Re: [boost] [math] boost::math::isfinite fails with --fast-math

Subject: Re: [boost] [math] boost::math::isfinite fails with --fast-math
From: Gaetano Mendola (mendola_at_[hidden])
Date: 2012-11-26 09:47:37

On 11/26/2012 03:37 PM, Roland Bock wrote:
> On 2012-11-26 15:07, Gaetano Mendola wrote:
>> On 11/26/2012 02:42 PM, Tim Blechmann wrote:
>>>>>> I'm wandering if this is to be expected, the following code
>>>>>> fails if compiled with --fast-math:
>>>>>>
>>>>>> //====================================================
>>>>>> #include <boost/math/special_functions/fpclassify.hpp>
>>>>>> int main() {
>>>>>>     const float a = 0.0f/0.0f;
>>>>>>     assert(not boost::math::isfinite(a));
>>>>>> }
>>>>>
>>>>> Which fails - does the 0/0 actually yield an infinity?  Or is it
>>>>> isfinite that fails?
>>>>>
>>>>> Either way is hard to make guarentees once you enable an option
>>>>> like that.
>>>>
>>>> The following code:
>>>>
>>> [snip]
>>>>
>>>> so I believe somehow even with --fast-math it should be possible to
>>>> make it
>>>> "working" (if it has to be).
>>>
>>> rtfm: you asked the compiler to assume that neither arguments nor
>>> results are NaNs or Infs. if your code uses or generates NaNs or Infs
>>> its behavior is undefined.
>>
>> rtfp (p = post):  I'm saying that "if it has to be fixed" somehow
>> boost::math::isfinite
>> can still detect if a float has a "nan" configuration I was even
>> asking if that was
>> expected behavior by "boost::math::isfinite" or not.
>>
>> If boost::math::isfinite has to be "compatible" with ::isfinite() then
>> yes it's normal,
>> this can be specified in the boost documentation.
>>
>> Gaetano
>>
> Interesting as this may be, I am receiving all your mails twice (maybe a
> result of sending a copy to gmane.comp.lib.boost.devel?). Can you please
> try to change your settings?

Ops sorry, you are right, replying to all has that effect, thank you for pointing
it out.

Gaetano