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

Subject: Re: [boost] [math] Support for libquadmath/ __float128
From: Jonathan Wakely (jwakely.boost_at_[hidden])
Date: 2013-02-25 14:53:44

On 25 February 2013 16:28, John Maddock wrote:
>>>> I haven't found one - gcc-4.7.2 has all sorts of __SIZEOF_XXX__ defines
>>>> for every last type
>>>
>>> *except*
>>>>
>>>> __float128 and __float80 :-(
>>>
>>>
>> Sorry for a possibly stupid questio, but is it not possible to use any of
>> the FLT128_XXX defines listed here:
>>
>>
>> http://gcc.gnu.org/onlinedocs/libquadmath/Typedef-and-constants.html#Typedef-and-constants
>
>
> 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.)