[R-pkg-devel] R_registerRoutines, etc.

[Avraham Adler]

On Sat, Apr 22, 2017 at 6:13 PM, Rolf Turner <r.turner at auckland.ac.nz> wrote:
>
> The foregoing "official" way would seem to apply to functions called by
> ".Call" (which I never use; it is way over my head).  What about functions
> called by ".Fortran()" or ".C()"?
>
>> |     (b) For the sake of completeness, how *does* one replace the "void
>> *"
>> |         constructions with "actual types" in a correct manner?
>> |
>> |          Example:  In my init.c file I currently have (as produced by
>> |          package_native_routine_registration_skeleton()) :
>> |
>> | > extern void F77_NAME(mnnd)(void *, void *, void *, void *, void *);
>> |
>> |          The code in mnnd.f reads:
>> |
>> | > subroutine mnnd(x,y,n,dminbig,dminav)
>> | > implicit double precision(a-h,o-z)
>> | > .....
>> |
>> |          I.e. the "actual types are "double precision",
>> |          "double precision", "integer", "double precision",
>> |          "double precision".
>> |
>> |          So in this case I should (?) replace
>> |
>> | > extern void F77_NAME(mnnd)(void *, void *, void *, void *, void *);
>> |
>> |          by .... what?  Can anyone tell me?
>>
>> No idea. I don't deal in Fortran. C++ is more than enough fun for me ;-)
>
>
> Well, C++ is too much for me.  I find Fortran generally very easy.  Be that
> as it were, are there any Fortran users out there who can answer my
> question, above?
>

I cannot answer your question completely, as I use .Call() to call
Fortran from R via C instead of using .Fortran—from what I have read
and researched, it is faster.

That being said, maybe this will help. Given a subroutine in Fortran
which starts like:

    subroutine ddelap_f(x, nx, a, na, b, nb, l, nl, lg, pmfv) bind(C,
name="ddelap_f")

    integer(kind = c_int), intent(in), value         :: nx, na, nb, nl
    ! Sizes
    real(kind = c_double), intent(in), dimension(nx) :: x
    ! Observations
    real(kind = c_double), intent(out), dimension(nx):: pmfv
    ! Result
    real(kind = c_double), intent(in)                :: a(na), b(nb),
l(nl)! Parameters
    integer(kind = c_int), intent(in)                :: lg
    ! Log flag
    integer                                          :: i
    ! Integer

The corresponding C code which calls it is

    void ddelap_f(double *x, int nx, double *a, int na, double *b, int
nb, double *l, int nl,
                  int *lg, double *ret);

and the actual code called by R is:

    extern SEXP ddelap_C(SEXP x, SEXP alpha, SEXP beta, SEXP lambda, SEXP lg){
      const int nx = LENGTH(x);
      const int na = LENGTH(alpha);
      const int nb = LENGTH(beta);
      const int nl = LENGTH(lambda);
      SEXP ret;
      PROTECT(ret = allocVector(REALSXP, nx));
      ddelap_f(REAL(x), nx, REAL(alpha), na, REAL(beta), nb,
REAL(lambda), nl, INTEGER(lg), REAL(ret));
      UNPROTECT(1);
      return(ret);
    }

Also, I don't use the "automatic" concatenation of the "c_" to my
Fortran functions, but name them individually and use Fortran 2003 ISO
C bindings (except for booleans).

If it helps, take a look at the source code at
<https://bitbucket.org/aadler/delaporte>. As of now, it passes all R
checks and so must have appeased the registration requirements 8-)

Thank you,

Avi