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 <algorithm> // For std::min

#include <cassert>

#include <cstring>   // For std::memset

#include "material.h"

#include "thread.h"

using namespace std;

namespace {

  // Polynomial material imbalance parameters

  constexpr int QuadraticOurs[][PIECE_TYPE_NB] = {

    //            OUR PIECES

    // pair pawn knight bishop rook queen

    {1438                               }, // Bishop pair

    {  40,   38                         }, // Pawn

    {  32,  255, -62                    }, // Knight      OUR PIECES

    {   0,  104,   4,    0              }, // Bishop

    { -26,   -2,  47,   105,  -208      }, // Rook

    {-189,   24, 117,   133,  -134, -6  }  // Queen

  };

  constexpr int QuadraticTheirs[][PIECE_TYPE_NB] = {

    //           THEIR PIECES

    // pair pawn knight bishop rook queen

    {   0                               }, // Bishop pair

    {  36,    0                         }, // Pawn

    {   9,   63,   0                    }, // Knight      OUR PIECES

    {  59,   65,  42,     0             }, // Bishop

    {  46,   39,  24,   -24,    0       }, // Rook

    {  97,  100, -42,   137,  268,    0 }  // Queen

  };

  // Endgame evaluation and scaling functions are accessed directly and not through

  // the function maps because they correspond to more than one material hash key.

  Endgame<KXK>    EvaluateKXK[] = { Endgame<KXK>(WHITE),    Endgame<KXK>(BLACK) };

  Endgame<KBPsK>  ScaleKBPsK[]  = { Endgame<KBPsK>(WHITE),  Endgame<KBPsK>(BLACK) };

  Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };

  Endgame<KPsK>   ScaleKPsK[]   = { Endgame<KPsK>(WHITE),   Endgame<KPsK>(BLACK) };

  Endgame<KPKP>   ScaleKPKP[]   = { Endgame<KPKP>(WHITE),   Endgame<KPKP>(BLACK) };

  // Helper used to detect a given material distribution

  bool is_KXK(const Position& pos, Color us) {

    return  !more_than_one(pos.pieces(~us))

          && pos.non_pawn_material(us) >= RookValueMg;

  }

  bool is_KBPsK(const Position& pos, Color us) {

    return   pos.non_pawn_material(us) == BishopValueMg

          && pos.count<BISHOP>(us) == 1

          && pos.count<PAWN  >(us) >= 1;

  }

  bool is_KQKRPs(const Position& pos, Color us) {

    return  !pos.count<PAWN>(us)

          && pos.non_pawn_material(us) == QueenValueMg

          && pos.count<QUEEN>(us) == 1

          && pos.count<ROOK>(~us) == 1

          && pos.count<PAWN>(~us) >= 1;

  }

  /// imbalance() calculates the imbalance by comparing the piece count of each

  /// piece type for both colors.

  template<Color Us>

  int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {

    constexpr Color Them = (Us == WHITE ? BLACK : WHITE);

    int bonus = 0;

    // Second-degree polynomial material imbalance, by Tord Romstad

    for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)

    {

        if (!pieceCount[Us][pt1])

            continue;

        int v = 0;

        for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)

            v +=  QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]

                + QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];

        bonus += pieceCount[Us][pt1] * v;

    }

    return bonus;

  }

} // namespace

namespace Material {

/// Material::probe() looks up the current position's material configuration in

/// the material hash table. It returns a pointer to the Entry if the position

/// is found. Otherwise a new Entry is computed and stored there, so we don't

/// have to recompute all when the same material configuration occurs again.

Entry* probe(const Position& pos) {

  Key key = pos.material_key();

  Entry* e = pos.this_thread()->materialTable[key];

  if (e->key == key)

      return e;

  std::memset(e, 0, sizeof(Entry));

  e->key = key;

  e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;

  Value npm_w = pos.non_pawn_material(WHITE);

  Value npm_b = pos.non_pawn_material(BLACK);

  Value npm = std::max(EndgameLimit, std::min(npm_w + npm_b, MidgameLimit));

  // Map total non-pawn material into [PHASE_ENDGAME, PHASE_MIDGAME]

  e->gamePhase = Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));

  // Let's look if we have a specialized evaluation function for this particular

  // material configuration. Firstly we look for a fixed configuration one, then

  // for a generic one if the previous search failed.

  if ((e->evaluationFunction = pos.this_thread()->endgames.probe<Value>(key)) != nullptr)

      return e;

  for (Color c = WHITE; c <= BLACK; ++c)

      if (is_KXK(pos, c))

      {

          e->evaluationFunction = &EvaluateKXK[c];

          return e;

      }

  // OK, we didn't find any special evaluation function for the current material

  // configuration. Is there a suitable specialized scaling function?

  const EndgameBase<ScaleFactor>* sf;

  if ((sf = pos.this_thread()->endgames.probe<ScaleFactor>(key)) != nullptr)

  {

      e->scalingFunction[sf->strongSide] = sf; // Only strong color assigned

      return e;

  }

  // We didn't find any specialized scaling function, so fall back on generic

  // ones that refer to more than one material distribution. Note that in this

  // case we don't return after setting the function.

  for (Color c = WHITE; c <= BLACK; ++c)

  {

    if (is_KBPsK(pos, c))

        e->scalingFunction[c] = &ScaleKBPsK[c];

    else if (is_KQKRPs(pos, c))

        e->scalingFunction[c] = &ScaleKQKRPs[c];

  }

  if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board

  {

      if (!pos.count<PAWN>(BLACK))

      {

          assert(pos.count<PAWN>(WHITE) >= 2);

          e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];

      }

      else if (!pos.count<PAWN>(WHITE))

      {

          assert(pos.count<PAWN>(BLACK) >= 2);

          e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];

      }

      else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)

      {

          // This is a special case because we set scaling functions

          // for both colors instead of only one.

          e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];

          e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];

      }

  }

  // Zero or just one pawn makes it difficult to win, even with a small material

  // advantage. This catches some trivial draws like KK, KBK and KNK and gives a

  // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).

  if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)

      e->factor[WHITE] = uint8_t(npm_w <  RookValueMg   ? SCALE_FACTOR_DRAW :

                                 npm_b <= BishopValueMg ? 4 : 14);

  if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)

      e->factor[BLACK] = uint8_t(npm_b <  RookValueMg   ? SCALE_FACTOR_DRAW :

                                 npm_w <= BishopValueMg ? 4 : 14);

  // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder

  // for the bishop pair "extended piece", which allows us to be more flexible

  // in defining bishop pair bonuses.

  const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {

  { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),

    pos.count<BISHOP>(WHITE)    , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },

  { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),

    pos.count<BISHOP>(BLACK)    , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };

  e->value = int16_t((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);

  return e;

}

} // namespace Material