Of course, there will be cases where you need to check some of the initial values regardless, but often you just care if the result is valid. From a defensive p

Of course, there will be cases where you need to check some of the initial values regardless, but often you just care if the result is valid. From a defensive programming stand-point, if you don't expect any of those values to be zero, you just check for NaN at the end rather then carefully reviewing your calculations for which values you have to check. I would REALLY hate having to write a geometry library without NaN values. Both because of error checking, and the fact that NAN/INF is often the 'correct' answer when it's the result of a calculation.