src/movegen.cpp

   1 /*
   2   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   3   Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008 Marco Costalba
   4
   5   Stockfish is free software: you can redistribute it and/or modify
   6   it under the terms of the GNU General Public License as published by
   7   the Free Software Foundation, either version 3 of the License, or
   8   (at your option) any later version.
   9
  10   Stockfish is distributed in the hope that it will be useful,
  11   but WITHOUT ANY WARRANTY; without even the implied warranty of
  12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13   GNU General Public License for more details.
  14
  15   You should have received a copy of the GNU General Public License
  16   along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19
  20 ////
  21 //// Includes
  22 ////
  23
  24 #include <cassert>
  25
  26 #include "movegen.h"
  27
  28 // Simple macro to wrap a very common while loop, no facny, no flexibility,
  29 // hardcoded list name 'mlist' and from square 'from'.
  30 #define SERIALIZE_MOVES(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit(&b))
  31
  32 ////
  33 //// Local definitions
  34 ////
  35
  36 namespace {
  37
  38   enum CastlingSide {
  39     KING_SIDE,
  40     QUEEN_SIDE
  41   };
  42
  43   enum MoveType {
  44     CAPTURE,
  45     NON_CAPTURE
  46   };
  47
  48   // Functions
  49   bool castling_is_check(const Position&, CastlingSide);
  50
  51   // Helper templates
  52   template<CastlingSide Side>
  53   MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist);
  54
  55   template<Color Us, Rank, Bitboard, SquareDelta>
  56   MoveStack* generate_pawn_blocking_evasions(const Position&, Bitboard, Bitboard, MoveStack*);
  57
  58   template<Color, Color, Bitboard, SquareDelta, SquareDelta, SquareDelta>
  59   MoveStack* generate_pawn_captures(const Position& pos, MoveStack* mlist);
  60
  61   template<Color, Color, Bitboard, Bitboard, SquareDelta, SquareDelta, SquareDelta>
  62   MoveStack* generate_pawn_noncaptures(const Position& pos, MoveStack* mlist);
  63
  64   template<Color, Color, Bitboard, Bitboard, SquareDelta>
  65   MoveStack* generate_pawn_checks(const Position&, Bitboard, Square, MoveStack*);
  66
  67   template<Color Us, SquareDelta Direction>
  68   inline Bitboard move_pawns(Bitboard p) {
  69
  70     if (Direction == DELTA_N)
  71         return Us == WHITE ? p << 8 : p >> 8;
  72     else if (Direction == DELTA_NE)
  73         return Us == WHITE ? p << 9 : p >> 7;
  74     else if (Direction == DELTA_NW)
  75         return Us == WHITE ? p << 7 : p >> 9;
  76     else
  77         return p;
  78   }
  79
  80   // Template generate_piece_checks() with specializations
  81   template<PieceType>
  82   MoveStack* generate_piece_checks(const Position&, MoveStack*, Color, Bitboard, Square);
  83
  84   template<>
  85   inline MoveStack* generate_piece_checks<PAWN>(const Position& p, MoveStack* m, Color us, Bitboard dc, Square ksq) {
  86
  87     if (us == WHITE)
  88         return generate_pawn_checks<WHITE, BLACK, Rank8BB, Rank3BB, DELTA_N>(p, dc, ksq, m);
  89     else
  90         return generate_pawn_checks<BLACK, WHITE, Rank1BB, Rank6BB, DELTA_S>(p, dc, ksq, m);
  91
  92   }
  93
  94   // Template generate_piece_moves() with specializations and overloads
  95   template<PieceType>
  96   MoveStack* generate_piece_moves(const Position&, MoveStack*, Color us, Bitboard);
  97
  98   template<>
  99   MoveStack* generate_piece_moves<KING>(const Position&, MoveStack*, Color, Bitboard);
 100
 101   template<PieceType Piece, MoveType Type>
 102   inline MoveStack* generate_piece_moves(const Position& p, MoveStack* m, Color us) {
 103
 104       assert(Piece == PAWN);
 105
 106       if (Type == CAPTURE)
 107           return (us == WHITE ? generate_pawn_captures<WHITE, BLACK, Rank8BB, DELTA_NE, DELTA_NW, DELTA_N>(p, m)
 108                               : generate_pawn_captures<BLACK, WHITE, Rank1BB, DELTA_SE, DELTA_SW, DELTA_S>(p, m));
 109       else
 110           return (us == WHITE ? generate_pawn_noncaptures<WHITE, BLACK, Rank8BB, Rank3BB, DELTA_NE, DELTA_NW, DELTA_N>(p, m)
 111                               : generate_pawn_noncaptures<BLACK, WHITE, Rank1BB, Rank6BB, DELTA_SE, DELTA_SW, DELTA_S>(p, m));
 112   }
 113
 114   template<PieceType>
 115   MoveStack* generate_piece_moves(const Position&, MoveStack*, Color us, Bitboard, Bitboard);
 116
 117   template<>
 118   inline MoveStack* generate_piece_moves<PAWN>(const Position& p, MoveStack* m,
 119                                                Color us, Bitboard t, Bitboard pnd) {
 120     if (us == WHITE)
 121         return generate_pawn_blocking_evasions<WHITE, RANK_8, Rank3BB, DELTA_N>(p, pnd, t, m);
 122     else
 123         return generate_pawn_blocking_evasions<BLACK, RANK_1, Rank6BB, DELTA_S>(p, pnd, t, m);
 124   }
 125 }
 126
 127
 128 ////
 129 //// Functions
 130 ////
 131
 132
 133 /// generate_captures generates() all pseudo-legal captures and queen
 134 /// promotions.  The return value is the number of moves generated.
 135
 136 int generate_captures(const Position& pos, MoveStack* mlist) {
 137
 138   assert(pos.is_ok());
 139   assert(!pos.is_check());
 140
 141   Color us = pos.side_to_move();
 142   Bitboard target = pos.pieces_of_color(opposite_color(us));
 143   MoveStack* mlist_start = mlist;
 144
 145   mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
 146   mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
 147   mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
 148   mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
 149   mlist = generate_piece_moves<PAWN, CAPTURE>(pos, mlist, us);
 150   mlist = generate_piece_moves<KING>(pos, mlist, us, target);
 151   return int(mlist - mlist_start);
 152 }
 153
 154
 155 /// generate_noncaptures() generates all pseudo-legal non-captures and
 156 /// underpromotions. The return value is the number of moves generated.
 157
 158 int generate_noncaptures(const Position& pos, MoveStack* mlist) {
 159
 160   assert(pos.is_ok());
 161   assert(!pos.is_check());
 162
 163   Color us = pos.side_to_move();
 164   Bitboard target = pos.empty_squares();
 165   MoveStack* mlist_start = mlist;
 166
 167   mlist = generate_piece_moves<PAWN, NON_CAPTURE>(pos, mlist, us);
 168   mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
 169   mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
 170   mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
 171   mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
 172   mlist = generate_piece_moves<KING>(pos, mlist, us, target);
 173   mlist = generate_castle_moves<KING_SIDE>(pos, mlist);
 174   mlist = generate_castle_moves<QUEEN_SIDE>(pos, mlist);
 175   return int(mlist - mlist_start);
 176 }
 177
 178
 179 /// generate_non_capture_checks() generates all pseudo-legal non-capturing,
 180 /// non-promoting checks. It returns the number of generated moves.
 181
 182 int generate_non_capture_checks(const Position& pos, MoveStack* mlist, Bitboard dc) {
 183
 184   assert(pos.is_ok());
 185   assert(!pos.is_check());
 186
 187   Color us = pos.side_to_move();
 188   Square ksq = pos.king_square(opposite_color(us));
 189   MoveStack* mlist_start = mlist;
 190
 191   assert(pos.piece_on(ksq) == piece_of_color_and_type(opposite_color(us), KING));
 192
 193   // Pieces moves
 194   mlist = generate_piece_checks<PAWN>(pos, mlist, us, dc, ksq);
 195   mlist = generate_piece_checks<KNIGHT>(pos, mlist, us, dc, ksq);
 196   mlist = generate_piece_checks<BISHOP>(pos, mlist, us, dc, ksq);
 197   mlist = generate_piece_checks<ROOK>(pos, mlist, us, dc, ksq);
 198   mlist = generate_piece_checks<QUEEN>(pos, mlist, us, dc, ksq);
 199   mlist = generate_piece_checks<KING>(pos, mlist, us, dc, ksq);
 200
 201   // Castling moves that give check. Very rare but nice to have!
 202   if (   pos.can_castle_queenside(us)
 203       && (square_rank(ksq) == square_rank(pos.king_square(us)) || square_file(ksq) == FILE_D)
 204       && castling_is_check(pos, QUEEN_SIDE))
 205       mlist = generate_castle_moves<QUEEN_SIDE>(pos, mlist);
 206
 207   if (   pos.can_castle_kingside(us)
 208       && (square_rank(ksq) == square_rank(pos.king_square(us)) || square_file(ksq) == FILE_F)
 209       && castling_is_check(pos, KING_SIDE))
 210       mlist = generate_castle_moves<KING_SIDE>(pos, mlist);
 211
 212   return int(mlist - mlist_start);
 213 }
 214
 215
 216 /// generate_evasions() generates all check evasions when the side to move is
 217 /// in check. Unlike the other move generation functions, this one generates
 218 /// only legal moves. It returns the number of generated moves.
 219
 220 int generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pinned) {
 221
 222   assert(pos.is_ok());
 223   assert(pos.is_check());
 224
 225   Square from, to;
 226   Color us = pos.side_to_move();
 227   Color them = opposite_color(us);
 228   Square ksq = pos.king_square(us);
 229   MoveStack* mlist_start = mlist;
 230
 231   assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
 232
 233   // The bitboard of occupied pieces without our king
 234   Bitboard b_noKing = pos.occupied_squares();
 235   clear_bit(&b_noKing, ksq);
 236
 237   // Find squares attacked by slider checkers, we will
 238   // remove them from king evasions set so to avoid a couple
 239   // of cycles in the slow king evasions legality check loop
 240   // and to be able to use square_is_attacked().
 241   Bitboard checkers = pos.checkers();
 242   Bitboard checkersAttacks = EmptyBoardBB;
 243   Bitboard b = checkers & (pos.queens() | pos.bishops());
 244   while (b)
 245   {
 246       from = pop_1st_bit(&b);
 247       checkersAttacks |= bishop_attacks_bb(from, b_noKing);
 248   }
 249
 250   b = checkers & (pos.queens() | pos.rooks());
 251   while (b)
 252   {
 253       from = pop_1st_bit(&b);
 254       checkersAttacks |= rook_attacks_bb(from, b_noKing);
 255   }
 256
 257   // Generate evasions for king
 258   Bitboard b1 = pos.piece_attacks<KING>(ksq) & ~pos.pieces_of_color(us) & ~checkersAttacks;
 259   while (b1)
 260   {
 261       to = pop_1st_bit(&b1);
 262       // Note that we can use square_is_attacked() only because we
 263       // have already removed slider checkers.
 264       if (!pos.square_is_attacked(to, them))
 265           (*mlist++).move = make_move(ksq, to);
 266   }
 267
 268   // Generate evasions for other pieces only if not double check. We use a
 269   // simple bit twiddling hack here rather than calling count_1s in order to
 270   // save some time (we know that pos.checkers() has at most two nonzero bits).
 271   if (!(checkers & (checkers - 1))) // Only one bit set?
 272   {
 273       Square checksq = first_1(checkers);
 274
 275       assert(pos.color_of_piece_on(checksq) == them);
 276
 277       // Generate captures of the checking piece
 278
 279       // Pawn captures
 280       b1 = pos.pawn_attacks(them, checksq) & pos.pawns(us) & ~pinned;
 281       while (b1)
 282       {
 283           from = pop_1st_bit(&b1);
 284           if (relative_rank(us, checksq) == RANK_8)
 285           {
 286               (*mlist++).move = make_promotion_move(from, checksq, QUEEN);
 287               (*mlist++).move = make_promotion_move(from, checksq, ROOK);
 288               (*mlist++).move = make_promotion_move(from, checksq, BISHOP);
 289               (*mlist++).move = make_promotion_move(from, checksq, KNIGHT);
 290           } else
 291               (*mlist++).move = make_move(from, checksq);
 292       }
 293
 294       // Pieces captures
 295       b1 = (  (pos.piece_attacks<KNIGHT>(checksq) & pos.knights(us))
 296             | (pos.piece_attacks<BISHOP>(checksq) & pos.bishops_and_queens(us))
 297             | (pos.piece_attacks<ROOK>(checksq)   & pos.rooks_and_queens(us)) ) & ~pinned;
 298
 299       while (b1)
 300       {
 301           from = pop_1st_bit(&b1);
 302           (*mlist++).move = make_move(from, checksq);
 303       }
 304
 305       // Blocking check evasions are possible only if the checking piece is
 306       // a slider.
 307       if (checkers & pos.sliders())
 308       {
 309           Bitboard blockSquares = squares_between(checksq, ksq);
 310
 311           assert((pos.occupied_squares() & blockSquares) == EmptyBoardBB);
 312
 313           if (blockSquares != EmptyBoardBB)
 314           {
 315               mlist = generate_piece_moves<PAWN>(pos, mlist, us, blockSquares, pinned);
 316               mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, blockSquares, pinned);
 317               mlist = generate_piece_moves<BISHOP>(pos, mlist, us, blockSquares, pinned);
 318               mlist = generate_piece_moves<ROOK>(pos, mlist, us, blockSquares, pinned);
 319               mlist = generate_piece_moves<QUEEN>(pos, mlist, us, blockSquares, pinned);
 320           }
 321       }
 322
 323       // Finally, the special case of en passant captures. An en passant
 324       // capture can only be a check evasion if the check is not a discovered
 325       // check. If pos.ep_square() is set, the last move made must have been
 326       // a double pawn push. If, furthermore, the checking piece is a pawn,
 327       // an en passant check evasion may be possible.
 328       if (pos.ep_square() != SQ_NONE && (checkers & pos.pawns(them)))
 329       {
 330           to = pos.ep_square();
 331           b1 = pos.pawn_attacks(them, to) & pos.pawns(us);
 332
 333           // The checking pawn cannot be a discovered (bishop) check candidate
 334           // otherwise we were in check also before last double push move.
 335           assert(!bit_is_set(pos.discovered_check_candidates(them), checksq));
 336           assert(count_1s(b1) == 1 || count_1s(b1) == 2);
 337
 338           b1 &= ~pinned;
 339           while (b1)
 340           {
 341               from = pop_1st_bit(&b1);
 342               // Move is always legal because checking pawn is not a discovered
 343               // check candidate and our capturing pawn has been already tested
 344               // against pinned pieces.
 345               (*mlist++).move = make_ep_move(from, to);
 346           }
 347       }
 348   }
 349   return int(mlist - mlist_start);
 350 }
 351
 352
 353 /// generate_legal_moves() computes a complete list of legal moves in the
 354 /// current position. This function is not very fast, and should be used
 355 /// only in situations where performance is unimportant. It wouldn't be
 356 /// very hard to write an efficient legal move generator, but for the moment
 357 /// we don't need it.
 358
 359 int generate_legal_moves(const Position& pos, MoveStack* mlist) {
 360
 361   assert(pos.is_ok());
 362
 363   Bitboard pinned = pos.pinned_pieces(pos.side_to_move());
 364
 365   if (pos.is_check())
 366       return generate_evasions(pos, mlist, pinned);
 367
 368   // Generate pseudo-legal moves
 369   int n = generate_captures(pos, mlist);
 370   n += generate_noncaptures(pos, mlist + n);
 371
 372   // Remove illegal moves from the list
 373   for (int i = 0; i < n; i++)
 374       if (!pos.pl_move_is_legal(mlist[i].move, pinned))
 375           mlist[i--].move = mlist[--n].move;
 376
 377   return n;
 378 }
 379
 380
 381 /// move_is_legal() takes a position and a (not necessarily pseudo-legal)
 382 /// move and a pinned pieces bitboard as input, and tests whether
 383 /// the move is legal.  If the move is legal, the move itself is
 384 /// returned. If not, the function returns false.  This function must
 385 /// only be used when the side to move is not in check.
 386
 387 bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
 388
 389   assert(pos.is_ok());
 390   assert(!pos.is_check());
 391   assert(move_is_ok(m));
 392   assert(pinned == pos.pinned_pieces(pos.side_to_move()));
 393
 394   Color us = pos.side_to_move();
 395   Color them = opposite_color(us);
 396   Square from = move_from(m);
 397   Piece pc = pos.piece_on(from);
 398
 399   // If the from square is not occupied by a piece belonging to the side to
 400   // move, the move is obviously not legal.
 401   if (color_of_piece(pc) != us)
 402       return false;
 403
 404   Square to = move_to(m);
 405
 406   // En passant moves
 407   if (move_is_ep(m))
 408   {
 409       // The piece must be a pawn and destination square must be the
 410       // en passant square.
 411       if (   type_of_piece(pc) != PAWN
 412           || to != pos.ep_square())
 413           return false;
 414
 415       assert(pos.square_is_empty(to));
 416       assert(pos.piece_on(to - pawn_push(us)) == piece_of_color_and_type(them, PAWN));
 417
 418       // The move is pseudo-legal, check if it is also legal
 419       return pos.pl_move_is_legal(m, pinned);
 420   }
 421
 422   // Castling moves
 423   if (move_is_short_castle(m))
 424   {
 425       // The piece must be a king and side to move must still have
 426       // the right to castle kingside.
 427       if (   type_of_piece(pc) != KING
 428           ||!pos.can_castle_kingside(us))
 429           return false;
 430
 431       assert(from == pos.king_square(us));
 432       assert(to == pos.initial_kr_square(us));
 433       assert(pos.piece_on(to) == piece_of_color_and_type(us, ROOK));
 434
 435       Square g1 = relative_square(us, SQ_G1);
 436       Square f1 = relative_square(us, SQ_F1);
 437       Square s;
 438       bool illegal = false;
 439
 440       // Check if any of the squares between king and rook
 441       // is occupied or under attack.
 442       for (s = Min(from, g1); s <= Max(from, g1); s++)
 443           if (  (s != from && s != to && !pos.square_is_empty(s))
 444               || pos.square_is_attacked(s, them))
 445               illegal = true;
 446
 447       // Check if any of the squares between king and rook
 448       // is occupied.
 449       for (s = Min(to, f1); s <= Max(to, f1); s++)
 450           if (s != from && s != to && !pos.square_is_empty(s))
 451               illegal = true;
 452
 453       return !illegal;
 454   }
 455
 456   if (move_is_long_castle(m))
 457   {
 458       // The piece must be a king and side to move must still have
 459       // the right to castle kingside.
 460       if (   type_of_piece(pc) != KING
 461           ||!pos.can_castle_queenside(us))
 462           return false;
 463
 464       assert(from == pos.king_square(us));
 465       assert(to == pos.initial_qr_square(us));
 466       assert(pos.piece_on(to) == piece_of_color_and_type(us, ROOK));
 467
 468       Square c1 = relative_square(us, SQ_C1);
 469       Square d1 = relative_square(us, SQ_D1);
 470       Square s;
 471       bool illegal = false;
 472
 473       for (s = Min(from, c1); s <= Max(from, c1); s++)
 474           if(  (s != from && s != to && !pos.square_is_empty(s))
 475              || pos.square_is_attacked(s, them))
 476               illegal = true;
 477
 478       for (s = Min(to, d1); s <= Max(to, d1); s++)
 479           if(s != from && s != to && !pos.square_is_empty(s))
 480               illegal = true;
 481
 482       if (   square_file(to) == FILE_B
 483           && (   pos.piece_on(to + DELTA_W) == piece_of_color_and_type(them, ROOK)
 484               || pos.piece_on(to + DELTA_W) == piece_of_color_and_type(them, QUEEN)))
 485           illegal = true;
 486
 487       return !illegal;
 488   }
 489
 490   // Normal moves
 491
 492   // The destination square cannot be occupied by a friendly piece
 493   if (pos.color_of_piece_on(to) == us)
 494       return false;
 495
 496   // Proceed according to the type of the moving piece.
 497   if (type_of_piece(pc) == PAWN)
 498   {
 499       // Move direction must be compatible with pawn color
 500       int direction = to - from;
 501       if ((us == WHITE) != (direction > 0))
 502           return false;
 503
 504       // If the destination square is on the 8/1th rank, the move must
 505       // be a promotion.
 506       if (   (  (square_rank(to) == RANK_8 && us == WHITE)
 507               ||(square_rank(to) == RANK_1 && us != WHITE))
 508            && !move_promotion(m))
 509           return false;
 510
 511       // Proceed according to the square delta between the source and
 512       // destionation squares.
 513       switch (direction)
 514       {
 515       case DELTA_NW:
 516       case DELTA_NE:
 517       case DELTA_SW:
 518       case DELTA_SE:
 519       // Capture. The destination square must be occupied by an enemy
 520       // piece (en passant captures was handled earlier).
 521           if (pos.color_of_piece_on(to) != them)
 522               return false;
 523           break;
 524
 525       case DELTA_N:
 526       case DELTA_S:
 527       // Pawn push. The destination square must be empty.
 528           if (!pos.square_is_empty(to))
 529               return false;
 530           break;
 531
 532       case DELTA_NN:
 533       // Double white pawn push. The destination square must be on the fourth
 534       // rank, and both the destination square and the square between the
 535       // source and destination squares must be empty.
 536       if (   square_rank(to) != RANK_4
 537           || !pos.square_is_empty(to)
 538           || !pos.square_is_empty(from + DELTA_N))
 539           return false;
 540           break;
 541
 542       case DELTA_SS:
 543       // Double black pawn push. The destination square must be on the fifth
 544       // rank, and both the destination square and the square between the
 545       // source and destination squares must be empty.
 546           if (   square_rank(to) != RANK_5
 547               || !pos.square_is_empty(to)
 548               || !pos.square_is_empty(from + DELTA_S))
 549               return false;
 550           break;
 551
 552       default:
 553           return false;
 554       }
 555       // The move is pseudo-legal, check if it is also legal
 556       return pos.pl_move_is_legal(m, pinned);
 557   }
 558
 559   // Luckly we can handle all the other pieces in one go
 560   return (   pos.piece_attacks_square(pos.piece_on(from), from, to)
 561           && pos.pl_move_is_legal(m, pinned)
 562           && !move_promotion(m));
 563 }
 564
 565
 566 namespace {
 567
 568   template<PieceType Piece>
 569   MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
 570
 571     Square from;
 572     Bitboard b;
 573
 574     for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++)
 575     {
 576         from = pos.piece_list(us, Piece, i);
 577         b = pos.piece_attacks<Piece>(from) & target;
 578         SERIALIZE_MOVES(b);
 579     }
 580     return mlist;
 581   }
 582
 583   template<PieceType Piece>
 584   MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist,
 585                                   Color us, Bitboard target, Bitboard pinned) {
 586     Square from;
 587     Bitboard b;
 588
 589     for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++)
 590     {
 591         from = pos.piece_list(us, Piece, i);
 592         if (pinned && bit_is_set(pinned, from))
 593             continue;
 594
 595         b = pos.piece_attacks<Piece>(from) & target;
 596         SERIALIZE_MOVES(b);
 597     }
 598     return mlist;
 599   }
 600
 601   template<>
 602   MoveStack* generate_piece_moves<KING>(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {
 603
 604     Bitboard b;
 605     Square from = pos.king_square(us);
 606
 607     b = pos.piece_attacks<KING>(from) & target;
 608     SERIALIZE_MOVES(b);
 609     return mlist;
 610   }
 611
 612   template<Color Us, Color Them, Bitboard TRank8BB, SquareDelta TDELTA_NE,
 613            SquareDelta TDELTA_NW, SquareDelta TDELTA_N
 614           >
 615   MoveStack* generate_pawn_captures(const Position& pos, MoveStack* mlist) {
 616
 617     Square to;
 618     Bitboard pawns = pos.pawns(Us);
 619     Bitboard enemyPieces = pos.pieces_of_color(Them);
 620
 621     // Captures in the a1-h8 (a8-h1 for black) direction
 622     Bitboard b1 = move_pawns<Us, DELTA_NE>(pawns) & ~FileABB & enemyPieces;
 623
 624     // Capturing promotions
 625     Bitboard b2 = b1 & TRank8BB;
 626     while (b2)
 627     {
 628         to = pop_1st_bit(&b2);
 629         (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, QUEEN);
 630     }
 631
 632     // Capturing non-promotions
 633     b2 = b1 & ~TRank8BB;
 634     while (b2)
 635     {
 636         to = pop_1st_bit(&b2);
 637         (*mlist++).move = make_move(to - TDELTA_NE, to);
 638     }
 639
 640     // Captures in the h1-a8 (h8-a1 for black) direction
 641     b1 = move_pawns<Us, DELTA_NW>(pawns) & ~FileHBB & enemyPieces;
 642
 643     // Capturing promotions
 644     b2 = b1 & TRank8BB;
 645     while (b2)
 646     {
 647         to = pop_1st_bit(&b2);
 648         (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, QUEEN);
 649     }
 650
 651     // Capturing non-promotions
 652     b2 = b1 & ~TRank8BB;
 653     while (b2)
 654     {
 655         to = pop_1st_bit(&b2);
 656         (*mlist++).move = make_move(to - TDELTA_NW, to);
 657     }
 658
 659     // Non-capturing promotions
 660     b1 = move_pawns<Us, DELTA_N>(pawns) & pos.empty_squares() & TRank8BB;
 661     while (b1)
 662     {
 663         to = pop_1st_bit(&b1);
 664         (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
 665     }
 666
 667     // En passant captures
 668     if (pos.ep_square() != SQ_NONE)
 669     {
 670         assert(Us != WHITE || square_rank(pos.ep_square()) == RANK_6);
 671         assert(Us != BLACK || square_rank(pos.ep_square()) == RANK_3);
 672
 673         b1 = pawns & pos.pawn_attacks(Them, pos.ep_square());
 674         assert(b1 != EmptyBoardBB);
 675
 676         while (b1)
 677         {
 678             to = pop_1st_bit(&b1);
 679             (*mlist++).move = make_ep_move(to, pos.ep_square());
 680         }
 681     }
 682     return mlist;
 683   }
 684
 685   template<Color Us, Color Them, Bitboard TRank8BB, Bitboard TRank3BB,
 686            SquareDelta TDELTA_NE, SquareDelta TDELTA_NW, SquareDelta TDELTA_N
 687           >
 688   MoveStack* generate_pawn_noncaptures(const Position& pos, MoveStack* mlist) {
 689
 690     Bitboard pawns = pos.pawns(Us);
 691     Bitboard enemyPieces = pos.pieces_of_color(Them);
 692     Bitboard emptySquares = pos.empty_squares();
 693     Bitboard b1, b2;
 694     Square to;
 695
 696     // Underpromotion captures in the a1-h8 (a8-h1 for black) direction
 697     b1 = move_pawns<Us, DELTA_NE>(pawns) & ~FileABB & enemyPieces & TRank8BB;
 698     while (b1)
 699     {
 700         to = pop_1st_bit(&b1);
 701         (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, ROOK);
 702         (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, BISHOP);
 703         (*mlist++).move = make_promotion_move(to - TDELTA_NE, to, KNIGHT);
 704     }
 705
 706     // Underpromotion captures in the h1-a8 (h8-a1 for black) direction
 707     b1 = move_pawns<Us, DELTA_NW>(pawns) & ~FileHBB & enemyPieces & TRank8BB;
 708     while (b1)
 709     {
 710         to = pop_1st_bit(&b1);
 711         (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, ROOK);
 712         (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, BISHOP);
 713         (*mlist++).move = make_promotion_move(to - TDELTA_NW, to, KNIGHT);
 714     }
 715
 716     // Single pawn pushes
 717     b1 = move_pawns<Us, DELTA_N>(pawns) & emptySquares;
 718     b2 = b1 & TRank8BB;
 719     while (b2)
 720     {
 721         to = pop_1st_bit(&b2);
 722         (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
 723         (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
 724         (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
 725     }
 726     b2 = b1 & ~TRank8BB;
 727     while (b2)
 728     {
 729         to = pop_1st_bit(&b2);
 730         (*mlist++).move = make_move(to - TDELTA_N, to);
 731     }
 732
 733     // Double pawn pushes
 734     b2 = move_pawns<Us, DELTA_N>(b1 & TRank3BB) & emptySquares;
 735     while (b2)
 736     {
 737         to = pop_1st_bit(&b2);
 738         (*mlist++).move = make_move(to - TDELTA_N - TDELTA_N, to);
 739     }
 740     return mlist;
 741   }
 742
 743
 744   template<Color Us, Color Them, Bitboard TRank8BB, Bitboard TRank3BB, SquareDelta TDELTA_N>
 745   MoveStack* generate_pawn_checks(const Position& pos, Bitboard dc, Square ksq, MoveStack* mlist)
 746   {
 747     // Find all friendly pawns not on the enemy king's file
 748     Bitboard b1, b2, b3;
 749     Bitboard empty = pos.empty_squares();
 750
 751     if (dc != EmptyBoardBB)
 752     {
 753         // Pawn moves which gives discovered check. This is possible only if the
 754         // pawn is not on the same file as the enemy king, because we don't
 755         // generate captures.
 756         b1 = pos.pawns(Us) & ~file_bb(ksq);
 757
 758         // Discovered checks, single pawn pushes, no promotions
 759         b2 = b3 = move_pawns<Us, DELTA_N>(b1 & dc) & empty & ~TRank8BB;
 760         while (b3)
 761         {
 762             Square to = pop_1st_bit(&b3);
 763             (*mlist++).move = make_move(to - TDELTA_N, to);
 764         }
 765
 766         // Discovered checks, double pawn pushes
 767         b3 = move_pawns<Us, DELTA_N>(b2 & TRank3BB) & empty;
 768         while (b3)
 769         {
 770             Square to = pop_1st_bit(&b3);
 771             (*mlist++).move = make_move(to - TDELTA_N - TDELTA_N, to);
 772         }
 773     }
 774
 775     // Direct checks. These are possible only for pawns on neighboring files
 776     // of the enemy king.
 777     b1 = pos.pawns(Us) & neighboring_files_bb(ksq) & ~dc;
 778
 779     // Direct checks, single pawn pushes
 780     b2 = move_pawns<Us, DELTA_N>(b1) & empty;
 781     b3 = b2 & pos.pawn_attacks(Them, ksq);
 782     while (b3)
 783     {
 784         Square to = pop_1st_bit(&b3);
 785         (*mlist++).move = make_move(to - TDELTA_N, to);
 786     }
 787
 788     // Direct checks, double pawn pushes
 789     b3 =  move_pawns<Us, DELTA_N>(b2 & TRank3BB) & empty & pos.pawn_attacks(Them, ksq);
 790     while (b3)
 791     {
 792         Square to = pop_1st_bit(&b3);
 793         (*mlist++).move = make_move(to - TDELTA_N - TDELTA_N, to);
 794     }
 795     return mlist;
 796   }
 797
 798   template<PieceType Piece>
 799   MoveStack* generate_piece_checks(const Position& pos, MoveStack* mlist, Color us,
 800                                    Bitboard dc, Square ksq) {
 801
 802     Bitboard target = pos.pieces_of_color_and_type(us, Piece);
 803
 804     // Discovered checks
 805     Bitboard b = target & dc;
 806     while (b)
 807     {
 808         Square from = pop_1st_bit(&b);
 809         Bitboard bb = pos.piece_attacks<Piece>(from) & pos.empty_squares();
 810         if (Piece == KING)
 811             bb &= ~QueenPseudoAttacks[ksq];
 812
 813         SERIALIZE_MOVES(bb);
 814     }
 815
 816     // Direct checks
 817     b = target & ~dc;
 818     if (Piece == KING || !b)
 819         return mlist;
 820
 821     Bitboard checkSqs = pos.piece_attacks<Piece>(ksq) & pos.empty_squares();
 822     if (!checkSqs)
 823         return mlist;
 824
 825     while (b)
 826     {
 827         Square from = pop_1st_bit(&b);
 828         if (   (Piece == QUEEN  && !(QueenPseudoAttacks[from]  & checkSqs))
 829             || (Piece == ROOK   && !(RookPseudoAttacks[from]   & checkSqs))
 830             || (Piece == BISHOP && !(BishopPseudoAttacks[from] & checkSqs)))
 831             continue;
 832
 833         Bitboard bb = pos.piece_attacks<Piece>(from) & checkSqs;
 834         SERIALIZE_MOVES(bb);
 835     }
 836     return mlist;
 837   }
 838
 839   template<Color Us, Rank TRANK_8, Bitboard TRank3BB, SquareDelta TDELTA_N>
 840   MoveStack* generate_pawn_blocking_evasions(const Position& pos, Bitboard pinned,
 841                                              Bitboard blockSquares, MoveStack* mlist) {
 842     Square to;
 843
 844     // Find non-pinned pawns and push them one square
 845     Bitboard b1 = move_pawns<Us, DELTA_N>(pos.pawns(Us) & ~pinned);
 846
 847     // We don't have to AND with empty squares here,
 848     // because the blocking squares will always be empty.
 849     Bitboard b2 = b1 & blockSquares;
 850     while (b2)
 851     {
 852         to = pop_1st_bit(&b2);
 853
 854         assert(pos.piece_on(to) == EMPTY);
 855
 856         if (square_rank(to) == TRANK_8)
 857         {
 858             (*mlist++).move = make_promotion_move(to - TDELTA_N, to, QUEEN);
 859             (*mlist++).move = make_promotion_move(to - TDELTA_N, to, ROOK);
 860             (*mlist++).move = make_promotion_move(to - TDELTA_N, to, BISHOP);
 861             (*mlist++).move = make_promotion_move(to - TDELTA_N, to, KNIGHT);
 862         } else
 863             (*mlist++).move = make_move(to - TDELTA_N, to);
 864     }
 865
 866     // Double pawn pushes
 867     b2 = b1 & pos.empty_squares() & TRank3BB;
 868     b2 = move_pawns<Us, DELTA_N>(b2) & blockSquares;
 869     while (b2)
 870     {
 871         to = pop_1st_bit(&b2);
 872
 873         assert(pos.piece_on(to) == EMPTY);
 874         assert(Us != WHITE || square_rank(to) == RANK_4);
 875         assert(Us != BLACK || square_rank(to) == RANK_5);
 876
 877         (*mlist++).move = make_move(to - TDELTA_N - TDELTA_N, to);
 878     }
 879     return mlist;
 880   }
 881
 882   template<CastlingSide Side>
 883   MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist) {
 884
 885     Color us = pos.side_to_move();
 886
 887     if (  (Side == KING_SIDE && pos.can_castle_kingside(us))
 888         ||(Side == QUEEN_SIDE && pos.can_castle_queenside(us)))
 889     {
 890         Color them = opposite_color(us);
 891         Square ksq = pos.king_square(us);
 892
 893         assert(pos.piece_on(ksq) == piece_of_color_and_type(us, KING));
 894
 895         Square rsq = (Side == KING_SIDE ? pos.initial_kr_square(us) : pos.initial_qr_square(us));
 896         Square s1 = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
 897         Square s2 = relative_square(us, Side == KING_SIDE ? SQ_F1 : SQ_D1);
 898         Square s;
 899         bool illegal = false;
 900
 901         assert(pos.piece_on(rsq) == piece_of_color_and_type(us, ROOK));
 902
 903         // It is a bit complicated to correctly handle Chess960
 904         for (s = Min(ksq, s1); s <= Max(ksq, s1); s++)
 905             if (  (s != ksq && s != rsq && pos.square_is_occupied(s))
 906                 || pos.square_is_attacked(s, them))
 907                 illegal = true;
 908
 909         for (s = Min(rsq, s2); s <= Max(rsq, s2); s++)
 910             if (s != ksq && s != rsq && pos.square_is_occupied(s))
 911                 illegal = true;
 912
 913         if (   Side == QUEEN_SIDE
 914             && square_file(rsq) == FILE_B
 915             && (   pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, ROOK)
 916                 || pos.piece_on(relative_square(us, SQ_A1)) == piece_of_color_and_type(them, QUEEN)))
 917             illegal = true;
 918
 919         if (!illegal)
 920             (*mlist++).move = make_castle_move(ksq, rsq);
 921     }
 922     return mlist;
 923   }
 924
 925   bool castling_is_check(const Position& pos, CastlingSide side) {
 926
 927     // After castling opponent king is attacked by the castled rook?
 928     File rookFile = (side == QUEEN_SIDE ? FILE_D : FILE_F);
 929     Color us = pos.side_to_move();
 930     Square ksq = pos.king_square(us);
 931     Bitboard occ = pos.occupied_squares();
 932
 933     clear_bit(&occ, ksq); // Remove our king from the board
 934     Square rsq = make_square(rookFile, square_rank(ksq));
 935     return bit_is_set(rook_attacks_bb(rsq, occ), pos.king_square(opposite_color(us)));
 936   }
 937 }