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

/****************************************************************/
/* This implements a compare-split operation.			*/
/* nlocal is the number of elements stored here			*/
/* elmnts is my local copy of the array				*/
/* relmnts is the copy I've received				*/
/* wspace is a working array					*/
/* keepsmall tells local processor whether it takes the smaller	*/
/* or larger half.						*/
/****************************************************************/
void CompareSplit(int nlocal, int *elmnts, int *relmnts, int *wspace,
             int keepsmall) {
  int i, j, k;

  for (i = 0; i < nlocal; i++)
    wspace[i] = elmnts[i];	/* copy elts into wspace	*/

  /**************************************************************/
  /* copying the smaller values into my "elmnts" array.		*/
  /**************************************************************/
  if (keepsmall) {
    for (i = j = k = 0; k < nlocal; k++) {
      if (j == nlocal || (i < nlocal && wspace[i] < relmnts[j]))
        elmnts[k] = wspace[i++];
      else
        elmnts[k] = relmnts[j++];
    }
  }
  /**************************************************************/
  /* else - copying the larger values.				*/
  /**************************************************************/
  else {
    for (i = k = nlocal - 1, j = nlocal - 1; k >= 0; k--) {
      if (j == 0 || (i >= 0 && wspace[i] >= relmnts[j]))
        elmnts[k] = wspace[i--];
      else
        elmnts[k] = relmnts[j--];
    }
  }
}

/****************************************************************/
/* This is the comparison function for the call to qsort.	*/
/****************************************************************/
int IncOrder(const void *e1, const void *e2 ) {
  return (*((int *)e1) - *((int *)e2));
}

main(int argc, char* argv[]) {
  int n;		/* total number of elts to be sorted	*/
  unsigned int seed;	/* random number seed			*/
  int npes, myrank;	/* total processes, self ID		*/
  int nlocal;		/* How much data on local PE		*/
  int *elmnts;		/* array storing local elements		*/
  int *relmnts;		/* array storing received elements	*/
  int oddrank;		/* my rank during odd-phase comm.	*/
  int evenrank;		/* my rank during even-phase comm.	*/
  int *wspace;		/* working space during compare-split	*/
  int i, j;
  MPI_Status status;
  
  MPI_Comm comm = MPI_COMM_WORLD;

  int tag = MPI_ANY_TAG;
  
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &npes);
  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

  seed = atoi(argv[1]);		/* Random number seed.		*/
  n = atoi(argv[2]);		/* How many elts to produce.	*/

  nlocal = n/npes;		/* How many I get.		*/

  elmnts = malloc(nlocal*npes*sizeof(int));
  relmnts = malloc(nlocal*sizeof(int));
  wspace = malloc(nlocal*sizeof(int));

  
  if (myrank == 0) {
	  printf("- there are %i total processes\n" ,npes);
	
	// Process 0
	// Generate all the random numbers
	  seed = seed * (myrank+1);
	  srand(seed);
	  
	  elmnts[0] = 7;
	  elmnts[1] = 6;
	  elmnts[2] = 3;
	  elmnts[3] = 10;
	  elmnts[4] = 1;
	  elmnts[5] = 2;
	  
	  printf("- p0 generates %i numbers: ", n);
	  for (i = 0; i < n; i++)
	  {
		  // Print intial elements
		  printf("%i ", elmnts[i]);
          }
	  printf("\n");
	  
	  printf("- p0 sends ");
	  for (i = 1; i < npes; i++) {
		for (j = i*nlocal; j < (i*nlocal)+nlocal; j++) {
			printf("%i,", elmnts[j]);
		}
		printf(" to p%i\n", i);
	  }
		
	  for (i = 1; i < npes; i++) {
			// Send the random numbers nlocal at a time to all other processes
			MPI_Send(&elmnts[i*nlocal], nlocal, MPI_INT, i, myrank, comm);
	  }
	  
	  // Run the algorithm for itself
          evenrank = myrank + 1;
	  oddrank = MPI_PROC_NULL;

	qsort(elmnts, nlocal, sizeof(int), IncOrder);
	printf("- p0 sorts its own elements, giving ");
	for ( i = 0; i < nlocal; i++) {
		printf("%i, ", elmnts[i]);
	}
	printf("\n");
	
	  for (i = 1; i < npes; i++) {
		if (i % 2 == 1)	// odd phase
		  MPI_Sendrecv(elmnts, nlocal, MPI_INT, oddrank, 1, relmnts,
					   nlocal, MPI_INT, oddrank, 1, MPI_COMM_WORLD, &status);
		else
		  MPI_Sendrecv(elmnts, nlocal, MPI_INT, evenrank, 1, relmnts,
					   nlocal, MPI_INT, evenrank, 1, MPI_COMM_WORLD, &status);
	
		CompareSplit(nlocal, elmnts, relmnts, wspace,
					 myrank < status.MPI_SOURCE);
	  }
	  
	  // Print my sublist
	  for (i = 0; i < nlocal; i++) 
	  {
		    printf("processor 0 element: %i\n", elmnts[i]);
	  }
	  
	  for (i = 1; i < npes; i++)
	  {
	  	// Receive all other processes sublists
		MPI_Recv(relmnts, nlocal, MPI_INT, i, tag, comm, &status);
	    
		for (j = 0; j < nlocal; j++)
		//for (j = i*nlocal; j < (i*nlocal)+nlocal; j++)
		{
			// Print all other processes sublist
			//printf("p0 Received element: %i from p%i\n", elmnts[j], i);
			printf("- p0 receives %i , from p%i\n", relmnts[j], i);
		}
	  }
	  
  }
  else {
  
  	// The rest of the processes
	printf("nlocal %i\n", nlocal);
	printf("n %i\n", n);
	printf("npes %i\n", npes);
	
	// Receive nlocal randomly generated elements from process 0
	MPI_Recv(relmnts, nlocal, MPI_INT, 0, tag, comm, &status); 
	
	// Print the received elements
	printf("- p%i receives ", myrank);
	for ( i = 0; i < n/npes; i++)
	{
		//printf("p%i receives elmnts[%i]: %i from p0\n", myrank, i, elmnts[i]);
		printf("%i, ", relmnts[i]);
	}
	printf("\n");
	
	qsort(relmnts, nlocal, sizeof(int), IncOrder); // does it matter where we sort at?
	
	printf("- p%i sorts, making ", myrank);
	for ( i = 0; i < n/npes; i++)
	{
		//printf("p%i sorted elmnts[%i]: %i\n", myrank, i, elmnts[i]);
		printf("%i, ", relmnts[i]);
	}
	
	  /**************************************************************/
	  /* Calculate the locations of my neighbors in advance.	*/
	  /**************************************************************/
	  if (myrank % 2 == 0) {
		oddrank = myrank - 1;
		evenrank = myrank + 1;
	  }
	  else {
		oddrank = myrank + 1;
		evenrank = myrank - 1;
	  }

	  
	  /**************************************************************/
	  /* Set ranks of processors at end of linear array - boundary	*/
	  /* conditions.						*/
	  /**************************************************************/
	  
	  if (oddrank == -1 || oddrank == npes)
		oddrank = MPI_PROC_NULL;
	  if (evenrank == -1 || evenrank == npes)
		evenrank = MPI_PROC_NULL;
  
		if (i % 2 == 1)	// odd phase
		  MPI_Sendrecv(elmnts, nlocal, MPI_INT, oddrank, 1, relmnts,
					   nlocal, MPI_INT, oddrank, 1, MPI_COMM_WORLD, &status);
		else
		  MPI_Sendrecv(elmnts, nlocal, MPI_INT, evenrank, 1, relmnts,
					   nlocal, MPI_INT, evenrank, 1, MPI_COMM_WORLD, &status);

		CompareSplit(nlocal, elmnts, relmnts, wspace,
					 myrank < status.MPI_SOURCE);
	
	printf("p%i sends ", myrank);
	
	for ( i = 0; i < n/npes; i++)
	//for ( i = 0; i < sizeof(elmnts)/sizeof(int); i++)
	{
		printf("%i, ", relmnts[i]);
	}
	printf("\n");
	
	// Send results back to process 0
	MPI_Send(relmnts, nlocal, MPI_INT, 0, myrank, comm);
  }

  free(elmnts);
  free(relmnts);
  free(wspace);
  MPI_Finalize();
}