2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
33 #include "ucioption.h"
39 Key Position::zobrist[2][8][64];
40 Key Position::zobEp[64];
41 Key Position::zobCastle[16];
42 Key Position::zobSideToMove;
43 Key Position::zobExclusion;
45 Score Position::PieceSquareTable[16][64];
47 // Material values arrays, indexed by Piece
48 const Value PieceValueMidgame[17] = {
50 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
51 RookValueMidgame, QueenValueMidgame,
52 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
53 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
54 RookValueMidgame, QueenValueMidgame
57 const Value PieceValueEndgame[17] = {
59 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
60 RookValueEndgame, QueenValueEndgame,
61 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
62 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
63 RookValueEndgame, QueenValueEndgame
69 // Bonus for having the side to move (modified by Joona Kiiski)
70 const Score TempoValue = make_score(48, 22);
72 // To convert a Piece to and from a FEN char
73 const string PieceToChar(".PNBRQK pnbrqk ");
79 CheckInfo::CheckInfo(const Position& pos) {
81 Color us = pos.side_to_move();
82 Color them = opposite_color(us);
83 Square ksq = pos.king_square(them);
85 dcCandidates = pos.discovered_check_candidates(us);
86 pinned = pos.pinned_pieces(us);
88 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
89 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
90 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
91 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
92 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
93 checkSq[KING] = EmptyBoardBB;
97 /// Position c'tors. Here we always create a copy of the original position
98 /// or the FEN string, we want the new born Position object do not depend
99 /// on any external data so we detach state pointer from the source one.
101 Position::Position(const Position& pos, int th) {
103 memcpy(this, &pos, sizeof(Position));
104 detach(); // Always detach() in copy c'tor to avoid surprises
109 Position::Position(const string& fen, bool isChess960, int th) {
111 from_fen(fen, isChess960);
116 /// Position::detach() copies the content of the current state and castling
117 /// masks inside the position itself. This is needed when the st pointee could
118 /// become stale, as example because the caller is about to going out of scope.
120 void Position::detach() {
124 st->previous = NULL; // As a safe guard
128 /// Position::from_fen() initializes the position object with the given FEN
129 /// string. This function is not very robust - make sure that input FENs are
130 /// correct (this is assumed to be the responsibility of the GUI).
132 void Position::from_fen(const string& fen, bool isChess960) {
134 A FEN string defines a particular position using only the ASCII character set.
136 A FEN string contains six fields. The separator between fields is a space. The fields are:
138 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
139 with rank 1; within each rank, the contents of each square are described from file A through file H.
140 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
141 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
142 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
143 of blank squares), and "/" separate ranks.
145 2) Active color. "w" means white moves next, "b" means black.
147 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
148 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
149 kingside), and/or "q" (Black can castle queenside).
151 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
152 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
153 regardless of whether there is a pawn in position to make an en passant capture.
155 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
156 to determine if a draw can be claimed under the fifty-move rule.
158 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
165 std::istringstream ss(fen);
168 ss >> std::skipws >> token >> std::noskipws;
170 // 1. Piece placement
171 while (!isspace(token))
174 sq -= Square(16); // Jump back of 2 rows
176 else if (isdigit(token))
177 sq += Square(token - '0'); // Skip the given number of files
179 else if ((p = PieceToChar.find(token)) != string::npos)
181 put_piece(Piece(p), sq);
189 ss >> std::skipws >> token;
190 sideToMove = (token == 'w' ? WHITE : BLACK);
192 // 3. Castling availability
193 ss >> token >> std::noskipws;
194 while (token != '-' && !isspace(token))
196 set_castling_rights(token);
200 // 4. En passant square. Ignore if no pawn capture is possible
201 ss >> std::skipws >> ep;
204 st->epSquare = make_square(File(ep[0] - 'a'), Rank(ep[1] - '1'));
206 if (!(attackers_to(st->epSquare) & pieces(PAWN, sideToMove)))
207 st->epSquare = SQ_NONE;
210 // 5-6. Halfmove clock and fullmove number
211 ss >> st->rule50 >> fullMoves;
213 // Various initialisations
214 chess960 = isChess960;
217 st->key = compute_key();
218 st->pawnKey = compute_pawn_key();
219 st->materialKey = compute_material_key();
220 st->value = compute_value();
221 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
222 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
226 /// Position::set_castle() is an helper function used to set
227 /// correct castling related flags.
229 void Position::set_castle(int f, Square ksq, Square rsq) {
231 st->castleRights |= f;
232 castleRightsMask[ksq] ^= f;
233 castleRightsMask[rsq] ^= f;
234 castleRookSquare[f] = rsq;
238 /// Position::set_castling_rights() sets castling parameters castling avaiability.
239 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
240 /// that uses the letters of the columns on which the rooks began the game instead
241 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
242 /// associated with the castling right, the traditional castling tag will be replaced
243 /// by the file letter of the involved rook as for the Shredder-FEN.
245 void Position::set_castling_rights(char token) {
247 Color c = islower(token) ? BLACK : WHITE;
249 Square sqA = relative_square(c, SQ_A1);
250 Square sqH = relative_square(c, SQ_H1);
252 Square rsq, ksq = king_square(c);
254 if (toupper(token) == 'K')
256 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
257 set_castle(WHITE_OO << c, ksq, rsq);
259 else if (toupper(token) == 'Q')
261 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
262 set_castle(WHITE_OOO << c, ksq, rsq);
264 else if (toupper(token) >= 'A' && toupper(token) <= 'H')
266 Square rsq = make_square(File(toupper(token) - 'A'), RANK_1);
268 if (square_file(rsq) < square_file(ksq))
269 set_castle(WHITE_OOO << c, ksq, rsq);
271 set_castle(WHITE_OO << c, ksq, rsq);
276 /// Position::to_fen() returns a FEN representation of the position. In case
277 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
279 const string Position::to_fen() const {
285 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
289 for (File file = FILE_A; file <= FILE_H; file++)
291 sq = make_square(file, rank);
293 if (square_is_occupied(sq))
300 fen += PieceToChar[piece_on(sq)];
309 fen += (sideToMove == WHITE ? " w " : " b ");
311 if (st->castleRights != CASTLES_NONE)
313 if (can_castle(WHITE_OO))
314 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K';
316 if (can_castle(WHITE_OOO))
317 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q';
319 if (can_castle(BLACK_OO))
320 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k';
322 if (can_castle(BLACK_OOO))
323 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q';
327 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
332 /// Position::print() prints an ASCII representation of the position to
333 /// the standard output. If a move is given then also the san is printed.
335 void Position::print(Move move) const {
337 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
341 Position p(*this, thread());
342 string dd = (piece_color(piece_on(move_from(move))) == BLACK ? ".." : "");
343 cout << "\nMove is: " << dd << move_to_san(p, move);
346 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
348 cout << dottedLine << '|';
349 for (File file = FILE_A; file <= FILE_H; file++)
351 Square sq = make_square(file, rank);
352 Piece piece = piece_on(sq);
354 if (piece == PIECE_NONE && square_color(sq) == DARK)
355 piece = PIECE_NONE_DARK_SQ;
357 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
358 cout << c << PieceToChar[piece] << c << '|';
361 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
365 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
366 /// king) pieces for the given color and for the given pinner type. Or, when
367 /// template parameter FindPinned is false, the pieces of the given color
368 /// candidate for a discovery check against the enemy king.
369 /// Bitboard checkersBB must be already updated when looking for pinners.
371 template<bool FindPinned>
372 Bitboard Position::hidden_checkers(Color c) const {
374 Bitboard result = EmptyBoardBB;
375 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
377 // Pinned pieces protect our king, dicovery checks attack
379 Square ksq = king_square(FindPinned ? c : opposite_color(c));
381 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
382 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
384 if (FindPinned && pinners)
385 pinners &= ~st->checkersBB;
389 Square s = pop_1st_bit(&pinners);
390 Bitboard b = squares_between(s, ksq) & occupied_squares();
394 if ( !(b & (b - 1)) // Only one bit set?
395 && (b & pieces_of_color(c))) // Is an our piece?
402 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
403 /// king) pieces for the given color. Note that checkersBB bitboard must
404 /// be already updated.
406 Bitboard Position::pinned_pieces(Color c) const {
408 return hidden_checkers<true>(c);
412 /// Position:discovered_check_candidates() returns a bitboard containing all
413 /// pieces for the given side which are candidates for giving a discovered
414 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
415 /// to be already updated.
417 Bitboard Position::discovered_check_candidates(Color c) const {
419 return hidden_checkers<false>(c);
422 /// Position::attackers_to() computes a bitboard containing all pieces which
423 /// attacks a given square.
425 Bitboard Position::attackers_to(Square s) const {
427 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
428 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
429 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
430 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
431 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
432 | (attacks_from<KING>(s) & pieces(KING));
435 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
437 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
438 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
439 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
440 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
441 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
442 | (attacks_from<KING>(s) & pieces(KING));
445 /// Position::attacks_from() computes a bitboard of all attacks
446 /// of a given piece put in a given square.
448 Bitboard Position::attacks_from(Piece p, Square s) const {
450 assert(square_is_ok(s));
454 case WB: case BB: return attacks_from<BISHOP>(s);
455 case WR: case BR: return attacks_from<ROOK>(s);
456 case WQ: case BQ: return attacks_from<QUEEN>(s);
457 default: return StepAttacksBB[p][s];
461 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
463 assert(square_is_ok(s));
467 case WB: case BB: return bishop_attacks_bb(s, occ);
468 case WR: case BR: return rook_attacks_bb(s, occ);
469 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
470 default: return StepAttacksBB[p][s];
475 /// Position::move_attacks_square() tests whether a move from the current
476 /// position attacks a given square.
478 bool Position::move_attacks_square(Move m, Square s) const {
480 assert(move_is_ok(m));
481 assert(square_is_ok(s));
484 Square f = move_from(m), t = move_to(m);
486 assert(square_is_occupied(f));
488 if (bit_is_set(attacks_from(piece_on(f), t), s))
491 // Move the piece and scan for X-ray attacks behind it
492 occ = occupied_squares();
493 do_move_bb(&occ, make_move_bb(f, t));
494 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
495 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
496 & pieces_of_color(piece_color(piece_on(f)));
498 // If we have attacks we need to verify that are caused by our move
499 // and are not already existent ones.
500 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
504 /// Position::find_checkers() computes the checkersBB bitboard, which
505 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
506 /// currently works by calling Position::attackers_to, which is probably
507 /// inefficient. Consider rewriting this function to use the last move
508 /// played, like in non-bitboard versions of Glaurung.
510 void Position::find_checkers() {
512 Color us = side_to_move();
513 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
517 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
519 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
522 assert(move_is_ok(m));
523 assert(pinned == pinned_pieces(side_to_move()));
525 Color us = side_to_move();
526 Square from = move_from(m);
528 assert(piece_color(piece_on(from)) == us);
529 assert(piece_on(king_square(us)) == make_piece(us, KING));
531 // En passant captures are a tricky special case. Because they are
532 // rather uncommon, we do it simply by testing whether the king is attacked
533 // after the move is made
536 Color them = opposite_color(us);
537 Square to = move_to(m);
538 Square capsq = make_square(square_file(to), square_rank(from));
539 Square ksq = king_square(us);
540 Bitboard b = occupied_squares();
542 assert(to == ep_square());
543 assert(piece_on(from) == make_piece(us, PAWN));
544 assert(piece_on(capsq) == make_piece(them, PAWN));
545 assert(piece_on(to) == PIECE_NONE);
548 clear_bit(&b, capsq);
551 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
552 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
555 // If the moving piece is a king, check whether the destination
556 // square is attacked by the opponent. Castling moves are checked
557 // for legality during move generation.
558 if (piece_type(piece_on(from)) == KING)
559 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
561 // A non-king move is legal if and only if it is not pinned or it
562 // is moving along the ray towards or away from the king.
564 || !bit_is_set(pinned, from)
565 || squares_aligned(from, move_to(m), king_square(us));
569 /// Position::move_is_pl_slow() takes a move and tests whether the move
570 /// is pseudo legal. This version is not very fast and should be used
571 /// only in non time-critical paths.
573 bool Position::move_is_pl_slow(const Move m) const {
575 MoveStack mlist[MAX_MOVES];
576 MoveStack *cur, *last;
578 last = in_check() ? generate<MV_EVASION>(*this, mlist)
579 : generate<MV_NON_EVASION>(*this, mlist);
581 for (cur = mlist; cur != last; cur++)
589 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
590 /// of pinned pieces as input, and tests whether the move is pseudo legal.
592 bool Position::move_is_pl(const Move m) const {
596 Color us = sideToMove;
597 Color them = opposite_color(sideToMove);
598 Square from = move_from(m);
599 Square to = move_to(m);
600 Piece pc = piece_on(from);
602 // Use a slower but simpler function for uncommon cases
603 if (move_is_special(m))
604 return move_is_pl_slow(m);
606 // Is not a promotion, so promotion piece must be empty
607 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
610 // If the from square is not occupied by a piece belonging to the side to
611 // move, the move is obviously not legal.
612 if (pc == PIECE_NONE || piece_color(pc) != us)
615 // The destination square cannot be occupied by a friendly piece
616 if (piece_color(piece_on(to)) == us)
619 // Handle the special case of a pawn move
620 if (piece_type(pc) == PAWN)
622 // Move direction must be compatible with pawn color
623 int direction = to - from;
624 if ((us == WHITE) != (direction > 0))
627 // We have already handled promotion moves, so destination
628 // cannot be on the 8/1th rank.
629 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
632 // Proceed according to the square delta between the origin and
633 // destination squares.
640 // Capture. The destination square must be occupied by an enemy
641 // piece (en passant captures was handled earlier).
642 if (piece_color(piece_on(to)) != them)
645 // From and to files must be one file apart, avoids a7h5
646 if (abs(square_file(from) - square_file(to)) != 1)
652 // Pawn push. The destination square must be empty.
653 if (!square_is_empty(to))
658 // Double white pawn push. The destination square must be on the fourth
659 // rank, and both the destination square and the square between the
660 // source and destination squares must be empty.
661 if ( square_rank(to) != RANK_4
662 || !square_is_empty(to)
663 || !square_is_empty(from + DELTA_N))
668 // Double black pawn push. The destination square must be on the fifth
669 // rank, and both the destination square and the square between the
670 // source and destination squares must be empty.
671 if ( square_rank(to) != RANK_5
672 || !square_is_empty(to)
673 || !square_is_empty(from + DELTA_S))
681 else if (!bit_is_set(attacks_from(pc, from), to))
686 // In case of king moves under check we have to remove king so to catch
687 // as invalid moves like b1a1 when opposite queen is on c1.
688 if (piece_type(piece_on(from)) == KING)
690 Bitboard b = occupied_squares();
692 if (attackers_to(move_to(m), b) & pieces_of_color(opposite_color(us)))
697 Bitboard target = checkers();
698 Square checksq = pop_1st_bit(&target);
700 if (target) // double check ? In this case a king move is required
703 // Our move must be a blocking evasion or a capture of the checking piece
704 target = squares_between(checksq, king_square(us)) | checkers();
705 if (!bit_is_set(target, move_to(m)))
714 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
716 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
719 assert(move_is_ok(m));
720 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
721 assert(piece_color(piece_on(move_from(m))) == side_to_move());
723 Square from = move_from(m);
724 Square to = move_to(m);
725 PieceType pt = piece_type(piece_on(from));
728 if (bit_is_set(ci.checkSq[pt], to))
732 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
734 // For pawn and king moves we need to verify also direction
735 if ( (pt != PAWN && pt != KING)
736 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
740 // Can we skip the ugly special cases ?
741 if (!move_is_special(m))
744 Color us = side_to_move();
745 Bitboard b = occupied_squares();
746 Square ksq = king_square(opposite_color(us));
748 // Promotion with check ?
749 if (move_is_promotion(m))
753 switch (promotion_piece_type(m))
756 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
758 return bit_is_set(bishop_attacks_bb(to, b), ksq);
760 return bit_is_set(rook_attacks_bb(to, b), ksq);
762 return bit_is_set(queen_attacks_bb(to, b), ksq);
768 // En passant capture with check ? We have already handled the case
769 // of direct checks and ordinary discovered check, the only case we
770 // need to handle is the unusual case of a discovered check through
771 // the captured pawn.
774 Square capsq = make_square(square_file(to), square_rank(from));
776 clear_bit(&b, capsq);
778 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
779 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
782 // Castling with check ?
783 if (move_is_castle(m))
785 Square kfrom, kto, rfrom, rto;
791 kto = relative_square(us, SQ_G1);
792 rto = relative_square(us, SQ_F1);
794 kto = relative_square(us, SQ_C1);
795 rto = relative_square(us, SQ_D1);
797 clear_bit(&b, kfrom);
798 clear_bit(&b, rfrom);
801 return bit_is_set(rook_attacks_bb(rto, b), ksq);
808 /// Position::do_setup_move() makes a permanent move on the board. It should
809 /// be used when setting up a position on board. You can't undo the move.
811 void Position::do_setup_move(Move m) {
815 // Update the number of full moves after black's move
816 if (sideToMove == BLACK)
821 // Reset "game ply" in case we made a non-reversible move.
822 // "game ply" is used for repetition detection.
826 // Our StateInfo newSt is about going out of scope so copy
827 // its content before it disappears.
832 /// Position::do_move() makes a move, and saves all information necessary
833 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
834 /// moves should be filtered out before this function is called.
836 void Position::do_move(Move m, StateInfo& newSt) {
839 do_move(m, newSt, ci, move_gives_check(m, ci));
842 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
845 assert(move_is_ok(m));
846 assert(&newSt != st);
851 // Copy some fields of old state to our new StateInfo object except the
852 // ones which are recalculated from scratch anyway, then switch our state
853 // pointer to point to the new, ready to be updated, state.
854 struct ReducedStateInfo {
855 Key pawnKey, materialKey;
856 int castleRights, rule50, gamePly, pliesFromNull;
862 memcpy(&newSt, st, sizeof(ReducedStateInfo));
867 // Save the current key to the history[] array, in order to be able to
868 // detect repetition draws.
869 history[st->gamePly++] = key;
871 // Update side to move
872 key ^= zobSideToMove;
874 // Increment the 50 moves rule draw counter. Resetting it to zero in the
875 // case of non-reversible moves is taken care of later.
879 if (move_is_castle(m))
886 Color us = side_to_move();
887 Color them = opposite_color(us);
888 Square from = move_from(m);
889 Square to = move_to(m);
890 bool ep = move_is_ep(m);
891 bool pm = move_is_promotion(m);
893 Piece piece = piece_on(from);
894 PieceType pt = piece_type(piece);
895 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
897 assert(piece_color(piece_on(from)) == us);
898 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
899 assert(!(ep || pm) || piece == make_piece(us, PAWN));
900 assert(!pm || relative_rank(us, to) == RANK_8);
903 do_capture_move(key, capture, them, to, ep);
906 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
908 // Reset en passant square
909 if (st->epSquare != SQ_NONE)
911 key ^= zobEp[st->epSquare];
912 st->epSquare = SQ_NONE;
915 // Update castle rights if needed
916 if ( st->castleRights != CASTLES_NONE
917 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
919 key ^= zobCastle[st->castleRights];
920 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
921 key ^= zobCastle[st->castleRights];
924 // Prefetch TT access as soon as we know key is updated
925 prefetch((char*)TT.first_entry(key));
928 Bitboard move_bb = make_move_bb(from, to);
929 do_move_bb(&(byColorBB[us]), move_bb);
930 do_move_bb(&(byTypeBB[pt]), move_bb);
931 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
933 board[to] = board[from];
934 board[from] = PIECE_NONE;
936 // Update piece lists, note that index[from] is not updated and
937 // becomes stale. This works as long as index[] is accessed just
938 // by known occupied squares.
939 index[to] = index[from];
940 pieceList[us][pt][index[to]] = to;
942 // If the moving piece was a pawn do some special extra work
945 // Reset rule 50 draw counter
948 // Update pawn hash key and prefetch in L1/L2 cache
949 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
951 // Set en passant square, only if moved pawn can be captured
952 if ((to ^ from) == 16)
954 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
956 st->epSquare = Square((int(from) + int(to)) / 2);
957 key ^= zobEp[st->epSquare];
961 if (pm) // promotion ?
963 PieceType promotion = promotion_piece_type(m);
965 assert(promotion >= KNIGHT && promotion <= QUEEN);
967 // Insert promoted piece instead of pawn
968 clear_bit(&(byTypeBB[PAWN]), to);
969 set_bit(&(byTypeBB[promotion]), to);
970 board[to] = make_piece(us, promotion);
972 // Update piece counts
973 pieceCount[us][promotion]++;
974 pieceCount[us][PAWN]--;
976 // Update material key
977 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
978 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
980 // Update piece lists, move the last pawn at index[to] position
981 // and shrink the list. Add a new promotion piece to the list.
982 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
983 index[lastPawnSquare] = index[to];
984 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
985 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
986 index[to] = pieceCount[us][promotion] - 1;
987 pieceList[us][promotion][index[to]] = to;
989 // Partially revert hash keys update
990 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
991 st->pawnKey ^= zobrist[us][PAWN][to];
993 // Partially revert and update incremental scores
994 st->value -= pst(us, PAWN, to);
995 st->value += pst(us, promotion, to);
998 st->npMaterial[us] += PieceValueMidgame[promotion];
1002 // Prefetch pawn and material hash tables
1003 Threads[threadID].pawnTable.prefetch(st->pawnKey);
1004 Threads[threadID].materialTable.prefetch(st->materialKey);
1006 // Update incremental scores
1007 st->value += pst_delta(piece, from, to);
1009 // Set capture piece
1010 st->capturedType = capture;
1012 // Update the key with the final value
1015 // Update checkers bitboard, piece must be already moved
1016 st->checkersBB = EmptyBoardBB;
1021 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1025 if (bit_is_set(ci.checkSq[pt], to))
1026 st->checkersBB = SetMaskBB[to];
1029 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1032 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1035 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1041 sideToMove = opposite_color(sideToMove);
1042 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1048 /// Position::do_capture_move() is a private method used to update captured
1049 /// piece info. It is called from the main Position::do_move function.
1051 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1053 assert(capture != KING);
1057 // If the captured piece was a pawn, update pawn hash key,
1058 // otherwise update non-pawn material.
1059 if (capture == PAWN)
1061 if (ep) // en passant ?
1063 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1065 assert(to == st->epSquare);
1066 assert(relative_rank(opposite_color(them), to) == RANK_6);
1067 assert(piece_on(to) == PIECE_NONE);
1068 assert(piece_on(capsq) == make_piece(them, PAWN));
1070 board[capsq] = PIECE_NONE;
1072 st->pawnKey ^= zobrist[them][PAWN][capsq];
1075 st->npMaterial[them] -= PieceValueMidgame[capture];
1077 // Remove captured piece
1078 clear_bit(&(byColorBB[them]), capsq);
1079 clear_bit(&(byTypeBB[capture]), capsq);
1080 clear_bit(&(byTypeBB[0]), capsq);
1083 key ^= zobrist[them][capture][capsq];
1085 // Update incremental scores
1086 st->value -= pst(them, capture, capsq);
1088 // Update piece count
1089 pieceCount[them][capture]--;
1091 // Update material hash key
1092 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1094 // Update piece list, move the last piece at index[capsq] position
1096 // WARNING: This is a not perfectly revresible operation. When we
1097 // will reinsert the captured piece in undo_move() we will put it
1098 // at the end of the list and not in its original place, it means
1099 // index[] and pieceList[] are not guaranteed to be invariant to a
1100 // do_move() + undo_move() sequence.
1101 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1102 index[lastPieceSquare] = index[capsq];
1103 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1104 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1106 // Reset rule 50 counter
1111 /// Position::do_castle_move() is a private method used to make a castling
1112 /// move. It is called from the main Position::do_move function. Note that
1113 /// castling moves are encoded as "king captures friendly rook" moves, for
1114 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1116 void Position::do_castle_move(Move m) {
1118 assert(move_is_ok(m));
1119 assert(move_is_castle(m));
1121 Color us = side_to_move();
1122 Color them = opposite_color(us);
1124 // Reset capture field
1125 st->capturedType = PIECE_TYPE_NONE;
1127 // Find source squares for king and rook
1128 Square kfrom = move_from(m);
1129 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1132 assert(piece_on(kfrom) == make_piece(us, KING));
1133 assert(piece_on(rfrom) == make_piece(us, ROOK));
1135 // Find destination squares for king and rook
1136 if (rfrom > kfrom) // O-O
1138 kto = relative_square(us, SQ_G1);
1139 rto = relative_square(us, SQ_F1);
1141 kto = relative_square(us, SQ_C1);
1142 rto = relative_square(us, SQ_D1);
1145 // Remove pieces from source squares:
1146 clear_bit(&(byColorBB[us]), kfrom);
1147 clear_bit(&(byTypeBB[KING]), kfrom);
1148 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1149 clear_bit(&(byColorBB[us]), rfrom);
1150 clear_bit(&(byTypeBB[ROOK]), rfrom);
1151 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1153 // Put pieces on destination squares:
1154 set_bit(&(byColorBB[us]), kto);
1155 set_bit(&(byTypeBB[KING]), kto);
1156 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1157 set_bit(&(byColorBB[us]), rto);
1158 set_bit(&(byTypeBB[ROOK]), rto);
1159 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1161 // Update board array
1162 Piece king = make_piece(us, KING);
1163 Piece rook = make_piece(us, ROOK);
1164 board[kfrom] = board[rfrom] = PIECE_NONE;
1168 // Update piece lists
1169 pieceList[us][KING][index[kfrom]] = kto;
1170 pieceList[us][ROOK][index[rfrom]] = rto;
1171 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1172 index[kto] = index[kfrom];
1175 // Update incremental scores
1176 st->value += pst_delta(king, kfrom, kto);
1177 st->value += pst_delta(rook, rfrom, rto);
1180 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1181 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1183 // Clear en passant square
1184 if (st->epSquare != SQ_NONE)
1186 st->key ^= zobEp[st->epSquare];
1187 st->epSquare = SQ_NONE;
1190 // Update castling rights
1191 st->key ^= zobCastle[st->castleRights];
1192 st->castleRights &= castleRightsMask[kfrom];
1193 st->key ^= zobCastle[st->castleRights];
1195 // Reset rule 50 counter
1198 // Update checkers BB
1199 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1202 sideToMove = opposite_color(sideToMove);
1203 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1209 /// Position::undo_move() unmakes a move. When it returns, the position should
1210 /// be restored to exactly the same state as before the move was made.
1212 void Position::undo_move(Move m) {
1215 assert(move_is_ok(m));
1217 sideToMove = opposite_color(sideToMove);
1219 if (move_is_castle(m))
1221 undo_castle_move(m);
1225 Color us = side_to_move();
1226 Color them = opposite_color(us);
1227 Square from = move_from(m);
1228 Square to = move_to(m);
1229 bool ep = move_is_ep(m);
1230 bool pm = move_is_promotion(m);
1232 PieceType pt = piece_type(piece_on(to));
1234 assert(square_is_empty(from));
1235 assert(piece_color(piece_on(to)) == us);
1236 assert(!pm || relative_rank(us, to) == RANK_8);
1237 assert(!ep || to == st->previous->epSquare);
1238 assert(!ep || relative_rank(us, to) == RANK_6);
1239 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1241 if (pm) // promotion ?
1243 PieceType promotion = promotion_piece_type(m);
1246 assert(promotion >= KNIGHT && promotion <= QUEEN);
1247 assert(piece_on(to) == make_piece(us, promotion));
1249 // Replace promoted piece with a pawn
1250 clear_bit(&(byTypeBB[promotion]), to);
1251 set_bit(&(byTypeBB[PAWN]), to);
1253 // Update piece counts
1254 pieceCount[us][promotion]--;
1255 pieceCount[us][PAWN]++;
1257 // Update piece list replacing promotion piece with a pawn
1258 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1259 index[lastPromotionSquare] = index[to];
1260 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1261 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1262 index[to] = pieceCount[us][PAWN] - 1;
1263 pieceList[us][PAWN][index[to]] = to;
1266 // Put the piece back at the source square
1267 Bitboard move_bb = make_move_bb(to, from);
1268 do_move_bb(&(byColorBB[us]), move_bb);
1269 do_move_bb(&(byTypeBB[pt]), move_bb);
1270 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1272 board[from] = make_piece(us, pt);
1273 board[to] = PIECE_NONE;
1275 // Update piece list
1276 index[from] = index[to];
1277 pieceList[us][pt][index[from]] = from;
1279 if (st->capturedType)
1284 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1286 assert(st->capturedType != KING);
1287 assert(!ep || square_is_empty(capsq));
1289 // Restore the captured piece
1290 set_bit(&(byColorBB[them]), capsq);
1291 set_bit(&(byTypeBB[st->capturedType]), capsq);
1292 set_bit(&(byTypeBB[0]), capsq);
1294 board[capsq] = make_piece(them, st->capturedType);
1296 // Update piece count
1297 pieceCount[them][st->capturedType]++;
1299 // Update piece list, add a new captured piece in capsq square
1300 index[capsq] = pieceCount[them][st->capturedType] - 1;
1301 pieceList[them][st->capturedType][index[capsq]] = capsq;
1304 // Finally point our state pointer back to the previous state
1311 /// Position::undo_castle_move() is a private method used to unmake a castling
1312 /// move. It is called from the main Position::undo_move function. Note that
1313 /// castling moves are encoded as "king captures friendly rook" moves, for
1314 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1316 void Position::undo_castle_move(Move m) {
1318 assert(move_is_ok(m));
1319 assert(move_is_castle(m));
1321 // When we have arrived here, some work has already been done by
1322 // Position::undo_move. In particular, the side to move has been switched,
1323 // so the code below is correct.
1324 Color us = side_to_move();
1326 // Find source squares for king and rook
1327 Square kfrom = move_from(m);
1328 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1331 // Find destination squares for king and rook
1332 if (rfrom > kfrom) // O-O
1334 kto = relative_square(us, SQ_G1);
1335 rto = relative_square(us, SQ_F1);
1337 kto = relative_square(us, SQ_C1);
1338 rto = relative_square(us, SQ_D1);
1341 assert(piece_on(kto) == make_piece(us, KING));
1342 assert(piece_on(rto) == make_piece(us, ROOK));
1344 // Remove pieces from destination squares:
1345 clear_bit(&(byColorBB[us]), kto);
1346 clear_bit(&(byTypeBB[KING]), kto);
1347 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1348 clear_bit(&(byColorBB[us]), rto);
1349 clear_bit(&(byTypeBB[ROOK]), rto);
1350 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1352 // Put pieces on source squares:
1353 set_bit(&(byColorBB[us]), kfrom);
1354 set_bit(&(byTypeBB[KING]), kfrom);
1355 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1356 set_bit(&(byColorBB[us]), rfrom);
1357 set_bit(&(byTypeBB[ROOK]), rfrom);
1358 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1361 board[rto] = board[kto] = PIECE_NONE;
1362 board[rfrom] = make_piece(us, ROOK);
1363 board[kfrom] = make_piece(us, KING);
1365 // Update piece lists
1366 pieceList[us][KING][index[kto]] = kfrom;
1367 pieceList[us][ROOK][index[rto]] = rfrom;
1368 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1369 index[kfrom] = index[kto];
1372 // Finally point our state pointer back to the previous state
1379 /// Position::do_null_move makes() a "null move": It switches the side to move
1380 /// and updates the hash key without executing any move on the board.
1382 void Position::do_null_move(StateInfo& backupSt) {
1385 assert(!in_check());
1387 // Back up the information necessary to undo the null move to the supplied
1388 // StateInfo object.
1389 // Note that differently from normal case here backupSt is actually used as
1390 // a backup storage not as a new state to be used.
1391 backupSt.key = st->key;
1392 backupSt.epSquare = st->epSquare;
1393 backupSt.value = st->value;
1394 backupSt.previous = st->previous;
1395 backupSt.pliesFromNull = st->pliesFromNull;
1396 st->previous = &backupSt;
1398 // Save the current key to the history[] array, in order to be able to
1399 // detect repetition draws.
1400 history[st->gamePly++] = st->key;
1402 // Update the necessary information
1403 if (st->epSquare != SQ_NONE)
1404 st->key ^= zobEp[st->epSquare];
1406 st->key ^= zobSideToMove;
1407 prefetch((char*)TT.first_entry(st->key));
1409 sideToMove = opposite_color(sideToMove);
1410 st->epSquare = SQ_NONE;
1412 st->pliesFromNull = 0;
1413 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1417 /// Position::undo_null_move() unmakes a "null move".
1419 void Position::undo_null_move() {
1422 assert(!in_check());
1424 // Restore information from the our backup StateInfo object
1425 StateInfo* backupSt = st->previous;
1426 st->key = backupSt->key;
1427 st->epSquare = backupSt->epSquare;
1428 st->value = backupSt->value;
1429 st->previous = backupSt->previous;
1430 st->pliesFromNull = backupSt->pliesFromNull;
1432 // Update the necessary information
1433 sideToMove = opposite_color(sideToMove);
1439 /// Position::see() is a static exchange evaluator: It tries to estimate the
1440 /// material gain or loss resulting from a move. There are three versions of
1441 /// this function: One which takes a destination square as input, one takes a
1442 /// move, and one which takes a 'from' and a 'to' square. The function does
1443 /// not yet understand promotions captures.
1445 int Position::see_sign(Move m) const {
1447 assert(move_is_ok(m));
1449 Square from = move_from(m);
1450 Square to = move_to(m);
1452 // Early return if SEE cannot be negative because captured piece value
1453 // is not less then capturing one. Note that king moves always return
1454 // here because king midgame value is set to 0.
1455 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1461 int Position::see(Move m) const {
1464 Bitboard occupied, attackers, stmAttackers, b;
1465 int swapList[32], slIndex = 1;
1466 PieceType capturedType, pt;
1469 assert(move_is_ok(m));
1471 // As castle moves are implemented as capturing the rook, they have
1472 // SEE == RookValueMidgame most of the times (unless the rook is under
1474 if (move_is_castle(m))
1477 from = move_from(m);
1479 capturedType = piece_type(piece_on(to));
1480 occupied = occupied_squares();
1482 // Handle en passant moves
1483 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1485 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1487 assert(capturedType == PIECE_TYPE_NONE);
1488 assert(piece_type(piece_on(capQq)) == PAWN);
1490 // Remove the captured pawn
1491 clear_bit(&occupied, capQq);
1492 capturedType = PAWN;
1495 // Find all attackers to the destination square, with the moving piece
1496 // removed, but possibly an X-ray attacker added behind it.
1497 clear_bit(&occupied, from);
1498 attackers = attackers_to(to, occupied);
1500 // If the opponent has no attackers we are finished
1501 stm = opposite_color(piece_color(piece_on(from)));
1502 stmAttackers = attackers & pieces_of_color(stm);
1504 return PieceValueMidgame[capturedType];
1506 // The destination square is defended, which makes things rather more
1507 // difficult to compute. We proceed by building up a "swap list" containing
1508 // the material gain or loss at each stop in a sequence of captures to the
1509 // destination square, where the sides alternately capture, and always
1510 // capture with the least valuable piece. After each capture, we look for
1511 // new X-ray attacks from behind the capturing piece.
1512 swapList[0] = PieceValueMidgame[capturedType];
1513 capturedType = piece_type(piece_on(from));
1516 // Locate the least valuable attacker for the side to move. The loop
1517 // below looks like it is potentially infinite, but it isn't. We know
1518 // that the side to move still has at least one attacker left.
1519 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1522 // Remove the attacker we just found from the 'occupied' bitboard,
1523 // and scan for new X-ray attacks behind the attacker.
1524 b = stmAttackers & pieces(pt);
1525 occupied ^= (b & (~b + 1));
1526 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1527 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1529 attackers &= occupied; // Cut out pieces we've already done
1531 // Add the new entry to the swap list
1532 assert(slIndex < 32);
1533 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1536 // Remember the value of the capturing piece, and change the side to
1537 // move before beginning the next iteration.
1539 stm = opposite_color(stm);
1540 stmAttackers = attackers & pieces_of_color(stm);
1542 // Stop before processing a king capture
1543 if (capturedType == KING && stmAttackers)
1545 assert(slIndex < 32);
1546 swapList[slIndex++] = QueenValueMidgame*10;
1549 } while (stmAttackers);
1551 // Having built the swap list, we negamax through it to find the best
1552 // achievable score from the point of view of the side to move.
1554 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1560 /// Position::clear() erases the position object to a pristine state, with an
1561 /// empty board, white to move, and no castling rights.
1563 void Position::clear() {
1566 memset(st, 0, sizeof(StateInfo));
1567 st->epSquare = SQ_NONE;
1571 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1572 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1573 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1574 memset(index, 0, sizeof(int) * 64);
1576 for (int i = 0; i < 64; i++)
1577 board[i] = PIECE_NONE;
1579 for (int i = 0; i < 8; i++)
1580 for (int j = 0; j < 16; j++)
1581 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1583 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1584 castleRightsMask[sq] = ALL_CASTLES;
1590 /// Position::put_piece() puts a piece on the given square of the board,
1591 /// updating the board array, pieces list, bitboards, and piece counts.
1593 void Position::put_piece(Piece p, Square s) {
1595 Color c = piece_color(p);
1596 PieceType pt = piece_type(p);
1599 index[s] = pieceCount[c][pt]++;
1600 pieceList[c][pt][index[s]] = s;
1602 set_bit(&(byTypeBB[pt]), s);
1603 set_bit(&(byColorBB[c]), s);
1604 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1608 /// Position::compute_key() computes the hash key of the position. The hash
1609 /// key is usually updated incrementally as moves are made and unmade, the
1610 /// compute_key() function is only used when a new position is set up, and
1611 /// to verify the correctness of the hash key when running in debug mode.
1613 Key Position::compute_key() const {
1615 Key result = zobCastle[st->castleRights];
1617 for (Square s = SQ_A1; s <= SQ_H8; s++)
1618 if (square_is_occupied(s))
1619 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1621 if (ep_square() != SQ_NONE)
1622 result ^= zobEp[ep_square()];
1624 if (side_to_move() == BLACK)
1625 result ^= zobSideToMove;
1631 /// Position::compute_pawn_key() computes the hash key of the position. The
1632 /// hash key is usually updated incrementally as moves are made and unmade,
1633 /// the compute_pawn_key() function is only used when a new position is set
1634 /// up, and to verify the correctness of the pawn hash key when running in
1637 Key Position::compute_pawn_key() const {
1642 for (Color c = WHITE; c <= BLACK; c++)
1644 b = pieces(PAWN, c);
1646 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1652 /// Position::compute_material_key() computes the hash key of the position.
1653 /// The hash key is usually updated incrementally as moves are made and unmade,
1654 /// the compute_material_key() function is only used when a new position is set
1655 /// up, and to verify the correctness of the material hash key when running in
1658 Key Position::compute_material_key() const {
1663 for (Color c = WHITE; c <= BLACK; c++)
1664 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1666 count = piece_count(c, pt);
1667 for (int i = 0; i < count; i++)
1668 result ^= zobrist[c][pt][i];
1674 /// Position::compute_value() compute the incremental scores for the middle
1675 /// game and the endgame. These functions are used to initialize the incremental
1676 /// scores when a new position is set up, and to verify that the scores are correctly
1677 /// updated by do_move and undo_move when the program is running in debug mode.
1678 Score Position::compute_value() const {
1681 Score result = SCORE_ZERO;
1683 for (Color c = WHITE; c <= BLACK; c++)
1684 for (PieceType pt = PAWN; pt <= KING; pt++)
1688 result += pst(c, pt, pop_1st_bit(&b));
1691 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1696 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1697 /// game material value for the given side. Material values are updated
1698 /// incrementally during the search, this function is only used while
1699 /// initializing a new Position object.
1701 Value Position::compute_non_pawn_material(Color c) const {
1703 Value result = VALUE_ZERO;
1705 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1706 result += piece_count(c, pt) * PieceValueMidgame[pt];
1712 /// Position::is_draw() tests whether the position is drawn by material,
1713 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1714 /// must be done by the search.
1715 template<bool SkipRepetition>
1716 bool Position::is_draw() const {
1718 // Draw by material?
1720 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1723 // Draw by the 50 moves rule?
1724 if (st->rule50 > 99 && !is_mate())
1727 // Draw by repetition?
1728 if (!SkipRepetition)
1729 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1730 if (history[st->gamePly - i] == st->key)
1736 // Explicit template instantiations
1737 template bool Position::is_draw<false>() const;
1738 template bool Position::is_draw<true>() const;
1741 /// Position::is_mate() returns true or false depending on whether the
1742 /// side to move is checkmated.
1744 bool Position::is_mate() const {
1746 MoveStack moves[MAX_MOVES];
1747 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1751 /// Position::init() is a static member function which initializes at
1752 /// startup the various arrays used to compute hash keys and the piece
1753 /// square tables. The latter is a two-step operation: First, the white
1754 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1755 /// Second, the black halves of the tables are initialized by mirroring
1756 /// and changing the sign of the corresponding white scores.
1758 void Position::init() {
1762 for (Color c = WHITE; c <= BLACK; c++)
1763 for (PieceType pt = PAWN; pt <= KING; pt++)
1764 for (Square s = SQ_A1; s <= SQ_H8; s++)
1765 zobrist[c][pt][s] = rk.rand<Key>();
1767 for (Square s = SQ_A1; s <= SQ_H8; s++)
1768 zobEp[s] = rk.rand<Key>();
1770 for (int i = 0; i < 16; i++)
1771 zobCastle[i] = rk.rand<Key>();
1773 zobSideToMove = rk.rand<Key>();
1774 zobExclusion = rk.rand<Key>();
1776 for (Square s = SQ_A1; s <= SQ_H8; s++)
1777 for (Piece p = WP; p <= WK; p++)
1778 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1780 for (Square s = SQ_A1; s <= SQ_H8; s++)
1781 for (Piece p = BP; p <= BK; p++)
1782 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1786 /// Position::flip() flips position with the white and black sides reversed. This
1787 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1789 void Position::flip() {
1793 // Make a copy of current position before to start changing
1794 const Position pos(*this, threadID);
1797 threadID = pos.thread();
1800 for (Square s = SQ_A1; s <= SQ_H8; s++)
1801 if (!pos.square_is_empty(s))
1802 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1805 sideToMove = opposite_color(pos.side_to_move());
1808 if (pos.can_castle(WHITE_OO))
1809 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1810 if (pos.can_castle(WHITE_OOO))
1811 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1812 if (pos.can_castle(BLACK_OO))
1813 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1814 if (pos.can_castle(BLACK_OOO))
1815 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1817 // En passant square
1818 if (pos.st->epSquare != SQ_NONE)
1819 st->epSquare = flip_square(pos.st->epSquare);
1825 st->key = compute_key();
1826 st->pawnKey = compute_pawn_key();
1827 st->materialKey = compute_material_key();
1829 // Incremental scores
1830 st->value = compute_value();
1833 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1834 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1840 /// Position::is_ok() performs some consitency checks for the position object.
1841 /// This is meant to be helpful when debugging.
1843 bool Position::is_ok(int* failedStep) const {
1845 // What features of the position should be verified?
1846 const bool debugAll = false;
1848 const bool debugBitboards = debugAll || false;
1849 const bool debugKingCount = debugAll || false;
1850 const bool debugKingCapture = debugAll || false;
1851 const bool debugCheckerCount = debugAll || false;
1852 const bool debugKey = debugAll || false;
1853 const bool debugMaterialKey = debugAll || false;
1854 const bool debugPawnKey = debugAll || false;
1855 const bool debugIncrementalEval = debugAll || false;
1856 const bool debugNonPawnMaterial = debugAll || false;
1857 const bool debugPieceCounts = debugAll || false;
1858 const bool debugPieceList = debugAll || false;
1859 const bool debugCastleSquares = debugAll || false;
1861 if (failedStep) *failedStep = 1;
1864 if (side_to_move() != WHITE && side_to_move() != BLACK)
1867 // Are the king squares in the position correct?
1868 if (failedStep) (*failedStep)++;
1869 if (piece_on(king_square(WHITE)) != WK)
1872 if (failedStep) (*failedStep)++;
1873 if (piece_on(king_square(BLACK)) != BK)
1876 // Do both sides have exactly one king?
1877 if (failedStep) (*failedStep)++;
1880 int kingCount[2] = {0, 0};
1881 for (Square s = SQ_A1; s <= SQ_H8; s++)
1882 if (piece_type(piece_on(s)) == KING)
1883 kingCount[piece_color(piece_on(s))]++;
1885 if (kingCount[0] != 1 || kingCount[1] != 1)
1889 // Can the side to move capture the opponent's king?
1890 if (failedStep) (*failedStep)++;
1891 if (debugKingCapture)
1893 Color us = side_to_move();
1894 Color them = opposite_color(us);
1895 Square ksq = king_square(them);
1896 if (attackers_to(ksq) & pieces_of_color(us))
1900 // Is there more than 2 checkers?
1901 if (failedStep) (*failedStep)++;
1902 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1906 if (failedStep) (*failedStep)++;
1909 // The intersection of the white and black pieces must be empty
1910 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1913 // The union of the white and black pieces must be equal to all
1915 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1918 // Separate piece type bitboards must have empty intersections
1919 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1920 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1921 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1925 // En passant square OK?
1926 if (failedStep) (*failedStep)++;
1927 if (ep_square() != SQ_NONE)
1929 // The en passant square must be on rank 6, from the point of view of the
1931 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1936 if (failedStep) (*failedStep)++;
1937 if (debugKey && st->key != compute_key())
1940 // Pawn hash key OK?
1941 if (failedStep) (*failedStep)++;
1942 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1945 // Material hash key OK?
1946 if (failedStep) (*failedStep)++;
1947 if (debugMaterialKey && st->materialKey != compute_material_key())
1950 // Incremental eval OK?
1951 if (failedStep) (*failedStep)++;
1952 if (debugIncrementalEval && st->value != compute_value())
1955 // Non-pawn material OK?
1956 if (failedStep) (*failedStep)++;
1957 if (debugNonPawnMaterial)
1959 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1962 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1967 if (failedStep) (*failedStep)++;
1968 if (debugPieceCounts)
1969 for (Color c = WHITE; c <= BLACK; c++)
1970 for (PieceType pt = PAWN; pt <= KING; pt++)
1971 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1974 if (failedStep) (*failedStep)++;
1976 for (Color c = WHITE; c <= BLACK; c++)
1977 for (PieceType pt = PAWN; pt <= KING; pt++)
1978 for (int i = 0; i < pieceCount[c][pt]; i++)
1980 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
1983 if (index[piece_list(c, pt, i)] != i)
1987 if (failedStep) (*failedStep)++;
1988 if (debugCastleSquares)
1989 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1994 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1996 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1997 || piece_on(castleRookSquare[f]) != rook)
2001 if (failedStep) *failedStep = 0;