[Bug c++/49813] [C++0x] sinh vs asinh vs constexpr

[ghazi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49813

--- Comment #50 from Kaveh Ghazi <ghazi at gcc dot gnu.org> 2011-07-27 23:13:18 UTC ---
(In reply to comment #46)
> Another note, about std::nextafter, std::nexttoward, & co: I see mpfr provides
> an mpfr_nexttoward, which likely could be exploited in builtins.c pretty
> easily. 
> Kaveh, do you have any plan about those?

It's been several years since I did the mpfr work so my memory is a little
foggy, but I think I intentionally skipped the next* functions.  IIRC, these
functions are very sensitive to the target floating point format.  It wasn't
clear to me that the "next" FP value in mpfr actually corresponded to the
"next" value in the target FP format or how to verify if it was so.  (I'm
thinking mainly of the non-ieee formats here.)  

If these odd formats aren't used in GCC anymore then it might be okay to
implement the builtins using mpfr.  Alternatively, you can implement the
builtins only for the formats where mpfr's format is identical to the target fp
format.  But then the optimization won't work everywhere so your library
testcase will fail on some cpus.

I'm not sure it's worth the trouble (and to answer your question I don't have
any plans to work on it.)