--- /dev/null
+#include "colls_private.h"
+
+/*****************************************************************************
+
+ * Function: alltoall_pair
+
+ * Return: int
+
+ * Inputs:
+ send_buff: send input buffer
+ send_count: number of elements to send
+ send_type: data type of elements being sent
+ recv_buff: receive output buffer
+ recv_count: number of elements to received
+ recv_type: data type of elements being received
+ comm: communicator
+
+ * Descrp: Function works when P is power of two. In each phase of P - 1
+ phases, nodes in pair communicate their data.
+
+ * Auther: Ahmad Faraj
+
+ ****************************************************************************/
+int smpi_coll_tuned_alltoallv_pair(void *send_buff, int *send_counts, int *send_disps,
+ MPI_Datatype send_type,
+ void *recv_buff, int *recv_counts, int *recv_disps,
+ MPI_Datatype recv_type, MPI_Comm comm)
+{
+
+ MPI_Aint send_chunk, recv_chunk;
+ MPI_Status s;
+ int i, src, dst, rank, num_procs;
+ int tag = 1;
+ char *send_ptr = (char *) send_buff;
+ char *recv_ptr = (char *) recv_buff;
+
+ rank = smpi_comm_rank(comm);
+ num_procs = smpi_comm_size(comm);
+ send_chunk = smpi_datatype_get_extent(send_type);
+ recv_chunk = smpi_datatype_get_extent(recv_type);
+
+ for (i = 0; i < num_procs; i++) {
+ src = dst = rank ^ i;
+ 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;
+}