Prime Sieve, Frost.

frost_sieve.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define u64 unsigned long long

typedef unsigned short int bool;
#define false (unsigned short)0
#define true  (unsigned short)1

u64 int *sieve(unsigned int upto)
{
  bool *is_prime = malloc(sizeof(bool) * upto);
  is_prime[0, 1] = 0;
  for (int i = 2; i <= upto; i++)
    is_prime[i] = true;

  u64 int *primes = malloc(sizeof(u64 int) * upto);

  for (u64 int i = 2; i < ceil(sqrt(upto)); i++) {
    for (u64 int j = 2; j < upto; j++) {
      if (i * j > upto) break;
      is_prime[i * j] = false;
    }
  }
  
  unsigned int prime_index = 0;
  for (u64 int prime = 0; prime <= upto; prime++) {
    if (is_prime[prime]) {
      primes[prime_index] = prime;
      prime_index++;
    }
  }

  free(is_prime);
  return primes;
}

int main(int argc, char *argv[])
{
  if (argc < 2) {
    printf("Supply command line argument to choose\n");
    printf("which primes to generate under a certain value.\n");
    return EXIT_FAILURE;
  }

  unsigned int n_primes = atoi(argv[1]);
  u64 int *primes = sieve(n_primes);
  u64 int sum = 0;
  
  for (u64 int i = 0; i < n_primes; i++) {
    printf("%lu%s", primes[i], (primes[i + 1] == 0) ? "\n" : ", ");
    sum += primes[i];
    if (primes[i + 1] == 0) break;
  }
  
  printf("Summation of primes down from %u:\n%lu\n", n_primes, sum);
  free(primes);
  return EXIT_SUCCESS;
}