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/>.
38 Key Position::zobrist[2][8][64];
39 Key Position::zobEp[64];
40 Key Position::zobCastle[16];
41 Key Position::zobSideToMove;
42 Key Position::zobExclusion;
44 Score Position::pieceSquareTable[16][64];
46 // Material values arrays, indexed by Piece
47 const Value PieceValueMidgame[17] = {
49 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
50 RookValueMidgame, QueenValueMidgame,
51 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
52 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
53 RookValueMidgame, QueenValueMidgame
56 const Value PieceValueEndgame[17] = {
58 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
59 RookValueEndgame, QueenValueEndgame,
60 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
61 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
62 RookValueEndgame, QueenValueEndgame
68 // Bonus for having the side to move (modified by Joona Kiiski)
69 const Score TempoValue = make_score(48, 22);
71 // To convert a Piece to and from a FEN char
72 const string PieceToChar(".PNBRQK pnbrqk ");
78 CheckInfo::CheckInfo(const Position& pos) {
80 Color them = opposite_color(pos.side_to_move());
81 Square ksq = pos.king_square(them);
83 pinned = pos.pinned_pieces();
84 dcCandidates = pos.discovered_check_candidates();
86 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
87 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
88 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
89 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
90 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
91 checkSq[KING] = EmptyBoardBB;
95 /// Position c'tors. Here we always create a copy of the original position
96 /// or the FEN string, we want the new born Position object do not depend
97 /// on any external data so we detach state pointer from the source one.
99 Position::Position(const Position& pos, int th) {
101 memcpy(this, &pos, sizeof(Position));
108 Position::Position(const string& fen, bool isChess960, int th) {
110 from_fen(fen, isChess960);
115 /// Position::from_fen() initializes the position object with the given FEN
116 /// string. This function is not very robust - make sure that input FENs are
117 /// correct (this is assumed to be the responsibility of the GUI).
119 void Position::from_fen(const string& fenStr, bool isChess960) {
121 A FEN string defines a particular position using only the ASCII character set.
123 A FEN string contains six fields. The separator between fields is a space. The fields are:
125 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
126 with rank 1; within each rank, the contents of each square are described from file A through file H.
127 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
128 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
129 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
130 of blank squares), and "/" separate ranks.
132 2) Active color. "w" means white moves next, "b" means black.
134 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
135 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
136 kingside), and/or "q" (Black can castle queenside).
138 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
139 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
140 regardless of whether there is a pawn in position to make an en passant capture.
142 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
143 to determine if a draw can be claimed under the fifty-move rule.
145 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
148 char col, row, token;
151 std::istringstream fen(fenStr);
154 fen >> std::noskipws;
156 // 1. Piece placement
157 while ((fen >> token) && !isspace(token))
160 sq -= Square(16); // Jump back of 2 rows
162 else if (isdigit(token))
163 sq += Square(token - '0'); // Skip the given number of files
165 else if ((p = PieceToChar.find(token)) != string::npos)
167 put_piece(Piece(p), sq);
174 sideToMove = (token == 'w' ? WHITE : BLACK);
177 // 3. Castling availability
178 while ((fen >> token) && !isspace(token))
179 set_castling_rights(token);
181 // 4. En passant square. Ignore if no pawn capture is possible
182 if ( ((fen >> col) && (col >= 'a' && col <= 'h'))
183 && ((fen >> row) && (row == '3' || row == '6')))
185 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
186 Color them = opposite_color(sideToMove);
188 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
189 st->epSquare = SQ_NONE;
192 // 5-6. Halfmove clock and fullmove number
193 fen >> std::skipws >> st->rule50 >> startPosPly;
195 // Convert from fullmove starting from 1 to ply starting from 0,
196 // handle also common incorrect FEN with fullmove = 0.
197 startPosPly = Max(2 * (startPosPly - 1), 0) + int(sideToMove == BLACK);
199 // Various initialisations
200 chess960 = isChess960;
201 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
203 st->key = compute_key();
204 st->pawnKey = compute_pawn_key();
205 st->materialKey = compute_material_key();
206 st->value = compute_value();
207 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
208 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
214 /// Position::set_castle() is an helper function used to set
215 /// correct castling related flags.
217 void Position::set_castle(int f, Square ksq, Square rsq) {
219 st->castleRights |= f;
220 castleRightsMask[ksq] ^= f;
221 castleRightsMask[rsq] ^= f;
222 castleRookSquare[f] = rsq;
226 /// Position::set_castling_rights() sets castling parameters castling avaiability.
227 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
228 /// that uses the letters of the columns on which the rooks began the game instead
229 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
230 /// associated with the castling right, the traditional castling tag will be replaced
231 /// by the file letter of the involved rook as for the Shredder-FEN.
233 void Position::set_castling_rights(char token) {
235 Color c = islower(token) ? BLACK : WHITE;
237 Square sqA = relative_square(c, SQ_A1);
238 Square sqH = relative_square(c, SQ_H1);
239 Square rsq, ksq = king_square(c);
241 token = char(toupper(token));
244 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
246 else if (token == 'Q')
247 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
249 else if (token >= 'A' && token <= 'H')
250 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
254 if (square_file(rsq) < square_file(ksq))
255 set_castle(WHITE_OOO << c, ksq, rsq);
257 set_castle(WHITE_OO << c, ksq, rsq);
261 /// Position::to_fen() returns a FEN representation of the position. In case
262 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
264 const string Position::to_fen() const {
266 std::ostringstream fen;
270 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
274 for (File file = FILE_A; file <= FILE_H; file++)
276 sq = make_square(file, rank);
278 if (!square_is_empty(sq))
285 fen << PieceToChar[piece_on(sq)];
298 fen << (sideToMove == WHITE ? " w " : " b ");
300 if (st->castleRights != CASTLES_NONE)
302 if (can_castle(WHITE_OO))
303 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K');
305 if (can_castle(WHITE_OOO))
306 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q');
308 if (can_castle(BLACK_OO))
309 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k');
311 if (can_castle(BLACK_OOO))
312 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q');
316 fen << (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()))
317 << " " << st->rule50 << " " << 1 + (startPosPly - int(sideToMove == BLACK)) / 2;
323 /// Position::print() prints an ASCII representation of the position to
324 /// the standard output. If a move is given then also the san is printed.
326 void Position::print(Move move) const {
328 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
332 Position p(*this, thread());
333 string dd = (sideToMove == BLACK ? ".." : "");
334 cout << "\nMove is: " << dd << move_to_san(p, move);
337 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
339 cout << dottedLine << '|';
340 for (File file = FILE_A; file <= FILE_H; file++)
342 Square sq = make_square(file, rank);
343 Piece piece = piece_on(sq);
345 if (piece == PIECE_NONE && square_color(sq) == DARK)
346 piece = PIECE_NONE_DARK_SQ;
348 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
349 cout << c << PieceToChar[piece] << c << '|';
352 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
356 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
357 /// king) pieces for the given color. Or, when template parameter FindPinned is
358 /// false, the function return the pieces of the given color candidate for a
359 /// discovery check against the enemy king.
361 template<bool FindPinned>
362 Bitboard Position::hidden_checkers() const {
364 // Pinned pieces protect our king, dicovery checks attack the enemy king
365 Bitboard b, result = EmptyBoardBB;
366 Bitboard pinners = pieces(FindPinned ? opposite_color(sideToMove) : sideToMove);
367 Square ksq = king_square(FindPinned ? sideToMove : opposite_color(sideToMove));
369 // Pinners are sliders, that give check when candidate pinned is removed
370 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq])
371 | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
375 b = squares_between(ksq, pop_1st_bit(&pinners)) & occupied_squares();
377 // Only one bit set and is an our piece?
378 if (b && !(b & (b - 1)) && (b & pieces(sideToMove)))
385 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
386 /// king) pieces for the side to move.
388 Bitboard Position::pinned_pieces() const {
390 return hidden_checkers<true>();
394 /// Position:discovered_check_candidates() returns a bitboard containing all
395 /// pieces for the side to move which are candidates for giving a discovered
398 Bitboard Position::discovered_check_candidates() const {
400 return hidden_checkers<false>();
403 /// Position::attackers_to() computes a bitboard containing all pieces which
404 /// attacks a given square.
406 Bitboard Position::attackers_to(Square s) const {
408 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
409 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
410 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
411 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
412 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
413 | (attacks_from<KING>(s) & pieces(KING));
416 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
418 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
419 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
420 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
421 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
422 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
423 | (attacks_from<KING>(s) & pieces(KING));
426 /// Position::attacks_from() computes a bitboard of all attacks
427 /// of a given piece put in a given square.
429 Bitboard Position::attacks_from(Piece p, Square s) const {
431 assert(square_is_ok(s));
435 case WB: case BB: return attacks_from<BISHOP>(s);
436 case WR: case BR: return attacks_from<ROOK>(s);
437 case WQ: case BQ: return attacks_from<QUEEN>(s);
438 default: return StepAttacksBB[p][s];
442 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
444 assert(square_is_ok(s));
448 case WB: case BB: return bishop_attacks_bb(s, occ);
449 case WR: case BR: return rook_attacks_bb(s, occ);
450 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
451 default: return StepAttacksBB[p][s];
456 /// Position::move_attacks_square() tests whether a move from the current
457 /// position attacks a given square.
459 bool Position::move_attacks_square(Move m, Square s) const {
461 assert(move_is_ok(m));
462 assert(square_is_ok(s));
465 Square f = move_from(m), t = move_to(m);
467 assert(!square_is_empty(f));
469 if (bit_is_set(attacks_from(piece_on(f), t), s))
472 // Move the piece and scan for X-ray attacks behind it
473 occ = occupied_squares();
474 do_move_bb(&occ, make_move_bb(f, t));
475 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
476 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
477 & pieces(piece_color(piece_on(f)));
479 // If we have attacks we need to verify that are caused by our move
480 // and are not already existent ones.
481 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
485 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
487 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
489 assert(move_is_ok(m));
490 assert(pinned == pinned_pieces());
492 Color us = side_to_move();
493 Square from = move_from(m);
495 assert(piece_color(piece_on(from)) == us);
496 assert(piece_on(king_square(us)) == make_piece(us, KING));
498 // En passant captures are a tricky special case. Because they are rather
499 // uncommon, we do it simply by testing whether the king is attacked after
503 Color them = opposite_color(us);
504 Square to = move_to(m);
505 Square capsq = to + pawn_push(them);
506 Square ksq = king_square(us);
507 Bitboard b = occupied_squares();
509 assert(to == ep_square());
510 assert(piece_on(from) == make_piece(us, PAWN));
511 assert(piece_on(capsq) == make_piece(them, PAWN));
512 assert(piece_on(to) == PIECE_NONE);
515 clear_bit(&b, capsq);
518 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
519 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
522 // If the moving piece is a king, check whether the destination
523 // square is attacked by the opponent. Castling moves are checked
524 // for legality during move generation.
525 if (piece_type(piece_on(from)) == KING)
526 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces(opposite_color(us)));
528 // A non-king move is legal if and only if it is not pinned or it
529 // is moving along the ray towards or away from the king.
531 || !bit_is_set(pinned, from)
532 || squares_aligned(from, move_to(m), king_square(us));
536 /// Position::move_is_legal() takes a move and tests whether the move
537 /// is legal. This version is not very fast and should be used only
538 /// in non time-critical paths.
540 bool Position::move_is_legal(const Move m) const {
542 for (MoveList<MV_LEGAL> ml(*this); !ml.end(); ++ml)
550 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
551 /// of pinned pieces as input, and tests whether the move is pseudo legal.
553 bool Position::move_is_pl(const Move m) const {
555 Color us = sideToMove;
556 Color them = opposite_color(sideToMove);
557 Square from = move_from(m);
558 Square to = move_to(m);
559 Piece pc = piece_on(from);
561 // Use a slower but simpler function for uncommon cases
562 if (move_is_special(m))
563 return move_is_legal(m);
565 // Is not a promotion, so promotion piece must be empty
566 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
569 // If the from square is not occupied by a piece belonging to the side to
570 // move, the move is obviously not legal.
571 if (pc == PIECE_NONE || piece_color(pc) != us)
574 // The destination square cannot be occupied by a friendly piece
575 if (piece_color(piece_on(to)) == us)
578 // Handle the special case of a pawn move
579 if (piece_type(pc) == PAWN)
581 // Move direction must be compatible with pawn color
582 int direction = to - from;
583 if ((us == WHITE) != (direction > 0))
586 // We have already handled promotion moves, so destination
587 // cannot be on the 8/1th rank.
588 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
591 // Proceed according to the square delta between the origin and
592 // destination squares.
599 // Capture. The destination square must be occupied by an enemy
600 // piece (en passant captures was handled earlier).
601 if (piece_color(piece_on(to)) != them)
604 // From and to files must be one file apart, avoids a7h5
605 if (abs(square_file(from) - square_file(to)) != 1)
611 // Pawn push. The destination square must be empty.
612 if (!square_is_empty(to))
617 // Double white pawn push. The destination square must be on the fourth
618 // rank, and both the destination square and the square between the
619 // source and destination squares must be empty.
620 if ( square_rank(to) != RANK_4
621 || !square_is_empty(to)
622 || !square_is_empty(from + DELTA_N))
627 // Double black pawn push. The destination square must be on the fifth
628 // rank, and both the destination square and the square between the
629 // source and destination squares must be empty.
630 if ( square_rank(to) != RANK_5
631 || !square_is_empty(to)
632 || !square_is_empty(from + DELTA_S))
640 else if (!bit_is_set(attacks_from(pc, from), to))
645 // In case of king moves under check we have to remove king so to catch
646 // as invalid moves like b1a1 when opposite queen is on c1.
647 if (piece_type(piece_on(from)) == KING)
649 Bitboard b = occupied_squares();
651 if (attackers_to(move_to(m), b) & pieces(opposite_color(us)))
656 Bitboard target = checkers();
657 Square checksq = pop_1st_bit(&target);
659 if (target) // double check ? In this case a king move is required
662 // Our move must be a blocking evasion or a capture of the checking piece
663 target = squares_between(checksq, king_square(us)) | checkers();
664 if (!bit_is_set(target, move_to(m)))
673 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
675 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
677 assert(move_is_ok(m));
678 assert(ci.dcCandidates == discovered_check_candidates());
679 assert(piece_color(piece_on(move_from(m))) == side_to_move());
681 Square from = move_from(m);
682 Square to = move_to(m);
683 PieceType pt = piece_type(piece_on(from));
686 if (bit_is_set(ci.checkSq[pt], to))
690 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
692 // For pawn and king moves we need to verify also direction
693 if ( (pt != PAWN && pt != KING)
694 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
698 // Can we skip the ugly special cases ?
699 if (!move_is_special(m))
702 Color us = side_to_move();
703 Bitboard b = occupied_squares();
704 Square ksq = king_square(opposite_color(us));
706 // Promotion with check ?
707 if (move_is_promotion(m))
711 switch (promotion_piece_type(m))
714 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
716 return bit_is_set(bishop_attacks_bb(to, b), ksq);
718 return bit_is_set(rook_attacks_bb(to, b), ksq);
720 return bit_is_set(queen_attacks_bb(to, b), ksq);
726 // En passant capture with check ? We have already handled the case
727 // of direct checks and ordinary discovered check, the only case we
728 // need to handle is the unusual case of a discovered check through
729 // the captured pawn.
732 Square capsq = make_square(square_file(to), square_rank(from));
734 clear_bit(&b, capsq);
736 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
737 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
740 // Castling with check ?
741 if (move_is_castle(m))
743 Square kfrom, kto, rfrom, rto;
749 kto = relative_square(us, SQ_G1);
750 rto = relative_square(us, SQ_F1);
752 kto = relative_square(us, SQ_C1);
753 rto = relative_square(us, SQ_D1);
755 clear_bit(&b, kfrom);
756 clear_bit(&b, rfrom);
759 return bit_is_set(rook_attacks_bb(rto, b), ksq);
766 /// Position::do_move() makes a move, and saves all information necessary
767 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
768 /// moves should be filtered out before this function is called.
770 void Position::do_move(Move m, StateInfo& newSt) {
773 do_move(m, newSt, ci, move_gives_check(m, ci));
776 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
778 assert(move_is_ok(m));
779 assert(&newSt != st);
784 // Copy some fields of old state to our new StateInfo object except the
785 // ones which are recalculated from scratch anyway, then switch our state
786 // pointer to point to the new, ready to be updated, state.
787 struct ReducedStateInfo {
788 Key pawnKey, materialKey;
790 int castleRights, rule50, pliesFromNull;
795 memcpy(&newSt, st, sizeof(ReducedStateInfo));
800 // Update side to move
801 key ^= zobSideToMove;
803 // Increment the 50 moves rule draw counter. Resetting it to zero in the
804 // case of non-reversible moves is taken care of later.
808 if (move_is_castle(m))
815 Color us = side_to_move();
816 Color them = opposite_color(us);
817 Square from = move_from(m);
818 Square to = move_to(m);
819 bool ep = move_is_ep(m);
820 bool pm = move_is_promotion(m);
822 Piece piece = piece_on(from);
823 PieceType pt = piece_type(piece);
824 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
826 assert(piece_color(piece_on(from)) == us);
827 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
828 assert(!(ep || pm) || piece == make_piece(us, PAWN));
829 assert(!pm || relative_rank(us, to) == RANK_8);
832 do_capture_move(key, capture, them, to, ep);
835 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
837 // Reset en passant square
838 if (st->epSquare != SQ_NONE)
840 key ^= zobEp[st->epSquare];
841 st->epSquare = SQ_NONE;
844 // Update castle rights if needed
845 if ( st->castleRights != CASTLES_NONE
846 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
848 key ^= zobCastle[st->castleRights];
849 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
850 key ^= zobCastle[st->castleRights];
853 // Prefetch TT access as soon as we know key is updated
854 prefetch((char*)TT.first_entry(key));
857 Bitboard move_bb = make_move_bb(from, to);
858 do_move_bb(&byColorBB[us], move_bb);
859 do_move_bb(&byTypeBB[pt], move_bb);
860 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
862 board[to] = board[from];
863 board[from] = PIECE_NONE;
865 // Update piece lists, note that index[from] is not updated and
866 // becomes stale. This works as long as index[] is accessed just
867 // by known occupied squares.
868 index[to] = index[from];
869 pieceList[us][pt][index[to]] = to;
871 // If the moving piece was a pawn do some special extra work
874 // Reset rule 50 draw counter
877 // Update pawn hash key and prefetch in L1/L2 cache
878 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
880 // Set en passant square, only if moved pawn can be captured
881 if ((to ^ from) == 16)
883 if (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(PAWN, them))
885 st->epSquare = Square((int(from) + int(to)) / 2);
886 key ^= zobEp[st->epSquare];
890 if (pm) // promotion ?
892 PieceType promotion = promotion_piece_type(m);
894 assert(promotion >= KNIGHT && promotion <= QUEEN);
896 // Insert promoted piece instead of pawn
897 clear_bit(&byTypeBB[PAWN], to);
898 set_bit(&byTypeBB[promotion], to);
899 board[to] = make_piece(us, promotion);
901 // Update piece counts
902 pieceCount[us][promotion]++;
903 pieceCount[us][PAWN]--;
905 // Update material key
906 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
907 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
909 // Update piece lists, move the last pawn at index[to] position
910 // and shrink the list. Add a new promotion piece to the list.
911 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
912 index[lastPawnSquare] = index[to];
913 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
914 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
915 index[to] = pieceCount[us][promotion] - 1;
916 pieceList[us][promotion][index[to]] = to;
918 // Partially revert hash keys update
919 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
920 st->pawnKey ^= zobrist[us][PAWN][to];
922 // Partially revert and update incremental scores
923 st->value -= pst(make_piece(us, PAWN), to);
924 st->value += pst(make_piece(us, promotion), to);
927 st->npMaterial[us] += PieceValueMidgame[promotion];
931 // Prefetch pawn and material hash tables
932 Threads[threadID].pawnTable.prefetch(st->pawnKey);
933 Threads[threadID].materialTable.prefetch(st->materialKey);
935 // Update incremental scores
936 st->value += pst_delta(piece, from, to);
939 st->capturedType = capture;
941 // Update the key with the final value
944 // Update checkers bitboard, piece must be already moved
945 st->checkersBB = EmptyBoardBB;
950 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
954 if (bit_is_set(ci.checkSq[pt], to))
955 st->checkersBB = SetMaskBB[to];
958 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
961 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
964 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
970 sideToMove = opposite_color(sideToMove);
971 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
977 /// Position::do_capture_move() is a private method used to update captured
978 /// piece info. It is called from the main Position::do_move function.
980 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
982 assert(capture != KING);
986 // If the captured piece was a pawn, update pawn hash key,
987 // otherwise update non-pawn material.
990 if (ep) // en passant ?
992 capsq = to + pawn_push(them);
994 assert(to == st->epSquare);
995 assert(relative_rank(opposite_color(them), to) == RANK_6);
996 assert(piece_on(to) == PIECE_NONE);
997 assert(piece_on(capsq) == make_piece(them, PAWN));
999 board[capsq] = PIECE_NONE;
1001 st->pawnKey ^= zobrist[them][PAWN][capsq];
1004 st->npMaterial[them] -= PieceValueMidgame[capture];
1006 // Remove captured piece
1007 clear_bit(&byColorBB[them], capsq);
1008 clear_bit(&byTypeBB[capture], capsq);
1009 clear_bit(&byTypeBB[0], capsq);
1012 key ^= zobrist[them][capture][capsq];
1014 // Update incremental scores
1015 st->value -= pst(make_piece(them, capture), capsq);
1017 // Update piece count
1018 pieceCount[them][capture]--;
1020 // Update material hash key
1021 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1023 // Update piece list, move the last piece at index[capsq] position
1025 // WARNING: This is a not perfectly revresible operation. When we
1026 // will reinsert the captured piece in undo_move() we will put it
1027 // at the end of the list and not in its original place, it means
1028 // index[] and pieceList[] are not guaranteed to be invariant to a
1029 // do_move() + undo_move() sequence.
1030 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1031 index[lastPieceSquare] = index[capsq];
1032 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1033 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1035 // Reset rule 50 counter
1040 /// Position::do_castle_move() is a private method used to make a castling
1041 /// move. It is called from the main Position::do_move function. Note that
1042 /// castling moves are encoded as "king captures friendly rook" moves, for
1043 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1045 void Position::do_castle_move(Move m) {
1047 assert(move_is_ok(m));
1048 assert(move_is_castle(m));
1050 Color us = side_to_move();
1051 Color them = opposite_color(us);
1053 // Find source squares for king and rook
1054 Square kfrom = move_from(m);
1055 Square rfrom = move_to(m);
1058 assert(piece_on(kfrom) == make_piece(us, KING));
1059 assert(piece_on(rfrom) == make_piece(us, ROOK));
1061 // Find destination squares for king and rook
1062 if (rfrom > kfrom) // O-O
1064 kto = relative_square(us, SQ_G1);
1065 rto = relative_square(us, SQ_F1);
1069 kto = relative_square(us, SQ_C1);
1070 rto = relative_square(us, SQ_D1);
1073 // Remove pieces from source squares
1074 clear_bit(&byColorBB[us], kfrom);
1075 clear_bit(&byTypeBB[KING], kfrom);
1076 clear_bit(&byTypeBB[0], kfrom);
1077 clear_bit(&byColorBB[us], rfrom);
1078 clear_bit(&byTypeBB[ROOK], rfrom);
1079 clear_bit(&byTypeBB[0], rfrom);
1081 // Put pieces on destination squares
1082 set_bit(&byColorBB[us], kto);
1083 set_bit(&byTypeBB[KING], kto);
1084 set_bit(&byTypeBB[0], kto);
1085 set_bit(&byColorBB[us], rto);
1086 set_bit(&byTypeBB[ROOK], rto);
1087 set_bit(&byTypeBB[0], rto);
1090 Piece king = make_piece(us, KING);
1091 Piece rook = make_piece(us, ROOK);
1092 board[kfrom] = board[rfrom] = PIECE_NONE;
1096 // Update piece lists
1097 pieceList[us][KING][index[kfrom]] = kto;
1098 pieceList[us][ROOK][index[rfrom]] = rto;
1099 int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
1100 index[kto] = index[kfrom];
1103 // Reset capture field
1104 st->capturedType = PIECE_TYPE_NONE;
1106 // Update incremental scores
1107 st->value += pst_delta(king, kfrom, kto);
1108 st->value += pst_delta(rook, rfrom, rto);
1111 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1112 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1114 // Clear en passant square
1115 if (st->epSquare != SQ_NONE)
1117 st->key ^= zobEp[st->epSquare];
1118 st->epSquare = SQ_NONE;
1121 // Update castling rights
1122 st->key ^= zobCastle[st->castleRights];
1123 st->castleRights &= castleRightsMask[kfrom];
1124 st->key ^= zobCastle[st->castleRights];
1126 // Reset rule 50 counter
1129 // Update checkers BB
1130 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1133 sideToMove = opposite_color(sideToMove);
1134 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1140 /// Position::undo_move() unmakes a move. When it returns, the position should
1141 /// be restored to exactly the same state as before the move was made.
1143 void Position::undo_move(Move m) {
1145 assert(move_is_ok(m));
1147 sideToMove = opposite_color(sideToMove);
1149 if (move_is_castle(m))
1151 undo_castle_move(m);
1155 Color us = side_to_move();
1156 Color them = opposite_color(us);
1157 Square from = move_from(m);
1158 Square to = move_to(m);
1159 bool ep = move_is_ep(m);
1160 bool pm = move_is_promotion(m);
1162 PieceType pt = piece_type(piece_on(to));
1164 assert(square_is_empty(from));
1165 assert(piece_color(piece_on(to)) == us);
1166 assert(!pm || relative_rank(us, to) == RANK_8);
1167 assert(!ep || to == st->previous->epSquare);
1168 assert(!ep || relative_rank(us, to) == RANK_6);
1169 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1171 if (pm) // promotion ?
1173 PieceType promotion = promotion_piece_type(m);
1176 assert(promotion >= KNIGHT && promotion <= QUEEN);
1177 assert(piece_on(to) == make_piece(us, promotion));
1179 // Replace promoted piece with a pawn
1180 clear_bit(&byTypeBB[promotion], to);
1181 set_bit(&byTypeBB[PAWN], to);
1183 // Update piece counts
1184 pieceCount[us][promotion]--;
1185 pieceCount[us][PAWN]++;
1187 // Update piece list replacing promotion piece with a pawn
1188 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1189 index[lastPromotionSquare] = index[to];
1190 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1191 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1192 index[to] = pieceCount[us][PAWN] - 1;
1193 pieceList[us][PAWN][index[to]] = to;
1196 // Put the piece back at the source square
1197 Bitboard move_bb = make_move_bb(to, from);
1198 do_move_bb(&byColorBB[us], move_bb);
1199 do_move_bb(&byTypeBB[pt], move_bb);
1200 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
1202 board[from] = make_piece(us, pt);
1203 board[to] = PIECE_NONE;
1205 // Update piece list
1206 index[from] = index[to];
1207 pieceList[us][pt][index[from]] = from;
1209 if (st->capturedType)
1214 capsq = to - pawn_push(us);
1216 assert(st->capturedType != KING);
1217 assert(!ep || square_is_empty(capsq));
1219 // Restore the captured piece
1220 set_bit(&byColorBB[them], capsq);
1221 set_bit(&byTypeBB[st->capturedType], capsq);
1222 set_bit(&byTypeBB[0], capsq);
1224 board[capsq] = make_piece(them, st->capturedType);
1226 // Update piece count
1227 pieceCount[them][st->capturedType]++;
1229 // Update piece list, add a new captured piece in capsq square
1230 index[capsq] = pieceCount[them][st->capturedType] - 1;
1231 pieceList[them][st->capturedType][index[capsq]] = capsq;
1234 // Finally point our state pointer back to the previous state
1241 /// Position::undo_castle_move() is a private method used to unmake a castling
1242 /// move. It is called from the main Position::undo_move function. Note that
1243 /// castling moves are encoded as "king captures friendly rook" moves, for
1244 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1246 void Position::undo_castle_move(Move m) {
1248 assert(move_is_ok(m));
1249 assert(move_is_castle(m));
1251 // When we have arrived here, some work has already been done by
1252 // Position::undo_move. In particular, the side to move has been switched,
1253 // so the code below is correct.
1254 Color us = side_to_move();
1256 // Find source squares for king and rook
1257 Square kfrom = move_from(m);
1258 Square rfrom = move_to(m);
1261 // Find destination squares for king and rook
1262 if (rfrom > kfrom) // O-O
1264 kto = relative_square(us, SQ_G1);
1265 rto = relative_square(us, SQ_F1);
1269 kto = relative_square(us, SQ_C1);
1270 rto = relative_square(us, SQ_D1);
1273 assert(piece_on(kto) == make_piece(us, KING));
1274 assert(piece_on(rto) == make_piece(us, ROOK));
1276 // Remove pieces from destination squares
1277 clear_bit(&byColorBB[us], kto);
1278 clear_bit(&byTypeBB[KING], kto);
1279 clear_bit(&byTypeBB[0], kto);
1280 clear_bit(&byColorBB[us], rto);
1281 clear_bit(&byTypeBB[ROOK], rto);
1282 clear_bit(&byTypeBB[0], rto);
1284 // Put pieces on source squares
1285 set_bit(&byColorBB[us], kfrom);
1286 set_bit(&byTypeBB[KING], kfrom);
1287 set_bit(&byTypeBB[0], kfrom);
1288 set_bit(&byColorBB[us], rfrom);
1289 set_bit(&byTypeBB[ROOK], rfrom);
1290 set_bit(&byTypeBB[0], rfrom);
1293 Piece king = make_piece(us, KING);
1294 Piece rook = make_piece(us, ROOK);
1295 board[kto] = board[rto] = PIECE_NONE;
1296 board[kfrom] = king;
1297 board[rfrom] = rook;
1299 // Update piece lists
1300 pieceList[us][KING][index[kto]] = kfrom;
1301 pieceList[us][ROOK][index[rto]] = rfrom;
1302 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1303 index[kfrom] = index[kto];
1306 // Finally point our state pointer back to the previous state
1313 /// Position::do_null_move makes() a "null move": It switches the side to move
1314 /// and updates the hash key without executing any move on the board.
1316 void Position::do_null_move(StateInfo& backupSt) {
1318 assert(!in_check());
1320 // Back up the information necessary to undo the null move to the supplied
1321 // StateInfo object.
1322 // Note that differently from normal case here backupSt is actually used as
1323 // a backup storage not as a new state to be used.
1324 backupSt.key = st->key;
1325 backupSt.epSquare = st->epSquare;
1326 backupSt.value = st->value;
1327 backupSt.previous = st->previous;
1328 backupSt.pliesFromNull = st->pliesFromNull;
1329 st->previous = &backupSt;
1331 // Update the necessary information
1332 if (st->epSquare != SQ_NONE)
1333 st->key ^= zobEp[st->epSquare];
1335 st->key ^= zobSideToMove;
1336 prefetch((char*)TT.first_entry(st->key));
1338 sideToMove = opposite_color(sideToMove);
1339 st->epSquare = SQ_NONE;
1341 st->pliesFromNull = 0;
1342 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1348 /// Position::undo_null_move() unmakes a "null move".
1350 void Position::undo_null_move() {
1352 assert(!in_check());
1354 // Restore information from the our backup StateInfo object
1355 StateInfo* backupSt = st->previous;
1356 st->key = backupSt->key;
1357 st->epSquare = backupSt->epSquare;
1358 st->value = backupSt->value;
1359 st->previous = backupSt->previous;
1360 st->pliesFromNull = backupSt->pliesFromNull;
1362 // Update the necessary information
1363 sideToMove = opposite_color(sideToMove);
1370 /// Position::see() is a static exchange evaluator: It tries to estimate the
1371 /// material gain or loss resulting from a move. There are three versions of
1372 /// this function: One which takes a destination square as input, one takes a
1373 /// move, and one which takes a 'from' and a 'to' square. The function does
1374 /// not yet understand promotions captures.
1376 int Position::see_sign(Move m) const {
1378 assert(move_is_ok(m));
1380 Square from = move_from(m);
1381 Square to = move_to(m);
1383 // Early return if SEE cannot be negative because captured piece value
1384 // is not less then capturing one. Note that king moves always return
1385 // here because king midgame value is set to 0.
1386 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1392 int Position::see(Move m) const {
1395 Bitboard occupied, attackers, stmAttackers, b;
1396 int swapList[32], slIndex = 1;
1397 PieceType capturedType, pt;
1400 assert(move_is_ok(m));
1402 // As castle moves are implemented as capturing the rook, they have
1403 // SEE == RookValueMidgame most of the times (unless the rook is under
1405 if (move_is_castle(m))
1408 from = move_from(m);
1410 capturedType = piece_type(piece_on(to));
1411 occupied = occupied_squares();
1413 // Handle en passant moves
1414 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1416 Square capQq = to - pawn_push(side_to_move());
1418 assert(capturedType == PIECE_TYPE_NONE);
1419 assert(piece_type(piece_on(capQq)) == PAWN);
1421 // Remove the captured pawn
1422 clear_bit(&occupied, capQq);
1423 capturedType = PAWN;
1426 // Find all attackers to the destination square, with the moving piece
1427 // removed, but possibly an X-ray attacker added behind it.
1428 clear_bit(&occupied, from);
1429 attackers = attackers_to(to, occupied);
1431 // If the opponent has no attackers we are finished
1432 stm = opposite_color(piece_color(piece_on(from)));
1433 stmAttackers = attackers & pieces(stm);
1435 return PieceValueMidgame[capturedType];
1437 // The destination square is defended, which makes things rather more
1438 // difficult to compute. We proceed by building up a "swap list" containing
1439 // the material gain or loss at each stop in a sequence of captures to the
1440 // destination square, where the sides alternately capture, and always
1441 // capture with the least valuable piece. After each capture, we look for
1442 // new X-ray attacks from behind the capturing piece.
1443 swapList[0] = PieceValueMidgame[capturedType];
1444 capturedType = piece_type(piece_on(from));
1447 // Locate the least valuable attacker for the side to move. The loop
1448 // below looks like it is potentially infinite, but it isn't. We know
1449 // that the side to move still has at least one attacker left.
1450 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1453 // Remove the attacker we just found from the 'occupied' bitboard,
1454 // and scan for new X-ray attacks behind the attacker.
1455 b = stmAttackers & pieces(pt);
1456 occupied ^= (b & (~b + 1));
1457 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1458 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1460 attackers &= occupied; // Cut out pieces we've already done
1462 // Add the new entry to the swap list
1463 assert(slIndex < 32);
1464 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1467 // Remember the value of the capturing piece, and change the side to
1468 // move before beginning the next iteration.
1470 stm = opposite_color(stm);
1471 stmAttackers = attackers & pieces(stm);
1473 // Stop before processing a king capture
1474 if (capturedType == KING && stmAttackers)
1476 assert(slIndex < 32);
1477 swapList[slIndex++] = QueenValueMidgame*10;
1480 } while (stmAttackers);
1482 // Having built the swap list, we negamax through it to find the best
1483 // achievable score from the point of view of the side to move.
1485 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1491 /// Position::clear() erases the position object to a pristine state, with an
1492 /// empty board, white to move, and no castling rights.
1494 void Position::clear() {
1497 memset(st, 0, sizeof(StateInfo));
1498 st->epSquare = SQ_NONE;
1500 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1501 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1502 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1503 memset(index, 0, sizeof(int) * 64);
1505 for (int i = 0; i < 8; i++)
1506 for (int j = 0; j < 16; j++)
1507 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1509 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1511 board[sq] = PIECE_NONE;
1512 castleRightsMask[sq] = ALL_CASTLES;
1519 /// Position::put_piece() puts a piece on the given square of the board,
1520 /// updating the board array, pieces list, bitboards, and piece counts.
1522 void Position::put_piece(Piece p, Square s) {
1524 Color c = piece_color(p);
1525 PieceType pt = piece_type(p);
1528 index[s] = pieceCount[c][pt]++;
1529 pieceList[c][pt][index[s]] = s;
1531 set_bit(&byTypeBB[pt], s);
1532 set_bit(&byColorBB[c], s);
1533 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1537 /// Position::compute_key() computes the hash key of the position. The hash
1538 /// key is usually updated incrementally as moves are made and unmade, the
1539 /// compute_key() function is only used when a new position is set up, and
1540 /// to verify the correctness of the hash key when running in debug mode.
1542 Key Position::compute_key() const {
1544 Key result = zobCastle[st->castleRights];
1546 for (Square s = SQ_A1; s <= SQ_H8; s++)
1547 if (!square_is_empty(s))
1548 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1550 if (ep_square() != SQ_NONE)
1551 result ^= zobEp[ep_square()];
1553 if (side_to_move() == BLACK)
1554 result ^= zobSideToMove;
1560 /// Position::compute_pawn_key() computes the hash key of the position. The
1561 /// hash key is usually updated incrementally as moves are made and unmade,
1562 /// the compute_pawn_key() function is only used when a new position is set
1563 /// up, and to verify the correctness of the pawn hash key when running in
1566 Key Position::compute_pawn_key() const {
1571 for (Color c = WHITE; c <= BLACK; c++)
1573 b = pieces(PAWN, c);
1575 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1581 /// Position::compute_material_key() computes the hash key of the position.
1582 /// The hash key is usually updated incrementally as moves are made and unmade,
1583 /// the compute_material_key() function is only used when a new position is set
1584 /// up, and to verify the correctness of the material hash key when running in
1587 Key Position::compute_material_key() const {
1591 for (Color c = WHITE; c <= BLACK; c++)
1592 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1593 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1594 result ^= zobrist[c][pt][i];
1600 /// Position::compute_value() compute the incremental scores for the middle
1601 /// game and the endgame. These functions are used to initialize the incremental
1602 /// scores when a new position is set up, and to verify that the scores are correctly
1603 /// updated by do_move and undo_move when the program is running in debug mode.
1604 Score Position::compute_value() const {
1607 Score result = SCORE_ZERO;
1609 for (Color c = WHITE; c <= BLACK; c++)
1610 for (PieceType pt = PAWN; pt <= KING; pt++)
1614 result += pst(make_piece(c, pt), pop_1st_bit(&b));
1617 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1622 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1623 /// game material value for the given side. Material values are updated
1624 /// incrementally during the search, this function is only used while
1625 /// initializing a new Position object.
1627 Value Position::compute_non_pawn_material(Color c) const {
1629 Value result = VALUE_ZERO;
1631 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1632 result += piece_count(c, pt) * PieceValueMidgame[pt];
1638 /// Position::is_draw() tests whether the position is drawn by material,
1639 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1640 /// must be done by the search.
1641 template<bool SkipRepetition>
1642 bool Position::is_draw() const {
1644 // Draw by material?
1646 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1649 // Draw by the 50 moves rule?
1650 if (st->rule50 > 99 && !is_mate())
1653 // Draw by repetition?
1654 if (!SkipRepetition)
1656 int i = 4, e = Min(st->rule50, st->pliesFromNull);
1660 StateInfo* stp = st->previous->previous;
1663 stp = stp->previous->previous;
1665 if (stp->key == st->key)
1677 // Explicit template instantiations
1678 template bool Position::is_draw<false>() const;
1679 template bool Position::is_draw<true>() const;
1682 /// Position::is_mate() returns true or false depending on whether the
1683 /// side to move is checkmated.
1685 bool Position::is_mate() const {
1687 return in_check() && !MoveList<MV_LEGAL>(*this).size();
1691 /// Position::init() is a static member function which initializes at
1692 /// startup the various arrays used to compute hash keys and the piece
1693 /// square tables. The latter is a two-step operation: First, the white
1694 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1695 /// Second, the black halves of the tables are initialized by mirroring
1696 /// and changing the sign of the corresponding white scores.
1698 void Position::init() {
1702 for (Color c = WHITE; c <= BLACK; c++)
1703 for (PieceType pt = PAWN; pt <= KING; pt++)
1704 for (Square s = SQ_A1; s <= SQ_H8; s++)
1705 zobrist[c][pt][s] = rk.rand<Key>();
1707 for (Square s = SQ_A1; s <= SQ_H8; s++)
1708 zobEp[s] = rk.rand<Key>();
1710 for (int i = 0; i < 16; i++)
1711 zobCastle[i] = rk.rand<Key>();
1713 zobSideToMove = rk.rand<Key>();
1714 zobExclusion = rk.rand<Key>();
1716 for (Square s = SQ_A1; s <= SQ_H8; s++)
1717 for (Piece p = WP; p <= WK; p++)
1718 pieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1720 for (Square s = SQ_A1; s <= SQ_H8; s++)
1721 for (Piece p = BP; p <= BK; p++)
1722 pieceSquareTable[p][s] = -pieceSquareTable[p-8][flip_square(s)];
1726 /// Position::flip() flips position with the white and black sides reversed. This
1727 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1729 void Position::flip() {
1731 // Make a copy of current position before to start changing
1732 const Position pos(*this, threadID);
1735 threadID = pos.thread();
1738 for (Square s = SQ_A1; s <= SQ_H8; s++)
1739 if (!pos.square_is_empty(s))
1740 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1743 sideToMove = opposite_color(pos.side_to_move());
1746 if (pos.can_castle(WHITE_OO))
1747 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1748 if (pos.can_castle(WHITE_OOO))
1749 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1750 if (pos.can_castle(BLACK_OO))
1751 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1752 if (pos.can_castle(BLACK_OOO))
1753 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1755 // En passant square
1756 if (pos.st->epSquare != SQ_NONE)
1757 st->epSquare = flip_square(pos.st->epSquare);
1760 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
1763 st->key = compute_key();
1764 st->pawnKey = compute_pawn_key();
1765 st->materialKey = compute_material_key();
1767 // Incremental scores
1768 st->value = compute_value();
1771 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1772 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1778 /// Position::is_ok() performs some consitency checks for the position object.
1779 /// This is meant to be helpful when debugging.
1781 bool Position::is_ok(int* failedStep) const {
1783 // What features of the position should be verified?
1784 const bool debugAll = false;
1786 const bool debugBitboards = debugAll || false;
1787 const bool debugKingCount = debugAll || false;
1788 const bool debugKingCapture = debugAll || false;
1789 const bool debugCheckerCount = debugAll || false;
1790 const bool debugKey = debugAll || false;
1791 const bool debugMaterialKey = debugAll || false;
1792 const bool debugPawnKey = debugAll || false;
1793 const bool debugIncrementalEval = debugAll || false;
1794 const bool debugNonPawnMaterial = debugAll || false;
1795 const bool debugPieceCounts = debugAll || false;
1796 const bool debugPieceList = debugAll || false;
1797 const bool debugCastleSquares = debugAll || false;
1799 if (failedStep) *failedStep = 1;
1802 if (side_to_move() != WHITE && side_to_move() != BLACK)
1805 // Are the king squares in the position correct?
1806 if (failedStep) (*failedStep)++;
1807 if (piece_on(king_square(WHITE)) != WK)
1810 if (failedStep) (*failedStep)++;
1811 if (piece_on(king_square(BLACK)) != BK)
1814 // Do both sides have exactly one king?
1815 if (failedStep) (*failedStep)++;
1818 int kingCount[2] = {0, 0};
1819 for (Square s = SQ_A1; s <= SQ_H8; s++)
1820 if (piece_type(piece_on(s)) == KING)
1821 kingCount[piece_color(piece_on(s))]++;
1823 if (kingCount[0] != 1 || kingCount[1] != 1)
1827 // Can the side to move capture the opponent's king?
1828 if (failedStep) (*failedStep)++;
1829 if (debugKingCapture)
1831 Color us = side_to_move();
1832 Color them = opposite_color(us);
1833 Square ksq = king_square(them);
1834 if (attackers_to(ksq) & pieces(us))
1838 // Is there more than 2 checkers?
1839 if (failedStep) (*failedStep)++;
1840 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1844 if (failedStep) (*failedStep)++;
1847 // The intersection of the white and black pieces must be empty
1848 if ((pieces(WHITE) & pieces(BLACK)) != EmptyBoardBB)
1851 // The union of the white and black pieces must be equal to all
1853 if ((pieces(WHITE) | pieces(BLACK)) != occupied_squares())
1856 // Separate piece type bitboards must have empty intersections
1857 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1858 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1859 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1863 // En passant square OK?
1864 if (failedStep) (*failedStep)++;
1865 if (ep_square() != SQ_NONE)
1867 // The en passant square must be on rank 6, from the point of view of the
1869 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1874 if (failedStep) (*failedStep)++;
1875 if (debugKey && st->key != compute_key())
1878 // Pawn hash key OK?
1879 if (failedStep) (*failedStep)++;
1880 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1883 // Material hash key OK?
1884 if (failedStep) (*failedStep)++;
1885 if (debugMaterialKey && st->materialKey != compute_material_key())
1888 // Incremental eval OK?
1889 if (failedStep) (*failedStep)++;
1890 if (debugIncrementalEval && st->value != compute_value())
1893 // Non-pawn material OK?
1894 if (failedStep) (*failedStep)++;
1895 if (debugNonPawnMaterial)
1897 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1900 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1905 if (failedStep) (*failedStep)++;
1906 if (debugPieceCounts)
1907 for (Color c = WHITE; c <= BLACK; c++)
1908 for (PieceType pt = PAWN; pt <= KING; pt++)
1909 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1912 if (failedStep) (*failedStep)++;
1914 for (Color c = WHITE; c <= BLACK; c++)
1915 for (PieceType pt = PAWN; pt <= KING; pt++)
1916 for (int i = 0; i < pieceCount[c][pt]; i++)
1918 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1921 if (index[piece_list(c, pt)[i]] != i)
1925 if (failedStep) (*failedStep)++;
1926 if (debugCastleSquares)
1927 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1932 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1934 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1935 || piece_on(castleRookSquare[f]) != rook)
1939 if (failedStep) *failedStep = 0;