X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fmovegen.cpp;h=7cbd157a75b5a008e6d0f92ae8bfc93f2fcf8366;hp=0b052e5bb105dd822e771c4ba3f098164ae84bd4;hb=d655147e8c;hpb=9f28d8a854d05c6c6edcd6f8911b352477f82c91 diff --git a/src/movegen.cpp b/src/movegen.cpp index 0b052e5b..7cbd157a 100644 --- a/src/movegen.cpp +++ b/src/movegen.cpp @@ -1,7 +1,7 @@ /* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) - Copyright (C) 2008-2009 Marco Costalba + Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -17,15 +17,13 @@ along with this program. If not, see . */ - -//// -//// Includes -//// - #include +#include #include "bitcount.h" #include "movegen.h" +#include "position.h" +#include "misc.h" // Simple macro to wrap a very common while loop, no facny, no flexibility, // hardcoded list name 'mlist' and from square 'from'. @@ -34,943 +32,489 @@ // Version used for pawns, where the 'from' square is given as a delta from the 'to' square #define SERIALIZE_MOVES_D(b, d) while (b) { to = pop_1st_bit(&b); (*mlist++).move = make_move(to + (d), to); } -//// -//// Local definitions -//// - namespace { - enum CastlingSide { - KING_SIDE, - QUEEN_SIDE - }; - - enum MoveType { - CAPTURE, - NON_CAPTURE - }; - - // Functions - bool castling_is_check(const Position&, CastlingSide); + enum CastlingSide { KING_SIDE, QUEEN_SIDE }; - // Helper templates template - MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist); + MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist, Color us) { - template - MoveStack* generate_pawn_blocking_evasions(const Position&, Bitboard, Bitboard, MoveStack*); + const CastleRight CR[] = { Side ? WHITE_OOO : WHITE_OO, + Side ? BLACK_OOO : BLACK_OO }; - template - MoveStack* generate_pawn_captures(const Position& pos, MoveStack* mlist); + if (!pos.can_castle(CR[us])) + return mlist; - template - MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool promotion); + // After castling, the rook and king final positions are the same in Chess960 + // as they would be in standard chess. + Square kfrom = pos.king_square(us); + Square rfrom = pos.castle_rook_square(CR[us]); + Square kto = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1); + Square rto = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1); + Bitboard enemies = pos.pieces(flip(us)); + + assert(!pos.in_check()); + assert(pos.piece_on(kfrom) == make_piece(us, KING)); + assert(pos.piece_on(rfrom) == make_piece(us, ROOK)); + + // Unimpeded rule: All the squares between the king's initial and final squares + // (including the final square), and all the squares between the rook's initial + // and final squares (including the final square), must be vacant except for + // the king and castling rook. + for (Square s = std::min(rfrom, rto), e = std::max(rfrom, rto); s <= e; s++) + if (s != kfrom && s != rfrom && !pos.square_is_empty(s)) + return mlist; - template - MoveStack* generate_pawn_noncaptures(const Position& pos, MoveStack* mlist); + for (Square s = std::min(kfrom, kto), e = std::max(kfrom, kto); s <= e; s++) + if ( (s != kfrom && s != rfrom && !pos.square_is_empty(s)) + ||(pos.attackers_to(s) & enemies)) + return mlist; - template - MoveStack* generate_pawn_checks(const Position&, Bitboard, Square, MoveStack*); + // Because we generate only legal castling moves we need to verify that + // when moving the castling rook we do not discover some hidden checker. + // For instance an enemy queen in SQ_A1 when castling rook is in SQ_B1. + if (pos.is_chess960()) + { + Bitboard occ = pos.occupied_squares(); + clear_bit(&occ, rfrom); + if (pos.attackers_to(kto, occ) & enemies) + return mlist; + } - template - inline Bitboard move_pawns(Bitboard p) { + (*mlist++).move = make_castle(kfrom, rfrom); - if (Direction == DELTA_N) - return Us == WHITE ? p << 8 : p >> 8; - else if (Direction == DELTA_NE) - return Us == WHITE ? p << 9 : p >> 7; - else if (Direction == DELTA_NW) - return Us == WHITE ? p << 7 : p >> 9; - else - return p; + return mlist; } - // Template generate_piece_checks() with specializations - template - MoveStack* generate_piece_checks(const Position&, MoveStack*, Color, Bitboard, Square); - template<> - inline MoveStack* generate_piece_checks(const Position& p, MoveStack* m, Color us, Bitboard dc, Square ksq) { + template + inline Bitboard move_pawns(Bitboard p) { - return (us == WHITE ? generate_pawn_checks(p, dc, ksq, m) - : generate_pawn_checks(p, dc, ksq, m)); + return Delta == DELTA_N ? p << 8 : Delta == DELTA_S ? p >> 8 : + Delta == DELTA_NE ? p << 9 : Delta == DELTA_SE ? p >> 7 : + Delta == DELTA_NW ? p << 7 : Delta == DELTA_SW ? p >> 9 : p; } - // Template generate_piece_moves() with specializations and overloads - template - MoveStack* generate_piece_moves(const Position&, MoveStack*, Color us, Bitboard); - - template<> - MoveStack* generate_piece_moves(const Position&, MoveStack*, Color, Bitboard); - - template - inline MoveStack* generate_piece_moves(const Position& p, MoveStack* m, Color us) { - - assert(Piece == PAWN); - - if (Type == CAPTURE) - return (us == WHITE ? generate_pawn_captures(p, m) - : generate_pawn_captures(p, m)); - else - return (us == WHITE ? generate_pawn_noncaptures(p, m) - : generate_pawn_noncaptures(p, m)); - } - template - MoveStack* generate_piece_moves(const Position&, MoveStack*, Color us, Bitboard, Bitboard); + template + inline MoveStack* generate_pawn_captures(MoveStack* mlist, Bitboard pawns, Bitboard target) { - template<> - inline MoveStack* generate_piece_moves(const Position& p, MoveStack* m, - Color us, Bitboard t, Bitboard pnd) { + const Bitboard TFileABB = ( Delta == DELTA_NE + || Delta == DELTA_SE ? FileABB : FileHBB); + Bitboard b; + Square to; - return (us == WHITE ? generate_pawn_blocking_evasions(p, pnd, t, m) - : generate_pawn_blocking_evasions(p, pnd, t, m)); + b = move_pawns(pawns) & target & ~TFileABB; + SERIALIZE_MOVES_D(b, -Delta); + return mlist; } -} - - -//// -//// Functions -//// - -/// generate_captures generates() all pseudo-legal captures and queen -/// promotions. The return value is the number of moves generated. -MoveStack* generate_captures(const Position& pos, MoveStack* mlist) { - - assert(pos.is_ok()); - assert(!pos.is_check()); - - Color us = pos.side_to_move(); - Bitboard target = pos.pieces_of_color(opposite_color(us)); - - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us); - return generate_piece_moves(pos, mlist, us, target); -} - - -/// generate_noncaptures() generates all pseudo-legal non-captures and -/// underpromotions. The return value is the number of moves generated. - -MoveStack* generate_noncaptures(const Position& pos, MoveStack* mlist) { - - assert(pos.is_ok()); - assert(!pos.is_check()); - - Color us = pos.side_to_move(); - Bitboard target = pos.empty_squares(); - - mlist = generate_piece_moves(pos, mlist, us); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_piece_moves(pos, mlist, us, target); - mlist = generate_castle_moves(pos, mlist); - return generate_castle_moves(pos, mlist); -} + template + inline MoveStack* generate_promotions(MoveStack* mlist, Bitboard pawnsOn7, Bitboard target, Square ksq) { + const Bitboard TFileABB = ( Delta == DELTA_NE + || Delta == DELTA_SE ? FileABB : FileHBB); + Bitboard b; + Square to; -/// generate_non_capture_checks() generates all pseudo-legal non-capturing, -/// non-promoting checks. It returns the number of generated moves. + b = move_pawns(pawnsOn7) & target; -MoveStack* generate_non_capture_checks(const Position& pos, MoveStack* mlist, Bitboard dc) { + if (Delta != DELTA_N && Delta != DELTA_S) + b &= ~TFileABB; - assert(pos.is_ok()); - assert(!pos.is_check()); + while (b) + { + to = pop_1st_bit(&b); - Color us = pos.side_to_move(); - Square ksq = pos.king_square(opposite_color(us)); + if (Type == MV_CAPTURE || Type == MV_EVASION || Type == MV_NON_EVASION) + (*mlist++).move = make_promotion(to - Delta, to, QUEEN); - assert(pos.piece_on(ksq) == piece_of_color_and_type(opposite_color(us), KING)); + if (Type == MV_NON_CAPTURE || Type == MV_EVASION || Type == MV_NON_EVASION) + { + (*mlist++).move = make_promotion(to - Delta, to, ROOK); + (*mlist++).move = make_promotion(to - Delta, to, BISHOP); + (*mlist++).move = make_promotion(to - Delta, to, KNIGHT); + } - // Pieces moves - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); - mlist = generate_piece_checks(pos, mlist, us, dc, ksq); + // Knight-promotion is the only one that can give a check (direct or + // discovered) not already included in the queen-promotion. + if ( Type == MV_CHECK + && bit_is_set(StepAttacksBB[W_KNIGHT][to], ksq)) + (*mlist++).move = make_promotion(to - Delta, to, KNIGHT); + else + (void)ksq; // Silence a warning under MSVC + } + return mlist; + } - // Castling moves that give check. Very rare but nice to have! - if ( pos.can_castle_queenside(us) - && (square_rank(ksq) == square_rank(pos.king_square(us)) || square_file(ksq) == FILE_D) - && castling_is_check(pos, QUEEN_SIDE)) - mlist = generate_castle_moves(pos, mlist); - if ( pos.can_castle_kingside(us) - && (square_rank(ksq) == square_rank(pos.king_square(us)) || square_file(ksq) == FILE_F) - && castling_is_check(pos, KING_SIDE)) - mlist = generate_castle_moves(pos, mlist); + template + MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist, Bitboard target, Square ksq) { - return mlist; -} + // Calculate our parametrized parameters at compile time, named according to + // the point of view of white side. + const Color Them = (Us == WHITE ? BLACK : WHITE); + const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB); + const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB); + const Square UP = (Us == WHITE ? DELTA_N : DELTA_S); + const Square RIGHT = (Us == WHITE ? DELTA_NE : DELTA_SW); + const Square LEFT = (Us == WHITE ? DELTA_NW : DELTA_SE); + Square to; + Bitboard b1, b2, dc1, dc2, emptySquares; -/// generate_evasions() generates all check evasions when the side to move is -/// in check. Unlike the other move generation functions, this one generates -/// only legal moves. It returns the number of generated moves. + Bitboard pawns = pos.pieces(PAWN, Us); + Bitboard pawnsOn7 = pawns & TRank7BB; + Bitboard pawnsNotOn7 = pawns & ~TRank7BB; -MoveStack* generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pinned) { + Bitboard enemies = (Type == MV_EVASION ? pos.pieces(Them) & target: + Type == MV_CAPTURE ? target : pos.pieces(Them)); - assert(pos.is_ok()); - assert(pos.is_check()); + // Single and double pawn pushes, no promotions + if (Type != MV_CAPTURE) + { + emptySquares = (Type == MV_NON_CAPTURE ? target : pos.empty_squares()); - Square from, to; - Color us = pos.side_to_move(); - Color them = opposite_color(us); - Square ksq = pos.king_square(us); + b1 = move_pawns(pawnsNotOn7) & emptySquares; + b2 = move_pawns(b1 & TRank3BB) & emptySquares; - assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING)); + if (Type == MV_EVASION) + { + b1 &= target; // Consider only blocking squares + b2 &= target; + } - // The bitboard of occupied pieces without our king - Bitboard b_noKing = pos.occupied_squares(); - clear_bit(&b_noKing, ksq); + if (Type == MV_CHECK) + { + // Consider only direct checks + b1 &= pos.attacks_from(ksq, Them); + b2 &= pos.attacks_from(ksq, Them); + + // Add pawn pushes which give discovered check. This is possible only + // if the pawn is not on the same file as the enemy king, because we + // don't generate captures. Note that a possible discovery check + // promotion has been already generated among captures. + if (pawnsNotOn7 & target) // For CHECK type target is dc bitboard + { + dc1 = move_pawns(pawnsNotOn7 & target) & emptySquares & ~file_bb(ksq); + dc2 = move_pawns(dc1 & TRank3BB) & emptySquares; + + b1 |= dc1; + b2 |= dc2; + } + } - // Find squares attacked by slider checkers, we will - // remove them from king evasions set so to avoid a couple - // of cycles in the slow king evasions legality check loop - // and to be able to use square_is_attacked(). - Bitboard checkers = pos.checkers(); - Bitboard checkersAttacks = EmptyBoardBB; - Bitboard b = checkers & pos.pieces(BISHOP, QUEEN); - while (b) - { - from = pop_1st_bit(&b); - checkersAttacks |= bishop_attacks_bb(from, b_noKing); - } + SERIALIZE_MOVES_D(b1, -UP); + SERIALIZE_MOVES_D(b2, -UP -UP); + } - b = checkers & pos.pieces(ROOK, QUEEN); - while (b) - { - from = pop_1st_bit(&b); - checkersAttacks |= rook_attacks_bb(from, b_noKing); - } + // Promotions and underpromotions + if (pawnsOn7) + { + if (Type == MV_CAPTURE) + emptySquares = pos.empty_squares(); - // Generate evasions for king - Bitboard b1 = pos.piece_attacks(ksq) & ~pos.pieces_of_color(us) & ~checkersAttacks; - while (b1) - { - to = pop_1st_bit(&b1); - // Note that we can use square_is_attacked() only because we - // have already removed slider checkers. - if (!pos.square_is_attacked(to, them)) - (*mlist++).move = make_move(ksq, to); - } + if (Type == MV_EVASION) + emptySquares &= target; - // Generate evasions for other pieces only if not double check. We use a - // simple bit twiddling hack here rather than calling count_1s in order to - // save some time (we know that pos.checkers() has at most two nonzero bits). - if (!(checkers & (checkers - 1))) // Only one bit set? - { - Square checksq = first_1(checkers); + mlist = generate_promotions(mlist, pawnsOn7, enemies, ksq); + mlist = generate_promotions(mlist, pawnsOn7, enemies, ksq); + mlist = generate_promotions(mlist, pawnsOn7, emptySquares, ksq); + } - assert(pos.color_of_piece_on(checksq) == them); + // Standard and en-passant captures + if (Type == MV_CAPTURE || Type == MV_EVASION || Type == MV_NON_EVASION) + { + mlist = generate_pawn_captures(mlist, pawnsNotOn7, enemies); + mlist = generate_pawn_captures(mlist, pawnsNotOn7, enemies); - // Generate captures of the checking piece + if (pos.ep_square() != SQ_NONE) + { + assert(rank_of(pos.ep_square()) == (Us == WHITE ? RANK_6 : RANK_3)); - // Pawn captures - b1 = pos.pawn_attacks(them, checksq) & pos.pieces(PAWN, us) & ~pinned; - while (b1) - { - from = pop_1st_bit(&b1); - if (relative_rank(us, checksq) == RANK_8) - { - (*mlist++).move = make_promotion_move(from, checksq, QUEEN); - (*mlist++).move = make_promotion_move(from, checksq, ROOK); - (*mlist++).move = make_promotion_move(from, checksq, BISHOP); - (*mlist++).move = make_promotion_move(from, checksq, KNIGHT); - } else - (*mlist++).move = make_move(from, checksq); - } + // An en passant capture can be an evasion only if the checking piece + // is the double pushed pawn and so is in the target. Otherwise this + // is a discovery check and we are forced to do otherwise. + if (Type == MV_EVASION && !bit_is_set(target, pos.ep_square() - UP)) + return mlist; - // Pieces captures - b1 = ( (pos.piece_attacks(checksq) & pos.pieces(KNIGHT, us)) - | (pos.piece_attacks(checksq) & pos.pieces(BISHOP, QUEEN, us)) - | (pos.piece_attacks(checksq) & pos.pieces(ROOK, QUEEN, us)) ) & ~pinned; + b1 = pawnsNotOn7 & pos.attacks_from(pos.ep_square(), Them); - while (b1) - { - from = pop_1st_bit(&b1); - (*mlist++).move = make_move(from, checksq); - } + assert(b1); - // Blocking check evasions are possible only if the checking piece is - // a slider. - if (checkers & (pos.pieces(BISHOP) | pos.pieces(ROOK) | pos.pieces(QUEEN))) - { - Bitboard blockSquares = squares_between(checksq, ksq); - - assert((pos.occupied_squares() & blockSquares) == EmptyBoardBB); - - if (blockSquares != EmptyBoardBB) - { - mlist = generate_piece_moves(pos, mlist, us, blockSquares, pinned); - mlist = generate_piece_moves(pos, mlist, us, blockSquares, pinned); - mlist = generate_piece_moves(pos, mlist, us, blockSquares, pinned); - mlist = generate_piece_moves(pos, mlist, us, blockSquares, pinned); - mlist = generate_piece_moves(pos, mlist, us, blockSquares, pinned); - } - } + while (b1) + (*mlist++).move = make_enpassant(pop_1st_bit(&b1), pos.ep_square()); + } + } - // Finally, the special case of en passant captures. An en passant - // capture can only be a check evasion if the check is not a discovered - // check. If pos.ep_square() is set, the last move made must have been - // a double pawn push. If, furthermore, the checking piece is a pawn, - // an en passant check evasion may be possible. - if (pos.ep_square() != SQ_NONE && (checkers & pos.pieces(PAWN, them))) - { - to = pos.ep_square(); - b1 = pos.pawn_attacks(them, to) & pos.pieces(PAWN, us); - - // The checking pawn cannot be a discovered (bishop) check candidate - // otherwise we were in check also before last double push move. - assert(!bit_is_set(pos.discovered_check_candidates(them), checksq)); - assert(count_1s(b1) == 1 || count_1s(b1) == 2); - - b1 &= ~pinned; - while (b1) - { - from = pop_1st_bit(&b1); - // Move is always legal because checking pawn is not a discovered - // check candidate and our capturing pawn has been already tested - // against pinned pieces. - (*mlist++).move = make_ep_move(from, to); - } - } + return mlist; } - return mlist; -} - -/// generate_legal_moves() computes a complete list of legal moves in the -/// current position. This function is not very fast, and should be used -/// only in situations where performance is unimportant. It wouldn't be -/// very hard to write an efficient legal move generator, but for the moment -/// we don't need it. -MoveStack* generate_legal_moves(const Position& pos, MoveStack* mlist) { + template + inline MoveStack* generate_direct_checks(const Position& pos, MoveStack* mlist, Color us, + Bitboard dc, Square ksq) { + assert(Pt != KING && Pt != PAWN); - assert(pos.is_ok()); - - Bitboard pinned = pos.pinned_pieces(pos.side_to_move()); - - if (pos.is_check()) - return generate_evasions(pos, mlist, pinned); - - // Generate pseudo-legal moves - MoveStack* last = generate_captures(pos, mlist); - last = generate_noncaptures(pos, last); - - // Remove illegal moves from the list - for (MoveStack* cur = mlist; cur != last; cur++) - if (!pos.pl_move_is_legal(cur->move, pinned)) - { - cur->move = (--last)->move; - cur--; - } - return last; -} - - -/// move_is_legal() takes a position and a (not necessarily pseudo-legal) -/// move and a pinned pieces bitboard as input, and tests whether -/// the move is legal. If the move is legal, the move itself is -/// returned. If not, the function returns false. This function must -/// only be used when the side to move is not in check. - -bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) { - - assert(pos.is_ok()); - assert(!pos.is_check()); - assert(move_is_ok(m)); - assert(pinned == pos.pinned_pieces(pos.side_to_move())); - - Color us = pos.side_to_move(); - Square from = move_from(m); - Piece pc = pos.piece_on(from); + Bitboard checkSqs, b; + Square from; + const Square* pl = pos.piece_list(us, Pt); - // If the from square is not occupied by a piece belonging to the side to - // move, the move is obviously not legal. - if (color_of_piece(pc) != us) - return false; + if ((from = *pl++) == SQ_NONE) + return mlist; - Color them = opposite_color(us); - Square to = move_to(m); + checkSqs = pos.attacks_from(ksq) & pos.empty_squares(); - // En passant moves - if (move_is_ep(m)) - { - // The piece must be a pawn and destination square must be the - // en passant square. - if ( type_of_piece(pc) != PAWN - || to != pos.ep_square()) - return false; + do + { + if ( (Pt == QUEEN && !(QueenPseudoAttacks[from] & checkSqs)) + || (Pt == ROOK && !(RookPseudoAttacks[from] & checkSqs)) + || (Pt == BISHOP && !(BishopPseudoAttacks[from] & checkSqs))) + continue; - assert(pos.square_is_empty(to)); - assert(pos.piece_on(to - pawn_push(us)) == piece_of_color_and_type(them, PAWN)); + if (dc && bit_is_set(dc, from)) + continue; - // The move is pseudo-legal, check if it is also legal - return pos.pl_move_is_legal(m, pinned); - } + b = pos.attacks_from(from) & checkSqs; + SERIALIZE_MOVES(b); - // Castling moves - if (move_is_short_castle(m)) - { - // The piece must be a king and side to move must still have - // the right to castle kingside. - if ( type_of_piece(pc) != KING - ||!pos.can_castle_kingside(us)) - return false; - - assert(from == pos.king_square(us)); - assert(to == pos.initial_kr_square(us)); - assert(pos.piece_on(to) == piece_of_color_and_type(us, ROOK)); - - Square g1 = relative_square(us, SQ_G1); - Square f1 = relative_square(us, SQ_F1); - Square s; - bool illegal = false; - - // Check if any of the squares between king and rook - // is occupied or under attack. - for (s = Min(from, g1); s <= Max(from, g1); s++) - if ( (s != from && s != to && !pos.square_is_empty(s)) - || pos.square_is_attacked(s, them)) - illegal = true; - - // Check if any of the squares between king and rook - // is occupied. - for (s = Min(to, f1); s <= Max(to, f1); s++) - if (s != from && s != to && !pos.square_is_empty(s)) - illegal = true; - - return !illegal; - } + } while ((from = *pl++) != SQ_NONE); - if (move_is_long_castle(m)) - { - // The piece must be a king and side to move must still have - // the right to castle kingside. - if ( type_of_piece(pc) != KING - ||!pos.can_castle_queenside(us)) - return false; - - assert(from == pos.king_square(us)); - assert(to == pos.initial_qr_square(us)); - assert(pos.piece_on(to) == piece_of_color_and_type(us, ROOK)); - - Square c1 = relative_square(us, SQ_C1); - Square d1 = relative_square(us, SQ_D1); - Square s; - bool illegal = false; - - for (s = Min(from, c1); s <= Max(from, c1); s++) - if( (s != from && s != to && !pos.square_is_empty(s)) - || pos.square_is_attacked(s, them)) - illegal = true; - - for (s = Min(to, d1); s <= Max(to, d1); s++) - if(s != from && s != to && !pos.square_is_empty(s)) - illegal = true; - - if ( square_file(to) == FILE_B - && ( pos.piece_on(to + DELTA_W) == piece_of_color_and_type(them, ROOK) - || pos.piece_on(to + DELTA_W) == piece_of_color_and_type(them, QUEEN))) - illegal = true; - - return !illegal; + return mlist; } - // Normal moves - // The destination square cannot be occupied by a friendly piece - if (pos.color_of_piece_on(to) == us) - return false; - - // Proceed according to the type of the moving piece. - if (type_of_piece(pc) == PAWN) - { - // Move direction must be compatible with pawn color - int direction = to - from; - if ((us == WHITE) != (direction > 0)) - return false; - - // If the destination square is on the 8/1th rank, the move must - // be a promotion. - if ( ( (square_rank(to) == RANK_8 && us == WHITE) - ||(square_rank(to) == RANK_1 && us != WHITE)) - && !move_is_promotion(m)) - return false; - - // Proceed according to the square delta between the source and - // destionation squares. - switch (direction) - { - case DELTA_NW: - case DELTA_NE: - case DELTA_SW: - case DELTA_SE: - // Capture. The destination square must be occupied by an enemy - // piece (en passant captures was handled earlier). - if (pos.color_of_piece_on(to) != them) - return false; - break; - - case DELTA_N: - case DELTA_S: - // Pawn push. The destination square must be empty. - if (!pos.square_is_empty(to)) - return false; - break; - - case DELTA_NN: - // Double white pawn push. The destination square must be on the fourth - // rank, and both the destination square and the square between the - // source and destination squares must be empty. - if ( square_rank(to) != RANK_4 - || !pos.square_is_empty(to) - || !pos.square_is_empty(from + DELTA_N)) - return false; - break; - - case DELTA_SS: - // Double black pawn push. The destination square must be on the fifth - // rank, and both the destination square and the square between the - // source and destination squares must be empty. - if ( square_rank(to) != RANK_5 - || !pos.square_is_empty(to) - || !pos.square_is_empty(from + DELTA_S)) - return false; - break; + template<> + FORCE_INLINE MoveStack* generate_direct_checks(const Position& p, MoveStack* m, Color us, Bitboard dc, Square ksq) { - default: - return false; - } - // The move is pseudo-legal, check if it is also legal - return pos.pl_move_is_legal(m, pinned); + return (us == WHITE ? generate_pawn_moves(p, m, dc, ksq) + : generate_pawn_moves(p, m, dc, ksq)); } - // Luckly we can handle all the other pieces in one go - return ( pos.piece_attacks_square(pos.piece_on(from), from, to) - && pos.pl_move_is_legal(m, pinned) - && !move_is_promotion(m)); -} - -/// Another version of move_is_legal(), which takes only a position and a move -/// as input. This function does not require that the side to move is not in -/// check. It is not optimized for speed, and is only used for verifying move -/// legality when building a PV from the transposition table. + template + FORCE_INLINE MoveStack* generate_piece_moves(const Position& p, MoveStack* m, Color us, Bitboard t) { -bool move_is_legal(const Position& pos, const Move m) { - - Bitboard pinned = pos.pinned_pieces(pos.side_to_move()); - if (!pos.is_check()) - return move_is_legal(pos, m, pinned); - else - { - Position p(pos); - MoveStack mlist[64]; - MoveStack* last = generate_evasions(p, mlist, pinned); - for (MoveStack* cur = mlist; cur != last; cur++) - if (cur->move == m) - return true; - - return false; + assert(Pt == PAWN); + return (us == WHITE ? generate_pawn_moves(p, m, t, SQ_NONE) + : generate_pawn_moves(p, m, t, SQ_NONE)); } -} - -namespace { - template - MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) { + template + FORCE_INLINE MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) { - Square from; Bitboard b; - - for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++) - { - from = pos.piece_list(us, Piece, i); - b = pos.piece_attacks(from) & target; - SERIALIZE_MOVES(b); - } - return mlist; - } - - template - MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, - Color us, Bitboard target, Bitboard pinned) { Square from; - Bitboard b; + const Square* pl = pos.piece_list(us, Pt); - for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++) + if (*pl != SQ_NONE) { - from = pos.piece_list(us, Piece, i); - if (pinned && bit_is_set(pinned, from)) - continue; - - b = pos.piece_attacks(from) & target; - SERIALIZE_MOVES(b); + do { + from = *pl; + b = pos.attacks_from(from) & target; + SERIALIZE_MOVES(b); + } while (*++pl != SQ_NONE); } return mlist; } + template<> - MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) { + FORCE_INLINE MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) { Bitboard b; Square from = pos.king_square(us); - b = pos.piece_attacks(from) & target; + b = pos.attacks_from(from) & target; SERIALIZE_MOVES(b); return mlist; } - template - MoveStack* generate_pawn_captures_diagonal(MoveStack* mlist, Bitboard pawns, Bitboard enemyPieces, bool promotion) { +} // namespace - // Calculate our parametrized parameters at compile time - const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB); - const Bitboard TFileABB = (Diagonal == DELTA_NE ? FileABB : FileHBB); - const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE); - const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW); - const SquareDelta TTDELTA_NE = (Diagonal == DELTA_NE ? TDELTA_NE : TDELTA_NW); - Square to; +/// generate generates all pseudo-legal captures and queen +/// promotions. Returns a pointer to the end of the move list. +/// +/// generate generates all pseudo-legal non-captures and +/// underpromotions. Returns a pointer to the end of the move list. +/// +/// generate generates all pseudo-legal captures and +/// non-captures. Returns a pointer to the end of the move list. - // Captures in the a1-h8 (a8-h1 for black) diagonal or in the h1-a8 (h8-a1 for black) - Bitboard b1 = move_pawns(pawns) & ~TFileABB & enemyPieces; +template +MoveStack* generate(const Position& pos, MoveStack* mlist) { - // Capturing promotions - if (promotion) - { - Bitboard b2 = b1 & TRank8BB; - b1 &= ~TRank8BB; - while (b2) - { - to = pop_1st_bit(&b2); - (*mlist++).move = make_promotion_move(to - TTDELTA_NE, to, QUEEN); - } - } + assert(Type == MV_CAPTURE || Type == MV_NON_CAPTURE || Type == MV_NON_EVASION); + assert(!pos.in_check()); - // Capturing non-promotions - SERIALIZE_MOVES_D(b1, -TTDELTA_NE); - return mlist; - } - - template - MoveStack* generate_pawn_captures(const Position& pos, MoveStack* mlist) { + Color us = pos.side_to_move(); + Bitboard target; - // Calculate our parametrized parameters at compile time - const Color Them = (Us == WHITE ? BLACK : WHITE); - const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB); - const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB); - const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S); + if (Type == MV_CAPTURE) + target = pos.pieces(flip(us)); - Square to; - Bitboard pawns = pos.pieces(PAWN, Us); - Bitboard enemyPieces = pos.pieces_of_color(opposite_color(Us)); - bool possiblePromotion = (pawns & TRank7BB); + else if (Type == MV_NON_CAPTURE) + target = pos.empty_squares(); - // Standard captures and capturing promotions in both directions - mlist = generate_pawn_captures_diagonal(mlist, pawns, enemyPieces, possiblePromotion); - mlist = generate_pawn_captures_diagonal(mlist, pawns, enemyPieces, possiblePromotion); + else if (Type == MV_NON_EVASION) + target = pos.pieces(flip(us)) | pos.empty_squares(); - // Non-capturing promotions - if (possiblePromotion) - { - Bitboard b1 = move_pawns(pawns) & pos.empty_squares() & TRank8BB; - while (b1) - { - to = pop_1st_bit(&b1); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN); - } - } - - // En passant captures - if (pos.ep_square() != SQ_NONE) - { - assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6); - assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3); - - Bitboard b1 = pawns & pos.pawn_attacks(Them, pos.ep_square()); - assert(b1 != EmptyBoardBB); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); - while (b1) - { - to = pop_1st_bit(&b1); - (*mlist++).move = make_ep_move(to, pos.ep_square()); - } - } - return mlist; + if (Type != MV_CAPTURE && pos.can_castle(us)) + { + mlist = generate_castle_moves(pos, mlist, us); + mlist = generate_castle_moves(pos, mlist, us); } - template - MoveStack* generate_pawn_noncaptures(const Position& pos, MoveStack* mlist) { - - // Calculate our parametrized parameters at compile time - const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB); - const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB); - const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB); - const SquareDelta TDELTA_NE = (Us == WHITE ? DELTA_NE : DELTA_SE); - const SquareDelta TDELTA_NW = (Us == WHITE ? DELTA_NW : DELTA_SW); - const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S); + return mlist; +} - Bitboard b1, b2; - Square to; - Bitboard pawns = pos.pieces(PAWN, Us); - Bitboard emptySquares = pos.empty_squares(); +// Explicit template instantiations +template MoveStack* generate(const Position& pos, MoveStack* mlist); +template MoveStack* generate(const Position& pos, MoveStack* mlist); +template MoveStack* generate(const Position& pos, MoveStack* mlist); - if (pawns & TRank7BB) // There is some promotion candidate ? - { - Bitboard enemyPieces = pos.pieces_of_color(opposite_color(Us)); - // Underpromotion captures in the a1-h8 (a8-h1 for black) direction - b1 = move_pawns(pawns) & ~FileABB & enemyPieces & TRank8BB; - while (b1) - { - to = pop_1st_bit(&b1); - (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, ROOK); - (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, BISHOP); - (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, KNIGHT); - } +/// generate generates all pseudo-legal non-captures and knight +/// underpromotions that give check. Returns a pointer to the end of the move list. +template<> +MoveStack* generate(const Position& pos, MoveStack* mlist) { - // Underpromotion captures in the h1-a8 (h8-a1 for black) direction - b1 = move_pawns(pawns) & ~FileHBB & enemyPieces & TRank8BB; - while (b1) - { - to = pop_1st_bit(&b1); - (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, ROOK); - (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, BISHOP); - (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, KNIGHT); - } + assert(!pos.in_check()); - // Underpromotion pawn pushes - b1 = move_pawns(pawns) & emptySquares & TRank8BB; - while (b1) - { - to = pop_1st_bit(&b1); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT); - } - } - - // Single pawn pushes - b2 = b1 = move_pawns(pawns) & emptySquares & ~TRank8BB; - SERIALIZE_MOVES_D(b2, -TDELTA_N); + Bitboard b, dc; + Square from; + PieceType pt; + Color us = pos.side_to_move(); + Square ksq = pos.king_square(flip(us)); - // Double pawn pushes - b2 = move_pawns(b1 & TRank3BB) & emptySquares; - SERIALIZE_MOVES_D(b2, -TDELTA_N -TDELTA_N); - return mlist; - } + assert(pos.piece_on(ksq) == make_piece(flip(us), KING)); + // Discovered non-capture checks + b = dc = pos.discovered_check_candidates(); - template - MoveStack* generate_pawn_checks(const Position& pos, Bitboard dc, Square ksq, MoveStack* mlist) + while (b) { - // Calculate our parametrized parameters at compile time - const Color Them = (Us == WHITE ? BLACK : WHITE); - const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB); - const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB); - const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S); - const SquareDelta TDELTA_S = (Us == WHITE ? DELTA_S : DELTA_N); - - Square to; - Bitboard b1, b2, b3; - Bitboard pawns = pos.pieces(PAWN, Us); + from = pop_1st_bit(&b); + pt = type_of(pos.piece_on(from)); - if (dc & pawns) - { - Bitboard empty = pos.empty_squares(); + if (pt == PAWN) + continue; // Will be generated togheter with direct checks - // Pawn moves which gives discovered check. This is possible only if the - // pawn is not on the same file as the enemy king, because we don't - // generate captures. - b1 = pawns & ~file_bb(ksq); + b = pos.attacks_from(Piece(pt), from) & pos.empty_squares(); - // Discovered checks, single pawn pushes, no promotions - b2 = b3 = move_pawns(b1 & dc) & empty & ~TRank8BB; - SERIALIZE_MOVES_D(b3, -TDELTA_N); + if (pt == KING) + b &= ~QueenPseudoAttacks[ksq]; - // Discovered checks, double pawn pushes - b3 = move_pawns(b2 & TRank3BB) & empty; - SERIALIZE_MOVES_D(b3, -TDELTA_N -TDELTA_N); - } - - // Direct checks. These are possible only for pawns on neighboring files - // and in the two ranks that, after the push, are in front of the enemy king. - b1 = pawns & neighboring_files_bb(ksq) & ~dc; - - // We can get false positives if (ksq + x) is not in [0,63] range but - // is not a problem, they will be filtered out later. - b2 = b1 & (rank_bb(ksq + 2 * TDELTA_S) | rank_bb(ksq + 3 * TDELTA_S)); - if (!b2) - return mlist; - - // Direct checks, single pawn pushes - Bitboard empty = pos.empty_squares(); - b2 = move_pawns(b1) & empty; - b3 = b2 & pos.pawn_attacks(Them, ksq); - SERIALIZE_MOVES_D(b3, -TDELTA_N); - - // Direct checks, double pawn pushes - b3 = move_pawns(b2 & TRank3BB) & empty & pos.pawn_attacks(Them, ksq); - SERIALIZE_MOVES_D(b3, -TDELTA_N -TDELTA_N); - return mlist; + SERIALIZE_MOVES(b); } - template - MoveStack* generate_piece_checks(const Position& pos, MoveStack* mlist, Color us, - Bitboard dc, Square ksq) { - - Bitboard target = pos.pieces(Piece, us); - - // Discovered checks - Bitboard b = target & dc; - while (b) - { - Square from = pop_1st_bit(&b); - Bitboard bb = pos.piece_attacks(from) & pos.empty_squares(); - if (Piece == KING) - bb &= ~QueenPseudoAttacks[ksq]; - - SERIALIZE_MOVES(bb); - } - - // Direct checks - b = target & ~dc; - if (Piece != KING || b) - { - Bitboard checkSqs = pos.piece_attacks(ksq) & pos.empty_squares(); - if (!checkSqs) - return mlist; - - while (b) - { - Square from = pop_1st_bit(&b); - if ( (Piece == QUEEN && !(QueenPseudoAttacks[from] & checkSqs)) - || (Piece == ROOK && !(RookPseudoAttacks[from] & checkSqs)) - || (Piece == BISHOP && !(BishopPseudoAttacks[from] & checkSqs))) - continue; - - Bitboard bb = pos.piece_attacks(from) & checkSqs; - SERIALIZE_MOVES(bb); - } - } - return mlist; - } - - template - MoveStack* generate_pawn_blocking_evasions(const Position& pos, Bitboard pinned, - Bitboard blockSquares, MoveStack* mlist) { - - // Calculate our parametrized parameters at compile time - const Rank TRANK_8 = (Us == WHITE ? RANK_8 : RANK_1); - const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB); - const SquareDelta TDELTA_N = (Us == WHITE ? DELTA_N : DELTA_S); + // Direct non-capture checks + mlist = generate_direct_checks(pos, mlist, us, dc, ksq); + mlist = generate_direct_checks(pos, mlist, us, dc, ksq); + mlist = generate_direct_checks(pos, mlist, us, dc, ksq); + mlist = generate_direct_checks(pos, mlist, us, dc, ksq); + return generate_direct_checks(pos, mlist, us, dc, ksq); +} - Square to; - // Find non-pinned pawns and push them one square - Bitboard b1 = move_pawns(pos.pieces(PAWN, Us) & ~pinned); +/// generate generates all pseudo-legal check evasions when the side +/// to move is in check. Returns a pointer to the end of the move list. +template<> +MoveStack* generate(const Position& pos, MoveStack* mlist) { - // We don't have to AND with empty squares here, - // because the blocking squares will always be empty. - Bitboard b2 = b1 & blockSquares; - while (b2) - { - to = pop_1st_bit(&b2); + assert(pos.in_check()); - assert(pos.piece_on(to) == EMPTY); + Bitboard b, target; + Square from, checksq; + int checkersCnt = 0; + Color us = pos.side_to_move(); + Square ksq = pos.king_square(us); + Bitboard checkers = pos.checkers(); + Bitboard sliderAttacks = 0; - if (square_rank(to) == TRANK_8) - { - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP); - (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT); - } else - (*mlist++).move = make_move(to - TDELTA_N, to); - } + assert(pos.piece_on(ksq) == make_piece(us, KING)); + assert(checkers); - // Double pawn pushes - b2 = b1 & pos.empty_squares() & TRank3BB; - b2 = move_pawns(b2) & blockSquares; - while (b2) - { - to = pop_1st_bit(&b2); - - assert(pos.piece_on(to) == EMPTY); - assert(Us != WHITE || square_rank(to) == RANK_4); - assert(Us != BLACK || square_rank(to) == RANK_5); + // Find squares attacked by slider checkers, we will remove + // them from the king evasions set so to early skip known + // illegal moves and avoid an useless legality check later. + b = checkers; + do + { + checkersCnt++; + checksq = pop_1st_bit(&b); - (*mlist++).move = make_move(to - TDELTA_N - TDELTA_N, to); - } - return mlist; - } + assert(color_of(pos.piece_on(checksq)) == flip(us)); - template - MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist) { + switch (type_of(pos.piece_on(checksq))) + { + case BISHOP: sliderAttacks |= BishopPseudoAttacks[checksq]; break; + case ROOK: sliderAttacks |= RookPseudoAttacks[checksq]; break; + case QUEEN: + // If queen and king are far we can safely remove all the squares attacked + // in the other direction becuase are not reachable by the king anyway. + if (squares_between(ksq, checksq) || (RookPseudoAttacks[checksq] & (1ULL << ksq))) + sliderAttacks |= QueenPseudoAttacks[checksq]; + + // Otherwise, if king and queen are adjacent and on a diagonal line, we need to + // use real rook attacks to check if king is safe to move in the other direction. + // For example: king in B2, queen in A1 a knight in B1, and we can safely move to C1. + else + sliderAttacks |= BishopPseudoAttacks[checksq] | pos.attacks_from(checksq); - Color us = pos.side_to_move(); + default: + break; + } + } while (b); - if ( (Side == KING_SIDE && pos.can_castle_kingside(us)) - ||(Side == QUEEN_SIDE && pos.can_castle_queenside(us))) - { - Color them = opposite_color(us); - Square ksq = pos.king_square(us); + // Generate evasions for king, capture and non capture moves + b = pos.attacks_from(ksq) & ~pos.pieces(us) & ~sliderAttacks; + from = ksq; + SERIALIZE_MOVES(b); - assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING)); + // Generate evasions for other pieces only if not double check + if (checkersCnt > 1) + return mlist; - Square rsq = (Side == KING_SIDE ? pos.initial_kr_square(us) : pos.initial_qr_square(us)); - Square s1 = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1); - Square s2 = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1); - Square s; - bool illegal = false; + // Find squares where a blocking evasion or a capture of the + // checker piece is possible. + target = squares_between(checksq, ksq) | checkers; - assert(pos.piece_on(rsq) == piece_of_color_and_type(us, ROOK)); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + mlist = generate_piece_moves(pos, mlist, us, target); + return generate_piece_moves(pos, mlist, us, target); +} - // It is a bit complicated to correctly handle Chess960 - for (s = Min(ksq, s1); s <= Max(ksq, s1); s++) - if ( (s != ksq && s != rsq && pos.square_is_occupied(s)) - || pos.square_is_attacked(s, them)) - illegal = true; - for (s = Min(rsq, s2); s <= Max(rsq, s2); s++) - if (s != ksq && s != rsq && pos.square_is_occupied(s)) - illegal = true; +/// generate computes a complete list of legal moves in the current position - if ( Side == QUEEN_SIDE - && square_file(rsq) == FILE_B - && ( pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, ROOK) - || pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, QUEEN))) - illegal = true; +template<> +MoveStack* generate(const Position& pos, MoveStack* mlist) { - if (!illegal) - (*mlist++).move = make_castle_move(ksq, rsq); - } - return mlist; - } + MoveStack *last, *cur = mlist; + Bitboard pinned = pos.pinned_pieces(); - bool castling_is_check(const Position& pos, CastlingSide side) { + last = pos.in_check() ? generate(pos, mlist) + : generate(pos, mlist); - // After castling opponent king is attacked by the castled rook? - File rookFile = (side == QUEEN_SIDE ? FILE_D : FILE_F); - Color us = pos.side_to_move(); - Square ksq = pos.king_square(us); - Bitboard occ = pos.occupied_squares(); + // Remove illegal moves from the list + while (cur != last) + if (!pos.pl_move_is_legal(cur->move, pinned)) + cur->move = (--last)->move; + else + cur++; - clear_bit(&occ, ksq); // Remove our king from the board - Square rsq = make_square(rookFile, square_rank(ksq)); - return bit_is_set(rook_attacks_bb(rsq, occ), pos.king_square(opposite_color(us))); - } + return last; }