def calc_x(f, t):
    """Calc x coordinate by params.

    :param f: the interp params
    :type f: dict
    :param t: the accumulation of steps
    :type t: int
    :return: x coordinate
    :rtype: float
    """
    return f['a_x'] + f['b_x'] * t + f['c_x'] * t * t + f['d_x'] * t * t * t