/// Mate with KX vs K. This function is used to evaluate positions with
/// king and plenty of material vs a lone king. It simply gives the
/// attacking side a bonus for driving the defending king towards the edge
/// of the board, and for keeping the distance between the two kings small.
public Value KXK(Position pos)
{
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 0));
Debug.Assert(0 == pos.checkers()); // Eval is never called when in check
// Stalemate detection with lone king
if (pos.side_to_move() == weakSide && 0 == (new MoveList(pos, GenTypeS.LEGAL)).size())
{
return(ValueS.VALUE_DRAW);
}
Square winnerKSq = pos.king_square(strongSide);
Square loserKSq = pos.king_square(weakSide);
Value result = pos.non_pawn_material(strongSide)
+ pos.count(strongSide, PieceTypeS.PAWN) * ValueS.PawnValueEg
+ PushToEdges[loserKSq]
+ PushClose[BitBoard.square_distance(winnerKSq, loserKSq)];
if (pos.count(strongSide, PieceTypeS.QUEEN) != 0 ||
pos.count(strongSide, PieceTypeS.ROOK) != 0 ||
(pos.count(strongSide, PieceTypeS.BISHOP) != 0 && pos.count(strongSide, PieceTypeS.KNIGHT) != 0) ||
pos.bishop_pair(strongSide))
{
result += ValueS.VALUE_KNOWN_WIN;
}
return(strongSide == pos.side_to_move() ? result : -result);
}
public KPKPosition(uint idx)
{
wksq = (Square)((idx >> 0) & 0x3F);
bksq = (Square)((idx >> 6) & 0x3F);
us = (Color)((idx >> 12) & 0x01);
psq = Types.make_square((File)((idx >> 13) & 0x03), (Rank)(RankS.RANK_7 - (idx >> 15)));
result = Result.UNKNOWN;
// Check if two pieces are on the same square or if a king can be captured
if (BitBoard.square_distance(wksq, bksq) <= 1 ||
wksq == psq ||
bksq == psq ||
(us == ColorS.WHITE && (BitBoard.StepAttacksBB[PieceTypeS.PAWN][psq] & BitBoard.SquareBB[bksq]) != 0))
{
result = Result.INVALID;
}
else if (us == ColorS.WHITE)
{
// Immediate win if pawn can be promoted without getting captured
if (Types.rank_of(psq) == RankS.RANK_7 &&
wksq != psq + SquareS.DELTA_N &&
(BitBoard.square_distance(bksq, psq + SquareS.DELTA_N) > 1 ||
(BitBoard.StepAttacksBB[PieceTypeS.KING][wksq] & BitBoard.SquareBB[psq + SquareS.DELTA_N]) != 0))
{
result = Result.WIN;
}
}
// Immediate draw if it is a stalemate or a king captures undefended pawn
else if (0 == (BitBoard.StepAttacksBB[PieceTypeS.KING][bksq] & ~(BitBoard.StepAttacksBB[PieceTypeS.KING][wksq] | BitBoard.StepAttacksBB[PieceTypeS.PAWN][psq])) ||
(BitBoard.StepAttacksBB[PieceTypeS.KING][bksq] & BitBoard.SquareBB[psq] & ~BitBoard.StepAttacksBB[PieceTypeS.KING][wksq]) != 0)
{
result = Result.DRAW;
}
}
/// KBP vs KB. There are two rules: if the defending king is somewhere along the
/// path of the pawn, and the square of the king is not of the same color as the
/// stronger side's bishop, it's a draw. If the two bishops have opposite color,
/// it's almost always a draw.
public ScaleFactor KBPKB(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.BishopValueMg, 1));
Debug.Assert(verify_material(pos, weakSide, ValueS.BishopValueMg, 0));
Square pawnSq = pos.list(strongSide, PieceTypeS.PAWN)[0];
Square strongerBishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
Square weakerBishopSq = pos.list(weakSide, PieceTypeS.BISHOP)[0];
Square weakerKingSq = pos.king_square(weakSide);
// Case 1: Defending king blocks the pawn, and cannot be driven away
if (Types.file_of(weakerKingSq) == Types.file_of(pawnSq) &&
Types.relative_rank_square(strongSide, pawnSq) < Types.relative_rank_square(strongSide, weakerKingSq) &&
(Types.opposite_colors(weakerKingSq, strongerBishopSq) ||
Types.relative_rank_square(strongSide, weakerKingSq) <= RankS.RANK_6))
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
// Case 2: Opposite colored bishops
if (Types.opposite_colors(strongerBishopSq, weakerBishopSq))
{
// We assume that the position is drawn in the following three situations:
//
// a. The pawn is on rank 5 or further back.
// b. The defending king is somewhere in the pawn's path.
// c. The defending bishop attacks some square along the pawn's path,
// and is at least three squares away from the pawn.
//
// These rules are probably not perfect, but in practice they work
// reasonably well.
if (Types.relative_rank_square(strongSide, pawnSq) <= RankS.RANK_5)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
else
{
Bitboard path = BitBoard.forward_bb(strongSide, pawnSq);
if ((path & pos.pieces_color_piecetype(weakSide, PieceTypeS.KING)) != 0)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
if (((pos.attacks_from_square_piecetype(weakerBishopSq, PieceTypeS.BISHOP) & path) != 0) &&
BitBoard.square_distance(weakerBishopSq, pawnSq) >= 3)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
}
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
/// KR vs KN. The attacking side has slightly better winning chances than
/// in KR vs KB, particularly if the king and the knight are far apart.
public Value KRKN(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.RookValueMg, 0));
Debug.Assert(verify_material(pos, weakSide, ValueS.KnightValueMg, 0));
Square bksq = pos.king_square(weakSide);
Square bnsq = pos.list(weakSide, PieceTypeS.KNIGHT)[0];
Value result = (PushToEdges[bksq] + PushAway[BitBoard.square_distance(bksq, bnsq)]);
return(strongSide == pos.side_to_move() ? result : -result);
}
/// KNP vs KB. If knight can block bishop from taking pawn, it's a win.
/// Otherwise the position is drawn.
public ScaleFactor KNPKB(Position pos)
{
Square pawnSq = pos.list(strongSide, PieceTypeS.PAWN)[0];
Square bishopSq = pos.list(weakSide, PieceTypeS.BISHOP)[0];
Square weakerKingSq = pos.king_square(weakSide);
// King needs to get close to promoting pawn to prevent knight from blocking.
// Rules for this are very tricky, so just approximate.
if ((BitBoard.forward_bb(strongSide, pawnSq) & pos.attacks_from_square_piecetype(bishopSq, PieceTypeS.BISHOP)) != 0)
{
return(BitBoard.square_distance(weakerKingSq, pawnSq));
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
/// KQ vs KR. This is almost identical to KX vs K: We give the attacking
/// king a bonus for having the kings close together, and for forcing the
/// defending king towards the edge. If we also take care to avoid null move for
/// the defending side in the search, this is usually sufficient to win KQ vs KR.
public Value KQKR(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.QueenValueMg, 0));
Debug.Assert(verify_material(pos, weakSide, ValueS.RookValueMg, 0));
Square winnerKSq = pos.king_square(strongSide);
Square loserKSq = pos.king_square(weakSide);
Value result = ValueS.QueenValueEg
- ValueS.RookValueEg
+ PushToEdges[loserKSq]
+ PushClose[BitBoard.square_distance(winnerKSq, loserKSq)];
return(strongSide == pos.side_to_move() ? result : -result);
}
public ScaleFactor KRPKB(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.RookValueMg, 1));
Debug.Assert(verify_material(pos, weakSide, ValueS.BishopValueMg, 0));
// Test for a rook pawn
if ((pos.pieces_piecetype(PieceTypeS.PAWN) & (BitBoard.FileABB | BitBoard.FileHBB)) != 0)
{
Square ksq = pos.king_square(weakSide);
Square bsq = pos.list(weakSide, PieceTypeS.BISHOP)[0];
Square psq = pos.list(strongSide, PieceTypeS.PAWN)[0];
Rank rk = Types.relative_rank_square(strongSide, psq);
Square push = Types.pawn_push(strongSide);
// If the pawn is on the 5th rank and the pawn (currently) is on
// the same color square as the bishop then there is a chance of
// a fortress. Depending on the king position give a moderate
// reduction or a stronger one if the defending king is near the
// corner but not trapped there.
if (rk == RankS.RANK_5 && !Types.opposite_colors(bsq, psq))
{
int d = BitBoard.square_distance(psq + 3 * push, ksq);
if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongSide) + 2 * push))
{
return(24);
}
else
{
return(48);
}
}
// When the pawn has moved to the 6th rank we can be fairly sure
// it's drawn if the bishop attacks the square in front of the
// pawn from a reasonable distance and the defending king is near
// the corner
if (rk == RankS.RANK_6 &&
BitBoard.square_distance(psq + 2 * push, ksq) <= 1 &&
(BitBoard.PseudoAttacks[PieceTypeS.BISHOP][bsq] & BitBoard.SquareBB[(psq + push)]) != 0 &&
BitBoard.file_distance(bsq, psq) >= 2)
{
return(8);
}
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
/// KNP vs K. There is a single rule: if the pawn is a rook pawn on the 7th rank
/// and the defending king prevents the pawn from advancing, the position is drawn.
public ScaleFactor KNPK(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.KnightValueMg, 1));
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
Square pawnSq = normalize(pos, strongSide, pos.list(strongSide, PieceTypeS.PAWN)[0]);
Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
if (pawnSq == SquareS.SQ_A7 && BitBoard.square_distance(SquareS.SQ_A8, weakKingSq) <= 1)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
/// KR vs KP. This is a somewhat tricky endgame to evaluate precisely without
/// a bitbase. The function below returns drawish scores when the pawn is
/// far advanced with support of the king, while the attacking king is far
/// away.
public Value KRKP(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.RookValueMg, 0));
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 1));
Square wksq = Types.relative_square(strongSide, pos.king_square(strongSide));
Square bksq = Types.relative_square(strongSide, pos.king_square(weakSide));
Square rsq = Types.relative_square(strongSide, pos.list(strongSide, PieceTypeS.ROOK)[0]);
Square psq = Types.relative_square(strongSide, pos.list(weakSide, PieceTypeS.PAWN)[0]);
Square queeningSq = Types.make_square(Types.file_of(psq), RankS.RANK_1);
Value result;
// If the stronger side's king is in front of the pawn, it's a win
if (wksq < psq && Types.file_of(wksq) == Types.file_of(psq))
{
result = ValueS.RookValueEg - (BitBoard.square_distance(wksq, psq));
}
// If the weaker side's king is too far from the pawn and the rook,
// it's a win
else if (BitBoard.square_distance(bksq, psq) >= 3 + ((pos.side_to_move() == weakSide)?1:0) &&
BitBoard.square_distance(bksq, rsq) >= 3)
{
result = ValueS.RookValueEg - (BitBoard.square_distance(wksq, psq));
}
// If the pawn is far advanced and supported by the defending king,
// the position is drawish
else if (Types.rank_of(bksq) <= RankS.RANK_3 &&
BitBoard.square_distance(bksq, psq) == 1 &&
Types.rank_of(wksq) >= RankS.RANK_4 &&
BitBoard.square_distance(wksq, psq) > 2 + ((pos.side_to_move() == strongSide)?1:0))
{
result = 80 - 8 * BitBoard.square_distance(wksq, psq);
}
else
{
result = (Value)(200) - 8 * (BitBoard.square_distance(wksq, psq + SquareS.DELTA_S)
- BitBoard.square_distance(bksq, psq + SquareS.DELTA_S)
- BitBoard.square_distance(psq, queeningSq));
}
return(strongSide == pos.side_to_move() ? result : -result);
}
/// KQ vs KP. In general, this is a win for the stronger side, but there are a
/// few important exceptions. A pawn on 7th rank and on the A,C,F or H files
/// with a king positioned next to it can be a draw, so in that case, we only
/// use the distance between the kings.
public Value KQKP(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.QueenValueMg, 0));
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 1));
Square winnerKSq = pos.king_square(strongSide);
Square loserKSq = pos.king_square(weakSide);
Square pawnSq = pos.list(weakSide, PieceTypeS.PAWN)[0];
Value result = (PushClose[BitBoard.square_distance(winnerKSq, loserKSq)]);
if (Types.relative_rank_square(weakSide, pawnSq) != RankS.RANK_7 ||
BitBoard.square_distance(loserKSq, pawnSq) != 1 ||
0 == ((BitBoard.FileABB | BitBoard.FileCBB | BitBoard.FileFBB | BitBoard.FileHBB) & BitBoard.SquareBB[pawnSq]))
{
result += ValueS.QueenValueEg - ValueS.PawnValueEg;
}
return(strongSide == pos.side_to_move() ? result : -result);
}
public static Bitboard sliding_attack(Square[] deltas, Square sq, Bitboard occupied)
{
Bitboard attack = 0;
for (int i = 0; i < 4; ++i)
{
for (Square s = sq + deltas[i];
Types.is_ok_square(s) && BitBoard.square_distance(s, s - deltas[i]) == 1;
s += deltas[i])
{
attack |= SquareBB[s];
if ((occupied & SquareBB[s]) != 0)
{
break;
}
}
}
return(attack);
}
/// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the
/// defending king towards a corner square of the right color.
public Value KBNK(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.KnightValueMg + ValueS.BishopValueMg, 0));
Debug.Assert(verify_material(pos, weakSide, ValueS.VALUE_ZERO, 0));
Square winnerKSq = pos.king_square(strongSide);
Square loserKSq = pos.king_square(weakSide);
Square bishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
// kbnk_mate_table() tries to drive toward corners A1 or H8. If we have a
// bishop that cannot reach the above squares, we flip the kings in order
// to drive the enemy toward corners A8 or H1.
if (Types.opposite_colors(bishopSq, SquareS.SQ_A1))
{
winnerKSq = Types.notSquare(winnerKSq);
loserKSq = Types.notSquare(loserKSq);
}
Value result = ValueS.VALUE_KNOWN_WIN
+ PushClose[BitBoard.square_distance(winnerKSq, loserKSq)]
+ PushToCorners[loserKSq];
return(strongSide == pos.side_to_move() ? result : -result);
}
/// Bitboards::init() initializes various bitboard tables. It is called at
/// startup and relies on global objects to be already zero-initialized.
public static void init()
{
for (Square s = SquareS.SQ_A1; s <= SquareS.SQ_H8; ++s)
{
BSFTable[bsf_index(SquareBB[s] = 1UL << s)] = s;
}
for (Bitboard b = 1; b < 256; ++b)
{
MS1BTable[b] = more_than_one(b) ? MS1BTable[b - 1] : lsb(b);
}
for (File f = FileS.FILE_A; f <= FileS.FILE_H; ++f)
{
FileBB[f] = f > FileS.FILE_A ? FileBB[f - 1] << 1 : FileABB;
}
for (Rank r = RankS.RANK_1; r <= RankS.RANK_8; ++r)
{
RankBB[r] = r > RankS.RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
}
for (File f = FileS.FILE_A; f <= FileS.FILE_H; ++f)
{
AdjacentFilesBB[f] = (f > FileS.FILE_A ? FileBB[f - 1] : 0) | (f < FileS.FILE_H ? FileBB[f + 1] : 0);
}
for (int c = ColorS.WHITE; c <= ColorS.BLACK; c++)
{
InFrontBB[c] = new Bitboard[RankS.RANK_NB];
}
for (Rank r = RankS.RANK_1; r < RankS.RANK_8; ++r)
{
InFrontBB[ColorS.WHITE][r] = ~(InFrontBB[ColorS.BLACK][r + 1] = InFrontBB[ColorS.BLACK][r] | RankBB[r]);
}
for (int c = ColorS.WHITE; c <= ColorS.BLACK; c++)
{
ForwardBB[c] = new Bitboard[SquareS.SQUARE_NB];
PawnAttackSpan[c] = new Bitboard[SquareS.SQUARE_NB];
PassedPawnMask[c] = new Bitboard[SquareS.SQUARE_NB];
}
for (Color c = ColorS.WHITE; c <= ColorS.BLACK; ++c)
{
for (Square s = SquareS.SQ_A1; s <= SquareS.SQ_H8; ++s)
{
ForwardBB[c][s] = InFrontBB[c][Types.rank_of(s)] & FileBB[Types.file_of(s)];
PawnAttackSpan[c][s] = InFrontBB[c][Types.rank_of(s)] & AdjacentFilesBB[Types.file_of(s)];
PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
}
}
for (Square c = 0; c < SquareS.SQUARE_NB; c++)
{
SquareDistance[c] = new int[SquareS.SQUARE_NB];
DistanceRingsBB[c] = new Bitboard[8];
}
for (Square s1 = SquareS.SQ_A1; s1 <= SquareS.SQ_H8; ++s1)
{
for (Square s2 = SquareS.SQ_A1; s2 <= SquareS.SQ_H8; ++s2)
{
if (s1 != s2)
{
SquareDistance[s1][s2] = Math.Max(file_distance(s1, s2), rank_distance(s1, s2));
DistanceRingsBB[s1][SquareDistance[s1][s2] - 1] |= SquareBB[s2];
}
}
}
int[][] steps = new int[7][];
steps[0] = new int[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
steps[1] = new int[] { 7, 9, 0, 0, 0, 0, 0, 0, 0 };
steps[2] = new int[] { 17, 15, 10, 6, -6, -10, -15, -17, 0 };
steps[3] = new int[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
steps[4] = new int[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
steps[5] = new int[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
steps[6] = new int[] { 9, 7, -7, -9, 8, 1, -1, -8, 0 };
for (Piece p = PieceS.NO_PIECE; p < PieceS.PIECE_NB; p++)
{
StepAttacksBB[p] = new Bitboard[SquareS.SQUARE_NB];
}
for (Color c = ColorS.WHITE; c <= ColorS.BLACK; ++c)
{
for (PieceType pt = PieceTypeS.PAWN; pt <= PieceTypeS.KING; ++pt)
{
for (Square s = SquareS.SQ_A1; s <= SquareS.SQ_H8; ++s)
{
for (int i = 0; steps[pt][i] != 0; ++i)
{
Square to = s + (Square)(c == ColorS.WHITE ? steps[pt][i] : -steps[pt][i]);
if (Types.is_ok_square(to) && BitBoard.square_distance(s, to) < 3)
{
StepAttacksBB[Types.make_piece(c, pt)][s] |= SquareBB[to];
}
}
}
}
}
Square[] RDeltas = new Square[] { SquareS.DELTA_N, SquareS.DELTA_E, SquareS.DELTA_S, SquareS.DELTA_W };
Square[] BDeltas = new Square[] { SquareS.DELTA_NE, SquareS.DELTA_SE, SquareS.DELTA_SW, SquareS.DELTA_NW };
init_magics(PieceTypeS.ROOK, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index);
init_magics(PieceTypeS.BISHOP, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index);
for (PieceType pt = PieceTypeS.NO_PIECE_TYPE; pt < PieceTypeS.PIECE_TYPE_NB; pt++)
{
PseudoAttacks[pt] = new Bitboard[SquareS.SQUARE_NB];
}
for (Square s = SquareS.SQ_A1; s <= SquareS.SQ_H8; s++)
{
BetweenBB[s] = new Bitboard[SquareS.SQUARE_NB];
LineBB[s] = new Bitboard[SquareS.SQUARE_NB];
}
for (Square s1 = SquareS.SQ_A1; s1 <= SquareS.SQ_H8; ++s1)
{
PseudoAttacks[PieceTypeS.QUEEN][s1] = PseudoAttacks[PieceTypeS.BISHOP][s1] = attacks_bb_SBBPT(s1, 0, PieceTypeS.BISHOP);
PseudoAttacks[PieceTypeS.QUEEN][s1] |= PseudoAttacks[PieceTypeS.ROOK][s1] = attacks_bb_SBBPT(s1, 0, PieceTypeS.ROOK);
for (Square s2 = SquareS.SQ_A1; s2 <= SquareS.SQ_H8; ++s2)
{
Piece pc = (PseudoAttacks[PieceTypeS.BISHOP][s1] & SquareBB[s2]) != 0 ? PieceS.W_BISHOP :
(PseudoAttacks[PieceTypeS.ROOK][s1] & SquareBB[s2]) != 0 ? PieceS.W_ROOK : PieceS.NO_PIECE;
if (pc == PieceS.NO_PIECE)
{
continue;
}
LineBB[s1][s2] = (attacks_bb_PSBB(pc, s1, 0) & attacks_bb_PSBB(pc, s2, 0)) | SquareBB[s1] | SquareBB[s2];
BetweenBB[s1][s2] = attacks_bb_PSBB(pc, s1, SquareBB[s2]) & attacks_bb_PSBB(pc, s2, SquareBB[s1]);
}
}
}
/// KRP vs KR. This function knows a handful of the most important classes of
/// drawn positions, but is far from perfect. It would probably be a good idea
/// to add more knowledge in the future.
///
/// It would also be nice to rewrite the actual code for this function,
/// which is mostly copied from Glaurung 1.x, and isn't very pretty.
public ScaleFactor KRPKR(Position pos)
{
Debug.Assert(verify_material(pos, strongSide, ValueS.RookValueMg, 1));
Debug.Assert(verify_material(pos, weakSide, ValueS.RookValueMg, 0));
// Assume strongSide is white and the pawn is on files A-D
Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
Square wrsq = normalize(pos, strongSide, pos.list(strongSide, PieceTypeS.ROOK)[0]);
Square wpsq = normalize(pos, strongSide, pos.list(strongSide, PieceTypeS.PAWN)[0]);
Square brsq = normalize(pos, strongSide, pos.list(weakSide, PieceTypeS.ROOK)[0]);
File f = Types.file_of(wpsq);
Rank r = Types.rank_of(wpsq);
Square queeningSq = Types.make_square(f, RankS.RANK_8);
int tempo = (pos.side_to_move() == strongSide ? 1 : 0);
// If the pawn is not too far advanced and the defending king defends the
// queening square, use the third-rank defence.
if (r <= RankS.RANK_5 &&
BitBoard.square_distance(bksq, queeningSq) <= 1 &&
wksq <= SquareS.SQ_H5 &&
(Types.rank_of(brsq) == RankS.RANK_6 || (r <= RankS.RANK_3 && Types.rank_of(wrsq) != RankS.RANK_6)))
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
// The defending side saves a draw by checking from behind in case the pawn
// has advanced to the 6th rank with the king behind.
if (r == RankS.RANK_6 &&
BitBoard.square_distance(bksq, queeningSq) <= 1 &&
Types.rank_of(wksq) + tempo <= RankS.RANK_6 &&
(Types.rank_of(brsq) == RankS.RANK_1 || (0 == tempo && Math.Abs(Types.file_of(brsq) - f) >= 3)))
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
if (r >= RankS.RANK_6 &&
bksq == queeningSq &&
Types.rank_of(brsq) == RankS.RANK_1 &&
(0 == tempo || BitBoard.square_distance(wksq, wpsq) >= 2))
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
// White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
// and the black rook is behind the pawn.
if (wpsq == SquareS.SQ_A7 &&
wrsq == SquareS.SQ_A8 &&
(bksq == SquareS.SQ_H7 || bksq == SquareS.SQ_G7) &&
Types.file_of(brsq) == FileS.FILE_A &&
(Types.rank_of(brsq) <= RankS.RANK_3 || Types.file_of(wksq) >= FileS.FILE_D || Types.rank_of(wksq) <= RankS.RANK_5))
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
// If the defending king blocks the pawn and the attacking king is too far
// away, it's a draw.
if (r <= RankS.RANK_5 &&
bksq == wpsq + SquareS.DELTA_N &&
BitBoard.square_distance(wksq, wpsq) - tempo >= 2 &&
BitBoard.square_distance(wksq, brsq) - tempo >= 2)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
// Pawn on the 7th rank supported by the rook from behind usually wins if the
// attacking king is closer to the queening square than the defending king,
// and the defending king cannot gain tempi by threatening the attacking rook.
if (r == RankS.RANK_7 &&
f != FileS.FILE_A &&
Types.file_of(wrsq) == f &&
wrsq != queeningSq &&
(BitBoard.square_distance(wksq, queeningSq) < BitBoard.square_distance(bksq, queeningSq) - 2 + tempo) &&
(BitBoard.square_distance(wksq, queeningSq) < BitBoard.square_distance(bksq, wrsq) + tempo))
{
return((ScaleFactor)(ScaleFactorS.SCALE_FACTOR_MAX - 2 * BitBoard.square_distance(wksq, queeningSq)));
}
// Similar to the above, but with the pawn further back
if (f != FileS.FILE_A &&
Types.file_of(wrsq) == f &&
wrsq < wpsq &&
(BitBoard.square_distance(wksq, queeningSq) < BitBoard.square_distance(bksq, queeningSq) - 2 + tempo) &&
(BitBoard.square_distance(wksq, wpsq + SquareS.DELTA_N) < BitBoard.square_distance(bksq, wpsq + SquareS.DELTA_N) - 2 + tempo) &&
(BitBoard.square_distance(bksq, wrsq) + tempo >= 3 ||
(BitBoard.square_distance(wksq, queeningSq) < BitBoard.square_distance(bksq, wrsq) + tempo &&
(BitBoard.square_distance(wksq, wpsq + SquareS.DELTA_N) < BitBoard.square_distance(bksq, wrsq) + tempo))))
{
return((ScaleFactor)(ScaleFactorS.SCALE_FACTOR_MAX
- 8 * BitBoard.square_distance(wpsq, queeningSq)
- 2 * BitBoard.square_distance(wksq, queeningSq)));
}
// If the pawn is not far advanced, and the defending king is somewhere in
// the pawn's path, it's probably a draw.
if (r <= RankS.RANK_4 && bksq > wpsq)
{
if (Types.file_of(bksq) == Types.file_of(wpsq))
{
return(10);
}
if (Math.Abs(Types.file_of(bksq) - Types.file_of(wpsq)) == 1 &&
BitBoard.square_distance(wksq, bksq) > 2)
{
return(24 - 2 * BitBoard.square_distance(wksq, bksq));
}
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
/// KB and one or more pawns vs K. It checks for draws with rook pawns and
/// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
/// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
/// will be used.
public ScaleFactor KBPsK(Position pos)
{
Debug.Assert(pos.non_pawn_material(strongSide) == ValueS.BishopValueMg);
Debug.Assert(pos.count(strongSide, PieceTypeS.PAWN) >= 1);
// No assertions about the material of weakSide, because we want draws to
// be detected even when the weaker side has some pawns.
Bitboard pawns = pos.pieces_color_piecetype(strongSide, PieceTypeS.PAWN);
File pawnFile = Types.file_of(pos.list(strongSide, PieceTypeS.PAWN)[0]);
// All pawns are on a single rook file ?
if ((pawnFile == FileS.FILE_A || pawnFile == FileS.FILE_H) &&
0 == (pawns & ~BitBoard.file_bb_file(pawnFile)))
{
Square bishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
Square queeningSq = Types.relative_square(strongSide, Types.make_square(pawnFile, RankS.RANK_8));
Square kingSq = pos.king_square(weakSide);
if (Types.opposite_colors(queeningSq, bishopSq) &&
BitBoard.square_distance(queeningSq, kingSq) <= 1)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
}
// If all the pawns are on the same B or G file, then it's potentially a draw
if ((pawnFile == FileS.FILE_B || pawnFile == FileS.FILE_G) &&
0 == (pos.pieces_piecetype(PieceTypeS.PAWN) & ~BitBoard.file_bb_file(pawnFile)) &&
pos.non_pawn_material(weakSide) == 0 &&
pos.count(weakSide, PieceTypeS.PAWN) >= 1)
{
// Get weakSide pawn that is closest to the home rank
Square weakPawnSq = BitBoard.backmost_sq(weakSide, pos.pieces_color_piecetype(weakSide, PieceTypeS.PAWN));
Square strongKingSq = pos.king_square(strongSide);
Square weakKingSq = pos.king_square(weakSide);
Square bishopSq = pos.list(strongSide, PieceTypeS.BISHOP)[0];
// There's potential for a draw if our pawn is blocked on the 7th rank,
// the bishop cannot attack it or they only have one pawn left
if (Types.relative_rank_square(strongSide, weakPawnSq) == RankS.RANK_7 &&
(pos.pieces_color_piecetype(strongSide, PieceTypeS.PAWN) & BitBoard.SquareBB[(weakPawnSq + Types.pawn_push(weakSide))]) != 0 &&
(Types.opposite_colors(bishopSq, weakPawnSq) || pos.count(strongSide, PieceTypeS.PAWN) == 1))
{
int strongKingDist = BitBoard.square_distance(weakPawnSq, strongKingSq);
int weakKingDist = BitBoard.square_distance(weakPawnSq, weakKingSq);
// It's a draw if the weak king is on its back two ranks, within 2
// squares of the blocking pawn and the strong king is not
// closer. (I think this rule only fails in practically
// unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
// and positions where qsearch will immediately correct the
// problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
if (Types.relative_rank_square(strongSide, weakKingSq) >= RankS.RANK_7 &&
weakKingDist <= 2 &&
weakKingDist <= strongKingDist)
{
return(ScaleFactorS.SCALE_FACTOR_DRAW);
}
}
}
return(ScaleFactorS.SCALE_FACTOR_NONE);
}
// evaluate_passed_pawns() evaluates the passed pawns of the given color
public static Score evaluate_passed_pawns(Position pos, EvalInfo ei, Color Us, bool Trace)
{
Color Them = (Us == ColorS.WHITE ? ColorS.BLACK : ColorS.WHITE);
Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
Score score = ScoreS.SCORE_ZERO;
b = ei.pi.passed_pawns(Us);
while (b != 0)
{
Square s = BitBoard.pop_lsb(ref b);
Debug.Assert(pos.pawn_passed(Us, s));
int r = (int)(Types.relative_rank_square(Us, s) - RankS.RANK_2);
int rr = r * (r - 1);
// Base bonus based on rank
Value mbonus = (17 * rr), ebonus = (7 * (rr + r + 1));
if (rr != 0)
{
Square blockSq = s + Types.pawn_push(Us);
// Adjust bonus based on kings proximity
ebonus += (BitBoard.square_distance(pos.king_square(Them), blockSq) * 5 * rr)
- (BitBoard.square_distance(pos.king_square(Us), blockSq) * 2 * rr);
// If blockSq is not the queening square then consider also a second push
if (Types.relative_rank_square(Us, blockSq) != RankS.RANK_8)
{
ebonus -= (BitBoard.square_distance(pos.king_square(Us), blockSq + Types.pawn_push(Us)) * rr);
}
// If the pawn is free to advance, increase bonus
if (pos.empty(blockSq))
{
squaresToQueen = BitBoard.forward_bb(Us, s);
// If there is an enemy rook or queen attacking the pawn from behind,
// add all X-ray attacks by the rook or queen. Otherwise consider only
// the squares in the pawn's path attacked or occupied by the enemy.
if ((BitBoard.forward_bb(Them, s) & pos.pieces_color_piecetype(Them, PieceTypeS.ROOK, PieceTypeS.QUEEN)) != 0 &&
(BitBoard.forward_bb(Them, s) & pos.pieces_color_piecetype(Them, PieceTypeS.ROOK, PieceTypeS.QUEEN) & pos.attacks_from_square_piecetype(s, PieceTypeS.ROOK)) != 0)
{
unsafeSquares = squaresToQueen;
}
else
{
unsafeSquares = squaresToQueen & (ei.attackedBy[Them][PieceTypeS.ALL_PIECES] | pos.pieces_color(Them));
}
if ((BitBoard.forward_bb(Them, s) & pos.pieces_color_piecetype(Us, PieceTypeS.ROOK, PieceTypeS.QUEEN)) != 0 &&
(BitBoard.forward_bb(Them, s) & pos.pieces_color_piecetype(Us, PieceTypeS.ROOK, PieceTypeS.QUEEN) & pos.attacks_from_square_piecetype(s, PieceTypeS.ROOK)) != 0)
{
defendedSquares = squaresToQueen;
}
else
{
defendedSquares = squaresToQueen & ei.attackedBy[Us][PieceTypeS.ALL_PIECES];
}
// If there aren't any enemy attacks, assign a big bonus. Otherwise
// assign a smaller bonus if the block square isn't attacked.
int k = 0 == unsafeSquares? 15 : 0 == (unsafeSquares & BitBoard.SquareBB[blockSq]) ? 9 : 0;
// If the path to queen is fully defended, assign a big bonus.
// Otherwise assign a smaller bonus if the block square is defended.
if (defendedSquares == squaresToQueen)
{
k += 6;
}
else if ((defendedSquares & BitBoard.SquareBB[blockSq]) != 0)
{
k += 4;
}
mbonus += (k * rr); ebonus += (k * rr);
}
} // rr != 0
if (pos.count(Us, PieceTypeS.PAWN) < pos.count(Them, PieceTypeS.PAWN))
{
ebonus += ebonus / 4;
}
score += Types.make_score(mbonus, ebonus);
}
if (Trace)
{
Tracing.terms[Us][TermsS.PASSED] = apply_weight(score, Weights[EvalWeightS.PassedPawns]);
}
// Add the scores to the middle game and endgame eval
return(Eval.apply_weight(score, Weights[EvalWeightS.PassedPawns]));
}