/*
Short Discrete Cosine Transform
    data length :8x8
    method      :row-column, radix 4 FFT
functions
    ddct8x8s  : 8x8 DCT
function prototypes
    void ddct8x8s(int isgn, float **a);
*/


/*
-------- 8x8 DCT (Discrete Cosine Transform) / Inverse of DCT --------
    [definition]
        <case1> Normalized 8x8 IDCT
            C[k1][k2] = (1/4) * sum_j1=0^7 sum_j2=0^7 
                            a[j1][j2] * s[j1] * s[j2] * 
                            cos(pi*j1*(k1+1/2)/8) * 
                            cos(pi*j2*(k2+1/2)/8), 0<=k1<8, 0<=k2<8
                            (s[0] = 1/sqrt(2), s[j] = 1, j > 0)
        <case2> Normalized 8x8 DCT
            C[k1][k2] = (1/4) * s[k1] * s[k2] * sum_j1=0^7 sum_j2=0^7 
                            a[j1][j2] * 
                            cos(pi*(j1+1/2)*k1/8) * 
                            cos(pi*(j2+1/2)*k2/8), 0<=k1<8, 0<=k2<8
                            (s[0] = 1/sqrt(2), s[j] = 1, j > 0)
    [usage]
        <case1>
            ddct8x8s(1, a);
        <case2>
            ddct8x8s(-1, a);
    [parameters]
        a[0...7][0...7] :input/output data (double **)
                         output data
                             a[k1][k2] = C[k1][k2], 0<=k1<8, 0<=k2<8
*/


/* Cn_kR = sqrt(2.0/n) * cos(pi/2*k/n) */
/* Cn_kI = sqrt(2.0/n) * sin(pi/2*k/n) */
/* Wn_kR = cos(pi/2*k/n) */
/* Wn_kI = sin(pi/2*k/n) */
#define C8_1R   0.49039264020161522456
#define C8_1I   0.09754516100806413392
#define C8_2R   0.46193976625564337806
#define C8_2I   0.19134171618254488586
#define C8_3R   0.41573480615127261854
#define C8_3I   0.27778511650980111237
#define C8_4R   0.35355339059327376220
#define W8_4R   0.70710678118654752440


void ddct8x8s(int isgn, float **a)
{
    int j;
    float x0r, x0i, x1r, x1i, x2r, x2i, x3r, x3i;
    float xr, xi;
    
    if (isgn < 0) {
        for (j = 0; j <= 7; j++) {
            x0r = a[0][j] + a[7][j];
            x1r = a[0][j] - a[7][j];
            x0i = a[2][j] + a[5][j];
            x1i = a[2][j] - a[5][j];
            x2r = a[4][j] + a[3][j];
            x3r = a[4][j] - a[3][j];
            x2i = a[6][j] + a[1][j];
            x3i = a[6][j] - a[1][j];
            xr = x0r + x2r;
            xi = x0i + x2i;
            a[0][j] = C8_4R * (xr + xi);
            a[4][j] = C8_4R * (xr - xi);
            xr = x0r - x2r;
            xi = x0i - x2i;
            a[2][j] = C8_2R * xr - C8_2I * xi;
            a[6][j] = C8_2R * xi + C8_2I * xr;
            xr = W8_4R * (x1i - x3i);
            x1i = W8_4R * (x1i + x3i);
            x3i = x1i - x3r;
            x1i += x3r;
            x3r = x1r - xr;
            x1r += xr;
            a[1][j] = C8_1R * x1r - C8_1I * x1i;
            a[7][j] = C8_1R * x1i + C8_1I * x1r;
            a[3][j] = C8_3R * x3r - C8_3I * x3i;
            a[5][j] = C8_3R * x3i + C8_3I * x3r;
        }
        for (j = 0; j <= 7; j++) {
            x0r = a[j][0] + a[j][7];
            x1r = a[j][0] - a[j][7];
            x0i = a[j][2] + a[j][5];
            x1i = a[j][2] - a[j][5];
            x2r = a[j][4] + a[j][3];
            x3r = a[j][4] - a[j][3];
            x2i = a[j][6] + a[j][1];
            x3i = a[j][6] - a[j][1];
            xr = x0r + x2r;
            xi = x0i + x2i;
            a[j][0] = C8_4R * (xr + xi);
            a[j][4] = C8_4R * (xr - xi);
            xr = x0r - x2r;
            xi = x0i - x2i;
            a[j][2] = C8_2R * xr - C8_2I * xi;
            a[j][6] = C8_2R * xi + C8_2I * xr;
            xr = W8_4R * (x1i - x3i);
            x1i = W8_4R * (x1i + x3i);
            x3i = x1i - x3r;
            x1i += x3r;
            x3r = x1r - xr;
            x1r += xr;
            a[j][1] = C8_1R * x1r - C8_1I * x1i;
            a[j][7] = C8_1R * x1i + C8_1I * x1r;
            a[j][3] = C8_3R * x3r - C8_3I * x3i;
            a[j][5] = C8_3R * x3i + C8_3I * x3r;
        }
    } else {
        for (j = 0; j <= 7; j++) {
            x1r = C8_1R * a[1][j] + C8_1I * a[7][j];
            x1i = C8_1R * a[7][j] - C8_1I * a[1][j];
            x3r = C8_3R * a[3][j] + C8_3I * a[5][j];
            x3i = C8_3R * a[5][j] - C8_3I * a[3][j];
            xr = x1r - x3r;
            xi = x1i + x3i;
            x1r += x3r;
            x3i -= x1i;
            x1i = W8_4R * (xr + xi);
            x3r = W8_4R * (xr - xi);
            xr = C8_2R * a[2][j] + C8_2I * a[6][j];
            xi = C8_2R * a[6][j] - C8_2I * a[2][j];
            x0r = C8_4R * (a[0][j] + a[4][j]);
            x0i = C8_4R * (a[0][j] - a[4][j]);
            x2r = x0r - xr;
            x2i = x0i - xi;
            x0r += xr;
            x0i += xi;
            a[0][j] = x0r + x1r;
            a[7][j] = x0r - x1r;
            a[2][j] = x0i + x1i;
            a[5][j] = x0i - x1i;
            a[4][j] = x2r - x3i;
            a[3][j] = x2r + x3i;
            a[6][j] = x2i - x3r;
            a[1][j] = x2i + x3r;
        }
        for (j = 0; j <= 7; j++) {
            x1r = C8_1R * a[j][1] + C8_1I * a[j][7];
            x1i = C8_1R * a[j][7] - C8_1I * a[j][1];
            x3r = C8_3R * a[j][3] + C8_3I * a[j][5];
            x3i = C8_3R * a[j][5] - C8_3I * a[j][3];
            xr = x1r - x3r;
            xi = x1i + x3i;
            x1r += x3r;
            x3i -= x1i;
            x1i = W8_4R * (xr + xi);
            x3r = W8_4R * (xr - xi);
            xr = C8_2R * a[j][2] + C8_2I * a[j][6];
            xi = C8_2R * a[j][6] - C8_2I * a[j][2];
            x0r = C8_4R * (a[j][0] + a[j][4]);
            x0i = C8_4R * (a[j][0] - a[j][4]);
            x2r = x0r - xr;
            x2i = x0i - xi;
            x0r += xr;
            x0i += xi;
            a[j][0] = x0r + x1r;
            a[j][7] = x0r - x1r;
            a[j][2] = x0i + x1i;
            a[j][5] = x0i - x1i;
            a[j][4] = x2r - x3i;
            a[j][3] = x2r + x3i;
            a[j][6] = x2i - x3r;
            a[j][1] = x2i + x3r;
        }
    }
}