[Rd] Calling FORTRAN function from R issue?

[Berwin A Turlach]

G'day Dominick,

On Mon, 5 Mar 2012 19:21:01 -0500
Dominick Samperi <djsamperi at gmail.com> wrote:

> Section 5.2 of the R manual (on Extending R) says that only
> FORTRAN subroutines can be called (not functions), probably
> because of the non-standard way the compilers map FORTRAN
> function names to symbols in the DLL.

Section 5.2 deals with calling C/FORTRAN code from R via .C()
or .Fortran(), and is not directly relevant to the question on how to
call FORTRAN code from C code. :)
 
> This is consistent with the interface prototype for the BLAS
> routine zdotc contained in <R>/include/R_ext/BLAS.h, namely,
> 
> BLAS_extern Rcomplex
>     F77_NAME(zdotc)(Rcomplex * ret_val, int *n,
> 		    Rcomplex *zx, int *incx, Rcomplex *zy, int *incy);
> 
>[...]
>
> On the other hand, this is not consistent with the standard
> FORTRAN definition for zdotc that is contained in
> <R>/src/extra/blas/cmplxblas.f, where the first argument is
> n, not ret_val. 

This seems to be indeed inconsistent and, presumably, a bug.  Applying
the attach patch to R's development version (compiles, installs and
passes all checks with this patch), and changing in your code the line

	F77_CALL(zdotc)(&ret_val, &n, zx, &incx, zy, &incy);

to

	ret_val = F77_CALL(zdotc)(&n, zx, &incx, zy, &incy);

produces the expected output.

> Consequently, it is not clear where the wrapper
> is defined that is called via the prototype.

The F77_xxxx macros seem to be defined in <R>/include/R_ext/RS.h, and
their sole purpose seems to be to append a _ to the argument if
needed.  

Cheers,

	Berwin
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