[Rd] From .Fortran to .Call?

[Koenker, Roger W]

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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