DCT

        static void Main(string[] args)
        {
            double[] ValIn = new double[] {
                -76, -73, -67, -62, -58, -67, -64, -55,
                -65, -69, -73, -38, -19, -43, -59, -56,
                -66, -69, -60, -15,  16, -24, -62, -55,
                -65, -70, -57, - 6,  26, -22, -58, -59,
                -61, -67, -60, -24, - 2, -40, -60, -58,
                -49, -63, -68, -58, -51, -60, -70, -53,
                -43, -57, -64, -69, -73, -67, -63, -45,
                -41, -49, -59, -60, -63, -52, -50, -34
            };
            double[] ValDCT = DCT (ValIn);
            for (int i = 0; i < 64; i++) ValDCT[i] = Math.Round(ValDCT[i] / Q[i]);
            for (int i = 0; i < 64; i++) ValDCT[i] = ValDCT[i] * Q[i];
            double[] ValOut = IDCT(ValDCT );
            for (int i = 0; i < 64; i++) ValDCT[i] = KKtMain.CFTI(ValDCT[i] * 100) / 100.0;
            for (int i = 0; i < 64; i++) ValOut[i] = KKtMain.CFTI(ValOut    [i]);
            double[] ValDiff     = new double[64];
            for (int i = 0; i < 64; i++) ValDiff[i] = ValOut[i] - ValIn[i];
        }

        static readonly int[] Q = new int[] {
            16, 11, 10, 16,  24,  40,  51,  61,
            12, 12, 14, 19,  26,  58,  60,  55,
            14, 13, 16, 24,  40,  57,  69,  56,
            14, 17, 22, 29,  51,  87,  80,  62,
            18, 22, 37, 56,  68, 109, 103,  77,
            24, 35, 55, 64,  81, 104, 113,  92,
            49, 64, 78, 87, 103, 121, 120, 101,
            72, 92, 95, 98, 112, 100, 103,  99,
        };

        static readonly double[] Coeff = new double[] {
            D(0x3ff0000000000000), D(0x3FF0000000000000), D(0x3FF0000000000000), D(0x3FF0000000000000),
            D(0x3FF0000000000000), D(0x3FF0000000000000), D(0x3FF0000000000000), D(0x3FF0000000000000),
            D(0x3fef6297cff75cb0), D(0x3fea9b66290ea1a3), D(0x3fe1c73b39ae68c9), D(0x3fc8f8b83c69a60d),
            D(0xbfc8f8b83c69a608), D(0xbfe1c73b39ae68c6), D(0xbfea9b66290ea1a4), D(0xbfef6297cff75cb0),
            D(0x3fed906bcf328d46), D(0x3fd87de2a6aea964), D(0xbfd87de2a6aea962), D(0xbfed906bcf328d46),
            D(0xbfed906bcf328d47), D(0xbfd87de2a6aea96d), D(0x3fd87de2a6aea967), D(0x3fed906bcf328d44),
            D(0x3fea9b66290ea1a3), D(0xbfc8f8b83c69a608), D(0xbfef6297cff75cb0), D(0xbfe1c73b39ae68c8),
            D(0x3fe1c73b39ae68c5), D(0x3fef6297cff75cb0), D(0x3fc8f8b83c69a61d), D(0xbfea9b66290ea1a2),
            D(0x3fe6a09e667f3bcd), D(0xbfe6a09e667f3bcc), D(0xbfe6a09e667f3bce), D(0x3fe6a09e667f3bcb),
            D(0x3fe6a09e667f3bce), D(0xbfe6a09e667f3bc5), D(0xbfe6a09e667f3bc9), D(0x3fe6a09e667f3bc4),
            D(0x3fe1c73b39ae68c9), D(0xbfef6297cff75cb0), D(0x3fc8f8b83c69a60c), D(0x3fea9b66290ea1a5),
            D(0xbfea9b66290ea1a2), D(0xbfc8f8b83c69a602), D(0x3fef6297cff75cb2), D(0xbfe1c73b39ae68c2),
            D(0x3fd87de2a6aea964), D(0xbfed906bcf328d47), D(0x3fed906bcf328d44), D(0xbfd87de2a6aea965),
            D(0xbfd87de2a6aea971), D(0x3fed906bcf328d46), D(0xbfed906bcf328d43), D(0x3fd87de2a6aea95f),
            D(0x3fc8f8b83c69a60d), D(0xbfe1c73b39ae68c8), D(0x3fea9b66290ea1a5), D(0xbfef6297cff75cb2),
            D(0x3fef6297cff75cb0), D(0xbfea9b66290ea1a1), D(0x3fe1c73b39ae68c2), D(0xbfc8f8b83c69a616),
        };

        unsafe static double D( ulong val) => *(double*)&val;
        unsafe static  ulong I(double val) => *( ulong*)&val;

        static readonly double[] C = new double[] { 1 / Math.Sqrt(2), 1, 1, 1, 1, 1, 1, 1, };

        static double[] DCT(double[] In)
        {
            int u, v, x, y;
            double q, z;
            double[] Out = new double[64];

            for (v = 0; v < 8; v++)
                for (u = 0; u < 8; u++)
                {
                    z = 0;

                    for (y = 0; y < 8; y++)
                        for (x = 0; x < 8; x++)
                        {
                            q = In[(y << 3) + x] * Coeff[(u << 3) + x] * Coeff[(v << 3) + y];
                            z += q;
                        }

                    Out[(v << 3) + u] = 0.25 * C[u] * C[v] * z;
                }
            return Out;
        }

        static double[] IDCT(double[] In)
        {
            int u, v, x, y;
            double q, z;
            double[] Out = new double[64];
            for (y = 0; y < 8; y++)
                for (x = 0; x < 8; x++)
                {
                    z = 0;

                    for (v = 0; v < 8; v++)
                        for (u = 0; u < 8; u++)
                        {
                            q = C[u] * C[v] * In[(v << 3) + u] * Coeff[(u << 3) + x] * Coeff[(v << 3) + y];
                            z += q;
                        }

                    z *= 0.25;

                    Out[(x << 3) + y] = z;
                }
            return Out;
        }