/// <summary>
/// signed subtraction of 2 numbers.
/// </summary>
/// <param name="n1"></param>
/// <param name="n2"></param>
/// <returns></returns>
public static BigInt Sub(BigInt n1, BigInt n2)
{
if (n1.digitArray.Length != n2.digitArray.Length) MakeSafe(ref n1, ref n2);
BigInt result;
if ((n1.sign && !n2.sign) || (!n1.sign && n2.sign))
{
result = new BigInt(n1);
result.AddInternal(n2);
result.sign = n1.sign;
}
else
{
bool lessThan = LtInt(n1, n2);
if (lessThan)
{
result = new BigInt(n2);
result.SubInternal(n1);
result.sign = !n1.sign;
}
else
{
result = new BigInt(n1);
result.SubInternal(n2);
result.sign = n1.sign;
}
}
return result;
}