This code for Delaunay triangulations (Voronoi diagrams) is very old
now, but I occasionally get requests for it. 

This program is based on

Dwyer, R.A., A faster divide-and-conquer algorithm for constructing
Delaunay triangulations. Algorithmica 2(2):137-151, 1987.

This was my very first paper.  Oddly, I can't seem to find tex source
(though I did find the tex source for other papers nearly as old.)
You can buy the conference version (2nd Symposium on Computational
Geometry -- ACM) for less than the Algorithmica version (Springer).
This work is mentioned in the Wikipedia entry for "Delaunay
Triangulation".

There's a short int in there that may need to be changed to an
int. Back when, I was optimizing for what now seems like a small
number of points.  Try to imagine that it took minutes to
run my largest simulations, which I think involved 32K or 64K points.
(I don't recall, but I may have been up against memory limitations, too!)

I'm including a review of several Delaunay triangulation algorithms written
by Peter Su and Scot Drysdale that showed that this was the ONE AND
ONLY VERY BEST algorithm when the survey was written.  This was later confirmed
by JR Shewchuk, http://www.cs.cmu.edu/~quake/tripaper/triangle2.html

There's also a little postscript file with a picture.  I believe this
picture was on my business cards when I was at NC State.

That's all I have to say about that, but if you have questions, you
can contact me at [email protected].  In fact, if you use this code,
why not drop me a line to let me know?