stockfish/src/movegen.cpp

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  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
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <algorithm>
#include <cassert>

#include "movegen.h"
#include "position.h"

/// Simple macro to wrap a very common while loop, no facny, no flexibility,
/// hardcoded names 'mlist' and 'from'.
#define SERIALIZE(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit(&b))

/// Version used for pawns, where the 'from' square is given as a delta from the 'to' square
#define SERIALIZE_PAWNS(b, d) while (b) { Square to = pop_1st_bit(&b); \
                                         (*mlist++).move = make_move(to + (d), to); }
namespace {

  enum CastlingSide { KING_SIDE, QUEEN_SIDE };

  template<CastlingSide Side, bool OnlyChecks>
  MoveStack* generate_castle_moves(const Position& pos, MoveStack* mlist, Color us) {

    const CastleRight CR[] = { Side ? WHITE_OOO : WHITE_OO,
                               Side ? BLACK_OOO : BLACK_OO };

    if (!pos.can_castle(CR[us]))
        return mlist;

    // 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(~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;

    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;

    // 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;
    }

    (*mlist++).move = make_castle(kfrom, rfrom);

    if (OnlyChecks && !pos.move_gives_check((mlist - 1)->move, CheckInfo(pos)))
        mlist--;

    return mlist;
  }


  template<Square Delta>
  inline Bitboard move_pawns(Bitboard p) {

    return  Delta == DELTA_N  ?  p << 8
          : Delta == DELTA_S  ?  p >> 8
          : Delta == DELTA_NE ? (p & ~FileHBB) << 9
          : Delta == DELTA_SE ? (p & ~FileHBB) >> 7
          : Delta == DELTA_NW ? (p & ~FileABB) << 7
          : Delta == DELTA_SW ? (p & ~FileABB) >> 9 : p;
  }


  template<Square Delta>
  inline MoveStack* generate_pawn_captures(MoveStack* mlist, Bitboard pawns, Bitboard target) {

    Bitboard b = move_pawns<Delta>(pawns) & target;
    SERIALIZE_PAWNS(b, -Delta);
    return mlist;
  }


  template<MoveType Type, Square Delta>
  inline MoveStack* generate_promotions(MoveStack* mlist, Bitboard pawnsOn7, Bitboard target, Square ksq) {

    Bitboard b = move_pawns<Delta>(pawnsOn7) & target;

    while (b)
    {
        Square to = pop_1st_bit(&b);

        if (Type == MV_CAPTURE || Type == MV_EVASION || Type == MV_NON_EVASION)
            (*mlist++).move = make_promotion(to - Delta, to, QUEEN);

        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);
        }

        // Knight-promotion is the only one that can give a check (direct or
        // discovered) not already included in the queen-promotion.
        if (Type == MV_NON_CAPTURE_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;
  }


  template<Color Us, MoveType Type>
  MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist, Bitboard target, Square ksq = SQ_NONE) {

    // 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);

    Bitboard b1, b2, dc1, dc2, emptySquares;

    Bitboard pawnsOn7    = pos.pieces(PAWN, Us) &  TRank7BB;
    Bitboard pawnsNotOn7 = pos.pieces(PAWN, Us) & ~TRank7BB;

    Bitboard enemies = (Type == MV_EVASION ? pos.pieces(Them) & target:
                        Type == MV_CAPTURE ? target : pos.pieces(Them));

    // Single and double pawn pushes, no promotions
    if (Type != MV_CAPTURE)
    {
        emptySquares = (Type == MV_NON_CAPTURE ? target : pos.empty_squares());

        b1 = move_pawns<UP>(pawnsNotOn7)   & emptySquares;
        b2 = move_pawns<UP>(b1 & TRank3BB) & emptySquares;

        if (Type == MV_EVASION) // Consider only blocking squares
        {
            b1 &= target;
            b2 &= target;
        }

        if (Type == MV_NON_CAPTURE_CHECK)
        {
            // Consider only direct checks
            b1 &= pos.attacks_from<PAWN>(ksq, Them);
            b2 &= pos.attacks_from<PAWN>(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) // Target is dc bitboard
            {
                dc1 = move_pawns<UP>(pawnsNotOn7 & target) & emptySquares & ~file_bb(ksq);
                dc2 = move_pawns<UP>(dc1 & TRank3BB) & emptySquares;

                b1 |= dc1;
                b2 |= dc2;
            }
        }

        SERIALIZE_PAWNS(b1, -UP);
        SERIALIZE_PAWNS(b2, -UP -UP);
    }

    // Promotions and underpromotions
    if (pawnsOn7)
    {
        if (Type == MV_CAPTURE)
            emptySquares = pos.empty_squares();

        if (Type == MV_EVASION)
            emptySquares &= target;

        mlist = generate_promotions<Type, RIGHT>(mlist, pawnsOn7, enemies, ksq);
        mlist = generate_promotions<Type, LEFT>(mlist, pawnsOn7, enemies, ksq);
        mlist = generate_promotions<Type, UP>(mlist, pawnsOn7, emptySquares, ksq);
    }

    // Standard and en-passant captures
    if (Type == MV_CAPTURE || Type == MV_EVASION || Type == MV_NON_EVASION)
    {
        mlist = generate_pawn_captures<RIGHT>(mlist, pawnsNotOn7, enemies);
        mlist = generate_pawn_captures<LEFT >(mlist, pawnsNotOn7, enemies);

        if (pos.ep_square() != SQ_NONE)
        {
            assert(rank_of(pos.ep_square()) == (Us == WHITE ? RANK_6 : RANK_3));

            // 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;

            b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);

            assert(b1);

            while (b1)
                (*mlist++).move = make_enpassant(pop_1st_bit(&b1), pos.ep_square());
        }
    }

    return mlist;
  }


  template<PieceType Pt>
  inline MoveStack* generate_direct_checks(const Position& pos, MoveStack* mlist,
                                           Color us, const CheckInfo& ci) {
    assert(Pt != KING && Pt != PAWN);

    Square from;
    const Square* pl = pos.piece_list(us, Pt);

    if ((from = *pl++) == SQ_NONE)
        return mlist;

    Bitboard checkSqs = ci.checkSq[Pt] & pos.empty_squares();

    do
    {
        if (    (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
            && !(PseudoAttacks[Pt][from] & checkSqs))
            continue;

        if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
            continue;

        Bitboard b = pos.attacks_from<Pt>(from) & checkSqs;
        SERIALIZE(b);

    } while ((from = *pl++) != SQ_NONE);

    return mlist;
  }


  template<PieceType Pt>
  FORCE_INLINE MoveStack* generate_piece_moves(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {

    Bitboard b;
    Square from;
    const Square* pl = pos.piece_list(us, Pt);

    if (*pl != SQ_NONE)
    {
        do {
            from = *pl;
            b = pos.attacks_from<Pt>(from) & target;
            SERIALIZE(b);
        } while (*++pl != SQ_NONE);
    }

    return mlist;
  }


  template<>
  FORCE_INLINE MoveStack* generate_piece_moves<KING>(const Position& pos, MoveStack* mlist, Color us, Bitboard target) {

    Square from = pos.king_square(us);
    Bitboard b = pos.attacks_from<KING>(from) & target;
    SERIALIZE(b);
    return mlist;
  }

} // namespace


/// generate<MV_CAPTURE> generates all pseudo-legal captures and queen
/// promotions. Returns a pointer to the end of the move list.
///
/// generate<MV_NON_CAPTURE> generates all pseudo-legal non-captures and
/// underpromotions. Returns a pointer to the end of the move list.
///
/// generate<MV_NON_EVASION> generates all pseudo-legal captures and
/// non-captures. Returns a pointer to the end of the move list.

template<MoveType Type>
MoveStack* generate(const Position& pos, MoveStack* mlist) {

  assert(Type == MV_CAPTURE || Type == MV_NON_CAPTURE || Type == MV_NON_EVASION);
  assert(!pos.in_check());

  Color us = pos.side_to_move();
  Bitboard target;

  if (Type == MV_CAPTURE)
      target = pos.pieces(~us);

  else if (Type == MV_NON_CAPTURE)
      target = pos.empty_squares();

  else if (Type == MV_NON_EVASION)
      target = pos.pieces(~us) | pos.empty_squares();

  mlist = (us == WHITE ? generate_pawn_moves<WHITE, Type>(pos, mlist, target)
                       : generate_pawn_moves<BLACK, Type>(pos, mlist, target));

  mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
  mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
  mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
  mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
  mlist = generate_piece_moves<KING>(pos, mlist, us, target);

  if (Type != MV_CAPTURE && pos.can_castle(us))
  {
      mlist = generate_castle_moves<KING_SIDE, false>(pos, mlist, us);
      mlist = generate_castle_moves<QUEEN_SIDE, false>(pos, mlist, us);
  }

  return mlist;
}

// Explicit template instantiations
template MoveStack* generate<MV_CAPTURE>(const Position& pos, MoveStack* mlist);
template MoveStack* generate<MV_NON_CAPTURE>(const Position& pos, MoveStack* mlist);
template MoveStack* generate<MV_NON_EVASION>(const Position& pos, MoveStack* mlist);


/// generate<MV_NON_CAPTURE_CHECK> 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<MV_NON_CAPTURE_CHECK>(const Position& pos, MoveStack* mlist) {

  assert(!pos.in_check());

  Color us = pos.side_to_move();
  CheckInfo ci(pos);
  Bitboard dc = ci.dcCandidates;

  while (dc)
  {
     Square from = pop_1st_bit(&dc);
     PieceType pt = type_of(pos.piece_on(from));

     if (pt == PAWN)
         continue; // Will be generated togheter with direct checks

     Bitboard b = pos.attacks_from(Piece(pt), from) & pos.empty_squares();

     if (pt == KING)
         b &= ~PseudoAttacks[QUEEN][ci.ksq];

     SERIALIZE(b);
  }

  mlist = (us == WHITE ? generate_pawn_moves<WHITE, MV_NON_CAPTURE_CHECK>(pos, mlist, ci.dcCandidates, ci.ksq)
                       : generate_pawn_moves<BLACK, MV_NON_CAPTURE_CHECK>(pos, mlist, ci.dcCandidates, ci.ksq));

  mlist = generate_direct_checks<KNIGHT>(pos, mlist, us, ci);
  mlist = generate_direct_checks<BISHOP>(pos, mlist, us, ci);
  mlist = generate_direct_checks<ROOK>(pos, mlist, us, ci);
  mlist = generate_direct_checks<QUEEN>(pos, mlist, us, ci);

  if (pos.can_castle(us))
  {
      mlist = generate_castle_moves<KING_SIDE, true>(pos, mlist, us);
      mlist = generate_castle_moves<QUEEN_SIDE, true>(pos, mlist, us);
  }

  return mlist;
}


/// generate<MV_EVASION> 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<MV_EVASION>(const Position& pos, MoveStack* mlist) {

  assert(pos.in_check());

  Bitboard b, target;
  Square from, checksq;
  int checkersCnt = 0;
  Color us = pos.side_to_move();
  Square ksq = pos.king_square(us);
  Bitboard sliderAttacks = 0;
  Bitboard checkers = pos.checkers();

  assert(checkers);

  // Find squares attacked by slider checkers, we will remove them from the king
  // evasions so to skip known illegal moves avoiding useless legality check later.
  b = checkers;
  do
  {
      checkersCnt++;
      checksq = pop_1st_bit(&b);

      assert(color_of(pos.piece_on(checksq)) == ~us);

      switch (type_of(pos.piece_on(checksq)))
      {
      case BISHOP: sliderAttacks |= PseudoAttacks[BISHOP][checksq]; break;
      case ROOK:   sliderAttacks |= PseudoAttacks[ROOK][checksq];   break;
      case QUEEN:
          // If queen and king are far or not on a diagonal line 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) || !bit_is_set(PseudoAttacks[BISHOP][checksq], ksq))
              sliderAttacks |= PseudoAttacks[QUEEN][checksq];

          // Otherwise 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 |= PseudoAttacks[BISHOP][checksq] | pos.attacks_from<ROOK>(checksq);

      default:
          break;
      }
  } while (b);

  // Generate evasions for king, capture and non capture moves
  b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
  from = ksq;
  SERIALIZE(b);

  // Generate evasions for other pieces only if not under a double check
  if (checkersCnt > 1)
      return mlist;

  // Blocking evasions or captures of the checking piece
  target = squares_between(checksq, ksq) | checkers;

  mlist = (us == WHITE ? generate_pawn_moves<WHITE, MV_EVASION>(pos, mlist, target)
                       : generate_pawn_moves<BLACK, MV_EVASION>(pos, mlist, target));

  mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
  mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
  mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
  return  generate_piece_moves<QUEEN>(pos, mlist, us, target);
}


/// generate<MV_LEGAL> generates all the legal moves in the given position

template<>
MoveStack* generate<MV_LEGAL>(const Position& pos, MoveStack* mlist) {

  MoveStack *last, *cur = mlist;
  Bitboard pinned = pos.pinned_pieces();

  last = pos.in_check() ? generate<MV_EVASION>(pos, mlist)
                        : generate<MV_NON_EVASION>(pos, mlist);
  while (cur != last)
      if (!pos.pl_move_is_legal(cur->move, pinned))
          cur->move = (--last)->move;
      else
          cur++;

  return last;
}