Question

I need to write a function
f(x1, x2, a1, a2)
where 0 <= x1, x2,a1,a2 < 24.
x1, x2 are points on a clock (or circle circumference) and so are a1, a2.
I need to calculate the size of the overlap between the two ranges.
For example:
f(10, 22, 6, 8) = 0 (no overlap)
f(22, 7, 6, 8) = 1 (6->7 is the overlap)
f(20, 4, 22, 6) = 6 (22->4 is the overlap)
I will appreciate any help. Thanks :)