mar4-msg-sum.c

#include <stdio.h>
#include <mpi.h>
#include "l17.h"

int main(int argc, char** argv) {
    int rc;
    rc = MPI_Init(&argc, &argv);
    L17_CHECK_ERROR(MPI_Init, rc);

    int size;
    rc = MPI_Comm_size(MPI_COMM_WORLD, &size);
    L17_CHECK_ERROR(MPI_Comm_size, rc);

    int rank;
    rc = MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    L17_CHECK_ERROR(MPI_Comm_rank, rc);

    if (size == 1) {
        printf("No messages if there's only one process\n");
        exit(1);
    }

    if (rank == 0) {
        int i = 0;
        printf("Process %d: the number is %d\n", rank, i);

        rc = MPI_Send(&i, 1, MPI_INT, 1, 1, MPI_COMM_WORLD);
        L17_CHECK_ERROR(MPI_Send, rc);

        rc = MPI_Recv(&i, 1, MPI_INT, size - 1, 1, MPI_COMM_WORLD, NULL);
        L17_CHECK_ERROR(MPI_Recv, rc);
        printf("Process %d: the number is %d\n", rank, i);
    }
    else {
        int i;
        rc = MPI_Recv(&i, 1, MPI_INT, rank - 1, 1, MPI_COMM_WORLD, NULL);
        L17_CHECK_ERROR(MPI_Recv, rc);

        i += rank;
        printf("Process %d: the number is %d\n", rank, i);

        int torank = (rank == size - 1) ? 0 : rank + 1;
        rc = MPI_Send(&i, 1, MPI_INT, torank, 1, MPI_COMM_WORLD);
        L17_CHECK_ERROR(MPI_Send, rc);
    }

    MPI_Finalize();

    return 0;
}