What can this circuit be useful for?

I have calculated the boolean functions for $$r$$ and $$f$$:

$$f = \overline{s_1} \cdot s_0 + s_1 \cdot \overline{s_0}$$.

$$r = \overline{s_0 \cdot s_1 \cdot s_2 \cdot s_3}$$.

Do you have an idea what an application for this circuit can be? I don't know where we would use it.