Subject: Re: [boost] [math] boost::math::isfinite fails with --fast-math
From: Roland Bock (rbock_at_[hidden])
Date: 2012-11-26 09:37:05
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?
Thanks and regards,
Roland