/* 
* This is a benchmarking program for mpi.  This is a varient of bench1.c.
* This program does basically the same thing, except each node sends a
* message to the next node.  A barrier is used at the end to make sure
* each node terminates at the same time. 
*/

#include<stdio.h>      /* for input/output       */
#include<mpi.h>        /* for mpi routines       */

#define BUFSIZE 64     /* The size of the messege being passed */
#define LOOPS 1000     /* The number of times around the loop */

main( int argc, char** argv)
{
	double start, finish;
	int my_rank;                     /* the rank of this process       */
	int n_processes;                 /* the total number of processes  */
	int buf[BUFSIZE];                /* a buffer for the messege       */
	int count,i;                     /* index variables                */
	int tag=0;                       /* not important here             */
	double aveTime;                  /* fot timing information         */
	MPI_Status status;               /* not important here             */

	MPI_Init(&argc, &argv);                      /* Initializing mpi       */

	MPI_Comm_size(MPI_COMM_WORLD, &n_processes); /* Getting # of processes */

	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);     /* Getting my rank        */

	/* 
	* Each process sends to the next node, then recieves from the previous
	* node.  A barrier is used at the end to make sure that no process
	* finishes before other processes.
	*/

	start=MPI_Wtime();

	for(count=0;count < LOOPS; count++)
	{
		for(i=0;i<n_processes;i++)
		{
			if( my_rank == 0 )
			{ 
				/* send to the next node */

				MPI_Send(buf, BUFSIZE, MPI_INT, my_rank+1, tag,
				MPI_COMM_WORLD);

				/* recieve from the last node */

				MPI_Recv(buf, BUFSIZE, MPI_INT, n_processes-1, tag, MPI_COMM_WORLD, &status);
			}
			if( my_rank != 0)
			{
				MPI_Send(buf, BUFSIZE, MPI_INT, (my_rank+1)%n_processes, tag, MPI_COMM_WORLD);
				MPI_Recv(buf, BUFSIZE, MPI_INT, my_rank-1, tag, MPI_COMM_WORLD, &status);
			}
		}
	}

	MPI_Barrier(MPI_COMM_WORLD); /* Make sure the processes are synced */

	finish=MPI_Wtime();

	MPI_Finalize(); /* I'm done with mpi stuff */

	/* Print out the results. */

	if (my_rank == 0)
	{
		aveTime=(finish-start)/count;
		printf("Total time for %d loops was %f seconds\n",count, finish-start);
		printf("Average time for a loop was %f seconds\n",aveTime);
	}

	return 0;
}