public static bool IsKrkpDrawish(ChessBoard cb)
{
var leadingColor = cb.Pieces[White][Rook] != 0 ? White : Black;
var rook = cb.Pieces[leadingColor][Rook];
var pawn = cb.Pieces[1 - leadingColor][Pawn];
var pawnIndex = BitOperations.TrailingZeroCount(pawn);
var winningKing = cb.Pieces[leadingColor][King];
var losingKing = cb.Pieces[1 - leadingColor][King];
if ((Bitboard.GetFile(pawn) & winningKing) != 0 &&
(leadingColor == White && pawnIndex > cb.KingIndex[leadingColor] ||
leadingColor == Black && pawnIndex < cb.KingIndex[leadingColor]))
{
// If the stronger side's king is in front of the pawn, it's a win
return(false);
}
if (Util.GetDistance(losingKing, pawn) >= 3 + (cb.ColorToMove == 1 - leadingColor ? 1 : 0) &&
Util.GetDistance(losingKing, rook) >= 3)
{
// If the weaker side's king is too far from the pawn and the rook, it's a win.
return(false);
}
if (leadingColor == White)
{
if (Bitboard.GetRank(losingKing) <= Bitboard.Rank3 && Util.GetDistance(losingKing, pawn) == 1 &&
Bitboard.GetRank(winningKing) >= Bitboard.Rank4 &&
Util.GetDistance(winningKing, pawn) > 2 + (cb.ColorToMove == leadingColor ? 1 : 0))
{
// If the pawn is far advanced and supported by the defending king, the position is drawish
return(true);
}
}
else
{
if (Bitboard.GetRank(losingKing) >= Bitboard.Rank5 && Util.GetDistance(losingKing, pawn) == 1 &&
Bitboard.GetRank(winningKing) <= Bitboard.Rank5 &&
Util.GetDistance(winningKing, pawn) > 2 + (cb.ColorToMove == leadingColor ? 1 : 0))
{
// If the pawn is far advanced and supported by the defending king, the position is drawish
return(true);
}
}
return(false);
}
