Re: [Patch v3 Fortran] Fix c_float128 and c_float128_complex on targets with 128-bit long double.

[Iain Sandoe <idsandoe@googlemail.com>]

Hi Folks

> On 11 Aug 2021, at 11:55, Segher Boessenkool <segher@kernel.crashing.org> wrote:

> On Tue, Aug 10, 2021 at 04:46:11PM -0600, Sandra Loosemore wrote:
>> OK.  I used your wording verbatim for the first one.  For the second 
>> one, I'm still pretty confused as I think it is at least theoretically 
>> possible on PowerPC to have a target with 64-bit long double (AIX?) that 
> 
> Some embedded and embedded-like subtargets use 64-bit long double by
> default.  You can also configure this on any Power target (not that it
> will necessarily work ;-) )
> 
> I don't know if any subtarget with default 64-bit long double supports
> Fortran.

I realize that this is not directly relevant to unscrambling the PPC 128bit stuff,
but aarch64-apple-darwin2x has only 64b long double and supports gfortran.
(on both the new M1 desktop macOS and embedded iOS)

 - it is not clear to me yet if there will at some point be a transition to a 128b
   long double for at least the desktop version.

So the permutation definitely exists for at least one non-legacy, non-embedded
platform (and gfortran is very much in demand from the new M1 users).

Iain

>> also supports the __ibm128 format, and it would be wrong to assume that 
>> *any* 128-bit mode that's not long double is IEEE.
> 
> Absolutely.  Modes are not types, and types are not modes.  There are
> 128-bit floating point modes that are not IEEE, there are that are, and
> either can be used for long double, or neither.
> 
> 
> Segher