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& fenStr, 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 fen(fenStr);
167 fen >> std::noskipws;
169 // 1. Piece placement
170 while ((fen >> 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 ((fen >> token) && !isspace(token))
192 set_castling_rights(token);
194 // 4. En passant square. Ignore if no pawn capture is possible
195 if ( ((fen >> col) && (col >= 'a' && col <= 'h'))
196 && ((fen >> 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 fen >> std::skipws >> st->rule50 >> fullMoves;
208 // Various initialisations
209 chess960 = isChess960;
210 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
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 = char(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 {
273 std::ostringstream fen;
277 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
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)];
305 fen << (sideToMove == WHITE ? " w " : " b ");
307 if (st->castleRights != CASTLES_NONE)
309 if (can_castle(WHITE_OO))
310 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K');
312 if (can_castle(WHITE_OOO))
313 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q');
315 if (can_castle(BLACK_OO))
316 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k');
318 if (can_castle(BLACK_OOO))
319 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q');
323 fen << (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()))
324 << " " << st->rule50 << " " << fullMoves;
330 /// Position::print() prints an ASCII representation of the position to
331 /// the standard output. If a move is given then also the san is printed.
333 void Position::print(Move move) const {
335 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
339 Position p(*this, thread());
340 string dd = (sideToMove == BLACK ? ".." : "");
341 cout << "\nMove is: " << dd << move_to_san(p, move);
344 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
346 cout << dottedLine << '|';
347 for (File file = FILE_A; file <= FILE_H; file++)
349 Square sq = make_square(file, rank);
350 Piece piece = piece_on(sq);
352 if (piece == PIECE_NONE && square_color(sq) == DARK)
353 piece = PIECE_NONE_DARK_SQ;
355 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
356 cout << c << PieceToChar[piece] << c << '|';
359 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
363 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
364 /// king) pieces for the given color and for the given pinner type. Or, when
365 /// template parameter FindPinned is false, the pieces of the given color
366 /// candidate for a discovery check against the enemy king.
367 /// Bitboard checkersBB must be already updated when looking for pinners.
369 template<bool FindPinned>
370 Bitboard Position::hidden_checkers(Color c) const {
372 Bitboard result = EmptyBoardBB;
373 Bitboard pinners = pieces(FindPinned ? opposite_color(c) : c);
375 // Pinned pieces protect our king, dicovery checks attack
377 Square ksq = king_square(FindPinned ? c : opposite_color(c));
379 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
380 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
382 if (FindPinned && pinners)
383 pinners &= ~st->checkersBB;
387 Square s = pop_1st_bit(&pinners);
388 Bitboard b = squares_between(s, ksq) & occupied_squares();
392 if ( !(b & (b - 1)) // Only one bit set?
393 && (b & pieces(c))) // Is an our piece?
400 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
401 /// king) pieces for the given color. Note that checkersBB bitboard must
402 /// be already updated.
404 Bitboard Position::pinned_pieces(Color c) const {
406 return hidden_checkers<true>(c);
410 /// Position:discovered_check_candidates() returns a bitboard containing all
411 /// pieces for the given side which are candidates for giving a discovered
412 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
413 /// to be already updated.
415 Bitboard Position::discovered_check_candidates(Color c) const {
417 return hidden_checkers<false>(c);
420 /// Position::attackers_to() computes a bitboard containing all pieces which
421 /// attacks a given square.
423 Bitboard Position::attackers_to(Square s) const {
425 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
426 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
427 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
428 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
429 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
430 | (attacks_from<KING>(s) & pieces(KING));
433 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
435 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
436 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
437 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
438 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
439 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
440 | (attacks_from<KING>(s) & pieces(KING));
443 /// Position::attacks_from() computes a bitboard of all attacks
444 /// of a given piece put in a given square.
446 Bitboard Position::attacks_from(Piece p, Square s) const {
448 assert(square_is_ok(s));
452 case WB: case BB: return attacks_from<BISHOP>(s);
453 case WR: case BR: return attacks_from<ROOK>(s);
454 case WQ: case BQ: return attacks_from<QUEEN>(s);
455 default: return StepAttacksBB[p][s];
459 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
461 assert(square_is_ok(s));
465 case WB: case BB: return bishop_attacks_bb(s, occ);
466 case WR: case BR: return rook_attacks_bb(s, occ);
467 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
468 default: return StepAttacksBB[p][s];
473 /// Position::move_attacks_square() tests whether a move from the current
474 /// position attacks a given square.
476 bool Position::move_attacks_square(Move m, Square s) const {
478 assert(move_is_ok(m));
479 assert(square_is_ok(s));
482 Square f = move_from(m), t = move_to(m);
484 assert(!square_is_empty(f));
486 if (bit_is_set(attacks_from(piece_on(f), t), s))
489 // Move the piece and scan for X-ray attacks behind it
490 occ = occupied_squares();
491 do_move_bb(&occ, make_move_bb(f, t));
492 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
493 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
494 & pieces(piece_color(piece_on(f)));
496 // If we have attacks we need to verify that are caused by our move
497 // and are not already existent ones.
498 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
502 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
504 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
507 assert(move_is_ok(m));
508 assert(pinned == pinned_pieces(side_to_move()));
510 Color us = side_to_move();
511 Square from = move_from(m);
513 assert(piece_color(piece_on(from)) == us);
514 assert(piece_on(king_square(us)) == make_piece(us, KING));
516 // En passant captures are a tricky special case. Because they are
517 // rather uncommon, we do it simply by testing whether the king is attacked
518 // after the move is made
521 Color them = opposite_color(us);
522 Square to = move_to(m);
523 Square capsq = make_square(square_file(to), square_rank(from));
524 Square ksq = king_square(us);
525 Bitboard b = occupied_squares();
527 assert(to == ep_square());
528 assert(piece_on(from) == make_piece(us, PAWN));
529 assert(piece_on(capsq) == make_piece(them, PAWN));
530 assert(piece_on(to) == PIECE_NONE);
533 clear_bit(&b, capsq);
536 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
537 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
540 // If the moving piece is a king, check whether the destination
541 // square is attacked by the opponent. Castling moves are checked
542 // for legality during move generation.
543 if (piece_type(piece_on(from)) == KING)
544 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces(opposite_color(us)));
546 // A non-king move is legal if and only if it is not pinned or it
547 // is moving along the ray towards or away from the king.
549 || !bit_is_set(pinned, from)
550 || squares_aligned(from, move_to(m), king_square(us));
554 /// Position::move_is_legal() takes a move and tests whether the move
555 /// is legal. This version is not very fast and should be used only
556 /// in non time-critical paths.
558 bool Position::move_is_legal(const Move m) const {
560 for (MoveList<MV_LEGAL> ml(*this); !ml.end(); ++ml)
568 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
569 /// of pinned pieces as input, and tests whether the move is pseudo legal.
571 bool Position::move_is_pl(const Move m) const {
575 Color us = sideToMove;
576 Color them = opposite_color(sideToMove);
577 Square from = move_from(m);
578 Square to = move_to(m);
579 Piece pc = piece_on(from);
581 // Use a slower but simpler function for uncommon cases
582 if (move_is_special(m))
583 return move_is_legal(m);
585 // Is not a promotion, so promotion piece must be empty
586 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
589 // If the from square is not occupied by a piece belonging to the side to
590 // move, the move is obviously not legal.
591 if (pc == PIECE_NONE || piece_color(pc) != us)
594 // The destination square cannot be occupied by a friendly piece
595 if (piece_color(piece_on(to)) == us)
598 // Handle the special case of a pawn move
599 if (piece_type(pc) == PAWN)
601 // Move direction must be compatible with pawn color
602 int direction = to - from;
603 if ((us == WHITE) != (direction > 0))
606 // We have already handled promotion moves, so destination
607 // cannot be on the 8/1th rank.
608 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
611 // Proceed according to the square delta between the origin and
612 // destination squares.
619 // Capture. The destination square must be occupied by an enemy
620 // piece (en passant captures was handled earlier).
621 if (piece_color(piece_on(to)) != them)
624 // From and to files must be one file apart, avoids a7h5
625 if (abs(square_file(from) - square_file(to)) != 1)
631 // Pawn push. The destination square must be empty.
632 if (!square_is_empty(to))
637 // Double white pawn push. The destination square must be on the fourth
638 // rank, and both the destination square and the square between the
639 // source and destination squares must be empty.
640 if ( square_rank(to) != RANK_4
641 || !square_is_empty(to)
642 || !square_is_empty(from + DELTA_N))
647 // Double black pawn push. The destination square must be on the fifth
648 // rank, and both the destination square and the square between the
649 // source and destination squares must be empty.
650 if ( square_rank(to) != RANK_5
651 || !square_is_empty(to)
652 || !square_is_empty(from + DELTA_S))
660 else if (!bit_is_set(attacks_from(pc, from), to))
665 // In case of king moves under check we have to remove king so to catch
666 // as invalid moves like b1a1 when opposite queen is on c1.
667 if (piece_type(piece_on(from)) == KING)
669 Bitboard b = occupied_squares();
671 if (attackers_to(move_to(m), b) & pieces(opposite_color(us)))
676 Bitboard target = checkers();
677 Square checksq = pop_1st_bit(&target);
679 if (target) // double check ? In this case a king move is required
682 // Our move must be a blocking evasion or a capture of the checking piece
683 target = squares_between(checksq, king_square(us)) | checkers();
684 if (!bit_is_set(target, move_to(m)))
693 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
695 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
698 assert(move_is_ok(m));
699 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
700 assert(piece_color(piece_on(move_from(m))) == side_to_move());
702 Square from = move_from(m);
703 Square to = move_to(m);
704 PieceType pt = piece_type(piece_on(from));
707 if (bit_is_set(ci.checkSq[pt], to))
711 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
713 // For pawn and king moves we need to verify also direction
714 if ( (pt != PAWN && pt != KING)
715 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
719 // Can we skip the ugly special cases ?
720 if (!move_is_special(m))
723 Color us = side_to_move();
724 Bitboard b = occupied_squares();
725 Square ksq = king_square(opposite_color(us));
727 // Promotion with check ?
728 if (move_is_promotion(m))
732 switch (promotion_piece_type(m))
735 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
737 return bit_is_set(bishop_attacks_bb(to, b), ksq);
739 return bit_is_set(rook_attacks_bb(to, b), ksq);
741 return bit_is_set(queen_attacks_bb(to, b), ksq);
747 // En passant capture with check ? We have already handled the case
748 // of direct checks and ordinary discovered check, the only case we
749 // need to handle is the unusual case of a discovered check through
750 // the captured pawn.
753 Square capsq = make_square(square_file(to), square_rank(from));
755 clear_bit(&b, capsq);
757 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
758 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
761 // Castling with check ?
762 if (move_is_castle(m))
764 Square kfrom, kto, rfrom, rto;
770 kto = relative_square(us, SQ_G1);
771 rto = relative_square(us, SQ_F1);
773 kto = relative_square(us, SQ_C1);
774 rto = relative_square(us, SQ_D1);
776 clear_bit(&b, kfrom);
777 clear_bit(&b, rfrom);
780 return bit_is_set(rook_attacks_bb(rto, b), ksq);
787 /// Position::do_setup_move() makes a permanent move on the board. It should
788 /// be used when setting up a position on board. You can't undo the move.
790 void Position::do_setup_move(Move m) {
794 // Update the number of full moves after black's move
795 if (sideToMove == BLACK)
800 // Reset "game ply" in case we made a non-reversible move.
801 // "game ply" is used for repetition detection.
805 // Our StateInfo newSt is about going out of scope so copy
806 // its content before it disappears.
811 /// Position::do_move() makes a move, and saves all information necessary
812 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
813 /// moves should be filtered out before this function is called.
815 void Position::do_move(Move m, StateInfo& newSt) {
818 do_move(m, newSt, ci, move_gives_check(m, ci));
821 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
824 assert(move_is_ok(m));
825 assert(&newSt != st);
830 // Copy some fields of old state to our new StateInfo object except the
831 // ones which are recalculated from scratch anyway, then switch our state
832 // pointer to point to the new, ready to be updated, state.
833 struct ReducedStateInfo {
834 Key pawnKey, materialKey;
835 int castleRights, rule50, gamePly, pliesFromNull;
841 memcpy(&newSt, st, sizeof(ReducedStateInfo));
846 // Save the current key to the history[] array, in order to be able to
847 // detect repetition draws.
848 history[st->gamePly++] = key;
850 // Update side to move
851 key ^= zobSideToMove;
853 // Increment the 50 moves rule draw counter. Resetting it to zero in the
854 // case of non-reversible moves is taken care of later.
858 if (move_is_castle(m))
865 Color us = side_to_move();
866 Color them = opposite_color(us);
867 Square from = move_from(m);
868 Square to = move_to(m);
869 bool ep = move_is_ep(m);
870 bool pm = move_is_promotion(m);
872 Piece piece = piece_on(from);
873 PieceType pt = piece_type(piece);
874 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
876 assert(piece_color(piece_on(from)) == us);
877 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
878 assert(!(ep || pm) || piece == make_piece(us, PAWN));
879 assert(!pm || relative_rank(us, to) == RANK_8);
882 do_capture_move(key, capture, them, to, ep);
885 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
887 // Reset en passant square
888 if (st->epSquare != SQ_NONE)
890 key ^= zobEp[st->epSquare];
891 st->epSquare = SQ_NONE;
894 // Update castle rights if needed
895 if ( st->castleRights != CASTLES_NONE
896 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
898 key ^= zobCastle[st->castleRights];
899 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
900 key ^= zobCastle[st->castleRights];
903 // Prefetch TT access as soon as we know key is updated
904 prefetch((char*)TT.first_entry(key));
907 Bitboard move_bb = make_move_bb(from, to);
908 do_move_bb(&byColorBB[us], move_bb);
909 do_move_bb(&byTypeBB[pt], move_bb);
910 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
912 board[to] = board[from];
913 board[from] = PIECE_NONE;
915 // Update piece lists, note that index[from] is not updated and
916 // becomes stale. This works as long as index[] is accessed just
917 // by known occupied squares.
918 index[to] = index[from];
919 pieceList[us][pt][index[to]] = to;
921 // If the moving piece was a pawn do some special extra work
924 // Reset rule 50 draw counter
927 // Update pawn hash key and prefetch in L1/L2 cache
928 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
930 // Set en passant square, only if moved pawn can be captured
931 if ((to ^ from) == 16)
933 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
935 st->epSquare = Square((int(from) + int(to)) / 2);
936 key ^= zobEp[st->epSquare];
940 if (pm) // promotion ?
942 PieceType promotion = promotion_piece_type(m);
944 assert(promotion >= KNIGHT && promotion <= QUEEN);
946 // Insert promoted piece instead of pawn
947 clear_bit(&byTypeBB[PAWN], to);
948 set_bit(&byTypeBB[promotion], to);
949 board[to] = make_piece(us, promotion);
951 // Update piece counts
952 pieceCount[us][promotion]++;
953 pieceCount[us][PAWN]--;
955 // Update material key
956 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
957 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
959 // Update piece lists, move the last pawn at index[to] position
960 // and shrink the list. Add a new promotion piece to the list.
961 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
962 index[lastPawnSquare] = index[to];
963 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
964 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
965 index[to] = pieceCount[us][promotion] - 1;
966 pieceList[us][promotion][index[to]] = to;
968 // Partially revert hash keys update
969 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
970 st->pawnKey ^= zobrist[us][PAWN][to];
972 // Partially revert and update incremental scores
973 st->value -= pst(make_piece(us, PAWN), to);
974 st->value += pst(make_piece(us, promotion), to);
977 st->npMaterial[us] += PieceValueMidgame[promotion];
981 // Prefetch pawn and material hash tables
982 Threads[threadID].pawnTable.prefetch(st->pawnKey);
983 Threads[threadID].materialTable.prefetch(st->materialKey);
985 // Update incremental scores
986 st->value += pst_delta(piece, from, to);
989 st->capturedType = capture;
991 // Update the key with the final value
994 // Update checkers bitboard, piece must be already moved
995 st->checkersBB = EmptyBoardBB;
1000 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1004 if (bit_is_set(ci.checkSq[pt], to))
1005 st->checkersBB = SetMaskBB[to];
1008 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1011 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1014 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1020 sideToMove = opposite_color(sideToMove);
1021 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1027 /// Position::do_capture_move() is a private method used to update captured
1028 /// piece info. It is called from the main Position::do_move function.
1030 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1032 assert(capture != KING);
1036 // If the captured piece was a pawn, update pawn hash key,
1037 // otherwise update non-pawn material.
1038 if (capture == PAWN)
1040 if (ep) // en passant ?
1042 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1044 assert(to == st->epSquare);
1045 assert(relative_rank(opposite_color(them), to) == RANK_6);
1046 assert(piece_on(to) == PIECE_NONE);
1047 assert(piece_on(capsq) == make_piece(them, PAWN));
1049 board[capsq] = PIECE_NONE;
1051 st->pawnKey ^= zobrist[them][PAWN][capsq];
1054 st->npMaterial[them] -= PieceValueMidgame[capture];
1056 // Remove captured piece
1057 clear_bit(&byColorBB[them], capsq);
1058 clear_bit(&byTypeBB[capture], capsq);
1059 clear_bit(&byTypeBB[0], capsq);
1062 key ^= zobrist[them][capture][capsq];
1064 // Update incremental scores
1065 st->value -= pst(make_piece(them, capture), capsq);
1067 // Update piece count
1068 pieceCount[them][capture]--;
1070 // Update material hash key
1071 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1073 // Update piece list, move the last piece at index[capsq] position
1075 // WARNING: This is a not perfectly revresible operation. When we
1076 // will reinsert the captured piece in undo_move() we will put it
1077 // at the end of the list and not in its original place, it means
1078 // index[] and pieceList[] are not guaranteed to be invariant to a
1079 // do_move() + undo_move() sequence.
1080 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1081 index[lastPieceSquare] = index[capsq];
1082 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1083 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1085 // Reset rule 50 counter
1090 /// Position::do_castle_move() is a private method used to make a castling
1091 /// move. It is called from the main Position::do_move function. Note that
1092 /// castling moves are encoded as "king captures friendly rook" moves, for
1093 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1095 void Position::do_castle_move(Move m) {
1097 assert(move_is_ok(m));
1098 assert(move_is_castle(m));
1100 Color us = side_to_move();
1101 Color them = opposite_color(us);
1103 // Find source squares for king and rook
1104 Square kfrom = move_from(m);
1105 Square rfrom = move_to(m);
1108 assert(piece_on(kfrom) == make_piece(us, KING));
1109 assert(piece_on(rfrom) == make_piece(us, ROOK));
1111 // Find destination squares for king and rook
1112 if (rfrom > kfrom) // O-O
1114 kto = relative_square(us, SQ_G1);
1115 rto = relative_square(us, SQ_F1);
1119 kto = relative_square(us, SQ_C1);
1120 rto = relative_square(us, SQ_D1);
1123 // Remove pieces from source squares
1124 clear_bit(&byColorBB[us], kfrom);
1125 clear_bit(&byTypeBB[KING], kfrom);
1126 clear_bit(&byTypeBB[0], kfrom);
1127 clear_bit(&byColorBB[us], rfrom);
1128 clear_bit(&byTypeBB[ROOK], rfrom);
1129 clear_bit(&byTypeBB[0], rfrom);
1131 // Put pieces on destination squares
1132 set_bit(&byColorBB[us], kto);
1133 set_bit(&byTypeBB[KING], kto);
1134 set_bit(&byTypeBB[0], kto);
1135 set_bit(&byColorBB[us], rto);
1136 set_bit(&byTypeBB[ROOK], rto);
1137 set_bit(&byTypeBB[0], rto);
1140 Piece king = make_piece(us, KING);
1141 Piece rook = make_piece(us, ROOK);
1142 board[kfrom] = board[rfrom] = PIECE_NONE;
1146 // Update piece lists
1147 pieceList[us][KING][index[kfrom]] = kto;
1148 pieceList[us][ROOK][index[rfrom]] = rto;
1149 int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
1150 index[kto] = index[kfrom];
1153 // Reset capture field
1154 st->capturedType = PIECE_TYPE_NONE;
1156 // Update incremental scores
1157 st->value += pst_delta(king, kfrom, kto);
1158 st->value += pst_delta(rook, rfrom, rto);
1161 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1162 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1164 // Clear en passant square
1165 if (st->epSquare != SQ_NONE)
1167 st->key ^= zobEp[st->epSquare];
1168 st->epSquare = SQ_NONE;
1171 // Update castling rights
1172 st->key ^= zobCastle[st->castleRights];
1173 st->castleRights &= castleRightsMask[kfrom];
1174 st->key ^= zobCastle[st->castleRights];
1176 // Reset rule 50 counter
1179 // Update checkers BB
1180 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1183 sideToMove = opposite_color(sideToMove);
1184 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1190 /// Position::undo_move() unmakes a move. When it returns, the position should
1191 /// be restored to exactly the same state as before the move was made.
1193 void Position::undo_move(Move m) {
1196 assert(move_is_ok(m));
1198 sideToMove = opposite_color(sideToMove);
1200 if (move_is_castle(m))
1202 undo_castle_move(m);
1206 Color us = side_to_move();
1207 Color them = opposite_color(us);
1208 Square from = move_from(m);
1209 Square to = move_to(m);
1210 bool ep = move_is_ep(m);
1211 bool pm = move_is_promotion(m);
1213 PieceType pt = piece_type(piece_on(to));
1215 assert(square_is_empty(from));
1216 assert(piece_color(piece_on(to)) == us);
1217 assert(!pm || relative_rank(us, to) == RANK_8);
1218 assert(!ep || to == st->previous->epSquare);
1219 assert(!ep || relative_rank(us, to) == RANK_6);
1220 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1222 if (pm) // promotion ?
1224 PieceType promotion = promotion_piece_type(m);
1227 assert(promotion >= KNIGHT && promotion <= QUEEN);
1228 assert(piece_on(to) == make_piece(us, promotion));
1230 // Replace promoted piece with a pawn
1231 clear_bit(&byTypeBB[promotion], to);
1232 set_bit(&byTypeBB[PAWN], to);
1234 // Update piece counts
1235 pieceCount[us][promotion]--;
1236 pieceCount[us][PAWN]++;
1238 // Update piece list replacing promotion piece with a pawn
1239 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1240 index[lastPromotionSquare] = index[to];
1241 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1242 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1243 index[to] = pieceCount[us][PAWN] - 1;
1244 pieceList[us][PAWN][index[to]] = to;
1247 // Put the piece back at the source square
1248 Bitboard move_bb = make_move_bb(to, from);
1249 do_move_bb(&byColorBB[us], move_bb);
1250 do_move_bb(&byTypeBB[pt], move_bb);
1251 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
1253 board[from] = make_piece(us, pt);
1254 board[to] = PIECE_NONE;
1256 // Update piece list
1257 index[from] = index[to];
1258 pieceList[us][pt][index[from]] = from;
1260 if (st->capturedType)
1265 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1267 assert(st->capturedType != KING);
1268 assert(!ep || square_is_empty(capsq));
1270 // Restore the captured piece
1271 set_bit(&byColorBB[them], capsq);
1272 set_bit(&byTypeBB[st->capturedType], capsq);
1273 set_bit(&byTypeBB[0], capsq);
1275 board[capsq] = make_piece(them, st->capturedType);
1277 // Update piece count
1278 pieceCount[them][st->capturedType]++;
1280 // Update piece list, add a new captured piece in capsq square
1281 index[capsq] = pieceCount[them][st->capturedType] - 1;
1282 pieceList[them][st->capturedType][index[capsq]] = capsq;
1285 // Finally point our state pointer back to the previous state
1292 /// Position::undo_castle_move() is a private method used to unmake a castling
1293 /// move. It is called from the main Position::undo_move function. Note that
1294 /// castling moves are encoded as "king captures friendly rook" moves, for
1295 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1297 void Position::undo_castle_move(Move m) {
1299 assert(move_is_ok(m));
1300 assert(move_is_castle(m));
1302 // When we have arrived here, some work has already been done by
1303 // Position::undo_move. In particular, the side to move has been switched,
1304 // so the code below is correct.
1305 Color us = side_to_move();
1307 // Find source squares for king and rook
1308 Square kfrom = move_from(m);
1309 Square rfrom = move_to(m);
1312 // Find destination squares for king and rook
1313 if (rfrom > kfrom) // O-O
1315 kto = relative_square(us, SQ_G1);
1316 rto = relative_square(us, SQ_F1);
1320 kto = relative_square(us, SQ_C1);
1321 rto = relative_square(us, SQ_D1);
1324 assert(piece_on(kto) == make_piece(us, KING));
1325 assert(piece_on(rto) == make_piece(us, ROOK));
1327 // Remove pieces from destination squares
1328 clear_bit(&byColorBB[us], kto);
1329 clear_bit(&byTypeBB[KING], kto);
1330 clear_bit(&byTypeBB[0], kto);
1331 clear_bit(&byColorBB[us], rto);
1332 clear_bit(&byTypeBB[ROOK], rto);
1333 clear_bit(&byTypeBB[0], rto);
1335 // Put pieces on source squares
1336 set_bit(&byColorBB[us], kfrom);
1337 set_bit(&byTypeBB[KING], kfrom);
1338 set_bit(&byTypeBB[0], kfrom);
1339 set_bit(&byColorBB[us], rfrom);
1340 set_bit(&byTypeBB[ROOK], rfrom);
1341 set_bit(&byTypeBB[0], rfrom);
1344 Piece king = make_piece(us, KING);
1345 Piece rook = make_piece(us, ROOK);
1346 board[kto] = board[rto] = PIECE_NONE;
1347 board[kfrom] = king;
1348 board[rfrom] = rook;
1350 // Update piece lists
1351 pieceList[us][KING][index[kto]] = kfrom;
1352 pieceList[us][ROOK][index[rto]] = rfrom;
1353 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1354 index[kfrom] = index[kto];
1357 // Finally point our state pointer back to the previous state
1364 /// Position::do_null_move makes() a "null move": It switches the side to move
1365 /// and updates the hash key without executing any move on the board.
1367 void Position::do_null_move(StateInfo& backupSt) {
1370 assert(!in_check());
1372 // Back up the information necessary to undo the null move to the supplied
1373 // StateInfo object.
1374 // Note that differently from normal case here backupSt is actually used as
1375 // a backup storage not as a new state to be used.
1376 backupSt.key = st->key;
1377 backupSt.epSquare = st->epSquare;
1378 backupSt.value = st->value;
1379 backupSt.previous = st->previous;
1380 backupSt.pliesFromNull = st->pliesFromNull;
1381 st->previous = &backupSt;
1383 // Save the current key to the history[] array, in order to be able to
1384 // detect repetition draws.
1385 history[st->gamePly++] = st->key;
1387 // Update the necessary information
1388 if (st->epSquare != SQ_NONE)
1389 st->key ^= zobEp[st->epSquare];
1391 st->key ^= zobSideToMove;
1392 prefetch((char*)TT.first_entry(st->key));
1394 sideToMove = opposite_color(sideToMove);
1395 st->epSquare = SQ_NONE;
1397 st->pliesFromNull = 0;
1398 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1402 /// Position::undo_null_move() unmakes a "null move".
1404 void Position::undo_null_move() {
1407 assert(!in_check());
1409 // Restore information from the our backup StateInfo object
1410 StateInfo* backupSt = st->previous;
1411 st->key = backupSt->key;
1412 st->epSquare = backupSt->epSquare;
1413 st->value = backupSt->value;
1414 st->previous = backupSt->previous;
1415 st->pliesFromNull = backupSt->pliesFromNull;
1417 // Update the necessary information
1418 sideToMove = opposite_color(sideToMove);
1424 /// Position::see() is a static exchange evaluator: It tries to estimate the
1425 /// material gain or loss resulting from a move. There are three versions of
1426 /// this function: One which takes a destination square as input, one takes a
1427 /// move, and one which takes a 'from' and a 'to' square. The function does
1428 /// not yet understand promotions captures.
1430 int Position::see_sign(Move m) const {
1432 assert(move_is_ok(m));
1434 Square from = move_from(m);
1435 Square to = move_to(m);
1437 // Early return if SEE cannot be negative because captured piece value
1438 // is not less then capturing one. Note that king moves always return
1439 // here because king midgame value is set to 0.
1440 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1446 int Position::see(Move m) const {
1449 Bitboard occupied, attackers, stmAttackers, b;
1450 int swapList[32], slIndex = 1;
1451 PieceType capturedType, pt;
1454 assert(move_is_ok(m));
1456 // As castle moves are implemented as capturing the rook, they have
1457 // SEE == RookValueMidgame most of the times (unless the rook is under
1459 if (move_is_castle(m))
1462 from = move_from(m);
1464 capturedType = piece_type(piece_on(to));
1465 occupied = occupied_squares();
1467 // Handle en passant moves
1468 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1470 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1472 assert(capturedType == PIECE_TYPE_NONE);
1473 assert(piece_type(piece_on(capQq)) == PAWN);
1475 // Remove the captured pawn
1476 clear_bit(&occupied, capQq);
1477 capturedType = PAWN;
1480 // Find all attackers to the destination square, with the moving piece
1481 // removed, but possibly an X-ray attacker added behind it.
1482 clear_bit(&occupied, from);
1483 attackers = attackers_to(to, occupied);
1485 // If the opponent has no attackers we are finished
1486 stm = opposite_color(piece_color(piece_on(from)));
1487 stmAttackers = attackers & pieces(stm);
1489 return PieceValueMidgame[capturedType];
1491 // The destination square is defended, which makes things rather more
1492 // difficult to compute. We proceed by building up a "swap list" containing
1493 // the material gain or loss at each stop in a sequence of captures to the
1494 // destination square, where the sides alternately capture, and always
1495 // capture with the least valuable piece. After each capture, we look for
1496 // new X-ray attacks from behind the capturing piece.
1497 swapList[0] = PieceValueMidgame[capturedType];
1498 capturedType = piece_type(piece_on(from));
1501 // Locate the least valuable attacker for the side to move. The loop
1502 // below looks like it is potentially infinite, but it isn't. We know
1503 // that the side to move still has at least one attacker left.
1504 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1507 // Remove the attacker we just found from the 'occupied' bitboard,
1508 // and scan for new X-ray attacks behind the attacker.
1509 b = stmAttackers & pieces(pt);
1510 occupied ^= (b & (~b + 1));
1511 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1512 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1514 attackers &= occupied; // Cut out pieces we've already done
1516 // Add the new entry to the swap list
1517 assert(slIndex < 32);
1518 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1521 // Remember the value of the capturing piece, and change the side to
1522 // move before beginning the next iteration.
1524 stm = opposite_color(stm);
1525 stmAttackers = attackers & pieces(stm);
1527 // Stop before processing a king capture
1528 if (capturedType == KING && stmAttackers)
1530 assert(slIndex < 32);
1531 swapList[slIndex++] = QueenValueMidgame*10;
1534 } while (stmAttackers);
1536 // Having built the swap list, we negamax through it to find the best
1537 // achievable score from the point of view of the side to move.
1539 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1545 /// Position::clear() erases the position object to a pristine state, with an
1546 /// empty board, white to move, and no castling rights.
1548 void Position::clear() {
1551 memset(st, 0, sizeof(StateInfo));
1552 st->epSquare = SQ_NONE;
1554 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1555 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1556 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1557 memset(index, 0, sizeof(int) * 64);
1559 for (int i = 0; i < 8; i++)
1560 for (int j = 0; j < 16; j++)
1561 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1563 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1565 board[sq] = PIECE_NONE;
1566 castleRightsMask[sq] = ALL_CASTLES;
1574 /// Position::put_piece() puts a piece on the given square of the board,
1575 /// updating the board array, pieces list, bitboards, and piece counts.
1577 void Position::put_piece(Piece p, Square s) {
1579 Color c = piece_color(p);
1580 PieceType pt = piece_type(p);
1583 index[s] = pieceCount[c][pt]++;
1584 pieceList[c][pt][index[s]] = s;
1586 set_bit(&byTypeBB[pt], s);
1587 set_bit(&byColorBB[c], s);
1588 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1592 /// Position::compute_key() computes the hash key of the position. The hash
1593 /// key is usually updated incrementally as moves are made and unmade, the
1594 /// compute_key() function is only used when a new position is set up, and
1595 /// to verify the correctness of the hash key when running in debug mode.
1597 Key Position::compute_key() const {
1599 Key result = zobCastle[st->castleRights];
1601 for (Square s = SQ_A1; s <= SQ_H8; s++)
1602 if (!square_is_empty(s))
1603 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1605 if (ep_square() != SQ_NONE)
1606 result ^= zobEp[ep_square()];
1608 if (side_to_move() == BLACK)
1609 result ^= zobSideToMove;
1615 /// Position::compute_pawn_key() computes the hash key of the position. The
1616 /// hash key is usually updated incrementally as moves are made and unmade,
1617 /// the compute_pawn_key() function is only used when a new position is set
1618 /// up, and to verify the correctness of the pawn hash key when running in
1621 Key Position::compute_pawn_key() const {
1626 for (Color c = WHITE; c <= BLACK; c++)
1628 b = pieces(PAWN, c);
1630 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1636 /// Position::compute_material_key() computes the hash key of the position.
1637 /// The hash key is usually updated incrementally as moves are made and unmade,
1638 /// the compute_material_key() function is only used when a new position is set
1639 /// up, and to verify the correctness of the material hash key when running in
1642 Key Position::compute_material_key() const {
1646 for (Color c = WHITE; c <= BLACK; c++)
1647 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1648 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1649 result ^= zobrist[c][pt][i];
1655 /// Position::compute_value() compute the incremental scores for the middle
1656 /// game and the endgame. These functions are used to initialize the incremental
1657 /// scores when a new position is set up, and to verify that the scores are correctly
1658 /// updated by do_move and undo_move when the program is running in debug mode.
1659 Score Position::compute_value() const {
1662 Score result = SCORE_ZERO;
1664 for (Color c = WHITE; c <= BLACK; c++)
1665 for (PieceType pt = PAWN; pt <= KING; pt++)
1669 result += pst(make_piece(c, pt), pop_1st_bit(&b));
1672 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1677 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1678 /// game material value for the given side. Material values are updated
1679 /// incrementally during the search, this function is only used while
1680 /// initializing a new Position object.
1682 Value Position::compute_non_pawn_material(Color c) const {
1684 Value result = VALUE_ZERO;
1686 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1687 result += piece_count(c, pt) * PieceValueMidgame[pt];
1693 /// Position::is_draw() tests whether the position is drawn by material,
1694 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1695 /// must be done by the search.
1696 template<bool SkipRepetition>
1697 bool Position::is_draw() const {
1699 // Draw by material?
1701 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1704 // Draw by the 50 moves rule?
1705 if (st->rule50 > 99 && !is_mate())
1708 // Draw by repetition?
1709 if (!SkipRepetition)
1710 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1711 if (history[st->gamePly - i] == st->key)
1717 // Explicit template instantiations
1718 template bool Position::is_draw<false>() const;
1719 template bool Position::is_draw<true>() const;
1722 /// Position::is_mate() returns true or false depending on whether the
1723 /// side to move is checkmated.
1725 bool Position::is_mate() const {
1727 return in_check() && !MoveList<MV_LEGAL>(*this).size();
1731 /// Position::init() is a static member function which initializes at
1732 /// startup the various arrays used to compute hash keys and the piece
1733 /// square tables. The latter is a two-step operation: First, the white
1734 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1735 /// Second, the black halves of the tables are initialized by mirroring
1736 /// and changing the sign of the corresponding white scores.
1738 void Position::init() {
1742 for (Color c = WHITE; c <= BLACK; c++)
1743 for (PieceType pt = PAWN; pt <= KING; pt++)
1744 for (Square s = SQ_A1; s <= SQ_H8; s++)
1745 zobrist[c][pt][s] = rk.rand<Key>();
1747 for (Square s = SQ_A1; s <= SQ_H8; s++)
1748 zobEp[s] = rk.rand<Key>();
1750 for (int i = 0; i < 16; i++)
1751 zobCastle[i] = rk.rand<Key>();
1753 zobSideToMove = rk.rand<Key>();
1754 zobExclusion = rk.rand<Key>();
1756 for (Square s = SQ_A1; s <= SQ_H8; s++)
1757 for (Piece p = WP; p <= WK; p++)
1758 pieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1760 for (Square s = SQ_A1; s <= SQ_H8; s++)
1761 for (Piece p = BP; p <= BK; p++)
1762 pieceSquareTable[p][s] = -pieceSquareTable[p-8][flip_square(s)];
1766 /// Position::flip() flips position with the white and black sides reversed. This
1767 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1769 void Position::flip() {
1773 // Make a copy of current position before to start changing
1774 const Position pos(*this, threadID);
1777 threadID = pos.thread();
1780 for (Square s = SQ_A1; s <= SQ_H8; s++)
1781 if (!pos.square_is_empty(s))
1782 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1785 sideToMove = opposite_color(pos.side_to_move());
1788 if (pos.can_castle(WHITE_OO))
1789 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1790 if (pos.can_castle(WHITE_OOO))
1791 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1792 if (pos.can_castle(BLACK_OO))
1793 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1794 if (pos.can_castle(BLACK_OOO))
1795 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1797 // En passant square
1798 if (pos.st->epSquare != SQ_NONE)
1799 st->epSquare = flip_square(pos.st->epSquare);
1802 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
1805 st->key = compute_key();
1806 st->pawnKey = compute_pawn_key();
1807 st->materialKey = compute_material_key();
1809 // Incremental scores
1810 st->value = compute_value();
1813 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1814 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1820 /// Position::is_ok() performs some consitency checks for the position object.
1821 /// This is meant to be helpful when debugging.
1823 bool Position::is_ok(int* failedStep) const {
1825 // What features of the position should be verified?
1826 const bool debugAll = false;
1828 const bool debugBitboards = debugAll || false;
1829 const bool debugKingCount = debugAll || false;
1830 const bool debugKingCapture = debugAll || false;
1831 const bool debugCheckerCount = debugAll || false;
1832 const bool debugKey = debugAll || false;
1833 const bool debugMaterialKey = debugAll || false;
1834 const bool debugPawnKey = debugAll || false;
1835 const bool debugIncrementalEval = debugAll || false;
1836 const bool debugNonPawnMaterial = debugAll || false;
1837 const bool debugPieceCounts = debugAll || false;
1838 const bool debugPieceList = debugAll || false;
1839 const bool debugCastleSquares = debugAll || false;
1841 if (failedStep) *failedStep = 1;
1844 if (side_to_move() != WHITE && side_to_move() != BLACK)
1847 // Are the king squares in the position correct?
1848 if (failedStep) (*failedStep)++;
1849 if (piece_on(king_square(WHITE)) != WK)
1852 if (failedStep) (*failedStep)++;
1853 if (piece_on(king_square(BLACK)) != BK)
1856 // Do both sides have exactly one king?
1857 if (failedStep) (*failedStep)++;
1860 int kingCount[2] = {0, 0};
1861 for (Square s = SQ_A1; s <= SQ_H8; s++)
1862 if (piece_type(piece_on(s)) == KING)
1863 kingCount[piece_color(piece_on(s))]++;
1865 if (kingCount[0] != 1 || kingCount[1] != 1)
1869 // Can the side to move capture the opponent's king?
1870 if (failedStep) (*failedStep)++;
1871 if (debugKingCapture)
1873 Color us = side_to_move();
1874 Color them = opposite_color(us);
1875 Square ksq = king_square(them);
1876 if (attackers_to(ksq) & pieces(us))
1880 // Is there more than 2 checkers?
1881 if (failedStep) (*failedStep)++;
1882 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1886 if (failedStep) (*failedStep)++;
1889 // The intersection of the white and black pieces must be empty
1890 if ((pieces(WHITE) & pieces(BLACK)) != EmptyBoardBB)
1893 // The union of the white and black pieces must be equal to all
1895 if ((pieces(WHITE) | pieces(BLACK)) != occupied_squares())
1898 // Separate piece type bitboards must have empty intersections
1899 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1900 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1901 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1905 // En passant square OK?
1906 if (failedStep) (*failedStep)++;
1907 if (ep_square() != SQ_NONE)
1909 // The en passant square must be on rank 6, from the point of view of the
1911 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1916 if (failedStep) (*failedStep)++;
1917 if (debugKey && st->key != compute_key())
1920 // Pawn hash key OK?
1921 if (failedStep) (*failedStep)++;
1922 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1925 // Material hash key OK?
1926 if (failedStep) (*failedStep)++;
1927 if (debugMaterialKey && st->materialKey != compute_material_key())
1930 // Incremental eval OK?
1931 if (failedStep) (*failedStep)++;
1932 if (debugIncrementalEval && st->value != compute_value())
1935 // Non-pawn material OK?
1936 if (failedStep) (*failedStep)++;
1937 if (debugNonPawnMaterial)
1939 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1942 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1947 if (failedStep) (*failedStep)++;
1948 if (debugPieceCounts)
1949 for (Color c = WHITE; c <= BLACK; c++)
1950 for (PieceType pt = PAWN; pt <= KING; pt++)
1951 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1954 if (failedStep) (*failedStep)++;
1956 for (Color c = WHITE; c <= BLACK; c++)
1957 for (PieceType pt = PAWN; pt <= KING; pt++)
1958 for (int i = 0; i < pieceCount[c][pt]; i++)
1960 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1963 if (index[piece_list(c, pt)[i]] != i)
1967 if (failedStep) (*failedStep)++;
1968 if (debugCastleSquares)
1969 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1974 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1976 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1977 || piece_on(castleRookSquare[f]) != rook)
1981 if (failedStep) *failedStep = 0;