main.c

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

/*
Commands :
cd 'B:\Mes Documents\progra\calcInt\'
C:\MPICH2\bin\mpiexec.exe -localonly 10
*/

// explications given at the bottom of this file
int whoSendNext(int loop,int rank); // to know who to send next
int whoSendBef(int rank); // to know who send the message to the process

int main (int argc, char *argv[]) {
    int rank, size, next, numLoopRecv;
    MPI_Status status;

    int test=0;
    int message_to_send=7;
    int numLoop=1;

    MPI_Init (&argc, &argv); /* starts MPI */

    if(argc==2){
        message_to_send = atoi(argv[1]);
    }
/*
    for(int i=1;i!=10;i++){
        numLoopRecv=((int)(log2((double)i)+2.01));
        printf("###\n numLoopRecv : %d\n",numLoopRecv);
        printf("\nrank %d wait for %d\n",i,whoSendBef(numLoopRecv,i));
        printf("\nrank %d send for %d\n",i,whoSendNext(numLoopRecv,i));
    }
    return 0;
*/
    MPI_Comm_rank(MPI_COMM_WORLD, &rank); /* get current process id */
    MPI_Comm_size(MPI_COMM_WORLD, &size); /* get number of processes */

    int numMaxLoop=((int)log2((double)size)+2.01); // get the rank of the final loop

    if(!(rank==0 && numLoop==1)){
        numLoop=((int)(log2((double)rank)+2.01)); // get the rank of the loop it will be when the process will receive the message
        printf("%d wait for reception from %d\n",rank,whoSendBef(numLoopRecv,rank));
        MPI_Recv(&message_to_send,1,MPI_INT,whoSendBef(numLoop,rank),10,MPI_COMM_WORLD,&status);
    }
    while(numLoop<=numMaxLoop){
        next=whoSendNext(numLoop,rank);
        if(next<size){ // will stop broadcast when all process have been reached
            printf("%d wait for a sending to %d\n",rank,next);
            MPI_Send(&message_to_send,1,MPI_INT,whoSendNext(numLoop,rank),10,MPI_COMM_WORLD);
        }
        numLoop+=1;
    }
    MPI_Finalize();
}

/*
* Logic used is :
*        (turn : 1      2      3      4)
* 0 will send to 1 then 2 then 4 then 8
* 1 will send to        3 then 5 then 9
* 2 will send to               6 then 10
* 3 will send to               7 then 11
* ...
* n will send to        ...    n+2^(turn-1) then  n+2^(turn) ...
*/


int whoSendNext(int loop,int rank){ // OK
    int inc=((int)(pow(2.0,((double)loop)-1.0)+0.01));
    return rank+inc;
}
int whoSendBef(int loop,int rank){
    int inc=((int)(pow(2.0,((int)log2((double)rank)+0.01))+0.01));
    return rank-inc;
}