/************************************************************************
 * This file has been written as a sample solution to an exercise in a 
 * course given at the Edinburgh Parallel Computing Centre. It is made
 * freely available with the understanding that every copy of this file
 * must include this header and that EPCC takes no responsibility for
 * the use of the enclosed teaching material.
 *
 * Authors:     Joel Malard, Alan Simpson
 *
 * Contact:     epcc-tec@epcc.ed.ac.uk
 *
 * Purpose:     A program to experiment with point-to-point
 *              communications.   
 *
 * Contents:    C source code.
 *
 ************************************************************************/

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

#define proc_A 0
#define proc_B 1
#define ping 101
#define pong 101

#define NMAX 700000

float buffer[NMAX];

void processor_A (void);
void processor_B (void);

void main( int argc, char *argv[] )
{
  int ierror, rank, size;

  MPI_Init(&argc, &argv);
  
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  
  if (rank == proc_A) processor_A();
  else if (rank == proc_B) processor_B();
  
  MPI_Finalize();
  
}

void processor_A( void )
{
  int i, ierror;
  MPI_Status status;
  double start, finish, time;
  extern float buffer[NMAX];
  int length;
  
  printf("Length\tTotal Time\tTransfer Rate(MB/s)\n");
  
  for (length = 1; length <=  NMAX; length *= 2){ 
    
    start = MPI_Wtime();
    
    for (i = 1; i <= 100; i++){
      MPI_Ssend(buffer, length, MPI_FLOAT, proc_B, ping, MPI_COMM_WORLD);
      MPI_Recv( buffer, length, MPI_FLOAT, proc_B, pong, MPI_COMM_WORLD, &status);
    }

    finish = MPI_Wtime();
    time = finish - start;
    printf("%d\t%f\t%8f\n", length, time/200.,
	   0.000001*(float)(2 * 4 * 100 * length)/time); 
  } 
}

void processor_B( void )
{
  int i, ierror;
  MPI_Status status;
  extern float buffer[NMAX];
  int length;
  
  for (length = 1; length <=  NMAX; length *= 2){ 
    //  for (length = 1; length <= 100000; length += 1000) { 
    for (i = 1; i <= 100; i++) {
      MPI_Recv( buffer, length, MPI_FLOAT, proc_A, ping, MPI_COMM_WORLD, &status);
      MPI_Ssend(buffer, length, MPI_FLOAT, proc_A, pong, MPI_COMM_WORLD);
    }
  }
}