How dangerous is it to compare floating point values?

Question

I know UIKit uses CGFloat because of the resolution independent coordinate system.

But every time I want to check if for example fram

Answer 1

Since 0 is exactly representable as an IEEE754 floating-point number (or using any other implementation of f-p numbers I've ever worked with) comparison with 0 is probably safe. You might get bitten, however, if your program computes a value (such as theView.frame.origin.x) which you have reason to believe ought to be 0 but which your computation cannot guarantee to be 0.

To clarify a little, a computation such as :

areal = 0.0

will (unless your language or system is broken) create a value such that (areal==0.0) returns true but another computation such as

areal = 1.386 - 2.1*(0.66)

may not.

If you can assure yourself that your computations produce values which are 0 (and not just that they produce values which ought to be 0) then you can go ahead and compare f-p values with 0. If you can't assure yourself to the required degree, best stick to the usual approach of 'toleranced equality'.

In the worst cases the careless comparison of f-p values can be extremely dangerous: think avionics, weapons-guidance, power-plant operations, vehicle navigation, almost any application in which computation meets the real world.

For Angry Birds, not so dangerous.