Probably known better as a CPU stress test in the overclocking world - the famous Prime95. People run it for x hours straight to prove system stability.

Linux overclockers can get in on the fun too. On Gentoo it's installed with "emerge gimps" and the stress test is launched with "/opt/gimps/mprime -t".

Wow. I feel old. I used to run this in old x86 clusters on breadracks in my basement when I was in highschool (1997-2000).

Folklore goes Intel used to use Prime95 for stress testing it was so thorough.

If you want to see what a very well optimized piece of code looks like dig into the source code of this project. Especially the fft bit.