/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   ft_is_prime.c                                      :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: tosuman </var/spool/mail/tosuman>          +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2023/03/30 16:48:48 by tosuman           #+#    #+#             */
/*   Updated: 2023/03/30 16:48:49 by tosuman          ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

#define INT_MAX_SQRT 46340
#define FIRST_PRIMES_LEN 2
#define SIEVE_LEN 2
#define WHEEL 6
// #define FIRST_PRIMES_LEN 3
// #define SIEVE_LEN 8
// #define WHEEL 30

int	ft_int_sqrt(int nb)
{
	int	sqrt;
	int	old_sqrt;
	int	max;
	int	min;

	min = 0;
	max = nb;
	if (nb > INT_MAX_SQRT)
		max = INT_MAX_SQRT;
	sqrt = max;
	while (1)
	{
		old_sqrt = sqrt;
		if (sqrt * sqrt == nb)
			return (sqrt);
		if (sqrt * sqrt > nb)
			max = sqrt;
		if (sqrt * sqrt < nb)
			min = sqrt;
		sqrt = (max + min) / 2;
		if (sqrt == old_sqrt)
			break ;
	}
	return (sqrt);
}

int	first_divisor(int nb)
{
	int	wheel;
	int	idx;
	int	int_sqrt;
	int	first_primes[FIRST_PRIMES_LEN];
	int	sieve6[SIEVE_LEN];

	first_primes[0] = 2;
	first_primes[1] = 3;
	sieve6[0] = 5;
	sieve6[1] = 7;
	idx = -1;
	while (++idx < FIRST_PRIMES_LEN)
		if (nb % first_primes[idx] == 0)
			return (first_primes[idx]);
	int_sqrt = ft_int_sqrt(nb);
	wheel = 0;
	while (wheel < int_sqrt)
	{
		idx = -1;
		while (++idx < SIEVE_LEN)
			if (nb % (sieve6[idx] + wheel) == 0)
				return (sieve6[idx] + wheel);
		wheel += WHEEL;
	}
	return (nb);
}

int	ft_is_prime(int nb)
{
	if (nb < 2)
		return (0);
	return (first_divisor(nb) == nb);
}

/* ////
#include <stdio.h>
#include <limits.h>

int	main(void)
{
	int	i;
	int	prime_count;

	prime_count = 0;
	i = -10;
	while (++i <= INT_MAX / 1000)
	{
		if (ft_is_prime(i))
		{
			// printf("Prime: %d\n", i);
			++prime_count;
		}
	}
	printf("Prime count up until %d: %d\n", INT_MAX / 1000, prime_count);
	return (0);
}
	// first_primes[2] = 5;
	// sieve30[0] = 7;
	// sieve30[1] = 11;
	// sieve30[2] = 13;
	// sieve30[3] = 17;
	// sieve30[4] = 19;
	// sieve30[5] = 23;
	// sieve30[6] = 29;
	// sieve30[7] = 31;
*/ ////