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 _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
