DCT

const MtxDCT = (function(N) {
    var dct = new Array(N);
    for(var i=0; i<N; i++) {
        var Ci = Math.sqrt(i ? 2/N : 1/N);
        dct[i] = new Array(N);
        for(var j=0; j<N; j++)
            dct[i][j] = Ci*Math.cos(Math.PI*(j+0.5)*i/N);
    }
    return dct;
})(8);

const MtxIDCT = (function(dct) {
    var N = dct.length;
    var idct = new Array(N);
    for(var i=0; i<N; i++) {
        idct[i] = new Array(N);
        for(var j=0; j<N; j++)
            idct[i][j] = dct[j][i];
    }
    return idct;
})(MtxDCT);

function Mul(left, right) {
    if (left.length !== right.length)
        throw new Error('left.length !== right.length');

    var N = left.length;
    var Y = new Array(N);
    for(var i=0; i<N; i++) {
        Y[i] = new Array(N);
        for(var j=0; j<N; j++) {
            Y[i][j] = 0;
            for(var k=0; k<N; k++)
                Y[i][j] += left[i][k]*right[k][j];
        }
    }
    return Y;
}

function INT(block) {
    var Y = new Array(block.length);
    for(var i=0; i<block.length; i++) {
        Y[i] = new Array(block[i].length);
        for(var j=0; j<block[i].length; j++)
            Y[i][j] = Math.round(block[i][j]);
    }
    return Y;
}

module.exports = {
    F: block => Mul(Mul(MtxDCT, block), MtxIDCT),
    f: block => Mul(Mul(MtxIDCT, block), MtxDCT),
    INT
}

////////////////////// TEST ////////////////////////////

const dct = require('./dct');
const D = [
    [ 36, 242, 131,  90,  35,  19, 156,  26],
    [ 32, 176, 160, 189, 198,  45, 132,  86],
    [  6, 253, 191,  99, 246, 223, 196,  28],
    [234,  61,  98, 159, 141, 134, 221,  90],
    [102, 221,  98, 253, 167,  72,  81,  78],
    [ 46,   8, 243, 124, 119, 170, 166, 212],
    [ 91, 187, 112, 186, 210, 228, 125, 114],
    [ 71, 117, 207, 188,  66, 192,  27, 112]
];

console.log(D);
console.log(dct.INT(dct.f(dct.F(D))));