Ejemplo n.º 1
0
        public static Score evaluate(Position pos, Pawns.Entry e, Color Us)
        {
            Color  Them  = (Us == ColorS.WHITE ? ColorS.BLACK : ColorS.WHITE);
            Square Up    = (Us == ColorS.WHITE ? SquareS.DELTA_N : SquareS.DELTA_S);
            Square Right = (Us == ColorS.WHITE ? SquareS.DELTA_NE : SquareS.DELTA_SW);
            Square Left  = (Us == ColorS.WHITE ? SquareS.DELTA_NW : SquareS.DELTA_SE);

            Bitboard b, p, doubled;
            Square   s;
            File     f;
            Rank     r;
            bool     passed, isolated, opposed, connected, backward, candidate, unsupported;
            Score    value = ScoreS.SCORE_ZERO;

            Square[] pl    = pos.list(Us, PieceTypeS.PAWN);
            int      plPos = 0;

            Bitboard ourPawns   = pos.pieces_color_piecetype(Us, PieceTypeS.PAWN);
            Bitboard theirPawns = pos.pieces_color_piecetype(Them, PieceTypeS.PAWN);

            e.passedPawns[Us]   = e.candidatePawns[Us] = 0;
            e.kingSquares[Us]   = SquareS.SQ_NONE;
            e.semiopenFiles[Us] = 0xFF;
            e.pawnAttacks[Us]   = BitBoard.shift_bb(ourPawns, Right) | BitBoard.shift_bb(ourPawns, Left);
            e.pawnsOnSquares[Us][ColorS.BLACK] = Bitcount.popcount_Max15(ourPawns & BitBoard.DarkSquares);
            e.pawnsOnSquares[Us][ColorS.WHITE] = pos.count(Us, PieceTypeS.PAWN) - e.pawnsOnSquares[Us][ColorS.BLACK];

            // Loop through all pawns of the current color and score each pawn
            while ((s = pl[plPos++]) != SquareS.SQ_NONE)
            {
                Debug.Assert(pos.piece_on(s) == Types.make_piece(Us, PieceTypeS.PAWN));

                f = Types.file_of(s);


                // This file cannot be semi-open
                e.semiopenFiles[Us] &= ~(1 << f);

                // Previous rank
                p = BitBoard.rank_bb_square(s - Types.pawn_push(Us));

                // Our rank plus previous one
                b = BitBoard.rank_bb_square(s) | p;

                // Flag the pawn as passed, isolated, doubled,
                // unsupported or connected (but not the backward one).
                connected   = (ourPawns & BitBoard.adjacent_files_bb(f) & b) != 0;
                unsupported = (0 == (ourPawns & BitBoard.adjacent_files_bb(f) & p));
                isolated    = (0 == (ourPawns & BitBoard.adjacent_files_bb(f)));
                doubled     = ourPawns & BitBoard.forward_bb(Us, s);
                opposed     = (theirPawns & BitBoard.forward_bb(Us, s)) != 0;
                passed      = (0 == (theirPawns & BitBoard.passed_pawn_mask(Us, s)));

                // Test for backward pawn.
                // If the pawn is passed, isolated, or connected it cannot be
                // backward. If there are friendly pawns behind on adjacent files
                // or if it can capture an enemy pawn it cannot be backward either.
                if ((passed | isolated | connected) ||
                    (ourPawns & BitBoard.pawn_attack_span(Them, s)) != 0 ||
                    (pos.attacks_from_pawn(s, Us) & theirPawns) != 0)
                {
                    backward = false;
                }
                else
                {
                    // We now know that there are no friendly pawns beside or behind this
                    // pawn on adjacent files. We now check whether the pawn is
                    // backward by looking in the forward direction on the adjacent
                    // files, and picking the closest pawn there.
                    b = BitBoard.pawn_attack_span(Us, s) & (ourPawns | theirPawns);
                    b = BitBoard.pawn_attack_span(Us, s) & BitBoard.rank_bb_square(BitBoard.backmost_sq(Us, b));

                    // If we have an enemy pawn in the same or next rank, the pawn is
                    // backward because it cannot advance without being captured.
                    backward = ((b | BitBoard.shift_bb(b, Up)) & theirPawns) != 0;
                }

                Debug.Assert(opposed | passed | (BitBoard.pawn_attack_span(Us, s) & theirPawns) != 0);

                // A not-passed pawn is a candidate to become passed, if it is free to
                // advance and if the number of friendly pawns beside or behind this
                // pawn on adjacent files is higher than or equal to the number of
                // enemy pawns in the forward direction on the adjacent files.
                candidate = !(opposed | passed | backward | isolated) &&
                            (b = BitBoard.pawn_attack_span(Them, s + Types.pawn_push(Us)) & ourPawns) != 0 &&
                            Bitcount.popcount_Max15(b) >= Bitcount.popcount_Max15(BitBoard.pawn_attack_span(Us, s) & theirPawns);

                // Passed pawns will be properly scored in evaluation because we need
                // full attack info to evaluate passed pawns. Only the frontmost passed
                // pawn on each file is considered a true passed pawn.
                if (passed && 0 == doubled)
                {
                    e.passedPawns[Us] |= BitBoard.SquareBB[s];
                }

                // Score this pawn
                if (isolated)
                {
                    value -= Isolated[opposed ? 1 : 0][f];
                }

                if (unsupported && !isolated)
                {
                    value -= UnsupportedPawnPenalty;
                }

                if (doubled != 0)
                {
                    value -= Types.divScore(Doubled[f], BitBoard.rank_distance(s, BitBoard.lsb(doubled)));
                }

                if (backward)
                {
                    value -= Backward[opposed ? 1 : 0][f];
                }

                if (connected)
                {
                    value += Connected[f][Types.relative_rank_square(Us, s)];
                }

                if (candidate)
                {
                    value += CandidatePassed[Types.relative_rank_square(Us, s)];

                    if (0 == doubled)
                    {
                        e.candidatePawns[Us] |= BitBoard.SquareBB[s];
                    }
                }
            }

            // In endgame it's better to have pawns on both wings. So give a bonus according
            // to file distance between left and right outermost pawns.
            if (pos.count(Us, PieceTypeS.PAWN) > 1)
            {
                b      = (Bitboard)(e.semiopenFiles[Us] ^ 0xFF);
                value += PawnsFileSpan * (BitBoard.msb(b) - BitBoard.lsb(b));
            }

            return(value);
        }