Algorithm for sunrise and sunset?

Hello all,

I'm sorry if this question is out of place here, but I have no idea
where to look.

I'm looking for a way to calculate the time of sunrise and sunset
given a UTC date & time and a set of coordinates.

I don't care about a specific programming language, as long as I can
figure out the formulae behind the thing.

Thanks in advance,
--
Martijn @ Coppoolse .com