On Thu, Aug 11, 2022 at 08:44:17PM +0000, Joseph Myers wrote:
> On Thu, 11 Aug 2022, Michael Meissner via Gcc-patches wrote:
>
> > In looking at it, I now believe that the type for _Float128 and __float128
> > should always be the same within the compiler. Whether we would continue to
> > use the same type for long double and _Float128/__float128 remains to be
> > seen.
>
> long double and _Float128 must always be different types; that's how it's
> defined in C23.
And when we implement C++23 P1467R9, if std::float128_t will be
_Float128 under the hood, then long double and _Float128 have to remain
distinct types and mangle differently, long double (and __float128 if
long double is IEEE quad and __float128 exists?) need to mangle the way
they currently do and _Float128 should mangle as DF128_ .
::= DF <number> _ # ISO/IEC TS 18661 binary floating point type
_FloatN (N bits)
Wonder how shall we mangle the underlying type of std::bfloat16_t though.
I assume e.g. for libstdc++ implementation purposes we need to have
__ibm128 and __float128 types mangling as long double mangles when the
-mabi={ibm,ieee}longdouble option is used, because otherwise it would be
really hard to implement it.
Jakub
