Re: [Cppunit-devel] CPPUNIT_ASSERT_DOUBLES_EQUAL() with non-finite numbers

[CppUnit d. m. l. <cpp...@li...>]

CppUnit development mailing list wrote:
>> C99 is non-standard in the context of C++, which is a superset of C90.
>> So, all C++ compilers might not support this.
> 
> True, they might not; do you know of a current compiler that has  
> neither isfinite() nor the older, BSD finite()?

You're right, I don't.
Then again, I'm sure I don't know all compilers currently in use.
I prefer to erring to side of caution as it isn't standard.


> Hmm.  Now that I think of it, just flipping the expression from
> testing "is not equal" to "is equal" fixes the problem with NaNs
> anyway: all boolean expressions involving a NaN are false.
> Maybe we don't need the isfinite() test after all ... or maybe
> we do; I can't remember whether "Inf - Inf" evaluates to 0.

Inf - Inf evaluates to NaN. But that assumes the right signs, I think.

How about (0.0 * <x>)?
That should evaluate to NaN only if <x> is Inf, -Inf or NaN.
So something like ((0.0 * <x>) == 0.0), if not optimized away, should be
equal to finite(<x>).


http://steve.hollasch.net/cgindex/coding/ieeefloat.html


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