/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   ft_find_next_prime.c                               :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: tosuman </var/spool/mail/tosuman>          +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2023/03/30 17:03:18 by tosuman           #+#    #+#             */
/*   Updated: 2023/03/30 17:03:19 by tosuman          ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

#define INT_MAX_SQRT 46340
#define FIRST_PRIMES_LEN 2
#define SIEVE_LEN 2
#define WHEEL 6

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);
}

int	ft_find_next_prime(int nb)
{
	--nb;
	while (++nb)
		if (ft_is_prime(nb))
			return (nb);
	return (2);
}

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

int	main(void)
{
	printf("Given %d, next prime is %d\n", INT_MIN,
    ft_find_next_prime(INT_MIN));
	printf("Given %d, next prime is %d\n", -2, ft_find_next_prime(-2));
	printf("Given %d, next prime is %d\n", -1, ft_find_next_prime(-1));
	printf("Given %d, next prime is %d\n", 0, ft_find_next_prime(0));
	printf("Given %d, next prime is %d\n", 1, ft_find_next_prime(1));
	printf("Given %d, next prime is %d\n", 2, ft_find_next_prime(2));
	printf("Given %d, next prime is %d\n", 3, ft_find_next_prime(3));
	printf("Given %d, next prime is %d\n", 4, ft_find_next_prime(4));
	printf("Given %d, next prime is %d\n", 5, ft_find_next_prime(5));
	printf("Given %d, next prime is %d\n", 6, ft_find_next_prime(6));
	printf("Given %d, next prime is %d\n", 7, ft_find_next_prime(7));
	printf("Given %d, next prime is %d\n", 8, ft_find_next_prime(8));
	printf("Given %d, next prime is %d\n", 9, ft_find_next_prime(9));
	printf("Given %d, next prime is %d\n", 10, ft_find_next_prime(10));
	printf("Given %d, next prime is %d\n", 11, ft_find_next_prime(11));
	printf("Given %d, next prime is %d\n", 12, ft_find_next_prime(12));
	printf("Given %d, next prime is %d\n", INT_MAX - 1000,
    ft_find_next_prime(INT_MAX - 1000));
	printf("Given %d, next prime is %d\n", INT_MAX - 3,
    ft_find_next_prime(INT_MAX - 3));
	printf("Given %d, next prime is %d\n", INT_MAX - 2,
   ft_find_next_prime(INT_MAX - 2));
	printf("Given %d, next prime is %d\n", INT_MAX - 1,
    ft_find_next_prime(INT_MAX - 1));
	printf("Given %d, next prime is %d\n", INT_MAX,
    ft_find_next_prime(INT_MAX));
	return (0);
}
*/ ////