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->mgValue = compute_value<MidGame>();
217 st->egValue = compute_value<EndGame>();
218 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
219 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
223 /// Position::to_fen() converts the position object to a FEN string. This is
224 /// probably only useful for debugging.
226 const string Position::to_fen() const {
228 static const string pieceLetters = " PNBRQK pnbrqk";
232 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
235 for (File file = FILE_A; file <= FILE_H; file++)
237 Square sq = make_square(file, rank);
238 if (!square_is_occupied(sq))
244 fen += (char)skip + '0';
247 fen += pieceLetters[piece_on(sq)];
250 fen += (char)skip + '0';
252 fen += (rank > RANK_1 ? '/' : ' ');
254 fen += (sideToMove == WHITE ? "w " : "b ");
255 if (st->castleRights != NO_CASTLES)
257 if (can_castle_kingside(WHITE)) fen += 'K';
258 if (can_castle_queenside(WHITE)) fen += 'Q';
259 if (can_castle_kingside(BLACK)) fen += 'k';
260 if (can_castle_queenside(BLACK)) fen += 'q';
265 if (ep_square() != SQ_NONE)
266 fen += square_to_string(ep_square());
274 /// Position::print() prints an ASCII representation of the position to
275 /// the standard output. If a move is given then also the san is print.
277 void Position::print(Move m) const {
279 static const string pieceLetters = " PNBRQK PNBRQK .";
281 // Check for reentrancy, as example when called from inside
282 // MovePicker that is used also here in move_to_san()
286 RequestPending = true;
288 std::cout << std::endl;
291 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
292 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
294 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
296 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
297 for (File file = FILE_A; file <= FILE_H; file++)
299 Square sq = make_square(file, rank);
300 Piece piece = piece_on(sq);
301 if (piece == EMPTY && square_color(sq) == WHITE)
304 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
305 std::cout << '|' << col << pieceLetters[piece] << col;
307 std::cout << '|' << std::endl;
309 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
310 << "Fen is: " << to_fen() << std::endl
311 << "Key is: " << st->key << std::endl;
313 RequestPending = false;
317 /// Position::copy() creates a copy of the input position.
319 void Position::copy(const Position& pos) {
321 memcpy(this, &pos, sizeof(Position));
322 saveState(); // detach and copy state info
326 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
327 /// king) pieces for the given color and for the given pinner type. Or, when
328 /// template parameter FindPinned is false, the pieces of the given color
329 /// candidate for a discovery check against the enemy king.
330 /// Note that checkersBB bitboard must be already updated.
332 template<bool FindPinned>
333 Bitboard Position::hidden_checkers(Color c) const {
335 Bitboard pinners, result = EmptyBoardBB;
337 // Pinned pieces protect our king, dicovery checks attack
339 Square ksq = king_square(FindPinned ? c : opposite_color(c));
341 // Pinners are sliders, not checkers, that give check when
342 // candidate pinned is removed.
343 pinners = (pieces(ROOK, QUEEN, FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
344 | (pieces(BISHOP, QUEEN, FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
346 if (FindPinned && pinners)
347 pinners &= ~st->checkersBB;
351 Square s = pop_1st_bit(&pinners);
352 Bitboard b = squares_between(s, ksq) & occupied_squares();
356 if ( !(b & (b - 1)) // Only one bit set?
357 && (b & pieces_of_color(c))) // Is an our piece?
364 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
365 /// king) pieces for the given color.
367 Bitboard Position::pinned_pieces(Color c) const {
369 return hidden_checkers<true>(c);
373 /// Position:discovered_check_candidates() returns a bitboard containing all
374 /// pieces for the given side which are candidates for giving a discovered
377 Bitboard Position::discovered_check_candidates(Color c) const {
379 return hidden_checkers<false>(c);
382 /// Position::attackers_to() computes a bitboard containing all pieces which
383 /// attacks a given square.
385 Bitboard Position::attackers_to(Square s) const {
387 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
388 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
389 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
390 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
391 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
392 | (attacks_from<KING>(s) & pieces(KING));
395 /// Position::attacks_from() computes a bitboard of all attacks
396 /// of a given piece put in a given square.
398 Bitboard Position::attacks_from(Piece p, Square s) const {
400 assert(square_is_ok(s));
404 case WP: return attacks_from<PAWN>(s, WHITE);
405 case BP: return attacks_from<PAWN>(s, BLACK);
406 case WN: case BN: return attacks_from<KNIGHT>(s);
407 case WB: case BB: return attacks_from<BISHOP>(s);
408 case WR: case BR: return attacks_from<ROOK>(s);
409 case WQ: case BQ: return attacks_from<QUEEN>(s);
410 case WK: case BK: return attacks_from<KING>(s);
417 /// Position::move_attacks_square() tests whether a move from the current
418 /// position attacks a given square.
420 bool Position::move_attacks_square(Move m, Square s) const {
422 assert(move_is_ok(m));
423 assert(square_is_ok(s));
425 Square f = move_from(m), t = move_to(m);
427 assert(square_is_occupied(f));
429 if (bit_is_set(attacks_from(piece_on(f), t), s))
432 // Move the piece and scan for X-ray attacks behind it
433 Bitboard occ = occupied_squares();
434 Color us = color_of_piece_on(f);
437 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
438 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
440 // If we have attacks we need to verify that are caused by our move
441 // and are not already existent ones.
442 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
446 /// Position::find_checkers() computes the checkersBB bitboard, which
447 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
448 /// currently works by calling Position::attackers_to, which is probably
449 /// inefficient. Consider rewriting this function to use the last move
450 /// played, like in non-bitboard versions of Glaurung.
452 void Position::find_checkers() {
454 Color us = side_to_move();
455 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
459 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
461 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
464 assert(move_is_ok(m));
465 assert(pinned == pinned_pieces(side_to_move()));
467 // Castling moves are checked for legality during move generation.
468 if (move_is_castle(m))
471 Color us = side_to_move();
472 Square from = move_from(m);
474 assert(color_of_piece_on(from) == us);
475 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
477 // En passant captures are a tricky special case. Because they are
478 // rather uncommon, we do it simply by testing whether the king is attacked
479 // after the move is made
482 Color them = opposite_color(us);
483 Square to = move_to(m);
484 Square capsq = make_square(square_file(to), square_rank(from));
485 Bitboard b = occupied_squares();
486 Square ksq = king_square(us);
488 assert(to == ep_square());
489 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
490 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
491 assert(piece_on(to) == EMPTY);
494 clear_bit(&b, capsq);
497 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
498 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
501 // If the moving piece is a king, check whether the destination
502 // square is attacked by the opponent.
503 if (type_of_piece_on(from) == KING)
504 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
506 // A non-king move is legal if and only if it is not pinned or it
507 // is moving along the ray towards or away from the king.
509 || !bit_is_set(pinned, from)
510 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
514 /// Position::move_is_check() tests whether a pseudo-legal move is a check
516 bool Position::move_is_check(Move m) const {
518 Bitboard dc = discovered_check_candidates(side_to_move());
519 return move_is_check(m, dc);
522 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
525 assert(move_is_ok(m));
526 assert(dcCandidates == discovered_check_candidates(side_to_move()));
528 Color us = side_to_move();
529 Color them = opposite_color(us);
530 Square from = move_from(m);
531 Square to = move_to(m);
532 Square ksq = king_square(them);
534 assert(color_of_piece_on(from) == us);
535 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
537 // Proceed according to the type of the moving piece
538 switch (type_of_piece_on(from))
542 if (bit_is_set(attacks_from<PAWN>(ksq, them), to)) // Normal check?
545 if ( dcCandidates // Discovered check?
546 && bit_is_set(dcCandidates, from)
547 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
550 if (move_is_promotion(m)) // Promotion with check?
552 Bitboard b = occupied_squares();
555 switch (move_promotion_piece(m))
558 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
560 return bit_is_set(bishop_attacks_bb(to, b), ksq);
562 return bit_is_set(rook_attacks_bb(to, b), ksq);
564 return bit_is_set(queen_attacks_bb(to, b), ksq);
569 // En passant capture with check? We have already handled the case
570 // of direct checks and ordinary discovered check, the only case we
571 // need to handle is the unusual case of a discovered check through the
573 else if (move_is_ep(m))
575 Square capsq = make_square(square_file(to), square_rank(from));
576 Bitboard b = occupied_squares();
578 clear_bit(&b, capsq);
580 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
581 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
585 // Test discovered check and normal check according to piece type
587 return (dcCandidates && bit_is_set(dcCandidates, from))
588 || bit_is_set(attacks_from<KNIGHT>(ksq), to);
591 return (dcCandidates && bit_is_set(dcCandidates, from))
592 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to));
595 return (dcCandidates && bit_is_set(dcCandidates, from))
596 || (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to));
599 // Discovered checks are impossible!
600 assert(!bit_is_set(dcCandidates, from));
601 return ( (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to))
602 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to)));
606 if ( bit_is_set(dcCandidates, from)
607 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
610 // Castling with check?
611 if (move_is_castle(m))
613 Square kfrom, kto, rfrom, rto;
614 Bitboard b = occupied_squares();
620 kto = relative_square(us, SQ_G1);
621 rto = relative_square(us, SQ_F1);
623 kto = relative_square(us, SQ_C1);
624 rto = relative_square(us, SQ_D1);
626 clear_bit(&b, kfrom);
627 clear_bit(&b, rfrom);
630 return bit_is_set(rook_attacks_bb(rto, b), ksq);
634 default: // NO_PIECE_TYPE
642 /// Position::update_checkers() udpates chekers info given the move. It is called
643 /// in do_move() and is faster then find_checkers().
645 template<PieceType Piece>
646 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
647 Square to, Bitboard dcCandidates) {
649 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
650 const bool Rook = (Piece == QUEEN || Piece == ROOK);
651 const bool Slider = Bishop || Rook;
654 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
655 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
656 && bit_is_set(attacks_from<Piece>(ksq), to)) // slow, try to early skip
657 set_bit(pCheckersBB, to);
659 else if ( Piece != KING
661 && bit_is_set(Piece == PAWN ? attacks_from<PAWN>(ksq, opposite_color(sideToMove))
662 : attacks_from<Piece>(ksq), to))
663 set_bit(pCheckersBB, to);
666 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
669 (*pCheckersBB) |= (attacks_from<ROOK>(ksq) & pieces(ROOK, QUEEN, side_to_move()));
672 (*pCheckersBB) |= (attacks_from<BISHOP>(ksq) & pieces(BISHOP, QUEEN, side_to_move()));
677 /// Position::do_move() makes a move, and saves all information necessary
678 /// to a StateInfo object. The move is assumed to be legal.
679 /// Pseudo-legal moves should be filtered out before this function is called.
681 void Position::do_move(Move m, StateInfo& newSt) {
683 do_move(m, newSt, discovered_check_candidates(side_to_move()));
686 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
689 assert(move_is_ok(m));
691 Bitboard key = st->key;
693 // Copy some fields of old state to our new StateInfo object except the
694 // ones which are recalculated from scratch anyway, then switch our state
695 // pointer to point to the new, ready to be updated, state.
696 struct ReducedStateInfo {
697 Key key, pawnKey, materialKey;
698 int castleRights, rule50, pliesFromNull;
700 Value mgValue, egValue;
704 memcpy(&newSt, st, sizeof(ReducedStateInfo));
708 // Save the current key to the history[] array, in order to be able to
709 // detect repetition draws.
710 history[gamePly] = key;
713 // Update side to move
714 key ^= zobSideToMove;
716 // Increment the 50 moves rule draw counter. Resetting it to zero in the
717 // case of non-reversible moves is taken care of later.
721 if (move_is_castle(m))
728 Color us = side_to_move();
729 Color them = opposite_color(us);
730 Square from = move_from(m);
731 Square to = move_to(m);
732 bool ep = move_is_ep(m);
733 bool pm = move_is_promotion(m);
735 Piece piece = piece_on(from);
736 PieceType pt = type_of_piece(piece);
738 assert(color_of_piece_on(from) == us);
739 assert(color_of_piece_on(to) == them || square_is_empty(to));
740 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
741 assert(!pm || relative_rank(us, to) == RANK_8);
743 st->capture = ep ? PAWN : type_of_piece_on(to);
746 do_capture_move(key, st->capture, them, to, ep);
749 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
751 // Reset en passant square
752 if (st->epSquare != SQ_NONE)
754 key ^= zobEp[st->epSquare];
755 st->epSquare = SQ_NONE;
758 // Update castle rights, try to shortcut a common case
759 int cm = castleRightsMask[from] & castleRightsMask[to];
760 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
762 key ^= zobCastle[st->castleRights];
763 st->castleRights &= castleRightsMask[from];
764 st->castleRights &= castleRightsMask[to];
765 key ^= zobCastle[st->castleRights];
768 // Prefetch TT access as soon as we know key is updated
772 Bitboard move_bb = make_move_bb(from, to);
773 do_move_bb(&(byColorBB[us]), move_bb);
774 do_move_bb(&(byTypeBB[pt]), move_bb);
775 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
777 board[to] = board[from];
780 // Update piece lists, note that index[from] is not updated and
781 // becomes stale. This works as long as index[] is accessed just
782 // by known occupied squares.
783 index[to] = index[from];
784 pieceList[us][pt][index[to]] = to;
786 // If the moving piece was a pawn do some special extra work
789 // Reset rule 50 draw counter
792 // Update pawn hash key
793 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
795 // Set en passant square, only if moved pawn can be captured
796 if (abs(int(to) - int(from)) == 16)
798 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
800 st->epSquare = Square((int(from) + int(to)) / 2);
801 key ^= zobEp[st->epSquare];
806 // Update incremental scores
807 st->mgValue += pst_delta<MidGame>(piece, from, to);
808 st->egValue += pst_delta<EndGame>(piece, from, to);
810 if (pm) // promotion ?
812 PieceType promotion = move_promotion_piece(m);
814 assert(promotion >= KNIGHT && promotion <= QUEEN);
816 // Insert promoted piece instead of pawn
817 clear_bit(&(byTypeBB[PAWN]), to);
818 set_bit(&(byTypeBB[promotion]), to);
819 board[to] = piece_of_color_and_type(us, promotion);
821 // Update material key
822 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
823 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
825 // Update piece counts
826 pieceCount[us][PAWN]--;
827 pieceCount[us][promotion]++;
829 // Update piece lists, move the last pawn at index[to] position
830 // and shrink the list. Add a new promotion piece to the list.
831 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
832 index[lastPawnSquare] = index[to];
833 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
834 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
835 index[to] = pieceCount[us][promotion] - 1;
836 pieceList[us][promotion][index[to]] = to;
838 // Partially revert hash keys update
839 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
840 st->pawnKey ^= zobrist[us][PAWN][to];
842 // Partially revert and update incremental scores
843 st->mgValue -= pst<MidGame>(us, PAWN, to);
844 st->mgValue += pst<MidGame>(us, promotion, to);
845 st->egValue -= pst<EndGame>(us, PAWN, to);
846 st->egValue += pst<EndGame>(us, promotion, to);
849 st->npMaterial[us] += piece_value_midgame(promotion);
852 // Update the key with the final value
855 // Update checkers bitboard, piece must be already moved
857 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
860 st->checkersBB = EmptyBoardBB;
861 Square ksq = king_square(them);
864 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
865 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
866 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
867 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
868 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
869 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
870 default: assert(false); break;
875 sideToMove = opposite_color(sideToMove);
877 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
878 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
884 /// Position::do_capture_move() is a private method used to update captured
885 /// piece info. It is called from the main Position::do_move function.
887 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
889 assert(capture != KING);
893 if (ep) // en passant ?
895 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
897 assert(to == st->epSquare);
898 assert(relative_rank(opposite_color(them), to) == RANK_6);
899 assert(piece_on(to) == EMPTY);
900 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
902 board[capsq] = EMPTY;
905 // Remove captured piece
906 clear_bit(&(byColorBB[them]), capsq);
907 clear_bit(&(byTypeBB[capture]), capsq);
908 clear_bit(&(byTypeBB[0]), capsq);
911 key ^= zobrist[them][capture][capsq];
913 // Update incremental scores
914 st->mgValue -= pst<MidGame>(them, capture, capsq);
915 st->egValue -= pst<EndGame>(them, capture, capsq);
917 // If the captured piece was a pawn, update pawn hash key,
918 // otherwise update non-pawn material.
920 st->pawnKey ^= zobrist[them][PAWN][capsq];
922 st->npMaterial[them] -= piece_value_midgame(capture);
924 // Update material hash key
925 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
927 // Update piece count
928 pieceCount[them][capture]--;
930 // Update piece list, move the last piece at index[capsq] position
932 // WARNING: This is a not perfectly revresible operation. When we
933 // will reinsert the captured piece in undo_move() we will put it
934 // at the end of the list and not in its original place, it means
935 // index[] and pieceList[] are not guaranteed to be invariant to a
936 // do_move() + undo_move() sequence.
937 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
938 index[lastPieceSquare] = index[capsq];
939 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
940 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
942 // Reset rule 50 counter
947 /// Position::do_castle_move() is a private method used to make a castling
948 /// move. It is called from the main Position::do_move function. Note that
949 /// castling moves are encoded as "king captures friendly rook" moves, for
950 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
952 void Position::do_castle_move(Move m) {
954 assert(move_is_ok(m));
955 assert(move_is_castle(m));
957 Color us = side_to_move();
958 Color them = opposite_color(us);
960 // Reset capture field
961 st->capture = NO_PIECE_TYPE;
963 // Find source squares for king and rook
964 Square kfrom = move_from(m);
965 Square rfrom = move_to(m); // HACK: See comment at beginning of function
968 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
969 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
971 // Find destination squares for king and rook
972 if (rfrom > kfrom) // O-O
974 kto = relative_square(us, SQ_G1);
975 rto = relative_square(us, SQ_F1);
977 kto = relative_square(us, SQ_C1);
978 rto = relative_square(us, SQ_D1);
981 // Remove pieces from source squares:
982 clear_bit(&(byColorBB[us]), kfrom);
983 clear_bit(&(byTypeBB[KING]), kfrom);
984 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
985 clear_bit(&(byColorBB[us]), rfrom);
986 clear_bit(&(byTypeBB[ROOK]), rfrom);
987 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
989 // Put pieces on destination squares:
990 set_bit(&(byColorBB[us]), kto);
991 set_bit(&(byTypeBB[KING]), kto);
992 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
993 set_bit(&(byColorBB[us]), rto);
994 set_bit(&(byTypeBB[ROOK]), rto);
995 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
997 // Update board array
998 Piece king = piece_of_color_and_type(us, KING);
999 Piece rook = piece_of_color_and_type(us, ROOK);
1000 board[kfrom] = board[rfrom] = EMPTY;
1004 // Update piece lists
1005 pieceList[us][KING][index[kfrom]] = kto;
1006 pieceList[us][ROOK][index[rfrom]] = rto;
1007 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1008 index[kto] = index[kfrom];
1011 // Update incremental scores
1012 st->mgValue += pst_delta<MidGame>(king, kfrom, kto);
1013 st->egValue += pst_delta<EndGame>(king, kfrom, kto);
1014 st->mgValue += pst_delta<MidGame>(rook, rfrom, rto);
1015 st->egValue += pst_delta<EndGame>(rook, rfrom, rto);
1018 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1019 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1021 // Clear en passant square
1022 if (st->epSquare != SQ_NONE)
1024 st->key ^= zobEp[st->epSquare];
1025 st->epSquare = SQ_NONE;
1028 // Update castling rights
1029 st->key ^= zobCastle[st->castleRights];
1030 st->castleRights &= castleRightsMask[kfrom];
1031 st->key ^= zobCastle[st->castleRights];
1033 // Reset rule 50 counter
1036 // Update checkers BB
1037 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1040 sideToMove = opposite_color(sideToMove);
1042 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1043 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1049 /// Position::undo_move() unmakes a move. When it returns, the position should
1050 /// be restored to exactly the same state as before the move was made.
1052 void Position::undo_move(Move m) {
1055 assert(move_is_ok(m));
1058 sideToMove = opposite_color(sideToMove);
1060 if (move_is_castle(m))
1062 undo_castle_move(m);
1066 Color us = side_to_move();
1067 Color them = opposite_color(us);
1068 Square from = move_from(m);
1069 Square to = move_to(m);
1070 bool ep = move_is_ep(m);
1071 bool pm = move_is_promotion(m);
1073 PieceType pt = type_of_piece_on(to);
1075 assert(square_is_empty(from));
1076 assert(color_of_piece_on(to) == us);
1077 assert(!pm || relative_rank(us, to) == RANK_8);
1078 assert(!ep || to == st->previous->epSquare);
1079 assert(!ep || relative_rank(us, to) == RANK_6);
1080 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1082 if (pm) // promotion ?
1084 PieceType promotion = move_promotion_piece(m);
1087 assert(promotion >= KNIGHT && promotion <= QUEEN);
1088 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1090 // Replace promoted piece with a pawn
1091 clear_bit(&(byTypeBB[promotion]), to);
1092 set_bit(&(byTypeBB[PAWN]), to);
1094 // Update piece counts
1095 pieceCount[us][promotion]--;
1096 pieceCount[us][PAWN]++;
1098 // Update piece list replacing promotion piece with a pawn
1099 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1100 index[lastPromotionSquare] = index[to];
1101 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1102 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1103 index[to] = pieceCount[us][PAWN] - 1;
1104 pieceList[us][PAWN][index[to]] = to;
1108 // Put the piece back at the source square
1109 Bitboard move_bb = make_move_bb(to, from);
1110 do_move_bb(&(byColorBB[us]), move_bb);
1111 do_move_bb(&(byTypeBB[pt]), move_bb);
1112 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1114 board[from] = piece_of_color_and_type(us, pt);
1117 // Update piece list
1118 index[from] = index[to];
1119 pieceList[us][pt][index[from]] = from;
1126 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1128 assert(st->capture != KING);
1129 assert(!ep || square_is_empty(capsq));
1131 // Restore the captured piece
1132 set_bit(&(byColorBB[them]), capsq);
1133 set_bit(&(byTypeBB[st->capture]), capsq);
1134 set_bit(&(byTypeBB[0]), capsq);
1136 board[capsq] = piece_of_color_and_type(them, st->capture);
1138 // Update piece count
1139 pieceCount[them][st->capture]++;
1141 // Update piece list, add a new captured piece in capsq square
1142 index[capsq] = pieceCount[them][st->capture] - 1;
1143 pieceList[them][st->capture][index[capsq]] = capsq;
1146 // Finally point our state pointer back to the previous state
1153 /// Position::undo_castle_move() is a private method used to unmake a castling
1154 /// move. It is called from the main Position::undo_move function. Note that
1155 /// castling moves are encoded as "king captures friendly rook" moves, for
1156 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1158 void Position::undo_castle_move(Move m) {
1160 assert(move_is_ok(m));
1161 assert(move_is_castle(m));
1163 // When we have arrived here, some work has already been done by
1164 // Position::undo_move. In particular, the side to move has been switched,
1165 // so the code below is correct.
1166 Color us = side_to_move();
1168 // Find source squares for king and rook
1169 Square kfrom = move_from(m);
1170 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1173 // Find destination squares for king and rook
1174 if (rfrom > kfrom) // O-O
1176 kto = relative_square(us, SQ_G1);
1177 rto = relative_square(us, SQ_F1);
1179 kto = relative_square(us, SQ_C1);
1180 rto = relative_square(us, SQ_D1);
1183 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1184 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1186 // Remove pieces from destination squares:
1187 clear_bit(&(byColorBB[us]), kto);
1188 clear_bit(&(byTypeBB[KING]), kto);
1189 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1190 clear_bit(&(byColorBB[us]), rto);
1191 clear_bit(&(byTypeBB[ROOK]), rto);
1192 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1194 // Put pieces on source squares:
1195 set_bit(&(byColorBB[us]), kfrom);
1196 set_bit(&(byTypeBB[KING]), kfrom);
1197 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1198 set_bit(&(byColorBB[us]), rfrom);
1199 set_bit(&(byTypeBB[ROOK]), rfrom);
1200 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1203 board[rto] = board[kto] = EMPTY;
1204 board[rfrom] = piece_of_color_and_type(us, ROOK);
1205 board[kfrom] = piece_of_color_and_type(us, KING);
1207 // Update piece lists
1208 pieceList[us][KING][index[kto]] = kfrom;
1209 pieceList[us][ROOK][index[rto]] = rfrom;
1210 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1211 index[kfrom] = index[kto];
1214 // Finally point our state pointer back to the previous state
1221 /// Position::do_null_move makes() a "null move": It switches the side to move
1222 /// and updates the hash key without executing any move on the board.
1224 void Position::do_null_move(StateInfo& backupSt) {
1227 assert(!is_check());
1229 // Back up the information necessary to undo the null move to the supplied
1230 // StateInfo object.
1231 // Note that differently from normal case here backupSt is actually used as
1232 // a backup storage not as a new state to be used.
1233 backupSt.key = st->key;
1234 backupSt.epSquare = st->epSquare;
1235 backupSt.mgValue = st->mgValue;
1236 backupSt.egValue = st->egValue;
1237 backupSt.previous = st->previous;
1238 backupSt.pliesFromNull = st->pliesFromNull;
1239 st->previous = &backupSt;
1241 // Save the current key to the history[] array, in order to be able to
1242 // detect repetition draws.
1243 history[gamePly] = st->key;
1245 // Update the necessary information
1246 if (st->epSquare != SQ_NONE)
1247 st->key ^= zobEp[st->epSquare];
1249 st->key ^= zobSideToMove;
1250 TT.prefetch(st->key);
1252 sideToMove = opposite_color(sideToMove);
1253 st->epSquare = SQ_NONE;
1255 st->pliesFromNull = 0;
1258 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1259 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1263 /// Position::undo_null_move() unmakes a "null move".
1265 void Position::undo_null_move() {
1268 assert(!is_check());
1270 // Restore information from the our backup StateInfo object
1271 StateInfo* backupSt = st->previous;
1272 st->key = backupSt->key;
1273 st->epSquare = backupSt->epSquare;
1274 st->mgValue = backupSt->mgValue;
1275 st->egValue = backupSt->egValue;
1276 st->previous = backupSt->previous;
1277 st->pliesFromNull = backupSt->pliesFromNull;
1279 // Update the necessary information
1280 sideToMove = opposite_color(sideToMove);
1286 /// Position::see() is a static exchange evaluator: It tries to estimate the
1287 /// material gain or loss resulting from a move. There are three versions of
1288 /// this function: One which takes a destination square as input, one takes a
1289 /// move, and one which takes a 'from' and a 'to' square. The function does
1290 /// not yet understand promotions captures.
1292 int Position::see(Square to) const {
1294 assert(square_is_ok(to));
1295 return see(SQ_NONE, to);
1298 int Position::see(Move m) const {
1300 assert(move_is_ok(m));
1301 return see(move_from(m), move_to(m));
1304 int Position::see_sign(Move m) const {
1306 assert(move_is_ok(m));
1308 Square from = move_from(m);
1309 Square to = move_to(m);
1311 // Early return if SEE cannot be negative because capturing piece value
1312 // is not bigger then captured one.
1313 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1314 && type_of_piece_on(from) != KING)
1317 return see(from, to);
1320 int Position::see(Square from, Square to) const {
1323 static const int seeValues[18] = {
1324 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1325 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1326 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1327 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1331 Bitboard attackers, stmAttackers, b;
1333 assert(square_is_ok(from) || from == SQ_NONE);
1334 assert(square_is_ok(to));
1336 // Initialize colors
1337 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1338 Color them = opposite_color(us);
1340 // Initialize pieces
1341 Piece piece = piece_on(from);
1342 Piece capture = piece_on(to);
1343 Bitboard occ = occupied_squares();
1345 // King cannot be recaptured
1346 if (type_of_piece(piece) == KING)
1347 return seeValues[capture];
1349 // Handle en passant moves
1350 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1352 assert(capture == EMPTY);
1354 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1355 capture = piece_on(capQq);
1356 assert(type_of_piece_on(capQq) == PAWN);
1358 // Remove the captured pawn
1359 clear_bit(&occ, capQq);
1364 // Find all attackers to the destination square, with the moving piece
1365 // removed, but possibly an X-ray attacker added behind it.
1366 clear_bit(&occ, from);
1367 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1368 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1369 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1370 | (attacks_from<KING>(to) & pieces(KING))
1371 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1372 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1374 if (from != SQ_NONE)
1377 // If we don't have any attacker we are finished
1378 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1381 // Locate the least valuable attacker to the destination square
1382 // and use it to initialize from square.
1383 stmAttackers = attackers & pieces_of_color(us);
1385 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1388 from = first_1(stmAttackers & pieces(pt));
1389 piece = piece_on(from);
1392 // If the opponent has no attackers we are finished
1393 stmAttackers = attackers & pieces_of_color(them);
1395 return seeValues[capture];
1397 attackers &= occ; // Remove the moving piece
1399 // The destination square is defended, which makes things rather more
1400 // difficult to compute. We proceed by building up a "swap list" containing
1401 // the material gain or loss at each stop in a sequence of captures to the
1402 // destination square, where the sides alternately capture, and always
1403 // capture with the least valuable piece. After each capture, we look for
1404 // new X-ray attacks from behind the capturing piece.
1405 int lastCapturingPieceValue = seeValues[piece];
1406 int swapList[32], n = 1;
1410 swapList[0] = seeValues[capture];
1413 // Locate the least valuable attacker for the side to move. The loop
1414 // below looks like it is potentially infinite, but it isn't. We know
1415 // that the side to move still has at least one attacker left.
1416 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1419 // Remove the attacker we just found from the 'attackers' bitboard,
1420 // and scan for new X-ray attacks behind the attacker.
1421 b = stmAttackers & pieces(pt);
1422 occ ^= (b & (~b + 1));
1423 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1424 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1428 // Add the new entry to the swap list
1430 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1433 // Remember the value of the capturing piece, and change the side to move
1434 // before beginning the next iteration
1435 lastCapturingPieceValue = seeValues[pt];
1436 c = opposite_color(c);
1437 stmAttackers = attackers & pieces_of_color(c);
1439 // Stop after a king capture
1440 if (pt == KING && stmAttackers)
1443 swapList[n++] = QueenValueMidgame*10;
1446 } while (stmAttackers);
1448 // Having built the swap list, we negamax through it to find the best
1449 // achievable score from the point of view of the side to move
1451 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1457 /// Position::saveState() copies the content of the current state
1458 /// inside startState and makes st point to it. This is needed
1459 /// when the st pointee could become stale, as example because
1460 /// the caller is about to going out of scope.
1462 void Position::saveState() {
1466 st->previous = NULL; // as a safe guard
1470 /// Position::clear() erases the position object to a pristine state, with an
1471 /// empty board, white to move, and no castling rights.
1473 void Position::clear() {
1476 memset(st, 0, sizeof(StateInfo));
1477 st->epSquare = SQ_NONE;
1479 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1480 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1481 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1482 memset(index, 0, sizeof(int) * 64);
1484 for (int i = 0; i < 64; i++)
1487 for (int i = 0; i < 8; i++)
1488 for (int j = 0; j < 16; j++)
1489 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1493 initialKFile = FILE_E;
1494 initialKRFile = FILE_H;
1495 initialQRFile = FILE_A;
1499 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1500 /// UCI interface code, whenever a non-reversible move is made in a
1501 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1502 /// for the program to handle games of arbitrary length, as long as the GUI
1503 /// handles draws by the 50 move rule correctly.
1505 void Position::reset_game_ply() {
1511 /// Position::put_piece() puts a piece on the given square of the board,
1512 /// updating the board array, bitboards, and piece counts.
1514 void Position::put_piece(Piece p, Square s) {
1516 Color c = color_of_piece(p);
1517 PieceType pt = type_of_piece(p);
1520 index[s] = pieceCount[c][pt];
1521 pieceList[c][pt][index[s]] = s;
1523 set_bit(&(byTypeBB[pt]), s);
1524 set_bit(&(byColorBB[c]), s);
1525 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1527 pieceCount[c][pt]++;
1531 /// Position::allow_oo() gives the given side the right to castle kingside.
1532 /// Used when setting castling rights during parsing of FEN strings.
1534 void Position::allow_oo(Color c) {
1536 st->castleRights |= (1 + int(c));
1540 /// Position::allow_ooo() gives the given side the right to castle queenside.
1541 /// Used when setting castling rights during parsing of FEN strings.
1543 void Position::allow_ooo(Color c) {
1545 st->castleRights |= (4 + 4*int(c));
1549 /// Position::compute_key() computes the hash key of the position. The hash
1550 /// key is usually updated incrementally as moves are made and unmade, the
1551 /// compute_key() function is only used when a new position is set up, and
1552 /// to verify the correctness of the hash key when running in debug mode.
1554 Key Position::compute_key() const {
1556 Key result = Key(0ULL);
1558 for (Square s = SQ_A1; s <= SQ_H8; s++)
1559 if (square_is_occupied(s))
1560 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1562 if (ep_square() != SQ_NONE)
1563 result ^= zobEp[ep_square()];
1565 result ^= zobCastle[st->castleRights];
1566 if (side_to_move() == BLACK)
1567 result ^= zobSideToMove;
1573 /// Position::compute_pawn_key() computes the hash key of the position. The
1574 /// hash key is usually updated incrementally as moves are made and unmade,
1575 /// the compute_pawn_key() function is only used when a new position is set
1576 /// up, and to verify the correctness of the pawn hash key when running in
1579 Key Position::compute_pawn_key() const {
1581 Key result = Key(0ULL);
1585 for (Color c = WHITE; c <= BLACK; c++)
1587 b = pieces(PAWN, c);
1590 s = pop_1st_bit(&b);
1591 result ^= zobrist[c][PAWN][s];
1598 /// Position::compute_material_key() computes the hash key of the position.
1599 /// The hash key is usually updated incrementally as moves are made and unmade,
1600 /// the compute_material_key() function is only used when a new position is set
1601 /// up, and to verify the correctness of the material hash key when running in
1604 Key Position::compute_material_key() const {
1606 Key result = Key(0ULL);
1607 for (Color c = WHITE; c <= BLACK; c++)
1608 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1610 int count = piece_count(c, pt);
1611 for (int i = 0; i <= count; i++)
1612 result ^= zobMaterial[c][pt][i];
1618 /// Position::compute_value() compute the incremental scores for the middle
1619 /// game and the endgame. These functions are used to initialize the incremental
1620 /// scores when a new position is set up, and to verify that the scores are correctly
1621 /// updated by do_move and undo_move when the program is running in debug mode.
1622 template<Position::GamePhase Phase>
1623 Value Position::compute_value() const {
1625 Value result = Value(0);
1629 for (Color c = WHITE; c <= BLACK; c++)
1630 for (PieceType pt = PAWN; pt <= KING; pt++)
1635 s = pop_1st_bit(&b);
1636 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1637 result += pst<Phase>(c, pt, s);
1641 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1642 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1647 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1648 /// game material score for the given side. Material scores are updated
1649 /// incrementally during the search, this function is only used while
1650 /// initializing a new Position object.
1652 Value Position::compute_non_pawn_material(Color c) const {
1654 Value result = Value(0);
1656 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1658 Bitboard b = pieces(pt, c);
1661 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1663 result += piece_value_midgame(pt);
1670 /// Position::is_draw() tests whether the position is drawn by material,
1671 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1672 /// must be done by the search.
1674 bool Position::is_draw() const {
1676 // Draw by material?
1678 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1681 // Draw by the 50 moves rule?
1682 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1685 // Draw by repetition?
1686 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1687 if (history[gamePly - i] == st->key)
1694 /// Position::is_mate() returns true or false depending on whether the
1695 /// side to move is checkmated.
1697 bool Position::is_mate() const {
1699 MoveStack moves[256];
1700 return is_check() && (generate_moves(*this, moves, false) == moves);
1704 /// Position::has_mate_threat() tests whether a given color has a mate in one
1705 /// from the current position.
1707 bool Position::has_mate_threat(Color c) {
1710 Color stm = side_to_move();
1715 // If the input color is not equal to the side to move, do a null move
1719 MoveStack mlist[120];
1720 bool result = false;
1721 Bitboard dc = discovered_check_candidates(sideToMove);
1722 Bitboard pinned = pinned_pieces(sideToMove);
1724 // Generate pseudo-legal non-capture and capture check moves
1725 MoveStack* last = generate_non_capture_checks(*this, mlist, dc);
1726 last = generate_captures(*this, last);
1728 // Loop through the moves, and see if one of them is mate
1729 for (MoveStack* cur = mlist; cur != last; cur++)
1731 Move move = cur->move;
1732 if (!pl_move_is_legal(move, pinned))
1742 // Undo null move, if necessary
1750 /// Position::init_zobrist() is a static member function which initializes the
1751 /// various arrays used to compute hash keys.
1753 void Position::init_zobrist() {
1755 for (int i = 0; i < 2; i++)
1756 for (int j = 0; j < 8; j++)
1757 for (int k = 0; k < 64; k++)
1758 zobrist[i][j][k] = Key(genrand_int64());
1760 for (int i = 0; i < 64; i++)
1761 zobEp[i] = Key(genrand_int64());
1763 for (int i = 0; i < 16; i++)
1764 zobCastle[i] = genrand_int64();
1766 zobSideToMove = genrand_int64();
1768 for (int i = 0; i < 2; i++)
1769 for (int j = 0; j < 8; j++)
1770 for (int k = 0; k < 16; k++)
1771 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1773 for (int i = 0; i < 16; i++)
1774 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1778 /// Position::init_piece_square_tables() initializes the piece square tables.
1779 /// This is a two-step operation: First, the white halves of the tables are
1780 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1781 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1782 /// Second, the black halves of the tables are initialized by mirroring
1783 /// and changing the sign of the corresponding white scores.
1785 void Position::init_piece_square_tables() {
1787 int r = get_option_value_int("Randomness"), i;
1788 for (Square s = SQ_A1; s <= SQ_H8; s++)
1789 for (Piece p = WP; p <= WK; p++)
1791 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1792 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1793 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1796 for (Square s = SQ_A1; s <= SQ_H8; s++)
1797 for (Piece p = BP; p <= BK; p++)
1799 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1800 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1805 /// Position::flipped_copy() makes a copy of the input position, but with
1806 /// the white and black sides reversed. This is only useful for debugging,
1807 /// especially for finding evaluation symmetry bugs.
1809 void Position::flipped_copy(const Position& pos) {
1811 assert(pos.is_ok());
1816 for (Square s = SQ_A1; s <= SQ_H8; s++)
1817 if (!pos.square_is_empty(s))
1818 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1821 sideToMove = opposite_color(pos.side_to_move());
1824 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1825 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1826 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1827 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1829 initialKFile = pos.initialKFile;
1830 initialKRFile = pos.initialKRFile;
1831 initialQRFile = pos.initialQRFile;
1833 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1834 castleRightsMask[sq] = ALL_CASTLES;
1836 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1837 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1838 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1839 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1840 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1841 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1843 // En passant square
1844 if (pos.st->epSquare != SQ_NONE)
1845 st->epSquare = flip_square(pos.st->epSquare);
1851 st->key = compute_key();
1852 st->pawnKey = compute_pawn_key();
1853 st->materialKey = compute_material_key();
1855 // Incremental scores
1856 st->mgValue = compute_value<MidGame>();
1857 st->egValue = compute_value<EndGame>();
1860 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1861 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1867 /// Position::is_ok() performs some consitency checks for the position object.
1868 /// This is meant to be helpful when debugging.
1870 bool Position::is_ok(int* failedStep) const {
1872 // What features of the position should be verified?
1873 static const bool debugBitboards = false;
1874 static const bool debugKingCount = false;
1875 static const bool debugKingCapture = false;
1876 static const bool debugCheckerCount = false;
1877 static const bool debugKey = false;
1878 static const bool debugMaterialKey = false;
1879 static const bool debugPawnKey = false;
1880 static const bool debugIncrementalEval = false;
1881 static const bool debugNonPawnMaterial = false;
1882 static const bool debugPieceCounts = false;
1883 static const bool debugPieceList = false;
1885 if (failedStep) *failedStep = 1;
1888 if (!color_is_ok(side_to_move()))
1891 // Are the king squares in the position correct?
1892 if (failedStep) (*failedStep)++;
1893 if (piece_on(king_square(WHITE)) != WK)
1896 if (failedStep) (*failedStep)++;
1897 if (piece_on(king_square(BLACK)) != BK)
1901 if (failedStep) (*failedStep)++;
1902 if (!file_is_ok(initialKRFile))
1905 if (!file_is_ok(initialQRFile))
1908 // Do both sides have exactly one king?
1909 if (failedStep) (*failedStep)++;
1912 int kingCount[2] = {0, 0};
1913 for (Square s = SQ_A1; s <= SQ_H8; s++)
1914 if (type_of_piece_on(s) == KING)
1915 kingCount[color_of_piece_on(s)]++;
1917 if (kingCount[0] != 1 || kingCount[1] != 1)
1921 // Can the side to move capture the opponent's king?
1922 if (failedStep) (*failedStep)++;
1923 if (debugKingCapture)
1925 Color us = side_to_move();
1926 Color them = opposite_color(us);
1927 Square ksq = king_square(them);
1928 if (attackers_to(ksq) & pieces_of_color(us))
1932 // Is there more than 2 checkers?
1933 if (failedStep) (*failedStep)++;
1934 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1938 if (failedStep) (*failedStep)++;
1941 // The intersection of the white and black pieces must be empty
1942 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1945 // The union of the white and black pieces must be equal to all
1947 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1950 // Separate piece type bitboards must have empty intersections
1951 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1952 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1953 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1957 // En passant square OK?
1958 if (failedStep) (*failedStep)++;
1959 if (ep_square() != SQ_NONE)
1961 // The en passant square must be on rank 6, from the point of view of the
1963 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1968 if (failedStep) (*failedStep)++;
1969 if (debugKey && st->key != compute_key())
1972 // Pawn hash key OK?
1973 if (failedStep) (*failedStep)++;
1974 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1977 // Material hash key OK?
1978 if (failedStep) (*failedStep)++;
1979 if (debugMaterialKey && st->materialKey != compute_material_key())
1982 // Incremental eval OK?
1983 if (failedStep) (*failedStep)++;
1984 if (debugIncrementalEval)
1986 if (st->mgValue != compute_value<MidGame>())
1989 if (st->egValue != compute_value<EndGame>())
1993 // Non-pawn material OK?
1994 if (failedStep) (*failedStep)++;
1995 if (debugNonPawnMaterial)
1997 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2000 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2005 if (failedStep) (*failedStep)++;
2006 if (debugPieceCounts)
2007 for (Color c = WHITE; c <= BLACK; c++)
2008 for (PieceType pt = PAWN; pt <= KING; pt++)
2009 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
2012 if (failedStep) (*failedStep)++;
2015 for(Color c = WHITE; c <= BLACK; c++)
2016 for(PieceType pt = PAWN; pt <= KING; pt++)
2017 for(int i = 0; i < pieceCount[c][pt]; i++)
2019 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2022 if (index[piece_list(c, pt, i)] != i)
2026 if (failedStep) *failedStep = 0;