private static DecimalX expTaylor(DecimalX x, int scale)
{
DecimalX sumPrev;
var factorial = DecimalX.Create(1);
var xPower = x;
// 1 + x
var sum = x.Add(DecimalX.Create(1));
// Loop until the sums converge
// (two successive sums are equal after rounding).
var i = 2;
do
{
// x^i
xPower = xPower.Multiply(x);
xPower = DecimalX.Rescale(xPower, -scale, RoundingMode.HalfEven);
// i!
factorial = factorial.Multiply(DecimalX.Create(i));
// x^i/i!
var term = xPower.CDivide(factorial, scale, RoundingMode.HalfEven);
// sum = sum + x^i/i!
sumPrev = sum;
sum = sum.Add(term);
i++;
} while (sum.CompareTo(sumPrev) != 0);
return(sum);
}