[Re-]Fix #1463 with a little thing that I like to call "the right

way".

Don't modify coords in the top-level API function because coords is an
IN variable.  Instead, as Nysal noted, the real cause of the problem
was a missing ! down in topo_base_cart_rank.c.  Put a comment down in
topo_base_cart_rank.c explaining what's going on so that the code is
not so cryptic.

Refs trac:1363.

This commit was SVN r19487.

The following Trac tickets were found above:
  Ticket 1363 --> https://svn.open-mpi.org/trac/ompi/ticket/1363

ompi/mca/topo/base/topo_base_cart_rank.c

@@ -63,14 +63,18 @@ int mca_topo_base_cart_rank (MPI_Comm comm,
    for (; i >= 0; --i, --c, --d, --p) {
        dim = *d;
        ord = *c;
-        if ((ord < 0) || (ord >= dim)) {
-          if (*p) {
-             return MPI_ERR_ARG;
-          }
-          ord %= dim;
-          if (ord < 0) {
-             ord += dim;
-          }
+       /* Per MPI-2.1 7.5.4 (description of MPI_CART_RANK), if the
+          dimension is periodic and the coordinate is outside of 0 <=
+          coord(i) < dim, then normalize it.  If the dimension is not
+          periodic, it's an error. */
+       if ((ord < 0) || (ord >= dim)) {
+           if (!*p) {
+               return MPI_ERR_ARG;
+           }
+           ord %= dim;
+           if (ord < 0) {
+               ord += dim;
+           }
        }
        prank += factor * ord;
        factor *= dim;

ompi/mpi/c/cart_rank.c

@@ -79,22 +79,6 @@ int MPI_Cart_rank(MPI_Comm comm, int *coords, int *rank)
 
     OPAL_CR_ENTER_LIBRARY();
 
-    /* Normalize any coords[i] that is outside the appropriate range
-       for dimensions that are periodic */
-    for (i = 0; i < comm->c_topo_comm->mtc_ndims_or_nnodes; ++i) {
-        if (comm->c_topo_comm->mtc_periods_or_edges[i] &&
-            (coords[i] < 0 || 
-             coords[i] >= comm->c_topo_comm->mtc_dims_or_index[i])) {
-            if (coords[i] < 0) {
-                coords[i] = (-coords[i]) %
-                    comm->c_topo_comm->mtc_dims_or_index[i];
-                coords[i] = comm->c_topo_comm->mtc_dims_or_index[i] - coords[i];
-            } else {
-                coords[i] = coords[i] % comm->c_topo_comm->mtc_dims_or_index[i];
-            }
-        }
-    }
-
     /* get the function pointer on this communicator */
     func = comm->c_topo->topo_cart_rank;