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git-svn-id: https://svn.r-project.org/R/trunk@87102 00db46b3-68df-0310-9c12-caf00c1e9a41

src/include/R_ext/RS.h

@@ -74,7 +74,22 @@ extern void R_chk_free(void *);
 
 /* S Like Fortran Interface */
 /* These may not be adequate everywhere. Convex had _ prepending common
- blocks, and some compilers may need to specify Fortran linkage */
+ blocks, and some compilers may need to specify Fortran linkage.
+
+ Note that this is an F77 interface, intended only for valid F77
+ names of <= 6 ASCII characters (and no underscores) and there is an
+ implicit assumption that the Fortran compiler maps names to
+ lower-case (and 'x' is lower-case when called).
+
+ The configure code has
+
+ HAVE_F77_EXTRA_UNDERSCORE
+ Define if your Fortran compiler appends an extra_underscore to
+ external names containing an underscore.
+
+ but that is not used here (and none of gfortran, flang-new nor
+ x86_64 ifx do so: earlier Intel x86 compilere might have).
+ */
 
 #ifdef HAVE_F77_UNDERSCORE
 # define F77_CALL(x) x ## _