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

        private static void TransformBluestein(Complex[] data)
        {
            int n = data.Length;
            int m = HighestOneBit(n * 2 + 1) << 1;

            // Trignometric tables
            var cosTable = new double[n];
            var sinTable = new double[n];
            for (int i = 0; i < cosTable.Length; i++)
            {
                int j = (int)((long)i * i % (n * 2));  // This is more accurate than j = i * i
                cosTable[i] = Math.Cos(Math.PI * j / n);
                sinTable[i] = Math.Sin(Math.PI * j / n);
            }

            // Temporary vectors and preprocessing
            var areal = new double[m];
            var aimag = new double[m];

            for (int i = 0; i < data.Length; i++)
            {
                double re = data[i].Real;
                double im = data[i].Imaginary;

                areal[i] = +re * cosTable[i] + im * sinTable[i];
                aimag[i] = -re * sinTable[i] + im * cosTable[i];
            }

            var breal = new double[m];
            var bimag = new double[m];
            breal[0] = cosTable[0];
            bimag[0] = sinTable[0];

            for (int i = 1; i < cosTable.Length; i++)
            {
                breal[i] = breal[m - i] = cosTable[i];
                bimag[i] = bimag[m - i] = sinTable[i];
            }

            // Convolution
            var creal = new double[m];
            var cimag = new double[m];
            Convolve(areal, aimag, breal, bimag, creal, cimag);

            // Postprocessing
            for (int i = 0; i < data.Length; i++)
            {
                double re = +creal[i] * cosTable[i] + cimag[i] * sinTable[i];
                double im = -creal[i] * sinTable[i] + cimag[i] * cosTable[i];
                data[i] = new Complex(re, im);
            }
        }