[petsc-dev] fortran literals

[Blaise A Bourdin]

Neat.
I was not aware of this.

Blaise

> On Sep 1, 2016, at 9:26 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
> 
> https://gcc.gnu.org/onlinedocs/gfortran/ISO_005fFORTRAN_005fENV.htmlhas real{32,64,128} that does a nice job for this situation. 
> 
> Jeff
> 
> Sent from my iPhone
> 
>> On Sep 1, 2016, at 4:15 PM, Blaise A Bourdin <bourdin at lsu.edu> wrote:
>> 
>> 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
>> 
>> -- 
>> Department of Mathematics and Center for Computation & Technology
>> Louisiana State University, Baton Rouge, LA 70803, USA
>> Tel. +1 (225) 578 1612, Fax  +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin
>> 
>> 
>> 
>> 
>> 
>> 
>> 

-- 
Department of Mathematics and Center for Computation & Technology
Louisiana State University, Baton Rouge, LA 70803, USA
Tel. +1 (225) 578 1612, Fax  +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin