Oh, yes... This. Had a project like this not long ago. NaNs almost killed me. The code used complex numbers, and you know who their userbase is. Anyway, exact floating point comparisons made all of this possible.

In the process my coworker and found something we believed to be a bug with complex nans in some recent GCC versions, but where not smart enough to understand whether it is actually a bug or undefined behaviour in the standart.

Anyway, we where so exhausted from the refactor, we didn't follow it up again.