Artemis.Engine.Maths.SpecialFunctions.Gamma C# (CSharp) Method

        public static double Gamma(double x)
        {
            double p, z;

            double q = Math.Abs(x);

            if (q > 33.0)
            {
                if (x < 0.0)
                {
                    p = Math.Floor(q);
                    if (p == q) throw new ArithmeticException("gamma: overflow");
                    //int i = (int)p;
                    z = q - p;
                    if (z > 0.5)
                    {
                        p += 1.0;
                        z = q - p;
                    }
                    z = q * Math.Sin(Math.PI * z);
                    if (z == 0.0) throw new ArithmeticException("gamma: overflow");
                    z = Math.Abs(z);
                    z = Math.PI / (z * Stirf(q));

                    return -z;
                }
                else
                {
                    return Stirf(x);
                }
            }

            z = 1.0;
            while (x >= 3.0)
            {
                x -= 1.0;
                z *= x;
            }

            while (x < 0.0)
            {
                if (x == 0.0)
                {
                    throw new ArithmeticException("gamma: singular");
                }
                else if (x > -1.0E-9)
                {
                    return (z / ((1.0 + GAMMA * x) * x));
                }
                z /= x;
                x += 1.0;
            }

            while (x < 2.0)
            {
                if (x == 0.0)
                {
                    throw new ArithmeticException("gamma: singular");
                }
                else if (x < 1.0E-9)
                {
                    return (z / ((1.0 + GAMMA * x) * x));
                }
                z /= x;
                x += 1.0;
            }

            if ((x == 2.0) || (x == 3.0)) return z;

            x -= 2.0;
            p = polevl(x, GAMMA_P, 6);
            q = polevl(x, GAMMA_Q, 7);
            return z*p/q;
        }