[PATCH] gfortran -- Map REAL128 to REAL kind type with widest precision

[Steve Kargl]

On Thu, Feb 09, 2017 at 07:35:11PM -0800, Jerry DeLisle wrote:
> On 02/09/2017 12:40 PM, Janne Blomqvist wrote:
> > On Thu, Feb 9, 2017 at 8:33 PM, Steve Kargl
> > <sgk@troutmask.apl.washington.edu> wrote:
> >> On Thu, Feb 09, 2017 at 12:10:02PM +0200, Janne Blomqvist wrote:
> >>>
> >>> That being said, I think even with Steve's patch, it's not guaranteed
> >>> to give you IEEE 754-2008 binary128. E.g. on IBM POWER targets,
> >>> depending on the ABI you may get an IBM extended double (double-double
> >>> or __ibm128) format. Although if IEEE binary128 is also available,
> >>> with Steve's patch you should get that one has it has more precision
> >>> that __ibm128.
> >>
> >> I do not have to a IBM POWER system, so cannot easily check the
> >> effect of my patch.
> 
> On IBM Power
> 
> program foo
>     use iso_fortran_env
>     REAL(REAL128) x
>     print '(3(I0,1X))', kind(x), digits(x), precision(x)
> end program foo
> 
> $ gfc -static foo.f90
> $ ./a.out
> 16 106 31
> 

That is the double-double format.  The gcc manual says that
powerpc takes a -mfloat128 option (among others).  This will
probably give you 16 113 33.

-- 
Steve
20161221 https://www.youtube.com/watch?v=IbCHE-hONow