https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50060
--- Comment #11 from Paul A. Bristow <pbristow at hetp dot u-net.com> ---
Thanks for all this, which looks helpful, but I am not able to use unreleased
compiler versions, so meanwhile I am working to use a workaround (to allow me
to see what other pitfalls lie ahead for the novice ;-). FWIW my proof of
concept is
// Version that returns both mantissa and exponent as a tuple.
// Proof of concept only, ignoring sign, overflow, denorm, infinite and NaNs.
constexpr std::tuple<float, int> frexp(float f)
{
int e = 0;
if (f >= 1.f)
{
f /= 2 ;
e++;
}
else if (f <= 0.1f)
{
f *= 2;
e--;
}
return std::make_tuple(f, e);
}
allowing
constexpr std::tuple<float, int> ee = frexp(1.f);
(I can confirm by checking that debugging will not step into the function, and
also I can assign the tuple or the elements to a constexpr variable.)
Of course, this isn't a 'drop-in' for std::frexp, nor templated on other
floating-point types, like Boost.Multiprecision types, but it will help for
now.
I hope that this can be resolved somehow eventually, though I fear the pointer
update will always be a nono for constexpr, preventing a truely 'drop-in'
solution thus preventing any function that uses frexp from being constexpr.
