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314 ira 1 
/*******************************************************************************
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 * prob3.c - implement a parallel (pipelined approach) system for the
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 *           Sieve of Eratosthenes problem.
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 *
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 * Copyright (c) 2006, Ira W. Snyder (devel@irasnyder.com)
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 ******************************************************************************/
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#include <mpi.h>
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#include <stdio.h>
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#include <stdlib.h>
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#define TAG_DATA   0x1010
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#define TERMINATOR 0xffff
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#define BAD_NUM    -1
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#define FALSE 0
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#define TRUE  1
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int should_pass (int num, int mynumber)
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{
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    if (num % mynumber == 0)
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        return FALSE; // evenly divisible, DO NOT PASS
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    return TRUE; // not evenly divisible, GO AHEAD
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}
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void print_num (int myrank, int mynumber)
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{
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    if (mynumber == BAD_NUM)
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        return;
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    if (myrank < 10)
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        printf ("Proc 0%d's Prime: %d\n", myrank, mynumber);
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    else
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        printf ("Proc %d's Prime: %d\n", myrank, mynumber);
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}
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void send_term (int to_proc)
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{
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    int temp = TERMINATOR;
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    MPI_Send (&temp, 1, MPI_INT, to_proc, TAG_DATA, MPI_COMM_WORLD);
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}
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int main (int argc, char *argv[])
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{
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    int myrank, numprocs;
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    int mynumber = BAD_NUM;
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    int temp_recv;
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    MPI_Status status;
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    MPI_Init (&argc, &argv);
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    MPI_Comm_rank (MPI_COMM_WORLD, &myrank);
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    MPI_Comm_size (MPI_COMM_WORLD, &numprocs);
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    if (myrank == 0)
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    {
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        int i;
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        mynumber = 2;
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        for (i=3; i<=100; i++)
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            if (should_pass (i, mynumber))
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                MPI_Send (&i, 1, MPI_INT, myrank+1, TAG_DATA, MPI_COMM_WORLD);
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        send_term (myrank+1);
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    }
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    else if (myrank < (numprocs - 1))
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    {
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        /* Save the first number we recieve */
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        MPI_Recv (&mynumber, 1, MPI_INT, myrank-1, TAG_DATA, MPI_COMM_WORLD, &status);
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        /* Check if we need to exit early */
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        if (mynumber == TERMINATOR)
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        {
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            send_term (myrank+1);
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            goto END_NOW;
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        }
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        /* Check all subsequent numbers */
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        while (TRUE)
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        {
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            MPI_Recv (&temp_recv, 1, MPI_INT, myrank-1, TAG_DATA, MPI_COMM_WORLD, &status);
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            if (temp_recv == TERMINATOR)
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            {
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                send_term (myrank+1);
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                break;
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            }
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            else
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            {
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                if (should_pass (temp_recv, mynumber))
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                    MPI_Send (&temp_recv, 1, MPI_INT, myrank+1, TAG_DATA, MPI_COMM_WORLD);
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            }
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        }
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    }
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    else
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    {
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        /* Save the first number we recieve */
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        MPI_Recv (&mynumber, 1, MPI_INT, myrank-1, TAG_DATA, MPI_COMM_WORLD, &status);
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        if (mynumber == TERMINATOR)
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            goto END_NOW;
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        while (TRUE)
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        {
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            MPI_Recv (&temp_recv, 1, MPI_INT, myrank-1, TAG_DATA, MPI_COMM_WORLD, &status);
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            if (temp_recv == TERMINATOR)
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                break;
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            else
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                if (should_pass (temp_recv, mynumber))
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                {
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                    printf ("ERROR: not enough processes.\n");
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                    printf ("Prime: %d\n", temp_recv);
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                }
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        }
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    }
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END_NOW:
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    print_num (myrank, mynumber);
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    MPI_Finalize ();
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    return 0;
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}