/* Calculates number of primes between 1 and 20 million.
 * CS 226 Lab 6  */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>
#include <pthread.h>

void failif(bool cond);

//returns whether num is prime
bool isPrime(long num) {
  int limit = (int) sqrt(num);
  for(long i=2; i<=limit; i++) {
    if(num % i == 0)
      return false;
  }
  return true;
}

// start should be odd.
void count_primes (long *pCount, long start, long finish)
{
  while(start < finish) {
    if(isPrime(start)) {
      ++*pCount;
    }
    start += 2;
  }
}

struct prime_arg {
  long *pCount;
  long start, finish;
};

void *prime_thread (void *arg) {
  struct prime_arg *parg = (struct prime_arg *) arg;
  count_primes (parg->pCount, parg->start, parg->finish);
  return parg->pCount;
}

int main () {
  long pCount = 1;   //(starting with 2)

  pthread_t t1, t2;
  struct prime_arg t1arg = { &pCount, 3, 10000000 };
  struct prime_arg t2arg = { &pCount, 10000001, 20000000 };

  failif (pthread_create(&t1, NULL, prime_thread, &t1arg) != 0);
  failif (pthread_create(&t2, NULL, prime_thread, &t2arg) != 0);

  printf ("%ld primes found", pCount);
}

// Checks if value is true, and if so, terminates
void failif(bool cond)
{
  if (cond)
  {
    perror("primes");
    exit(EXIT_FAILURE);
  }
}