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  1. /*
  2.   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  3.   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
  4.   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
  5.   Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
  6.  
  7.   Stockfish is free software: you can redistribute it and/or modify
  8.   it under the terms of the GNU General Public License as published by
  9.   the Free Software Foundation, either version 3 of the License, or
  10.   (at your option) any later version.
  11.  
  12.   Stockfish is distributed in the hope that it will be useful,
  13.   but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15.   GNU General Public License for more details.
  16.  
  17.   You should have received a copy of the GNU General Public License
  18.   along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19. */
  20.  
  21. #include <algorithm>
  22. #include <cassert>
  23. #include <cstring>   // For std::memset
  24. #include <iomanip>
  25. #include <sstream>
  26.  
  27. #include "bitboard.h"
  28. #include "evaluate.h"
  29. #include "material.h"
  30. #include "pawns.h"
  31.  
  32. namespace {
  33.  
  34.   namespace Trace {
  35.  
  36.     enum Term { // The first 8 entries are for PieceType
  37.       MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
  38.     };
  39.  
  40.     double scores[TERM_NB][COLOR_NB][PHASE_NB];
  41.  
  42.     double to_cp(Value v) { return double(v) / PawnValueEg; }
  43.  
  44.     void add(int idx, Color c, Score s) {
  45.       scores[idx][c][MG] = to_cp(mg_value(s));
  46.       scores[idx][c][EG] = to_cp(eg_value(s));
  47.     }
  48.  
  49.     void add(int idx, Score w, Score b = SCORE_ZERO) {
  50.       add(idx, WHITE, w); add(idx, BLACK, b);
  51.     }
  52.  
  53.     std::ostream& operator<<(std::ostream& os, Term t) {
  54.  
  55.       if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
  56.           os << "  ---   --- |   ---   --- | ";
  57.       else
  58.           os << std::setw(5) << scores[t][WHITE][MG] << " "
  59.              << std::setw(5) << scores[t][WHITE][EG] << " | "
  60.              << std::setw(5) << scores[t][BLACK][MG] << " "
  61.              << std::setw(5) << scores[t][BLACK][EG] << " | ";
  62.  
  63.       os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
  64.          << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
  65.  
  66.       return os;
  67.     }
  68.   }
  69.  
  70.   using namespace Trace;
  71.  
  72.   // Struct EvalInfo contains various information computed and collected
  73.   // by the evaluation functions.
  74.   struct EvalInfo {
  75.  
  76.     // attackedBy[color][piece type] is a bitboard representing all squares
  77.     // attacked by a given color and piece type (can be also ALL_PIECES).
  78.     Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
  79.  
  80.     // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
  81.     // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
  82.     // pawn or squares attacked by 2 pawns are not explicitly added.
  83.     Bitboard attackedBy2[COLOR_NB];
  84.  
  85.     // kingRing[color] is the zone around the king which is considered
  86.     // by the king safety evaluation. This consists of the squares directly
  87.     // adjacent to the king, and the three (or two, for a king on an edge file)
  88.     // squares two ranks in front of the king. For instance, if black's king
  89.     // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
  90.     // f7, g7, h7, f6, g6 and h6.
  91.     Bitboard kingRing[COLOR_NB];
  92.  
  93.     // kingAttackersCount[color] is the number of pieces of the given color
  94.     // which attack a square in the kingRing of the enemy king.
  95.     int kingAttackersCount[COLOR_NB];
  96.  
  97.     // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
  98.     // given color which attack a square in the kingRing of the enemy king. The
  99.     // weights of the individual piece types are given by the elements in the
  100.     // KingAttackWeights array.
  101.     int kingAttackersWeight[COLOR_NB];
  102.  
  103.     // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
  104.     // color to squares directly adjacent to the enemy king. Pieces which attack
  105.     // more than one square are counted multiple times. For instance, if there is
  106.     // a white knight on g5 and black's king is on g8, this white knight adds 2
  107.     // to kingAdjacentZoneAttacksCount[WHITE].
  108.     int kingAdjacentZoneAttacksCount[COLOR_NB];
  109.  
  110.     Bitboard pinnedPieces[COLOR_NB];
  111.     Material::Entry* me;
  112.     Pawns::Entry* pi;
  113.   };
  114.  
  115.   #define V(v) Value(v)
  116.   #define S(mg, eg) make_score(mg, eg)
  117.  
  118.   // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
  119.   // game, indexed by piece type and number of attacked squares in the MobilityArea.
  120.   const Score MobilityBonus[][32] = {
  121.     {}, {},
  122.     { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S(  6,  5), S( 15, 11), // Knights
  123.       S( 22, 26), S( 30, 28), S( 36, 29) },
  124.     { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
  125.       S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
  126.       S( 92, 90), S( 97, 94) },
  127.     { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
  128.       S(  8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
  129.       S( 43,165), S( 49,168), S( 59,169) },
  130.     { S(-40,-35), S(-25,-12), S(  2,  7), S(  4, 19), S( 14, 37), S( 24, 55), // Queens
  131.       S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
  132.       S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
  133.       S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
  134.       S(118,174), S(119,177), S(123,191), S(128,199) }
  135.   };
  136.  
  137.   // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
  138.   // bishops outposts, bigger if outpost piece is supported by a pawn.
  139.   const Score Outpost[][2] = {
  140.     { S(43,11), S(65,20) }, // Knights
  141.     { S(20, 3), S(29, 8) }  // Bishops
  142.   };
  143.  
  144.   // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
  145.   // knights and bishops which can reach an outpost square in one move, bigger
  146.   // if outpost square is supported by a pawn.
  147.   const Score ReachableOutpost[][2] = {
  148.     { S(21, 5), S(35, 8) }, // Knights
  149.     { S( 8, 0), S(14, 4) }  // Bishops
  150.   };
  151.  
  152.   // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
  153.   // friendly pawn on the rook file.
  154.   const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
  155.  
  156.   // ThreatBySafePawn[PieceType] contains bonuses according to which piece
  157.   // type is attacked by a pawn which is protected or is not attacked.
  158.   const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
  159.     S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
  160.   };
  161.  
  162.   // Threat[by minor/by rook][attacked PieceType] contains
  163.   // bonuses according to which piece type attacks which one.
  164.   // Attacks on lesser pieces which are pawn-defended are not considered.
  165.   const Score Threat[][PIECE_TYPE_NB] = {
  166.     { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
  167.     { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) }  // by Rook
  168.   };
  169.  
  170.   // ThreatByKing[on one/on many] contains bonuses for King attacks on
  171.   // pawns or pieces which are not pawn-defended.
  172.   const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
  173.  
  174.   // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
  175.   // We don't use a Score because we process the two components independently.
  176.   const Value Passed[][RANK_NB] = {
  177.     { V(5), V( 5), V(31), V(73), V(166), V(252) },
  178.     { V(7), V(14), V(38), V(73), V(166), V(252) }
  179.   };
  180.  
  181.   // PassedFile[File] contains a bonus according to the file of a passed pawn
  182.   const Score PassedFile[FILE_NB] = {
  183.     S(  9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
  184.     S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
  185.   };
  186.  
  187.   // Assorted bonuses and penalties used by evaluation
  188.   const Score MinorBehindPawn     = S(16,  0);
  189.   const Score BishopPawns         = S( 8, 12);
  190.   const Score RookOnPawn          = S( 8, 24);
  191.   const Score TrappedRook         = S(92,  0);
  192.   const Score CloseEnemies        = S( 7,  0);
  193.   const Score SafeCheck           = S(20, 20);
  194.   const Score OtherCheck          = S(10, 10);
  195.   const Score ThreatByHangingPawn = S(71, 61);
  196.   const Score LooseEnemies        = S( 0, 25);
  197.   const Score WeakQueen           = S(35,  0);
  198.   const Score Hanging             = S(48, 27);
  199.   const Score ThreatByPawnPush    = S(38, 22);
  200.   const Score Unstoppable         = S( 0, 20);
  201.   const Score PawnlessFlank       = S(20, 80);
  202.   const Score HinderPassedPawn    = S( 7,  0);
  203.  
  204.   // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
  205.   // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
  206.   // happen in Chess960 games.
  207.   const Score TrappedBishopA1H1 = S(50, 50);
  208.  
  209.   #undef S
  210.   #undef V
  211.  
  212.   // KingAttackWeights[PieceType] contains king attack weights by piece type
  213.   const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
  214.  
  215.   // Penalties for enemy's safe checks
  216.   const int QueenContactCheck = 997;
  217.   const int QueenCheck        = 695;
  218.   const int RookCheck         = 638;
  219.   const int BishopCheck       = 538;
  220.   const int KnightCheck       = 874;
  221.  
  222.  
  223.   // eval_init() initializes king and attack bitboards for a given color
  224.   // adding pawn attacks. To be done at the beginning of the evaluation.
  225.  
  226.   template<Color Us>
  227.   void eval_init(const Position& pos, EvalInfo& ei) {
  228.  
  229.     const Color  Them = (Us == WHITE ? BLACK : WHITE);
  230.     const Square Down = (Us == WHITE ? SOUTH : NORTH);
  231.  
  232.     ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
  233.     Bitboard b = ei.attackedBy[Them][KING];
  234.     ei.attackedBy[Them][ALL_PIECES] |= b;
  235.     ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
  236.     ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
  237.  
  238.     // Init king safety tables only if we are going to use them
  239.     if (pos.non_pawn_material(Us) >= QueenValueMg)
  240.     {
  241.         ei.kingRing[Them] = b | shift<Down>(b);
  242.         b &= ei.attackedBy[Us][PAWN];
  243.         ei.kingAttackersCount[Us] = popcount(b);
  244.         ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
  245.     }
  246.     else
  247.         ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
  248.   }
  249.  
  250.  
  251.   // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
  252.   // color and type.
  253.  
  254.   template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
  255.   Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
  256.                         const Bitboard* mobilityArea) {
  257.     Bitboard b, bb;
  258.     Square s;
  259.     Score score = SCORE_ZERO;
  260.  
  261.     const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
  262.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  263.     const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
  264.                                                : Rank5BB | Rank4BB | Rank3BB);
  265.     const Square* pl = pos.squares<Pt>(Us);
  266.  
  267.     ei.attackedBy[Us][Pt] = 0;
  268.  
  269.     while ((s = *pl++) != SQ_NONE)
  270.     {
  271.         // Find attacked squares, including x-ray attacks for bishops and rooks
  272.         b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
  273.           : Pt ==   ROOK ? attacks_bb<  ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
  274.                          : pos.attacks_from<Pt>(s);
  275.  
  276.         if (ei.pinnedPieces[Us] & s)
  277.             b &= LineBB[pos.square<KING>(Us)][s];
  278.  
  279.         ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
  280.         ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
  281.  
  282.         if (b & ei.kingRing[Them])
  283.         {
  284.             ei.kingAttackersCount[Us]++;
  285.             ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
  286.             ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
  287.         }
  288.  
  289.         if (Pt == QUEEN)
  290.             b &= ~(  ei.attackedBy[Them][KNIGHT]
  291.                    | ei.attackedBy[Them][BISHOP]
  292.                    | ei.attackedBy[Them][ROOK]);
  293.  
  294.         int mob = popcount(b & mobilityArea[Us]);
  295.  
  296.         mobility[Us] += MobilityBonus[Pt][mob];
  297.  
  298.         if (Pt == BISHOP || Pt == KNIGHT)
  299.         {
  300.             // Bonus for outpost squares
  301.             bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
  302.             if (bb & s)
  303.                 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
  304.             else
  305.             {
  306.                 bb &= b & ~pos.pieces(Us);
  307.                 if (bb)
  308.                    score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
  309.             }
  310.  
  311.             // Bonus when behind a pawn
  312.             if (    relative_rank(Us, s) < RANK_5
  313.                 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
  314.                 score += MinorBehindPawn;
  315.  
  316.             // Penalty for pawns on the same color square as the bishop
  317.             if (Pt == BISHOP)
  318.                 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
  319.  
  320.             // An important Chess960 pattern: A cornered bishop blocked by a friendly
  321.             // pawn diagonally in front of it is a very serious problem, especially
  322.             // when that pawn is also blocked.
  323.             if (   Pt == BISHOP
  324.                 && pos.is_chess960()
  325.                 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
  326.             {
  327.                 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
  328.                 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
  329.                     score -= !pos.empty(s + d + pawn_push(Us))                ? TrappedBishopA1H1 * 4
  330.                             : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
  331.                                                                               : TrappedBishopA1H1;
  332.             }
  333.         }
  334.  
  335.         if (Pt == ROOK)
  336.         {
  337.             // Bonus for aligning with enemy pawns on the same rank/file
  338.             if (relative_rank(Us, s) >= RANK_5)
  339.                 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
  340.  
  341.             // Bonus when on an open or semi-open file
  342.             if (ei.pi->semiopen_file(Us, file_of(s)))
  343.                 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
  344.  
  345.             // Penalize when trapped by the king, even more if the king cannot castle
  346.             else if (mob <= 3)
  347.             {
  348.                 Square ksq = pos.square<KING>(Us);
  349.  
  350.                 if (   ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
  351.                     && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
  352.                     && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
  353.                     score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
  354.             }
  355.         }
  356.  
  357.         if (Pt == QUEEN)
  358.         {
  359.             // Penalty if any relative pin or discovered attack against the queen
  360.             Bitboard pinners;
  361.             if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
  362.                 score -= WeakQueen;
  363.         }
  364.     }
  365.  
  366.     if (DoTrace)
  367.         Trace::add(Pt, Us, score);
  368.  
  369.     // Recursively call evaluate_pieces() of next piece type until KING is excluded
  370.     return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
  371.   }
  372.  
  373.   template<>
  374.   Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
  375.   template<>
  376.   Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
  377.  
  378.  
  379.   // evaluate_king() assigns bonuses and penalties to a king of a given color
  380.  
  381.   const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
  382.   const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
  383.   const Bitboard QueenSide   = FileABB | FileBBB | FileCBB | FileDBB;
  384.   const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
  385.   const Bitboard KingSide    = FileEBB | FileFBB | FileGBB | FileHBB;
  386.  
  387.   const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
  388.     { QueenSide   & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
  389.       CenterFiles & WhiteCamp, KingSide  & WhiteCamp, KingSide  & WhiteCamp, KingSide    & WhiteCamp },
  390.     { QueenSide   & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
  391.       CenterFiles & BlackCamp, KingSide  & BlackCamp, KingSide  & BlackCamp, KingSide    & BlackCamp },
  392.   };
  393.  
  394.   template<Color Us, bool DoTrace>
  395.   Score evaluate_king(const Position& pos, const EvalInfo& ei) {
  396.  
  397.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  398.     const Square  Up = (Us == WHITE ? NORTH : SOUTH);
  399.  
  400.     Bitboard undefended, b, b1, b2, safe, other;
  401.     int kingDanger;
  402.     const Square ksq = pos.square<KING>(Us);
  403.  
  404.     // King shelter and enemy pawns storm
  405.     Score score = ei.pi->king_safety<Us>(pos, ksq);
  406.  
  407.     // Main king safety evaluation
  408.     if (ei.kingAttackersCount[Them])
  409.     {
  410.         // Find the attacked squares which are defended only by the king...
  411.         undefended =   ei.attackedBy[Them][ALL_PIECES]
  412.                     &  ei.attackedBy[Us][KING]
  413.                     & ~ei.attackedBy2[Us];
  414.  
  415.         // ... and those which are not defended at all in the larger king ring
  416.         b =  ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
  417.            & ei.kingRing[Us] & ~pos.pieces(Them);
  418.  
  419.         // Initialize the 'kingDanger' variable, which will be transformed
  420.         // later into a king danger score. The initial value is based on the
  421.         // number and types of the enemy's attacking pieces, the number of
  422.         // attacked and undefended squares around our king and the quality of
  423.         // the pawn shelter (current 'score' value).
  424.         kingDanger =  std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
  425.                     + 101 * ei.kingAdjacentZoneAttacksCount[Them]
  426.                     + 235 * popcount(undefended)
  427.                     + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
  428.                     - 717 * !pos.count<QUEEN>(Them)
  429.                     -   7 * mg_value(score) / 5 - 5;
  430.  
  431.         // Analyse the enemy's safe queen contact checks. Firstly, find the
  432.         // undefended squares around the king reachable by the enemy queen...
  433.         b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
  434.  
  435.         // ...and keep squares supported by another enemy piece
  436.         kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
  437.  
  438.         // Analyse the safe enemy's checks which are possible on next move...
  439.         safe  = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
  440.  
  441.         // ... and some other potential checks, only requiring the square to be
  442.         // safe from pawn-attacks, and not being occupied by a blocked pawn.
  443.         other = ~(   ei.attackedBy[Us][PAWN]
  444.                   | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
  445.  
  446.         b1 = pos.attacks_from<ROOK  >(ksq);
  447.         b2 = pos.attacks_from<BISHOP>(ksq);
  448.  
  449.         // Enemy queen safe checks
  450.         if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
  451.             kingDanger += QueenCheck, score -= SafeCheck;
  452.  
  453.         // For other pieces, also consider the square safe if attacked twice,
  454.         // and only defended by a queen.
  455.         safe |=  ei.attackedBy2[Them]
  456.                & ~(ei.attackedBy2[Us] | pos.pieces(Them))
  457.                & ei.attackedBy[Us][QUEEN];
  458.  
  459.         // Enemy rooks safe and other checks
  460.         if (b1 & ei.attackedBy[Them][ROOK] & safe)
  461.             kingDanger += RookCheck, score -= SafeCheck;
  462.  
  463.         else if (b1 & ei.attackedBy[Them][ROOK] & other)
  464.             score -= OtherCheck;
  465.  
  466.         // Enemy bishops safe and other checks
  467.         if (b2 & ei.attackedBy[Them][BISHOP] & safe)
  468.             kingDanger += BishopCheck, score -= SafeCheck;
  469.  
  470.         else if (b2 & ei.attackedBy[Them][BISHOP] & other)
  471.             score -= OtherCheck;
  472.  
  473.         // Enemy knights safe and other checks
  474.         b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
  475.         if (b & safe)
  476.             kingDanger += KnightCheck, score -= SafeCheck;
  477.  
  478.         else if (b & other)
  479.             score -= OtherCheck;
  480.  
  481.         // Compute the king danger score and subtract it from the evaluation
  482.         if (kingDanger > 0)
  483.             score -= make_score(std::min(kingDanger * kingDanger / 4096,  2 * int(BishopValueMg)), 0);
  484.     }
  485.  
  486.     // King tropism: firstly, find squares that opponent attacks in our king flank
  487.     File kf = file_of(ksq);
  488.     b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][kf];
  489.  
  490.     assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
  491.     assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
  492.  
  493.     // Secondly, add the squares which are attacked twice in that flank and
  494.     // which are not defended by our pawns.
  495.     b =  (Us == WHITE ? b << 4 : b >> 4)
  496.        | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
  497.  
  498.     score -= CloseEnemies * popcount(b);
  499.  
  500.     // Penalty when our king is on a pawnless flank
  501.     if (!(pos.pieces(PAWN) & (KingFlank[WHITE][kf] | KingFlank[BLACK][kf])))
  502.         score -= PawnlessFlank;
  503.  
  504.     if (DoTrace)
  505.         Trace::add(KING, Us, score);
  506.  
  507.     return score;
  508.   }
  509.  
  510.  
  511.   // evaluate_threats() assigns bonuses according to the types of the attacking
  512.   // and the attacked pieces.
  513.  
  514.   template<Color Us, bool DoTrace>
  515.   Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
  516.  
  517.     const Color Them        = (Us == WHITE ? BLACK      : WHITE);
  518.     const Square Up         = (Us == WHITE ? NORTH      : SOUTH);
  519.     const Square Left       = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
  520.     const Square Right      = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
  521.     const Bitboard TRank2BB = (Us == WHITE ? Rank2BB    : Rank7BB);
  522.     const Bitboard TRank7BB = (Us == WHITE ? Rank7BB    : Rank2BB);
  523.  
  524.     enum { Minor, Rook };
  525.  
  526.     Bitboard b, weak, defended, safeThreats;
  527.     Score score = SCORE_ZERO;
  528.  
  529.     // Small bonus if the opponent has loose pawns or pieces
  530.     if (   (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
  531.         & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
  532.         score += LooseEnemies;
  533.  
  534.     // Non-pawn enemies attacked by a pawn
  535.     weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
  536.  
  537.     if (weak)
  538.     {
  539.         b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
  540.                                     | ei.attackedBy[Us][ALL_PIECES]);
  541.  
  542.         safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
  543.  
  544.         if (weak ^ safeThreats)
  545.             score += ThreatByHangingPawn;
  546.  
  547.         while (safeThreats)
  548.             score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
  549.     }
  550.  
  551.     // Non-pawn enemies defended by a pawn
  552.     defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
  553.  
  554.     // Enemies not defended by a pawn and under our attack
  555.     weak =   pos.pieces(Them)
  556.           & ~ei.attackedBy[Them][PAWN]
  557.           &  ei.attackedBy[Us][ALL_PIECES];
  558.  
  559.     // Add a bonus according to the kind of attacking pieces
  560.     if (defended | weak)
  561.     {
  562.         b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
  563.         while (b)
  564.             score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
  565.  
  566.         b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
  567.         while (b)
  568.             score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
  569.  
  570.         score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
  571.  
  572.         b = weak & ei.attackedBy[Us][KING];
  573.         if (b)
  574.             score += ThreatByKing[more_than_one(b)];
  575.     }
  576.  
  577.     // Bonus if some pawns can safely push and attack an enemy piece
  578.     b = pos.pieces(Us, PAWN) & ~TRank7BB;
  579.     b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
  580.  
  581.     b &=  ~pos.pieces()
  582.         & ~ei.attackedBy[Them][PAWN]
  583.         & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
  584.  
  585.     b =  (shift<Left>(b) | shift<Right>(b))
  586.        &  pos.pieces(Them)
  587.        & ~ei.attackedBy[Us][PAWN];
  588.  
  589.     score += ThreatByPawnPush * popcount(b);
  590.  
  591.     if (DoTrace)
  592.         Trace::add(THREAT, Us, score);
  593.  
  594.     return score;
  595.   }
  596.  
  597.  
  598.   // evaluate_passed_pawns() evaluates the passed pawns of the given color
  599.  
  600.   template<Color Us, bool DoTrace>
  601.   Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
  602.  
  603.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  604.  
  605.     Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
  606.     Score score = SCORE_ZERO;
  607.  
  608.     b = ei.pi->passed_pawns(Us);
  609.  
  610.     while (b)
  611.     {
  612.         Square s = pop_lsb(&b);
  613.  
  614.         assert(pos.pawn_passed(Us, s));
  615.         assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
  616.  
  617.         bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
  618.         score -= HinderPassedPawn * popcount(bb);
  619.  
  620.         int r = relative_rank(Us, s) - RANK_2;
  621.         int rr = r * (r - 1);
  622.  
  623.         Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
  624.  
  625.         if (rr)
  626.         {
  627.             Square blockSq = s + pawn_push(Us);
  628.  
  629.             // Adjust bonus based on the king's proximity
  630.             ebonus +=  distance(pos.square<KING>(Them), blockSq) * 5 * rr
  631.                      - distance(pos.square<KING>(Us  ), blockSq) * 2 * rr;
  632.  
  633.             // If blockSq is not the queening square then consider also a second push
  634.             if (relative_rank(Us, blockSq) != RANK_8)
  635.                 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
  636.  
  637.             // If the pawn is free to advance, then increase the bonus
  638.             if (pos.empty(blockSq))
  639.             {
  640.                 // If there is a rook or queen attacking/defending the pawn from behind,
  641.                 // consider all the squaresToQueen. Otherwise consider only the squares
  642.                 // in the pawn's path attacked or occupied by the enemy.
  643.                 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
  644.  
  645.                 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
  646.  
  647.                 if (!(pos.pieces(Us) & bb))
  648.                     defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
  649.  
  650.                 if (!(pos.pieces(Them) & bb))
  651.                     unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
  652.  
  653.                 // If there aren't any enemy attacks, assign a big bonus. Otherwise
  654.                 // assign a smaller bonus if the block square isn't attacked.
  655.                 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
  656.  
  657.                 // If the path to the queen is fully defended, assign a big bonus.
  658.                 // Otherwise assign a smaller bonus if the block square is defended.
  659.                 if (defendedSquares == squaresToQueen)
  660.                     k += 6;
  661.  
  662.                 else if (defendedSquares & blockSq)
  663.                     k += 4;
  664.  
  665.                 mbonus += k * rr, ebonus += k * rr;
  666.             }
  667.             else if (pos.pieces(Us) & blockSq)
  668.                 mbonus += rr + r * 2, ebonus += rr + r * 2;
  669.         } // rr != 0
  670.  
  671.         score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
  672.     }
  673.  
  674.     if (DoTrace)
  675.         Trace::add(PASSED, Us, score);
  676.  
  677.     // Add the scores to the middlegame and endgame eval
  678.     return score;
  679.   }
  680.  
  681.  
  682.   // evaluate_space() computes the space evaluation for a given side. The
  683.   // space evaluation is a simple bonus based on the number of safe squares
  684.   // available for minor pieces on the central four files on ranks 2--4. Safe
  685.   // squares one, two or three squares behind a friendly pawn are counted
  686.   // twice. Finally, the space bonus is multiplied by a weight. The aim is to
  687.   // improve play on game opening.
  688.   template<Color Us>
  689.   Score evaluate_space(const Position& pos, const EvalInfo& ei) {
  690.  
  691.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  692.     const Bitboard SpaceMask =
  693.       Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
  694.                   : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
  695.  
  696.     // Find the safe squares for our pieces inside the area defined by
  697.     // SpaceMask. A square is unsafe if it is attacked by an enemy
  698.     // pawn, or if it is undefended and attacked by an enemy piece.
  699.     Bitboard safe =   SpaceMask
  700.                    & ~pos.pieces(Us, PAWN)
  701.                    & ~ei.attackedBy[Them][PAWN]
  702.                    & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
  703.  
  704.     // Find all squares which are at most three squares behind some friendly pawn
  705.     Bitboard behind = pos.pieces(Us, PAWN);
  706.     behind |= (Us == WHITE ? behind >>  8 : behind <<  8);
  707.     behind |= (Us == WHITE ? behind >> 16 : behind << 16);
  708.  
  709.     // Since SpaceMask[Us] is fully on our half of the board...
  710.     assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
  711.  
  712.     // ...count safe + (behind & safe) with a single popcount
  713.     int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
  714.     bonus = std::min(16, bonus);
  715.     int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
  716.  
  717.     return make_score(bonus * weight * weight / 18, 0);
  718.   }
  719.  
  720.  
  721.   // evaluate_initiative() computes the initiative correction value for the
  722.   // position, i.e., second order bonus/malus based on the known attacking/defending
  723.   // status of the players.
  724.   Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
  725.  
  726.     int kingDistance =  distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
  727.                       - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
  728.     int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
  729.  
  730.     // Compute the initiative bonus for the attacking side
  731.     int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
  732.  
  733.     // Now apply the bonus: note that we find the attacking side by extracting
  734.     // the sign of the endgame value, and that we carefully cap the bonus so
  735.     // that the endgame score will never be divided by more than two.
  736.     int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
  737.  
  738.     return make_score(0, value);
  739.   }
  740.  
  741.  
  742.   // evaluate_scale_factor() computes the scale factor for the winning side
  743.   ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
  744.  
  745.     Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
  746.     ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
  747.  
  748.     // If we don't already have an unusual scale factor, check for certain
  749.     // types of endgames, and use a lower scale for those.
  750.     if (    ei.me->game_phase() < PHASE_MIDGAME
  751.         && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
  752.     {
  753.         if (pos.opposite_bishops())
  754.         {
  755.             // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
  756.             // is almost a draw, in case of KBP vs KB, it is even more a draw.
  757.             if (   pos.non_pawn_material(WHITE) == BishopValueMg
  758.                 && pos.non_pawn_material(BLACK) == BishopValueMg)
  759.                 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
  760.  
  761.             // Endgame with opposite-colored bishops, but also other pieces. Still
  762.             // a bit drawish, but not as drawish as with only the two bishops.
  763.             else
  764.                 sf = ScaleFactor(46);
  765.         }
  766.         // Endings where weaker side can place his king in front of the opponent's
  767.         // pawns are drawish.
  768.         else if (    abs(eg) <= BishopValueEg
  769.                  &&  pos.count<PAWN>(strongSide) <= 2
  770.                  && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
  771.             sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
  772.     }
  773.  
  774.     return sf;
  775.   }
  776.  
  777. } // namespace
  778.  
  779.  
  780. /// evaluate() is the main evaluation function. It returns a static evaluation
  781. /// of the position from the point of view of the side to move.
  782.  
  783. template<bool DoTrace>
  784. Value Eval::evaluate(const Position& pos) {
  785.  
  786.   assert(!pos.checkers());
  787.  
  788.   Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
  789.   EvalInfo ei;
  790.  
  791.   // Probe the material hash table
  792.   ei.me = Material::probe(pos);
  793.  
  794.   // If we have a specialized evaluation function for the current material
  795.   // configuration, call it and return.
  796.   if (ei.me->specialized_eval_exists())
  797.       return ei.me->evaluate(pos);
  798.  
  799.   // Initialize score by reading the incrementally updated scores included in
  800.   // the position object (material + piece square tables) and the material
  801.   // imbalance. Score is computed internally from the white point of view.
  802.   Score score = pos.psq_score() + ei.me->imbalance();
  803.  
  804.   // Probe the pawn hash table
  805.   ei.pi = Pawns::probe(pos);
  806.   score += ei.pi->pawns_score();
  807.  
  808.   // Initialize attack and king safety bitboards
  809.   ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
  810.   ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
  811.   ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
  812.   eval_init<WHITE>(pos, ei);
  813.   eval_init<BLACK>(pos, ei);
  814.  
  815.   // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
  816.   Bitboard blockedPawns[] = {
  817.     pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
  818.     pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
  819.   };
  820.  
  821.   // Do not include in mobility area squares protected by enemy pawns, or occupied
  822.   // by our blocked pawns or king.
  823.   Bitboard mobilityArea[] = {
  824.     ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
  825.     ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
  826.   };
  827.  
  828.   // Evaluate all pieces but king and pawns
  829.   score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
  830.   score += mobility[WHITE] - mobility[BLACK];
  831.  
  832.   // Evaluate kings after all other pieces because we need full attack
  833.   // information when computing the king safety evaluation.
  834.   score +=  evaluate_king<WHITE, DoTrace>(pos, ei)
  835.           - evaluate_king<BLACK, DoTrace>(pos, ei);
  836.  
  837.   // Evaluate tactical threats, we need full attack information including king
  838.   score +=  evaluate_threats<WHITE, DoTrace>(pos, ei)
  839.           - evaluate_threats<BLACK, DoTrace>(pos, ei);
  840.  
  841.   // Evaluate passed pawns, we need full attack information including king
  842.   score +=  evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
  843.           - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
  844.  
  845.   // If both sides have only pawns, score for potential unstoppable pawns
  846.   if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
  847.   {
  848.       Bitboard b;
  849.       if ((b = ei.pi->passed_pawns(WHITE)) != 0)
  850.           score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
  851.  
  852.       if ((b = ei.pi->passed_pawns(BLACK)) != 0)
  853.           score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
  854.   }
  855.  
  856.   // Evaluate space for both sides, only during opening
  857.   if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
  858.       score +=  evaluate_space<WHITE>(pos, ei)
  859.               - evaluate_space<BLACK>(pos, ei);
  860.  
  861.   // Evaluate position potential for the winning side
  862.   score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
  863.  
  864.   // Evaluate scale factor for the winning side
  865.   ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
  866.  
  867.   // Interpolate between a middlegame and a (scaled by 'sf') endgame score
  868.   Value v =  mg_value(score) * int(ei.me->game_phase())
  869.            + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
  870.  
  871.   v /= int(PHASE_MIDGAME);
  872.  
  873.   // In case of tracing add all remaining individual evaluation terms
  874.   if (DoTrace)
  875.   {
  876.       Trace::add(MATERIAL, pos.psq_score());
  877.       Trace::add(IMBALANCE, ei.me->imbalance());
  878.       Trace::add(PAWN, ei.pi->pawns_score());
  879.       Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
  880.       Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
  881.                       , evaluate_space<BLACK>(pos, ei));
  882.       Trace::add(TOTAL, score);
  883.   }
  884.  
  885.   return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
  886. }
  887.  
  888. // Explicit template instantiations
  889. template Value Eval::evaluate<true >(const Position&);
  890. template Value Eval::evaluate<false>(const Position&);
  891.  
  892.  
  893. /// trace() is like evaluate(), but instead of returning a value, it returns
  894. /// a string (suitable for outputting to stdout) that contains the detailed
  895. /// descriptions and values of each evaluation term. Useful for debugging.
  896.  
  897. std::string Eval::trace(const Position& pos) {
  898.  
  899.   std::memset(scores, 0, sizeof(scores));
  900.  
  901.   Value v = evaluate<true>(pos);
  902.   v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
  903.  
  904.   std::stringstream ss;
  905.   ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
  906.      << "      Eval term |    White    |    Black    |    Total    \n"
  907.      << "                |   MG    EG  |   MG    EG  |   MG    EG  \n"
  908.      << "----------------+-------------+-------------+-------------\n"
  909.      << "       Material | " << Term(MATERIAL)
  910.      << "      Imbalance | " << Term(IMBALANCE)
  911.      << "          Pawns | " << Term(PAWN)
  912.      << "        Knights | " << Term(KNIGHT)
  913.      << "         Bishop | " << Term(BISHOP)
  914.      << "          Rooks | " << Term(ROOK)
  915.      << "         Queens | " << Term(QUEEN)
  916.      << "       Mobility | " << Term(MOBILITY)
  917.      << "    King safety | " << Term(KING)
  918.      << "        Threats | " << Term(THREAT)
  919.      << "   Passed pawns | " << Term(PASSED)
  920.      << "          Space | " << Term(SPACE)
  921.      << "----------------+-------------+-------------+-------------\n"
  922.      << "          Total | " << Term(TOTAL);
  923.  
  924.   ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
  925.  
  926.   return ss.str();
  927. }
  928.