Re: [boost] [math] Support for libquadmath/ __float128

Subject: Re: [boost] [math] Support for libquadmath/ __float128
From: John Maddock (boost.regex_at_[hidden])
Date: 2013-03-07 04:20:23

>> Including that header will only work (as in not generate a compiler 
>> error)
>> if the compiler supports __float128 as a native type, which is what we 
>> want
>> to work out... basically whether the GCC build was configured to support 
>> it
>> or not.
>
> The current libstdc++ headers define _GLIBCXX_USE_FLOAT128 if
> __float128 is supported, but that's an implementation detail and
> shouldn't be relied on (relying on _GLIBCXX_HAS_GTHREADS broke
> Boost.Threads recently when GCC 4.7 stopped defining it.)

I've added minimal __float128 support in Boost.Math Trunk: it's enabled 
whenever BOOST_MATH_USE_FLOAT128 is set, which it is automatically when the 
above macro is detected (which I note libstdc++ doesn't seem to use anywhere 
itself).  Also filed a gcc bug report on the lack of a __SIZEOF__ macro for 
__float128: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56540

HTH, John.