Accord.Math.Special.Log1p C# (CSharp) Method

        public static double Log1p(double x)
        {
            if (x <= -1.0)
                return Double.NaN;

            if (Math.Abs(x) > 1e-4)
                return Math.Log(1.0 + x);

            // Use Taylor approx. log(1 + x) = x - x^2/2 with error roughly x^3/3
            // Since |x| < 10^-4, |x|^3 < 10^-12, relative error less than 10^-8
            return (-0.5 * x + 1.0) * x;
        }

        public static double LogSum(float lnx, float lny)
        {
            if (lnx == Single.NegativeInfinity)
            {
                return(lny);
            }
            if (lny == Single.NegativeInfinity)
            {
                return(lnx);
            }

            if (lnx > lny)
            {
                return(lnx + Special.Log1p(Math.Exp(lny - lnx)));
            }

            return(lny + Special.Log1p(Math.Exp(lnx - lny)));
        }