Generate sieving primes

segmented_sieve3.cpp

// generate sieving primes using simple sieve of Eratosthenes
for (; i * i <= high; i += 2)
  if (is_prime[i])
    for (int64_t j = i * i; j <= sqrt; j += i)
      is_prime[j] = false;

// initialize sieving primes for segmented sieve
for (; s * s <= high; s += 2)
{
  if (is_prime[s])
  {
       primes.push_back(s);
    multiples.push_back(s * s - low);
  }
}