Re: [PATCH] Fortran: add Fortran 2018 IEEE_{MIN,MAX} functions

[Thomas Koenig <tkoenig@netcologne.de>]

Hi Steve,

> On Thu, Jun 08, 2023 at 12:17:02PM +0200, Thomas Koenig wrote:
[...]

> Thanks for the explanation.  As I likely will not use a POWER-based
> system, I only loosely followed the discussion.  I don't remember
> if ibm double-double is REAL(16) or REAL(17).  If ieee 128-bit is
> REAL(16), then everything should (I believe) be okay.

 From a user standpoint, REAL(16) is always used. We only use the 17
as a marker in the library, and to be able to have library versions
of IBM long double co-reside with IEEE long double.

>> There is a virutal POWER machine at OSUL dedicated to the IEEE QP
>> gfortran effort. It hasn't been used for some time, but it's still
>> active. I just bootstrapped trunk there and ran all the IEEE from the
>> testsuite manually, with
>>
>> $ for a in *.f90; do echo "Testing $a"; gfortran -o $a.exe -fno-range-check
>> -mcpu=power9 -mabi=ieeelongdouble -static-libgfortran $a signaling_1_c.c
>> signaling_2_c.c ; ./$a.exe ; done 2>&1 | grep -v command-line
>> Testing fma_1.f90
> 
> These could be misleading.  gfortran has pre-processor tokens
> for REAL(10) and REAL(16).   If __GFC_REAL_16__ isn't defined
> the ieee testing is skipped.

Hmm... need to check.  With the recently-built compiler:

$ cat tst.F90
program memain
#if __GFC_REAL_16__
   print *,"__GFC_REAL_16 found"
#endif
#if __GFC_REAL_17__
   print *,"__GFC_REAL_17 found"
#endif
   print *,"digits is ",digits(1._16)
end program memain
$ gfortran -static-libgfortran tst.F90 && ./a.out
  __GFC_REAL_16 found
  digits is          106
$ gfortran -static-libgfortran -mabi=ieeelongdouble -mcpu=power9 tst.F90 
&& ./a.out
  __GFC_REAL_16 found
  digits is          113

Looks clean.

[...]

> Should we have a __GFC_REAL_17__?

I don't think we need it - REAL(KIND=17) is not supported in
the compiler (we discussed and rejected that), and people
who mix IBM long double and IEEE long double will have no
joy with their programs; they need to recompile everything.

But we may have to do something about the files in the
thelibgfortran/ieee subdirectory.

Best regards

	Thomas