function getXY(ps: number[][]): number[][] {
    if (ps.length === 4) {
        let [[x0,y0], [x1,y1], [x2,y2], [x3,y3]] = ps;
        return [[
            x3 + 3*(x1 - x2) - x0, // t^3 - max bitlength increase 3
            3*(x2 - 2*x1 + x0),    // t^2 - max bitlength increase 4
            3*(x1 - x0),           // t^1 - max bitlength increase 3
            x0,                    // t^0 - max bitlength increase 0
        ], [
            y3 + 3*(y1 - y2) - y0, // t^3 - max bitlength increase 3
            3*(y2 - 2*y1 + y0),    // t^2 - max bitlength increase 4
            3*(y1 - y0),           // t^1 - max bitlength increase 3
            y0,                    // t^0 - max bitlength increase 0
        ]];
    } else if (ps.length === 3) {
        let [[x0,y0], [x1,y1], [x2,y2]] = ps;
        return [[
            x2 - 2*x1 + x0,  // t^2 - max bitlength increase 2
            2*(x1 - x0),     // t^1 - max bitlength increase 2
            x0,              // t^0 - max bitlength increase 0
        ], [
            y2 - 2*y1 + y0,  // t^2 - max bitlength increase 2
            2*(y1 - y0),     // t^1 - max bitlength increase 2
            y0,              // t^0 - max bitlength increase 0            
        ]];
    } else if (ps.length === 2) {
        let [[x0,y0], [x1,y1]] = ps;
        return [[
            x1 - x0,  // t^1 - max bitlength increase 1
            x0,       // t^0 - max bitlength increase 0
        ], [
            y1 - y0,  // t^1 - max bitlength increase 1
            y0,       // t^0 - max bitlength increase 0
        ]];
    }

    throw new Error('must be of length 2, 3 or 4');
}


export { getXY }