Re: Best way to compare CGFloats
Re: Best way to compare CGFloats
- Subject: Re: Best way to compare CGFloats
- From: Jean-Daniel Dupas <email@hidden>
- Date: Wed, 30 Jun 2010 10:41:37 +0200
Le 30 juin 2010 à 10:35, Rimas M. a écrit :
> Hello,
>
> I am stuck with floats (doubles, to be precise) comparison.
> In part of my app, I am dealing with NSPoint components (x, y)
> comparison. On 32bit architecture NSPoint components are floats, and
> direct comparison ( float1 == float2 ) works fine. But on 64bit, they
> are doubles and '==' does not work due to precision.
>
> Lets take an example: C and D are NSPoints. Lets say C is
> (1.000000000000000444089209850063, whatever) and D is
> (1.000000000000000000000000000000, whatever).
> If my code is: if (C.x == D.x) thenDoSomething; , then thenDoSomething
> is not called. Of course.
>
> But on my needs, float is more than enough for precision.
>
> So question is, what is the most efficient (performance side) and
> simplest (coding side) way to compare those bastards?
>
> At the moment I am thinking about:
>
> a) BOOL _floatsOrDoublesAreEqual = ( (float)C.x == (float)D.x);
>
> b) BOOL _floatsOrDoublesAreEqual = ( fabs(C.x - D.x) <= _epsilon ); ,
> where _epsilon is something like 0.0001.
>
You should not rely on the fact that it works with float. Comparing floating point value is never safe.
So, as the solution a does not solve the problem (you cannot safely compare floating point value), I would choose the b.
-- Jean-Daniel
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