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

Subject: Re: [boost] [math] boost::math::isfinite fails with --fast-math
From: Tim Blechmann (tim_at_[hidden])
Date: 2012-11-26 08:42:36

>>> 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.