[Rd] From .Fortran to .Call?

[Balasubramanian Narasimhan]

I think it should be pretty easy to fix up SUtools to use the .Call 
instead of .Fortran following along the lines of

https://github.com/wrathematics/Romp

I too deal with a lot of f77 and so I will most likely finish it before 
the new year, if not earlier. (Would welcome testers besides myself.)

Incidentally, any idea of what the performance hit is, quantitatively? I 
confess I never paid attention to it myself as most Fortran code I use 
seems pretty fast, i.e. glmnet.

-Naras


On 12/23/20 3:57 AM, Koenker, Roger W wrote:
> Thanks to all and best wishes for a better 2021.
>
> Unfortunately I remain somewhat confused:
>
> 	o  Bill reveals an elegant way to get from my rudimentary  registration setup to
> 	one that would explicitly type the C interface functions,
>
> 	o Ivan seems to suggest that there would be no performance gain from doing this.
>
> 	o  Naras’s pcLasso package does use the explicit C typing, but then uses .Fortran
> 	not .Call.
>
> 	o  Avi uses .Call and cites the Romp package https://github.com/wrathematics/Romp
> 	where it is asserted that "there is a (nearly) deprecated interface .Fortran() which you
> 	should not use due to its large performance overhead.”
>
> As the proverbial naive R (ab)user I’m left wondering:
>
> 	o  if I updated my quantreg_init.c file in accordance with Bill’s suggestion could I
> 	then simply change my .Fortran calls to .Call?
>
> 	o  and if so, do I need to include ALL the fortran subroutines in my src directory
> 	or only the ones called from R?
>
> 	o  and in either case could I really expect to see a significant performance gain?
>
> Finally, perhaps I should stipulate that my fortran is strictly f77, so no modern features
> are in play, indeed most of the code is originally written in ratfor, Brian Kernighan’s
> dialect from ancient times at Bell Labs.
>
> Again,  thanks to all for any advice,
> Roger
>
>
>> On Dec 23, 2020, at 1:11 AM, Avraham Adler <avraham.adler using gmail.com> wrote:
>>
>> Hello, Ivan.
>>
>> I used .Call instead of .Fortran in the Delaporte package [1]. What
>> helped me out a lot was Drew Schmidt's Romp examples and descriptions
>> [2]. If you are more comfortable with the older Fortran interface,
>> Tomasz Kalinowski has a package which uses Fortran 2018 more
>> efficiently [3]. I haven't tried this last in practice, however.
>>
>> Hope that helps,
>>
>> Avi
>>
>> [1] https://urldefense.com/v3/__https://CRAN.R-project.org/package=Delaporte__;!!DZ3fjg!s1-ihrZ9DPUtXpxdIpJPA1VedpZFt12Ahmn4CycOmile_uSahFZnJPn_5KPITBN5NK8$
>> [2] https://urldefense.com/v3/__https://github.com/wrathematics/Romp__;!!DZ3fjg!s1-ihrZ9DPUtXpxdIpJPA1VedpZFt12Ahmn4CycOmile_uSahFZnJPn_5KPISF5aCYs$
>> [3] https://urldefense.com/v3/__https://github.com/t-kalinowski/RFI__;!!DZ3fjg!s1-ihrZ9DPUtXpxdIpJPA1VedpZFt12Ahmn4CycOmile_uSahFZnJPn_5KPIbwXmXqY$
>>
>> Tomasz Kalinowski
>>
>>
>>
>> On Tue, Dec 22, 2020 at 7:24 PM Balasubramanian Narasimhan
>> <naras using stanford.edu> wrote:
>>> To deal with such Fortran issues in several packages I deal with, I
>>> wrote the SUtools package (https://urldefense.com/v3/__https://github.com/bnaras/SUtools__;!!DZ3fjg!s1-ihrZ9DPUtXpxdIpJPA1VedpZFt12Ahmn4CycOmile_uSahFZnJPn_5KPIJ5BbDwA$ ) that you
>>> can try.  The current version generates the registration assuming
>>> implicit Fortran naming conventions though. (I've been meaning to
>>> upgrade it to use the gfortran -fc-prototypes-external flag which should
>>> be easy; I might just finish that during these holidays.)
>>>
>>> There's a vignette as well:
>>> https://urldefense.com/v3/__https://bnaras.github.io/SUtools/articles/SUtools.html__;!!DZ3fjg!s1-ihrZ9DPUtXpxdIpJPA1VedpZFt12Ahmn4CycOmile_uSahFZnJPn_5KPITq9-Quc$
>>>
>>> -Naras
>>>
>>>
>>> On 12/19/20 9:53 AM, Ivan Krylov wrote:
>>>> On Sat, 19 Dec 2020 17:04:59 +0000
>>>> "Koenker, Roger W" <rkoenker using illinois.edu> wrote:
>>>>
>>>>> There are comments in various places, including R-extensions §5.4
>>>>> suggesting that .Fortran is (nearly) deprecated and hinting that use
>>>>> of .Call is more efficient and now preferred for packages.
>>>> My understanding of §5.4 and 5.5 is that explicit routine registration
>>>> is what's important for efficiency, and your package already does that
>>>> (i.e. calls R_registerRoutines()). The only two things left to add
>>>> would be types (REALSXP/INTSXP/...) and styles (R_ARG_IN,
>>>> R_ARG_OUT/...) of the arguments of each subroutine.
>>>>
>>>> Switching to .Call makes sense if you want to change the interface of
>>>> your native subroutines to accept arbitrary heavily structured SEXPs
>>>> (and switching to .External could be useful if you wanted to play with
>>>> evaluation of the arguments).
>>>>
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