2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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 #include "ucioption.h"
47 int Position::castleRightsMask[64];
49 Key Position::zobrist[2][8][64];
50 Key Position::zobEp[64];
51 Key Position::zobCastle[16];
52 Key Position::zobMaterial[2][8][16];
53 Key Position::zobSideToMove;
55 Value Position::MgPieceSquareTable[16][64];
56 Value Position::EgPieceSquareTable[16][64];
58 static bool RequestPending = false;
66 Position::Position(const Position& pos) {
70 Position::Position(const string& fen) {
75 /// Position::from_fen() initializes the position object with the given FEN
76 /// string. This function is not very robust - make sure that input FENs are
77 /// correct (this is assumed to be the responsibility of the GUI).
79 void Position::from_fen(const string& fen) {
81 static const string pieceLetters = "KQRBNPkqrbnp";
82 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
90 for ( ; fen[i] != ' '; i++)
94 // Skip the given number of files
95 file += (fen[i] - '1' + 1);
98 else if (fen[i] == '/')
104 size_t idx = pieceLetters.find(fen[i]);
105 if (idx == string::npos)
107 std::cout << "Error in FEN at character " << i << std::endl;
110 Square square = make_square(file, rank);
111 put_piece(pieces[idx], square);
117 if (fen[i] != 'w' && fen[i] != 'b')
119 std::cout << "Error in FEN at character " << i << std::endl;
122 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
128 std::cout << "Error in FEN at character " << i << std::endl;
133 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
139 else if(fen[i] == 'K') allow_oo(WHITE);
140 else if(fen[i] == 'Q') allow_ooo(WHITE);
141 else if(fen[i] == 'k') allow_oo(BLACK);
142 else if(fen[i] == 'q') allow_ooo(BLACK);
143 else if(fen[i] >= 'A' && fen[i] <= 'H') {
144 File rookFile, kingFile = FILE_NONE;
145 for(Square square = SQ_B1; square <= SQ_G1; square++)
146 if(piece_on(square) == WK)
147 kingFile = square_file(square);
148 if(kingFile == FILE_NONE) {
149 std::cout << "Error in FEN at character " << i << std::endl;
152 initialKFile = kingFile;
153 rookFile = File(fen[i] - 'A') + FILE_A;
154 if(rookFile < initialKFile) {
156 initialQRFile = rookFile;
160 initialKRFile = rookFile;
163 else if(fen[i] >= 'a' && fen[i] <= 'h') {
164 File rookFile, kingFile = FILE_NONE;
165 for(Square square = SQ_B8; square <= SQ_G8; square++)
166 if(piece_on(square) == BK)
167 kingFile = square_file(square);
168 if(kingFile == FILE_NONE) {
169 std::cout << "Error in FEN at character " << i << std::endl;
172 initialKFile = kingFile;
173 rookFile = File(fen[i] - 'a') + FILE_A;
174 if(rookFile < initialKFile) {
176 initialQRFile = rookFile;
180 initialKRFile = rookFile;
184 std::cout << "Error in FEN at character " << i << std::endl;
191 while (fen[i] == ' ')
195 if ( i <= fen.length() - 2
196 && (fen[i] >= 'a' && fen[i] <= 'h')
197 && (fen[i+1] == '3' || fen[i+1] == '6'))
198 st->epSquare = square_from_string(fen.substr(i, 2));
200 // Various initialisation
201 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
202 castleRightsMask[sq] = ALL_CASTLES;
204 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
205 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
206 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
207 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
208 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
209 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
213 st->key = compute_key();
214 st->pawnKey = compute_pawn_key();
215 st->materialKey = compute_material_key();
216 st->value = Score(compute_value<MidGame>(), compute_value<EndGame>());
217 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
218 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
222 /// Position::to_fen() converts the position object to a FEN string. This is
223 /// probably only useful for debugging.
225 const string Position::to_fen() const {
227 static const string pieceLetters = " PNBRQK pnbrqk";
231 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
234 for (File file = FILE_A; file <= FILE_H; file++)
236 Square sq = make_square(file, rank);
237 if (!square_is_occupied(sq))
243 fen += (char)skip + '0';
246 fen += pieceLetters[piece_on(sq)];
249 fen += (char)skip + '0';
251 fen += (rank > RANK_1 ? '/' : ' ');
253 fen += (sideToMove == WHITE ? "w " : "b ");
254 if (st->castleRights != NO_CASTLES)
256 if (can_castle_kingside(WHITE)) fen += 'K';
257 if (can_castle_queenside(WHITE)) fen += 'Q';
258 if (can_castle_kingside(BLACK)) fen += 'k';
259 if (can_castle_queenside(BLACK)) fen += 'q';
264 if (ep_square() != SQ_NONE)
265 fen += square_to_string(ep_square());
273 /// Position::print() prints an ASCII representation of the position to
274 /// the standard output. If a move is given then also the san is print.
276 void Position::print(Move m) const {
278 static const string pieceLetters = " PNBRQK PNBRQK .";
280 // Check for reentrancy, as example when called from inside
281 // MovePicker that is used also here in move_to_san()
285 RequestPending = true;
287 std::cout << std::endl;
290 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
291 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
293 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
295 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
296 for (File file = FILE_A; file <= FILE_H; file++)
298 Square sq = make_square(file, rank);
299 Piece piece = piece_on(sq);
300 if (piece == EMPTY && square_color(sq) == WHITE)
303 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
304 std::cout << '|' << col << pieceLetters[piece] << col;
306 std::cout << '|' << std::endl;
308 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
309 << "Fen is: " << to_fen() << std::endl
310 << "Key is: " << st->key << std::endl;
312 RequestPending = false;
316 /// Position::copy() creates a copy of the input position.
318 void Position::copy(const Position& pos) {
320 memcpy(this, &pos, sizeof(Position));
321 saveState(); // detach and copy state info
325 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
326 /// king) pieces for the given color and for the given pinner type. Or, when
327 /// template parameter FindPinned is false, the pieces of the given color
328 /// candidate for a discovery check against the enemy king.
329 /// Note that checkersBB bitboard must be already updated.
331 template<bool FindPinned>
332 Bitboard Position::hidden_checkers(Color c) const {
334 Bitboard pinners, result = EmptyBoardBB;
336 // Pinned pieces protect our king, dicovery checks attack
338 Square ksq = king_square(FindPinned ? c : opposite_color(c));
340 // Pinners are sliders, not checkers, that give check when
341 // candidate pinned is removed.
342 pinners = (pieces(ROOK, QUEEN, FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
343 | (pieces(BISHOP, QUEEN, FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
345 if (FindPinned && pinners)
346 pinners &= ~st->checkersBB;
350 Square s = pop_1st_bit(&pinners);
351 Bitboard b = squares_between(s, ksq) & occupied_squares();
355 if ( !(b & (b - 1)) // Only one bit set?
356 && (b & pieces_of_color(c))) // Is an our piece?
363 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
364 /// king) pieces for the given color.
366 Bitboard Position::pinned_pieces(Color c) const {
368 return hidden_checkers<true>(c);
372 /// Position:discovered_check_candidates() returns a bitboard containing all
373 /// pieces for the given side which are candidates for giving a discovered
376 Bitboard Position::discovered_check_candidates(Color c) const {
378 return hidden_checkers<false>(c);
381 /// Position::attackers_to() computes a bitboard containing all pieces which
382 /// attacks a given square.
384 Bitboard Position::attackers_to(Square s) const {
386 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
387 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
388 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
389 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
390 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
391 | (attacks_from<KING>(s) & pieces(KING));
394 /// Position::attacks_from() computes a bitboard of all attacks
395 /// of a given piece put in a given square.
397 Bitboard Position::attacks_from(Piece p, Square s) const {
399 assert(square_is_ok(s));
403 case WP: return attacks_from<PAWN>(s, WHITE);
404 case BP: return attacks_from<PAWN>(s, BLACK);
405 case WN: case BN: return attacks_from<KNIGHT>(s);
406 case WB: case BB: return attacks_from<BISHOP>(s);
407 case WR: case BR: return attacks_from<ROOK>(s);
408 case WQ: case BQ: return attacks_from<QUEEN>(s);
409 case WK: case BK: return attacks_from<KING>(s);
416 /// Position::move_attacks_square() tests whether a move from the current
417 /// position attacks a given square.
419 bool Position::move_attacks_square(Move m, Square s) const {
421 assert(move_is_ok(m));
422 assert(square_is_ok(s));
424 Square f = move_from(m), t = move_to(m);
426 assert(square_is_occupied(f));
428 if (bit_is_set(attacks_from(piece_on(f), t), s))
431 // Move the piece and scan for X-ray attacks behind it
432 Bitboard occ = occupied_squares();
433 Color us = color_of_piece_on(f);
436 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
437 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
439 // If we have attacks we need to verify that are caused by our move
440 // and are not already existent ones.
441 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
445 /// Position::find_checkers() computes the checkersBB bitboard, which
446 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
447 /// currently works by calling Position::attackers_to, which is probably
448 /// inefficient. Consider rewriting this function to use the last move
449 /// played, like in non-bitboard versions of Glaurung.
451 void Position::find_checkers() {
453 Color us = side_to_move();
454 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
458 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
460 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
463 assert(move_is_ok(m));
464 assert(pinned == pinned_pieces(side_to_move()));
466 // Castling moves are checked for legality during move generation.
467 if (move_is_castle(m))
470 Color us = side_to_move();
471 Square from = move_from(m);
473 assert(color_of_piece_on(from) == us);
474 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
476 // En passant captures are a tricky special case. Because they are
477 // rather uncommon, we do it simply by testing whether the king is attacked
478 // after the move is made
481 Color them = opposite_color(us);
482 Square to = move_to(m);
483 Square capsq = make_square(square_file(to), square_rank(from));
484 Bitboard b = occupied_squares();
485 Square ksq = king_square(us);
487 assert(to == ep_square());
488 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
489 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
490 assert(piece_on(to) == EMPTY);
493 clear_bit(&b, capsq);
496 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
497 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
500 // If the moving piece is a king, check whether the destination
501 // square is attacked by the opponent.
502 if (type_of_piece_on(from) == KING)
503 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
505 // A non-king move is legal if and only if it is not pinned or it
506 // is moving along the ray towards or away from the king.
508 || !bit_is_set(pinned, from)
509 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
513 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
515 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
519 Color us = side_to_move();
520 Square from = move_from(m);
521 Square to = move_to(m);
523 // King moves and en-passant captures are verified in pl_move_is_legal()
524 if (type_of_piece_on(from) == KING || move_is_ep(m))
525 return pl_move_is_legal(m, pinned);
527 Bitboard target = checkers();
528 Square checksq = pop_1st_bit(&target);
530 if (target) // double check ?
533 // Our move must be a blocking evasion or a capture of the checking piece
534 target = squares_between(checksq, king_square(us)) | checkers();
535 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
539 /// Position::move_is_check() tests whether a pseudo-legal move is a check
541 bool Position::move_is_check(Move m) const {
543 Bitboard dc = discovered_check_candidates(side_to_move());
544 return move_is_check(m, dc);
547 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
550 assert(move_is_ok(m));
551 assert(dcCandidates == discovered_check_candidates(side_to_move()));
553 Color us = side_to_move();
554 Color them = opposite_color(us);
555 Square from = move_from(m);
556 Square to = move_to(m);
557 Square ksq = king_square(them);
559 assert(color_of_piece_on(from) == us);
560 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
562 // Proceed according to the type of the moving piece
563 switch (type_of_piece_on(from))
567 if (bit_is_set(attacks_from<PAWN>(ksq, them), to)) // Normal check?
570 if ( dcCandidates // Discovered check?
571 && bit_is_set(dcCandidates, from)
572 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
575 if (move_is_promotion(m)) // Promotion with check?
577 Bitboard b = occupied_squares();
580 switch (move_promotion_piece(m))
583 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
585 return bit_is_set(bishop_attacks_bb(to, b), ksq);
587 return bit_is_set(rook_attacks_bb(to, b), ksq);
589 return bit_is_set(queen_attacks_bb(to, b), ksq);
594 // En passant capture with check? We have already handled the case
595 // of direct checks and ordinary discovered check, the only case we
596 // need to handle is the unusual case of a discovered check through the
598 else if (move_is_ep(m))
600 Square capsq = make_square(square_file(to), square_rank(from));
601 Bitboard b = occupied_squares();
603 clear_bit(&b, capsq);
605 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
606 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
610 // Test discovered check and normal check according to piece type
612 return (dcCandidates && bit_is_set(dcCandidates, from))
613 || bit_is_set(attacks_from<KNIGHT>(ksq), to);
616 return (dcCandidates && bit_is_set(dcCandidates, from))
617 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to));
620 return (dcCandidates && bit_is_set(dcCandidates, from))
621 || (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to));
624 // Discovered checks are impossible!
625 assert(!bit_is_set(dcCandidates, from));
626 return ( (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to))
627 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to)));
631 if ( bit_is_set(dcCandidates, from)
632 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
635 // Castling with check?
636 if (move_is_castle(m))
638 Square kfrom, kto, rfrom, rto;
639 Bitboard b = occupied_squares();
645 kto = relative_square(us, SQ_G1);
646 rto = relative_square(us, SQ_F1);
648 kto = relative_square(us, SQ_C1);
649 rto = relative_square(us, SQ_D1);
651 clear_bit(&b, kfrom);
652 clear_bit(&b, rfrom);
655 return bit_is_set(rook_attacks_bb(rto, b), ksq);
659 default: // NO_PIECE_TYPE
667 /// Position::update_checkers() udpates chekers info given the move. It is called
668 /// in do_move() and is faster then find_checkers().
670 template<PieceType Piece>
671 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
672 Square to, Bitboard dcCandidates) {
674 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
675 const bool Rook = (Piece == QUEEN || Piece == ROOK);
676 const bool Slider = Bishop || Rook;
679 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
680 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
681 && bit_is_set(attacks_from<Piece>(ksq), to)) // slow, try to early skip
682 set_bit(pCheckersBB, to);
684 else if ( Piece != KING
686 && bit_is_set(Piece == PAWN ? attacks_from<PAWN>(ksq, opposite_color(sideToMove))
687 : attacks_from<Piece>(ksq), to))
688 set_bit(pCheckersBB, to);
691 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
694 (*pCheckersBB) |= (attacks_from<ROOK>(ksq) & pieces(ROOK, QUEEN, side_to_move()));
697 (*pCheckersBB) |= (attacks_from<BISHOP>(ksq) & pieces(BISHOP, QUEEN, side_to_move()));
702 /// Position::do_move() makes a move, and saves all information necessary
703 /// to a StateInfo object. The move is assumed to be legal.
704 /// Pseudo-legal moves should be filtered out before this function is called.
706 void Position::do_move(Move m, StateInfo& newSt) {
708 do_move(m, newSt, discovered_check_candidates(side_to_move()));
711 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
714 assert(move_is_ok(m));
716 Bitboard key = st->key;
718 // Copy some fields of old state to our new StateInfo object except the
719 // ones which are recalculated from scratch anyway, then switch our state
720 // pointer to point to the new, ready to be updated, state.
721 struct ReducedStateInfo {
722 Key key, pawnKey, materialKey;
723 int castleRights, rule50, pliesFromNull;
725 Value mgValue, egValue;
729 memcpy(&newSt, st, sizeof(ReducedStateInfo));
733 // Save the current key to the history[] array, in order to be able to
734 // detect repetition draws.
735 history[gamePly] = key;
738 // Update side to move
739 key ^= zobSideToMove;
741 // Increment the 50 moves rule draw counter. Resetting it to zero in the
742 // case of non-reversible moves is taken care of later.
746 if (move_is_castle(m))
753 Color us = side_to_move();
754 Color them = opposite_color(us);
755 Square from = move_from(m);
756 Square to = move_to(m);
757 bool ep = move_is_ep(m);
758 bool pm = move_is_promotion(m);
760 Piece piece = piece_on(from);
761 PieceType pt = type_of_piece(piece);
763 assert(color_of_piece_on(from) == us);
764 assert(color_of_piece_on(to) == them || square_is_empty(to));
765 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
766 assert(!pm || relative_rank(us, to) == RANK_8);
768 st->capture = ep ? PAWN : type_of_piece_on(to);
771 do_capture_move(key, st->capture, them, to, ep);
774 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
776 // Reset en passant square
777 if (st->epSquare != SQ_NONE)
779 key ^= zobEp[st->epSquare];
780 st->epSquare = SQ_NONE;
783 // Update castle rights, try to shortcut a common case
784 int cm = castleRightsMask[from] & castleRightsMask[to];
785 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
787 key ^= zobCastle[st->castleRights];
788 st->castleRights &= castleRightsMask[from];
789 st->castleRights &= castleRightsMask[to];
790 key ^= zobCastle[st->castleRights];
793 // Prefetch TT access as soon as we know key is updated
797 Bitboard move_bb = make_move_bb(from, to);
798 do_move_bb(&(byColorBB[us]), move_bb);
799 do_move_bb(&(byTypeBB[pt]), move_bb);
800 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
802 board[to] = board[from];
805 // Update piece lists, note that index[from] is not updated and
806 // becomes stale. This works as long as index[] is accessed just
807 // by known occupied squares.
808 index[to] = index[from];
809 pieceList[us][pt][index[to]] = to;
811 // If the moving piece was a pawn do some special extra work
814 // Reset rule 50 draw counter
817 // Update pawn hash key
818 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
820 // Set en passant square, only if moved pawn can be captured
821 if (abs(int(to) - int(from)) == 16)
823 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
825 st->epSquare = Square((int(from) + int(to)) / 2);
826 key ^= zobEp[st->epSquare];
831 // Update incremental scores
832 st->value += Score(pst_delta<MidGame>(piece, from, to), pst_delta<EndGame>(piece, from, to));
834 if (pm) // promotion ?
836 PieceType promotion = move_promotion_piece(m);
838 assert(promotion >= KNIGHT && promotion <= QUEEN);
840 // Insert promoted piece instead of pawn
841 clear_bit(&(byTypeBB[PAWN]), to);
842 set_bit(&(byTypeBB[promotion]), to);
843 board[to] = piece_of_color_and_type(us, promotion);
845 // Update material key
846 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
847 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
849 // Update piece counts
850 pieceCount[us][PAWN]--;
851 pieceCount[us][promotion]++;
853 // Update piece lists, move the last pawn at index[to] position
854 // and shrink the list. Add a new promotion piece to the list.
855 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
856 index[lastPawnSquare] = index[to];
857 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
858 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
859 index[to] = pieceCount[us][promotion] - 1;
860 pieceList[us][promotion][index[to]] = to;
862 // Partially revert hash keys update
863 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
864 st->pawnKey ^= zobrist[us][PAWN][to];
866 // Partially revert and update incremental scores
867 st->value -= Score(pst<MidGame>(us, PAWN, to), pst<EndGame>(us, PAWN, to));
868 st->value += Score(pst<MidGame>(us, promotion, to), pst<EndGame>(us, promotion, to));
871 st->npMaterial[us] += piece_value_midgame(promotion);
874 // Update the key with the final value
877 // Update checkers bitboard, piece must be already moved
879 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
882 st->checkersBB = EmptyBoardBB;
883 Square ksq = king_square(them);
886 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
887 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
888 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
889 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
890 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
891 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
892 default: assert(false); break;
897 sideToMove = opposite_color(sideToMove);
898 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
904 /// Position::do_capture_move() is a private method used to update captured
905 /// piece info. It is called from the main Position::do_move function.
907 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
909 assert(capture != KING);
913 if (ep) // en passant ?
915 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
917 assert(to == st->epSquare);
918 assert(relative_rank(opposite_color(them), to) == RANK_6);
919 assert(piece_on(to) == EMPTY);
920 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
922 board[capsq] = EMPTY;
925 // Remove captured piece
926 clear_bit(&(byColorBB[them]), capsq);
927 clear_bit(&(byTypeBB[capture]), capsq);
928 clear_bit(&(byTypeBB[0]), capsq);
931 key ^= zobrist[them][capture][capsq];
933 // Update incremental scores
934 st->value -= Score(pst<MidGame>(them, capture, capsq), pst<EndGame>(them, capture, capsq));
936 // If the captured piece was a pawn, update pawn hash key,
937 // otherwise update non-pawn material.
939 st->pawnKey ^= zobrist[them][PAWN][capsq];
941 st->npMaterial[them] -= piece_value_midgame(capture);
943 // Update material hash key
944 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
946 // Update piece count
947 pieceCount[them][capture]--;
949 // Update piece list, move the last piece at index[capsq] position
951 // WARNING: This is a not perfectly revresible operation. When we
952 // will reinsert the captured piece in undo_move() we will put it
953 // at the end of the list and not in its original place, it means
954 // index[] and pieceList[] are not guaranteed to be invariant to a
955 // do_move() + undo_move() sequence.
956 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
957 index[lastPieceSquare] = index[capsq];
958 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
959 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
961 // Reset rule 50 counter
966 /// Position::do_castle_move() is a private method used to make a castling
967 /// move. It is called from the main Position::do_move function. Note that
968 /// castling moves are encoded as "king captures friendly rook" moves, for
969 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
971 void Position::do_castle_move(Move m) {
973 assert(move_is_ok(m));
974 assert(move_is_castle(m));
976 Color us = side_to_move();
977 Color them = opposite_color(us);
979 // Reset capture field
980 st->capture = NO_PIECE_TYPE;
982 // Find source squares for king and rook
983 Square kfrom = move_from(m);
984 Square rfrom = move_to(m); // HACK: See comment at beginning of function
987 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
988 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
990 // Find destination squares for king and rook
991 if (rfrom > kfrom) // O-O
993 kto = relative_square(us, SQ_G1);
994 rto = relative_square(us, SQ_F1);
996 kto = relative_square(us, SQ_C1);
997 rto = relative_square(us, SQ_D1);
1000 // Remove pieces from source squares:
1001 clear_bit(&(byColorBB[us]), kfrom);
1002 clear_bit(&(byTypeBB[KING]), kfrom);
1003 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1004 clear_bit(&(byColorBB[us]), rfrom);
1005 clear_bit(&(byTypeBB[ROOK]), rfrom);
1006 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1008 // Put pieces on destination squares:
1009 set_bit(&(byColorBB[us]), kto);
1010 set_bit(&(byTypeBB[KING]), kto);
1011 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1012 set_bit(&(byColorBB[us]), rto);
1013 set_bit(&(byTypeBB[ROOK]), rto);
1014 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1016 // Update board array
1017 Piece king = piece_of_color_and_type(us, KING);
1018 Piece rook = piece_of_color_and_type(us, ROOK);
1019 board[kfrom] = board[rfrom] = EMPTY;
1023 // Update piece lists
1024 pieceList[us][KING][index[kfrom]] = kto;
1025 pieceList[us][ROOK][index[rfrom]] = rto;
1026 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1027 index[kto] = index[kfrom];
1030 // Update incremental scores
1031 st->value += Score(pst_delta<MidGame>(king, kfrom, kto), pst_delta<EndGame>(king, kfrom, kto));
1032 st->value += Score(pst_delta<MidGame>(rook, rfrom, rto), pst_delta<EndGame>(rook, rfrom, rto));
1035 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1036 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1038 // Clear en passant square
1039 if (st->epSquare != SQ_NONE)
1041 st->key ^= zobEp[st->epSquare];
1042 st->epSquare = SQ_NONE;
1045 // Update castling rights
1046 st->key ^= zobCastle[st->castleRights];
1047 st->castleRights &= castleRightsMask[kfrom];
1048 st->key ^= zobCastle[st->castleRights];
1050 // Reset rule 50 counter
1053 // Update checkers BB
1054 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1057 sideToMove = opposite_color(sideToMove);
1058 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1064 /// Position::undo_move() unmakes a move. When it returns, the position should
1065 /// be restored to exactly the same state as before the move was made.
1067 void Position::undo_move(Move m) {
1070 assert(move_is_ok(m));
1073 sideToMove = opposite_color(sideToMove);
1075 if (move_is_castle(m))
1077 undo_castle_move(m);
1081 Color us = side_to_move();
1082 Color them = opposite_color(us);
1083 Square from = move_from(m);
1084 Square to = move_to(m);
1085 bool ep = move_is_ep(m);
1086 bool pm = move_is_promotion(m);
1088 PieceType pt = type_of_piece_on(to);
1090 assert(square_is_empty(from));
1091 assert(color_of_piece_on(to) == us);
1092 assert(!pm || relative_rank(us, to) == RANK_8);
1093 assert(!ep || to == st->previous->epSquare);
1094 assert(!ep || relative_rank(us, to) == RANK_6);
1095 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1097 if (pm) // promotion ?
1099 PieceType promotion = move_promotion_piece(m);
1102 assert(promotion >= KNIGHT && promotion <= QUEEN);
1103 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1105 // Replace promoted piece with a pawn
1106 clear_bit(&(byTypeBB[promotion]), to);
1107 set_bit(&(byTypeBB[PAWN]), to);
1109 // Update piece counts
1110 pieceCount[us][promotion]--;
1111 pieceCount[us][PAWN]++;
1113 // Update piece list replacing promotion piece with a pawn
1114 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1115 index[lastPromotionSquare] = index[to];
1116 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1117 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1118 index[to] = pieceCount[us][PAWN] - 1;
1119 pieceList[us][PAWN][index[to]] = to;
1123 // Put the piece back at the source square
1124 Bitboard move_bb = make_move_bb(to, from);
1125 do_move_bb(&(byColorBB[us]), move_bb);
1126 do_move_bb(&(byTypeBB[pt]), move_bb);
1127 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1129 board[from] = piece_of_color_and_type(us, pt);
1132 // Update piece list
1133 index[from] = index[to];
1134 pieceList[us][pt][index[from]] = from;
1141 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1143 assert(st->capture != KING);
1144 assert(!ep || square_is_empty(capsq));
1146 // Restore the captured piece
1147 set_bit(&(byColorBB[them]), capsq);
1148 set_bit(&(byTypeBB[st->capture]), capsq);
1149 set_bit(&(byTypeBB[0]), capsq);
1151 board[capsq] = piece_of_color_and_type(them, st->capture);
1153 // Update piece count
1154 pieceCount[them][st->capture]++;
1156 // Update piece list, add a new captured piece in capsq square
1157 index[capsq] = pieceCount[them][st->capture] - 1;
1158 pieceList[them][st->capture][index[capsq]] = capsq;
1161 // Finally point our state pointer back to the previous state
1168 /// Position::undo_castle_move() is a private method used to unmake a castling
1169 /// move. It is called from the main Position::undo_move function. Note that
1170 /// castling moves are encoded as "king captures friendly rook" moves, for
1171 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1173 void Position::undo_castle_move(Move m) {
1175 assert(move_is_ok(m));
1176 assert(move_is_castle(m));
1178 // When we have arrived here, some work has already been done by
1179 // Position::undo_move. In particular, the side to move has been switched,
1180 // so the code below is correct.
1181 Color us = side_to_move();
1183 // Find source squares for king and rook
1184 Square kfrom = move_from(m);
1185 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1188 // Find destination squares for king and rook
1189 if (rfrom > kfrom) // O-O
1191 kto = relative_square(us, SQ_G1);
1192 rto = relative_square(us, SQ_F1);
1194 kto = relative_square(us, SQ_C1);
1195 rto = relative_square(us, SQ_D1);
1198 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1199 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1201 // Remove pieces from destination squares:
1202 clear_bit(&(byColorBB[us]), kto);
1203 clear_bit(&(byTypeBB[KING]), kto);
1204 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1205 clear_bit(&(byColorBB[us]), rto);
1206 clear_bit(&(byTypeBB[ROOK]), rto);
1207 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1209 // Put pieces on source squares:
1210 set_bit(&(byColorBB[us]), kfrom);
1211 set_bit(&(byTypeBB[KING]), kfrom);
1212 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1213 set_bit(&(byColorBB[us]), rfrom);
1214 set_bit(&(byTypeBB[ROOK]), rfrom);
1215 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1218 board[rto] = board[kto] = EMPTY;
1219 board[rfrom] = piece_of_color_and_type(us, ROOK);
1220 board[kfrom] = piece_of_color_and_type(us, KING);
1222 // Update piece lists
1223 pieceList[us][KING][index[kto]] = kfrom;
1224 pieceList[us][ROOK][index[rto]] = rfrom;
1225 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1226 index[kfrom] = index[kto];
1229 // Finally point our state pointer back to the previous state
1236 /// Position::do_null_move makes() a "null move": It switches the side to move
1237 /// and updates the hash key without executing any move on the board.
1239 void Position::do_null_move(StateInfo& backupSt) {
1242 assert(!is_check());
1244 // Back up the information necessary to undo the null move to the supplied
1245 // StateInfo object.
1246 // Note that differently from normal case here backupSt is actually used as
1247 // a backup storage not as a new state to be used.
1248 backupSt.key = st->key;
1249 backupSt.epSquare = st->epSquare;
1250 backupSt.value = st->value;
1251 backupSt.previous = st->previous;
1252 backupSt.pliesFromNull = st->pliesFromNull;
1253 st->previous = &backupSt;
1255 // Save the current key to the history[] array, in order to be able to
1256 // detect repetition draws.
1257 history[gamePly] = st->key;
1259 // Update the necessary information
1260 if (st->epSquare != SQ_NONE)
1261 st->key ^= zobEp[st->epSquare];
1263 st->key ^= zobSideToMove;
1264 TT.prefetch(st->key);
1266 sideToMove = opposite_color(sideToMove);
1267 st->epSquare = SQ_NONE;
1269 st->pliesFromNull = 0;
1270 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1275 /// Position::undo_null_move() unmakes a "null move".
1277 void Position::undo_null_move() {
1280 assert(!is_check());
1282 // Restore information from the our backup StateInfo object
1283 StateInfo* backupSt = st->previous;
1284 st->key = backupSt->key;
1285 st->epSquare = backupSt->epSquare;
1286 st->value = backupSt->value;
1287 st->previous = backupSt->previous;
1288 st->pliesFromNull = backupSt->pliesFromNull;
1290 // Update the necessary information
1291 sideToMove = opposite_color(sideToMove);
1297 /// Position::see() is a static exchange evaluator: It tries to estimate the
1298 /// material gain or loss resulting from a move. There are three versions of
1299 /// this function: One which takes a destination square as input, one takes a
1300 /// move, and one which takes a 'from' and a 'to' square. The function does
1301 /// not yet understand promotions captures.
1303 int Position::see(Square to) const {
1305 assert(square_is_ok(to));
1306 return see(SQ_NONE, to);
1309 int Position::see(Move m) const {
1311 assert(move_is_ok(m));
1312 return see(move_from(m), move_to(m));
1315 int Position::see_sign(Move m) const {
1317 assert(move_is_ok(m));
1319 Square from = move_from(m);
1320 Square to = move_to(m);
1322 // Early return if SEE cannot be negative because capturing piece value
1323 // is not bigger then captured one.
1324 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1325 && type_of_piece_on(from) != KING)
1328 return see(from, to);
1331 int Position::see(Square from, Square to) const {
1334 static const int seeValues[18] = {
1335 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1336 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1337 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1338 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1342 Bitboard attackers, stmAttackers, b;
1344 assert(square_is_ok(from) || from == SQ_NONE);
1345 assert(square_is_ok(to));
1347 // Initialize colors
1348 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1349 Color them = opposite_color(us);
1351 // Initialize pieces
1352 Piece piece = piece_on(from);
1353 Piece capture = piece_on(to);
1354 Bitboard occ = occupied_squares();
1356 // King cannot be recaptured
1357 if (type_of_piece(piece) == KING)
1358 return seeValues[capture];
1360 // Handle en passant moves
1361 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1363 assert(capture == EMPTY);
1365 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1366 capture = piece_on(capQq);
1367 assert(type_of_piece_on(capQq) == PAWN);
1369 // Remove the captured pawn
1370 clear_bit(&occ, capQq);
1375 // Find all attackers to the destination square, with the moving piece
1376 // removed, but possibly an X-ray attacker added behind it.
1377 clear_bit(&occ, from);
1378 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1379 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1380 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1381 | (attacks_from<KING>(to) & pieces(KING))
1382 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1383 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1385 if (from != SQ_NONE)
1388 // If we don't have any attacker we are finished
1389 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1392 // Locate the least valuable attacker to the destination square
1393 // and use it to initialize from square.
1394 stmAttackers = attackers & pieces_of_color(us);
1396 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1399 from = first_1(stmAttackers & pieces(pt));
1400 piece = piece_on(from);
1403 // If the opponent has no attackers we are finished
1404 stmAttackers = attackers & pieces_of_color(them);
1406 return seeValues[capture];
1408 attackers &= occ; // Remove the moving piece
1410 // The destination square is defended, which makes things rather more
1411 // difficult to compute. We proceed by building up a "swap list" containing
1412 // the material gain or loss at each stop in a sequence of captures to the
1413 // destination square, where the sides alternately capture, and always
1414 // capture with the least valuable piece. After each capture, we look for
1415 // new X-ray attacks from behind the capturing piece.
1416 int lastCapturingPieceValue = seeValues[piece];
1417 int swapList[32], n = 1;
1421 swapList[0] = seeValues[capture];
1424 // Locate the least valuable attacker for the side to move. The loop
1425 // below looks like it is potentially infinite, but it isn't. We know
1426 // that the side to move still has at least one attacker left.
1427 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1430 // Remove the attacker we just found from the 'attackers' bitboard,
1431 // and scan for new X-ray attacks behind the attacker.
1432 b = stmAttackers & pieces(pt);
1433 occ ^= (b & (~b + 1));
1434 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1435 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1439 // Add the new entry to the swap list
1441 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1444 // Remember the value of the capturing piece, and change the side to move
1445 // before beginning the next iteration
1446 lastCapturingPieceValue = seeValues[pt];
1447 c = opposite_color(c);
1448 stmAttackers = attackers & pieces_of_color(c);
1450 // Stop after a king capture
1451 if (pt == KING && stmAttackers)
1454 swapList[n++] = QueenValueMidgame*10;
1457 } while (stmAttackers);
1459 // Having built the swap list, we negamax through it to find the best
1460 // achievable score from the point of view of the side to move
1462 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1468 /// Position::saveState() copies the content of the current state
1469 /// inside startState and makes st point to it. This is needed
1470 /// when the st pointee could become stale, as example because
1471 /// the caller is about to going out of scope.
1473 void Position::saveState() {
1477 st->previous = NULL; // as a safe guard
1481 /// Position::clear() erases the position object to a pristine state, with an
1482 /// empty board, white to move, and no castling rights.
1484 void Position::clear() {
1487 memset(st, 0, sizeof(StateInfo));
1488 st->epSquare = SQ_NONE;
1490 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1491 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1492 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1493 memset(index, 0, sizeof(int) * 64);
1495 for (int i = 0; i < 64; i++)
1498 for (int i = 0; i < 8; i++)
1499 for (int j = 0; j < 16; j++)
1500 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1504 initialKFile = FILE_E;
1505 initialKRFile = FILE_H;
1506 initialQRFile = FILE_A;
1510 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1511 /// UCI interface code, whenever a non-reversible move is made in a
1512 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1513 /// for the program to handle games of arbitrary length, as long as the GUI
1514 /// handles draws by the 50 move rule correctly.
1516 void Position::reset_game_ply() {
1522 /// Position::put_piece() puts a piece on the given square of the board,
1523 /// updating the board array, bitboards, and piece counts.
1525 void Position::put_piece(Piece p, Square s) {
1527 Color c = color_of_piece(p);
1528 PieceType pt = type_of_piece(p);
1531 index[s] = pieceCount[c][pt];
1532 pieceList[c][pt][index[s]] = s;
1534 set_bit(&(byTypeBB[pt]), s);
1535 set_bit(&(byColorBB[c]), s);
1536 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1538 pieceCount[c][pt]++;
1542 /// Position::allow_oo() gives the given side the right to castle kingside.
1543 /// Used when setting castling rights during parsing of FEN strings.
1545 void Position::allow_oo(Color c) {
1547 st->castleRights |= (1 + int(c));
1551 /// Position::allow_ooo() gives the given side the right to castle queenside.
1552 /// Used when setting castling rights during parsing of FEN strings.
1554 void Position::allow_ooo(Color c) {
1556 st->castleRights |= (4 + 4*int(c));
1560 /// Position::compute_key() computes the hash key of the position. The hash
1561 /// key is usually updated incrementally as moves are made and unmade, the
1562 /// compute_key() function is only used when a new position is set up, and
1563 /// to verify the correctness of the hash key when running in debug mode.
1565 Key Position::compute_key() const {
1567 Key result = Key(0ULL);
1569 for (Square s = SQ_A1; s <= SQ_H8; s++)
1570 if (square_is_occupied(s))
1571 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1573 if (ep_square() != SQ_NONE)
1574 result ^= zobEp[ep_square()];
1576 result ^= zobCastle[st->castleRights];
1577 if (side_to_move() == BLACK)
1578 result ^= zobSideToMove;
1584 /// Position::compute_pawn_key() computes the hash key of the position. The
1585 /// hash key is usually updated incrementally as moves are made and unmade,
1586 /// the compute_pawn_key() function is only used when a new position is set
1587 /// up, and to verify the correctness of the pawn hash key when running in
1590 Key Position::compute_pawn_key() const {
1592 Key result = Key(0ULL);
1596 for (Color c = WHITE; c <= BLACK; c++)
1598 b = pieces(PAWN, c);
1601 s = pop_1st_bit(&b);
1602 result ^= zobrist[c][PAWN][s];
1609 /// Position::compute_material_key() computes the hash key of the position.
1610 /// The hash key is usually updated incrementally as moves are made and unmade,
1611 /// the compute_material_key() function is only used when a new position is set
1612 /// up, and to verify the correctness of the material hash key when running in
1615 Key Position::compute_material_key() const {
1617 Key result = Key(0ULL);
1618 for (Color c = WHITE; c <= BLACK; c++)
1619 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1621 int count = piece_count(c, pt);
1622 for (int i = 0; i <= count; i++)
1623 result ^= zobMaterial[c][pt][i];
1629 /// Position::compute_value() compute the incremental scores for the middle
1630 /// game and the endgame. These functions are used to initialize the incremental
1631 /// scores when a new position is set up, and to verify that the scores are correctly
1632 /// updated by do_move and undo_move when the program is running in debug mode.
1633 template<Position::GamePhase Phase>
1634 Value Position::compute_value() const {
1636 Value result = Value(0);
1640 for (Color c = WHITE; c <= BLACK; c++)
1641 for (PieceType pt = PAWN; pt <= KING; pt++)
1646 s = pop_1st_bit(&b);
1647 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1648 result += pst<Phase>(c, pt, s);
1652 const Value tv = (Phase == MidGame ? TempoValue.mg() : TempoValue.eg());
1653 result += (side_to_move() == WHITE)? tv / 2 : -tv / 2;
1658 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1659 /// game material score for the given side. Material scores are updated
1660 /// incrementally during the search, this function is only used while
1661 /// initializing a new Position object.
1663 Value Position::compute_non_pawn_material(Color c) const {
1665 Value result = Value(0);
1667 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1669 Bitboard b = pieces(pt, c);
1672 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1674 result += piece_value_midgame(pt);
1681 /// Position::is_draw() tests whether the position is drawn by material,
1682 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1683 /// must be done by the search.
1685 bool Position::is_draw() const {
1687 // Draw by material?
1689 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1692 // Draw by the 50 moves rule?
1693 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1696 // Draw by repetition?
1697 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1698 if (history[gamePly - i] == st->key)
1705 /// Position::is_mate() returns true or false depending on whether the
1706 /// side to move is checkmated.
1708 bool Position::is_mate() const {
1710 MoveStack moves[256];
1711 return is_check() && (generate_moves(*this, moves, false) == moves);
1715 /// Position::has_mate_threat() tests whether a given color has a mate in one
1716 /// from the current position.
1718 bool Position::has_mate_threat(Color c) {
1721 Color stm = side_to_move();
1726 // If the input color is not equal to the side to move, do a null move
1730 MoveStack mlist[120];
1731 bool result = false;
1732 Bitboard pinned = pinned_pieces(sideToMove);
1734 // Generate pseudo-legal non-capture and capture check moves
1735 MoveStack* last = generate_non_capture_checks(*this, mlist);
1736 last = generate_captures(*this, last);
1738 // Loop through the moves, and see if one of them is mate
1739 for (MoveStack* cur = mlist; cur != last; cur++)
1741 Move move = cur->move;
1742 if (!pl_move_is_legal(move, pinned))
1752 // Undo null move, if necessary
1760 /// Position::init_zobrist() is a static member function which initializes the
1761 /// various arrays used to compute hash keys.
1763 void Position::init_zobrist() {
1765 for (int i = 0; i < 2; i++)
1766 for (int j = 0; j < 8; j++)
1767 for (int k = 0; k < 64; k++)
1768 zobrist[i][j][k] = Key(genrand_int64());
1770 for (int i = 0; i < 64; i++)
1771 zobEp[i] = Key(genrand_int64());
1773 for (int i = 0; i < 16; i++)
1774 zobCastle[i] = genrand_int64();
1776 zobSideToMove = genrand_int64();
1778 for (int i = 0; i < 2; i++)
1779 for (int j = 0; j < 8; j++)
1780 for (int k = 0; k < 16; k++)
1781 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1783 for (int i = 0; i < 16; i++)
1784 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1788 /// Position::init_piece_square_tables() initializes the piece square tables.
1789 /// This is a two-step operation: First, the white halves of the tables are
1790 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1791 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1792 /// Second, the black halves of the tables are initialized by mirroring
1793 /// and changing the sign of the corresponding white scores.
1795 void Position::init_piece_square_tables() {
1797 int r = get_option_value_int("Randomness"), i;
1798 for (Square s = SQ_A1; s <= SQ_H8; s++)
1799 for (Piece p = WP; p <= WK; p++)
1801 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1802 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1803 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1806 for (Square s = SQ_A1; s <= SQ_H8; s++)
1807 for (Piece p = BP; p <= BK; p++)
1809 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1810 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1815 /// Position::flipped_copy() makes a copy of the input position, but with
1816 /// the white and black sides reversed. This is only useful for debugging,
1817 /// especially for finding evaluation symmetry bugs.
1819 void Position::flipped_copy(const Position& pos) {
1821 assert(pos.is_ok());
1826 for (Square s = SQ_A1; s <= SQ_H8; s++)
1827 if (!pos.square_is_empty(s))
1828 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1831 sideToMove = opposite_color(pos.side_to_move());
1834 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1835 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1836 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1837 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1839 initialKFile = pos.initialKFile;
1840 initialKRFile = pos.initialKRFile;
1841 initialQRFile = pos.initialQRFile;
1843 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1844 castleRightsMask[sq] = ALL_CASTLES;
1846 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1847 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1848 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1849 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1850 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1851 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1853 // En passant square
1854 if (pos.st->epSquare != SQ_NONE)
1855 st->epSquare = flip_square(pos.st->epSquare);
1861 st->key = compute_key();
1862 st->pawnKey = compute_pawn_key();
1863 st->materialKey = compute_material_key();
1865 // Incremental scores
1866 st->value = Score(compute_value<MidGame>(), compute_value<EndGame>());
1869 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1870 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1876 /// Position::is_ok() performs some consitency checks for the position object.
1877 /// This is meant to be helpful when debugging.
1879 bool Position::is_ok(int* failedStep) const {
1881 // What features of the position should be verified?
1882 static const bool debugBitboards = false;
1883 static const bool debugKingCount = false;
1884 static const bool debugKingCapture = false;
1885 static const bool debugCheckerCount = false;
1886 static const bool debugKey = false;
1887 static const bool debugMaterialKey = false;
1888 static const bool debugPawnKey = false;
1889 static const bool debugIncrementalEval = false;
1890 static const bool debugNonPawnMaterial = false;
1891 static const bool debugPieceCounts = false;
1892 static const bool debugPieceList = false;
1894 if (failedStep) *failedStep = 1;
1897 if (!color_is_ok(side_to_move()))
1900 // Are the king squares in the position correct?
1901 if (failedStep) (*failedStep)++;
1902 if (piece_on(king_square(WHITE)) != WK)
1905 if (failedStep) (*failedStep)++;
1906 if (piece_on(king_square(BLACK)) != BK)
1910 if (failedStep) (*failedStep)++;
1911 if (!file_is_ok(initialKRFile))
1914 if (!file_is_ok(initialQRFile))
1917 // Do both sides have exactly one king?
1918 if (failedStep) (*failedStep)++;
1921 int kingCount[2] = {0, 0};
1922 for (Square s = SQ_A1; s <= SQ_H8; s++)
1923 if (type_of_piece_on(s) == KING)
1924 kingCount[color_of_piece_on(s)]++;
1926 if (kingCount[0] != 1 || kingCount[1] != 1)
1930 // Can the side to move capture the opponent's king?
1931 if (failedStep) (*failedStep)++;
1932 if (debugKingCapture)
1934 Color us = side_to_move();
1935 Color them = opposite_color(us);
1936 Square ksq = king_square(them);
1937 if (attackers_to(ksq) & pieces_of_color(us))
1941 // Is there more than 2 checkers?
1942 if (failedStep) (*failedStep)++;
1943 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1947 if (failedStep) (*failedStep)++;
1950 // The intersection of the white and black pieces must be empty
1951 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1954 // The union of the white and black pieces must be equal to all
1956 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1959 // Separate piece type bitboards must have empty intersections
1960 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1961 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1962 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1966 // En passant square OK?
1967 if (failedStep) (*failedStep)++;
1968 if (ep_square() != SQ_NONE)
1970 // The en passant square must be on rank 6, from the point of view of the
1972 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1977 if (failedStep) (*failedStep)++;
1978 if (debugKey && st->key != compute_key())
1981 // Pawn hash key OK?
1982 if (failedStep) (*failedStep)++;
1983 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1986 // Material hash key OK?
1987 if (failedStep) (*failedStep)++;
1988 if (debugMaterialKey && st->materialKey != compute_material_key())
1991 // Incremental eval OK?
1992 if (failedStep) (*failedStep)++;
1993 if (debugIncrementalEval)
1995 if (st->value.mg() != compute_value<MidGame>())
1998 if (st->value.eg() != compute_value<EndGame>())
2002 // Non-pawn material OK?
2003 if (failedStep) (*failedStep)++;
2004 if (debugNonPawnMaterial)
2006 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2009 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2014 if (failedStep) (*failedStep)++;
2015 if (debugPieceCounts)
2016 for (Color c = WHITE; c <= BLACK; c++)
2017 for (PieceType pt = PAWN; pt <= KING; pt++)
2018 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
2021 if (failedStep) (*failedStep)++;
2024 for(Color c = WHITE; c <= BLACK; c++)
2025 for(PieceType pt = PAWN; pt <= KING; pt++)
2026 for(int i = 0; i < pieceCount[c][pt]; i++)
2028 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2031 if (index[piece_list(c, pt, i)] != i)
2035 if (failedStep) *failedStep = 0;