Re: [boost] [test] comparing floating point values

From: Gennadiy Rozental (gennadiy.rozental_at_[hidden])
Date: 2007-05-16 01:36:59

"John Maddock" <john_at_[hidden]> wrote in message 
news:004001c7970b$6a2dcf50$ddff1b52_at_fuji...
> Jody Hagins wrote:
>> Here's a chance for someone to finally clear my understanding of how
>> to compare floating point value... please ?!?!?
>
> :-)
>
> Let's say you want the tolerance to be N*eps where eps is the machine
> epsilon and N is you level of tolerance, then you can use either:
>
> BOOST_CHECK_CLOSE(a, b, N*100*numeric_limits<T>::epsilon()); // tolerance 
> as
> a persent
>
> or:
>
> BOOST_CHECK_FRACTION(a, b, N*numeric_limits<T>::epsilon()); // tolerance 
> as
> a fraction.

Yes. This looks correct with current interfaces.

> There are still a couple of things that can get you:
>
> 1) This will fail if one of a and b is zero and the other isn't. 
> Generally
> speeking you may want to treat all values below some threshold as
> "effectively zero", but what that threshold is depends on your use case.
>
> 2) This fails if a and b are both infinity, probably a Boost.Test bug.

You mean it should fail and it passes?

Gennadiy