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/*

  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) 2015-2016 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>

#include <cassert>

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

#include <iomanip>

#include <sstream>

#include "bitboard.h"

#include "evaluate.h"

#include "material.h"

#include "pawns.h"

namespace {

  namespace Trace {

    enum Term { // The first 8 entries are for PieceType

      MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB

    };

    double scores[TERM_NB][COLOR_NB][PHASE_NB];

    double to_cp(Value v) { return double(v) / PawnValueEg; }

    void add(int idx, Color c, Score s) {

      scores[idx][c][MG] = to_cp(mg_value(s));

      scores[idx][c][EG] = to_cp(eg_value(s));

    }

    void add(int idx, Score w, Score b = SCORE_ZERO) {

      add(idx, WHITE, w); add(idx, BLACK, b);

    }

    std::ostream& operator<<(std::ostream& os, Term t) {

      if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)

          os << "  ---   --- |   ---   --- | ";

      else

          os << std::setw(5) << scores[t][WHITE][MG] << " "

             << std::setw(5) << scores[t][WHITE][EG] << " | "

             << std::setw(5) << scores[t][BLACK][MG] << " "

             << std::setw(5) << scores[t][BLACK][EG] << " | ";

      os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "

         << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";

      return os;

    }

  }

  using namespace Trace;

  // Struct EvalInfo contains various information computed and collected

  // by the evaluation functions.

  struct EvalInfo {

    // attackedBy[color][piece type] is a bitboard representing all squares

    // attacked by a given color and piece type (can be also ALL_PIECES).

    Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];

    // attackedBy2[color] are the squares attacked by 2 pieces of a given color,

    // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through

    // pawn or squares attacked by 2 pawns are not explicitly added.

    Bitboard attackedBy2[COLOR_NB];

    // kingRing[color] is the zone around the king which is considered

    // by the king safety evaluation. This consists of the squares directly

    // adjacent to the king, and the three (or two, for a king on an edge file)

    // squares two ranks in front of the king. For instance, if black's king

    // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,

    // f7, g7, h7, f6, g6 and h6.

    Bitboard kingRing[COLOR_NB];

    // kingAttackersCount[color] is the number of pieces of the given color

    // which attack a square in the kingRing of the enemy king.

    int kingAttackersCount[COLOR_NB];

    // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the

    // given color which attack a square in the kingRing of the enemy king. The

    // weights of the individual piece types are given by the elements in the

    // KingAttackWeights array.

    int kingAttackersWeight[COLOR_NB];

    // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given

    // color to squares directly adjacent to the enemy king. Pieces which attack

    // more than one square are counted multiple times. For instance, if there is

    // a white knight on g5 and black's king is on g8, this white knight adds 2

    // to kingAdjacentZoneAttacksCount[WHITE].

    int kingAdjacentZoneAttacksCount[COLOR_NB];

    Bitboard pinnedPieces[COLOR_NB];

    Material::Entry* me;

    Pawns::Entry* pi;

  };

  #define V(v) Value(v)

  #define S(mg, eg) make_score(mg, eg)

  // MobilityBonus[PieceType][attacked] contains bonuses for middle and end

  // game, indexed by piece type and number of attacked squares in the MobilityArea.

  const Score MobilityBonus[][32] = {

    {}, {},

    { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S(  6,  5), S( 15, 11), // Knights

      S( 22, 26), S( 30, 28), S( 36, 29) },

    { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops

      S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),

      S( 92, 90), S( 97, 94) },

    { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks

      S(  8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),

      S( 43,165), S( 49,168), S( 59,169) },

    { S(-40,-35), S(-25,-12), S(  2,  7), S(  4, 19), S( 14, 37), S( 24, 55), // Queens

      S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),

      S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),

      S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),

      S(118,174), S(119,177), S(123,191), S(128,199) }

  };

  // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and

  // bishops outposts, bigger if outpost piece is supported by a pawn.

  const Score Outpost[][2] = {

    { S(43,11), S(65,20) }, // Knights

    { S(20, 3), S(29, 8) }  // Bishops

  };

  // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for

  // knights and bishops which can reach an outpost square in one move, bigger

  // if outpost square is supported by a pawn.

  const Score ReachableOutpost[][2] = {

    { S(21, 5), S(35, 8) }, // Knights

    { S( 8, 0), S(14, 4) }  // Bishops

  };

  // RookOnFile[semiopen/open] contains bonuses for each rook when there is no

  // friendly pawn on the rook file.

  const Score RookOnFile[2] = { S(20, 7), S(45, 20) };

  // ThreatBySafePawn[PieceType] contains bonuses according to which piece

  // type is attacked by a pawn which is protected or is not attacked.

  const Score ThreatBySafePawn[PIECE_TYPE_NB] = {

    S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)

  };

  // Threat[by minor/by rook][attacked PieceType] contains

  // bonuses according to which piece type attacks which one.

  // Attacks on lesser pieces which are pawn-defended are not considered.

  const Score Threat[][PIECE_TYPE_NB] = {

    { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor

    { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) }  // by Rook

  };

  // ThreatByKing[on one/on many] contains bonuses for King attacks on

  // pawns or pieces which are not pawn-defended.

  const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };

  // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.

  // We don't use a Score because we process the two components independently.

  const Value Passed[][RANK_NB] = {

    { V(5), V( 5), V(31), V(73), V(166), V(252) },

    { V(7), V(14), V(38), V(73), V(166), V(252) }

  };

  // PassedFile[File] contains a bonus according to the file of a passed pawn

  const Score PassedFile[FILE_NB] = {

    S(  9, 10), S( 2, 10), S( 1, -8), S(-20,-12),

    S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)

  };

  // Assorted bonuses and penalties used by evaluation

  const Score MinorBehindPawn     = S(16,  0);

  const Score BishopPawns         = S( 8, 12);

  const Score RookOnPawn          = S( 8, 24);

  const Score TrappedRook         = S(92,  0);

  const Score CloseEnemies        = S( 7,  0);

  const Score SafeCheck           = S(20, 20);

  const Score OtherCheck          = S(10, 10);

  const Score ThreatByHangingPawn = S(71, 61);

  const Score LooseEnemies        = S( 0, 25);

  const Score WeakQueen           = S(35,  0);

  const Score Hanging             = S(48, 27);

  const Score ThreatByPawnPush    = S(38, 22);

  const Score Unstoppable         = S( 0, 20);

  const Score PawnlessFlank       = S(20, 80);

  const Score HinderPassedPawn    = S( 7,  0);

  // 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 Score TrappedBishopA1H1 = S(50, 50);

  #undef S

  #undef V

  // KingAttackWeights[PieceType] contains king attack weights by piece type

  const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };

  // Penalties for enemy's safe checks

  const int QueenContactCheck = 997;

  const int QueenCheck        = 695;

  const int RookCheck         = 638;

  const int BishopCheck       = 538;

  const int KnightCheck       = 874;

  // eval_init() initializes king and attack bitboards for a given color

  // adding pawn attacks. To be done at the beginning of the evaluation.

  template<Color Us>

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

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

    const Square Down = (Us == WHITE ? SOUTH : NORTH);

    ei.pinnedPieces[Us] = pos.pinned_pieces(Us);

    Bitboard b = ei.attackedBy[Them][KING];

    ei.attackedBy[Them][ALL_PIECES] |= b;

    ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);

    ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];

    // Init king safety tables only if we are going to use them

    if (pos.non_pawn_material(Us) >= QueenValueMg)

    {

        ei.kingRing[Them] = b | shift<Down>(b);

        b &= ei.attackedBy[Us][PAWN];

        ei.kingAttackersCount[Us] = popcount(b);

        ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;

    }

    else

        ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;

  }

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

  // color and type.

  template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>

  Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,

                        const Bitboard* mobilityArea) {

    Bitboard b, bb;

    Square s;

    Score score = SCORE_ZERO;

    const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));

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

    const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB

                                               : Rank5BB | Rank4BB | Rank3BB);

    const Square* pl = pos.squares<Pt>(Us);

    ei.attackedBy[Us][Pt] = 0;

    while ((s = *pl++) != SQ_NONE)

    {

        // Find attacked squares, including x-ray attacks for bishops and rooks

        b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))

          : Pt ==   ROOK ? attacks_bb<  ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))

                         : pos.attacks_from<Pt>(s);

        if (ei.pinnedPieces[Us] & s)

            b &= LineBB[pos.square<KING>(Us)][s];

        ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;

        ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;

        if (b & ei.kingRing[Them])

        {

            ei.kingAttackersCount[Us]++;

            ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];

            ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);

        }

        if (Pt == QUEEN)

            b &= ~(  ei.attackedBy[Them][KNIGHT]

                   | ei.attackedBy[Them][BISHOP]

                   | ei.attackedBy[Them][ROOK]);

        int mob = popcount(b & mobilityArea[Us]);

        mobility[Us] += MobilityBonus[Pt][mob];

        if (Pt == BISHOP || Pt == KNIGHT)

        {

            // Bonus for outpost squares

            bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);

            if (bb & s)

                score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];

            else

            {

                bb &= b & ~pos.pieces(Us);

                if (bb)

                   score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];

            }

            // Bonus when behind a pawn

            if (    relative_rank(Us, s) < RANK_5

                && (pos.pieces(PAWN) & (s + pawn_push(Us))))

                score += MinorBehindPawn;

            // Penalty for pawns on the same color square as the bishop

            if (Pt == BISHOP)

                score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);

            // An important Chess960 pattern: A cornered bishop blocked by a friendly

            // pawn diagonally in front of it is a very serious problem, especially

            // when that pawn is also blocked.

            if (   Pt == BISHOP

                && pos.is_chess960()

                && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))

            {

                Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);

                if (pos.piece_on(s + d) == make_piece(Us, PAWN))

                    score -= !pos.empty(s + d + pawn_push(Us))                ? TrappedBishopA1H1 * 4

                            : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2

                                                                              : TrappedBishopA1H1;

            }

        }

        if (Pt == ROOK)

        {

            // Bonus for aligning with enemy pawns on the same rank/file

            if (relative_rank(Us, s) >= RANK_5)

                score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);

            // Bonus when on an open or semi-open file

            if (ei.pi->semiopen_file(Us, file_of(s)))

                score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];

            // Penalize when trapped by the king, even more if the king cannot castle

            else if (mob <= 3)

            {

                Square ksq = pos.square<KING>(Us);

                if (   ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))

                    && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)

                    && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))

                    score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));

            }

        }

        if (Pt == QUEEN)

        {

            // Penalty if any relative pin or discovered attack against the queen

            Bitboard pinners;

            if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))

                score -= WeakQueen;

        }

    }

    if (DoTrace)

        Trace::add(Pt, Us, score);

    // Recursively call evaluate_pieces() of next piece type until KING is excluded

    return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);

  }

  template<>

  Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }

  template<>

  Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }

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

  const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;

  const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;

  const Bitboard QueenSide   = FileABB | FileBBB | FileCBB | FileDBB;

  const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;

  const Bitboard KingSide    = FileEBB | FileFBB | FileGBB | FileHBB;

  const Bitboard KingFlank[COLOR_NB][FILE_NB] = {

    { QueenSide   & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,

      CenterFiles & WhiteCamp, KingSide  & WhiteCamp, KingSide  & WhiteCamp, KingSide    & WhiteCamp },

    { QueenSide   & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,

      CenterFiles & BlackCamp, KingSide  & BlackCamp, KingSide  & BlackCamp, KingSide    & BlackCamp },

  };

  template<Color Us, bool DoTrace>

  Score evaluate_king(const Position& pos, const EvalInfo& ei) {

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

    const Square  Up = (Us == WHITE ? NORTH : SOUTH);

    Bitboard undefended, b, b1, b2, safe, other;

    int kingDanger;

    const Square ksq = pos.square<KING>(Us);

    // King shelter and enemy pawns storm

    Score score = ei.pi->king_safety<Us>(pos, ksq);

    // Main king safety evaluation

    if (ei.kingAttackersCount[Them])

    {

        // Find the attacked squares which are defended only by the king...

        undefended =   ei.attackedBy[Them][ALL_PIECES]

                    &  ei.attackedBy[Us][KING]

                    & ~ei.attackedBy2[Us];

        // ... and those which are not defended at all in the larger king ring

        b =  ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]

           & ei.kingRing[Us] & ~pos.pieces(Them);

        // Initialize the 'kingDanger' variable, which will be transformed

        // later into a king danger score. The initial value is based on the

        // number and types of the enemy's attacking pieces, the number of

        // attacked and undefended squares around our king and the quality of

        // the pawn shelter (current 'score' value).

        kingDanger =  std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])

                    + 101 * ei.kingAdjacentZoneAttacksCount[Them]

                    + 235 * popcount(undefended)

                    + 134 * (popcount(b) + !!ei.pinnedPieces[Us])

                    - 717 * !pos.count<QUEEN>(Them)

                    -   7 * mg_value(score) / 5 - 5;

        // Analyse the enemy's safe queen contact checks. Firstly, find the

        // undefended squares around the king reachable by the enemy queen...

        b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);

        // ...and keep squares supported by another enemy piece

        kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);

        // Analyse the safe enemy's checks which are possible on next move...

        safe  = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));

        // ... and some other potential checks, only requiring the square to be

        // safe from pawn-attacks, and not being occupied by a blocked pawn.

        other = ~(   ei.attackedBy[Us][PAWN]

                  | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));

        b1 = pos.attacks_from<ROOK  >(ksq);

        b2 = pos.attacks_from<BISHOP>(ksq);

        // Enemy queen safe checks

        if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)

            kingDanger += QueenCheck, score -= SafeCheck;

        // For other pieces, also consider the square safe if attacked twice,

        // and only defended by a queen.

        safe |=  ei.attackedBy2[Them]

               & ~(ei.attackedBy2[Us] | pos.pieces(Them))

               & ei.attackedBy[Us][QUEEN];

        // Enemy rooks safe and other checks

        if (b1 & ei.attackedBy[Them][ROOK] & safe)

            kingDanger += RookCheck, score -= SafeCheck;

        else if (b1 & ei.attackedBy[Them][ROOK] & other)

            score -= OtherCheck;

        // Enemy bishops safe and other checks

        if (b2 & ei.attackedBy[Them][BISHOP] & safe)

            kingDanger += BishopCheck, score -= SafeCheck;

        else if (b2 & ei.attackedBy[Them][BISHOP] & other)

            score -= OtherCheck;

        // Enemy knights safe and other checks

        b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];

        if (b & safe)

            kingDanger += KnightCheck, score -= SafeCheck;

        else if (b & other)

            score -= OtherCheck;

        // Compute the king danger score and subtract it from the evaluation

        if (kingDanger > 0)

            score -= make_score(std::min(kingDanger * kingDanger / 4096,  2 * int(BishopValueMg)), 0);

    }

    // King tropism: firstly, find squares that opponent attacks in our king flank

    File kf = file_of(ksq);

    b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][kf];

    assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);

    assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));

    // Secondly, add the squares which are attacked twice in that flank and

    // which are not defended by our pawns.

    b =  (Us == WHITE ? b << 4 : b >> 4)

       | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);

    score -= CloseEnemies * popcount(b);

    // Penalty when our king is on a pawnless flank

    if (!(pos.pieces(PAWN) & (KingFlank[WHITE][kf] | KingFlank[BLACK][kf])))

        score -= PawnlessFlank;

    if (DoTrace)

        Trace::add(KING, Us, score);

    return score;

  }

  // evaluate_threats() assigns bonuses according to the types of the attacking

  // and the attacked pieces.

  template<Color Us, bool DoTrace>

  Score evaluate_threats(const Position& pos, const EvalInfo& ei) {

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

    const Square Up         = (Us == WHITE ? NORTH      : SOUTH);

    const Square Left       = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);

    const Square Right      = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);

    const Bitboard TRank2BB = (Us == WHITE ? Rank2BB    : Rank7BB);

    const Bitboard TRank7BB = (Us == WHITE ? Rank7BB    : Rank2BB);

    enum { Minor, Rook };

    Bitboard b, weak, defended, safeThreats;

    Score score = SCORE_ZERO;

    // Small bonus if the opponent has loose pawns or pieces

    if (   (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))

        & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))

        score += LooseEnemies;

    // Non-pawn enemies attacked by a pawn

    weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];

    if (weak)

    {

        b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]

                                    | ei.attackedBy[Us][ALL_PIECES]);

        safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;

        if (weak ^ safeThreats)

            score += ThreatByHangingPawn;

        while (safeThreats)

            score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];

    }

    // Non-pawn enemies defended by a pawn

    defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];

    // Enemies not defended by a pawn and under our attack

    weak =   pos.pieces(Them)

          & ~ei.attackedBy[Them][PAWN]

          &  ei.attackedBy[Us][ALL_PIECES];

    // Add a bonus according to the kind of attacking pieces

    if (defended | weak)

    {

        b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);

        while (b)

            score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];

        b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];

        while (b)

            score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];

        score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);

        b = weak & ei.attackedBy[Us][KING];

        if (b)

            score += ThreatByKing[more_than_one(b)];

    }

    // Bonus if some pawns can safely push and attack an enemy piece

    b = pos.pieces(Us, PAWN) & ~TRank7BB;

    b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));

    b &=  ~pos.pieces()

        & ~ei.attackedBy[Them][PAWN]

        & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);

    b =  (shift<Left>(b) | shift<Right>(b))

       &  pos.pieces(Them)

       & ~ei.attackedBy[Us][PAWN];

    score += ThreatByPawnPush * popcount(b);

    if (DoTrace)

        Trace::add(THREAT, Us, score);

    return score;

  }

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

  template<Color Us, bool DoTrace>

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

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

    Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;

    Score score = SCORE_ZERO;

    b = ei.pi->passed_pawns(Us);

    while (b)

    {

        Square s = pop_lsb(&b);

        assert(pos.pawn_passed(Us, s));

        assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));

        bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));

        score -= HinderPassedPawn * popcount(bb);

        int r = relative_rank(Us, s) - RANK_2;

        int rr = r * (r - 1);

        Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];

        if (rr)

        {

            Square blockSq = s + pawn_push(Us);

            // Adjust bonus based on the king's proximity

            ebonus +=  distance(pos.square<KING>(Them), blockSq) * 5 * rr

                     - distance(pos.square<KING>(Us  ), blockSq) * 2 * rr;

            // If blockSq is not the queening square then consider also a second push

            if (relative_rank(Us, blockSq) != RANK_8)

                ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;

            // If the pawn is free to advance, then increase the bonus

            if (pos.empty(blockSq))

            {

                // If there is a rook or queen attacking/defending the pawn from behind,

                // consider all the squaresToQueen. Otherwise consider only the squares

                // in the pawn's path attacked or occupied by the enemy.

                defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);

                bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);

                if (!(pos.pieces(Us) & bb))

                    defendedSquares &= ei.attackedBy[Us][ALL_PIECES];

                if (!(pos.pieces(Them) & bb))

                    unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);

                // If there aren't any enemy attacks, assign a big bonus. Otherwise

                // assign a smaller bonus if the block square isn't attacked.

                int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;

                // If the path to the queen is fully defended, assign a big bonus.

                // Otherwise assign a smaller bonus if the block square is defended.

                if (defendedSquares == squaresToQueen)

                    k += 6;

                else if (defendedSquares & blockSq)

                    k += 4;

                mbonus += k * rr, ebonus += k * rr;

            }

            else if (pos.pieces(Us) & blockSq)

                mbonus += rr + r * 2, ebonus += rr + r * 2;

        } // rr != 0