In order to find the extrema, we need to solve the equation
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(the derivative equals zero),
and the roots of this equation are the extrema of this function:
$$\frac{d}{d x} f{\left(x \right)} = $$
the first derivative$$\frac{\left(x - 256\right) \left(x - 8\right) \left(x - 4\right) \left(x - 2\right) \left(- \left(x - 3\right) \left(x - 1\right) \left(x - 7\right) - \left(x - 255\right) \left(\left(x - 7\right) \left(2 x - 4\right) + \left(x - 3\right) \left(x - 1\right)\right)\right)}{\left(x - 255\right)^{2} \left(x - 7\right)^{2} \left(x - 3\right)^{2} \left(x - 1\right)^{2}} + \frac{1}{\left(x - 255\right) \left(x - 7\right) \left(x - 3\right) \left(x - 1\right)} \left(\left(x - 4\right) \left(x - 2\right) \left(x - 8\right) + \left(x - 256\right) \left(\left(x - 8\right) \left(2 x - 6\right) + \left(x - 4\right) \left(x - 2\right)\right)\right) = 0$$
Solve this equationSolutions are not found,
function may have no extrema