Accord.Math.Transforms.FourierTransform2.FFT C# (CSharp) Method

        public static void FFT(Complex[] data, FourierTransform.Direction direction)
        {
            int n = data.Length;

            if (n == 0)
                return;

            if (direction == FourierTransform.Direction.Backward)
            {
                for (int i = 0; i < data.Length; i++)
                    data[i] = new Complex(data[i].Imaginary, data[i].Real);
            }

            if ((n & (n - 1)) == 0)
            {
                // Is power of 2
                TransformRadix2(data);
            }
            else
            {
                // More complicated algorithm for arbitrary sizes
                TransformBluestein(data);
            }

            if (direction == FourierTransform.Direction.Backward)
            {
                for (int i = 0; i < data.Length; i++)
                {
                    double im = data[i].Imaginary;
                    double re = data[i].Real;
                    data[i] = new Complex(im / n, re / n);
                }
            }
        }

        /// <summary>
        ///   Performs the Fast Hilbert Transform over a double[] array.
        /// </summary>
        ///
        public static void FHT(double[] data, FourierTransform.Direction direction)
        {
            int N = data.Length;

            // Forward operation
            if (direction == FourierTransform.Direction.Forward)
            {
                // Copy the input to a complex array which can be processed
                //  in the complex domain by the FFT
                Complex[] cdata = new Complex[N];
                for (int i = 0; i < N; i++)
                {
                    cdata[i] = new Complex(data[i], 0.0);
                }

                // Perform FFT
                FourierTransform2.FFT(cdata, FourierTransform.Direction.Forward);

                //double positive frequencies
                for (int i = 1; i < (N / 2); i++)
                {
                    cdata[i] *= 2.0;
                }

                // zero out negative frequencies
                //  (leaving out the dc component)
                for (int i = (N / 2) + 1; i < N; i++)
                {
                    cdata[i] = Complex.Zero;
                }

                // Reverse the FFT
                FourierTransform2.FFT(cdata, FourierTransform.Direction.Backward);

                // Convert back to our initial double array
                for (int i = 0; i < N; i++)
                {
                    data[i] = cdata[i].Imaginary;
                }
            }

            else // Backward operation
            {
                // The inverse Hilbert can be calculated by
                //  negating the transform and reapplying the
                //  transformation.
                //
                // H^–1{h(t)} = –H{h(t)}

                FHT(data, FourierTransform.Direction.Forward);

                for (int i = 0; i < data.Length; i++)
                {
                    data[i] = -data[i];
                }
            }
        }