Key Position::compute_material_key() const {
1677 for (Color c = WHITE; c <= BLACK; c++)
1678 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1680 count = piece_count(c, pt);
1681 for (int i = 0; i < count; i++)
1682 result ^= zobrist[c][pt][i];
1688 /// Position::compute_value() compute the incremental scores for the middle
1689 /// game and the endgame. These functions are used to initialize the incremental
1690 /// scores when a new position is set up, and to verify that the scores are correctly
1691 /// updated by do_move and undo_move when the program is running in debug mode.
1692 Score Position::compute_value() const {
1695 Score result = SCORE_ZERO;
1697 for (Color c = WHITE; c <= BLACK; c++)
1698 for (PieceType pt = PAWN; pt <= KING; pt++)
1702 result += pst(c, pt, pop_1st_bit(&b));
1705 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1710 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1711 /// game material value for the given side. Material values are updated
1712 /// incrementally during the search, this function is only used while
1713 /// initializing a new Position object.
1715 Value Position::compute_non_pawn_material(Color c) const {
1717 Value result = VALUE_ZERO;
1719 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1720 result += piece_count(c, pt) * PieceValueMidgame[pt];
1726 /// Position::is_draw() tests whether the position is drawn by material,
1727 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1728 /// must be done by the search.
1729 template<bool SkipRepetition>
1730 bool Position::is_draw() const {
1732 // Draw by material?
1734 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1737 // Draw by the 50 moves rule?
1738 if (st->rule50 > 99 && !is_mate())
1741 // Draw by repetition?
1742 if (!SkipRepetition)
1743 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1744 if (history[st->gamePly - i] == st->key)
1750 // Explicit template instantiations
1751 template bool Position::is_draw<false>() const;
1752 template bool Position::is_draw<true>() const;
1755 /// Position::is_mate() returns true or false depending on whether the
1756 /// side to move is checkmated.
1758 bool Position::is_mate() const {
1760 MoveStack moves[MAX_MOVES];
1761 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1765 /// Position::init() is a static member function which initializes at
1766 /// startup the various arrays used to compute hash keys and the piece
1767 /// square tables. The latter is a two-step operation: First, the white
1768 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1769 /// Second, the black halves of the tables are initialized by mirroring
1770 /// and changing the sign of the corresponding white scores.
1772 void Position::init() {
1776 for (Color c = WHITE; c <= BLACK; c++)
1777 for (PieceType pt = PAWN; pt <= KING; pt++)
1778 for (Square s = SQ_A1; s <= SQ_H8; s++)
1779 zobrist[c][pt][s] = rk.rand<Key>();
1781 for (Square s = SQ_A1; s <= SQ_H8; s++)
1782 zobEp[s] = rk.rand<Key>();
1784 for (int i = 0; i < 16; i++)
1785 zobCastle[i] = rk.rand<Key>();
1787 zobSideToMove = rk.rand<Key>();
1788 zobExclusion = rk.rand<Key>();
1790 for (Square s = SQ_A1; s <= SQ_H8; s++)
1791 for (Piece p = WP; p <= WK; p++)
1792 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1794 for (Square s = SQ_A1; s <= SQ_H8; s++)
1795 for (Piece p = BP; p <= BK; p++)
1796 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1800 /// Position::flip() flips position with the white and black sides reversed. This
1801 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1803 void Position::flip() {
1807 // Make a copy of current position before to start changing
1808 const Position pos(*this, threadID);
1811 threadID = pos.thread();
1814 for (Square s = SQ_A1; s <= SQ_H8; s++)
1815 if (!pos.square_is_empty(s))
1816 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1819 sideToMove = opposite_color(pos.side_to_move());
1822 if (pos.can_castle_kingside(WHITE)) set_castle_kingside(BLACK);
1823 if (pos.can_castle_queenside(WHITE)) set_castle_queenside(BLACK);
1824 if (pos.can_castle_kingside(BLACK)) set_castle_kingside(WHITE);
1825 if (pos.can_castle_queenside(BLACK)) set_castle_queenside(WHITE);
1827 initialKFile = pos.initialKFile;
1828 initialKRFile = pos.initialKRFile;
1829 initialQRFile = pos.initialQRFile;
1831 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1832 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1833 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1834 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1835 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1836 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1838 // En passant square
1839 if (pos.st->epSquare != SQ_NONE)
1840 st->epSquare = flip_square(pos.st->epSquare);
1846 st->key = compute_key();
1847 st->pawnKey = compute_pawn_key();
1848 st->materialKey = compute_material_key();
1850 // Incremental scores
1851 st->value = compute_value();
1854 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1855 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1861 /// Position::is_ok() performs some consitency checks for the position object.
1862 /// This is meant to be helpful when debugging.
1864 bool Position::is_ok(int* failedStep) const {
1866 // What features of the position should be verified?
1867 const bool debugAll = false;
1869 const bool debugBitboards = debugAll || false;
1870 const bool debugKingCount = debugAll || false;
1871 const bool debugKingCapture = debugAll || false;
1872 const bool debugCheckerCount = debugAll || false;
1873 const bool debugKey = debugAll || false;
1874 const bool debugMaterialKey = debugAll || false;
1875 const bool debugPawnKey = debugAll || false;
1876 const bool debugIncrementalEval = debugAll || false;
1877 const bool debugNonPawnMaterial = debugAll || false;
1878 const bool debugPieceCounts = debugAll || false;
1879 const bool debugPieceList = debugAll || false;
1880 const bool debugCastleSquares = debugAll || false;
1882 if (failedStep) *failedStep = 1;
1885 if (side_to_move() != WHITE && side_to_move() != BLACK)
1888 // Are the king squares in the position correct?
1889 if (failedStep) (*failedStep)++;
1890 if (piece_on(king_square(WHITE)) != WK)
1893 if (failedStep) (*failedStep)++;
1894 if (piece_on(king_square(BLACK)) != BK)
1898 if (failedStep) (*failedStep)++;
1899 if (!square_is_ok(make_square(initialKRFile, RANK_1)))
1902 if (!square_is_ok(make_square(initialQRFile, RANK_1)))
1905 // Do both sides have exactly one king?
1906 if (failedStep) (*failedStep)++;
1909 int kingCount[2] = {0, 0};
1910 for (Square s = SQ_A1; s <= SQ_H8; s++)
1911 if (piece_type(piece_on(s)) == KING)
1912 kingCount[piece_color(piece_on(s))]++;
1914 if (kingCount[0] != 1 || kingCount[1] != 1)
1918 // Can the side to move capture the opponent's king?
1919 if (failedStep) (*failedStep)++;
1920 if (debugKingCapture)
1922 Color us = side_to_move();
1923 Color them = opposite_color(us);
1924 Square ksq = king_square(them);
1925 if (attackers_to(ksq) & pieces_of_color(us))
1929 // Is there more than 2 checkers?
1930 if (failedStep) (*failedStep)++;
1931 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1935 if (failedStep) (*failedStep)++;
1938 // The intersection of the white and black pieces must be empty
1939 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1942 // The union of the white and black pieces must be equal to all
1944 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1947 // Separate piece type bitboards must have empty intersections
1948 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1949 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1950 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1954 // En passant square OK?
1955 if (failedStep) (*failedStep)++;
1956 if (ep_square() != SQ_NONE)
1958 // The en passant square must be on rank 6, from the point of view of the
1960 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1965 if (failedStep) (*failedStep)++;
1966 if (debugKey && st->key != compute_key())
1969 // Pawn hash key OK?
1970 if (failedStep) (*failedStep)++;
1971 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1974 // Material hash key OK?
1975 if (failedStep) (*failedStep)++;
1976 if (debugMaterialKey && st->materialKey != compute_material_key())
1979 // Incremental eval OK?
1980 if (failedStep) (*failedStep)++;
1981 if (debugIncrementalEval && st->value != compute_value())
1984 // Non-pawn material OK?
1985 if (failedStep) (*failedStep)++;
1986 if (debugNonPawnMaterial)
1988 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1991 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1996 if (failedStep) (*failedStep)++;
1997 if (debugPieceCounts)
1998 for (Color c = WHITE; c <= BLACK; c++)
1999 for (PieceType pt = PAWN; pt <= KING; pt++)
2000 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
2003 if (failedStep) (*failedStep)++;
2005 for (Color c = WHITE; c <= BLACK; c++)
2006 for (PieceType pt = PAWN; pt <= KING; pt++)
2007 for (int i = 0; i < pieceCount[c][pt]; i++)
2009 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
2012 if (index[piece_list(c, pt, i)] != i)
2016 if (failedStep) (*failedStep)++;
2017 if (debugCastleSquares)
2019 for (Color c = WHITE; c <= BLACK; c++)
2021 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
2024 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
2027 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2029 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2031 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2033 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2037 if (failedStep) *failedStep = 0;