[petsc-dev] fortran literals

[Jeff Hammond]

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
> 
> 
> 
> 
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