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) 2015-2018 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_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,

    EVASION, EVASIONS_INIT, ALL_EVASIONS,

    PROBCUT, PROBCUT_INIT, PROBCUT_CAPTURES,

    QSEARCH_WITH_CHECKS, QCAPTURES_1_INIT, QCAPTURES_1, QCHECKS,

    QSEARCH_NO_CHECKS, QCAPTURES_2_INIT, QCAPTURES_2,

    QSEARCH_RECAPTURES, QRECAPTURES

  };

  // 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;

        }

  }

  // pick_best() finds the best move in the range (begin, end) and moves it to

  // the front. It's faster than sorting all the moves in advance when there

  // are few moves, e.g., the possible captures.

  Move pick_best(ExtMove* begin, ExtMove* end) {

    std::swap(*begin, *std::max_element(begin, end));

    return *begin;

  }

} // 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_p)

           : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch), countermove(cm),

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

  assert(d > DEPTH_ZERO);

  stage = pos.checkers() ? EVASION : MAIN_SEARCH;

  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, Square s)

           : pos(p), mainHistory(mh), captureHistory(cph) {

  assert(d <= DEPTH_ZERO);

  if (pos.checkers())

      stage = EVASION;

  else if (d > DEPTH_QS_NO_CHECKS)

      stage = QSEARCH_WITH_CHECKS;

  else if (d > DEPTH_QS_RECAPTURES)

      stage = QSEARCH_NO_CHECKS;

  else

  {

      stage = QSEARCH_RECAPTURES;

      recaptureSquare = s;

      return;

  }

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

  stage += (ttMove == MOVE_NONE);

}

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

/// 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;

  ttMove =   ttm

          && pos.pseudo_legal(ttm)

          && pos.capture(ttm)

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

  stage += (ttMove == MOVE_NONE);

}

/// 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 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))]

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

      else if (Type == QUIETS)

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

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

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

                   + (*contHistory[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)] - (1 << 28);

      }

}

/// 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. It picks the move with the biggest value from a list of generated moves

/// taking care not to return the ttMove if it has already been searched.

Move MovePicker::next_move(bool skipQuiets) {

  Move move;

  switch (stage) {

  case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:

  case QSEARCH_NO_CHECKS: case PROBCUT:

      ++stage;

      return ttMove;

  case CAPTURES_INIT:

      endBadCaptures = cur = moves;

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

      score<CAPTURES>();

      ++stage;

      /* fallthrough */

  case GOOD_CAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

          {

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

                  return move;

              // Losing capture, move it to the beginning of the array

              *endBadCaptures++ = move;

          }

      }

      ++stage;

      move = killers[0];  // First killer move

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

      /* fallthrough */

  case KILLERS:

      ++stage;

      move = killers[1]; // Second killer move

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

      /* fallthrough */

  case COUNTERMOVE:

      ++stage;

      move = countermove;

      if (    move != MOVE_NONE

          &&  move != ttMove

          &&  move != killers[0]

          &&  move != killers[1]

          &&  pos.pseudo_legal(move)

          && !pos.capture(move))

          return move;

      /* 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:

      while (    cur < endMoves

             && (!skipQuiets || cur->value >= VALUE_ZERO))

      {

          move = *cur++;

          if (   move != ttMove

              && move != killers[0]

              && move != killers[1]

              && move != countermove)

              return move;

      }

      ++stage;

      cur = moves; // Point to beginning of bad captures

      /* fallthrough */

  case BAD_CAPTURES:

      if (cur < endBadCaptures)

          return *cur++;

      break;

  case EVASIONS_INIT:

      cur = moves;

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

      score<EVASIONS>();

      ++stage;

      /* fallthrough */

  case ALL_EVASIONS:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

              return move;

      }

      break;

  case PROBCUT_INIT:

      cur = moves;

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

      score<CAPTURES>();

      ++stage;

      /* fallthrough */

  case PROBCUT_CAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (   move != ttMove

              && pos.see_ge(move, threshold))

              return move;

      }

      break;

  case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:

      cur = moves;

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

      score<CAPTURES>();

      ++stage;

      /* fallthrough */

  case QCAPTURES_1: case QCAPTURES_2:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (move != ttMove)

              return move;

      }

      if (stage == QCAPTURES_2)

          break;

      cur = moves;

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

      ++stage;

      /* fallthrough */

  case QCHECKS:

      while (cur < endMoves)

      {

          move = cur++->move;

          if (move != ttMove)

              return move;

      }

      break;

  case QSEARCH_RECAPTURES:

      cur = moves;

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

      score<CAPTURES>();

      ++stage;

      /* fallthrough */

  case QRECAPTURES:

      while (cur < endMoves)

      {

          move = pick_best(cur++, endMoves);

          if (to_sq(move) == recaptureSquare)

              return move;

      }

      break;

  default:

      assert(false);

  }

  return MOVE_NONE;

}