function flatTop( t, A, tau ) {
	var s = 2.0 / (tau-1);
	return A * (A0 - (A1*cospi(s*t)) + (A2*cospi(2.0*s*t)) - (A3*cospi(3.0*s*t)) + (A4*cospi(4.0*s*t))); // eslint-disable-line max-len
}
Evaluates the flat top window function.

@private
@param {integer} t - value at which to evaluate the function
@param {number} A - amplitude
@param {integer} tau - period
@returns {number} function value