private string ValidateKings(string error)
{
Span <Player> players = stackalloc Player[] { Player.White, Player.Black };
foreach (var player in players)
{
var count = _board.PieceCount(PieceTypes.King, player);
if (count != 1)
{
error = AddError(error, $"king count for player {player} was {count}");
}
}
if (!(_pos.AttacksTo(_pos.GetKingSquare(~_pos.SideToMove)) & _board.Pieces(_pos.SideToMove)).IsEmpty)
{
error = AddError(error, "kings appear to attack each other");
}
return(error);
}