/**********************************************************************
 * FILE: mpi_pi_send.c
 * DESCRIPTION:  
 *   MPI pi Calculation Example - C Version 
 *   Point-to-Point communications example
 *   This program calculates pi using a "dartboard" algorithm.  See
 *   Fox et al.(1988) Solving Problems on Concurrent Processors, vol.1
 *   page 207.  All processes contribute to the calculation, with the
 *   master averaging the values for pi. This version uses low level 
 *   sends and receives to collect results.
 * AUTHOR: Blaise Barney. Adapted from Ros Leibensperger, Cornell Theory
 *   Center. Converted to MPI: George L. Gusciora, MHPCC (1/95) 
 * LAST REVISED: 06/13/13 Blaise Barney
**********************************************************************/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>

void srandom (unsigned seed);
double dboard (int darts);
#define DARTS 50000     /* number of throws at dartboard */
#define ROUNDS 100      /* number of times "darts" is iterated */
#define MASTER 0        /* task ID of master task */

int main (int argc, char *argv[])
{
double	homepi,         /* value of pi calculated by current task */
	pi,             /* average of pi after "darts" is thrown */
	avepi,          /* average pi value for all iterations */
	pirecv,         /* pi received from worker */
	pisum;          /* sum of workers pi values */
int	taskid,         /* task ID - also used as seed number */
	numtasks,       /* number of tasks */
	source,         /* source of incoming message */ 
	mtype,          /* message type */
	rc,             /* return code */
	i, n;
MPI_Status status;

/* Obtain number of tasks and task ID */
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&numtasks);
MPI_Comm_rank(MPI_COMM_WORLD,&taskid);
printf ("MPI task %d has started...\n", taskid);

/* Set seed for random number generator equal to task ID */
srandom (taskid);

avepi = 0;
for (i = 0; i < ROUNDS; i++) {
   /* All tasks calculate pi using dartboard algorithm */
   homepi = dboard(DARTS);

   /* Workers send homepi to master */
   /* - Message type will be set to the iteration count */
   if (taskid != MASTER) {
      mtype = i;
      rc = MPI_Send(&homepi, 1, MPI_DOUBLE,
                    MASTER, mtype, MPI_COMM_WORLD);
      if (rc != MPI_SUCCESS)
         printf("%d: Send failure on round %d\n", taskid, mtype);
      } 
   else
      {
      /* Master receives messages from all workers */
      /* - Message type will be set to the iteration count */
      /* - Message source will be set to the wildcard DONTCARE: */
      /*   a message can be received from any task, as long as the */
      /*   message types match */
      /* - The return code will be checked, and a message displayed */
      /*   if a problem occurred */
      mtype = i;
      pisum = 0;
      for (n = 1; n < numtasks; n++) {
         rc = MPI_Recv(&pirecv, 1, MPI_DOUBLE, MPI_ANY_SOURCE,
                        mtype, MPI_COMM_WORLD, &status);
         if (rc != MPI_SUCCESS) 
            printf("%d: Receive failure on round %d\n", taskid, mtype);
         /* keep running total of pi */
         pisum = pisum + pirecv;
         }
      /* Master calculates the average value of pi for this iteration */
      pi = (pisum + homepi)/numtasks;
      /* Master calculates the average value of pi over all iterations */
      avepi = ((avepi * i) + pi)/(i + 1); 
      printf("   After %8d throws, average value of pi = %10.8f\n",
               (DARTS * (i + 1)),avepi);
      }    
   } 

if (taskid == MASTER)
   printf ("\nReal value of PI: 3.1415926535897 \n");

MPI_Finalize();
return 0;
}


/**************************************************************************
* subroutine dboard
* DESCRIPTION:
*   Used in pi calculation example codes. 
*   See mpi_pi_send.c and mpi_pi_reduce.c  
*   Throw darts at board.  Done by generating random numbers 
*   between 0 and 1 and converting them to values for x and y 
*   coordinates and then testing to see if they "land" in 
*   the circle."  If so, score is incremented.  After throwing the 
*   specified number of darts, pi is calculated.  The computed value 
*   of pi is returned as the value of this function, dboard. 
*
*   Explanation of constants and variables used in this function:
*   darts       = number of throws at dartboard
*   score       = number of darts that hit circle
*   n           = index variable
*   r           = random number scaled between 0 and 1
*   x_coord     = x coordinate, between -1 and 1
*   x_sqr       = square of x coordinate
*   y_coord     = y coordinate, between -1 and 1
*   y_sqr       = square of y coordinate
*   pi          = computed value of pi
****************************************************************************/

double dboard(int darts)
{
#define sqr(x)	((x)*(x))
long random(void);
double x_coord, y_coord, pi, r; 
int score, n;
unsigned int cconst;  /* must be 4-bytes in size */
/*************************************************************************
 * The cconst variable must be 4 bytes. We check this and bail if it is
 * not the right size
 ************************************************************************/
if (sizeof(cconst) != 4) {
   printf("Wrong data size for cconst variable in dboard routine!\n");
   printf("See comments in source file. Quitting.\n");
   exit(1);
   }
   /* 2 bit shifted to MAX_RAND later used to scale random number between 0 and 1 */
   cconst = 2 << (31 - 1);
   score = 0;

   /* "throw darts at board" */
   for (n = 1; n <= darts; n++)  {
      /* generate random numbers for x and y coordinates */
      r = (double)random()/cconst;
      x_coord = (2.0 * r) - 1.0;
      r = (double)random()/cconst;
      y_coord = (2.0 * r) - 1.0;

      /* if dart lands in circle, increment score */
      if ((sqr(x_coord) + sqr(y_coord)) <= 1.0)
           score++;
      }

/* calculate pi */
pi = 4.0 * (double)score/(double)darts;
return(pi);
}