#include <pthread.h> 
#include <stdlib.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; 
    pthread_create(&p_threads[i], &attr, compute_pi, 
		   (void *) &hits[i]); 
  } 
  for (i=0; i< num_threads; i++) { 
    pthread_join(p_threads[i], NULL); 
    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(" %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; 
  local_hits = 0; 
  for (i = 0; i < sample_points_per_thread; i++) { 
    rand_no_x =(double)(rand_r(&seed))/(double)((2<<14)-1); 
    rand_no_y =(double)(rand_r(&seed))/(double)((2<<14)-1); 
    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 ++; 
    seed *= i; 
  } 
  *hit_pointer = local_hits; 
  pthread_exit(0); 
}