[petsc-dev] fortran literals

[Blaise A Bourdin]

Hi,

If I recall correctly, fortran does not mandate that "selected_real_kind(5)" means the same across compilers, so that hardcoding kind values may not be portable.


Instead, I would recommend the following (not my idea, it was proposed by Michael Metcalf in comp.lang.fortran a _long_ time ago) in a top-level module.

   ! The following ensures that mef90 and PETSC real types are compatible:
   ! thanks to Michael Metcalf in comp.lang.fortran
   PetscReal,Parameter                 :: PReal = 1.0
   Integer,Parameter,Public            :: Kr = Selected_Real_Kind(Precision(PReal))
                                         
   PetscInt,Parameter                  :: PInt = 1
   Integer,Parameter,Public            :: Ki = Selected_Int_Kind(PInt)
   
   PetscLogDouble,Parameter            :: flop = 1.0
   Integer,Parameter,Public            :: PFlop = Selected_Real_Kind(Precision(flop))

so that Real(Kind = Kr) is the same as PetscReal, and literals can be written 1.234_Kr or 23_flop.

I guess PETSc could define them in the petsc module and inherited from "use petsc”. 

Blaise



> On Sep 1, 2016, at 5:37 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> 
>> On Sep 1, 2016, at 5:28 PM, Munson, Todd <tmunson at mcs.anl.gov> wrote:
>> 
>> 
>> Which platforms do not define PETSC_USE_FORTRANKIND?
> 
> It uses it everywhere the Fortran compiler supports it. 
> 
> # reverse of the above - but more standard thing to do for F90 compilers
>  def checkFortranKind(self):
>    '''Checks whether selected_int_kind etc work USE_FORTRANKIND'''
>    self.pushLanguage('FC')
>    body = '''
>        integer(kind=selected_int_kind(10)) i
>        real(kind=selected_real_kind(10)) d
> '''
>    if self.checkCompile('', body):
>      self.addDefine('USE_FORTRANKIND', 1)
>    self.popLanguage()
>    return
> 
>  Presumably any Fortran compiler that supports F90 supports it so it is not unreasonable for us to just require it and simplify PETSc in a few places.
> 
> 
> 
> 
>> Are they important
>> or can we drop support for them?
>> 
>> I could probably hack the D or Q for the others, but it would probably
>> be ugly.
>> 
>> Or I could just overrule my OCD today...
>> 
>> Todd.
>> 
>>> On Sep 1, 2016, at 5:08 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>> 
>>> 
>>>> On Sep 1, 2016, at 4:37 PM, Munson, Todd <tmunson at mcs.anl.gov> wrote:
>>>> 
>>>> 
>>>> Cool!
>>>> 
>>>> For what its worth, that only works when PETSC_USE_FORTRANKIND is true.
>>>> I'm not sure how many of the Petsc builds have this flag set.
>>> 
>>> in the other case could you try to tack on the D or Q business? 
>>> 
>>> Barry
>>> 
>>>> 
>>>> Any idea how to do the same thing in C?
>>>> 
>>>> Todd.
>>>> 
>>>>> On Sep 1, 2016, at 4:13 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
>>>>> 
>>>>> 
>>>>> On 1 September 2016 at 23:05, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>>>> I didn't have a solution to this
>>>>> 
>>>>> ! These lines should be added to $PETSC_DIR/include/petsc/finclude/petscsysdef.h
>>>>> #if defined(PETSC_USE_REAL_SINGLE)
>>>>> integer, parameter :: PETSC_REAL_KIND = selected_real_kind(5)
>>>>> #elif defined(PETSC_USE_REAL_DOUBLE)
>>>>> integer, parameter :: PETSC_REAL_KIND = selected_real_kind(10)
>>>>> #elif defined(PETSC_USE_REAL___FLOAT128)
>>>>> integer, parameter :: PETSC_REAL_KIND = selected_real_kind(20)
>>>>> #endif
>>>>> 
>>>>> ! User code should write literals this way
>>>>> PetscReal x
>>>>> x = 0.123456789123456789123456789_PETSC_REAL_KIND
>>>>> 
>>>>> 
>>>>> 
>>>>> -- 
>>>>> Lisandro Dalcin
>>>>> ============
>>>>> Research Scientist
>>>>> Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
>>>>> Extreme Computing Research Center (ECRC)
>>>>> King Abdullah University of Science and Technology (KAUST)
>>>>> http://ecrc.kaust.edu.sa/
>>>>> 
>>>>> 4700 King Abdullah University of Science and Technology
>>>>> al-Khawarizmi Bldg (Bldg 1), Office # 0109
>>>>> Thuwal 23955-6900, Kingdom of Saudi Arabia
>>>>> http://www.kaust.edu.sa
>>>>> 
>>>>> Office Phone: +966 12 808-0459
>>>> 
>>> 
>> 
> 

-- 
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