/// KP vs K. This endgame is evaluated with the help of a bitbase.
internal static Value Endgame_KPK(Color strongerSide, Position pos)
{
Color weakerSide = strongerSide ^ 1;
Debug.Assert(pos.non_pawn_material(strongerSide) == ValueC.VALUE_ZERO);
Debug.Assert(pos.non_pawn_material(weakerSide) == ValueC.VALUE_ZERO);
Debug.Assert(pos.piece_count(strongerSide, PieceTypeC.PAWN) == 1);
Debug.Assert(pos.piece_count(weakerSide, PieceTypeC.PAWN) == 0);
Square wksq, bksq, wpsq;
Color stm;
if (strongerSide == ColorC.WHITE)
{
wksq = pos.king_square(ColorC.WHITE);
bksq = pos.king_square(ColorC.BLACK);
wpsq = pos.pieceList[ColorC.WHITE][PieceTypeC.PAWN][0];
stm = pos.sideToMove;
}
else
{
wksq = Utils.flip_S(pos.king_square(ColorC.BLACK));
bksq = Utils.flip_S(pos.king_square(ColorC.WHITE));
wpsq = Utils.flip_S(pos.pieceList[ColorC.BLACK][PieceTypeC.PAWN][0]);
stm = Utils.flip_C(pos.sideToMove);
}
if (Utils.file_of(wpsq) >= FileC.FILE_E)
{
wksq = Utils.mirror(wksq);
bksq = Utils.mirror(bksq);
wpsq = Utils.mirror(wpsq);
}
if (KPKPosition.probe_kpk_bitbase(wksq, wpsq, bksq, stm) == 0)
{
return(ValueC.VALUE_DRAW);
}
Value result = ValueC.VALUE_KNOWN_WIN
+ Constants.PawnValueEndgame
+ Utils.rank_of(wpsq);
return(strongerSide == pos.sideToMove ? result : -result);
}
/// K and a pawn vs K and a pawn. This is done by removing the weakest side's
/// pawn and probing the KP vs K bitbase: If the weakest side has a draw without
/// the pawn, she probably has at least a draw with the pawn as well. The exception
/// is when the stronger side's pawn is far advanced and not on a rook file; in
/// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
internal static ScaleFactor Endgame_KPKP(Color strongerSide, Position pos)
{
Color weakerSide = strongerSide ^ 1;
Debug.Assert(pos.non_pawn_material(strongerSide) == ValueC.VALUE_ZERO);
Debug.Assert(pos.non_pawn_material(weakerSide) == ValueC.VALUE_ZERO);
Debug.Assert(pos.piece_count(ColorC.WHITE, PieceTypeC.PAWN) == 1);
Debug.Assert(pos.piece_count(ColorC.BLACK, PieceTypeC.PAWN) == 1);
Square wksq = pos.king_square(strongerSide);
Square bksq = pos.king_square(weakerSide);
Square wpsq = pos.pieceList[strongerSide][PieceTypeC.PAWN][0];
Color stm = pos.sideToMove;
if (strongerSide == ColorC.BLACK)
{
wksq = Utils.flip_S(wksq);
bksq = Utils.flip_S(bksq);
wpsq = Utils.flip_S(wpsq);
stm = Utils.flip_C(stm);
}
if (Utils.file_of(wpsq) >= FileC.FILE_E)
{
wksq = Utils.mirror(wksq);
bksq = Utils.mirror(bksq);
wpsq = Utils.mirror(wpsq);
}
// If the pawn has advanced to the fifth rank or further, and is not a
// rook pawn, it's too dangerous to assume that it's at least a draw.
if (Utils.rank_of(wpsq) >= RankC.RANK_5 &&
Utils.file_of(wpsq) != FileC.FILE_A)
{
return(ScaleFactorC.SCALE_FACTOR_NONE);
}
// Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
// it's probably at least a draw even with the pawn.
return((KPKPosition.probe_kpk_bitbase(wksq, wpsq, bksq, stm) != 0) ? ScaleFactorC.SCALE_FACTOR_NONE : ScaleFactorC.SCALE_FACTOR_DRAW);
}