Subversion Repositories Games.Chess Giants

/*

  Stockfish, a UCI chess playing engine derived from Glaurung 2.1

  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

  Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, 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 <cassert>

#include "movepick.h"

namespace {

  enum Stages {

    MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,

    EVASION_TT, EVASION_INIT, EVASION,

    PROBCUT_TT, PROBCUT_INIT, PROBCUT,

    QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK

  };

  // Helper filter used with select()

  const auto Any = [](){ return true; };

  // partial_insertion_sort() sorts moves in descending order up to and including

  // a given limit. The order of moves smaller than the limit is left unspecified.

  void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {

    for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)

        if (p->value >= limit)

        {

            ExtMove tmp = *p, *q;

            *p = *++sortedEnd;

            for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)

                *q = *(q - 1);

            *q = tmp;

        }

  }

} // namespace

/// Constructors of the MovePicker class. As arguments we pass information

/// to help it to return the (presumably) good moves first, to decide which

/// moves to return (in the quiescence search, for instance, we only want to

/// search captures, promotions, and some checks) and how important good move

/// ordering is at the current node.

/// MovePicker constructor for the main search

MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,

                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers)

           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),

             refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d) {

  assert(d > DEPTH_ZERO);

  stage = pos.checkers() ? EVASION_TT : MAIN_TT;

  ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

/// MovePicker constructor for quiescence search

MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,

                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)

           : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {

  assert(d <= DEPTH_ZERO);

  stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;

  ttMove =    ttm

           && pos.pseudo_legal(ttm)

           && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare) ? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

/// MovePicker constructor for ProbCut: we generate captures with SEE greater

/// than or equal to the given threshold.

MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)

           : pos(p), captureHistory(cph), threshold(th) {

  assert(!pos.checkers());

  stage = PROBCUT_TT;

  ttMove =   ttm

          && pos.pseudo_legal(ttm)

          && pos.capture(ttm)

          && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;

  stage += (ttMove == MOVE_NONE);

}

/// MovePicker::score() assigns a numerical value to each move in a list, used

/// for sorting. Captures are ordered by Most Valuable Victim (MVV), preferring

/// captures with a good history. Quiets moves are ordered using the histories.

template<GenType Type>

void MovePicker::score() {

  static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");

  for (auto& m : *this)

      if (Type == CAPTURES)

          m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]

                   + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))] / 8;

      else if (Type == QUIETS)

          m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]

                   + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]

                   + (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]

                   + (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)];

      else // Type == EVASIONS

      {

          if (pos.capture(m))

              m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]

                       - Value(type_of(pos.moved_piece(m)));

          else

              m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]

                       + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]

                       - (1 << 28);

      }

}

/// MovePicker::select() returns the next move satisfying a predicate function.

/// It never returns the TT move.

template<MovePicker::PickType T, typename Pred>

Move MovePicker::select(Pred filter) {

  while (cur < endMoves)

  {

      if (T == Best)

          std::swap(*cur, *std::max_element(cur, endMoves));

      move = *cur++;

      if (move != ttMove && filter())

          return move;

  }

  return move = MOVE_NONE;

}

/// MovePicker::next_move() is the most important method of the MovePicker class. It

/// returns a new pseudo legal move every time it is called until there are no more

/// moves left, picking the move with the highest score from a list of generated moves.

Move MovePicker::next_move(bool skipQuiets) {

top:

  switch (stage) {

  case MAIN_TT:

  case EVASION_TT:

  case QSEARCH_TT:

  case PROBCUT_TT:

      ++stage;

      return ttMove;

  case CAPTURE_INIT:

  case PROBCUT_INIT:

  case QCAPTURE_INIT:

      cur = endBadCaptures = moves;

      endMoves = generate<CAPTURES>(pos, cur);

      score<CAPTURES>();

      ++stage;

      goto top;

  case GOOD_CAPTURE:

      if (select<Best>([&](){

                       return pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)) ?

                              // Move losing capture to endBadCaptures to be tried later

                              true : (*endBadCaptures++ = move, false); }))

          return move;

      // Prepare the pointers to loop over the refutations array

      cur = std::begin(refutations);

      endMoves = std::end(refutations);

      // If the countermove is the same as a killer, skip it

      if (   refutations[0].move == refutations[2].move

          || refutations[1].move == refutations[2].move)

          --endMoves;

      ++stage;

      /* fallthrough */

  case REFUTATION:

      if (select<Next>([&](){ return    move != MOVE_NONE

                                    && !pos.capture(move)

                                    &&  pos.pseudo_legal(move); }))

          return move;

      ++stage;

      /* fallthrough */

  case QUIET_INIT:

      cur = endBadCaptures;

      endMoves = generate<QUIETS>(pos, cur);

      score<QUIETS>();

      partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);

      ++stage;

      /* fallthrough */

  case QUIET:

      if (   !skipQuiets

          && select<Next>([&](){return   move != refutations[0]

                                      && move != refutations[1]

                                      && move != refutations[2];}))

          return move;

      // Prepare the pointers to loop over the bad captures

      cur = moves;

      endMoves = endBadCaptures;

      ++stage;

      /* fallthrough */

  case BAD_CAPTURE:

      return select<Next>(Any);

  case EVASION_INIT:

      cur = moves;

      endMoves = generate<EVASIONS>(pos, cur);

      score<EVASIONS>();

      ++stage;

      /* fallthrough */

  case EVASION:

      return select<Best>(Any);

  case PROBCUT:

      return select<Best>([&](){ return pos.see_ge(move, threshold); });

  case QCAPTURE:

      if (select<Best>([&](){ return   depth > DEPTH_QS_RECAPTURES

                                    || to_sq(move) == recaptureSquare; }))

          return move;

      // If we did not find any move and we do not try checks, we have finished

      if (depth != DEPTH_QS_CHECKS)

          return MOVE_NONE;

      ++stage;

      /* fallthrough */

  case QCHECK_INIT:

      cur = moves;

      endMoves = generate<QUIET_CHECKS>(pos, cur);

      ++stage;

      /* fallthrough */

  case QCHECK:

      return select<Next>(Any);

  }

  assert(false);

  return MOVE_NONE; // Silence warning

}