/* Brute-force computation of the sum of a range of integers starting at zero.
 * Subrange assignments are distributed by the master.
 * Works for input values up to 2x10^9 (long int is apparently 61 bits)
 * Usage: sum_b [range]
 */
#include <stdio.h>
#include <mpi.h>
#include <unistd.h>
#include <stdlib.h>
#define HOST_NAME_MAX 127

int main (int argc, char *argv[])
{
	int rank, size;
	char hname[HOST_NAME_MAX+1];
	int i;
	unsigned long int part, result = 0;	/* partial and total result                     */
	unsigned long int range = 1000000;      /* default range                                */
	unsigned long subrange[2];		/* upper and lower subrange limits		*/
	MPI_Status stat;

	gethostname(hname, HOST_NAME_MAX);
	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &rank);   /* get this processor's unique ID               */
	MPI_Comm_size(MPI_COMM_WORLD, &size);   /* get total number of processors available     */

	if (argc > 1)
		range =  (unsigned long int) strtol(argv[1], (char **)NULL, 10);

	if (rank == 0) {	// Master distributes subranges 
		for (i = 1; i < size; i++) {
			subrange[0] = range/(size - 1)*(i - 1) + 1;	// lower limit
			subrange[1] = range/(size - 1)*i;		// upper limit
			MPI_Send(&subrange, 2, MPI_UNSIGNED_LONG, i, i, MPI_COMM_WORLD);
		}
		for (i = subrange[1] + 1; i <= range; i++)	// master sums partial subrange (if any)
			result += i;
		for (i = 1; i < size; i++) {			// master accumulates partial results
			MPI_Recv(&part, 1, MPI_UNSIGNED_LONG, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &stat);
//			printf("partial result %d from node %d of %d\n", part, stat.MPI_SOURCE, size);
			result += part;
		}
		printf ("%s, node %d of %d - Sum of integers from 0 to %ld = %ld\n", hname, rank, size, range, result);

	} else {	// Slave nodes
		MPI_Recv(&subrange, 2, MPI_UNSIGNED_LONG, 0, rank, MPI_COMM_WORLD, &stat);
		for (i = subrange[0]; i <= subrange[1]; i++) {
			result += i;
		}
		printf("%s, node %d of %d - partial result %ld to %ld = %ld\n", hname, rank, size, subrange[0], subrange[1], result);
		MPI_Send(&result, 1, MPI_UNSIGNED_LONG, 0, rank, MPI_COMM_WORLD);
	}
	MPI_Finalize();