gistfile1.c

#include <stdio.h>
#include <pthread.h>

struct range
{
  unsigned long long start;
  unsigned long long  end;
} range;

void *sumprimes(void *r);
int isprime(unsigned long int);

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
unsigned long long globaltotal = 2;

int main(int argc, char *argv)
{
  int rc1, rc2, rc3, rc4;
  pthread_t thread1, thread2, thread3, thread4;
  struct range range1, range2, range3, range4;

  range1.start = 3; range1.end = 500000;
  range2.start = 500001; range2.end = 1000000;
  range3.start = 1000001; range3.end = 1500000;
  range4.start = 1500001; range4.end = 2000000;

  rc1 = pthread_create(&thread1, NULL, &sumprimes, (void *)&range1);
  rc2 = pthread_create(&thread2, NULL, &sumprimes, (void *)&range2);
  rc3 = pthread_create(&thread3, NULL, &sumprimes, (void *)&range3);
  rc4 = pthread_create(&thread4, NULL, &sumprimes, (void *)&range4);

  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);
  pthread_join(thread3, NULL);
  pthread_join(thread4, NULL);

  printf("Total is: %llu\n", globaltotal);
  return 0;
}

void *sumprimes(void *r)
{
  struct range *x = (struct range *)r;
  unsigned long long start = x->start;
  unsigned long long end = x->end;
  unsigned long long n, total = 0;
  
  printf("Adding primes from %llu to %llu\n", start, end);
  for (n = start; n <= end; n+=2)
    {
      if (isprime(n))
  {
	  total = total + n;
	}
    }
  
  pthread_mutex_lock(&mutex1);
  globaltotal = globaltotal + total;
  pthread_mutex_unlock(&mutex1);
  printf("Done adding primes from %llu to %llu\n", start, end);
}

int isprime(unsigned long int x)
{
  unsigned long int index;

  if(x % 2 == 0) {return 0;}

  for (index = 3; index < x; index++)
    {
      if ((x % index) == 0)
	{
	  return 0;
	}
    }

  return 1;
}