num_procs = smpi_comm_size(comm);
send_chunk = smpi_datatype_get_extent(send_type);
recv_chunk = smpi_datatype_get_extent(recv_type);
-
+ int pof2 = ((num_procs != 0) && ((num_procs & (~num_procs + 1)) == num_procs));
for (i = 0; i < num_procs; i++) {
- src = (rank - i + num_procs) % num_procs;
- dst = (rank + i) % num_procs;
+
+ if (pof2 == 1) {
+ /* use exclusive-or algorithm */
+ src = dst = rank ^ i;
+ } else {
+ src = (rank - i + num_procs) % num_procs;
+ dst = (rank + i) % num_procs;
+ }
smpi_mpi_sendrecv(send_ptr + send_disps[dst] * send_chunk, send_counts[dst], send_type, dst,
tag, recv_ptr + recv_disps[src] * recv_chunk, recv_counts[src], recv_type,
src, tag, comm, &s);
+
}
return MPI_SUCCESS;
}