#include "nth_prime.h"

#include <cstddef>
#include <cstring>
#include <iostream>
#include <stdexcept>
#include <vector>


namespace prime {

using namespace std;

number_t nth(size_t n)
{
    if (n < 1)
        throw std::domain_error("invalid prime index");

    vector<number_t> primes = {2, 3, 5, 7, 11, 13};
    primes.reserve(n - 1);

    static const size_t sieve_size = 32*1024;

    bool sieve[sieve_size] = {0};
    sieve[0] = sieve[1] = true;

    size_t page = 0;

    while (primes.size() < n) {

        for (auto p : primes) {

            size_t start = page*sieve_size % p;

            for (size_t i = start; i < sieve_size; i += p) {

                sieve[i] = true;
            }
        }

        for (auto i : sieve) {

            if (!sieve[i]) {

                number_t new_prime = page*sieve_size + i;
                //cout <<  page << " " << i << " " << new_prime << endl;
                primes.push_back(new_prime);
                break;
            }
        }

        //if (
        //memset(sieve, 0, sieve_size);
    }
    
    return primes[n - 1];
}

}