2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
39 static const string PieceToChar(" PNBRQK pnbrqk");
43 Score pieceSquareTable[PIECE_NB][SQUARE_NB];
44 Value PieceValue[PHASE_NB][PIECE_NB] = {
45 { VALUE_ZERO, PawnValueMg, KnightValueMg, BishopValueMg, RookValueMg, QueenValueMg },
46 { VALUE_ZERO, PawnValueEg, KnightValueEg, BishopValueEg, RookValueEg, QueenValueEg } };
50 Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
51 Key enpassant[FILE_NB];
52 Key castle[CASTLE_RIGHT_NB];
56 /// init() initializes at startup the various arrays used to compute hash keys
57 /// and the piece square tables. The latter is a two-step operation: First, the
58 /// white halves of the tables are copied from PSQT[] tables. Second, the black
59 /// halves of the tables are initialized by flipping and changing the sign of
66 for (Color c = WHITE; c <= BLACK; c++)
67 for (PieceType pt = PAWN; pt <= KING; pt++)
68 for (Square s = SQ_A1; s <= SQ_H8; s++)
69 psq[c][pt][s] = rk.rand<Key>();
71 for (File f = FILE_A; f <= FILE_H; f++)
72 enpassant[f] = rk.rand<Key>();
74 for (int cr = CASTLES_NONE; cr <= ALL_CASTLES; cr++)
79 Key k = castle[1ULL << pop_lsb(&b)];
80 castle[cr] ^= k ? k : rk.rand<Key>();
84 side = rk.rand<Key>();
85 exclusion = rk.rand<Key>();
87 for (PieceType pt = PAWN; pt <= KING; pt++)
89 PieceValue[MG][make_piece(BLACK, pt)] = PieceValue[MG][pt];
90 PieceValue[EG][make_piece(BLACK, pt)] = PieceValue[EG][pt];
92 Score v = make_score(PieceValue[MG][pt], PieceValue[EG][pt]);
94 for (Square s = SQ_A1; s <= SQ_H8; s++)
96 pieceSquareTable[make_piece(WHITE, pt)][ s] = (v + PSQT[pt][s]);
97 pieceSquareTable[make_piece(BLACK, pt)][~s] = -(v + PSQT[pt][s]);
102 } // namespace Zobrist
107 /// next_attacker() is an helper function used by see() to locate the least
108 /// valuable attacker for the side to move, remove the attacker we just found
109 /// from the 'occupied' bitboard and scan for new X-ray attacks behind it.
111 template<int Pt> FORCE_INLINE
112 PieceType next_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
113 Bitboard& occupied, Bitboard& attackers) {
115 if (stmAttackers & bb[Pt])
117 Bitboard b = stmAttackers & bb[Pt];
118 occupied ^= b & ~(b - 1);
120 if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
121 attackers |= attacks_bb<BISHOP>(to, occupied) & (bb[BISHOP] | bb[QUEEN]);
123 if (Pt == ROOK || Pt == QUEEN)
124 attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
126 return (PieceType)Pt;
128 return next_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
131 template<> FORCE_INLINE
132 PieceType next_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {
133 return KING; // No need to update bitboards, it is the last cycle
141 CheckInfo::CheckInfo(const Position& pos) {
143 Color them = ~pos.side_to_move();
144 ksq = pos.king_square(them);
146 pinned = pos.pinned_pieces();
147 dcCandidates = pos.discovered_check_candidates();
149 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
150 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
151 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
152 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
153 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
158 /// Position::operator=() creates a copy of 'pos'. We want the new born Position
159 /// object do not depend on any external data so we detach state pointer from
162 Position& Position::operator=(const Position& pos) {
164 memcpy(this, &pos, sizeof(Position));
175 /// Position::set() initializes the position object with the given FEN string.
176 /// This function is not very robust - make sure that input FENs are correct,
177 /// this is assumed to be the responsibility of the GUI.
179 void Position::set(const string& fenStr, bool isChess960, Thread* th) {
181 A FEN string defines a particular position using only the ASCII character set.
183 A FEN string contains six fields separated by a space. The fields are:
185 1) Piece placement (from white's perspective). Each rank is described, starting
186 with rank 8 and ending with rank 1; within each rank, the contents of each
187 square are described from file A through file H. Following the Standard
188 Algebraic Notation (SAN), each piece is identified by a single letter taken
189 from the standard English names. White pieces are designated using upper-case
190 letters ("PNBRQK") while Black take lowercase ("pnbrqk"). Blank squares are
191 noted using digits 1 through 8 (the number of blank squares), and "/"
194 2) Active color. "w" means white moves next, "b" means black.
196 3) Castling availability. If neither side can castle, this is "-". Otherwise,
197 this has one or more letters: "K" (White can castle kingside), "Q" (White
198 can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
199 can castle queenside).
201 4) En passant target square (in algebraic notation). If there's no en passant
202 target square, this is "-". If a pawn has just made a 2-square move, this
203 is the position "behind" the pawn. This is recorded regardless of whether
204 there is a pawn in position to make an en passant capture.
206 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
207 or capture. This is used to determine if a draw can be claimed under the
210 6) Fullmove number. The number of the full move. It starts at 1, and is
211 incremented after Black's move.
214 char col, row, token;
217 std::istringstream ss(fenStr);
222 // 1. Piece placement
223 while ((ss >> token) && !isspace(token))
226 sq += Square(token - '0'); // Advance the given number of files
228 else if (token == '/')
231 else if ((p = PieceToChar.find(token)) != string::npos)
233 put_piece(Piece(p), sq);
240 sideToMove = (token == 'w' ? WHITE : BLACK);
243 // 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
244 // Shredder-FEN that uses the letters of the columns on which the rooks began
245 // the game instead of KQkq and also X-FEN standard that, in case of Chess960,
246 // if an inner rook is associated with the castling right, the castling tag is
247 // replaced by the file letter of the involved rook, as for the Shredder-FEN.
248 while ((ss >> token) && !isspace(token))
251 Color c = islower(token) ? BLACK : WHITE;
253 token = char(toupper(token));
256 for (rsq = relative_square(c, SQ_H1); type_of(piece_on(rsq)) != ROOK; rsq--) {}
258 else if (token == 'Q')
259 for (rsq = relative_square(c, SQ_A1); type_of(piece_on(rsq)) != ROOK; rsq++) {}
261 else if (token >= 'A' && token <= 'H')
262 rsq = File(token - 'A') | relative_rank(c, RANK_1);
267 set_castle_right(c, rsq);
270 // 4. En passant square. Ignore if no pawn capture is possible
271 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
272 && ((ss >> row) && (row == '3' || row == '6')))
274 st->epSquare = File(col - 'a') | Rank(row - '1');
276 if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))
277 st->epSquare = SQ_NONE;
280 // 5-6. Halfmove clock and fullmove number
281 ss >> std::skipws >> st->rule50 >> startPosPly;
283 // Convert from fullmove starting from 1 to ply starting from 0,
284 // handle also common incorrect FEN with fullmove = 0.
285 startPosPly = std::max(2 * (startPosPly - 1), 0) + int(sideToMove == BLACK);
287 st->key = compute_key();
288 st->pawnKey = compute_pawn_key();
289 st->materialKey = compute_material_key();
290 st->psqScore = compute_psq_score();
291 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
292 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
293 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
294 chess960 = isChess960;
301 /// Position::set_castle_right() is an helper function used to set castling
302 /// rights given the corresponding color and the rook starting square.
304 void Position::set_castle_right(Color c, Square rfrom) {
306 Square kfrom = king_square(c);
307 CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
308 CastleRight cr = make_castle_right(c, cs);
310 st->castleRights |= cr;
311 castleRightsMask[kfrom] |= cr;
312 castleRightsMask[rfrom] |= cr;
313 castleRookSquare[c][cs] = rfrom;
315 Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
316 Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
318 for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); s++)
319 if (s != kfrom && s != rfrom)
320 castlePath[c][cs] |= s;
322 for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); s++)
323 if (s != kfrom && s != rfrom)
324 castlePath[c][cs] |= s;
328 /// Position::fen() returns a FEN representation of the position. In case
329 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
331 const string Position::fen() const {
333 std::ostringstream ss;
335 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
337 for (File file = FILE_A; file <= FILE_H; file++)
339 Square sq = file | rank;
345 for ( ; file < FILE_H && is_empty(sq++); file++)
351 ss << PieceToChar[piece_on(sq)];
358 ss << (sideToMove == WHITE ? " w " : " b ");
360 if (can_castle(WHITE_OO))
361 ss << (chess960 ? file_to_char(file_of(castle_rook_square(WHITE, KING_SIDE)), false) : 'K');
363 if (can_castle(WHITE_OOO))
364 ss << (chess960 ? file_to_char(file_of(castle_rook_square(WHITE, QUEEN_SIDE)), false) : 'Q');
366 if (can_castle(BLACK_OO))
367 ss << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK, KING_SIDE)), true) : 'k');
369 if (can_castle(BLACK_OOO))
370 ss << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK, QUEEN_SIDE)), true) : 'q');
372 if (st->castleRights == CASTLES_NONE)
375 ss << (ep_square() == SQ_NONE ? " - " : " " + square_to_string(ep_square()) + " ")
376 << st->rule50 << " " << 1 + (startPosPly - int(sideToMove == BLACK)) / 2;
382 /// Position::pretty() returns an ASCII representation of the position to be
383 /// printed to the standard output together with the move's san notation.
385 const string Position::pretty(Move move) const {
387 const string dottedLine = "\n+---+---+---+---+---+---+---+---+";
388 const string twoRows = dottedLine + "\n| | . | | . | | . | | . |"
389 + dottedLine + "\n| . | | . | | . | | . | |";
391 string brd = twoRows + twoRows + twoRows + twoRows + dottedLine;
393 std::ostringstream ss;
396 ss << "\nMove: " << (sideToMove == BLACK ? ".." : "")
397 << move_to_san(*const_cast<Position*>(this), move);
399 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
400 if (piece_on(sq) != NO_PIECE)
401 brd[513 - 68*rank_of(sq) + 4*file_of(sq)] = PieceToChar[piece_on(sq)];
403 ss << brd << "\nFen: " << fen() << "\nKey: " << st->key << "\nCheckers: ";
405 for (Bitboard b = checkers(); b; )
406 ss << square_to_string(pop_lsb(&b)) << " ";
408 ss << "\nLegal moves: ";
409 for (MoveList<LEGAL> ml(*this); !ml.end(); ++ml)
410 ss << move_to_san(*const_cast<Position*>(this), ml.move()) << " ";
416 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
417 /// king) pieces for the given color. Or, when template parameter FindPinned is
418 /// false, the function return the pieces of the given color candidate for a
419 /// discovery check against the enemy king.
420 template<bool FindPinned>
421 Bitboard Position::hidden_checkers() const {
423 // Pinned pieces protect our king, dicovery checks attack the enemy king
424 Bitboard b, result = 0;
425 Bitboard pinners = pieces(FindPinned ? ~sideToMove : sideToMove);
426 Square ksq = king_square(FindPinned ? sideToMove : ~sideToMove);
428 // Pinners are sliders, that give check when candidate pinned is removed
429 pinners &= (pieces(ROOK, QUEEN) & PseudoAttacks[ROOK][ksq])
430 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq]);
434 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
436 if (b && !more_than_one(b) && (b & pieces(sideToMove)))
442 // Explicit template instantiations
443 template Bitboard Position::hidden_checkers<true>() const;
444 template Bitboard Position::hidden_checkers<false>() const;
447 /// Position::attackers_to() computes a bitboard of all pieces which attack a
448 /// given square. Slider attacks use occ bitboard as occupancy.
450 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
452 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
453 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
454 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
455 | (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
456 | (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
457 | (attacks_from<KING>(s) & pieces(KING));
461 /// Position::attacks_from() computes a bitboard of all attacks of a given piece
462 /// put in a given square. Slider attacks use occ bitboard as occupancy.
464 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
470 case BISHOP: return attacks_bb<BISHOP>(s, occ);
471 case ROOK : return attacks_bb<ROOK>(s, occ);
472 case QUEEN : return attacks_bb<BISHOP>(s, occ) | attacks_bb<ROOK>(s, occ);
473 default : return StepAttacksBB[p][s];
478 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
480 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
483 assert(pinned == pinned_pieces());
485 Color us = sideToMove;
486 Square from = from_sq(m);
488 assert(color_of(piece_moved(m)) == us);
489 assert(piece_on(king_square(us)) == make_piece(us, KING));
491 // En passant captures are a tricky special case. Because they are rather
492 // uncommon, we do it simply by testing whether the king is attacked after
494 if (type_of(m) == ENPASSANT)
497 Square to = to_sq(m);
498 Square capsq = to + pawn_push(them);
499 Square ksq = king_square(us);
500 Bitboard b = (pieces() ^ from ^ capsq) | to;
502 assert(to == ep_square());
503 assert(piece_moved(m) == make_piece(us, PAWN));
504 assert(piece_on(capsq) == make_piece(them, PAWN));
505 assert(piece_on(to) == NO_PIECE);
507 return !(attacks_bb< ROOK>(ksq, b) & pieces(them, QUEEN, ROOK))
508 && !(attacks_bb<BISHOP>(ksq, b) & pieces(them, QUEEN, BISHOP));
511 // If the moving piece is a king, check whether the destination
512 // square is attacked by the opponent. Castling moves are checked
513 // for legality during move generation.
514 if (type_of(piece_on(from)) == KING)
515 return type_of(m) == CASTLE || !(attackers_to(to_sq(m)) & pieces(~us));
517 // A non-king move is legal if and only if it is not pinned or it
518 // is moving along the ray towards or away from the king.
521 || squares_aligned(from, to_sq(m), king_square(us));
525 /// Position::is_pseudo_legal() takes a random move and tests whether the move
526 /// is pseudo legal. It is used to validate moves from TT that can be corrupted
527 /// due to SMP concurrent access or hash position key aliasing.
529 bool Position::is_pseudo_legal(const Move m) const {
531 Color us = sideToMove;
532 Square from = from_sq(m);
533 Square to = to_sq(m);
534 Piece pc = piece_moved(m);
536 // Use a slower but simpler function for uncommon cases
537 if (type_of(m) != NORMAL)
538 return MoveList<LEGAL>(*this).contains(m);
540 // Is not a promotion, so promotion piece must be empty
541 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
544 // If the from square is not occupied by a piece belonging to the side to
545 // move, the move is obviously not legal.
546 if (pc == NO_PIECE || color_of(pc) != us)
549 // The destination square cannot be occupied by a friendly piece
550 if (piece_on(to) != NO_PIECE && color_of(piece_on(to)) == us)
553 // Handle the special case of a pawn move
554 if (type_of(pc) == PAWN)
556 // Move direction must be compatible with pawn color
557 int direction = to - from;
558 if ((us == WHITE) != (direction > 0))
561 // We have already handled promotion moves, so destination
562 // cannot be on the 8/1th rank.
563 if (rank_of(to) == RANK_8 || rank_of(to) == RANK_1)
566 // Proceed according to the square delta between the origin and
567 // destination squares.
574 // Capture. The destination square must be occupied by an enemy
575 // piece (en passant captures was handled earlier).
576 if (piece_on(to) == NO_PIECE || color_of(piece_on(to)) != ~us)
579 // From and to files must be one file apart, avoids a7h5
580 if (abs(file_of(from) - file_of(to)) != 1)
586 // Pawn push. The destination square must be empty.
592 // Double white pawn push. The destination square must be on the fourth
593 // rank, and both the destination square and the square between the
594 // source and destination squares must be empty.
595 if ( rank_of(to) != RANK_4
597 || !is_empty(from + DELTA_N))
602 // Double black pawn push. The destination square must be on the fifth
603 // rank, and both the destination square and the square between the
604 // source and destination squares must be empty.
605 if ( rank_of(to) != RANK_5
607 || !is_empty(from + DELTA_S))
615 else if (!(attacks_from(pc, from) & to))
618 // Evasions generator already takes care to avoid some kind of illegal moves
619 // and pl_move_is_legal() relies on this. So we have to take care that the
620 // same kind of moves are filtered out here.
623 if (type_of(pc) != KING)
625 // Double check? In this case a king move is required
626 if (more_than_one(checkers()))
629 // Our move must be a blocking evasion or a capture of the checking piece
630 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
633 // In case of king moves under check we have to remove king so to catch
634 // as invalid moves like b1a1 when opposite queen is on c1.
635 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
643 /// Position::move_gives_check() tests whether a pseudo-legal move gives a check
645 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
648 assert(ci.dcCandidates == discovered_check_candidates());
649 assert(color_of(piece_moved(m)) == sideToMove);
651 Square from = from_sq(m);
652 Square to = to_sq(m);
653 PieceType pt = type_of(piece_on(from));
656 if (ci.checkSq[pt] & to)
660 if (ci.dcCandidates && (ci.dcCandidates & from))
662 // For pawn and king moves we need to verify also direction
663 if ( (pt != PAWN && pt != KING)
664 || !squares_aligned(from, to, king_square(~sideToMove)))
668 // Can we skip the ugly special cases ?
669 if (type_of(m) == NORMAL)
672 Color us = sideToMove;
673 Square ksq = king_square(~us);
678 return attacks_from(Piece(promotion_type(m)), to, pieces() ^ from) & ksq;
680 // En passant capture with check ? We have already handled the case
681 // of direct checks and ordinary discovered check, the only case we
682 // need to handle is the unusual case of a discovered check through
683 // the captured pawn.
686 Square capsq = file_of(to) | rank_of(from);
687 Bitboard b = (pieces() ^ from ^ capsq) | to;
689 return (attacks_bb< ROOK>(ksq, b) & pieces(us, QUEEN, ROOK))
690 | (attacks_bb<BISHOP>(ksq, b) & pieces(us, QUEEN, BISHOP));
695 Square rfrom = to; // 'King captures the rook' notation
696 Square kto = relative_square(us, rfrom > kfrom ? SQ_G1 : SQ_C1);
697 Square rto = relative_square(us, rfrom > kfrom ? SQ_F1 : SQ_D1);
698 Bitboard b = (pieces() ^ kfrom ^ rfrom) | rto | kto;
700 return attacks_bb<ROOK>(rto, b) & ksq;
709 /// Position::do_move() makes a move, and saves all information necessary
710 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
711 /// moves should be filtered out before this function is called.
713 void Position::do_move(Move m, StateInfo& newSt) {
716 do_move(m, newSt, ci, move_gives_check(m, ci));
719 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
722 assert(&newSt != st);
727 // Copy some fields of old state to our new StateInfo object except the ones
728 // which are going to be recalculated from scratch anyway, then switch our state
729 // pointer to point to the new, ready to be updated, state.
730 memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
735 // Update side to move
738 // Increment the 50 moves rule draw counter. Resetting it to zero in the
739 // case of a capture or a pawn move is taken care of later.
743 if (type_of(m) == CASTLE)
746 do_castle_move<true>(m);
750 Color us = sideToMove;
752 Square from = from_sq(m);
753 Square to = to_sq(m);
754 Piece piece = piece_on(from);
755 PieceType pt = type_of(piece);
756 PieceType capture = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
758 assert(color_of(piece) == us);
759 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them);
760 assert(capture != KING);
766 // If the captured piece is a pawn, update pawn hash key, otherwise
767 // update non-pawn material.
770 if (type_of(m) == ENPASSANT)
772 capsq += pawn_push(them);
775 assert(to == st->epSquare);
776 assert(relative_rank(us, to) == RANK_6);
777 assert(piece_on(to) == NO_PIECE);
778 assert(piece_on(capsq) == make_piece(them, PAWN));
780 board[capsq] = NO_PIECE;
783 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
786 st->npMaterial[them] -= PieceValue[MG][capture];
788 // Remove the captured piece
789 byTypeBB[ALL_PIECES] ^= capsq;
790 byTypeBB[capture] ^= capsq;
791 byColorBB[them] ^= capsq;
793 // Update piece list, move the last piece at index[capsq] position and
796 // WARNING: This is a not revresible operation. When we will reinsert the
797 // captured piece in undo_move() we will put it at the end of the list and
798 // not in its original place, it means index[] and pieceList[] are not
799 // guaranteed to be invariant to a do_move() + undo_move() sequence.
800 Square lastSquare = pieceList[them][capture][--pieceCount[them][capture]];
801 index[lastSquare] = index[capsq];
802 pieceList[them][capture][index[lastSquare]] = lastSquare;
803 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
805 // Update material hash key and prefetch access to materialTable
806 k ^= Zobrist::psq[them][capture][capsq];
807 st->materialKey ^= Zobrist::psq[them][capture][pieceCount[them][capture]];
808 prefetch((char*)thisThread->materialTable[st->materialKey]);
810 // Update incremental scores
811 st->psqScore -= pieceSquareTable[make_piece(them, capture)][capsq];
813 // Reset rule 50 counter
818 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
820 // Reset en passant square
821 if (st->epSquare != SQ_NONE)
823 k ^= Zobrist::enpassant[file_of(st->epSquare)];
824 st->epSquare = SQ_NONE;
827 // Update castle rights if needed
828 if (st->castleRights && (castleRightsMask[from] | castleRightsMask[to]))
830 int cr = castleRightsMask[from] | castleRightsMask[to];
831 k ^= Zobrist::castle[st->castleRights & cr];
832 st->castleRights &= ~cr;
835 // Prefetch TT access as soon as we know the new hash key
836 prefetch((char*)TT.first_entry(k));
839 Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
840 byTypeBB[ALL_PIECES] ^= from_to_bb;
841 byTypeBB[pt] ^= from_to_bb;
842 byColorBB[us] ^= from_to_bb;
844 board[to] = board[from];
845 board[from] = NO_PIECE;
847 // Update piece lists, index[from] is not updated and becomes stale. This
848 // works as long as index[] is accessed just by known occupied squares.
849 index[to] = index[from];
850 pieceList[us][pt][index[to]] = to;
852 // If the moving piece is a pawn do some special extra work
855 // Set en-passant square, only if moved pawn can be captured
856 if ( (int(to) ^ int(from)) == 16
857 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
859 st->epSquare = Square((from + to) / 2);
860 k ^= Zobrist::enpassant[file_of(st->epSquare)];
863 if (type_of(m) == PROMOTION)
865 PieceType promotion = promotion_type(m);
867 assert(relative_rank(us, to) == RANK_8);
868 assert(promotion >= KNIGHT && promotion <= QUEEN);
870 // Replace the pawn with the promoted piece
871 byTypeBB[PAWN] ^= to;
872 byTypeBB[promotion] |= to;
873 board[to] = make_piece(us, promotion);
875 // Update piece lists, move the last pawn at index[to] position
876 // and shrink the list. Add a new promotion piece to the list.
877 Square lastSquare = pieceList[us][PAWN][--pieceCount[us][PAWN]];
878 index[lastSquare] = index[to];
879 pieceList[us][PAWN][index[lastSquare]] = lastSquare;
880 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
881 index[to] = pieceCount[us][promotion];
882 pieceList[us][promotion][index[to]] = to;
885 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
886 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
887 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]++]
888 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
890 // Update incremental score
891 st->psqScore += pieceSquareTable[make_piece(us, promotion)][to]
892 - pieceSquareTable[make_piece(us, PAWN)][to];
895 st->npMaterial[us] += PieceValue[MG][promotion];
898 // Update pawn hash key and prefetch access to pawnsTable
899 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
900 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
902 // Reset rule 50 draw counter
906 // Update incremental scores
907 st->psqScore += psq_delta(piece, from, to);
910 st->capturedType = capture;
912 // Update the key with the final value
915 // Update checkers bitboard, piece must be already moved
920 if (type_of(m) != NORMAL)
921 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
925 if (ci.checkSq[pt] & to)
926 st->checkersBB |= to;
929 if (ci.dcCandidates && (ci.dcCandidates & from))
932 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
935 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
940 sideToMove = ~sideToMove;
946 /// Position::undo_move() unmakes a move. When it returns, the position should
947 /// be restored to exactly the same state as before the move was made.
949 void Position::undo_move(Move m) {
953 sideToMove = ~sideToMove;
955 if (type_of(m) == CASTLE)
956 return do_castle_move<false>(m);
958 Color us = sideToMove;
960 Square from = from_sq(m);
961 Square to = to_sq(m);
962 Piece piece = piece_on(to);
963 PieceType pt = type_of(piece);
964 PieceType capture = st->capturedType;
966 assert(is_empty(from));
967 assert(color_of(piece) == us);
968 assert(capture != KING);
970 if (type_of(m) == PROMOTION)
972 PieceType promotion = promotion_type(m);
974 assert(promotion == pt);
975 assert(relative_rank(us, to) == RANK_8);
976 assert(promotion >= KNIGHT && promotion <= QUEEN);
978 // Replace the promoted piece with the pawn
979 byTypeBB[promotion] ^= to;
980 byTypeBB[PAWN] |= to;
981 board[to] = make_piece(us, PAWN);
983 // Update piece lists, move the last promoted piece at index[to] position
984 // and shrink the list. Add a new pawn to the list.
985 Square lastSquare = pieceList[us][promotion][--pieceCount[us][promotion]];
986 index[lastSquare] = index[to];
987 pieceList[us][promotion][index[lastSquare]] = lastSquare;
988 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
989 index[to] = pieceCount[us][PAWN]++;
990 pieceList[us][PAWN][index[to]] = to;
995 // Put the piece back at the source square
996 Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
997 byTypeBB[ALL_PIECES] ^= from_to_bb;
998 byTypeBB[pt] ^= from_to_bb;
999 byColorBB[us] ^= from_to_bb;
1001 board[from] = board[to];
1002 board[to] = NO_PIECE;
1004 // Update piece lists, index[to] is not updated and becomes stale. This
1005 // works as long as index[] is accessed just by known occupied squares.
1006 index[from] = index[to];
1007 pieceList[us][pt][index[from]] = from;
1013 if (type_of(m) == ENPASSANT)
1015 capsq -= pawn_push(us);
1018 assert(to == st->previous->epSquare);
1019 assert(relative_rank(us, to) == RANK_6);
1020 assert(piece_on(capsq) == NO_PIECE);
1023 // Restore the captured piece
1024 byTypeBB[ALL_PIECES] |= capsq;
1025 byTypeBB[capture] |= capsq;
1026 byColorBB[them] |= capsq;
1028 board[capsq] = make_piece(them, capture);
1030 // Update piece list, add a new captured piece in capsq square
1031 index[capsq] = pieceCount[them][capture]++;
1032 pieceList[them][capture][index[capsq]] = capsq;
1035 // Finally point our state pointer back to the previous state
1038 assert(pos_is_ok());
1042 /// Position::do_castle_move() is a private method used to do/undo a castling
1043 /// move. Note that castling moves are encoded as "king captures friendly rook"
1044 /// moves, for instance white short castling in a non-Chess960 game is encoded
1047 void Position::do_castle_move(Move m) {
1050 assert(type_of(m) == CASTLE);
1052 Color us = sideToMove;
1053 Square kfrom, kto, rfrom, rto;
1055 bool kingSide = to_sq(m) > from_sq(m);
1056 kfrom = kto = from_sq(m);
1057 rfrom = rto = to_sq(m);
1061 kto = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
1062 rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
1066 kfrom = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
1067 rfrom = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
1070 assert(piece_on(kfrom) == make_piece(us, KING));
1071 assert(piece_on(rfrom) == make_piece(us, ROOK));
1073 // Move the pieces, with some care; in chess960 could be kto == rfrom
1074 Bitboard k_from_to_bb = SquareBB[kfrom] ^ SquareBB[kto];
1075 Bitboard r_from_to_bb = SquareBB[rfrom] ^ SquareBB[rto];
1076 byTypeBB[KING] ^= k_from_to_bb;
1077 byTypeBB[ROOK] ^= r_from_to_bb;
1078 byTypeBB[ALL_PIECES] ^= k_from_to_bb ^ r_from_to_bb;
1079 byColorBB[us] ^= k_from_to_bb ^ r_from_to_bb;
1082 board[kfrom] = board[rfrom] = NO_PIECE;
1083 board[kto] = make_piece(us, KING);
1084 board[rto] = make_piece(us, ROOK);
1086 // Update piece lists
1087 pieceList[us][KING][index[kfrom]] = kto;
1088 pieceList[us][ROOK][index[rfrom]] = rto;
1089 int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
1090 index[kto] = index[kfrom];
1095 // Reset capture field
1096 st->capturedType = NO_PIECE_TYPE;
1098 // Update incremental scores
1099 st->psqScore += psq_delta(make_piece(us, KING), kfrom, kto);
1100 st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);
1103 st->key ^= Zobrist::psq[us][KING][kfrom] ^ Zobrist::psq[us][KING][kto];
1104 st->key ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
1106 // Clear en passant square
1107 if (st->epSquare != SQ_NONE)
1109 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
1110 st->epSquare = SQ_NONE;
1113 // Update castling rights
1114 st->key ^= Zobrist::castle[st->castleRights & castleRightsMask[kfrom]];
1115 st->castleRights &= ~castleRightsMask[kfrom];
1117 // Update checkers BB
1118 st->checkersBB = attackers_to(king_square(~us)) & pieces(us);
1120 sideToMove = ~sideToMove;
1123 // Undo: point our state pointer back to the previous state
1126 assert(pos_is_ok());
1130 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
1131 /// the side to move without executing any move on the board.
1133 void Position::do_null_move(StateInfo& newSt) {
1135 assert(!checkers());
1137 memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
1139 newSt.previous = st;
1142 if (st->epSquare != SQ_NONE)
1144 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
1145 st->epSquare = SQ_NONE;
1148 st->key ^= Zobrist::side;
1149 prefetch((char*)TT.first_entry(st->key));
1152 st->pliesFromNull = 0;
1154 sideToMove = ~sideToMove;
1156 assert(pos_is_ok());
1159 void Position::undo_null_move() {
1161 assert(!checkers());
1164 sideToMove = ~sideToMove;
1168 /// Position::see() is a static exchange evaluator: It tries to estimate the
1169 /// material gain or loss resulting from a move. There are three versions of
1170 /// this function: One which takes a destination square as input, one takes a
1171 /// move, and one which takes a 'from' and a 'to' square. The function does
1172 /// not yet understand promotions captures.
1174 int Position::see_sign(Move m) const {
1178 // Early return if SEE cannot be negative because captured piece value
1179 // is not less then capturing one. Note that king moves always return
1180 // here because king midgame value is set to 0.
1181 if (PieceValue[MG][piece_on(to_sq(m))] >= PieceValue[MG][piece_moved(m)])
1187 int Position::see(Move m) const {
1190 Bitboard occupied, attackers, stmAttackers;
1191 int swapList[32], slIndex = 1;
1199 captured = type_of(piece_on(to));
1200 occupied = pieces() ^ from;
1202 // Handle en passant moves
1203 if (type_of(m) == ENPASSANT)
1205 Square capQq = to - pawn_push(sideToMove);
1208 assert(type_of(piece_on(capQq)) == PAWN);
1210 // Remove the captured pawn
1214 else if (type_of(m) == CASTLE)
1215 // Castle moves are implemented as king capturing the rook so cannot be
1216 // handled correctly. Simply return 0 that is always the correct value
1217 // unless the rook is ends up under attack.
1220 // Find all attackers to the destination square, with the moving piece
1221 // removed, but possibly an X-ray attacker added behind it.
1222 attackers = attackers_to(to, occupied);
1224 // If the opponent has no attackers we are finished
1225 stm = ~color_of(piece_on(from));
1226 stmAttackers = attackers & pieces(stm);
1228 return PieceValue[MG][captured];
1230 // The destination square is defended, which makes things rather more
1231 // difficult to compute. We proceed by building up a "swap list" containing
1232 // the material gain or loss at each stop in a sequence of captures to the
1233 // destination square, where the sides alternately capture, and always
1234 // capture with the least valuable piece. After each capture, we look for
1235 // new X-ray attacks from behind the capturing piece.
1236 swapList[0] = PieceValue[MG][captured];
1237 captured = type_of(piece_on(from));
1240 assert(slIndex < 32);
1242 // Add the new entry to the swap list
1243 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1246 // Locate and remove from 'occupied' the next least valuable attacker
1247 captured = next_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1249 attackers &= occupied; // Remove the just found attacker
1251 stmAttackers = attackers & pieces(stm);
1253 if (captured == KING)
1255 // Stop before processing a king capture
1257 swapList[slIndex++] = QueenValueMg * 16;
1262 } while (stmAttackers);
1264 // Having built the swap list, we negamax through it to find the best
1265 // achievable score from the point of view of the side to move.
1267 swapList[slIndex-1] = std::min(-swapList[slIndex], swapList[slIndex-1]);
1273 /// Position::clear() erases the position object to a pristine state, with an
1274 /// empty board, white to move, and no castling rights.
1276 void Position::clear() {
1278 memset(this, 0, sizeof(Position));
1279 startState.epSquare = SQ_NONE;
1282 for (int i = 0; i < 8; i++)
1283 for (int j = 0; j < 16; j++)
1284 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1288 /// Position::put_piece() puts a piece on the given square of the board,
1289 /// updating the board array, pieces list, bitboards, and piece counts.
1291 void Position::put_piece(Piece p, Square s) {
1293 Color c = color_of(p);
1294 PieceType pt = type_of(p);
1297 index[s] = pieceCount[c][pt]++;
1298 pieceList[c][pt][index[s]] = s;
1300 byTypeBB[ALL_PIECES] |= s;
1306 /// Position::compute_key() computes the hash key of the position. The hash
1307 /// key is usually updated incrementally as moves are made and unmade, the
1308 /// compute_key() function is only used when a new position is set up, and
1309 /// to verify the correctness of the hash key when running in debug mode.
1311 Key Position::compute_key() const {
1313 Key k = Zobrist::castle[st->castleRights];
1315 for (Bitboard b = pieces(); b; )
1317 Square s = pop_lsb(&b);
1318 k ^= Zobrist::psq[color_of(piece_on(s))][type_of(piece_on(s))][s];
1321 if (ep_square() != SQ_NONE)
1322 k ^= Zobrist::enpassant[file_of(ep_square())];
1324 if (sideToMove == BLACK)
1331 /// Position::compute_pawn_key() computes the hash key of the position. The
1332 /// hash key is usually updated incrementally as moves are made and unmade,
1333 /// the compute_pawn_key() function is only used when a new position is set
1334 /// up, and to verify the correctness of the pawn hash key when running in
1337 Key Position::compute_pawn_key() const {
1341 for (Bitboard b = pieces(PAWN); b; )
1343 Square s = pop_lsb(&b);
1344 k ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
1351 /// Position::compute_material_key() computes the hash key of the position.
1352 /// The hash key is usually updated incrementally as moves are made and unmade,
1353 /// the compute_material_key() function is only used when a new position is set
1354 /// up, and to verify the correctness of the material hash key when running in
1357 Key Position::compute_material_key() const {
1361 for (Color c = WHITE; c <= BLACK; c++)
1362 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1363 for (int cnt = 0; cnt < piece_count(c, pt); cnt++)
1364 k ^= Zobrist::psq[c][pt][cnt];
1370 /// Position::compute_psq_score() computes the incremental scores for the middle
1371 /// game and the endgame. These functions are used to initialize the incremental
1372 /// scores when a new position is set up, and to verify that the scores are correctly
1373 /// updated by do_move and undo_move when the program is running in debug mode.
1374 Score Position::compute_psq_score() const {
1376 Score score = SCORE_ZERO;
1378 for (Bitboard b = pieces(); b; )
1380 Square s = pop_lsb(&b);
1381 score += pieceSquareTable[piece_on(s)][s];
1388 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1389 /// game material value for the given side. Material values are updated
1390 /// incrementally during the search, this function is only used while
1391 /// initializing a new Position object.
1393 Value Position::compute_non_pawn_material(Color c) const {
1395 Value value = VALUE_ZERO;
1397 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1398 value += piece_count(c, pt) * PieceValue[MG][pt];
1404 /// Position::is_draw() tests whether the position is drawn by material,
1405 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1406 /// must be done by the search.
1407 template<bool CheckRepetition, bool CheckThreeFold>
1408 bool Position::is_draw() const {
1411 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
1414 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1417 if (CheckRepetition)
1419 int i = 4, e = std::min(st->rule50, st->pliesFromNull), cnt;
1423 StateInfo* stp = st->previous->previous;
1425 for (cnt = 0; i <= e; i += 2)
1427 stp = stp->previous->previous;
1429 if (stp->key == st->key && (!CheckThreeFold || ++cnt >= 2))
1438 // Explicit template instantiations
1439 template bool Position::is_draw<true, true>() const;
1440 template bool Position::is_draw<true, false>() const;
1441 template bool Position::is_draw<false,false>() const;
1444 /// Position::flip() flips position with the white and black sides reversed. This
1445 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1447 void Position::flip() {
1449 const Position pos(*this);
1453 sideToMove = ~pos.side_to_move();
1454 thisThread = pos.this_thread();
1455 nodes = pos.nodes_searched();
1456 chess960 = pos.is_chess960();
1457 startPosPly = pos.startpos_ply_counter();
1459 for (Square s = SQ_A1; s <= SQ_H8; s++)
1460 if (!pos.is_empty(s))
1461 put_piece(Piece(pos.piece_on(s) ^ 8), ~s);
1463 if (pos.can_castle(WHITE_OO))
1464 set_castle_right(BLACK, ~pos.castle_rook_square(WHITE, KING_SIDE));
1465 if (pos.can_castle(WHITE_OOO))
1466 set_castle_right(BLACK, ~pos.castle_rook_square(WHITE, QUEEN_SIDE));
1467 if (pos.can_castle(BLACK_OO))
1468 set_castle_right(WHITE, ~pos.castle_rook_square(BLACK, KING_SIDE));
1469 if (pos.can_castle(BLACK_OOO))
1470 set_castle_right(WHITE, ~pos.castle_rook_square(BLACK, QUEEN_SIDE));
1472 if (pos.st->epSquare != SQ_NONE)
1473 st->epSquare = ~pos.st->epSquare;
1475 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
1477 st->key = compute_key();
1478 st->pawnKey = compute_pawn_key();
1479 st->materialKey = compute_material_key();
1480 st->psqScore = compute_psq_score();
1481 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1482 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1484 assert(pos_is_ok());
1488 /// Position::pos_is_ok() performs some consitency checks for the position object.
1489 /// This is meant to be helpful when debugging.
1491 bool Position::pos_is_ok(int* failedStep) const {
1493 int dummy, *step = failedStep ? failedStep : &dummy;
1495 // What features of the position should be verified?
1496 const bool all = false;
1498 const bool debugBitboards = all || false;
1499 const bool debugKingCount = all || false;
1500 const bool debugKingCapture = all || false;
1501 const bool debugCheckerCount = all || false;
1502 const bool debugKey = all || false;
1503 const bool debugMaterialKey = all || false;
1504 const bool debugPawnKey = all || false;
1505 const bool debugIncrementalEval = all || false;
1506 const bool debugNonPawnMaterial = all || false;
1507 const bool debugPieceCounts = all || false;
1508 const bool debugPieceList = all || false;
1509 const bool debugCastleSquares = all || false;
1513 if (sideToMove != WHITE && sideToMove != BLACK)
1516 if ((*step)++, piece_on(king_square(WHITE)) != W_KING)
1519 if ((*step)++, piece_on(king_square(BLACK)) != B_KING)
1522 if ((*step)++, debugKingCount)
1524 int kingCount[COLOR_NB] = {};
1526 for (Square s = SQ_A1; s <= SQ_H8; s++)
1527 if (type_of(piece_on(s)) == KING)
1528 kingCount[color_of(piece_on(s))]++;
1530 if (kingCount[0] != 1 || kingCount[1] != 1)
1534 if ((*step)++, debugKingCapture)
1535 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1538 if ((*step)++, debugCheckerCount && popcount<Full>(st->checkersBB) > 2)
1541 if ((*step)++, debugBitboards)
1543 // The intersection of the white and black pieces must be empty
1544 if (pieces(WHITE) & pieces(BLACK))
1547 // The union of the white and black pieces must be equal to all
1549 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1552 // Separate piece type bitboards must have empty intersections
1553 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1554 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1555 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1559 if ((*step)++, ep_square() != SQ_NONE && relative_rank(sideToMove, ep_square()) != RANK_6)
1562 if ((*step)++, debugKey && st->key != compute_key())
1565 if ((*step)++, debugPawnKey && st->pawnKey != compute_pawn_key())
1568 if ((*step)++, debugMaterialKey && st->materialKey != compute_material_key())
1571 if ((*step)++, debugIncrementalEval && st->psqScore != compute_psq_score())
1574 if ((*step)++, debugNonPawnMaterial)
1576 if ( st->npMaterial[WHITE] != compute_non_pawn_material(WHITE)
1577 || st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1581 if ((*step)++, debugPieceCounts)
1582 for (Color c = WHITE; c <= BLACK; c++)
1583 for (PieceType pt = PAWN; pt <= KING; pt++)
1584 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1587 if ((*step)++, debugPieceList)
1588 for (Color c = WHITE; c <= BLACK; c++)
1589 for (PieceType pt = PAWN; pt <= KING; pt++)
1590 for (int i = 0; i < pieceCount[c][pt]; i++)
1592 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1595 if (index[piece_list(c, pt)[i]] != i)
1599 if ((*step)++, debugCastleSquares)
1600 for (Color c = WHITE; c <= BLACK; c++)
1601 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1603 CastleRight cr = make_castle_right(c, s);
1605 if (!can_castle(cr))
1608 if ((castleRightsMask[king_square(c)] & cr) != cr)
1611 if ( piece_on(castleRookSquare[c][s]) != make_piece(c, ROOK)
1612 || castleRightsMask[castleRookSquare[c][s]] != cr)