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    1 /*
    2   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
    3   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
    4   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
    5   Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
    6 
    7   Stockfish is free software: you can redistribute it and/or modify
    8   it under the terms of the GNU General Public License as published by
    9   the Free Software Foundation, either version 3 of the License, or
   10   (at your option) any later version.
   11 
   12   Stockfish is distributed in the hope that it will be useful,
   13   but WITHOUT ANY WARRANTY; without even the implied warranty of
   14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15   GNU General Public License for more details.
   16 
   17   You should have received a copy of the GNU General Public License
   18   along with this program.  If not, see <http://www.gnu.org/licenses/>.
   19 */
   20 
   21 #include <cassert>
   22 
   23 #include "movegen.h"
   24 #include "position.h"
   25 
   26 namespace {
   27 
   28   template<GenType Type, Direction D>
   29   ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
   30 
   31     if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
   32         *moveList++ = make<PROMOTION>(to - D, to, QUEEN);
   33 
   34     if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
   35     {
   36         *moveList++ = make<PROMOTION>(to - D, to, ROOK);
   37         *moveList++ = make<PROMOTION>(to - D, to, BISHOP);
   38         *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
   39     }
   40 
   41     // Knight promotion is the only promotion that can give a direct check
   42     // that's not already included in the queen promotion.
   43     if (Type == QUIET_CHECKS && (PseudoAttacks[KNIGHT][to] & ksq))
   44         *moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
   45     else
   46         (void)ksq; // Silence a warning under MSVC
   47 
   48     return moveList;
   49   }
   50 
   51 
   52   template<Color Us, GenType Type>
   53   ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
   54 
   55     // Compute some compile time parameters relative to the white side
   56     constexpr Color     Them     = (Us == WHITE ? BLACK      : WHITE);
   57     constexpr Bitboard  TRank7BB = (Us == WHITE ? Rank7BB    : Rank2BB);
   58     constexpr Bitboard  TRank3BB = (Us == WHITE ? Rank3BB    : Rank6BB);
   59     constexpr Direction Up       = pawn_push(Us);
   60     constexpr Direction UpRight  = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
   61     constexpr Direction UpLeft   = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
   62 
   63     const Square ksq = pos.square<KING>(Them);
   64     Bitboard emptySquares;
   65 
   66     Bitboard pawnsOn7    = pos.pieces(Us, PAWN) &  TRank7BB;
   67     Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
   68 
   69     Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
   70                         Type == CAPTURES ? target : pos.pieces(Them));
   71 
   72     // Single and double pawn pushes, no promotions
   73     if (Type != CAPTURES)
   74     {
   75         emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
   76 
   77         Bitboard b1 = shift<Up>(pawnsNotOn7)   & emptySquares;
   78         Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
   79 
   80         if (Type == EVASIONS) // Consider only blocking squares
   81         {
   82             b1 &= target;
   83             b2 &= target;
   84         }
   85 
   86         if (Type == QUIET_CHECKS)
   87         {
   88             b1 &= pos.attacks_from<PAWN>(ksq, Them);
   89             b2 &= pos.attacks_from<PAWN>(ksq, Them);
   90 
   91             // Add pawn pushes which give discovered check. This is possible only
   92             // if the pawn is not on the same file as the enemy king, because we
   93             // don't generate captures. Note that a possible discovery check
   94             // promotion has been already generated amongst the captures.
   95             Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
   96             if (dcCandidateQuiets)
   97             {
   98                 Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
   99                 Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
  100 
  101                 b1 |= dc1;
  102                 b2 |= dc2;
  103             }
  104         }
  105 
  106         while (b1)
  107         {
  108             Square to = pop_lsb(&b1);
  109             *moveList++ = make_move(to - Up, to);
  110         }
  111 
  112         while (b2)
  113         {
  114             Square to = pop_lsb(&b2);
  115             *moveList++ = make_move(to - Up - Up, to);
  116         }
  117     }
  118 
  119     // Promotions and underpromotions
  120     if (pawnsOn7)
  121     {
  122         if (Type == CAPTURES)
  123             emptySquares = ~pos.pieces();
  124 
  125         if (Type == EVASIONS)
  126             emptySquares &= target;
  127 
  128         Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
  129         Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
  130         Bitboard b3 = shift<Up     >(pawnsOn7) & emptySquares;
  131 
  132         while (b1)
  133             moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
  134 
  135         while (b2)
  136             moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
  137 
  138         while (b3)
  139             moveList = make_promotions<Type, Up     >(moveList, pop_lsb(&b3), ksq);
  140     }
  141 
  142     // Standard and en-passant captures
  143     if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
  144     {
  145         Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
  146         Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
  147 
  148         while (b1)
  149         {
  150             Square to = pop_lsb(&b1);
  151             *moveList++ = make_move(to - UpRight, to);
  152         }
  153 
  154         while (b2)
  155         {
  156             Square to = pop_lsb(&b2);
  157             *moveList++ = make_move(to - UpLeft, to);
  158         }
  159 
  160         if (pos.ep_square() != SQ_NONE)
  161         {
  162             assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
  163 
  164             // An en passant capture can be an evasion only if the checking piece
  165             // is the double pushed pawn and so is in the target. Otherwise this
  166             // is a discovery check and we are forced to do otherwise.
  167             if (Type == EVASIONS && !(target & (pos.ep_square() - Up)))
  168                 return moveList;
  169 
  170             b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);
  171 
  172             assert(b1);
  173 
  174             while (b1)
  175                 *moveList++ = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
  176         }
  177     }
  178 
  179     return moveList;
  180   }
  181 
  182 
  183   template<PieceType Pt, bool Checks>
  184   ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Color us,
  185                           Bitboard target) {
  186 
  187     static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
  188 
  189     const Square* pl = pos.squares<Pt>(us);
  190 
  191     for (Square from = *pl; from != SQ_NONE; from = *++pl)
  192     {
  193         if (Checks)
  194         {
  195             if (    (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
  196                 && !(PseudoAttacks[Pt][from] & target & pos.check_squares(Pt)))
  197                 continue;
  198 
  199             if (pos.blockers_for_king(~us) & from)
  200                 continue;
  201         }
  202 
  203         Bitboard b = pos.attacks_from<Pt>(from) & target;
  204 
  205         if (Checks)
  206             b &= pos.check_squares(Pt);
  207 
  208         while (b)
  209             *moveList++ = make_move(from, pop_lsb(&b));
  210     }
  211 
  212     return moveList;
  213   }
  214 
  215 
  216   template<Color Us, GenType Type>
  217   ExtMove* generate_all(const Position& pos, ExtMove* moveList, Bitboard target) {
  218 
  219     constexpr CastlingRights OO  = Us & KING_SIDE;
  220     constexpr CastlingRights OOO = Us & QUEEN_SIDE;
  221     constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantations
  222 
  223     moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
  224     moveList = generate_moves<KNIGHT, Checks>(pos, moveList, Us, target);
  225     moveList = generate_moves<BISHOP, Checks>(pos, moveList, Us, target);
  226     moveList = generate_moves<  ROOK, Checks>(pos, moveList, Us, target);
  227     moveList = generate_moves< QUEEN, Checks>(pos, moveList, Us, target);
  228 
  229     if (Type != QUIET_CHECKS && Type != EVASIONS)
  230     {
  231         Square ksq = pos.square<KING>(Us);
  232         Bitboard b = pos.attacks_from<KING>(ksq) & target;
  233         while (b)
  234             *moveList++ = make_move(ksq, pop_lsb(&b));
  235 
  236         if (Type != CAPTURES && pos.can_castle(CastlingRights(OO | OOO)))
  237         {
  238             if (!pos.castling_impeded(OO) && pos.can_castle(OO))
  239                 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OO));
  240 
  241             if (!pos.castling_impeded(OOO) && pos.can_castle(OOO))
  242                 *moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(OOO));
  243         }
  244     }
  245 
  246     return moveList;
  247   }
  248 
  249 } // namespace
  250 
  251 
  252 /// <CAPTURES>     Generates all pseudo-legal captures and queen promotions
  253 /// <QUIETS>       Generates all pseudo-legal non-captures and underpromotions
  254 /// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
  255 ///
  256 /// Returns a pointer to the end of the move list.
  257 
  258 template<GenType Type>
  259 ExtMove* generate(const Position& pos, ExtMove* moveList) {
  260 
  261   static_assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS, "Unsupported type in generate()");
  262   assert(!pos.checkers());
  263 
  264   Color us = pos.side_to_move();
  265 
  266   Bitboard target =  Type == CAPTURES     ?  pos.pieces(~us)
  267                    : Type == QUIETS       ? ~pos.pieces()
  268                    : Type == NON_EVASIONS ? ~pos.pieces(us) : 0;
  269 
  270   return us == WHITE ? generate_all<WHITE, Type>(pos, moveList, target)
  271                      : generate_all<BLACK, Type>(pos, moveList, target);
  272 }
  273 
  274 // Explicit template instantiations
  275 template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
  276 template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
  277 template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
  278 
  279 
  280 /// generate<QUIET_CHECKS> generates all pseudo-legal non-captures and knight
  281 /// underpromotions that give check. Returns a pointer to the end of the move list.
  282 template<>
  283 ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
  284 
  285   assert(!pos.checkers());
  286 
  287   Color us = pos.side_to_move();
  288   Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us);
  289 
  290   while (dc)
  291   {
  292      Square from = pop_lsb(&dc);
  293      PieceType pt = type_of(pos.piece_on(from));
  294 
  295      if (pt == PAWN)
  296          continue; // Will be generated together with direct checks
  297 
  298      Bitboard b = pos.attacks_from(pt, from) & ~pos.pieces();
  299 
  300      if (pt == KING)
  301          b &= ~PseudoAttacks[QUEEN][pos.square<KING>(~us)];
  302 
  303      while (b)
  304          *moveList++ = make_move(from, pop_lsb(&b));
  305   }
  306 
  307   return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList, ~pos.pieces())
  308                      : generate_all<BLACK, QUIET_CHECKS>(pos, moveList, ~pos.pieces());
  309 }
  310 
  311 
  312 /// generate<EVASIONS> generates all pseudo-legal check evasions when the side
  313 /// to move is in check. Returns a pointer to the end of the move list.
  314 template<>
  315 ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
  316 
  317   assert(pos.checkers());
  318 
  319   Color us = pos.side_to_move();
  320   Square ksq = pos.square<KING>(us);
  321   Bitboard sliderAttacks = 0;
  322   Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
  323 
  324   // Find all the squares attacked by slider checkers. We will remove them from
  325   // the king evasions in order to skip known illegal moves, which avoids any
  326   // useless legality checks later on.
  327   while (sliders)
  328   {
  329       Square checksq = pop_lsb(&sliders);
  330       sliderAttacks |= LineBB[checksq][ksq] ^ checksq;
  331   }
  332 
  333   // Generate evasions for king, capture and non capture moves
  334   Bitboard b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
  335   while (b)
  336       *moveList++ = make_move(ksq, pop_lsb(&b));
  337 
  338   if (more_than_one(pos.checkers()))
  339       return moveList; // Double check, only a king move can save the day
  340 
  341   // Generate blocking evasions or captures of the checking piece
  342   Square checksq = lsb(pos.checkers());
  343   Bitboard target = between_bb(checksq, ksq) | checksq;
  344 
  345   return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList, target)
  346                      : generate_all<BLACK, EVASIONS>(pos, moveList, target);
  347 }
  348 
  349 
  350 /// generate<LEGAL> generates all the legal moves in the given position
  351 
  352 template<>
  353 ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
  354 
  355   Color us = pos.side_to_move();
  356   Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
  357   Square ksq = pos.square<KING>(us);
  358   ExtMove* cur = moveList;
  359 
  360   moveList = pos.checkers() ? generate<EVASIONS    >(pos, moveList)
  361                             : generate<NON_EVASIONS>(pos, moveList);
  362   while (cur != moveList)
  363       if (   (pinned || from_sq(*cur) == ksq || type_of(*cur) == ENPASSANT)
  364           && !pos.legal(*cur))
  365           *cur = (--moveList)->move;
  366       else
  367           ++cur;
  368 
  369   return moveList;
  370 }