double GetFractionalPart(double num) {

    var frac = num;
    // ...
    if(frac >= 32) {
        frac -= 32;
    }
    if(frac >= 16) {
        frac -= 16;
    }
    if(frac >= 8) {
        frac -= 8;
    }
    if(frac >= 4) {
        frac -= 4;
    }
    if(frac >= 2) {
        frac -= 2;
    }
    if(frac >= 1) {
        frac -= 1;
    }

    return frac;

}

double Floor(double num) {
    var frac = GetFractionalPart(Math.Abs(num));
    if(num > 0) {
        num -= frac;
    }
    else {
        num += frac;
    }
    return num;

}