#include <pthread.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <sys/time.h>
 
#define MAX_THREADS 512 
void *compute_pi (void *); 
 
int total_hits, total_misses, hits[MAX_THREADS], 
  sample_points, sample_points_per_thread, num_threads; 
 
main() { 
  int i; 
  pthread_t p_threads[MAX_THREADS]; 
  pthread_attr_t attr; 
  double computed_pi; 
  double time_start, time_end; 
  struct timeval tv; 
  struct timezone tz; 
 
  pthread_attr_init (&attr); 
  pthread_attr_setscope (&attr,PTHREAD_SCOPE_SYSTEM); 
  printf("Enter number of sample points: "); 
  scanf("%d", &sample_points); 
  printf("Enter number of threads: "); 
  scanf("%d", &num_threads); 
 
  gettimeofday(&tv, &tz); 
  time_start = (double)tv.tv_sec + (double)tv.tv_usec / 1000000.0; 
 
  total_hits = 0; 
  sample_points_per_thread = sample_points / num_threads; 
  for (i=0; i< num_threads; i++) { 
    hits[i] = i+1; 
    pthread_create(&p_threads[i], &attr, compute_pi, (void *) &hits[i]); 
  } 
  for (i=0; i< num_threads; i++) 
    { 
      pthread_join(p_threads[i], NULL); 
      printf("hits[%d]= %d\n", i,hits[i]); 
      total_hits += hits[i]; 
    } 
  computed_pi = 4.0*(double) total_hits / ((double)(sample_points)); 
  gettimeofday(&tv, &tz); 
  time_end = (double)tv.tv_sec + (double)tv.tv_usec / 1000000.0; 
  printf("Computed PI = %lf\n", computed_pi); 
  printf("Time passed: %lf\n", time_end - time_start); 
} 
 
void *compute_pi (void *s) { 
  int seed, i, *hit_pointer; 
  double rand_no_x, rand_no_y; 
  int local_hits; 
 
  hit_pointer = (int *) s; 
  seed = *hit_pointer; 
  printf("sample_points_per_thread=%d \n",sample_points_per_thread);
  local_hits = 0; 
  for (i = 0; i < sample_points_per_thread; i++)
    { 
      rand_no_x =(double)(rand_r(&seed))/(double)((2<<30)-1); 
      rand_no_y =(double)(rand_r(&seed))/(double)((2<<30)-1); 
      // Decrease or increase the value in <<30, if it does not work properly. 
//        printf("rand_no_x=%f rand_no_y=%f \n",rand_no_x,rand_no_y);
      if (((rand_no_x - 0.5) * (rand_no_x - 0.5) + 
	   (rand_no_y - 0.5) * (rand_no_y - 0.5)) < 0.25) 
	{
	  local_hits ++; 
// 	  printf("local_hits=%d \n",local_hits);
	}
      seed *= i;
    } 
  *hit_pointer = local_hits; 
  pthread_exit(0); 
}