81.4 is evil

I know many of you all know pretty well that floating point precision and computers don’t play nicely with each other. I think I learned about it in the first book on ‘C’ I ever read, but I had never really been bitten by it until today. I was working with a piece of code today at the office that was throwing an error saying two values weren’t zeroing out when they clearly should have been. I narrowed down the problem and after a bit of time decided that 81.4 is a terrible, terrible number. For example:

So, let that be a lesson to us all. No matter how simple the calculation, don’t blindly trust floats.