[Rd] From .Fortran to .Call?

Koenker, Roger W rkoenker @end|ng |rom ||||no|@@edu
Sun Dec 27 11:27:18 CET 2020 

Erin,  I think rumors of the deprecation of .Fortran are greatly exaggerated, but I’d welcome some confirmation of this from
someone in R core.  There is quite a lot of .Fortran usage  in packages, and perhaps even in base R...

> On Dec 26, 2020, at 7:57 PM, Erin Hodgess <erinm.hodgess using gmail.com> wrote:
> 
> Is .Fortran going to be deprecated, please?  I have gotten amazing speed up with geostatistics processes using HPC type tools.
> 
> Thanks 
> 
> On Sat, Dec 26, 2020 at 9:48 AM Koenker, Roger W <rkoenker using illinois.edu> wrote:
> I’ve recoded a version of one of my quantile regression fitting functions to use .C64 from dotCall64 rather than .Fortran.
> For a moderately large problem with n = 500,000 and p = 5, and solving for  1:49/50 quantiles the new version shows
> a 3% speedup, although for smaller problems it is actually slower that the .Fortran version.  So, I’m (provisionally) 
> unimpressed by the claims that .Fortran has a big “overhead” performance penalty.  Compared to the(more than) an order of
> magnitude (base 10) improvement that moving from R to fortran produces,  3% isn’t really worth the (admittedly) minimal
> additional coding effort.
> 
> > On Dec 24, 2020, at 12:39 AM, Balasubramanian Narasimhan <naras using stanford.edu> wrote:
> > 
> > Also, just came to know about dotcall64::.C64() (on CRAN) which allows for Fortran to be called using .Call().
> > 
> > -Naras
> > 
> > On 12/23/20 8:34 AM, Balasubramanian Narasimhan wrote:
> >> I think it should be pretty easy to fix up SUtools to use the .Call instead of .Fortran following along the lines of
> >> 
> >> https://urldefense.com/v3/__https://github.com/wrathematics/Romp__;!!DZ3fjg!r3_sswU4ZHCe3huoGUy2boX-Vr7aUS-RaExyeh_Rsv8gvGiABcqzvOOKZinG4kC7RtA$ 
> >> 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://urldefense.com/v3/__https://github.com/wrathematics/Romp__;!!DZ3fjg!r3_sswU4ZHCe3huoGUy2boX-Vr7aUS-RaExyeh_Rsv8gvGiABcqzvOOKZinG4kC7RtA$     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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> >> 
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> -- 
> Erin Hodgess, PhD
> mailto: erinm.hodgess using gmail.com

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