libft/ft_atoi.c at master · Syooosuke/libft · GitHub

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/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   ft_atoi.c                                          :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: syokota <syokota@student.42tokyo.jp>       +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2026/04/23 17:28:25 by syokota           #+#    #+#             */
/*   Updated: 2026/05/06 17:38:02 by syokota          ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

#include "libft.h"

int	ft_atoi(const char *str)
{
	int				i;
	int				sign;
	unsigned long	res;
	unsigned long	max_div;

	i = 0;
	sign = 1;
	res = 0;
	max_div = 922337203685477580ULL;
	while (str[i] == ' ' || (str[i] >= 9 && str[i] <= 13))
		i++;
	if (str[i] == '-' || str[i] == '+')
	{
		if (str[i] == '-')
			sign = -1;
		i++;
	}
	while (str[i] >= '0' && str[i] <= '9')
	{
		if (res > max_div || (res == max_div && str[i] - '0' > 7))
		{
			if (sign == 1)
				return (-1);
			if (res > max_div || str[i] - '0' > 8)
				return (0);
		}
		res = res * 10 + (str[i] - '0');
		i++;
	}
	return ((int)(res * sign));
}