Determing whether two ranges overlap

[Robin Haswell]

Hey guys

I was wondering if you could give me a hand with something. If I have two
tuples that define a range, eg: (10, 20), (15, 30), I need to determine
whether the ranges overlap each other. The algo needs to catch:

(10, 20) (15, 25)
(15, 25) (10, 20)
(10, 25) (15, 20)
and
(15, 20) (10, 25)

I can think of lots of ways to do this but it's in a tight loop so I need
it to be as efficient as possible. Any help welcome :-)

Cheers

-Rob