fix for group_compare, adding MPI_GROUP_EMPTY as a result for group_intersection/difference/union

This commit was SVN r2562.

src/mpi/c/group_compare.c

@@ -91,11 +91,11 @@ int MPI_Group_compare(MPI_Group group1, MPI_Group group2, int *result) {
 
     /* set comparison result */
     if( identical ) {
-        *result=MPI_UNEQUAL;
+        *result=MPI_IDENT;
     } else if( similar ) {
         *result=MPI_SIMILAR;
     } else {
-        *result=MPI_IDENT;
+        *result=MPI_UNEQUAL;
     }
 
     return return_value;

src/mpi/c/group_difference.c

@@ -69,6 +69,12 @@ int MPI_Group_difference(MPI_Group group1, MPI_Group group2,
         new_group_size++;
     }  /* end proc loop */
 
+    if ( 0 == new_group_size ) {
+	*new_group = MPI_GROUP_EMPTY;
+	OBJ_RETAIN(MPI_GROUP_EMPTY);
+	return MPI_SUCCESS;
+    }
+
     /* allocate a new ompi_group_t structure */
     new_group_pointer=ompi_group_allocate(new_group_size);
     if( NULL == new_group_pointer ) {

src/mpi/c/group_intersection.c

@@ -64,6 +64,13 @@ int MPI_Group_intersection(MPI_Group group1, MPI_Group group2,
         }  /* end proc2 loop */
     }  /* end proc1 loop */
 
+    if ( 0 == group_size ) {
+	*new_group = MPI_GROUP_EMPTY;
+	OBJ_RETAIN(MPI_GROUP_EMPTY);
+	return MPI_SUCCESS;
+    }
+
+
     /* fill in new group */
     new_group_pointer=ompi_group_allocate(group_size);
     if( NULL == new_group_pointer ) {

src/mpi/c/group_union.c

@@ -72,6 +72,12 @@ int MPI_Group_union(MPI_Group group1, MPI_Group group2, MPI_Group *new_group)
         new_group_size++;
     }                           /* end proc loop */
 
+    if ( 0 == new_group_size ) {
+	*new_group = MPI_GROUP_EMPTY;
+	OBJ_RETAIN(MPI_GROUP_EMPTY);
+	return MPI_SUCCESS;
+    }
+
     /* get new group struct */
     new_group_pointer = ompi_group_allocate(new_group_size);
     if (NULL == new_group_pointer) {