Check whether an underscore is needed for linking

If a C program needs an underscore to link against a Fortran library
append it, otherwise not

configure.ac

@@ -947,6 +947,43 @@ dnl   __m128d h1 = _fjsp_neg_v2r8(q);
 dnl   return 0;
 dnl }
 AC_LANG_PUSH([C])
+dnl check whether one can link against Fortran programs from C
+AC_MSG_CHECKING(whether we need _ in C programs to link against a Fortran library)
+AC_LINK_IFELSE([AC_LANG_SOURCE([
+int main(int argc, char **argv) {
+
+  int m, n, k, lda, ldb, ldc;
+  double alpha, beta;
+  double *a, *b, *c;
+  dgemm_("N", "N", &m, &n, &k, &alpha, a, lda, b, &ldb, &beta, c, &ldc);
+}
+ ])],
+   [can_link_with_=yes],
+   [can_link_with_=no]
+ )
+AC_MSG_RESULT([${can_link_with_}])
+if test x"$can_link_with_" = x"yes"; then
+  AC_DEFINE([NEED_UNDERSCORE_TO_LINK_AGAINST_FORTRAN],[1],[need to append an underscore])
+fi
+  
+AC_MSG_CHECKING(whether we do not need _ in C programs to link against a Fortran library)
+AC_LINK_IFELSE([AC_LANG_SOURCE([
+int main(int argc, char **argv) {
+
+  int m, n, k, lda, ldb, ldc;
+  double alpha, beta;
+  double *a, *b, *c;
+  dgemm("N", "N", &m, &n, &k, &alpha, a, lda, b, &ldb, &beta, c, &ldc);
+}
+ ])],
+   [can_link_without_=yes],
+   [can_link_without_=no]
+ )
+AC_MSG_RESULT([${can_link_without_}])
+if test x"$can_link_with_" = x"yes"; then
+  AC_DEFINE([NEED_NO_UNDERSCORE_TO_LINK_AGAINST_FORTRAN],[1],[need not to append an underscore])
+fi
+
 
 if test x"${need_vsx}" = x"yes"; then
   AC_MSG_CHECKING(whether we can compile Altivec VSX with intrinsics in C)

src/elpa_generalized/cannon.c

@@ -86,25 +86,40 @@
 #ifdef WITH_MPI
 #include <mpi.h>
 
-#if 0
-#ifndef Add_
+#ifdef NEED_NO_UNDERSCORE_TO_LINK_AGAINST_FORTRAN
 #define numroc_ numroc
 #define dlacpy_ dlacpy
-#define pdtran_ pdtran
-#define dlacpy_ dlacpy
-#define pdlacpy_ pdlacpy
 #define slacpy_ slacpy
-#define pstran_ pstran
-#define pslacpy_ pslacpy
 #define zlacpy_ zlacpy
-#define pztranc_ pztranc
-#define pzlacpy_ pzlacpy
 #define clacpy_ clacpy
+#define pdtran_ pdtran
+#define pstran_ pstran
+#define pztranc_ pztranc
 #define pctranc_ pctranc
+#define pdlacpy_ pdlacpy
+#define pslacpy_ pslacpy
+#define pzlacpy_ pzlacpy
 #define pclacpy_ pclacpy
-#endif /* Add_ */
 #endif
 
+#ifdef NEED_UNDERSCORE_TO_LINK_AGAINST_FORTRAN
+#define numroc_ numroc_
+#define dlacpy_ dlacpy_
+#define slacpy_ slacpy_
+#define zlacpy_ zlacpy_
+#define clacpy_ clacpy_
+#define pdtran_ pdtran_
+#define pstran_ pstran_
+#define pztranc_ pztranc_
+#define pctranc_ pctranc_
+#define pdlacpy_ pdlacpy_
+#define pslacpy_ pslacpy_
+#define pzlacpy_ pzlacpy_
+#define pclacpy_ pclacpy_
+#endif
+
+
+
 //***********************************************************************************************************
 
 #define REALCASE 1