Re: [boost] MS VC10 std::numeric_limits<float>::max_digits10 iswrong for float

Subject: Re: [boost] MS VC10 std::numeric_limits<float>::max_digits10 iswrong for float
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2011-06-08 12:45:23

> -----Original Message-----
> From: boost-bounces_at_[hidden] [mailto:boost-bounces_at_[hidden]] On Behalf Of John
> Maddock
> Sent: Wednesday, June 08, 2011 5:05 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] MS VC10 std::numeric_limits<float>::max_digits10 iswrong for float
> 
> > Assuming I am right, I think this means that we need yet another macro
> > (Groans and Cries of Oh No, not another!)
> >
> > because
> >
> >  BOOST_NO_NUMERIC_LIMITS_LOWEST
> >
> > not defined is no longer an indicator that
> >
> >   max_digits10 is available (and its values correct).
> >
> > So do we need
> >
> >  BOOST_NO_NUMERIC_LIMITS_MAX_DIGITS10
> >
> > which should be defined by default, and only undefined for those
> > libraries supporting C++0X std::numeric_limits with correct values
> > like recent GCC - and others (but not <= VC10)?
> >
> > Views?
> 
> Sigh.... I guess so.  Care to submit a patch?

in dinkumware.hpp I think it should be

//  C++0x headers implemented in 520 (as shipped by Microsoft)
(assuming 520 is the version shipped with VC10 and that VC11 will correct and bump _CPPLIB_VER ?)

Note _CPPLIB_VER   <= rather than < 520 for other similar macros

#if !defined(_CPPLIB_VER) || _CPPLIB_VER <= 520
#  define BOOST_NO_NUMERIC_LIMITS_ MAX_DIGITS10
#endif

but there are many other compilers' config files and I'm not clear which versions implement C++0X
and thus presumably max_digits10 - and if anyone else has had a mental aberration/fat finger?

What I'm expecting people to be able to write is something like

int max_digits10;
#ifdef BOOST_NO_NUMERIC_LIMITS_ MAX_DIGITS10
  max_digits10 = 2 + std::numeric_limits<FPT>::digits * 3010/10000;
#else
  max_digits10 = std::numeric_limits<FPT>::max_digits10;
#endif

Paul

---
Paul A. Bristow,
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