[cxx-abi-dev] decimal floating point support for C++

[Lawrence Crowl]

On 8/4/09, David Vandevoorde <daveed at edg.com> wrote:
>  On Aug 4, 2009, at 2:26 PM, Janis Johnson wrote:
> > On Thu, 2009-07-30 at 11:09 -0700, Mark Mitchell wrote:
> > > Jason Merrill wrote:
> > > > > Given that libstdc++ is used with compilers other than G++, is it
> > > > > reasonable to depend on non-standard C++ compiler support?
> > > >
> > > > The question for this list is, rather, do we want to standardise the
> > > > necessary compiler support?
> > >
> > > What support would we be standardizing?  Special handling of these
> > > classes, or some source-level attribute for passing these classes as if
> > > they were scalars, or ...?
> >
> > First off would be allowing the classes to use, internally, something
> > like
> >
> >  typedef float _decfloat64 __attribute__((mode(DD)));
> >
> > or the equivalent for each compiler that uses libstdc++ and for which
> > <decimal> would be supported.
> >
> > Secondly, a way to use that type for extern "C" function declarations
> > (or perhaps a source-level attribute) to pass the class as a scalar
> > using the target's ABI for decimal float types.
>
> IMO the distinction should _not_ be based on extern "C" vs. extern "C++".
> The classes should be marked as being just generally "magical" in that
> they're transferred like native _DecimalN types no matter what the calling
> convention.
>
> We'd also need to clarify that such class types mangle with the Dd/De/Df
> codes and not the usual class type rules.

I agree with Daveed here.  The real problem is that compilers either
need to recognize the name or the libstdc++ source needs to specially
mark them.  I lean towards doing the former.

-- 
Lawrence Crowl