[stockfish] / src / evaluate.cpp

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  Copyright (C) 2008-2009 Marco Costalba

  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/>.
*/


////
//// Includes
////

#include <cassert>
#include <cstring>

#include "bitcount.h"
#include "evaluate.h"
#include "material.h"
#include "pawns.h"
#include "scale.h"
#include "thread.h"
#include "ucioption.h"


////
//// Local definitions
////

namespace {

  const int Sign[2] = { 1, -1 };

  // Evaluation grain size, must be a power of 2
  const int GrainSize = 8;

  // Evaluation weights, initialized from UCI options
  int WeightMobilityMidgame, WeightMobilityEndgame;
  int WeightPawnStructureMidgame, WeightPawnStructureEndgame;
  int WeightPassedPawnsMidgame, WeightPassedPawnsEndgame;
  int WeightKingSafety[2];
  int WeightSpace;

  // Internal evaluation weights. These are applied on top of the evaluation
  // weights read from UCI parameters. The purpose is to be able to change
  // the evaluation weights while keeping the default values of the UCI
  // parameters at 100, which looks prettier.
  //
  // Values modified by Joona Kiiski
  const int WeightMobilityMidgameInternal      = 248;
  const int WeightMobilityEndgameInternal      = 271;
  const int WeightPawnStructureMidgameInternal = 233;
  const int WeightPawnStructureEndgameInternal = 201;
  const int WeightPassedPawnsMidgameInternal   = 252;
  const int WeightPassedPawnsEndgameInternal   = 259;
  const int WeightKingSafetyInternal           = 247;
  const int WeightKingOppSafetyInternal        = 259;
  const int WeightSpaceInternal                = 46;

  // Mobility and outposts bonus modified by Joona Kiiski
  //
  // Visually better to define tables constants
  typedef Value V;
  typedef Score S;

  // Knight mobility bonus in middle game and endgame, indexed by the number
  // of attacked squares not occupied by friendly piecess.
  const Score KnightMobilityBonus[] = {
    S(-38,-33), S(-25,-23), S(-12,-13), S( 0,-3),
    S( 12,  7), S( 25, 17), S( 31, 22), S(38, 27), S(38, 27)
  };

  // Bishop mobility bonus in middle game and endgame, indexed by the number
  // of attacked squares not occupied by friendly pieces. X-ray attacks through
  // queens are also included.
  const Score BishopMobilityBonus[] = {
    S(-25,-30), S(-11,-16), S( 3, -2), S(17, 12),
    S( 31, 26), S( 45, 40), S(57, 52), S(65, 60),
    S( 71, 65), S( 74, 69), S(76, 71), S(78, 73),
    S( 79, 74), S( 80, 75), S(81, 76), S(81, 76)
  };

  // Rook mobility bonus in middle game and endgame, indexed by the number
  // of attacked squares not occupied by friendly pieces. X-ray attacks through
  // queens and rooks are also included.
  const Score RookMobilityBonus[] = {
    S(-20,-36), S(-14,-19), S(-8, -3), S(-2, 13),
    S(  4, 29), S( 10, 46), S(14, 62), S(19, 79),
    S( 23, 95), S( 26,106), S(27,111), S(28,114),
    S( 29,116), S( 30,117), S(31,118), S(32,118)
  };

  // Queen mobility bonus in middle game and endgame, indexed by the number
  // of attacked squares not occupied by friendly pieces.
  const Score QueenMobilityBonus[] = {
    S(-10,-18), S(-8,-13), S(-6, -7), S(-3, -2), S(-1,  3), S( 1,  8),
    S(  3, 13), S( 5, 19), S( 8, 23), S(10, 27), S(12, 32), S(15, 34),
    S( 16, 35), S(17, 35), S(18, 35), S(20, 35), S(20, 35), S(20, 35),
    S( 20, 35), S(20, 35), S(20, 35), S(20, 35), S(20, 35), S(20, 35),
    S( 20, 35), S(20, 35), S(20, 35), S(20, 35), S(20, 35), S(20, 35),
    S( 20, 35), S(20, 35)
  };

  // Pointers table to access mobility tables through piece type
  const Score* MobilityBonus[] = { 0, 0, KnightMobilityBonus, BishopMobilityBonus, RookMobilityBonus, QueenMobilityBonus };

  // Outpost bonuses for knights and bishops, indexed by square (from white's
  // point of view).
  const Value KnightOutpostBonus[64] = {
  //  A     B     C     D     E     F     G     H
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 1
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 2
    V(0), V(0), V(4), V(8), V(8), V(4), V(0), V(0), // 3
    V(0), V(4),V(17),V(26),V(26),V(17), V(4), V(0), // 4
    V(0), V(8),V(26),V(35),V(35),V(26), V(8), V(0), // 5
    V(0), V(4),V(17),V(17),V(17),V(17), V(4), V(0), // 6
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 7
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0)  // 8
  };

  const Value BishopOutpostBonus[64] = {
  //  A     B     C     D     E     F     G     H
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 1
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 2
    V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0), // 3
    V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0), // 4
    V(0),V(10),V(21),V(21),V(21),V(21),V(10), V(0), // 5
    V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0), // 6
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 7
    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0)  // 8
  };

  // Bonus for unstoppable passed pawns
  const Value UnstoppablePawnValue = Value(0x500);

  // Rooks and queens on the 7th rank (modified by Joona Kiiski)
  const Score RookOn7thBonus  = Score(47, 98);
  const Score QueenOn7thBonus = Score(27, 54);

  // Rooks on open files (modified by Joona Kiiski)
  const Value RookOpenFileBonus = Value(43);
  const Value RookHalfOpenFileBonus = Value(19);

  // Penalty for rooks trapped inside a friendly king which has lost the
  // right to castle.
  const Value TrappedRookPenalty = Value(180);

  // Penalty for a bishop on a7/h7 (a2/h2 for black) which is trapped by
  // enemy pawns.
  const Value TrappedBishopA7H7Penalty = Value(300);

  // Bitboard masks for detecting trapped bishops on a7/h7 (a2/h2 for black)
  const Bitboard MaskA7H7[2] = {
    ((1ULL << SQ_A7) | (1ULL << SQ_H7)),
    ((1ULL << SQ_A2) | (1ULL << SQ_H2))
  };

  // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
  // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
  // happen in Chess960 games.
  const Value TrappedBishopA1H1Penalty = Value(100);

  // Bitboard masks for detecting trapped bishops on a1/h1 (a8/h8 for black)
  const Bitboard MaskA1H1[2] = {
    ((1ULL << SQ_A1) | (1ULL << SQ_H1)),
    ((1ULL << SQ_A8) | (1ULL << SQ_H8))
  };

  // The SpaceMask[color] contains the area of the board which is considered
  // by the space evaluation. In the middle game, each side is given a bonus
  // based on how many squares inside this area are safe and available for
  // friendly minor pieces.
  const Bitboard SpaceMask[2] = {
    (1ULL<<SQ_C2) | (1ULL<<SQ_D2) | (1ULL<<SQ_E2) | (1ULL<<SQ_F2) |
    (1ULL<<SQ_C3) | (1ULL<<SQ_D3) | (1ULL<<SQ_E3) | (1ULL<<SQ_F3) |
    (1ULL<<SQ_C4) | (1ULL<<SQ_D4) | (1ULL<<SQ_E4) | (1ULL<<SQ_F4),
    (1ULL<<SQ_C7) | (1ULL<<SQ_D7) | (1ULL<<SQ_E7) | (1ULL<<SQ_F7) |
    (1ULL<<SQ_C6) | (1ULL<<SQ_D6) | (1ULL<<SQ_E6) | (1ULL<<SQ_F6) |
    (1ULL<<SQ_C5) | (1ULL<<SQ_D5) | (1ULL<<SQ_E5) | (1ULL<<SQ_F5)
  };

  /// King safety constants and variables. The king safety scores are taken
  /// from the array SafetyTable[]. Various little "meta-bonuses" measuring
  /// the strength of the attack are added up into an integer, which is used
  /// as an index to SafetyTable[].

  // Attack weights for each piece type and table indexed on piece type
  const int QueenAttackWeight  = 5;
  const int RookAttackWeight   = 3;
  const int BishopAttackWeight = 2;
  const int KnightAttackWeight = 2;

  const int AttackWeight[] = { 0, 0, KnightAttackWeight, BishopAttackWeight, RookAttackWeight, QueenAttackWeight };

  // Bonuses for safe checks, initialized from UCI options
  int QueenContactCheckBonus, DiscoveredCheckBonus;
  int QueenCheckBonus, RookCheckBonus, BishopCheckBonus, KnightCheckBonus;

  // Scan for queen contact mates?
  const bool QueenContactMates = true;

  // Bonus for having a mate threat, initialized from UCI options
  int MateThreatBonus;

  // ThreatBonus[][] contains bonus according to which piece type
  // attacks which one.
  const Score ThreatBonus[8][8] = {
  #define Z Score(0, 0)
      { Z, Z, Z, Z, Z, Z, Z, Z }, // not used
      { Z, S(18,37),       Z, S(37,47), S(55,97), S(55,97), Z, Z }, // KNIGHT attacks
      { Z, S(18,37), S(37,47),       Z, S(55,97), S(55,97), Z, Z }, // BISHOP attacks
      { Z, S( 9,27), S(27,47), S(27,47),       Z, S(37,47), Z, Z }, // ROOK attacks
      { Z, S(27,37), S(27,37), S(27,37), S(27,37),       Z, Z, Z }, // QUEEN attacks
      { Z, Z, Z, Z, Z, Z, Z, Z }, // not used
      { Z, Z, Z, Z, Z, Z, Z, Z }, // not used
      { Z, Z, Z, Z, Z, Z, Z, Z }  // not used
  #undef Z
  };

  // ThreatedByPawnPenalty[] contains a penalty according to which piece
  // type is attacked by an enemy pawn.
  const Value MidgameThreatedByPawnPenalty[8] = {
    V(0), V(0), V(56), V(56), V(76), V(86), V(0), V(0)
  };

  const Value EndgameThreatedByPawnPenalty[8] = {
    V(0), V(0), V(70), V(70), V(99), V(118), V(0), V(0)
  };

  // InitKingDanger[] contains bonuses based on the position of the defending
  // king.
  const int InitKingDanger[64] = {
     2,  0,  2,  5,  5,  2,  0,  2,
     2,  2,  4,  8,  8,  4,  2,  2,
     7, 10, 12, 12, 12, 12, 10,  7,
    15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15,
    15, 15, 15, 15, 15, 15, 15, 15
  };

  // SafetyTable[] contains the actual king safety scores. It is initialized
  // in init_safety().
  Value SafetyTable[100];

  // Pawn and material hash tables, indexed by the current thread id
  PawnInfoTable* PawnTable[8] = {0, 0, 0, 0, 0, 0, 0, 0};
  MaterialInfoTable* MaterialTable[8] = {0, 0, 0, 0, 0, 0, 0, 0};

  // Sizes of pawn and material hash tables
  const int PawnTableSize = 16384;
  const int MaterialTableSize = 1024;

  // Function prototypes
  template<bool HasPopCnt>
  Value do_evaluate(const Position& pos, EvalInfo& ei, int threadID);

  template<Color Us, bool HasPopCnt>
  void evaluate_pieces_of_color(const Position& pos, EvalInfo& ei);

  template<Color Us, bool HasPopCnt>
  void evaluate_king(const Position& pos, EvalInfo& ei);

  template<Color Us>
  void evaluate_threats(const Position& pos, EvalInfo& ei);

  template<Color Us, bool HasPopCnt>
  void evaluate_space(const Position& pos, EvalInfo& ei);

  void evaluate_passed_pawns(const Position& pos, EvalInfo& ei);
  void evaluate_trapped_bishop_a7h7(const Position& pos, Square s, Color us, EvalInfo& ei);
  void evaluate_trapped_bishop_a1h1(const Position& pos, Square s, Color us, EvalInfo& ei);
  inline Score apply_weight(Score v, int wmg, int weg);
  Value scale_by_game_phase(const Score& v, Phase ph, const ScaleFactor sf[]);
  int weight_option(const std::string& opt, int weight);
  void init_safety();
}


////
//// Functions
////

/// evaluate() is the main evaluation function. It always computes two
/// values, an endgame score and a middle game score, and interpolates
/// between them based on the remaining material.
Value evaluate(const Position& pos, EvalInfo& ei, int threadID) {

    return CpuHasPOPCNT ? do_evaluate<true>(pos, ei, threadID)
                        : do_evaluate<false>(pos, ei, threadID);
}

namespace {

template<bool HasPopCnt>
Value do_evaluate(const Position& pos, EvalInfo& ei, int threadID) {

  assert(pos.is_ok());
  assert(threadID >= 0 && threadID < THREAD_MAX);
  assert(!pos.is_check());

  memset(&ei, 0, sizeof(EvalInfo));

  // Initialize by reading the incrementally updated scores included in the
  // position object (material + piece square tables)
  ei.value = pos.value();

  // Probe the material hash table
  ei.mi = MaterialTable[threadID]->get_material_info(pos);
  ei.value += ei.mi->material_value();

  // If we have a specialized evaluation function for the current material
  // configuration, call it and return
  if (ei.mi->specialized_eval_exists())
      return ei.mi->evaluate(pos);

  // After get_material_info() call that modifies them
  ScaleFactor factor[2];
  factor[WHITE] = ei.mi->scale_factor(pos, WHITE);
  factor[BLACK] = ei.mi->scale_factor(pos, BLACK);

  // Probe the pawn hash table
  ei.pi = PawnTable[threadID]->get_pawn_info(pos);
  ei.value += apply_weight(ei.pi->value(), WeightPawnStructureMidgame, WeightPawnStructureEndgame);

  // Initialize king attack bitboards and king attack zones for both sides
  ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.king_square(WHITE));
  ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.king_square(BLACK));
  ei.kingZone[WHITE] = ei.attackedBy[BLACK][KING] | (ei.attackedBy[BLACK][KING] >> 8);
  ei.kingZone[BLACK] = ei.attackedBy[WHITE][KING] | (ei.attackedBy[WHITE][KING] << 8);

  // Initialize pawn attack bitboards for both sides
  ei.attackedBy[WHITE][PAWN] = ei.pi->pawn_attacks(WHITE);
  ei.attackedBy[BLACK][PAWN] = ei.pi->pawn_attacks(BLACK);
  Bitboard b1 = ei.attackedBy[WHITE][PAWN] & ei.attackedBy[BLACK][KING];
  Bitboard b2 = ei.attackedBy[BLACK][PAWN] & ei.attackedBy[WHITE][KING];
  if (b1)
      ei.kingAttackersCount[WHITE] = count_1s_max_15<HasPopCnt>(b1)/2;

  if (b2)
      ei.kingAttackersCount[BLACK] = count_1s_max_15<HasPopCnt>(b2)/2;

  // Evaluate pieces
  evaluate_pieces_of_color<WHITE, HasPopCnt>(pos, ei);
  evaluate_pieces_of_color<BLACK, HasPopCnt>(pos, ei);

  // Kings. Kings are evaluated after all other pieces for both sides,
  // because we need complete attack information for all pieces when computing
  // the king safety evaluation.
  evaluate_king<WHITE, HasPopCnt>(pos, ei);
  evaluate_king<BLACK, HasPopCnt>(pos, ei);

  // Evaluate tactical threats, we need full attack info
  evaluate_threats<WHITE>(pos, ei);
  evaluate_threats<BLACK>(pos, ei);

  // Evaluate passed pawns. We evaluate passed pawns for both sides at once,
  // because we need to know which side promotes first in positions where
  // both sides have an unstoppable passed pawn. To be called after all attacks
  // are computed, included king.
  if (ei.pi->passed_pawns())
      evaluate_passed_pawns(pos, ei);

  Phase phase = pos.game_phase();

  // Middle-game specific evaluation terms
  if (phase > PHASE_ENDGAME)
  {
    // Pawn storms in positions with opposite castling.
    if (   square_file(pos.king_square(WHITE)) >= FILE_E
        && square_file(pos.king_square(BLACK)) <= FILE_D)

        ei.value += Score(ei.pi->queenside_storm_value(WHITE) - ei.pi->kingside_storm_value(BLACK), 0);

    else if (   square_file(pos.king_square(WHITE)) <= FILE_D
             && square_file(pos.king_square(BLACK)) >= FILE_E)

        ei.value += Score(ei.pi->kingside_storm_value(WHITE) - ei.pi->queenside_storm_value(BLACK), 0);

    // Evaluate space for both sides
    if (ei.mi->space_weight() > 0)
    {
        evaluate_space<WHITE, HasPopCnt>(pos, ei);
        evaluate_space<BLACK, HasPopCnt>(pos, ei);
    }
  }

  // Mobility
  ei.value += apply_weight(ei.mobility, WeightMobilityMidgame, WeightMobilityEndgame);

  // If we don't already have an unusual scale factor, check for opposite
  // colored bishop endgames, and use a lower scale for those
  if (   phase < PHASE_MIDGAME
      && pos.opposite_colored_bishops()
      && (   (factor[WHITE] == SCALE_FACTOR_NORMAL && ei.value.eg() > Value(0))
          || (factor[BLACK] == SCALE_FACTOR_NORMAL && ei.value.eg() < Value(0))))
  {
      ScaleFactor sf;

      // Only the two bishops ?
      if (   pos.non_pawn_material(WHITE) == BishopValueMidgame
          && pos.non_pawn_material(BLACK) == BishopValueMidgame)
      {
          // Check for KBP vs KB with only a single pawn that is almost
          // certainly a draw or at least two pawns.
          bool one_pawn = (pos.piece_count(WHITE, PAWN) + pos.piece_count(BLACK, PAWN) == 1);
          sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
      }
      else
          // Endgame with opposite-colored bishops, but also other pieces. Still
          // a bit drawish, but not as drawish as with only the two bishops.
           sf = ScaleFactor(50);

      if (factor[WHITE] == SCALE_FACTOR_NORMAL)
          factor[WHITE] = sf;
      if (factor[BLACK] == SCALE_FACTOR_NORMAL)
          factor[BLACK] = sf;
  }

  // Interpolate between the middle game and the endgame score
  Color stm = pos.side_to_move();

  Value v = Sign[stm] * scale_by_game_phase(ei.value, phase, factor);

  return (ei.mateThreat[stm] == MOVE_NONE ? v : 8 * QueenValueMidgame - v);
}

} // namespace

/// quick_evaluate() does a very approximate evaluation of the current position.
/// It currently considers only material and piece square table scores. Perhaps
/// we should add scores from the pawn and material hash tables?

Value quick_evaluate(const Position &pos) {

  assert(pos.is_ok());

  static const
  ScaleFactor sf[2] = {SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL};

  Phase ph = pos.game_phase();
  Color stm = pos.side_to_move();

  return Sign[stm] * scale_by_game_phase(pos.value(), ph, sf);
}


/// init_eval() initializes various tables used by the evaluation function

void init_eval(int threads) {

  assert(threads <= THREAD_MAX);

  for (int i = 0; i < THREAD_MAX; i++)
  {
    if (i >= threads)
    {
        delete PawnTable[i];
        delete MaterialTable[i];
        PawnTable[i] = NULL;
        MaterialTable[i] = NULL;
        continue;
    }
    if (!PawnTable[i])
        PawnTable[i] = new PawnInfoTable(PawnTableSize);
    if (!MaterialTable[i])
        MaterialTable[i] = new MaterialInfoTable(MaterialTableSize);
  }
}


/// quit_eval() releases heap-allocated memory at program termination

void quit_eval() {

  for (int i = 0; i < THREAD_MAX; i++)
  {
      delete PawnTable[i];
      delete MaterialTable[i];
      PawnTable[i] = NULL;
      MaterialTable[i] = NULL;
  }
}


/// read_weights() reads evaluation weights from the corresponding UCI parameters

void read_weights(Color us) {

  Color them = opposite_color(us);

  WeightMobilityMidgame      = weight_option("Mobility (Middle Game)", WeightMobilityMidgameInternal);
  WeightMobilityEndgame      = weight_option("Mobility (Endgame)", WeightMobilityEndgameInternal);
  WeightPawnStructureMidgame = weight_option("Pawn Structure (Middle Game)", WeightPawnStructureMidgameInternal);
  WeightPawnStructureEndgame = weight_option("Pawn Structure (Endgame)", WeightPawnStructureEndgameInternal);
  WeightPassedPawnsMidgame   = weight_option("Passed Pawns (Middle Game)", WeightPassedPawnsMidgameInternal);
  WeightPassedPawnsEndgame   = weight_option("Passed Pawns (Endgame)", WeightPassedPawnsEndgameInternal);
  WeightSpace                = weight_option("Space", WeightSpaceInternal);
  WeightKingSafety[us]       = weight_option("Cowardice", WeightKingSafetyInternal);
  WeightKingSafety[them]     = weight_option("Aggressiveness", WeightKingOppSafetyInternal);

  // If running in analysis mode, make sure we use symmetrical king safety. We do this
  // by replacing both WeightKingSafety[us] and WeightKingSafety[them] by their average.
  if (get_option_value_bool("UCI_AnalyseMode"))
  {
      WeightKingSafety[us] = (WeightKingSafety[us] + WeightKingSafety[them]) / 2;
      WeightKingSafety[them] = WeightKingSafety[us];
  }
  init_safety();
}


namespace {

  // evaluate_mobility() computes mobility and attacks for every piece

  template<PieceType Piece, Color Us, bool HasPopCnt>
  int evaluate_mobility(Bitboard b, Bitboard mob_area, EvalInfo& ei) {

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

    // Update attack info
    ei.attackedBy[Us][Piece] |= b;

    // King attacks
    if (b & ei.kingZone[Us])
    {
        ei.kingAttackersCount[Us]++;
        ei.kingAttackersWeight[Us] += AttackWeight[Piece];
        Bitboard bb = (b & ei.attackedBy[Them][KING]);
        if (bb)
            ei.kingAdjacentZoneAttacksCount[Us] += count_1s_max_15<HasPopCnt>(bb);
    }

    // Mobility
    int mob = (Piece != QUEEN ? count_1s_max_15<HasPopCnt>(b & mob_area)
                              : count_1s<HasPopCnt>(b & mob_area));

    ei.mobility += Sign[Us] * MobilityBonus[Piece][mob];
    return mob;
  }


  // evaluate_outposts() evaluates bishop and knight outposts squares

  template<PieceType Piece, Color Us>
  void evaluate_outposts(const Position& pos, EvalInfo& ei, Square s) {

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

    // Initial bonus based on square
    Value bonus = (Piece == BISHOP ? BishopOutpostBonus[relative_square(Us, s)]
                                   : KnightOutpostBonus[relative_square(Us, s)]);

    // Increase bonus if supported by pawn, especially if the opponent has
    // no minor piece which can exchange the outpost piece
    if (bonus && (pos.attacks_from<PAWN>(s, Them) & pos.pieces(PAWN, Us)))
    {
        if (    pos.pieces(KNIGHT, Them) == EmptyBoardBB
            && (SquaresByColorBB[square_color(s)] & pos.pieces(BISHOP, Them)) == EmptyBoardBB)
            bonus += bonus + bonus / 2;
        else
            bonus += bonus / 2;
    }
    ei.value += Sign[Us] * Score(bonus, bonus);
  }


  // evaluate_pieces<>() assigns bonuses and penalties to the pieces of a given color

  template<PieceType Piece, Color Us, bool HasPopCnt>
  void evaluate_pieces(const Position& pos, EvalInfo& ei) {

    Bitboard b;
    Square s, ksq;
    int mob;
    File f;

    const Color Them = (Us == WHITE ? BLACK : WHITE);
    const Square* ptr = pos.piece_list_begin(Us, Piece);

    // Do not include in mobility squares protected by enemy pawns or occupied by our pieces
    const Bitboard mob_area = ~(ei.attackedBy[Them][PAWN] | pos.pieces_of_color(Us));

    while ((s = *ptr++) != SQ_NONE)
    {
        if (Piece == KNIGHT || Piece == QUEEN)
            b = pos.attacks_from<Piece>(s);
        else if (Piece == BISHOP)
            b = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
        else if (Piece == ROOK)
            b = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
        else
            assert(false);

        // Attacks and mobility
        mob = evaluate_mobility<Piece, Us, HasPopCnt>(b, mob_area, ei);

        // Decrease score if we are attacked by an enemy pawn. Remaining part
        // of threat evaluation must be done later when we have full attack info.
        if (bit_is_set(ei.attackedBy[Them][PAWN], s))
            ei.value -= Sign[Us] * Score(MidgameThreatedByPawnPenalty[Piece], EndgameThreatedByPawnPenalty[Piece]);

        // Bishop and knight outposts squares
        if ((Piece == BISHOP || Piece == KNIGHT) && pos.square_is_weak(s, Them))
            evaluate_outposts<Piece, Us>(pos, ei, s);

        // Special patterns: trapped bishops on a7/h7/a2/h2
        // and trapped bishops on a1/h1/a8/h8 in Chess960.
        if (Piece == BISHOP)
        {
            if (bit_is_set(MaskA7H7[Us], s))
                evaluate_trapped_bishop_a7h7(pos, s, Us, ei);

            if (Chess960 && bit_is_set(MaskA1H1[Us], s))
                evaluate_trapped_bishop_a1h1(pos, s, Us, ei);
        }

        if (Piece == ROOK || Piece == QUEEN)
        {
            // Queen or rook on 7th rank
            if (   relative_rank(Us, s) == RANK_7
                && relative_rank(Us, pos.king_square(Them)) == RANK_8)
            {
                ei.value += Sign[Us] * (Piece == ROOK ? RookOn7thBonus : QueenOn7thBonus);
            }
        }

        // Special extra evaluation for rooks
        if (Piece == ROOK)
        {
            // Open and half-open files
            f = square_file(s);
            if (ei.pi->file_is_half_open(Us, f))
            {
                if (ei.pi->file_is_half_open(Them, f))
                    ei.value += Sign[Us] * Score(RookOpenFileBonus, RookOpenFileBonus);
                else
                    ei.value += Sign[Us] * Score(RookHalfOpenFileBonus, RookHalfOpenFileBonus);
            }

            // Penalize rooks which are trapped inside a king. Penalize more if
            // king has lost right to castle.
            if (mob > 6 || ei.pi->file_is_half_open(Us, f))
                continue;

            ksq = pos.king_square(Us);

            if (    square_file(ksq) >= FILE_E
                &&  square_file(s) > square_file(ksq)
                && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
            {
                // Is there a half-open file between the king and the edge of the board?
                if (!ei.pi->has_open_file_to_right(Us, square_file(ksq)))
                    ei.value -= Sign[Us] * Score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
                                                                    : (TrappedRookPenalty - mob * 16), 0);
            }
            else if (    square_file(ksq) <= FILE_D
                    &&  square_file(s) < square_file(ksq)
                    && (relative_rank(Us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
            {
                // Is there a half-open file between the king and the edge of the board?
                if (!ei.pi->has_open_file_to_left(Us, square_file(ksq)))
                    ei.value -= Sign[Us] * Score(pos.can_castle(Us) ? (TrappedRookPenalty - mob * 16) / 2
                                                                    : (TrappedRookPenalty - mob * 16), 0);
            }
        }
    }
  }


  // evaluate_threats<>() assigns bonuses according to the type of attacking piece
  // and the type of attacked one.

  template<Color Us>
  void evaluate_threats(const Position& pos, EvalInfo& ei) {

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

    Bitboard b;
    Score bonus(0, 0);

    // Enemy pieces not defended by a pawn and under our attack
    Bitboard weakEnemies =  pos.pieces_of_color(Them)
                          & ~ei.attackedBy[Them][PAWN]
                          & ei.attackedBy[Us][0];
    if (!weakEnemies)
        return;

    // Add bonus according to type of attacked enemy pieces and to the
    // type of attacking piece, from knights to queens. Kings are not
    // considered because are already special handled in king evaluation.
    for (PieceType pt1 = KNIGHT; pt1 < KING; pt1++)
    {
        b = ei.attackedBy[Us][pt1] & weakEnemies;
        if (b)
            for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
                if (b & pos.pieces(pt2))
                    bonus += ThreatBonus[pt1][pt2];
    }
    ei.value += Sign[Us] * bonus;
  }


  // evaluate_pieces_of_color<>() assigns bonuses and penalties to all the
  // pieces of a given color.

  template<Color Us, bool HasPopCnt>
  void evaluate_pieces_of_color(const Position& pos, EvalInfo& ei) {

      evaluate_pieces<KNIGHT, Us, HasPopCnt>(pos, ei);
      evaluate_pieces<BISHOP, Us, HasPopCnt>(pos, ei);
      evaluate_pieces<ROOK,   Us, HasPopCnt>(pos, ei);
      evaluate_pieces<QUEEN,  Us, HasPopCnt>(pos, ei);

      // Sum up all attacked squares
      ei.attackedBy[Us][0] =   ei.attackedBy[Us][PAWN]   | ei.attackedBy[Us][KNIGHT]
                             | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
                             | ei.attackedBy[Us][QUEEN]  | ei.attackedBy[Us][KING];
  }


  // evaluate_king<>() assigns bonuses and penalties to a king of a given color

  template<Color Us, bool HasPopCnt>
  void evaluate_king(const Position& pos, EvalInfo& ei) {

    const Color Them = (Us == WHITE ? BLACK : WHITE);
    const Square s = pos.king_square(Us);
    int shelter = 0;

    // King shelter
    if (relative_rank(Us, s) <= RANK_4)
    {
        shelter = ei.pi->get_king_shelter(pos, Us, s);
        ei.value += Sign[Us] * Score(shelter, 0);
    }

    // King safety. This is quite complicated, and is almost certainly far
    // from optimally tuned.
    if (   pos.piece_count(Them, QUEEN) >= 1
        && ei.kingAttackersCount[Them] >= 2
        && pos.non_pawn_material(Them) >= QueenValueMidgame + RookValueMidgame
        && ei.kingAdjacentZoneAttacksCount[Them])
    {
      // Is it the attackers turn to move?
      bool sente = (Them == pos.side_to_move());

      // Find the attacked squares around the king which has no defenders
      // apart from the king itself
      Bitboard undefended =
             ei.attacked_by(Them)       & ~ei.attacked_by(Us, PAWN)
          & ~ei.attacked_by(Us, KNIGHT) & ~ei.attacked_by(Us, BISHOP)
          & ~ei.attacked_by(Us, ROOK)   & ~ei.attacked_by(Us, QUEEN)
          &  ei.attacked_by(Us, KING);

      Bitboard occ = pos.occupied_squares(), b, b2;

      // Initialize the 'attackUnits' variable, which is used later on as an
      // index to the SafetyTable[] array.  The initial value is based on the
      // number and types of the attacking pieces, the number of attacked and
      // undefended squares around the king, the square of the king, and the
      // quality of the pawn shelter.
      int attackUnits =
            Min((ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2, 25)
          + (ei.kingAdjacentZoneAttacksCount[Them] + count_1s_max_15<HasPopCnt>(undefended)) * 3
          + InitKingDanger[relative_square(Us, s)] - (shelter >> 5);

      // Analyse safe queen contact checks
      b = undefended & ei.attacked_by(Them, QUEEN) & ~pos.pieces_of_color(Them);
      if (b)
      {
        Bitboard attackedByOthers =
              ei.attacked_by(Them, PAWN)   | ei.attacked_by(Them, KNIGHT)
            | ei.attacked_by(Them, BISHOP) | ei.attacked_by(Them, ROOK);

        b &= attackedByOthers;
        if (b)
        {
          // The bitboard b now contains the squares available for safe queen
          // contact checks.
          int count = count_1s_max_15<HasPopCnt>(b);
          attackUnits += QueenContactCheckBonus * count * (sente ? 2 : 1);

          // Is there a mate threat?
          if (QueenContactMates && !pos.is_check())
          {
            Bitboard escapeSquares =
                pos.attacks_from<KING>(s) & ~pos.pieces_of_color(Us) & ~attackedByOthers;

            while (b)
            {
                Square from, to = pop_1st_bit(&b);
                if (!(escapeSquares & ~queen_attacks_bb(to, occ & ClearMaskBB[s])))
                {
                    // We have a mate, unless the queen is pinned or there
                    // is an X-ray attack through the queen.
                    for (int i = 0; i < pos.piece_count(Them, QUEEN); i++)
                    {
                        from = pos.piece_list(Them, QUEEN, i);
                        if (    bit_is_set(pos.attacks_from<QUEEN>(from), to)
                            && !bit_is_set(pos.pinned_pieces(Them), from)
                            && !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(ROOK, QUEEN, Us))
                            && !(bishop_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(BISHOP, QUEEN, Us)))

                            ei.mateThreat[Them] = make_move(from, to);
                    }
                }
            }
          }
        }
      }

      // Analyse safe distance checks
      if (QueenCheckBonus > 0 || RookCheckBonus > 0)
      {
          b = pos.attacks_from<ROOK>(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us);

          // Queen checks
          b2 = b & ei.attacked_by(Them, QUEEN);
          if (b2)
              attackUnits += QueenCheckBonus * count_1s_max_15<HasPopCnt>(b2);

          // Rook checks
          b2 = b & ei.attacked_by(Them, ROOK);
          if (b2)
              attackUnits += RookCheckBonus * count_1s_max_15<HasPopCnt>(b2);
      }
      if (QueenCheckBonus > 0 || BishopCheckBonus > 0)
      {
          b = pos.attacks_from<BISHOP>(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us);

          // Queen checks
          b2 = b & ei.attacked_by(Them, QUEEN);
          if (b2)
              attackUnits += QueenCheckBonus * count_1s_max_15<HasPopCnt>(b2);

          // Bishop checks
          b2 = b & ei.attacked_by(Them, BISHOP);
          if (b2)
              attackUnits += BishopCheckBonus * count_1s_max_15<HasPopCnt>(b2);
      }
      if (KnightCheckBonus > 0)
      {
          b = pos.attacks_from<KNIGHT>(s) & ~pos.pieces_of_color(Them) & ~ei.attacked_by(Us);

          // Knight checks
          b2 = b & ei.attacked_by(Them, KNIGHT);
          if (b2)
              attackUnits += KnightCheckBonus * count_1s_max_15<HasPopCnt>(b2);
      }

      // Analyse discovered checks (only for non-pawns right now, consider
      // adding pawns later).
      if (DiscoveredCheckBonus)
      {
        b = pos.discovered_check_candidates(Them) & ~pos.pieces(PAWN);
        if (b)
          attackUnits += DiscoveredCheckBonus * count_1s_max_15<HasPopCnt>(b) * (sente ? 2 : 1);
      }

      // Has a mate threat been found?  We don't do anything here if the
      // side with the mating move is the side to move, because in that
      // case the mating side will get a huge bonus at the end of the main
      // evaluation function instead.
      if (ei.mateThreat[Them] != MOVE_NONE)
          attackUnits += MateThreatBonus;

      // Ensure that attackUnits is between 0 and 99, in order to avoid array
      // out of bounds errors:
      if (attackUnits < 0)
          attackUnits = 0;

      if (attackUnits >= 100)
          attackUnits = 99;

      // Finally, extract the king safety score from the SafetyTable[] array.
      // Add the score to the evaluation, and also to ei.futilityMargin.  The
      // reason for adding the king safety score to the futility margin is
      // that the king safety scores can sometimes be very big, and that
      // capturing a single attacking piece can therefore result in a score
      // change far bigger than the value of the captured piece.
      Score v = apply_weight(Score(SafetyTable[attackUnits], 0), WeightKingSafety[Us], 0);

      ei.value -= Sign[Us] * v;

      if (Us == pos.side_to_move())
          ei.futilityMargin += v.mg();
    }
  }


  // evaluate_passed_pawns() evaluates the passed pawns of the given color

  template<Color Us>
  void evaluate_passed_pawns_of_color(const Position& pos, int movesToGo[], Square pawnToGo[], EvalInfo& ei) {

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

    Bitboard b2, b3, b4;
    Square ourKingSq = pos.king_square(Us);
    Square theirKingSq = pos.king_square(Them);
    Bitboard b = ei.pi->passed_pawns() & pos.pieces(PAWN, Us);

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

        assert(pos.piece_on(s) == piece_of_color_and_type(Us, PAWN));
        assert(pos.pawn_is_passed(Us, s));

        int r = int(relative_rank(Us, s) - RANK_2);
        int tr = Max(0, r * (r - 1));

        // Base bonus based on rank
        Value mbonus = Value(20 * tr);
        Value ebonus = Value(10 + r * r * 10);

        // Adjust bonus based on king proximity
        if (tr)
        {
            Square blockSq = s + pawn_push(Us);

            ebonus -= Value(square_distance(ourKingSq, blockSq) * 3 * tr);
            ebonus -= Value(square_distance(ourKingSq, blockSq + pawn_push(Us)) * 1 * tr);
            ebonus += Value(square_distance(theirKingSq, blockSq) * 6 * tr);

            // If the pawn is free to advance, increase bonus
            if (pos.square_is_empty(blockSq))
            {
                // There are no enemy pawns in the pawn's path
                b2 = squares_in_front_of(Us, s);

                assert((b2 & pos.pieces(PAWN, Them)) == EmptyBoardBB);

                // Squares attacked by us
                b4 = b2 & ei.attacked_by(Us);

                // Squares attacked or occupied by enemy pieces
                b3 = b2 & (ei.attacked_by(Them) | pos.pieces_of_color(Them));

                // If there is an enemy rook or queen attacking the pawn from behind,
                // add all X-ray attacks by the rook or queen.
                if (   (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them))
                    && (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<QUEEN>(s)))
                    b3 = b2;

                // Are any of the squares in the pawn's path attacked or occupied by the enemy?
                if (b3 == EmptyBoardBB)
                    // No enemy attacks or pieces, huge bonus!
                    // Even bigger if we protect the pawn's path
                    ebonus += Value(tr * (b2 == b4 ? 17 : 15));
                else
                    // OK, there are enemy attacks or pieces (but not pawns). Are those
                    // squares which are attacked by the enemy also attacked by us ?
                    // If yes, big bonus (but smaller than when there are no enemy attacks),
                    // if no, somewhat smaller bonus.
                    ebonus += Value(tr * ((b3 & b4) == b3 ? 13 : 8));

                // At last, add a small bonus when there are no *friendly* pieces
                // in the pawn's path.
                if ((b2 & pos.pieces_of_color(Us)) == EmptyBoardBB)
                    ebonus += Value(tr);
            }
        } // tr != 0

        // If the pawn is supported by a friendly pawn, increase bonus
        b2 = pos.pieces(PAWN, Us) & neighboring_files_bb(s);
        if (b2 & rank_bb(s))
            ebonus += Value(r * 20);
        else if (pos.attacks_from<PAWN>(s, Them) & b2)
            ebonus += Value(r * 12);

        // If the other side has only a king, check whether the pawn is
        // unstoppable
        if (pos.non_pawn_material(Them) == Value(0))
        {
            Square qsq;
            int d;

            qsq = relative_square(Us, make_square(square_file(s), RANK_8));
            d =  square_distance(s, qsq)
               - square_distance(theirKingSq, qsq)
               + (Us != pos.side_to_move());

            if (d < 0)
            {
                int mtg = RANK_8 - relative_rank(Us, s);
                int blockerCount = count_1s_max_15(squares_in_front_of(Us,s) & pos.occupied_squares());
                mtg += blockerCount;
                d += blockerCount;
                if (d < 0 && (!movesToGo[Us] || movesToGo[Us] > mtg))
                {
                    movesToGo[Us] = mtg;
                    pawnToGo[Us] = s;
                }
            }
        }

        // Rook pawns are a special case: They are sometimes worse, and
        // sometimes better than other passed pawns. It is difficult to find
        // good rules for determining whether they are good or bad. For now,
        // we try the following: Increase the value for rook pawns if the
        // other side has no pieces apart from a knight, and decrease the
        // value if the other side has a rook or queen.
        if (square_file(s) == FILE_A || square_file(s) == FILE_H)
        {
            if (   pos.non_pawn_material(Them) <= KnightValueMidgame
                && pos.piece_count(Them, KNIGHT) <= 1)
                ebonus += ebonus / 4;
            else if (pos.pieces(ROOK, QUEEN, Them))
                ebonus -= ebonus / 4;
        }

        // Add the scores for this pawn to the middle game and endgame eval.
        ei.value += Sign[Us] * apply_weight(Score(mbonus, ebonus), WeightPassedPawnsMidgame, WeightPassedPawnsEndgame);

    } // while
  }


  // evaluate_passed_pawns() evaluates the passed pawns for both sides

  void evaluate_passed_pawns(const Position& pos, EvalInfo& ei) {

    int movesToGo[2] = {0, 0};
    Square pawnToGo[2] = {SQ_NONE, SQ_NONE};

    // Evaluate pawns for each color
    evaluate_passed_pawns_of_color<WHITE>(pos, movesToGo, pawnToGo, ei);
    evaluate_passed_pawns_of_color<BLACK>(pos, movesToGo, pawnToGo, ei);

    // Neither side has an unstoppable passed pawn?
    if (!(movesToGo[WHITE] | movesToGo[BLACK]))
        return;

    // Does only one side have an unstoppable passed pawn?
    if (!movesToGo[WHITE] || !movesToGo[BLACK])
    {
        Color winnerSide = movesToGo[WHITE] ? WHITE : BLACK;
        ei.value += Score(0, Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * movesToGo[winnerSide])));
    }
    else
    {   // Both sides have unstoppable pawns! Try to find out who queens
        // first. We begin by transforming 'movesToGo' to the number of
        // plies until the pawn queens for both sides.
        movesToGo[WHITE] *= 2;
        movesToGo[BLACK] *= 2;
        movesToGo[pos.side_to_move()]--;

        Color winnerSide = movesToGo[WHITE] < movesToGo[BLACK] ? WHITE : BLACK;
        Color loserSide = opposite_color(winnerSide);

        // If one side queens at least three plies before the other, that side wins
        if (movesToGo[winnerSide] <= movesToGo[loserSide] - 3)
            ei.value += Score(0, Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * (movesToGo[winnerSide]/2))));

        // If one side queens one ply before the other and checks the king or attacks
        // the undefended opponent's queening square, that side wins. To avoid cases
        // where the opponent's king could move somewhere before first pawn queens we
        // consider only free paths to queen for both pawns.
        else if (   !(squares_in_front_of(WHITE, pawnToGo[WHITE]) & pos.occupied_squares())
                 && !(squares_in_front_of(BLACK, pawnToGo[BLACK]) & pos.occupied_squares()))
        {
            assert(movesToGo[loserSide] - movesToGo[winnerSide] == 1);

            Square winnerQSq = relative_square(winnerSide, make_square(square_file(pawnToGo[winnerSide]), RANK_8));
            Square loserQSq = relative_square(loserSide, make_square(square_file(pawnToGo[loserSide]), RANK_8));

            Bitboard b = pos.occupied_squares();
            clear_bit(&b, pawnToGo[winnerSide]);
            clear_bit(&b, pawnToGo[loserSide]);
            b = queen_attacks_bb(winnerQSq, b);

            if (  (b & pos.pieces(KING, loserSide))
                ||(bit_is_set(b, loserQSq) && !bit_is_set(ei.attacked_by(loserSide), loserQSq)))
                ei.value += Score(0, Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * (movesToGo[winnerSide]/2))));
        }
    }
  }


  // evaluate_trapped_bishop_a7h7() determines whether a bishop on a7/h7
  // (a2/h2 for black) is trapped by enemy pawns, and assigns a penalty
  // if it is.

  void evaluate_trapped_bishop_a7h7(const Position& pos, Square s, Color us, EvalInfo &ei) {

    assert(square_is_ok(s));
    assert(pos.piece_on(s) == piece_of_color_and_type(us, BISHOP));

    Square b6 = relative_square(us, (square_file(s) == FILE_A) ? SQ_B6 : SQ_G6);
    Square b8 = relative_square(us, (square_file(s) == FILE_A) ? SQ_B8 : SQ_G8);

    if (   pos.piece_on(b6) == piece_of_color_and_type(opposite_color(us), PAWN)
        && pos.see(s, b6) < 0
        && pos.see(s, b8) < 0)
    {
        ei.value -= Sign[us] * Score(TrappedBishopA7H7Penalty, TrappedBishopA7H7Penalty);
    }
  }


  // evaluate_trapped_bishop_a1h1() determines whether a bishop on a1/h1
  // (a8/h8 for black) is trapped by a friendly pawn on b2/g2 (b7/g7 for
  // black), and assigns a penalty if it is. This pattern can obviously
  // only occur in Chess960 games.

  void evaluate_trapped_bishop_a1h1(const Position& pos, Square s, Color us, EvalInfo& ei) {

    Piece pawn = piece_of_color_and_type(us, PAWN);
    Square b2, b3, c3;

    assert(Chess960);
    assert(square_is_ok(s));
    assert(pos.piece_on(s) == piece_of_color_and_type(us, BISHOP));

    if (square_file(s) == FILE_A)
    {
        b2 = relative_square(us, SQ_B2);
        b3 = relative_square(us, SQ_B3);
        c3 = relative_square(us, SQ_C3);
    }
    else
    {
        b2 = relative_square(us, SQ_G2);
        b3 = relative_square(us, SQ_G3);
        c3 = relative_square(us, SQ_F3);
    }

    if (pos.piece_on(b2) == pawn)
    {
        Value penalty;

        if (!pos.square_is_empty(b3))
            penalty = 2*TrappedBishopA1H1Penalty;
        else if (pos.piece_on(c3) == pawn)
            penalty = TrappedBishopA1H1Penalty;
        else
            penalty = TrappedBishopA1H1Penalty / 2;

        ei.value -= Sign[us] * Score(penalty, penalty);
    }
  }


  // evaluate_space() computes the space evaluation for a given side. The
  // space evaluation is a simple bonus based on the number of safe squares
  // available for minor pieces on the central four files on ranks 2--4. Safe
  // squares one, two or three squares behind a friendly pawn are counted
  // twice. Finally, the space bonus is scaled by a weight taken from the
  // material hash table.
  template<Color Us, bool HasPopCnt>
  void evaluate_space(const Position& pos, EvalInfo& ei) {

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

    // Find the safe squares for our pieces inside the area defined by
    // SpaceMask[us]. A square is unsafe if it is attacked by an enemy
    // pawn, or if it is undefended and attacked by an enemy piece.

    Bitboard safeSquares =   SpaceMask[Us]
                          & ~pos.pieces(PAWN, Us)
                          & ~ei.attacked_by(Them, PAWN)
                          & ~(~ei.attacked_by(Us) & ei.attacked_by(Them));

    // Find all squares which are at most three squares behind some friendly
    // pawn.
    Bitboard behindFriendlyPawns = pos.pieces(PAWN, Us);
    behindFriendlyPawns |= (Us == WHITE ? behindFriendlyPawns >>  8 : behindFriendlyPawns <<  8);
    behindFriendlyPawns |= (Us == WHITE ? behindFriendlyPawns >> 16 : behindFriendlyPawns << 16);

    int space =  count_1s_max_15<HasPopCnt>(safeSquares)
               + count_1s_max_15<HasPopCnt>(behindFriendlyPawns & safeSquares);

    ei.value += Sign[Us] * apply_weight(Score(space * ei.mi->space_weight(), 0), WeightSpace, 0);
  }


  // apply_weight() applies an evaluation weight to a value

  inline Score apply_weight(Score v, int wmg, int weg) {
      return Score(v.mg() * wmg, v.eg() * weg) / 0x100;
  }


  // scale_by_game_phase() interpolates between a middle game and an endgame
  // score, based on game phase.  It also scales the return value by a
  // ScaleFactor array.

  Value scale_by_game_phase(const Score& v, Phase ph, const ScaleFactor sf[]) {

    assert(v.mg() > -VALUE_INFINITE && v.mg() < VALUE_INFINITE);
    assert(v.eg() > -VALUE_INFINITE && v.eg() < VALUE_INFINITE);
    assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);

    Value ev = apply_scale_factor(v.eg(), sf[(v.eg() > Value(0) ? WHITE : BLACK)]);

    Value result = Value(int((v.mg() * ph + ev * (128 - ph)) / 128));
    return Value(int(result) & ~(GrainSize - 1));
  }


  // weight_option() computes the value of an evaluation weight, by combining
  // an UCI-configurable weight with an internal weight.

  int weight_option(const std::string& opt, int internalWeight) {

    int uciWeight = get_option_value_int(opt);
    uciWeight = (uciWeight * 0x100) / 100;
    return (uciWeight * internalWeight) / 0x100;
  }


  // init_safety() initizes the king safety evaluation, based on UCI
  // parameters.  It is called from read_weights().

  void init_safety() {

    QueenContactCheckBonus = get_option_value_int("Queen Contact Check Bonus");
    QueenCheckBonus        = get_option_value_int("Queen Check Bonus");
    RookCheckBonus         = get_option_value_int("Rook Check Bonus");
    BishopCheckBonus       = get_option_value_int("Bishop Check Bonus");
    KnightCheckBonus       = get_option_value_int("Knight Check Bonus");
    DiscoveredCheckBonus   = get_option_value_int("Discovered Check Bonus");
    MateThreatBonus        = get_option_value_int("Mate Threat Bonus");

    int maxSlope = get_option_value_int("King Safety Max Slope");
    int peak     = get_option_value_int("King Safety Max Value") * 256 / 100;
    double a     = get_option_value_int("King Safety Coefficient") / 100.0;
    double b     = get_option_value_int("King Safety X Intercept");
    bool quad    = (get_option_value_string("King Safety Curve") == "Quadratic");
    bool linear  = (get_option_value_string("King Safety Curve") == "Linear");

    for (int i = 0; i < 100; i++)
    {
        if (i < b)
            SafetyTable[i] = Value(0);
        else if (quad)
            SafetyTable[i] = Value((int)(a * (i - b) * (i - b)));
        else if (linear)
            SafetyTable[i] = Value((int)(100 * a * (i - b)));
    }

    for (int i = 0; i < 100; i++)
    {
        if (SafetyTable[i+1] - SafetyTable[i] > maxSlope)
            for (int j = i + 1; j < 100; j++)
                SafetyTable[j] = SafetyTable[j-1] + Value(maxSlope);

        if (SafetyTable[i]  > Value(peak))
            SafetyTable[i] = Value(peak);
    }
  }
}

std::ostream& operator<<(std::ostream &os, Score s) {

    return os << "(" << s.mg() << ", " << s.eg() << ")";
}