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.
161 char col, row, token;
164 std::istringstream ss(fen);
169 // 1. Piece placement
170 while ((ss >> token) && !isspace(token))
173 sq -= Square(16); // Jump back of 2 rows
175 else if (isdigit(token))
176 sq += Square(token - '0'); // Skip the given number of files
178 else if ((p = PieceToChar.find(token)) != string::npos)
180 put_piece(Piece(p), sq);
187 sideToMove = (token == 'w' ? WHITE : BLACK);
190 // 3. Castling availability
191 while ((ss >> token) && !isspace(token))
192 set_castling_rights(token);
194 // 4. En passant square. Ignore if no pawn capture is possible
195 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
196 && ((ss >> row) && (row == '3' || row == '6')))
198 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
199 Color them = opposite_color(sideToMove);
201 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
202 st->epSquare = SQ_NONE;
205 // 5-6. Halfmove clock and fullmove number
206 ss >> std::skipws >> st->rule50 >> fullMoves;
208 // Various initialisations
209 chess960 = isChess960;
212 st->key = compute_key();
213 st->pawnKey = compute_pawn_key();
214 st->materialKey = compute_material_key();
215 st->value = compute_value();
216 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
221 /// Position::set_castle() is an helper function used to set
222 /// correct castling related flags.
224 void Position::set_castle(int f, Square ksq, Square rsq) {
226 st->castleRights |= f;
227 castleRightsMask[ksq] ^= f;
228 castleRightsMask[rsq] ^= f;
229 castleRookSquare[f] = rsq;
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);
246 Square rsq, ksq = king_square(c);
248 token = toupper(token);
251 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
253 else if (token == 'Q')
254 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
256 else if (token >= 'A' && token <= 'H')
257 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
261 if (square_file(rsq) < square_file(ksq))
262 set_castle(WHITE_OOO << c, ksq, rsq);
264 set_castle(WHITE_OO << c, ksq, rsq);
268 /// Position::to_fen() returns a FEN representation of the position. In case
269 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
271 const string Position::to_fen() const {
277 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
281 for (File file = FILE_A; file <= FILE_H; file++)
283 sq = make_square(file, rank);
285 if (!square_is_empty(sq))
292 fen += PieceToChar[piece_on(sq)];
301 fen += (sideToMove == WHITE ? " w " : " b ");
303 if (st->castleRights != CASTLES_NONE)
305 if (can_castle(WHITE_OO))
306 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K';
308 if (can_castle(WHITE_OOO))
309 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q';
311 if (can_castle(BLACK_OO))
312 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k';
314 if (can_castle(BLACK_OOO))
315 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q';
319 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
324 /// Position::print() prints an ASCII representation of the position to
325 /// the standard output. If a move is given then also the san is printed.
327 void Position::print(Move move) const {
329 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
333 Position p(*this, thread());
334 string dd = (piece_color(piece_on(move_from(move))) == BLACK ? ".." : "");
335 cout << "\nMove is: " << dd << move_to_san(p, move);
338 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
340 cout << dottedLine << '|';
341 for (File file = FILE_A; file <= FILE_H; file++)
343 Square sq = make_square(file, rank);
344 Piece piece = piece_on(sq);
346 if (piece == PIECE_NONE && square_color(sq) == DARK)
347 piece = PIECE_NONE_DARK_SQ;
349 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
350 cout << c << PieceToChar[piece] << c << '|';
353 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
357 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
358 /// king) pieces for the given color and for the given pinner type. Or, when
359 /// template parameter FindPinned is false, the pieces of the given color
360 /// candidate for a discovery check against the enemy king.
361 /// Bitboard checkersBB must be already updated when looking for pinners.
363 template<bool FindPinned>
364 Bitboard Position::hidden_checkers(Color c) const {
366 Bitboard result = EmptyBoardBB;
367 Bitboard pinners = pieces(FindPinned ? opposite_color(c) : c);
369 // Pinned pieces protect our king, dicovery checks attack
371 Square ksq = king_square(FindPinned ? c : opposite_color(c));
373 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
374 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
376 if (FindPinned && pinners)
377 pinners &= ~st->checkersBB;
381 Square s = pop_1st_bit(&pinners);
382 Bitboard b = squares_between(s, ksq) & occupied_squares();
386 if ( !(b & (b - 1)) // Only one bit set?
387 && (b & pieces(c))) // Is an our piece?
394 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
395 /// king) pieces for the given color. Note that checkersBB bitboard must
396 /// be already updated.
398 Bitboard Position::pinned_pieces(Color c) const {
400 return hidden_checkers<true>(c);
404 /// Position:discovered_check_candidates() returns a bitboard containing all
405 /// pieces for the given side which are candidates for giving a discovered
406 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
407 /// to be already updated.
409 Bitboard Position::discovered_check_candidates(Color c) const {
411 return hidden_checkers<false>(c);
414 /// Position::attackers_to() computes a bitboard containing all pieces which
415 /// attacks a given square.
417 Bitboard Position::attackers_to(Square s) const {
419 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
420 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
421 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
422 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
423 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
424 | (attacks_from<KING>(s) & pieces(KING));
427 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
429 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
430 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
431 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
432 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
433 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
434 | (attacks_from<KING>(s) & pieces(KING));
437 /// Position::attacks_from() computes a bitboard of all attacks
438 /// of a given piece put in a given square.
440 Bitboard Position::attacks_from(Piece p, Square s) const {
442 assert(square_is_ok(s));
446 case WB: case BB: return attacks_from<BISHOP>(s);
447 case WR: case BR: return attacks_from<ROOK>(s);
448 case WQ: case BQ: return attacks_from<QUEEN>(s);
449 default: return StepAttacksBB[p][s];
453 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
455 assert(square_is_ok(s));
459 case WB: case BB: return bishop_attacks_bb(s, occ);
460 case WR: case BR: return rook_attacks_bb(s, occ);
461 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
462 default: return StepAttacksBB[p][s];
467 /// Position::move_attacks_square() tests whether a move from the current
468 /// position attacks a given square.
470 bool Position::move_attacks_square(Move m, Square s) const {
472 assert(move_is_ok(m));
473 assert(square_is_ok(s));
476 Square f = move_from(m), t = move_to(m);
478 assert(!square_is_empty(f));
480 if (bit_is_set(attacks_from(piece_on(f), t), s))
483 // Move the piece and scan for X-ray attacks behind it
484 occ = occupied_squares();
485 do_move_bb(&occ, make_move_bb(f, t));
486 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
487 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
488 & pieces(piece_color(piece_on(f)));
490 // If we have attacks we need to verify that are caused by our move
491 // and are not already existent ones.
492 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
496 /// Position::find_checkers() computes the checkersBB bitboard, which
497 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
498 /// currently works by calling Position::attackers_to, which is probably
499 /// inefficient. Consider rewriting this function to use the last move
500 /// played, like in non-bitboard versions of Glaurung.
502 void Position::find_checkers() {
504 Color us = side_to_move();
505 st->checkersBB = attackers_to(king_square(us)) & pieces(opposite_color(us));
509 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
511 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
514 assert(move_is_ok(m));
515 assert(pinned == pinned_pieces(side_to_move()));
517 Color us = side_to_move();
518 Square from = move_from(m);
520 assert(piece_color(piece_on(from)) == us);
521 assert(piece_on(king_square(us)) == make_piece(us, KING));
523 // En passant captures are a tricky special case. Because they are
524 // rather uncommon, we do it simply by testing whether the king is attacked
525 // after the move is made
528 Color them = opposite_color(us);
529 Square to = move_to(m);
530 Square capsq = make_square(square_file(to), square_rank(from));
531 Square ksq = king_square(us);
532 Bitboard b = occupied_squares();
534 assert(to == ep_square());
535 assert(piece_on(from) == make_piece(us, PAWN));
536 assert(piece_on(capsq) == make_piece(them, PAWN));
537 assert(piece_on(to) == PIECE_NONE);
540 clear_bit(&b, capsq);
543 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
544 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
547 // If the moving piece is a king, check whether the destination
548 // square is attacked by the opponent. Castling moves are checked
549 // for legality during move generation.
550 if (piece_type(piece_on(from)) == KING)
551 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces(opposite_color(us)));
553 // A non-king move is legal if and only if it is not pinned or it
554 // is moving along the ray towards or away from the king.
556 || !bit_is_set(pinned, from)
557 || squares_aligned(from, move_to(m), king_square(us));
561 /// Position::move_is_pl_slow() takes a move and tests whether the move
562 /// is pseudo legal. This version is not very fast and should be used
563 /// only in non time-critical paths.
565 bool Position::move_is_pl_slow(const Move m) const {
567 MoveStack mlist[MAX_MOVES];
568 MoveStack *cur, *last;
570 last = in_check() ? generate<MV_EVASION>(*this, mlist)
571 : generate<MV_NON_EVASION>(*this, mlist);
573 for (cur = mlist; cur != last; cur++)
581 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
582 /// of pinned pieces as input, and tests whether the move is pseudo legal.
584 bool Position::move_is_pl(const Move m) const {
588 Color us = sideToMove;
589 Color them = opposite_color(sideToMove);
590 Square from = move_from(m);
591 Square to = move_to(m);
592 Piece pc = piece_on(from);
594 // Use a slower but simpler function for uncommon cases
595 if (move_is_special(m))
596 return move_is_pl_slow(m);
598 // Is not a promotion, so promotion piece must be empty
599 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
602 // If the from square is not occupied by a piece belonging to the side to
603 // move, the move is obviously not legal.
604 if (pc == PIECE_NONE || piece_color(pc) != us)
607 // The destination square cannot be occupied by a friendly piece
608 if (piece_color(piece_on(to)) == us)
611 // Handle the special case of a pawn move
612 if (piece_type(pc) == PAWN)
614 // Move direction must be compatible with pawn color
615 int direction = to - from;
616 if ((us == WHITE) != (direction > 0))
619 // We have already handled promotion moves, so destination
620 // cannot be on the 8/1th rank.
621 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
624 // Proceed according to the square delta between the origin and
625 // destination squares.
632 // Capture. The destination square must be occupied by an enemy
633 // piece (en passant captures was handled earlier).
634 if (piece_color(piece_on(to)) != them)
637 // From and to files must be one file apart, avoids a7h5
638 if (abs(square_file(from) - square_file(to)) != 1)
644 // Pawn push. The destination square must be empty.
645 if (!square_is_empty(to))
650 // Double white pawn push. The destination square must be on the fourth
651 // rank, and both the destination square and the square between the
652 // source and destination squares must be empty.
653 if ( square_rank(to) != RANK_4
654 || !square_is_empty(to)
655 || !square_is_empty(from + DELTA_N))
660 // Double black pawn push. The destination square must be on the fifth
661 // rank, and both the destination square and the square between the
662 // source and destination squares must be empty.
663 if ( square_rank(to) != RANK_5
664 || !square_is_empty(to)
665 || !square_is_empty(from + DELTA_S))
673 else if (!bit_is_set(attacks_from(pc, from), to))
678 // In case of king moves under check we have to remove king so to catch
679 // as invalid moves like b1a1 when opposite queen is on c1.
680 if (piece_type(piece_on(from)) == KING)
682 Bitboard b = occupied_squares();
684 if (attackers_to(move_to(m), b) & pieces(opposite_color(us)))
689 Bitboard target = checkers();
690 Square checksq = pop_1st_bit(&target);
692 if (target) // double check ? In this case a king move is required
695 // Our move must be a blocking evasion or a capture of the checking piece
696 target = squares_between(checksq, king_square(us)) | checkers();
697 if (!bit_is_set(target, move_to(m)))
706 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
708 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
711 assert(move_is_ok(m));
712 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
713 assert(piece_color(piece_on(move_from(m))) == side_to_move());
715 Square from = move_from(m);
716 Square to = move_to(m);
717 PieceType pt = piece_type(piece_on(from));
720 if (bit_is_set(ci.checkSq[pt], to))
724 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
726 // For pawn and king moves we need to verify also direction
727 if ( (pt != PAWN && pt != KING)
728 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
732 // Can we skip the ugly special cases ?
733 if (!move_is_special(m))
736 Color us = side_to_move();
737 Bitboard b = occupied_squares();
738 Square ksq = king_square(opposite_color(us));
740 // Promotion with check ?
741 if (move_is_promotion(m))
745 switch (promotion_piece_type(m))
748 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
750 return bit_is_set(bishop_attacks_bb(to, b), ksq);
752 return bit_is_set(rook_attacks_bb(to, b), ksq);
754 return bit_is_set(queen_attacks_bb(to, b), ksq);
760 // En passant capture with check ? We have already handled the case
761 // of direct checks and ordinary discovered check, the only case we
762 // need to handle is the unusual case of a discovered check through
763 // the captured pawn.
766 Square capsq = make_square(square_file(to), square_rank(from));
768 clear_bit(&b, capsq);
770 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
771 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
774 // Castling with check ?
775 if (move_is_castle(m))
777 Square kfrom, kto, rfrom, rto;
783 kto = relative_square(us, SQ_G1);
784 rto = relative_square(us, SQ_F1);
786 kto = relative_square(us, SQ_C1);
787 rto = relative_square(us, SQ_D1);
789 clear_bit(&b, kfrom);
790 clear_bit(&b, rfrom);
793 return bit_is_set(rook_attacks_bb(rto, b), ksq);
800 /// Position::do_setup_move() makes a permanent move on the board. It should
801 /// be used when setting up a position on board. You can't undo the move.
803 void Position::do_setup_move(Move m) {
807 // Update the number of full moves after black's move
808 if (sideToMove == BLACK)
813 // Reset "game ply" in case we made a non-reversible move.
814 // "game ply" is used for repetition detection.
818 // Our StateInfo newSt is about going out of scope so copy
819 // its content before it disappears.
824 /// Position::do_move() makes a move, and saves all information necessary
825 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
826 /// moves should be filtered out before this function is called.
828 void Position::do_move(Move m, StateInfo& newSt) {
831 do_move(m, newSt, ci, move_gives_check(m, ci));
834 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
837 assert(move_is_ok(m));
838 assert(&newSt != st);
843 // Copy some fields of old state to our new StateInfo object except the
844 // ones which are recalculated from scratch anyway, then switch our state
845 // pointer to point to the new, ready to be updated, state.
846 struct ReducedStateInfo {
847 Key pawnKey, materialKey;
848 int castleRights, rule50, gamePly, pliesFromNull;
854 memcpy(&newSt, st, sizeof(ReducedStateInfo));
859 // Save the current key to the history[] array, in order to be able to
860 // detect repetition draws.
861 history[st->gamePly++] = key;
863 // Update side to move
864 key ^= zobSideToMove;
866 // Increment the 50 moves rule draw counter. Resetting it to zero in the
867 // case of non-reversible moves is taken care of later.
871 if (move_is_castle(m))
878 Color us = side_to_move();
879 Color them = opposite_color(us);
880 Square from = move_from(m);
881 Square to = move_to(m);
882 bool ep = move_is_ep(m);
883 bool pm = move_is_promotion(m);
885 Piece piece = piece_on(from);
886 PieceType pt = piece_type(piece);
887 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
889 assert(piece_color(piece_on(from)) == us);
890 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
891 assert(!(ep || pm) || piece == make_piece(us, PAWN));
892 assert(!pm || relative_rank(us, to) == RANK_8);
895 do_capture_move(key, capture, them, to, ep);
898 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
900 // Reset en passant square
901 if (st->epSquare != SQ_NONE)
903 key ^= zobEp[st->epSquare];
904 st->epSquare = SQ_NONE;
907 // Update castle rights if needed
908 if ( st->castleRights != CASTLES_NONE
909 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
911 key ^= zobCastle[st->castleRights];
912 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
913 key ^= zobCastle[st->castleRights];
916 // Prefetch TT access as soon as we know key is updated
917 prefetch((char*)TT.first_entry(key));
920 Bitboard move_bb = make_move_bb(from, to);
921 do_move_bb(&(byColorBB[us]), move_bb);
922 do_move_bb(&(byTypeBB[pt]), move_bb);
923 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
925 board[to] = board[from];
926 board[from] = PIECE_NONE;
928 // Update piece lists, note that index[from] is not updated and
929 // becomes stale. This works as long as index[] is accessed just
930 // by known occupied squares.
931 index[to] = index[from];
932 pieceList[us][pt][index[to]] = to;
934 // If the moving piece was a pawn do some special extra work
937 // Reset rule 50 draw counter
940 // Update pawn hash key and prefetch in L1/L2 cache
941 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
943 // Set en passant square, only if moved pawn can be captured
944 if ((to ^ from) == 16)
946 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
948 st->epSquare = Square((int(from) + int(to)) / 2);
949 key ^= zobEp[st->epSquare];
953 if (pm) // promotion ?
955 PieceType promotion = promotion_piece_type(m);
957 assert(promotion >= KNIGHT && promotion <= QUEEN);
959 // Insert promoted piece instead of pawn
960 clear_bit(&(byTypeBB[PAWN]), to);
961 set_bit(&(byTypeBB[promotion]), to);
962 board[to] = make_piece(us, promotion);
964 // Update piece counts
965 pieceCount[us][promotion]++;
966 pieceCount[us][PAWN]--;
968 // Update material key
969 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
970 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
972 // Update piece lists, move the last pawn at index[to] position
973 // and shrink the list. Add a new promotion piece to the list.
974 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
975 index[lastPawnSquare] = index[to];
976 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
977 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
978 index[to] = pieceCount[us][promotion] - 1;
979 pieceList[us][promotion][index[to]] = to;
981 // Partially revert hash keys update
982 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
983 st->pawnKey ^= zobrist[us][PAWN][to];
985 // Partially revert and update incremental scores
986 st->value -= pst(make_piece(us, PAWN), to);
987 st->value += pst(make_piece(us, promotion), to);
990 st->npMaterial[us] += PieceValueMidgame[promotion];
994 // Prefetch pawn and material hash tables
995 Threads[threadID].pawnTable.prefetch(st->pawnKey);
996 Threads[threadID].materialTable.prefetch(st->materialKey);
998 // Update incremental scores
999 st->value += pst_delta(piece, from, to);
1001 // Set capture piece
1002 st->capturedType = capture;
1004 // Update the key with the final value
1007 // Update checkers bitboard, piece must be already moved
1008 st->checkersBB = EmptyBoardBB;
1013 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1017 if (bit_is_set(ci.checkSq[pt], to))
1018 st->checkersBB = SetMaskBB[to];
1021 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1024 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1027 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1033 sideToMove = opposite_color(sideToMove);
1034 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1040 /// Position::do_capture_move() is a private method used to update captured
1041 /// piece info. It is called from the main Position::do_move function.
1043 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1045 assert(capture != KING);
1049 // If the captured piece was a pawn, update pawn hash key,
1050 // otherwise update non-pawn material.
1051 if (capture == PAWN)
1053 if (ep) // en passant ?
1055 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1057 assert(to == st->epSquare);
1058 assert(relative_rank(opposite_color(them), to) == RANK_6);
1059 assert(piece_on(to) == PIECE_NONE);
1060 assert(piece_on(capsq) == make_piece(them, PAWN));
1062 board[capsq] = PIECE_NONE;
1064 st->pawnKey ^= zobrist[them][PAWN][capsq];
1067 st->npMaterial[them] -= PieceValueMidgame[capture];
1069 // Remove captured piece
1070 clear_bit(&(byColorBB[them]), capsq);
1071 clear_bit(&(byTypeBB[capture]), capsq);
1072 clear_bit(&(byTypeBB[0]), capsq);
1075 key ^= zobrist[them][capture][capsq];
1077 // Update incremental scores
1078 st->value -= pst(make_piece(them, capture), capsq);
1080 // Update piece count
1081 pieceCount[them][capture]--;
1083 // Update material hash key
1084 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1086 // Update piece list, move the last piece at index[capsq] position
1088 // WARNING: This is a not perfectly revresible operation. When we
1089 // will reinsert the captured piece in undo_move() we will put it
1090 // at the end of the list and not in its original place, it means
1091 // index[] and pieceList[] are not guaranteed to be invariant to a
1092 // do_move() + undo_move() sequence.
1093 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1094 index[lastPieceSquare] = index[capsq];
1095 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1096 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1098 // Reset rule 50 counter
1103 /// Position::do_castle_move() is a private method used to make a castling
1104 /// move. It is called from the main Position::do_move function. Note that
1105 /// castling moves are encoded as "king captures friendly rook" moves, for
1106 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1108 void Position::do_castle_move(Move m) {
1110 assert(move_is_ok(m));
1111 assert(move_is_castle(m));
1113 Color us = side_to_move();
1114 Color them = opposite_color(us);
1116 // Reset capture field
1117 st->capturedType = PIECE_TYPE_NONE;
1119 // Find source squares for king and rook
1120 Square kfrom = move_from(m);
1121 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1124 assert(piece_on(kfrom) == make_piece(us, KING));
1125 assert(piece_on(rfrom) == make_piece(us, ROOK));
1127 // Find destination squares for king and rook
1128 if (rfrom > kfrom) // O-O
1130 kto = relative_square(us, SQ_G1);
1131 rto = relative_square(us, SQ_F1);
1133 kto = relative_square(us, SQ_C1);
1134 rto = relative_square(us, SQ_D1);
1137 // Remove pieces from source squares:
1138 clear_bit(&(byColorBB[us]), kfrom);
1139 clear_bit(&(byTypeBB[KING]), kfrom);
1140 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1141 clear_bit(&(byColorBB[us]), rfrom);
1142 clear_bit(&(byTypeBB[ROOK]), rfrom);
1143 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1145 // Put pieces on destination squares:
1146 set_bit(&(byColorBB[us]), kto);
1147 set_bit(&(byTypeBB[KING]), kto);
1148 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1149 set_bit(&(byColorBB[us]), rto);
1150 set_bit(&(byTypeBB[ROOK]), rto);
1151 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1153 // Update board array
1154 Piece king = make_piece(us, KING);
1155 Piece rook = make_piece(us, ROOK);
1156 board[kfrom] = board[rfrom] = PIECE_NONE;
1160 // Update piece lists
1161 pieceList[us][KING][index[kfrom]] = kto;
1162 pieceList[us][ROOK][index[rfrom]] = rto;
1163 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1164 index[kto] = index[kfrom];
1167 // Update incremental scores
1168 st->value += pst_delta(king, kfrom, kto);
1169 st->value += pst_delta(rook, rfrom, rto);
1172 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1173 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1175 // Clear en passant square
1176 if (st->epSquare != SQ_NONE)
1178 st->key ^= zobEp[st->epSquare];
1179 st->epSquare = SQ_NONE;
1182 // Update castling rights
1183 st->key ^= zobCastle[st->castleRights];
1184 st->castleRights &= castleRightsMask[kfrom];
1185 st->key ^= zobCastle[st->castleRights];
1187 // Reset rule 50 counter
1190 // Update checkers BB
1191 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1194 sideToMove = opposite_color(sideToMove);
1195 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1201 /// Position::undo_move() unmakes a move. When it returns, the position should
1202 /// be restored to exactly the same state as before the move was made.
1204 void Position::undo_move(Move m) {
1207 assert(move_is_ok(m));
1209 sideToMove = opposite_color(sideToMove);
1211 if (move_is_castle(m))
1213 undo_castle_move(m);
1217 Color us = side_to_move();
1218 Color them = opposite_color(us);
1219 Square from = move_from(m);
1220 Square to = move_to(m);
1221 bool ep = move_is_ep(m);
1222 bool pm = move_is_promotion(m);
1224 PieceType pt = piece_type(piece_on(to));
1226 assert(square_is_empty(from));
1227 assert(piece_color(piece_on(to)) == us);
1228 assert(!pm || relative_rank(us, to) == RANK_8);
1229 assert(!ep || to == st->previous->epSquare);
1230 assert(!ep || relative_rank(us, to) == RANK_6);
1231 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1233 if (pm) // promotion ?
1235 PieceType promotion = promotion_piece_type(m);
1238 assert(promotion >= KNIGHT && promotion <= QUEEN);
1239 assert(piece_on(to) == make_piece(us, promotion));
1241 // Replace promoted piece with a pawn
1242 clear_bit(&(byTypeBB[promotion]), to);
1243 set_bit(&(byTypeBB[PAWN]), to);
1245 // Update piece counts
1246 pieceCount[us][promotion]--;
1247 pieceCount[us][PAWN]++;
1249 // Update piece list replacing promotion piece with a pawn
1250 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1251 index[lastPromotionSquare] = index[to];
1252 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1253 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1254 index[to] = pieceCount[us][PAWN] - 1;
1255 pieceList[us][PAWN][index[to]] = to;
1258 // Put the piece back at the source square
1259 Bitboard move_bb = make_move_bb(to, from);
1260 do_move_bb(&(byColorBB[us]), move_bb);
1261 do_move_bb(&(byTypeBB[pt]), move_bb);
1262 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1264 board[from] = make_piece(us, pt);
1265 board[to] = PIECE_NONE;
1267 // Update piece list
1268 index[from] = index[to];
1269 pieceList[us][pt][index[from]] = from;
1271 if (st->capturedType)
1276 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1278 assert(st->capturedType != KING);
1279 assert(!ep || square_is_empty(capsq));
1281 // Restore the captured piece
1282 set_bit(&(byColorBB[them]), capsq);
1283 set_bit(&(byTypeBB[st->capturedType]), capsq);
1284 set_bit(&(byTypeBB[0]), capsq);
1286 board[capsq] = make_piece(them, st->capturedType);
1288 // Update piece count
1289 pieceCount[them][st->capturedType]++;
1291 // Update piece list, add a new captured piece in capsq square
1292 index[capsq] = pieceCount[them][st->capturedType] - 1;
1293 pieceList[them][st->capturedType][index[capsq]] = capsq;
1296 // Finally point our state pointer back to the previous state
1303 /// Position::undo_castle_move() is a private method used to unmake a castling
1304 /// move. It is called from the main Position::undo_move function. Note that
1305 /// castling moves are encoded as "king captures friendly rook" moves, for
1306 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1308 void Position::undo_castle_move(Move m) {
1310 assert(move_is_ok(m));
1311 assert(move_is_castle(m));
1313 // When we have arrived here, some work has already been done by
1314 // Position::undo_move. In particular, the side to move has been switched,
1315 // so the code below is correct.
1316 Color us = side_to_move();
1318 // Find source squares for king and rook
1319 Square kfrom = move_from(m);
1320 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1323 // Find destination squares for king and rook
1324 if (rfrom > kfrom) // O-O
1326 kto = relative_square(us, SQ_G1);
1327 rto = relative_square(us, SQ_F1);
1329 kto = relative_square(us, SQ_C1);
1330 rto = relative_square(us, SQ_D1);
1333 assert(piece_on(kto) == make_piece(us, KING));
1334 assert(piece_on(rto) == make_piece(us, ROOK));
1336 // Remove pieces from destination squares:
1337 clear_bit(&(byColorBB[us]), kto);
1338 clear_bit(&(byTypeBB[KING]), kto);
1339 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1340 clear_bit(&(byColorBB[us]), rto);
1341 clear_bit(&(byTypeBB[ROOK]), rto);
1342 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1344 // Put pieces on source squares:
1345 set_bit(&(byColorBB[us]), kfrom);
1346 set_bit(&(byTypeBB[KING]), kfrom);
1347 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1348 set_bit(&(byColorBB[us]), rfrom);
1349 set_bit(&(byTypeBB[ROOK]), rfrom);
1350 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1353 board[rto] = board[kto] = PIECE_NONE;
1354 board[rfrom] = make_piece(us, ROOK);
1355 board[kfrom] = make_piece(us, KING);
1357 // Update piece lists
1358 pieceList[us][KING][index[kto]] = kfrom;
1359 pieceList[us][ROOK][index[rto]] = rfrom;
1360 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1361 index[kfrom] = index[kto];
1364 // Finally point our state pointer back to the previous state
1371 /// Position::do_null_move makes() a "null move": It switches the side to move
1372 /// and updates the hash key without executing any move on the board.
1374 void Position::do_null_move(StateInfo& backupSt) {
1377 assert(!in_check());
1379 // Back up the information necessary to undo the null move to the supplied
1380 // StateInfo object.
1381 // Note that differently from normal case here backupSt is actually used as
1382 // a backup storage not as a new state to be used.
1383 backupSt.key = st->key;
1384 backupSt.epSquare = st->epSquare;
1385 backupSt.value = st->value;
1386 backupSt.previous = st->previous;
1387 backupSt.pliesFromNull = st->pliesFromNull;
1388 st->previous = &backupSt;
1390 // Save the current key to the history[] array, in order to be able to
1391 // detect repetition draws.
1392 history[st->gamePly++] = st->key;
1394 // Update the necessary information
1395 if (st->epSquare != SQ_NONE)
1396 st->key ^= zobEp[st->epSquare];
1398 st->key ^= zobSideToMove;
1399 prefetch((char*)TT.first_entry(st->key));
1401 sideToMove = opposite_color(sideToMove);
1402 st->epSquare = SQ_NONE;
1404 st->pliesFromNull = 0;
1405 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1409 /// Position::undo_null_move() unmakes a "null move".
1411 void Position::undo_null_move() {
1414 assert(!in_check());
1416 // Restore information from the our backup StateInfo object
1417 StateInfo* backupSt = st->previous;
1418 st->key = backupSt->key;
1419 st->epSquare = backupSt->epSquare;
1420 st->value = backupSt->value;
1421 st->previous = backupSt->previous;
1422 st->pliesFromNull = backupSt->pliesFromNull;
1424 // Update the necessary information
1425 sideToMove = opposite_color(sideToMove);
1431 /// Position::see() is a static exchange evaluator: It tries to estimate the
1432 /// material gain or loss resulting from a move. There are three versions of
1433 /// this function: One which takes a destination square as input, one takes a
1434 /// move, and one which takes a 'from' and a 'to' square. The function does
1435 /// not yet understand promotions captures.
1437 int Position::see_sign(Move m) const {
1439 assert(move_is_ok(m));
1441 Square from = move_from(m);
1442 Square to = move_to(m);
1444 // Early return if SEE cannot be negative because captured piece value
1445 // is not less then capturing one. Note that king moves always return
1446 // here because king midgame value is set to 0.
1447 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1453 int Position::see(Move m) const {
1456 Bitboard occupied, attackers, stmAttackers, b;
1457 int swapList[32], slIndex = 1;
1458 PieceType capturedType, pt;
1461 assert(move_is_ok(m));
1463 // As castle moves are implemented as capturing the rook, they have
1464 // SEE == RookValueMidgame most of the times (unless the rook is under
1466 if (move_is_castle(m))
1469 from = move_from(m);
1471 capturedType = piece_type(piece_on(to));
1472 occupied = occupied_squares();
1474 // Handle en passant moves
1475 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1477 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1479 assert(capturedType == PIECE_TYPE_NONE);
1480 assert(piece_type(piece_on(capQq)) == PAWN);
1482 // Remove the captured pawn
1483 clear_bit(&occupied, capQq);
1484 capturedType = PAWN;
1487 // Find all attackers to the destination square, with the moving piece
1488 // removed, but possibly an X-ray attacker added behind it.
1489 clear_bit(&occupied, from);
1490 attackers = attackers_to(to, occupied);
1492 // If the opponent has no attackers we are finished
1493 stm = opposite_color(piece_color(piece_on(from)));
1494 stmAttackers = attackers & pieces(stm);
1496 return PieceValueMidgame[capturedType];
1498 // The destination square is defended, which makes things rather more
1499 // difficult to compute. We proceed by building up a "swap list" containing
1500 // the material gain or loss at each stop in a sequence of captures to the
1501 // destination square, where the sides alternately capture, and always
1502 // capture with the least valuable piece. After each capture, we look for
1503 // new X-ray attacks from behind the capturing piece.
1504 swapList[0] = PieceValueMidgame[capturedType];
1505 capturedType = piece_type(piece_on(from));
1508 // Locate the least valuable attacker for the side to move. The loop
1509 // below looks like it is potentially infinite, but it isn't. We know
1510 // that the side to move still has at least one attacker left.
1511 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1514 // Remove the attacker we just found from the 'occupied' bitboard,
1515 // and scan for new X-ray attacks behind the attacker.
1516 b = stmAttackers & pieces(pt);
1517 occupied ^= (b & (~b + 1));
1518 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1519 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1521 attackers &= occupied; // Cut out pieces we've already done
1523 // Add the new entry to the swap list
1524 assert(slIndex < 32);
1525 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1528 // Remember the value of the capturing piece, and change the side to
1529 // move before beginning the next iteration.
1531 stm = opposite_color(stm);
1532 stmAttackers = attackers & pieces(stm);
1534 // Stop before processing a king capture
1535 if (capturedType == KING && stmAttackers)
1537 assert(slIndex < 32);
1538 swapList[slIndex++] = QueenValueMidgame*10;
1541 } while (stmAttackers);
1543 // Having built the swap list, we negamax through it to find the best
1544 // achievable score from the point of view of the side to move.
1546 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1552 /// Position::clear() erases the position object to a pristine state, with an
1553 /// empty board, white to move, and no castling rights.
1555 void Position::clear() {
1558 memset(st, 0, sizeof(StateInfo));
1559 st->epSquare = SQ_NONE;
1561 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1562 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1563 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1564 memset(index, 0, sizeof(int) * 64);
1566 for (int i = 0; i < 8; i++)
1567 for (int j = 0; j < 16; j++)
1568 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1570 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1572 board[sq] = PIECE_NONE;
1573 castleRightsMask[sq] = ALL_CASTLES;
1581 /// Position::put_piece() puts a piece on the given square of the board,
1582 /// updating the board array, pieces list, bitboards, and piece counts.
1584 void Position::put_piece(Piece p, Square s) {
1586 Color c = piece_color(p);
1587 PieceType pt = piece_type(p);
1590 index[s] = pieceCount[c][pt]++;
1591 pieceList[c][pt][index[s]] = s;
1593 set_bit(&byTypeBB[pt], s);
1594 set_bit(&byColorBB[c], s);
1595 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1599 /// Position::compute_key() computes the hash key of the position. The hash
1600 /// key is usually updated incrementally as moves are made and unmade, the
1601 /// compute_key() function is only used when a new position is set up, and
1602 /// to verify the correctness of the hash key when running in debug mode.
1604 Key Position::compute_key() const {
1606 Key result = zobCastle[st->castleRights];
1608 for (Square s = SQ_A1; s <= SQ_H8; s++)
1609 if (!square_is_empty(s))
1610 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1612 if (ep_square() != SQ_NONE)
1613 result ^= zobEp[ep_square()];
1615 if (side_to_move() == BLACK)
1616 result ^= zobSideToMove;
1622 /// Position::compute_pawn_key() computes the hash key of the position. The
1623 /// hash key is usually updated incrementally as moves are made and unmade,
1624 /// the compute_pawn_key() function is only used when a new position is set
1625 /// up, and to verify the correctness of the pawn hash key when running in
1628 Key Position::compute_pawn_key() const {
1633 for (Color c = WHITE; c <= BLACK; c++)
1635 b = pieces(PAWN, c);
1637 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1643 /// Position::compute_material_key() computes the hash key of the position.
1644 /// The hash key is usually updated incrementally as moves are made and unmade,
1645 /// the compute_material_key() function is only used when a new position is set
1646 /// up, and to verify the correctness of the material hash key when running in
1649 Key Position::compute_material_key() const {
1653 for (Color c = WHITE; c <= BLACK; c++)
1654 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1655 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1656 result ^= zobrist[c][pt][i];
1662 /// Position::compute_value() compute the incremental scores for the middle
1663 /// game and the endgame. These functions are used to initialize the incremental
1664 /// scores when a new position is set up, and to verify that the scores are correctly
1665 /// updated by do_move and undo_move when the program is running in debug mode.
1666 Score Position::compute_value() const {
1669 Score result = SCORE_ZERO;
1671 for (Color c = WHITE; c <= BLACK; c++)
1672 for (PieceType pt = PAWN; pt <= KING; pt++)
1676 result += pst(make_piece(c, pt), pop_1st_bit(&b));
1679 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1684 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1685 /// game material value for the given side. Material values are updated
1686 /// incrementally during the search, this function is only used while
1687 /// initializing a new Position object.
1689 Value Position::compute_non_pawn_material(Color c) const {
1691 Value result = VALUE_ZERO;
1693 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1694 result += piece_count(c, pt) * PieceValueMidgame[pt];
1700 /// Position::is_draw() tests whether the position is drawn by material,
1701 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1702 /// must be done by the search.
1703 template<bool SkipRepetition>
1704 bool Position::is_draw() const {
1706 // Draw by material?
1708 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1711 // Draw by the 50 moves rule?
1712 if (st->rule50 > 99 && !is_mate())
1715 // Draw by repetition?
1716 if (!SkipRepetition)
1717 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1718 if (history[st->gamePly - i] == st->key)
1724 // Explicit template instantiations
1725 template bool Position::is_draw<false>() const;
1726 template bool Position::is_draw<true>() const;
1729 /// Position::is_mate() returns true or false depending on whether the
1730 /// side to move is checkmated.
1732 bool Position::is_mate() const {
1734 MoveStack moves[MAX_MOVES];
1735 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1739 /// Position::init() is a static member function which initializes at
1740 /// startup the various arrays used to compute hash keys and the piece
1741 /// square tables. The latter is a two-step operation: First, the white
1742 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1743 /// Second, the black halves of the tables are initialized by mirroring
1744 /// and changing the sign of the corresponding white scores.
1746 void Position::init() {
1750 for (Color c = WHITE; c <= BLACK; c++)
1751 for (PieceType pt = PAWN; pt <= KING; pt++)
1752 for (Square s = SQ_A1; s <= SQ_H8; s++)
1753 zobrist[c][pt][s] = rk.rand<Key>();
1755 for (Square s = SQ_A1; s <= SQ_H8; s++)
1756 zobEp[s] = rk.rand<Key>();
1758 for (int i = 0; i < 16; i++)
1759 zobCastle[i] = rk.rand<Key>();
1761 zobSideToMove = rk.rand<Key>();
1762 zobExclusion = rk.rand<Key>();
1764 for (Square s = SQ_A1; s <= SQ_H8; s++)
1765 for (Piece p = WP; p <= WK; p++)
1766 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1768 for (Square s = SQ_A1; s <= SQ_H8; s++)
1769 for (Piece p = BP; p <= BK; p++)
1770 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1774 /// Position::flip() flips position with the white and black sides reversed. This
1775 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1777 void Position::flip() {
1781 // Make a copy of current position before to start changing
1782 const Position pos(*this, threadID);
1785 threadID = pos.thread();
1788 for (Square s = SQ_A1; s <= SQ_H8; s++)
1789 if (!pos.square_is_empty(s))
1790 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1793 sideToMove = opposite_color(pos.side_to_move());
1796 if (pos.can_castle(WHITE_OO))
1797 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1798 if (pos.can_castle(WHITE_OOO))
1799 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1800 if (pos.can_castle(BLACK_OO))
1801 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1802 if (pos.can_castle(BLACK_OOO))
1803 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1805 // En passant square
1806 if (pos.st->epSquare != SQ_NONE)
1807 st->epSquare = flip_square(pos.st->epSquare);
1813 st->key = compute_key();
1814 st->pawnKey = compute_pawn_key();
1815 st->materialKey = compute_material_key();
1817 // Incremental scores
1818 st->value = compute_value();
1821 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1822 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1828 /// Position::is_ok() performs some consitency checks for the position object.
1829 /// This is meant to be helpful when debugging.
1831 bool Position::is_ok(int* failedStep) const {
1833 // What features of the position should be verified?
1834 const bool debugAll = false;
1836 const bool debugBitboards = debugAll || false;
1837 const bool debugKingCount = debugAll || false;
1838 const bool debugKingCapture = debugAll || false;
1839 const bool debugCheckerCount = debugAll || false;
1840 const bool debugKey = debugAll || false;
1841 const bool debugMaterialKey = debugAll || false;
1842 const bool debugPawnKey = debugAll || false;
1843 const bool debugIncrementalEval = debugAll || false;
1844 const bool debugNonPawnMaterial = debugAll || false;
1845 const bool debugPieceCounts = debugAll || false;
1846 const bool debugPieceList = debugAll || false;
1847 const bool debugCastleSquares = debugAll || false;
1849 if (failedStep) *failedStep = 1;
1852 if (side_to_move() != WHITE && side_to_move() != BLACK)
1855 // Are the king squares in the position correct?
1856 if (failedStep) (*failedStep)++;
1857 if (piece_on(king_square(WHITE)) != WK)
1860 if (failedStep) (*failedStep)++;
1861 if (piece_on(king_square(BLACK)) != BK)
1864 // Do both sides have exactly one king?
1865 if (failedStep) (*failedStep)++;
1868 int kingCount[2] = {0, 0};
1869 for (Square s = SQ_A1; s <= SQ_H8; s++)
1870 if (piece_type(piece_on(s)) == KING)
1871 kingCount[piece_color(piece_on(s))]++;
1873 if (kingCount[0] != 1 || kingCount[1] != 1)
1877 // Can the side to move capture the opponent's king?
1878 if (failedStep) (*failedStep)++;
1879 if (debugKingCapture)
1881 Color us = side_to_move();
1882 Color them = opposite_color(us);
1883 Square ksq = king_square(them);
1884 if (attackers_to(ksq) & pieces(us))
1888 // Is there more than 2 checkers?
1889 if (failedStep) (*failedStep)++;
1890 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1894 if (failedStep) (*failedStep)++;
1897 // The intersection of the white and black pieces must be empty
1898 if ((pieces(WHITE) & pieces(BLACK)) != EmptyBoardBB)
1901 // The union of the white and black pieces must be equal to all
1903 if ((pieces(WHITE) | pieces(BLACK)) != occupied_squares())
1906 // Separate piece type bitboards must have empty intersections
1907 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1908 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1909 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1913 // En passant square OK?
1914 if (failedStep) (*failedStep)++;
1915 if (ep_square() != SQ_NONE)
1917 // The en passant square must be on rank 6, from the point of view of the
1919 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1924 if (failedStep) (*failedStep)++;
1925 if (debugKey && st->key != compute_key())
1928 // Pawn hash key OK?
1929 if (failedStep) (*failedStep)++;
1930 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1933 // Material hash key OK?
1934 if (failedStep) (*failedStep)++;
1935 if (debugMaterialKey && st->materialKey != compute_material_key())
1938 // Incremental eval OK?
1939 if (failedStep) (*failedStep)++;
1940 if (debugIncrementalEval && st->value != compute_value())
1943 // Non-pawn material OK?
1944 if (failedStep) (*failedStep)++;
1945 if (debugNonPawnMaterial)
1947 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1950 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1955 if (failedStep) (*failedStep)++;
1956 if (debugPieceCounts)
1957 for (Color c = WHITE; c <= BLACK; c++)
1958 for (PieceType pt = PAWN; pt <= KING; pt++)
1959 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1962 if (failedStep) (*failedStep)++;
1964 for (Color c = WHITE; c <= BLACK; c++)
1965 for (PieceType pt = PAWN; pt <= KING; pt++)
1966 for (int i = 0; i < pieceCount[c][pt]; i++)
1968 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1971 if (index[piece_list(c, pt)[i]] != i)
1975 if (failedStep) (*failedStep)++;
1976 if (debugCastleSquares)
1977 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1982 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1984 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1985 || piece_on(castleRookSquare[f]) != rook)
1989 if (failedStep) *failedStep = 0;