/// <summary>
/// if a number is A + B where A is integer and B is in [0; 1], it performs operations
/// for A and B separately and then concatenates
/// </summary>
/// <param name="num"></param>
/// <param name="N"></param>
/// <returns></returns>
internal static string ToBaseN(EDecimal num, int N)
{
if (N > ALPHABET_TOCHAR.Length)
{
throw new MathSException("N should be <= than " + ALPHABET_TOCHAR.Length);
}
string sign = EDecimalWrapper.IsLess(num, 0) ? "-" : "";
num = num.Abs();
var intPart = num.RoundToIntegerExact(FloorContext).ToEInteger();
EDecimal floatPart = RealNumber.CtxSubtract(num, intPart);
string rightPart = !EDecimalWrapper.IsEqual(floatPart, 0) ? "." + FloatToBaseN(floatPart, N) : "";
string leftPart = sign + IntToBaseN(intPart, N);
return(leftPart + rightPart);
}