#include <stdio.h>
#include "mpi.h"


#define ONE_MIL      (1000000)
#define MAX_SIZE_LOG (21)
#define MAX_SIZE     (1<<MAX_SIZE_LOG)

char sdata[MAX_SIZE];
char rdata[MAX_SIZE];

main( int argc, char **argv )
{
    int              rank, size, j, next, prev;
    long             rounds;
    int              msglen;
    MPI_Status       status;
    double           startt,endt;

    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );

    if (rank == 0) {
	printf("rank = %d, size = %d\n",rank,size);
	printf("MAX_SIZE = %d\n",MAX_SIZE);
	printf("STARTING LATENCY AND BANDWIDTH BENCHMARK\n");
	fflush(stdout);
    }

    next = (rank + 1 ) % size;
    prev = (rank + size - 1 ) % size;
    msglen = 0;

    while (msglen <= MAX_SIZE) {

	if (msglen <= (1<<9))       rounds = 1 << 15;
	else if (msglen <= (1<<12)) rounds = 1 << 12;
	else if (msglen <= (1<<18)) rounds = 1 << 10;
        else                        rounds = 1 << 8;                 
	
	MPI_Barrier ( MPI_COMM_WORLD );

	startt = MPI_Wtime();

	for (j=rounds; j--; ) {
	    if (rank == 0) {
		MPI_Send(sdata,msglen,MPI_BYTE,next,0,MPI_COMM_WORLD);
		MPI_Recv(rdata,msglen,MPI_BYTE,prev,0,MPI_COMM_WORLD,&status);
	    } else {
		MPI_Recv(rdata,msglen,MPI_BYTE,prev,0,MPI_COMM_WORLD,&status);
		MPI_Send(sdata,msglen,MPI_BYTE,next,0,MPI_COMM_WORLD);
	    }
	}

	if (rank == 0) {
	    double latency,bandwidth, elapse;

            endt = MPI_Wtime();
	    elapse = endt - startt;

	    latency   = elapse / (double)(size*rounds) * (double)ONE_MIL;
	    bandwidth = ((double)(unsigned)(size*rounds*msglen))/(elapse*(double)ONE_MIL);
	    printf("%3d %8.3f %8.3f\n",(int)msglen,latency,bandwidth);
	    fflush(stdout);
        }
	if (msglen == 0) msglen = 1;
	else msglen = 2 * msglen;
    }
    MPI_Finalize();
}