/**********************************************************
  File:          slave.cc                              
  Description:   A program that inputs an integer number 
                 and determines if it is a prime number or 
		 not in parallel.
		 Functions for the slave processes.
                                                         
  Author:        Dana Vrajitoru                          
  Organization:  IUSB                                    
  Date:          September 28, 2004
***********************************************************/

#include <mpi.h>
#include <cmath>
#include "slave.h"

// The slave function that checks if n is prime. While in the loop for
// testing the potential divisors, it also checks if the master has
// any information about the loop having to end, which means that some
// other process has found a non-trivial divisor in the meantime.
void Check_prime_slave(int start, int end, int n)
{
  MPI_Request request;
  MPI_Status status;
  int flag = 0, div=1, divisor = 1;

  MPI_Irecv(&div, 1, MPI_INT, MASTER_ID, 0, MPI_COMM_WORLD, &request);
  for (int i=start; i<=end && divisor == 1; i += 2) { 
    if (n % i == 0)
      divisor = i;
    MPI_Test(&request, &flag, &status);
    if (flag)
	divisor = div;
  }
  MPI_Send(&divisor, 1, MPI_INT, MASTER_ID, 0, MPI_COMM_WORLD);
  if (!flag)
    MPI_Wait(&request, &status);
}

// The slave function. It waits for the master to communicate the
// number to be checked, sets the limits of search for itself, then
// calls the function that checks if the number is prime.
void Slave(int proc_id, int nr_proc)
{
  int n;
  MPI_Bcast(&n, 1, MPI_INT, MASTER_ID, MPI_COMM_WORLD);

  if (n % 2 != 0) {
    int sqroot = sqrt(n), found_div = 0; 
    int steps = (sqroot - 2)/nr_proc;
    int start = 3 + steps * proc_id, end = start + steps-1;
    if (start % 2 == 0)
      start++;
    if (proc_id == nr_proc -1)
      end = sqroot;

    Check_prime_slave(start, end, n);
  }
}