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 Color us = sideToMove;
745 Square from = from_sq(m);
746 Square to = to_sq(m);
747 Piece piece = piece_on(from);
748 PieceType pt = type_of(piece);
749 PieceType capture = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
751 assert(color_of(piece) == us);
752 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLE);
753 assert(capture != KING);
755 if (type_of(m) == CASTLE)
757 assert(piece == make_piece(us, KING));
759 bool kingSide = to > from;
760 Square rfrom = to; // Castle is encoded as "king captures friendly rook"
761 Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
762 to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
763 capture = NO_PIECE_TYPE;
765 do_castle(from, to, rfrom, rto);
767 st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);
768 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
775 // If the captured piece is a pawn, update pawn hash key, otherwise
776 // update non-pawn material.
779 if (type_of(m) == ENPASSANT)
781 capsq += pawn_push(them);
784 assert(to == st->epSquare);
785 assert(relative_rank(us, to) == RANK_6);
786 assert(piece_on(to) == NO_PIECE);
787 assert(piece_on(capsq) == make_piece(them, PAWN));
789 board[capsq] = NO_PIECE;
792 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
795 st->npMaterial[them] -= PieceValue[MG][capture];
797 // Remove the captured piece
798 byTypeBB[ALL_PIECES] ^= capsq;
799 byTypeBB[capture] ^= capsq;
800 byColorBB[them] ^= capsq;
802 // Update piece list, move the last piece at index[capsq] position and
805 // WARNING: This is a not reversible operation. When we will reinsert the
806 // captured piece in undo_move() we will put it at the end of the list and
807 // not in its original place, it means index[] and pieceList[] are not
808 // guaranteed to be invariant to a do_move() + undo_move() sequence.
809 Square lastSquare = pieceList[them][capture][--pieceCount[them][capture]];
810 index[lastSquare] = index[capsq];
811 pieceList[them][capture][index[lastSquare]] = lastSquare;
812 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
814 // Update material hash key and prefetch access to materialTable
815 k ^= Zobrist::psq[them][capture][capsq];
816 st->materialKey ^= Zobrist::psq[them][capture][pieceCount[them][capture]];
817 prefetch((char*)thisThread->materialTable[st->materialKey]);
819 // Update incremental scores
820 st->psqScore -= pieceSquareTable[make_piece(them, capture)][capsq];
822 // Reset rule 50 counter
827 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
829 // Reset en passant square
830 if (st->epSquare != SQ_NONE)
832 k ^= Zobrist::enpassant[file_of(st->epSquare)];
833 st->epSquare = SQ_NONE;
836 // Update castle rights if needed
837 if (st->castleRights && (castleRightsMask[from] | castleRightsMask[to]))
839 int cr = castleRightsMask[from] | castleRightsMask[to];
840 k ^= Zobrist::castle[st->castleRights & cr];
841 st->castleRights &= ~cr;
844 // Prefetch TT access as soon as we know the new hash key
845 prefetch((char*)TT.first_entry(k));
847 // Move the piece. The tricky Chess960 castle is handled earlier
848 if (type_of(m) != CASTLE)
850 Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
851 byTypeBB[ALL_PIECES] ^= from_to_bb;
852 byTypeBB[pt] ^= from_to_bb;
853 byColorBB[us] ^= from_to_bb;
855 board[from] = NO_PIECE;
858 // Update piece lists, index[from] is not updated and becomes stale. This
859 // works as long as index[] is accessed just by known occupied squares.
860 index[to] = index[from];
861 pieceList[us][pt][index[to]] = to;
864 // If the moving piece is a pawn do some special extra work
867 // Set en-passant square, only if moved pawn can be captured
868 if ( (int(to) ^ int(from)) == 16
869 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
871 st->epSquare = Square((from + to) / 2);
872 k ^= Zobrist::enpassant[file_of(st->epSquare)];
875 if (type_of(m) == PROMOTION)
877 PieceType promotion = promotion_type(m);
879 assert(relative_rank(us, to) == RANK_8);
880 assert(promotion >= KNIGHT && promotion <= QUEEN);
882 // Replace the pawn with the promoted piece
883 byTypeBB[PAWN] ^= to;
884 byTypeBB[promotion] |= to;
885 board[to] = make_piece(us, promotion);
887 // Update piece lists, move the last pawn at index[to] position
888 // and shrink the list. Add a new promotion piece to the list.
889 Square lastSquare = pieceList[us][PAWN][--pieceCount[us][PAWN]];
890 index[lastSquare] = index[to];
891 pieceList[us][PAWN][index[lastSquare]] = lastSquare;
892 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
893 index[to] = pieceCount[us][promotion];
894 pieceList[us][promotion][index[to]] = to;
897 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
898 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
899 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]++]
900 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
902 // Update incremental score
903 st->psqScore += pieceSquareTable[make_piece(us, promotion)][to]
904 - pieceSquareTable[make_piece(us, PAWN)][to];
907 st->npMaterial[us] += PieceValue[MG][promotion];
910 // Update pawn hash key and prefetch access to pawnsTable
911 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
912 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
914 // Reset rule 50 draw counter
918 // Update incremental scores
919 st->psqScore += psq_delta(piece, from, to);
922 st->capturedType = capture;
924 // Update the key with the final value
927 // Update checkers bitboard, piece must be already moved
932 if (type_of(m) != NORMAL)
933 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
937 if (ci.checkSq[pt] & to)
938 st->checkersBB |= to;
941 if (ci.dcCandidates && (ci.dcCandidates & from))
944 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
947 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
952 sideToMove = ~sideToMove;
958 /// Position::undo_move() unmakes a move. When it returns, the position should
959 /// be restored to exactly the same state as before the move was made.
961 void Position::undo_move(Move m) {
965 sideToMove = ~sideToMove;
967 Color us = sideToMove;
969 Square from = from_sq(m);
970 Square to = to_sq(m);
971 PieceType pt = type_of(piece_on(to));
972 PieceType capture = st->capturedType;
974 assert(is_empty(from) || type_of(m) == CASTLE);
975 assert(capture != KING);
977 if (type_of(m) == PROMOTION)
979 PieceType promotion = promotion_type(m);
981 assert(promotion == pt);
982 assert(relative_rank(us, to) == RANK_8);
983 assert(promotion >= KNIGHT && promotion <= QUEEN);
985 // Replace the promoted piece with the pawn
986 byTypeBB[promotion] ^= to;
987 byTypeBB[PAWN] |= to;
988 board[to] = make_piece(us, PAWN);
990 // Update piece lists, move the last promoted piece at index[to] position
991 // and shrink the list. Add a new pawn to the list.
992 Square lastSquare = pieceList[us][promotion][--pieceCount[us][promotion]];
993 index[lastSquare] = index[to];
994 pieceList[us][promotion][index[lastSquare]] = lastSquare;
995 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
996 index[to] = pieceCount[us][PAWN]++;
997 pieceList[us][PAWN][index[to]] = to;
1002 if (type_of(m) == CASTLE)
1004 bool kingSide = to > from;
1005 Square rfrom = to; // Castle is encoded as "king captures friendly rook"
1006 Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
1007 to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
1008 capture = NO_PIECE_TYPE;
1010 do_castle(to, from, rto, rfrom);
1014 // Put the piece back at the source square
1015 Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
1016 byTypeBB[ALL_PIECES] ^= from_to_bb;
1017 byTypeBB[pt] ^= from_to_bb;
1018 byColorBB[us] ^= from_to_bb;
1020 board[to] = NO_PIECE;
1021 board[from] = make_piece(us, pt);
1023 // Update piece lists, index[to] is not updated and becomes stale. This
1024 // works as long as index[] is accessed just by known occupied squares.
1025 index[from] = index[to];
1026 pieceList[us][pt][index[from]] = from;
1033 if (type_of(m) == ENPASSANT)
1035 capsq -= pawn_push(us);
1038 assert(to == st->previous->epSquare);
1039 assert(relative_rank(us, to) == RANK_6);
1040 assert(piece_on(capsq) == NO_PIECE);
1043 // Restore the captured piece
1044 byTypeBB[ALL_PIECES] |= capsq;
1045 byTypeBB[capture] |= capsq;
1046 byColorBB[them] |= capsq;
1048 board[capsq] = make_piece(them, capture);
1050 // Update piece list, add a new captured piece in capsq square
1051 index[capsq] = pieceCount[them][capture]++;
1052 pieceList[them][capture][index[capsq]] = capsq;
1055 // Finally point our state pointer back to the previous state
1058 assert(pos_is_ok());
1062 /// Position::do_castle() is a helper used to do/undo a castling move. This
1063 /// is a bit tricky, especially in Chess960.
1065 void Position::do_castle(Square kfrom, Square kto, Square rfrom, Square rto) {
1067 Color us = sideToMove;
1068 Bitboard k_from_to_bb = SquareBB[kfrom] ^ SquareBB[kto];
1069 Bitboard r_from_to_bb = SquareBB[rfrom] ^ SquareBB[rto];
1070 byTypeBB[KING] ^= k_from_to_bb;
1071 byTypeBB[ROOK] ^= r_from_to_bb;
1072 byTypeBB[ALL_PIECES] ^= k_from_to_bb ^ r_from_to_bb;
1073 byColorBB[us] ^= k_from_to_bb ^ r_from_to_bb;
1075 // Could be from == to, so first set NO_PIECE then KING and ROOK
1076 board[kfrom] = board[rfrom] = NO_PIECE;
1077 board[kto] = make_piece(us, KING);
1078 board[rto] = make_piece(us, ROOK);
1080 // Could be kfrom == rto, so use a 'tmp' variable
1081 int tmp = index[kfrom];
1082 index[rto] = index[rfrom];
1084 pieceList[us][KING][index[kto]] = kto;
1085 pieceList[us][ROOK][index[rto]] = rto;
1089 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
1090 /// the side to move without executing any move on the board.
1092 void Position::do_null_move(StateInfo& newSt) {
1094 assert(!checkers());
1096 memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
1098 newSt.previous = st;
1101 if (st->epSquare != SQ_NONE)
1103 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
1104 st->epSquare = SQ_NONE;
1107 st->key ^= Zobrist::side;
1108 prefetch((char*)TT.first_entry(st->key));
1111 st->pliesFromNull = 0;
1113 sideToMove = ~sideToMove;
1115 assert(pos_is_ok());
1118 void Position::undo_null_move() {
1120 assert(!checkers());
1123 sideToMove = ~sideToMove;
1127 /// Position::see() is a static exchange evaluator: It tries to estimate the
1128 /// material gain or loss resulting from a move. There are three versions of
1129 /// this function: One which takes a destination square as input, one takes a
1130 /// move, and one which takes a 'from' and a 'to' square. The function does
1131 /// not yet understand promotions captures.
1133 int Position::see_sign(Move m) const {
1137 // Early return if SEE cannot be negative because captured piece value
1138 // is not less then capturing one. Note that king moves always return
1139 // here because king midgame value is set to 0.
1140 if (PieceValue[MG][piece_on(to_sq(m))] >= PieceValue[MG][piece_moved(m)])
1146 int Position::see(Move m) const {
1149 Bitboard occupied, attackers, stmAttackers;
1150 int swapList[32], slIndex = 1;
1158 captured = type_of(piece_on(to));
1159 occupied = pieces() ^ from;
1161 // Handle en passant moves
1162 if (type_of(m) == ENPASSANT)
1164 Square capQq = to - pawn_push(sideToMove);
1167 assert(type_of(piece_on(capQq)) == PAWN);
1169 // Remove the captured pawn
1173 else if (type_of(m) == CASTLE)
1174 // Castle moves are implemented as king capturing the rook so cannot be
1175 // handled correctly. Simply return 0 that is always the correct value
1176 // unless the rook is ends up under attack.
1179 // Find all attackers to the destination square, with the moving piece
1180 // removed, but possibly an X-ray attacker added behind it.
1181 attackers = attackers_to(to, occupied);
1183 // If the opponent has no attackers we are finished
1184 stm = ~color_of(piece_on(from));
1185 stmAttackers = attackers & pieces(stm);
1187 return PieceValue[MG][captured];
1189 // The destination square is defended, which makes things rather more
1190 // difficult to compute. We proceed by building up a "swap list" containing
1191 // the material gain or loss at each stop in a sequence of captures to the
1192 // destination square, where the sides alternately capture, and always
1193 // capture with the least valuable piece. After each capture, we look for
1194 // new X-ray attacks from behind the capturing piece.
1195 swapList[0] = PieceValue[MG][captured];
1196 captured = type_of(piece_on(from));
1199 assert(slIndex < 32);
1201 // Add the new entry to the swap list
1202 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1205 // Locate and remove from 'occupied' the next least valuable attacker
1206 captured = next_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1208 attackers &= occupied; // Remove the just found attacker
1210 stmAttackers = attackers & pieces(stm);
1212 if (captured == KING)
1214 // Stop before processing a king capture
1216 swapList[slIndex++] = QueenValueMg * 16;
1221 } while (stmAttackers);
1223 // Having built the swap list, we negamax through it to find the best
1224 // achievable score from the point of view of the side to move.
1226 swapList[slIndex-1] = std::min(-swapList[slIndex], swapList[slIndex-1]);
1232 /// Position::clear() erases the position object to a pristine state, with an
1233 /// empty board, white to move, and no castling rights.
1235 void Position::clear() {
1237 memset(this, 0, sizeof(Position));
1238 startState.epSquare = SQ_NONE;
1241 for (int i = 0; i < 8; i++)
1242 for (int j = 0; j < 16; j++)
1243 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1247 /// Position::put_piece() puts a piece on the given square of the board,
1248 /// updating the board array, pieces list, bitboards, and piece counts.
1250 void Position::put_piece(Piece p, Square s) {
1252 Color c = color_of(p);
1253 PieceType pt = type_of(p);
1256 index[s] = pieceCount[c][pt]++;
1257 pieceList[c][pt][index[s]] = s;
1259 byTypeBB[ALL_PIECES] |= s;
1265 /// Position::compute_key() computes the hash key of the position. The hash
1266 /// key is usually updated incrementally as moves are made and unmade, the
1267 /// compute_key() function is only used when a new position is set up, and
1268 /// to verify the correctness of the hash key when running in debug mode.
1270 Key Position::compute_key() const {
1272 Key k = Zobrist::castle[st->castleRights];
1274 for (Bitboard b = pieces(); b; )
1276 Square s = pop_lsb(&b);
1277 k ^= Zobrist::psq[color_of(piece_on(s))][type_of(piece_on(s))][s];
1280 if (ep_square() != SQ_NONE)
1281 k ^= Zobrist::enpassant[file_of(ep_square())];
1283 if (sideToMove == BLACK)
1290 /// Position::compute_pawn_key() computes the hash key of the position. The
1291 /// hash key is usually updated incrementally as moves are made and unmade,
1292 /// the compute_pawn_key() function is only used when a new position is set
1293 /// up, and to verify the correctness of the pawn hash key when running in
1296 Key Position::compute_pawn_key() const {
1300 for (Bitboard b = pieces(PAWN); b; )
1302 Square s = pop_lsb(&b);
1303 k ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
1310 /// Position::compute_material_key() computes the hash key of the position.
1311 /// The hash key is usually updated incrementally as moves are made and unmade,
1312 /// the compute_material_key() function is only used when a new position is set
1313 /// up, and to verify the correctness of the material hash key when running in
1316 Key Position::compute_material_key() const {
1320 for (Color c = WHITE; c <= BLACK; c++)
1321 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1322 for (int cnt = 0; cnt < piece_count(c, pt); cnt++)
1323 k ^= Zobrist::psq[c][pt][cnt];
1329 /// Position::compute_psq_score() computes the incremental scores for the middle
1330 /// game and the endgame. These functions are used to initialize the incremental
1331 /// scores when a new position is set up, and to verify that the scores are correctly
1332 /// updated by do_move and undo_move when the program is running in debug mode.
1333 Score Position::compute_psq_score() const {
1335 Score score = SCORE_ZERO;
1337 for (Bitboard b = pieces(); b; )
1339 Square s = pop_lsb(&b);
1340 score += pieceSquareTable[piece_on(s)][s];
1347 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1348 /// game material value for the given side. Material values are updated
1349 /// incrementally during the search, this function is only used while
1350 /// initializing a new Position object.
1352 Value Position::compute_non_pawn_material(Color c) const {
1354 Value value = VALUE_ZERO;
1356 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1357 value += piece_count(c, pt) * PieceValue[MG][pt];
1363 /// Position::is_draw() tests whether the position is drawn by material,
1364 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1365 /// must be done by the search.
1366 template<bool SkipRepetition>
1367 bool Position::is_draw() const {
1369 // Draw by material?
1371 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
1374 // Draw by the 50 moves rule?
1375 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1378 // Draw by repetition?
1379 if (!SkipRepetition)
1381 int i = 4, e = std::min(st->rule50, st->pliesFromNull);
1385 StateInfo* stp = st->previous->previous;
1388 stp = stp->previous->previous;
1390 if (stp->key == st->key)
1402 // Explicit template instantiations
1403 template bool Position::is_draw<false>() const;
1404 template bool Position::is_draw<true>() const;
1407 /// Position::flip() flips position with the white and black sides reversed. This
1408 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1410 void Position::flip() {
1412 const Position pos(*this);
1416 sideToMove = ~pos.side_to_move();
1417 thisThread = pos.this_thread();
1418 nodes = pos.nodes_searched();
1419 chess960 = pos.is_chess960();
1420 startPosPly = pos.startpos_ply_counter();
1422 for (Square s = SQ_A1; s <= SQ_H8; s++)
1423 if (!pos.is_empty(s))
1424 put_piece(Piece(pos.piece_on(s) ^ 8), ~s);
1426 if (pos.can_castle(WHITE_OO))
1427 set_castle_right(BLACK, ~pos.castle_rook_square(WHITE, KING_SIDE));
1428 if (pos.can_castle(WHITE_OOO))
1429 set_castle_right(BLACK, ~pos.castle_rook_square(WHITE, QUEEN_SIDE));
1430 if (pos.can_castle(BLACK_OO))
1431 set_castle_right(WHITE, ~pos.castle_rook_square(BLACK, KING_SIDE));
1432 if (pos.can_castle(BLACK_OOO))
1433 set_castle_right(WHITE, ~pos.castle_rook_square(BLACK, QUEEN_SIDE));
1435 if (pos.st->epSquare != SQ_NONE)
1436 st->epSquare = ~pos.st->epSquare;
1438 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
1440 st->key = compute_key();
1441 st->pawnKey = compute_pawn_key();
1442 st->materialKey = compute_material_key();
1443 st->psqScore = compute_psq_score();
1444 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1445 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1447 assert(pos_is_ok());
1451 /// Position::pos_is_ok() performs some consitency checks for the position object.
1452 /// This is meant to be helpful when debugging.
1454 bool Position::pos_is_ok(int* failedStep) const {
1456 int dummy, *step = failedStep ? failedStep : &dummy;
1458 // What features of the position should be verified?
1459 const bool all = false;
1461 const bool debugBitboards = all || false;
1462 const bool debugKingCount = all || false;
1463 const bool debugKingCapture = all || false;
1464 const bool debugCheckerCount = all || false;
1465 const bool debugKey = all || false;
1466 const bool debugMaterialKey = all || false;
1467 const bool debugPawnKey = all || false;
1468 const bool debugIncrementalEval = all || false;
1469 const bool debugNonPawnMaterial = all || false;
1470 const bool debugPieceCounts = all || false;
1471 const bool debugPieceList = all || false;
1472 const bool debugCastleSquares = all || false;
1476 if (sideToMove != WHITE && sideToMove != BLACK)
1479 if ((*step)++, piece_on(king_square(WHITE)) != W_KING)
1482 if ((*step)++, piece_on(king_square(BLACK)) != B_KING)
1485 if ((*step)++, debugKingCount)
1487 int kingCount[COLOR_NB] = {};
1489 for (Square s = SQ_A1; s <= SQ_H8; s++)
1490 if (type_of(piece_on(s)) == KING)
1491 kingCount[color_of(piece_on(s))]++;
1493 if (kingCount[0] != 1 || kingCount[1] != 1)
1497 if ((*step)++, debugKingCapture)
1498 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1501 if ((*step)++, debugCheckerCount && popcount<Full>(st->checkersBB) > 2)
1504 if ((*step)++, debugBitboards)
1506 // The intersection of the white and black pieces must be empty
1507 if (pieces(WHITE) & pieces(BLACK))
1510 // The union of the white and black pieces must be equal to all
1512 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1515 // Separate piece type bitboards must have empty intersections
1516 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1517 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1518 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1522 if ((*step)++, ep_square() != SQ_NONE && relative_rank(sideToMove, ep_square()) != RANK_6)
1525 if ((*step)++, debugKey && st->key != compute_key())
1528 if ((*step)++, debugPawnKey && st->pawnKey != compute_pawn_key())
1531 if ((*step)++, debugMaterialKey && st->materialKey != compute_material_key())
1534 if ((*step)++, debugIncrementalEval && st->psqScore != compute_psq_score())
1537 if ((*step)++, debugNonPawnMaterial)
1539 if ( st->npMaterial[WHITE] != compute_non_pawn_material(WHITE)
1540 || st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1544 if ((*step)++, debugPieceCounts)
1545 for (Color c = WHITE; c <= BLACK; c++)
1546 for (PieceType pt = PAWN; pt <= KING; pt++)
1547 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1550 if ((*step)++, debugPieceList)
1551 for (Color c = WHITE; c <= BLACK; c++)
1552 for (PieceType pt = PAWN; pt <= KING; pt++)
1553 for (int i = 0; i < pieceCount[c][pt]; i++)
1555 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1558 if (index[piece_list(c, pt)[i]] != i)
1562 if ((*step)++, debugCastleSquares)
1563 for (Color c = WHITE; c <= BLACK; c++)
1564 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1566 CastleRight cr = make_castle_right(c, s);
1568 if (!can_castle(cr))
1571 if ((castleRightsMask[king_square(c)] & cr) != cr)
1574 if ( piece_on(castleRookSquare[c][s]) != make_piece(c, ROOK)
1575 || castleRightsMask[castleRookSquare[c][s]] != cr)