A beautiful MPI clip from terminus-p.

probe_len_and_gather_total

void probe_len_and_gather_total()
{
 int i;
 int len;
 char *str, **allstr, *allstr_1dim;
 
 len=mpz_sizeinbase(eachtotal, BASE);
 MPI_Allreduce(&len, &i, 1, MPI_INT, MPI_MAX, MPI_COMM_WORLD);
 len=i+1; /*core + '\0'*/
 if(!commrank)
  printf("len is %d.\n", len);
 str=(char*)malloc(len*sizeof(char));
 assert(str);
 if(!commrank){
  allstr=(char**)malloc(commsize*sizeof(char*));
  assert(allstr);
  allstr_1dim=(char*)malloc(commsize*len*sizeof(char));
  assert(allstr_1dim);
  for(i=0; i<commsize; i++)
   allstr[i]=allstr_1dim+i*len;
 }
 mpz_get_str(str, BASE, eachtotal);
 MPI_Gather(str, len, MPI_CHAR, allstr_1dim, len, MPI_CHAR, 0, MPI_COMM_WORLD);
 if(!commrank){
  mpz_set(total, eachtotal);
  for(i=1; i<commsize; i++){
   mpz_set_str(eachtotal, allstr[i], BASE);
   mpz_add(total, total, eachtotal);
  }
  free(allstr);
  free(allstr_1dim);
 }
 free(str);
 
 return;
}