On 31/07/19 20:50 +0200, Jakub Jelinek wrote:
On Wed, Jul 31, 2019 at 07:37:03PM +0100, Jonathan Wakely wrote:
On 31/07/19 19:07 +0200, Marc Glisse wrote:
> On Wed, 31 Jul 2019, Jonathan Wakely wrote:
>
> > The values of the constants are taken from Glibc where the equivalent
> > constant exists, or by rounding the actual constant to the same number
> > of digits as the Glibc constants have.
>
> How does it behave with __float128? I think that with -std=gnu++2a, it
> counts as a floating point type, but the constant first becomes a long
> double and thus loses precision.
Indeed it does:
#if !defined(__STRICT_ANSI__) && defined(_GLIBCXX_USE_FLOAT128)
template<>
struct __is_floating_point_helper<__float128>
: public true_type { };
#endif
We could add explicit specializations for __float128 and use the Q
suffix. That's not valid when __STRICT_ANSI__ is defined (unless
-fext-numeric-literals is also used) but as the snippet above shows,
__float128 isn't a floating-point type when __STRICT_ANSI__ is
defined.
Perhaps add __extension__ before the literals too?
Does that do anything for Q literals? I thought I'd tried it
previously and decided it didn't. I'm happy to add it though.
I don't know if we need more accuracy for IBM double double.
I'd think the *L constants should be good enough.
OK, great.
