AForge.Math.Tools.Log2 C# (CSharp) Method

        public static int Log2(int x)
        {
            if (x <= 65536)
            {
                if (x <= 256)
                {
                    if (x <= 16)
                    {
                        if (x <= 4)
                        {
                            if (x <= 2)
                            {
                                if (x <= 1)
                                    return 0;
                                return 1;
                            }
                            return 2;
                        }
                        if (x <= 8)
                            return 3;
                        return 4;
                    }
                    if (x <= 64)
                    {
                        if (x <= 32)
                            return 5;
                        return 6;
                    }
                    if (x <= 128)
                        return 7;
                    return 8;
                }
                if (x <= 4096)
                {
                    if (x <= 1024)
                    {
                        if (x <= 512)
                            return 9;
                        return 10;
                    }
                    if (x <= 2048)
                        return 11;
                    return 12;
                }
                if (x <= 16384)
                {
                    if (x <= 8192)
                        return 13;
                    return 14;
                }
                if (x <= 32768)
                    return 15;
                return 16;
            }

            if (x <= 16777216)
            {
                if (x <= 1048576)
                {
                    if (x <= 262144)
                    {
                        if (x <= 131072)
                            return 17;
                        return 18;
                    }
                    if (x <= 524288)
                        return 19;
                    return 20;
                }
                if (x <= 4194304)
                {
                    if (x <= 2097152)
                        return 21;
                    return 22;
                }
                if (x <= 8388608)
                    return 23;
                return 24;
            }
            if (x <= 268435456)
            {
                if (x <= 67108864)
                {
                    if (x <= 33554432)
                        return 25;
                    return 26;
                }
                if (x <= 134217728)
                    return 27;
                return 28;
            }
            if (x <= 1073741824)
            {
                if (x <= 536870912)
                    return 29;
                return 30;
            }
            return 31;
        }
    }

        /// <summary>
        /// One dimensional Fast Fourier Transform.
        /// </summary>
        ///
        /// <param name="data">Data to transform.</param>
        /// <param name="direction">Transformation direction.</param>
        ///
        /// <remarks><para><note>The method accepts <paramref name="data"/> array of 2<sup>n</sup> size
        /// only, where <b>n</b> may vary in the [1, 14] range.</note></para></remarks>
        ///
        /// <exception cref="ArgumentException">Incorrect data length.</exception>
        ///
        public static void FFT(Complex[] data, Direction direction)
        {
            int n = data.Length;
            int m = Tools.Log2(n);

            // reorder data first
            ReorderData(data);

            // compute FFT
            int tn = 1, tm;

            for (int k = 1; k <= m; k++)
            {
                Complex[] rotation = FourierTransform.GetComplexRotation(k, direction);

                tm   = tn;
                tn <<= 1;

                for (int i = 0; i < tm; i++)
                {
                    Complex t = rotation[i];

                    for (int even = i; even < n; even += tn)
                    {
                        int     odd = even + tm;
                        Complex ce  = data[even];
                        Complex co  = data[odd];

                        double tr = co.Re * t.Re - co.Im * t.Im;
                        double ti = co.Re * t.Im + co.Im * t.Re;

                        data[even].Re += tr;
                        data[even].Im += ti;

                        data[odd].Re = ce.Re - tr;
                        data[odd].Im = ce.Im - ti;
                    }
                }
            }

            if (direction == Direction.Forward)
            {
                for (int i = 0; i < n; i++)
                {
                    data[i].Re /= (double)n;
                    data[i].Im /= (double)n;
                }
            }
        }