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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 "bitcount.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.     // kingRing[color] is the zone around the king which is considered
  81.     // by the king safety evaluation. This consists of the squares directly
  82.     // adjacent to the king, and the three (or two, for a king on an edge file)
  83.     // squares two ranks in front of the king. For instance, if black's king
  84.     // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
  85.     // f7, g7, h7, f6, g6 and h6.
  86.     Bitboard kingRing[COLOR_NB];
  87.  
  88.     // kingAttackersCount[color] is the number of pieces of the given color
  89.     // which attack a square in the kingRing of the enemy king.
  90.     int kingAttackersCount[COLOR_NB];
  91.  
  92.     // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
  93.     // given color which attack a square in the kingRing of the enemy king. The
  94.     // weights of the individual piece types are given by the elements in the
  95.     // KingAttackWeights array.
  96.     int kingAttackersWeight[COLOR_NB];
  97.  
  98.     // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
  99.     // color to squares directly adjacent to the enemy king. Pieces which attack
  100.     // more than one square are counted multiple times. For instance, if there is
  101.     // a white knight on g5 and black's king is on g8, this white knight adds 2
  102.     // to kingAdjacentZoneAttacksCount[WHITE].
  103.     int kingAdjacentZoneAttacksCount[COLOR_NB];
  104.  
  105.     Bitboard pinnedPieces[COLOR_NB];
  106.     Material::Entry* me;
  107.     Pawns::Entry* pi;
  108.   };
  109.  
  110.   #define V(v) Value(v)
  111.   #define S(mg, eg) make_score(mg, eg)
  112.  
  113.   // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
  114.   // game, indexed by piece type and number of attacked squares in the MobilityArea.
  115.   const Score MobilityBonus[][32] = {
  116.     {}, {},
  117.     { S(-75,-76), S(-56,-54), S(- 9,-26), S( -2,-10), S(  6,  5), S( 15, 11), // Knights
  118.       S( 22, 26), S( 30, 28), S( 36, 29) },
  119.     { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
  120.       S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
  121.       S( 92, 90), S( 97, 94) },
  122.     { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
  123.       S(  8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
  124.       S( 43,165), S( 49,168), S( 59,169) },
  125.     { S(-40,-35), S(-25,-12), S(  2,  7), S(  4, 19), S( 14, 37), S( 24, 55), // Queens
  126.       S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
  127.       S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
  128.       S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
  129.       S(118,174), S(119,177), S(123,191), S(128,199) }
  130.   };
  131.  
  132.   // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
  133.   // bishops outposts, bigger if outpost piece is supported by a pawn.
  134.   const Score Outpost[][2] = {
  135.     { S(42,11), S(63,17) }, // Knights
  136.     { S(18, 5), S(27, 8) }  // Bishops
  137.   };
  138.  
  139.   // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
  140.   // knights and bishops which can reach an outpost square in one move, bigger
  141.   // if outpost square is supported by a pawn.
  142.   const Score ReachableOutpost[][2] = {
  143.     { S(21, 5), S(31, 8) }, // Knights
  144.     { S( 8, 2), S(13, 4) }  // Bishops
  145.   };
  146.  
  147.   // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
  148.   // friendly pawn on the rook file.
  149.   const Score RookOnFile[2] = { S(19, 10), S(43, 21) };
  150.  
  151.   // ThreatBySafePawn[PieceType] contains bonuses according to which piece
  152.   // type is attacked by a pawn which is protected or is not attacked.
  153.   const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
  154.     S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215) };
  155.  
  156.   // Threat[by minor/by rook][attacked PieceType] contains
  157.   // bonuses according to which piece type attacks which one.
  158.   // Attacks on lesser pieces which are pawn-defended are not considered.
  159.   const Score Threat[][PIECE_TYPE_NB] = {
  160.     { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
  161.     { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) }  // by Rook
  162.   };
  163.  
  164.   // ThreatByKing[on one/on many] contains bonuses for King attacks on
  165.   // pawns or pieces which are not pawn-defended.
  166.   const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
  167.  
  168.   // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
  169.   // We don't use a Score because we process the two components independently.
  170.   const Value Passed[][RANK_NB] = {
  171.     { V(0), V( 1), V(26), V(68), V(161), V(247) },
  172.     { V(7), V(14), V(38), V(64), V(137), V(193) }
  173.   };
  174.  
  175.   // PassedFile[File] contains a bonus according to the file of a passed pawn
  176.   const Score PassedFile[FILE_NB] = {
  177.     S(  9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
  178.     S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
  179.   };
  180.  
  181.   // Assorted bonuses and penalties used by evaluation
  182.   const Score MinorBehindPawn     = S(16,  0);
  183.   const Score BishopPawns         = S( 8, 12);
  184.   const Score RookOnPawn          = S( 7, 27);
  185.   const Score TrappedRook         = S(92,  0);
  186.   const Score Checked             = S(20, 20);
  187.   const Score ThreatByHangingPawn = S(70, 63);
  188.   const Score Hanging             = S(48, 28);
  189.   const Score ThreatByPawnPush    = S(31, 19);
  190.   const Score Unstoppable         = S( 0, 20);
  191.  
  192.   // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
  193.   // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
  194.   // happen in Chess960 games.
  195.   const Score TrappedBishopA1H1 = S(50, 50);
  196.  
  197.   #undef S
  198.   #undef V
  199.  
  200.   // King danger constants and variables. The king danger scores are looked-up
  201.   // in KingDanger[]. Various little "meta-bonuses" measuring the strength
  202.   // of the enemy attack are added up into an integer, which is used as an
  203.   // index to KingDanger[].
  204.   Score KingDanger[512];
  205.  
  206.   // KingAttackWeights[PieceType] contains king attack weights by piece type
  207.   const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
  208.  
  209.   // Penalties for enemy's safe checks
  210.   const int QueenContactCheck = 89;
  211.   const int QueenCheck        = 50;
  212.   const int RookCheck         = 45;
  213.   const int BishopCheck       = 6;
  214.   const int KnightCheck       = 14;
  215.  
  216.  
  217.   // eval_init() initializes king and attack bitboards for a given color
  218.   // adding pawn attacks. To be done at the beginning of the evaluation.
  219.  
  220.   template<Color Us>
  221.   void eval_init(const Position& pos, EvalInfo& ei) {
  222.  
  223.     const Color  Them = (Us == WHITE ? BLACK   : WHITE);
  224.     const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
  225.  
  226.     ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
  227.     Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
  228.     ei.attackedBy[Them][ALL_PIECES] |= b;
  229.     ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
  230.  
  231.     // Init king safety tables only if we are going to use them
  232.     if (pos.non_pawn_material(Us) >= QueenValueMg)
  233.     {
  234.         ei.kingRing[Them] = b | shift_bb<Down>(b);
  235.         b &= ei.attackedBy[Us][PAWN];
  236.         ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
  237.         ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
  238.     }
  239.     else
  240.         ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
  241.   }
  242.  
  243.  
  244.   // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
  245.   // color and type.
  246.  
  247.   template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
  248.   Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
  249.                         const Bitboard* mobilityArea) {
  250.     Bitboard b, bb;
  251.     Square s;
  252.     Score score = SCORE_ZERO;
  253.  
  254.     const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
  255.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  256.     const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
  257.                                                : Rank5BB | Rank4BB | Rank3BB);
  258.     const Square* pl = pos.squares<Pt>(Us);
  259.  
  260.     ei.attackedBy[Us][Pt] = 0;
  261.  
  262.     while ((s = *pl++) != SQ_NONE)
  263.     {
  264.         // Find attacked squares, including x-ray attacks for bishops and rooks
  265.         b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
  266.           : Pt ==   ROOK ? attacks_bb<  ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
  267.                          : pos.attacks_from<Pt>(s);
  268.  
  269.         if (ei.pinnedPieces[Us] & s)
  270.             b &= LineBB[pos.square<KING>(Us)][s];
  271.  
  272.         ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
  273.  
  274.         if (b & ei.kingRing[Them])
  275.         {
  276.             ei.kingAttackersCount[Us]++;
  277.             ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
  278.             bb = b & ei.attackedBy[Them][KING];
  279.             if (bb)
  280.                 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
  281.         }
  282.  
  283.         if (Pt == QUEEN)
  284.             b &= ~(  ei.attackedBy[Them][KNIGHT]
  285.                    | ei.attackedBy[Them][BISHOP]
  286.                    | ei.attackedBy[Them][ROOK]);
  287.  
  288.         int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
  289.  
  290.         mobility[Us] += MobilityBonus[Pt][mob];
  291.  
  292.         if (Pt == BISHOP || Pt == KNIGHT)
  293.         {
  294.             // Bonus for outpost squares
  295.             bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
  296.             if (bb & s)
  297.                 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
  298.             else
  299.             {
  300.                 bb &= b & ~pos.pieces(Us);
  301.                 if (bb)
  302.                    score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
  303.             }
  304.  
  305.             // Bonus when behind a pawn
  306.             if (    relative_rank(Us, s) < RANK_5
  307.                 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
  308.                 score += MinorBehindPawn;
  309.  
  310.             // Penalty for pawns on the same color square as the bishop
  311.             if (Pt == BISHOP)
  312.                 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
  313.  
  314.             // An important Chess960 pattern: A cornered bishop blocked by a friendly
  315.             // pawn diagonally in front of it is a very serious problem, especially
  316.             // when that pawn is also blocked.
  317.             if (   Pt == BISHOP
  318.                 && pos.is_chess960()
  319.                 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
  320.             {
  321.                 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
  322.                 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
  323.                     score -= !pos.empty(s + d + pawn_push(Us))                ? TrappedBishopA1H1 * 4
  324.                             : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
  325.                                                                               : TrappedBishopA1H1;
  326.             }
  327.         }
  328.  
  329.         if (Pt == ROOK)
  330.         {
  331.             // Bonus for aligning with enemy pawns on the same rank/file
  332.             if (relative_rank(Us, s) >= RANK_5)
  333.             {
  334.                 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
  335.                 if (alignedPawns)
  336.                     score += RookOnPawn * popcount<Max15>(alignedPawns);
  337.             }
  338.  
  339.             // Bonus when on an open or semi-open file
  340.             if (ei.pi->semiopen_file(Us, file_of(s)))
  341.                 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
  342.  
  343.             // Penalize when trapped by the king, even more if the king cannot castle
  344.             else if (mob <= 3)
  345.             {
  346.                 Square ksq = pos.square<KING>(Us);
  347.  
  348.                 if (   ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
  349.                     && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
  350.                     && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
  351.                     score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
  352.             }
  353.         }
  354.     }
  355.  
  356.     if (DoTrace)
  357.         Trace::add(Pt, Us, score);
  358.  
  359.     // Recursively call evaluate_pieces() of next piece type until KING is excluded
  360.     return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
  361.   }
  362.  
  363.   template<>
  364.   Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
  365.   template<>
  366.   Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
  367.  
  368.  
  369.   // evaluate_king() assigns bonuses and penalties to a king of a given color
  370.  
  371.   template<Color Us, bool DoTrace>
  372.   Score evaluate_king(const Position& pos, const EvalInfo& ei) {
  373.  
  374.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  375.  
  376.     Bitboard undefended, b, b1, b2, safe;
  377.     int attackUnits;
  378.     const Square ksq = pos.square<KING>(Us);
  379.  
  380.     // King shelter and enemy pawns storm
  381.     Score score = ei.pi->king_safety<Us>(pos, ksq);
  382.  
  383.     // Main king safety evaluation
  384.     if (ei.kingAttackersCount[Them])
  385.     {
  386.         // Find the attacked squares around the king which have no defenders
  387.         // apart from the king itself.
  388.         undefended =  ei.attackedBy[Them][ALL_PIECES]
  389.                     & ei.attackedBy[Us][KING]
  390.                     & ~(  ei.attackedBy[Us][PAWN]   | ei.attackedBy[Us][KNIGHT]
  391.                         | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
  392.                         | ei.attackedBy[Us][QUEEN]);
  393.  
  394.         // Initialize the 'attackUnits' variable, which is used later on as an
  395.         // index into the KingDanger[] array. The initial value is based on the
  396.         // number and types of the enemy's attacking pieces, the number of
  397.         // attacked and undefended squares around our king and the quality of
  398.         // the pawn shelter (current 'score' value).
  399.         attackUnits =  std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
  400.                      +  9 * ei.kingAdjacentZoneAttacksCount[Them]
  401.                      + 27 * popcount<Max15>(undefended)
  402.                      + 11 * !!ei.pinnedPieces[Us]
  403.                      - 64 * !pos.count<QUEEN>(Them)
  404.                      - mg_value(score) / 8;
  405.  
  406.         // Analyse the enemy's safe queen contact checks. Firstly, find the
  407.         // undefended squares around the king reachable by the enemy queen...
  408.         b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
  409.         if (b)
  410.         {
  411.             // ...and then remove squares not supported by another enemy piece
  412.             b &=  ei.attackedBy[Them][PAWN]   | ei.attackedBy[Them][KNIGHT]
  413.                 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
  414.                 | ei.attackedBy[Them][KING];
  415.  
  416.             if (b)
  417.                 attackUnits += QueenContactCheck * popcount<Max15>(b);
  418.         }
  419.  
  420.         // Analyse the enemy's safe distance checks for sliders and knights
  421.         safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
  422.  
  423.         b1 = pos.attacks_from<ROOK  >(ksq) & safe;
  424.         b2 = pos.attacks_from<BISHOP>(ksq) & safe;
  425.  
  426.         // Enemy queen safe checks
  427.         b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
  428.         if (b)
  429.         {
  430.             attackUnits += QueenCheck * popcount<Max15>(b);
  431.             score -= Checked;
  432.         }
  433.  
  434.         // Enemy rooks safe checks
  435.         b = b1 & ei.attackedBy[Them][ROOK];
  436.         if (b)
  437.         {
  438.             attackUnits += RookCheck * popcount<Max15>(b);
  439.             score -= Checked;
  440.         }
  441.  
  442.         // Enemy bishops safe checks
  443.         b = b2 & ei.attackedBy[Them][BISHOP];
  444.         if (b)
  445.         {
  446.             attackUnits += BishopCheck * popcount<Max15>(b);
  447.             score -= Checked;
  448.         }
  449.  
  450.         // Enemy knights safe checks
  451.         b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
  452.         if (b)
  453.         {
  454.             attackUnits += KnightCheck * popcount<Max15>(b);
  455.             score -= Checked;
  456.         }
  457.  
  458.         // Finally, extract the king danger score from the KingDanger[]
  459.         // array and subtract the score from the evaluation.
  460.         score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
  461.     }
  462.  
  463.     if (DoTrace)
  464.         Trace::add(KING, Us, score);
  465.  
  466.     return score;
  467.   }
  468.  
  469.  
  470.   // evaluate_threats() assigns bonuses according to the types of the attacking
  471.   // and the attacked pieces.
  472.  
  473.   template<Color Us, bool DoTrace>
  474.   Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
  475.  
  476.     const Color Them        = (Us == WHITE ? BLACK    : WHITE);
  477.     const Square Up         = (Us == WHITE ? DELTA_N  : DELTA_S);
  478.     const Square Left       = (Us == WHITE ? DELTA_NW : DELTA_SE);
  479.     const Square Right      = (Us == WHITE ? DELTA_NE : DELTA_SW);
  480.     const Bitboard TRank2BB = (Us == WHITE ? Rank2BB  : Rank7BB);
  481.     const Bitboard TRank7BB = (Us == WHITE ? Rank7BB  : Rank2BB);
  482.  
  483.     enum { Minor, Rook };
  484.  
  485.     Bitboard b, weak, defended, safeThreats;
  486.     Score score = SCORE_ZERO;
  487.  
  488.     // Non-pawn enemies attacked by a pawn
  489.     weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
  490.  
  491.     if (weak)
  492.     {
  493.         b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
  494.                                     | ei.attackedBy[Us][ALL_PIECES]);
  495.  
  496.         safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
  497.  
  498.         if (weak ^ safeThreats)
  499.             score += ThreatByHangingPawn;
  500.  
  501.         while (safeThreats)
  502.             score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
  503.     }
  504.  
  505.     // Non-pawn enemies defended by a pawn
  506.     defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
  507.  
  508.     // Enemies not defended by a pawn and under our attack
  509.     weak =   pos.pieces(Them)
  510.           & ~ei.attackedBy[Them][PAWN]
  511.           &  ei.attackedBy[Us][ALL_PIECES];
  512.  
  513.     // Add a bonus according to the kind of attacking pieces
  514.     if (defended | weak)
  515.     {
  516.         b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
  517.         while (b)
  518.             score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
  519.  
  520.         b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
  521.         while (b)
  522.             score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
  523.  
  524.         b = weak & ~ei.attackedBy[Them][ALL_PIECES];
  525.         if (b)
  526.             score += Hanging * popcount<Max15>(b);
  527.  
  528.         b = weak & ei.attackedBy[Us][KING];
  529.         if (b)
  530.             score += ThreatByKing[more_than_one(b)];
  531.     }
  532.  
  533.     // Bonus if some pawns can safely push and attack an enemy piece
  534.     b = pos.pieces(Us, PAWN) & ~TRank7BB;
  535.     b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
  536.  
  537.     b &=  ~pos.pieces()
  538.         & ~ei.attackedBy[Them][PAWN]
  539.         & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
  540.  
  541.     b =  (shift_bb<Left>(b) | shift_bb<Right>(b))
  542.        &  pos.pieces(Them)
  543.        & ~ei.attackedBy[Us][PAWN];
  544.  
  545.     if (b)
  546.         score += ThreatByPawnPush * popcount<Max15>(b);
  547.  
  548.     if (DoTrace)
  549.         Trace::add(THREAT, Us, score);
  550.  
  551.     return score;
  552.   }
  553.  
  554.  
  555.   // evaluate_passed_pawns() evaluates the passed pawns of the given color
  556.  
  557.   template<Color Us, bool DoTrace>
  558.   Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
  559.  
  560.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  561.  
  562.     Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
  563.     Score score = SCORE_ZERO;
  564.  
  565.     b = ei.pi->passed_pawns(Us);
  566.  
  567.     while (b)
  568.     {
  569.         Square s = pop_lsb(&b);
  570.  
  571.         assert(pos.pawn_passed(Us, s));
  572.  
  573.         int r = relative_rank(Us, s) - RANK_2;
  574.         int rr = r * (r - 1);
  575.  
  576.         Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
  577.  
  578.         if (rr)
  579.         {
  580.             Square blockSq = s + pawn_push(Us);
  581.  
  582.             // Adjust bonus based on the king's proximity
  583.             ebonus +=  distance(pos.square<KING>(Them), blockSq) * 5 * rr
  584.                      - distance(pos.square<KING>(Us  ), blockSq) * 2 * rr;
  585.  
  586.             // If blockSq is not the queening square then consider also a second push
  587.             if (relative_rank(Us, blockSq) != RANK_8)
  588.                 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
  589.  
  590.             // If the pawn is free to advance, then increase the bonus
  591.             if (pos.empty(blockSq))
  592.             {
  593.                 // If there is a rook or queen attacking/defending the pawn from behind,
  594.                 // consider all the squaresToQueen. Otherwise consider only the squares
  595.                 // in the pawn's path attacked or occupied by the enemy.
  596.                 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
  597.  
  598.                 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
  599.  
  600.                 if (!(pos.pieces(Us) & bb))
  601.                     defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
  602.  
  603.                 if (!(pos.pieces(Them) & bb))
  604.                     unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
  605.  
  606.                 // If there aren't any enemy attacks, assign a big bonus. Otherwise
  607.                 // assign a smaller bonus if the block square isn't attacked.
  608.                 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
  609.  
  610.                 // If the path to the queen is fully defended, assign a big bonus.
  611.                 // Otherwise assign a smaller bonus if the block square is defended.
  612.                 if (defendedSquares == squaresToQueen)
  613.                     k += 6;
  614.  
  615.                 else if (defendedSquares & blockSq)
  616.                     k += 4;
  617.  
  618.                 mbonus += k * rr * 3 / 4, ebonus += k * rr;
  619.             }
  620.             else if (pos.pieces(Us) & blockSq)
  621.                 mbonus += (rr * 3 + r * 2 + 3) * 3 / 4, ebonus += rr + r * 2;
  622.         } // rr != 0
  623.  
  624.         if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
  625.             ebonus += ebonus / 4;
  626.  
  627.         score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
  628.     }
  629.  
  630.     if (DoTrace)
  631.         Trace::add(PASSED, Us, score);
  632.  
  633.     // Add the scores to the middlegame and endgame eval
  634.     return score;
  635.   }
  636.  
  637.  
  638.   // evaluate_space() computes the space evaluation for a given side. The
  639.   // space evaluation is a simple bonus based on the number of safe squares
  640.   // available for minor pieces on the central four files on ranks 2--4. Safe
  641.   // squares one, two or three squares behind a friendly pawn are counted
  642.   // twice. Finally, the space bonus is multiplied by a weight. The aim is to
  643.   // improve play on game opening.
  644.   template<Color Us>
  645.   Score evaluate_space(const Position& pos, const EvalInfo& ei) {
  646.  
  647.     const Color Them = (Us == WHITE ? BLACK : WHITE);
  648.     const Bitboard SpaceMask =
  649.       Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
  650.                   : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
  651.  
  652.     // Find the safe squares for our pieces inside the area defined by
  653.     // SpaceMask. A square is unsafe if it is attacked by an enemy
  654.     // pawn, or if it is undefended and attacked by an enemy piece.
  655.     Bitboard safe =   SpaceMask
  656.                    & ~pos.pieces(Us, PAWN)
  657.                    & ~ei.attackedBy[Them][PAWN]
  658.                    & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
  659.  
  660.     // Find all squares which are at most three squares behind some friendly pawn
  661.     Bitboard behind = pos.pieces(Us, PAWN);
  662.     behind |= (Us == WHITE ? behind >>  8 : behind <<  8);
  663.     behind |= (Us == WHITE ? behind >> 16 : behind << 16);
  664.  
  665.     // Since SpaceMask[Us] is fully on our half of the board...
  666.     assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
  667.  
  668.     // ...count safe + (behind & safe) with a single popcount
  669.     int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
  670.     int weight =  pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
  671.                 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
  672.  
  673.     return make_score(bonus * weight * weight * 2 / 11, 0);
  674.   }
  675.  
  676.  
  677.   // evaluate_initiative() computes the initiative correction value for the
  678.   // position, i.e., second order bonus/malus based on the known attacking/defending
  679.   // status of the players.
  680.   Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
  681.  
  682.     int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
  683.     int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
  684.  
  685.     // Compute the initiative bonus for the attacking side
  686.     int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
  687.  
  688.     // Now apply the bonus: note that we find the attacking side by extracting
  689.     // the sign of the endgame value, and that we carefully cap the bonus so
  690.     // that the endgame score will never be divided by more than two.
  691.     int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
  692.  
  693.     return make_score(0, value);
  694.   }
  695.  
  696.  
  697.   // evaluate_scale_factor() computes the scale factor for the winning side
  698.   ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Score score) {
  699.  
  700.     Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
  701.     ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
  702.  
  703.     // If we don't already have an unusual scale factor, check for certain
  704.     // types of endgames, and use a lower scale for those.
  705.     if (    ei.me->game_phase() < PHASE_MIDGAME
  706.         && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
  707.     {
  708.         if (pos.opposite_bishops())
  709.         {
  710.             // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
  711.             // is almost a draw, in case of KBP vs KB, it is even more a draw.
  712.             if (   pos.non_pawn_material(WHITE) == BishopValueMg
  713.                 && pos.non_pawn_material(BLACK) == BishopValueMg)
  714.                 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
  715.  
  716.             // Endgame with opposite-colored bishops, but also other pieces. Still
  717.             // a bit drawish, but not as drawish as with only the two bishops.
  718.             else
  719.                 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
  720.         }
  721.         // Endings where weaker side can place his king in front of the opponent's
  722.         // pawns are drawish.
  723.         else if (    abs(eg_value(score)) <= BishopValueEg
  724.                  &&  ei.pi->pawn_span(strongSide) <= 1
  725.                  && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
  726.             sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
  727.     }
  728.  
  729.     return sf;
  730.   }
  731.  
  732. } // namespace
  733.  
  734.  
  735. /// evaluate() is the main evaluation function. It returns a static evaluation
  736. /// of the position from the point of view of the side to move.
  737.  
  738. template<bool DoTrace>
  739. Value Eval::evaluate(const Position& pos) {
  740.  
  741.   assert(!pos.checkers());
  742.  
  743.   EvalInfo ei;
  744.   Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
  745.  
  746.   // Initialize score by reading the incrementally updated scores included in
  747.   // the position object (material + piece square tables). Score is computed
  748.   // internally from the white point of view.
  749.   score = pos.psq_score();
  750.  
  751.   // Probe the material hash table
  752.   ei.me = Material::probe(pos);
  753.   score += ei.me->imbalance();
  754.  
  755.   // If we have a specialized evaluation function for the current material
  756.   // configuration, call it and return.
  757.   if (ei.me->specialized_eval_exists())
  758.       return ei.me->evaluate(pos);
  759.  
  760.   // Probe the pawn hash table
  761.   ei.pi = Pawns::probe(pos);
  762.   score += ei.pi->pawns_score();
  763.  
  764.   // Initialize attack and king safety bitboards
  765.   ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
  766.   eval_init<WHITE>(pos, ei);
  767.   eval_init<BLACK>(pos, ei);
  768.  
  769.   // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
  770.   Bitboard blockedPawns[] = {
  771.     pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
  772.     pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
  773.   };
  774.  
  775.   // Do not include in mobility area squares protected by enemy pawns, or occupied
  776.   // by our blocked pawns or king.
  777.   Bitboard mobilityArea[] = {
  778.     ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
  779.     ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
  780.   };
  781.  
  782.   // Evaluate all pieces but king and pawns
  783.   score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
  784.   score += mobility[WHITE] - mobility[BLACK];
  785.  
  786.   // Evaluate kings after all other pieces because we need full attack
  787.   // information when computing the king safety evaluation.
  788.   score +=  evaluate_king<WHITE, DoTrace>(pos, ei)
  789.           - evaluate_king<BLACK, DoTrace>(pos, ei);
  790.  
  791.   // Evaluate tactical threats, we need full attack information including king
  792.   score +=  evaluate_threats<WHITE, DoTrace>(pos, ei)
  793.           - evaluate_threats<BLACK, DoTrace>(pos, ei);
  794.  
  795.   // Evaluate passed pawns, we need full attack information including king
  796.   score +=  evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
  797.           - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
  798.  
  799.   // If both sides have only pawns, score for potential unstoppable pawns
  800.   if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
  801.   {
  802.       Bitboard b;
  803.       if ((b = ei.pi->passed_pawns(WHITE)) != 0)
  804.           score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
  805.  
  806.       if ((b = ei.pi->passed_pawns(BLACK)) != 0)
  807.           score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
  808.   }
  809.  
  810.   // Evaluate space for both sides, only during opening
  811.   if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
  812.       score +=  evaluate_space<WHITE>(pos, ei)
  813.               - evaluate_space<BLACK>(pos, ei);
  814.  
  815.   // Evaluate position potential for the winning side
  816.   score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
  817.  
  818.   // Evaluate scale factor for the winning side
  819.   ScaleFactor sf = evaluate_scale_factor(pos, ei, score);
  820.  
  821.   // Interpolate between a middlegame and a (scaled by 'sf') endgame score
  822.   Value v =  mg_value(score) * int(ei.me->game_phase())
  823.            + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
  824.  
  825.   v /= int(PHASE_MIDGAME);
  826.  
  827.   // In case of tracing add all remaining individual evaluation terms
  828.   if (DoTrace)
  829.   {
  830.       Trace::add(MATERIAL, pos.psq_score());
  831.       Trace::add(IMBALANCE, ei.me->imbalance());
  832.       Trace::add(PAWN, ei.pi->pawns_score());
  833.       Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
  834.       Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
  835.                       , evaluate_space<BLACK>(pos, ei));
  836.       Trace::add(TOTAL, score);
  837.   }
  838.  
  839.   return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
  840. }
  841.  
  842. // Explicit template instantiations
  843. template Value Eval::evaluate<true >(const Position&);
  844. template Value Eval::evaluate<false>(const Position&);
  845.  
  846.  
  847. /// trace() is like evaluate(), but instead of returning a value, it returns
  848. /// a string (suitable for outputting to stdout) that contains the detailed
  849. /// descriptions and values of each evaluation term. Useful for debugging.
  850.  
  851. std::string Eval::trace(const Position& pos) {
  852.  
  853.   std::memset(scores, 0, sizeof(scores));
  854.  
  855.   Value v = evaluate<true>(pos);
  856.   v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
  857.  
  858.   std::stringstream ss;
  859.   ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
  860.      << "      Eval term |    White    |    Black    |    Total    \n"
  861.      << "                |   MG    EG  |   MG    EG  |   MG    EG  \n"
  862.      << "----------------+-------------+-------------+-------------\n"
  863.      << "       Material | " << Term(MATERIAL)
  864.      << "      Imbalance | " << Term(IMBALANCE)
  865.      << "          Pawns | " << Term(PAWN)
  866.      << "        Knights | " << Term(KNIGHT)
  867.      << "         Bishop | " << Term(BISHOP)
  868.      << "          Rooks | " << Term(ROOK)
  869.      << "         Queens | " << Term(QUEEN)
  870.      << "       Mobility | " << Term(MOBILITY)
  871.      << "    King safety | " << Term(KING)
  872.      << "        Threats | " << Term(THREAT)
  873.      << "   Passed pawns | " << Term(PASSED)
  874.      << "          Space | " << Term(SPACE)
  875.      << "----------------+-------------+-------------+-------------\n"
  876.      << "          Total | " << Term(TOTAL);
  877.  
  878.   ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
  879.  
  880.   return ss.str();
  881. }
  882.  
  883.  
  884. /// init() computes evaluation weights, usually at startup
  885.  
  886. void Eval::init() {
  887.  
  888.   const int MaxSlope = 322;
  889.   const int Peak = 47410;
  890.   int t = 0;
  891.  
  892.   for (int i = 0; i < 400; ++i)
  893.   {
  894.       t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
  895.       KingDanger[i] = make_score(t * 268 / 7700, 0);
  896.   }
  897. }
  898.