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;
54 Key Position::zobExclusion;
56 Score Position::PieceSquareTable[16][64];
58 static bool RequestPending = false;
63 CheckInfo::CheckInfo(const Position& pos) {
65 Color us = pos.side_to_move();
66 Color them = opposite_color(us);
68 ksq = pos.king_square(them);
69 dcCandidates = pos.discovered_check_candidates(us);
71 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
72 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
73 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
74 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
75 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
76 checkSq[KING] = EmptyBoardBB;
79 Position::Position(const Position& pos) {
83 Position::Position(const string& fen) {
88 /// Position::from_fen() initializes the position object with the given FEN
89 /// string. This function is not very robust - make sure that input FENs are
90 /// correct (this is assumed to be the responsibility of the GUI).
92 void Position::from_fen(const string& fen) {
94 static const string pieceLetters = "KQRBNPkqrbnp";
95 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
103 for ( ; fen[i] != ' '; i++)
107 // Skip the given number of files
108 file += (fen[i] - '1' + 1);
111 else if (fen[i] == '/')
117 size_t idx = pieceLetters.find(fen[i]);
118 if (idx == string::npos)
120 std::cout << "Error in FEN at character " << i << std::endl;
123 Square square = make_square(file, rank);
124 put_piece(pieces[idx], square);
130 if (fen[i] != 'w' && fen[i] != 'b')
132 std::cout << "Error in FEN at character " << i << std::endl;
135 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
141 std::cout << "Error in FEN at character " << i << std::endl;
146 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
152 else if(fen[i] == 'K') allow_oo(WHITE);
153 else if(fen[i] == 'Q') allow_ooo(WHITE);
154 else if(fen[i] == 'k') allow_oo(BLACK);
155 else if(fen[i] == 'q') allow_ooo(BLACK);
156 else if(fen[i] >= 'A' && fen[i] <= 'H') {
157 File rookFile, kingFile = FILE_NONE;
158 for(Square square = SQ_B1; square <= SQ_G1; square++)
159 if(piece_on(square) == WK)
160 kingFile = square_file(square);
161 if(kingFile == FILE_NONE) {
162 std::cout << "Error in FEN at character " << i << std::endl;
165 initialKFile = kingFile;
166 rookFile = File(fen[i] - 'A') + FILE_A;
167 if(rookFile < initialKFile) {
169 initialQRFile = rookFile;
173 initialKRFile = rookFile;
176 else if(fen[i] >= 'a' && fen[i] <= 'h') {
177 File rookFile, kingFile = FILE_NONE;
178 for(Square square = SQ_B8; square <= SQ_G8; square++)
179 if(piece_on(square) == BK)
180 kingFile = square_file(square);
181 if(kingFile == FILE_NONE) {
182 std::cout << "Error in FEN at character " << i << std::endl;
185 initialKFile = kingFile;
186 rookFile = File(fen[i] - 'a') + FILE_A;
187 if(rookFile < initialKFile) {
189 initialQRFile = rookFile;
193 initialKRFile = rookFile;
197 std::cout << "Error in FEN at character " << i << std::endl;
204 while (fen[i] == ' ')
207 // En passant square -- ignore if no capture is possible
208 if ( i <= fen.length() - 2
209 && (fen[i] >= 'a' && fen[i] <= 'h')
210 && (fen[i+1] == '3' || fen[i+1] == '6'))
212 Square fenEpSquare = square_from_string(fen.substr(i, 2));
213 Color them = opposite_color(sideToMove);
214 if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))
215 st->epSquare = square_from_string(fen.substr(i, 2));
218 // Various initialisation
219 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
220 castleRightsMask[sq] = ALL_CASTLES;
222 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
223 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
224 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
225 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
226 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
227 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
231 st->key = compute_key();
232 st->pawnKey = compute_pawn_key();
233 st->materialKey = compute_material_key();
234 st->value = compute_value();
235 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
236 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
240 /// Position::to_fen() converts the position object to a FEN string. This is
241 /// probably only useful for debugging.
243 const string Position::to_fen() const {
245 static const string pieceLetters = " PNBRQK pnbrqk";
249 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
252 for (File file = FILE_A; file <= FILE_H; file++)
254 Square sq = make_square(file, rank);
255 if (!square_is_occupied(sq))
261 fen += (char)skip + '0';
264 fen += pieceLetters[piece_on(sq)];
267 fen += (char)skip + '0';
269 fen += (rank > RANK_1 ? '/' : ' ');
271 fen += (sideToMove == WHITE ? "w " : "b ");
272 if (st->castleRights != NO_CASTLES)
274 if (can_castle_kingside(WHITE)) fen += 'K';
275 if (can_castle_queenside(WHITE)) fen += 'Q';
276 if (can_castle_kingside(BLACK)) fen += 'k';
277 if (can_castle_queenside(BLACK)) fen += 'q';
282 if (ep_square() != SQ_NONE)
283 fen += square_to_string(ep_square());
291 /// Position::print() prints an ASCII representation of the position to
292 /// the standard output. If a move is given then also the san is print.
294 void Position::print(Move m) const {
296 static const string pieceLetters = " PNBRQK PNBRQK .";
298 // Check for reentrancy, as example when called from inside
299 // MovePicker that is used also here in move_to_san()
303 RequestPending = true;
305 std::cout << std::endl;
308 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
309 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
311 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
313 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
314 for (File file = FILE_A; file <= FILE_H; file++)
316 Square sq = make_square(file, rank);
317 Piece piece = piece_on(sq);
318 if (piece == EMPTY && square_color(sq) == WHITE)
321 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
322 std::cout << '|' << col << pieceLetters[piece] << col;
324 std::cout << '|' << std::endl;
326 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
327 << "Fen is: " << to_fen() << std::endl
328 << "Key is: " << st->key << std::endl;
330 RequestPending = false;
334 /// Position::copy() creates a copy of the input position.
336 void Position::copy(const Position& pos) {
338 memcpy(this, &pos, sizeof(Position));
339 saveState(); // detach and copy state info
343 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
344 /// king) pieces for the given color and for the given pinner type. Or, when
345 /// template parameter FindPinned is false, the pieces of the given color
346 /// candidate for a discovery check against the enemy king.
347 /// Bitboard checkersBB must be already updated when looking for pinners.
349 template<bool FindPinned>
350 Bitboard Position::hidden_checkers(Color c) const {
352 Bitboard result = EmptyBoardBB;
353 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
355 // Pinned pieces protect our king, dicovery checks attack
357 Square ksq = king_square(FindPinned ? c : opposite_color(c));
359 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
360 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
362 if (FindPinned && pinners)
363 pinners &= ~st->checkersBB;
367 Square s = pop_1st_bit(&pinners);
368 Bitboard b = squares_between(s, ksq) & occupied_squares();
372 if ( !(b & (b - 1)) // Only one bit set?
373 && (b & pieces_of_color(c))) // Is an our piece?
380 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
381 /// king) pieces for the given color. Note that checkersBB bitboard must
382 /// be already updated.
384 Bitboard Position::pinned_pieces(Color c) const {
386 return hidden_checkers<true>(c);
390 /// Position:discovered_check_candidates() returns a bitboard containing all
391 /// pieces for the given side which are candidates for giving a discovered
392 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
393 /// to be already updated.
395 Bitboard Position::discovered_check_candidates(Color c) const {
397 return hidden_checkers<false>(c);
400 /// Position::attackers_to() computes a bitboard containing all pieces which
401 /// attacks a given square.
403 Bitboard Position::attackers_to(Square s) const {
405 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
406 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
407 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
408 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
409 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
410 | (attacks_from<KING>(s) & pieces(KING));
413 /// Position::attacks_from() computes a bitboard of all attacks
414 /// of a given piece put in a given square.
416 Bitboard Position::attacks_from(Piece p, Square s) const {
418 assert(square_is_ok(s));
422 case WP: return attacks_from<PAWN>(s, WHITE);
423 case BP: return attacks_from<PAWN>(s, BLACK);
424 case WN: case BN: return attacks_from<KNIGHT>(s);
425 case WB: case BB: return attacks_from<BISHOP>(s);
426 case WR: case BR: return attacks_from<ROOK>(s);
427 case WQ: case BQ: return attacks_from<QUEEN>(s);
428 case WK: case BK: return attacks_from<KING>(s);
435 /// Position::move_attacks_square() tests whether a move from the current
436 /// position attacks a given square.
438 bool Position::move_attacks_square(Move m, Square s) const {
440 assert(move_is_ok(m));
441 assert(square_is_ok(s));
443 Square f = move_from(m), t = move_to(m);
445 assert(square_is_occupied(f));
447 if (bit_is_set(attacks_from(piece_on(f), t), s))
450 // Move the piece and scan for X-ray attacks behind it
451 Bitboard occ = occupied_squares();
452 Color us = color_of_piece_on(f);
455 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
456 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
458 // If we have attacks we need to verify that are caused by our move
459 // and are not already existent ones.
460 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
464 /// Position::find_checkers() computes the checkersBB bitboard, which
465 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
466 /// currently works by calling Position::attackers_to, which is probably
467 /// inefficient. Consider rewriting this function to use the last move
468 /// played, like in non-bitboard versions of Glaurung.
470 void Position::find_checkers() {
472 Color us = side_to_move();
473 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
477 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
479 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
482 assert(move_is_ok(m));
483 assert(pinned == pinned_pieces(side_to_move()));
485 // Castling moves are checked for legality during move generation.
486 if (move_is_castle(m))
489 Color us = side_to_move();
490 Square from = move_from(m);
492 assert(color_of_piece_on(from) == us);
493 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
495 // En passant captures are a tricky special case. Because they are
496 // rather uncommon, we do it simply by testing whether the king is attacked
497 // after the move is made
500 Color them = opposite_color(us);
501 Square to = move_to(m);
502 Square capsq = make_square(square_file(to), square_rank(from));
503 Bitboard b = occupied_squares();
504 Square ksq = king_square(us);
506 assert(to == ep_square());
507 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
508 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
509 assert(piece_on(to) == EMPTY);
512 clear_bit(&b, capsq);
515 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
516 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
519 // If the moving piece is a king, check whether the destination
520 // square is attacked by the opponent.
521 if (type_of_piece_on(from) == KING)
522 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
524 // A non-king move is legal if and only if it is not pinned or it
525 // is moving along the ray towards or away from the king.
527 || !bit_is_set(pinned, from)
528 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
532 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
534 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
538 Color us = side_to_move();
539 Square from = move_from(m);
540 Square to = move_to(m);
542 // King moves and en-passant captures are verified in pl_move_is_legal()
543 if (type_of_piece_on(from) == KING || move_is_ep(m))
544 return pl_move_is_legal(m, pinned);
546 Bitboard target = checkers();
547 Square checksq = pop_1st_bit(&target);
549 if (target) // double check ?
552 // Our move must be a blocking evasion or a capture of the checking piece
553 target = squares_between(checksq, king_square(us)) | checkers();
554 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
558 /// Position::move_is_check() tests whether a pseudo-legal move is a check
560 bool Position::move_is_check(Move m) const {
562 return move_is_check(m, CheckInfo(*this));
565 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
568 assert(move_is_ok(m));
569 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
570 assert(color_of_piece_on(move_from(m)) == side_to_move());
571 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
573 Square from = move_from(m);
574 Square to = move_to(m);
575 PieceType pt = type_of_piece_on(from);
578 if (bit_is_set(ci.checkSq[pt], to))
582 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
584 // For pawn and king moves we need to verify also direction
585 if ( (pt != PAWN && pt != KING)
586 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
590 // Can we skip the ugly special cases ?
591 if (!move_is_special(m))
594 Color us = side_to_move();
595 Bitboard b = occupied_squares();
597 // Promotion with check ?
598 if (move_is_promotion(m))
602 switch (move_promotion_piece(m))
605 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
607 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
609 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
611 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
617 // En passant capture with check? We have already handled the case
618 // of direct checks and ordinary discovered check, the only case we
619 // need to handle is the unusual case of a discovered check through the
623 Square capsq = make_square(square_file(to), square_rank(from));
625 clear_bit(&b, capsq);
627 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
628 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
631 // Castling with check ?
632 if (move_is_castle(m))
634 Square kfrom, kto, rfrom, rto;
640 kto = relative_square(us, SQ_G1);
641 rto = relative_square(us, SQ_F1);
643 kto = relative_square(us, SQ_C1);
644 rto = relative_square(us, SQ_D1);
646 clear_bit(&b, kfrom);
647 clear_bit(&b, rfrom);
650 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
657 /// Position::do_move() makes a move, and saves all information necessary
658 /// to a StateInfo object. The move is assumed to be legal.
659 /// Pseudo-legal moves should be filtered out before this function is called.
661 void Position::do_move(Move m, StateInfo& newSt) {
664 do_move(m, newSt, ci, move_is_check(m, ci));
667 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
670 assert(move_is_ok(m));
672 Bitboard key = st->key;
674 // Copy some fields of old state to our new StateInfo object except the
675 // ones which are recalculated from scratch anyway, then switch our state
676 // pointer to point to the new, ready to be updated, state.
677 struct ReducedStateInfo {
678 Key pawnKey, materialKey;
679 int castleRights, rule50, pliesFromNull;
685 memcpy(&newSt, st, sizeof(ReducedStateInfo));
689 // Save the current key to the history[] array, in order to be able to
690 // detect repetition draws.
691 history[gamePly] = key;
694 // Update side to move
695 key ^= zobSideToMove;
697 // Increment the 50 moves rule draw counter. Resetting it to zero in the
698 // case of non-reversible moves is taken care of later.
702 if (move_is_castle(m))
709 Color us = side_to_move();
710 Color them = opposite_color(us);
711 Square from = move_from(m);
712 Square to = move_to(m);
713 bool ep = move_is_ep(m);
714 bool pm = move_is_promotion(m);
716 Piece piece = piece_on(from);
717 PieceType pt = type_of_piece(piece);
718 PieceType capture = ep ? PAWN : type_of_piece_on(to);
720 assert(color_of_piece_on(from) == us);
721 assert(color_of_piece_on(to) == them || square_is_empty(to));
722 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
723 assert(!pm || relative_rank(us, to) == RANK_8);
726 do_capture_move(key, capture, them, to, ep);
729 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
731 // Reset en passant square
732 if (st->epSquare != SQ_NONE)
734 key ^= zobEp[st->epSquare];
735 st->epSquare = SQ_NONE;
738 // Update castle rights, try to shortcut a common case
739 int cm = castleRightsMask[from] & castleRightsMask[to];
740 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
742 key ^= zobCastle[st->castleRights];
743 st->castleRights &= castleRightsMask[from];
744 st->castleRights &= castleRightsMask[to];
745 key ^= zobCastle[st->castleRights];
748 // Prefetch TT access as soon as we know key is updated
752 Bitboard move_bb = make_move_bb(from, to);
753 do_move_bb(&(byColorBB[us]), move_bb);
754 do_move_bb(&(byTypeBB[pt]), move_bb);
755 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
757 board[to] = board[from];
760 // Update piece lists, note that index[from] is not updated and
761 // becomes stale. This works as long as index[] is accessed just
762 // by known occupied squares.
763 index[to] = index[from];
764 pieceList[us][pt][index[to]] = to;
766 // If the moving piece was a pawn do some special extra work
769 // Reset rule 50 draw counter
772 // Update pawn hash key
773 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
775 // Set en passant square, only if moved pawn can be captured
776 if ((to ^ from) == 16)
778 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
780 st->epSquare = Square((int(from) + int(to)) / 2);
781 key ^= zobEp[st->epSquare];
786 // Update incremental scores
787 st->value += pst_delta(piece, from, to);
790 st->capture = capture;
792 if (pm) // promotion ?
794 PieceType promotion = move_promotion_piece(m);
796 assert(promotion >= KNIGHT && promotion <= QUEEN);
798 // Insert promoted piece instead of pawn
799 clear_bit(&(byTypeBB[PAWN]), to);
800 set_bit(&(byTypeBB[promotion]), to);
801 board[to] = piece_of_color_and_type(us, promotion);
803 // Update material key
804 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
805 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
807 // Update piece counts
808 pieceCount[us][PAWN]--;
809 pieceCount[us][promotion]++;
811 // Update piece lists, move the last pawn at index[to] position
812 // and shrink the list. Add a new promotion piece to the list.
813 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
814 index[lastPawnSquare] = index[to];
815 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
816 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
817 index[to] = pieceCount[us][promotion] - 1;
818 pieceList[us][promotion][index[to]] = to;
820 // Partially revert hash keys update
821 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
822 st->pawnKey ^= zobrist[us][PAWN][to];
824 // Partially revert and update incremental scores
825 st->value -= pst(us, PAWN, to);
826 st->value += pst(us, promotion, to);
829 st->npMaterial[us] += piece_value_midgame(promotion);
832 // Update the key with the final value
835 // Update checkers bitboard, piece must be already moved
836 st->checkersBB = EmptyBoardBB;
841 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
845 if (bit_is_set(ci.checkSq[pt], to))
846 st->checkersBB = SetMaskBB[to];
849 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
852 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
855 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
861 sideToMove = opposite_color(sideToMove);
862 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
868 /// Position::do_capture_move() is a private method used to update captured
869 /// piece info. It is called from the main Position::do_move function.
871 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
873 assert(capture != KING);
877 if (ep) // en passant ?
879 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
881 assert(to == st->epSquare);
882 assert(relative_rank(opposite_color(them), to) == RANK_6);
883 assert(piece_on(to) == EMPTY);
884 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
886 board[capsq] = EMPTY;
889 // Remove captured piece
890 clear_bit(&(byColorBB[them]), capsq);
891 clear_bit(&(byTypeBB[capture]), capsq);
892 clear_bit(&(byTypeBB[0]), capsq);
895 key ^= zobrist[them][capture][capsq];
897 // Update incremental scores
898 st->value -= pst(them, capture, capsq);
900 // If the captured piece was a pawn, update pawn hash key,
901 // otherwise update non-pawn material.
903 st->pawnKey ^= zobrist[them][PAWN][capsq];
905 st->npMaterial[them] -= piece_value_midgame(capture);
907 // Update material hash key
908 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
910 // Update piece count
911 pieceCount[them][capture]--;
913 // Update piece list, move the last piece at index[capsq] position
915 // WARNING: This is a not perfectly revresible operation. When we
916 // will reinsert the captured piece in undo_move() we will put it
917 // at the end of the list and not in its original place, it means
918 // index[] and pieceList[] are not guaranteed to be invariant to a
919 // do_move() + undo_move() sequence.
920 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
921 index[lastPieceSquare] = index[capsq];
922 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
923 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
925 // Reset rule 50 counter
930 /// Position::do_castle_move() is a private method used to make a castling
931 /// move. It is called from the main Position::do_move function. Note that
932 /// castling moves are encoded as "king captures friendly rook" moves, for
933 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
935 void Position::do_castle_move(Move m) {
937 assert(move_is_ok(m));
938 assert(move_is_castle(m));
940 Color us = side_to_move();
941 Color them = opposite_color(us);
943 // Reset capture field
944 st->capture = NO_PIECE_TYPE;
946 // Find source squares for king and rook
947 Square kfrom = move_from(m);
948 Square rfrom = move_to(m); // HACK: See comment at beginning of function
951 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
952 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
954 // Find destination squares for king and rook
955 if (rfrom > kfrom) // O-O
957 kto = relative_square(us, SQ_G1);
958 rto = relative_square(us, SQ_F1);
960 kto = relative_square(us, SQ_C1);
961 rto = relative_square(us, SQ_D1);
964 // Remove pieces from source squares:
965 clear_bit(&(byColorBB[us]), kfrom);
966 clear_bit(&(byTypeBB[KING]), kfrom);
967 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
968 clear_bit(&(byColorBB[us]), rfrom);
969 clear_bit(&(byTypeBB[ROOK]), rfrom);
970 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
972 // Put pieces on destination squares:
973 set_bit(&(byColorBB[us]), kto);
974 set_bit(&(byTypeBB[KING]), kto);
975 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
976 set_bit(&(byColorBB[us]), rto);
977 set_bit(&(byTypeBB[ROOK]), rto);
978 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
980 // Update board array
981 Piece king = piece_of_color_and_type(us, KING);
982 Piece rook = piece_of_color_and_type(us, ROOK);
983 board[kfrom] = board[rfrom] = EMPTY;
987 // Update piece lists
988 pieceList[us][KING][index[kfrom]] = kto;
989 pieceList[us][ROOK][index[rfrom]] = rto;
990 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
991 index[kto] = index[kfrom];
994 // Update incremental scores
995 st->value += pst_delta(king, kfrom, kto);
996 st->value += pst_delta(rook, rfrom, rto);
999 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1000 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1002 // Clear en passant square
1003 if (st->epSquare != SQ_NONE)
1005 st->key ^= zobEp[st->epSquare];
1006 st->epSquare = SQ_NONE;
1009 // Update castling rights
1010 st->key ^= zobCastle[st->castleRights];
1011 st->castleRights &= castleRightsMask[kfrom];
1012 st->key ^= zobCastle[st->castleRights];
1014 // Reset rule 50 counter
1017 // Update checkers BB
1018 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1021 sideToMove = opposite_color(sideToMove);
1022 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1028 /// Position::undo_move() unmakes a move. When it returns, the position should
1029 /// be restored to exactly the same state as before the move was made.
1031 void Position::undo_move(Move m) {
1034 assert(move_is_ok(m));
1037 sideToMove = opposite_color(sideToMove);
1039 if (move_is_castle(m))
1041 undo_castle_move(m);
1045 Color us = side_to_move();
1046 Color them = opposite_color(us);
1047 Square from = move_from(m);
1048 Square to = move_to(m);
1049 bool ep = move_is_ep(m);
1050 bool pm = move_is_promotion(m);
1052 PieceType pt = type_of_piece_on(to);
1054 assert(square_is_empty(from));
1055 assert(color_of_piece_on(to) == us);
1056 assert(!pm || relative_rank(us, to) == RANK_8);
1057 assert(!ep || to == st->previous->epSquare);
1058 assert(!ep || relative_rank(us, to) == RANK_6);
1059 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1061 if (pm) // promotion ?
1063 PieceType promotion = move_promotion_piece(m);
1066 assert(promotion >= KNIGHT && promotion <= QUEEN);
1067 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1069 // Replace promoted piece with a pawn
1070 clear_bit(&(byTypeBB[promotion]), to);
1071 set_bit(&(byTypeBB[PAWN]), to);
1073 // Update piece counts
1074 pieceCount[us][promotion]--;
1075 pieceCount[us][PAWN]++;
1077 // Update piece list replacing promotion piece with a pawn
1078 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1079 index[lastPromotionSquare] = index[to];
1080 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1081 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1082 index[to] = pieceCount[us][PAWN] - 1;
1083 pieceList[us][PAWN][index[to]] = to;
1087 // Put the piece back at the source square
1088 Bitboard move_bb = make_move_bb(to, from);
1089 do_move_bb(&(byColorBB[us]), move_bb);
1090 do_move_bb(&(byTypeBB[pt]), move_bb);
1091 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1093 board[from] = piece_of_color_and_type(us, pt);
1096 // Update piece list
1097 index[from] = index[to];
1098 pieceList[us][pt][index[from]] = from;
1105 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1107 assert(st->capture != KING);
1108 assert(!ep || square_is_empty(capsq));
1110 // Restore the captured piece
1111 set_bit(&(byColorBB[them]), capsq);
1112 set_bit(&(byTypeBB[st->capture]), capsq);
1113 set_bit(&(byTypeBB[0]), capsq);
1115 board[capsq] = piece_of_color_and_type(them, st->capture);
1117 // Update piece count
1118 pieceCount[them][st->capture]++;
1120 // Update piece list, add a new captured piece in capsq square
1121 index[capsq] = pieceCount[them][st->capture] - 1;
1122 pieceList[them][st->capture][index[capsq]] = capsq;
1125 // Finally point our state pointer back to the previous state
1132 /// Position::undo_castle_move() is a private method used to unmake a castling
1133 /// move. It is called from the main Position::undo_move function. Note that
1134 /// castling moves are encoded as "king captures friendly rook" moves, for
1135 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1137 void Position::undo_castle_move(Move m) {
1139 assert(move_is_ok(m));
1140 assert(move_is_castle(m));
1142 // When we have arrived here, some work has already been done by
1143 // Position::undo_move. In particular, the side to move has been switched,
1144 // so the code below is correct.
1145 Color us = side_to_move();
1147 // Find source squares for king and rook
1148 Square kfrom = move_from(m);
1149 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1152 // Find destination squares for king and rook
1153 if (rfrom > kfrom) // O-O
1155 kto = relative_square(us, SQ_G1);
1156 rto = relative_square(us, SQ_F1);
1158 kto = relative_square(us, SQ_C1);
1159 rto = relative_square(us, SQ_D1);
1162 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1163 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1165 // Remove pieces from destination squares:
1166 clear_bit(&(byColorBB[us]), kto);
1167 clear_bit(&(byTypeBB[KING]), kto);
1168 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1169 clear_bit(&(byColorBB[us]), rto);
1170 clear_bit(&(byTypeBB[ROOK]), rto);
1171 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1173 // Put pieces on source squares:
1174 set_bit(&(byColorBB[us]), kfrom);
1175 set_bit(&(byTypeBB[KING]), kfrom);
1176 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1177 set_bit(&(byColorBB[us]), rfrom);
1178 set_bit(&(byTypeBB[ROOK]), rfrom);
1179 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1182 board[rto] = board[kto] = EMPTY;
1183 board[rfrom] = piece_of_color_and_type(us, ROOK);
1184 board[kfrom] = piece_of_color_and_type(us, KING);
1186 // Update piece lists
1187 pieceList[us][KING][index[kto]] = kfrom;
1188 pieceList[us][ROOK][index[rto]] = rfrom;
1189 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1190 index[kfrom] = index[kto];
1193 // Finally point our state pointer back to the previous state
1200 /// Position::do_null_move makes() a "null move": It switches the side to move
1201 /// and updates the hash key without executing any move on the board.
1203 void Position::do_null_move(StateInfo& backupSt) {
1206 assert(!is_check());
1208 // Back up the information necessary to undo the null move to the supplied
1209 // StateInfo object.
1210 // Note that differently from normal case here backupSt is actually used as
1211 // a backup storage not as a new state to be used.
1212 backupSt.key = st->key;
1213 backupSt.epSquare = st->epSquare;
1214 backupSt.value = st->value;
1215 backupSt.previous = st->previous;
1216 backupSt.pliesFromNull = st->pliesFromNull;
1217 st->previous = &backupSt;
1219 // Save the current key to the history[] array, in order to be able to
1220 // detect repetition draws.
1221 history[gamePly] = st->key;
1223 // Update the necessary information
1224 if (st->epSquare != SQ_NONE)
1225 st->key ^= zobEp[st->epSquare];
1227 st->key ^= zobSideToMove;
1228 TT.prefetch(st->key);
1230 sideToMove = opposite_color(sideToMove);
1231 st->epSquare = SQ_NONE;
1233 st->pliesFromNull = 0;
1234 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1239 /// Position::undo_null_move() unmakes a "null move".
1241 void Position::undo_null_move() {
1244 assert(!is_check());
1246 // Restore information from the our backup StateInfo object
1247 StateInfo* backupSt = st->previous;
1248 st->key = backupSt->key;
1249 st->epSquare = backupSt->epSquare;
1250 st->value = backupSt->value;
1251 st->previous = backupSt->previous;
1252 st->pliesFromNull = backupSt->pliesFromNull;
1254 // Update the necessary information
1255 sideToMove = opposite_color(sideToMove);
1261 /// Position::see() is a static exchange evaluator: It tries to estimate the
1262 /// material gain or loss resulting from a move. There are three versions of
1263 /// this function: One which takes a destination square as input, one takes a
1264 /// move, and one which takes a 'from' and a 'to' square. The function does
1265 /// not yet understand promotions captures.
1267 int Position::see(Square to) const {
1269 assert(square_is_ok(to));
1270 return see(SQ_NONE, to);
1273 int Position::see(Move m) const {
1275 assert(move_is_ok(m));
1276 return see(move_from(m), move_to(m));
1279 int Position::see_sign(Move m) const {
1281 assert(move_is_ok(m));
1283 Square from = move_from(m);
1284 Square to = move_to(m);
1286 // Early return if SEE cannot be negative because capturing piece value
1287 // is not bigger then captured one.
1288 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1289 && type_of_piece_on(from) != KING)
1292 return see(from, to);
1295 int Position::see(Square from, Square to) const {
1298 static const int seeValues[18] = {
1299 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1300 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1301 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1302 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1306 Bitboard attackers, stmAttackers, b;
1308 assert(square_is_ok(from) || from == SQ_NONE);
1309 assert(square_is_ok(to));
1311 // Initialize colors
1312 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1313 Color them = opposite_color(us);
1315 // Initialize pieces
1316 Piece piece = piece_on(from);
1317 Piece capture = piece_on(to);
1318 Bitboard occ = occupied_squares();
1320 // King cannot be recaptured
1321 if (type_of_piece(piece) == KING)
1322 return seeValues[capture];
1324 // Handle en passant moves
1325 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1327 assert(capture == EMPTY);
1329 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1330 capture = piece_on(capQq);
1331 assert(type_of_piece_on(capQq) == PAWN);
1333 // Remove the captured pawn
1334 clear_bit(&occ, capQq);
1339 // Find all attackers to the destination square, with the moving piece
1340 // removed, but possibly an X-ray attacker added behind it.
1341 clear_bit(&occ, from);
1342 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1343 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1344 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1345 | (attacks_from<KING>(to) & pieces(KING))
1346 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1347 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1349 if (from != SQ_NONE)
1352 // If we don't have any attacker we are finished
1353 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1356 // Locate the least valuable attacker to the destination square
1357 // and use it to initialize from square.
1358 stmAttackers = attackers & pieces_of_color(us);
1360 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1363 from = first_1(stmAttackers & pieces(pt));
1364 piece = piece_on(from);
1367 // If the opponent has no attackers we are finished
1368 stmAttackers = attackers & pieces_of_color(them);
1370 return seeValues[capture];
1372 attackers &= occ; // Remove the moving piece
1374 // The destination square is defended, which makes things rather more
1375 // difficult to compute. We proceed by building up a "swap list" containing
1376 // the material gain or loss at each stop in a sequence of captures to the
1377 // destination square, where the sides alternately capture, and always
1378 // capture with the least valuable piece. After each capture, we look for
1379 // new X-ray attacks from behind the capturing piece.
1380 int lastCapturingPieceValue = seeValues[piece];
1381 int swapList[32], n = 1;
1385 swapList[0] = seeValues[capture];
1388 // Locate the least valuable attacker for the side to move. The loop
1389 // below looks like it is potentially infinite, but it isn't. We know
1390 // that the side to move still has at least one attacker left.
1391 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1394 // Remove the attacker we just found from the 'attackers' bitboard,
1395 // and scan for new X-ray attacks behind the attacker.
1396 b = stmAttackers & pieces(pt);
1397 occ ^= (b & (~b + 1));
1398 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1399 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1403 // Add the new entry to the swap list
1405 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1408 // Remember the value of the capturing piece, and change the side to move
1409 // before beginning the next iteration
1410 lastCapturingPieceValue = seeValues[pt];
1411 c = opposite_color(c);
1412 stmAttackers = attackers & pieces_of_color(c);
1414 // Stop after a king capture
1415 if (pt == KING && stmAttackers)
1418 swapList[n++] = QueenValueMidgame*10;
1421 } while (stmAttackers);
1423 // Having built the swap list, we negamax through it to find the best
1424 // achievable score from the point of view of the side to move
1426 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1432 /// Position::saveState() copies the content of the current state
1433 /// inside startState and makes st point to it. This is needed
1434 /// when the st pointee could become stale, as example because
1435 /// the caller is about to going out of scope.
1437 void Position::saveState() {
1441 st->previous = NULL; // as a safe guard
1445 /// Position::clear() erases the position object to a pristine state, with an
1446 /// empty board, white to move, and no castling rights.
1448 void Position::clear() {
1451 memset(st, 0, sizeof(StateInfo));
1452 st->epSquare = SQ_NONE;
1454 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1455 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1456 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1457 memset(index, 0, sizeof(int) * 64);
1459 for (int i = 0; i < 64; i++)
1462 for (int i = 0; i < 8; i++)
1463 for (int j = 0; j < 16; j++)
1464 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1468 initialKFile = FILE_E;
1469 initialKRFile = FILE_H;
1470 initialQRFile = FILE_A;
1474 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1475 /// UCI interface code, whenever a non-reversible move is made in a
1476 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1477 /// for the program to handle games of arbitrary length, as long as the GUI
1478 /// handles draws by the 50 move rule correctly.
1480 void Position::reset_game_ply() {
1486 /// Position::put_piece() puts a piece on the given square of the board,
1487 /// updating the board array, bitboards, and piece counts.
1489 void Position::put_piece(Piece p, Square s) {
1491 Color c = color_of_piece(p);
1492 PieceType pt = type_of_piece(p);
1495 index[s] = pieceCount[c][pt];
1496 pieceList[c][pt][index[s]] = s;
1498 set_bit(&(byTypeBB[pt]), s);
1499 set_bit(&(byColorBB[c]), s);
1500 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1502 pieceCount[c][pt]++;
1506 /// Position::allow_oo() gives the given side the right to castle kingside.
1507 /// Used when setting castling rights during parsing of FEN strings.
1509 void Position::allow_oo(Color c) {
1511 st->castleRights |= (1 + int(c));
1515 /// Position::allow_ooo() gives the given side the right to castle queenside.
1516 /// Used when setting castling rights during parsing of FEN strings.
1518 void Position::allow_ooo(Color c) {
1520 st->castleRights |= (4 + 4*int(c));
1524 /// Position::compute_key() computes the hash key of the position. The hash
1525 /// key is usually updated incrementally as moves are made and unmade, the
1526 /// compute_key() function is only used when a new position is set up, and
1527 /// to verify the correctness of the hash key when running in debug mode.
1529 Key Position::compute_key() const {
1531 Key result = Key(0ULL);
1533 for (Square s = SQ_A1; s <= SQ_H8; s++)
1534 if (square_is_occupied(s))
1535 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1537 if (ep_square() != SQ_NONE)
1538 result ^= zobEp[ep_square()];
1540 result ^= zobCastle[st->castleRights];
1541 if (side_to_move() == BLACK)
1542 result ^= zobSideToMove;
1548 /// Position::compute_pawn_key() computes the hash key of the position. The
1549 /// hash key is usually updated incrementally as moves are made and unmade,
1550 /// the compute_pawn_key() function is only used when a new position is set
1551 /// up, and to verify the correctness of the pawn hash key when running in
1554 Key Position::compute_pawn_key() const {
1556 Key result = Key(0ULL);
1560 for (Color c = WHITE; c <= BLACK; c++)
1562 b = pieces(PAWN, c);
1565 s = pop_1st_bit(&b);
1566 result ^= zobrist[c][PAWN][s];
1573 /// Position::compute_material_key() computes the hash key of the position.
1574 /// The hash key is usually updated incrementally as moves are made and unmade,
1575 /// the compute_material_key() function is only used when a new position is set
1576 /// up, and to verify the correctness of the material hash key when running in
1579 Key Position::compute_material_key() const {
1581 Key result = Key(0ULL);
1582 for (Color c = WHITE; c <= BLACK; c++)
1583 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1585 int count = piece_count(c, pt);
1586 for (int i = 0; i <= count; i++)
1587 result ^= zobMaterial[c][pt][i];
1593 /// Position::compute_value() compute the incremental scores for the middle
1594 /// game and the endgame. These functions are used to initialize the incremental
1595 /// scores when a new position is set up, and to verify that the scores are correctly
1596 /// updated by do_move and undo_move when the program is running in debug mode.
1597 Score Position::compute_value() const {
1599 Score result = make_score(0, 0);
1603 for (Color c = WHITE; c <= BLACK; c++)
1604 for (PieceType pt = PAWN; pt <= KING; pt++)
1609 s = pop_1st_bit(&b);
1610 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1611 result += pst(c, pt, s);
1615 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1620 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1621 /// game material score for the given side. Material scores are updated
1622 /// incrementally during the search, this function is only used while
1623 /// initializing a new Position object.
1625 Value Position::compute_non_pawn_material(Color c) const {
1627 Value result = Value(0);
1629 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1631 Bitboard b = pieces(pt, c);
1634 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1636 result += piece_value_midgame(pt);
1643 /// Position::is_draw() tests whether the position is drawn by material,
1644 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1645 /// must be done by the search.
1647 bool Position::is_draw() const {
1649 // Draw by material?
1651 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1654 // Draw by the 50 moves rule?
1655 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1658 // Draw by repetition?
1659 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1660 if (history[gamePly - i] == st->key)
1667 /// Position::is_mate() returns true or false depending on whether the
1668 /// side to move is checkmated.
1670 bool Position::is_mate() const {
1672 MoveStack moves[256];
1673 return is_check() && (generate_moves(*this, moves, false) == moves);
1677 /// Position::has_mate_threat() tests whether a given color has a mate in one
1678 /// from the current position.
1680 bool Position::has_mate_threat(Color c) {
1683 Color stm = side_to_move();
1688 // If the input color is not equal to the side to move, do a null move
1692 MoveStack mlist[120];
1693 bool result = false;
1694 Bitboard pinned = pinned_pieces(sideToMove);
1696 // Generate pseudo-legal non-capture and capture check moves
1697 MoveStack* last = generate_non_capture_checks(*this, mlist);
1698 last = generate_captures(*this, last);
1700 // Loop through the moves, and see if one of them is mate
1701 for (MoveStack* cur = mlist; cur != last; cur++)
1703 Move move = cur->move;
1704 if (!pl_move_is_legal(move, pinned))
1714 // Undo null move, if necessary
1722 /// Position::init_zobrist() is a static member function which initializes the
1723 /// various arrays used to compute hash keys.
1725 void Position::init_zobrist() {
1727 for (int i = 0; i < 2; i++)
1728 for (int j = 0; j < 8; j++)
1729 for (int k = 0; k < 64; k++)
1730 zobrist[i][j][k] = Key(genrand_int64());
1732 for (int i = 0; i < 64; i++)
1733 zobEp[i] = Key(genrand_int64());
1735 for (int i = 0; i < 16; i++)
1736 zobCastle[i] = genrand_int64();
1738 zobSideToMove = genrand_int64();
1740 for (int i = 0; i < 2; i++)
1741 for (int j = 0; j < 8; j++)
1742 for (int k = 0; k < 16; k++)
1743 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1745 for (int i = 0; i < 16; i++)
1746 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1748 zobExclusion = genrand_int64();
1752 /// Position::init_piece_square_tables() initializes the piece square tables.
1753 /// This is a two-step operation: First, the white halves of the tables are
1754 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1755 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1756 /// Second, the black halves of the tables are initialized by mirroring
1757 /// and changing the sign of the corresponding white scores.
1759 void Position::init_piece_square_tables() {
1761 int r = get_option_value_int("Randomness"), i;
1762 for (Square s = SQ_A1; s <= SQ_H8; s++)
1763 for (Piece p = WP; p <= WK; p++)
1765 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1766 PieceSquareTable[p][s] = make_score(MgPST[p][s] + i, EgPST[p][s] + i);
1769 for (Square s = SQ_A1; s <= SQ_H8; s++)
1770 for (Piece p = BP; p <= BK; p++)
1771 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1775 /// Position::flipped_copy() makes a copy of the input position, but with
1776 /// the white and black sides reversed. This is only useful for debugging,
1777 /// especially for finding evaluation symmetry bugs.
1779 void Position::flipped_copy(const Position& pos) {
1781 assert(pos.is_ok());
1786 for (Square s = SQ_A1; s <= SQ_H8; s++)
1787 if (!pos.square_is_empty(s))
1788 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1791 sideToMove = opposite_color(pos.side_to_move());
1794 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1795 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1796 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1797 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1799 initialKFile = pos.initialKFile;
1800 initialKRFile = pos.initialKRFile;
1801 initialQRFile = pos.initialQRFile;
1803 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1804 castleRightsMask[sq] = ALL_CASTLES;
1806 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1807 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1808 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1809 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1810 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1811 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1813 // En passant square
1814 if (pos.st->epSquare != SQ_NONE)
1815 st->epSquare = flip_square(pos.st->epSquare);
1821 st->key = compute_key();
1822 st->pawnKey = compute_pawn_key();
1823 st->materialKey = compute_material_key();
1825 // Incremental scores
1826 st->value = compute_value();
1829 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1830 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1836 /// Position::is_ok() performs some consitency checks for the position object.
1837 /// This is meant to be helpful when debugging.
1839 bool Position::is_ok(int* failedStep) const {
1841 // What features of the position should be verified?
1842 static const bool debugBitboards = false;
1843 static const bool debugKingCount = false;
1844 static const bool debugKingCapture = false;
1845 static const bool debugCheckerCount = false;
1846 static const bool debugKey = false;
1847 static const bool debugMaterialKey = false;
1848 static const bool debugPawnKey = false;
1849 static const bool debugIncrementalEval = false;
1850 static const bool debugNonPawnMaterial = false;
1851 static const bool debugPieceCounts = false;
1852 static const bool debugPieceList = false;
1854 if (failedStep) *failedStep = 1;
1857 if (!color_is_ok(side_to_move()))
1860 // Are the king squares in the position correct?
1861 if (failedStep) (*failedStep)++;
1862 if (piece_on(king_square(WHITE)) != WK)
1865 if (failedStep) (*failedStep)++;
1866 if (piece_on(king_square(BLACK)) != BK)
1870 if (failedStep) (*failedStep)++;
1871 if (!file_is_ok(initialKRFile))
1874 if (!file_is_ok(initialQRFile))
1877 // Do both sides have exactly one king?
1878 if (failedStep) (*failedStep)++;
1881 int kingCount[2] = {0, 0};
1882 for (Square s = SQ_A1; s <= SQ_H8; s++)
1883 if (type_of_piece_on(s) == KING)
1884 kingCount[color_of_piece_on(s)]++;
1886 if (kingCount[0] != 1 || kingCount[1] != 1)
1890 // Can the side to move capture the opponent's king?
1891 if (failedStep) (*failedStep)++;
1892 if (debugKingCapture)
1894 Color us = side_to_move();
1895 Color them = opposite_color(us);
1896 Square ksq = king_square(them);
1897 if (attackers_to(ksq) & pieces_of_color(us))
1901 // Is there more than 2 checkers?
1902 if (failedStep) (*failedStep)++;
1903 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1907 if (failedStep) (*failedStep)++;
1910 // The intersection of the white and black pieces must be empty
1911 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1914 // The union of the white and black pieces must be equal to all
1916 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1919 // Separate piece type bitboards must have empty intersections
1920 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1921 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1922 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1926 // En passant square OK?
1927 if (failedStep) (*failedStep)++;
1928 if (ep_square() != SQ_NONE)
1930 // The en passant square must be on rank 6, from the point of view of the
1932 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1937 if (failedStep) (*failedStep)++;
1938 if (debugKey && st->key != compute_key())
1941 // Pawn hash key OK?
1942 if (failedStep) (*failedStep)++;
1943 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1946 // Material hash key OK?
1947 if (failedStep) (*failedStep)++;
1948 if (debugMaterialKey && st->materialKey != compute_material_key())
1951 // Incremental eval OK?
1952 if (failedStep) (*failedStep)++;
1953 if (debugIncrementalEval && st->value != compute_value())
1956 // Non-pawn material OK?
1957 if (failedStep) (*failedStep)++;
1958 if (debugNonPawnMaterial)
1960 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1963 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1968 if (failedStep) (*failedStep)++;
1969 if (debugPieceCounts)
1970 for (Color c = WHITE; c <= BLACK; c++)
1971 for (PieceType pt = PAWN; pt <= KING; pt++)
1972 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
1975 if (failedStep) (*failedStep)++;
1978 for(Color c = WHITE; c <= BLACK; c++)
1979 for(PieceType pt = PAWN; pt <= KING; pt++)
1980 for(int i = 0; i < pieceCount[c][pt]; i++)
1982 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
1985 if (index[piece_list(c, pt, i)] != i)
1989 if (failedStep) *failedStep = 0;