Accord.Math.Transforms.FourierTransform2.TransformRadix2 C# (CSharp) Method

        private static void TransformRadix2(Complex[] complex)
        {
            int n = complex.Length;

            int levels = (int)Math.Floor(Math.Log(n, 2));

            if (1 << levels != n)
                throw new ArgumentException("Length is not a power of 2");

            // TODO: keep those tables in memory
            var cosTable = new double[n / 2];
            var sinTable = new double[n / 2];
            for (int i = 0; i < n / 2; i++)
            {
                cosTable[i] = Math.Cos(2 * Math.PI * i / n);
                sinTable[i] = Math.Sin(2 * Math.PI * i / n);
            }

            // Bit-reversed addressing permutation
            for (int i = 0; i < complex.Length; i++)
            {
                int j = unchecked((int)((uint)Reverse(i) >> (32 - levels)));

                if (j > i)
                {
                    var temp = complex[i];
                    complex[i] = complex[j];
                    complex[j] = temp;
                }
            }


            // Cooley-Tukey decimation-in-time radix-2 FFT
            for (int size = 2; size <= n; size *= 2)
            {
                int halfsize = size / 2;
                int tablestep = n / size;

                for (int i = 0; i < n; i += size)
                {
                    for (int j = i, k = 0; j < i + halfsize; j++, k += tablestep)
                    {
                        int h = j + halfsize;
                        double re = complex[h].Real;
                        double im = complex[h].Imaginary;

                        double tpre = +re * cosTable[k] + im * sinTable[k];
                        double tpim = -re * sinTable[k] + im * cosTable[k];

                        double rej = complex[j].Real;
                        double imj = complex[j].Imaginary;

                        complex[h] = new Complex(rej - tpre, imj - tpim);
                        complex[j] = new Complex(rej + tpre, imj + tpim);
                    }
                }

                // Prevent overflow in 'size *= 2'
                if (size == n)
                    break;
            }
        }