diff --git a/.gitignore b/.gitignore
index 088e750..844aedb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -53,6 +53,8 @@ dkms.conf
 
 # OS generated files #
 *.swp
+*.swo
+*.~
 .DS_Store
 .DS_Store?
 ._*
diff --git a/srcs/ft_convertbase.c b/srcs/ft_convertbase.c
index a934e81..a11fe5c 100644
--- a/srcs/ft_convertbase.c
+++ b/srcs/ft_convertbase.c
@@ -1,86 +1,159 @@
-/* ************************************************************************** */
-/*                                                                            */
-/*                                                        :::      ::::::::   */
-/*   ft_convertbase.c                                   :+:      :+:    :+:   */
-/*                                                    +:+ +:+         +:+     */
-/*   By: hulamy <marvin@42.fr>                      +#+  +:+       +#+        */
-/*                                                +#+#+#+#+#+   +#+           */
-/*   Created: 2018/11/16 15:15:55 by hulamy            #+#    #+#             */
-/*   Updated: 2020/02/19 18:47:35 by hulamy           ###   ########.fr       */
-/*                                                                            */
-/* ************************************************************************** */
+/*
+**	take a string that is a number in a certain and convert it in another base
+**	return the new string
+*/
+
+
+	#include <stdio.h>	// for printf
+	#include <stdlib.h>	// for atoi
+
+	char	*ft_convertbase(char *nbr, char *base_from, char *base_to);
+
+	int	main(int ac, char **av)
+	{
+		if (ac != 4)
+			printf("usage:\nchar *nbr, char *base_from, char *base_to\ntry the max long unsigned int : 9223372036854775807");
+		else
+			printf("[%s]\n",ft_convertbase(av[1], av[2], av[3]));
+		return (0);
+	}
+
 
 #include "libft.h"
 
-static int	ft_malloc_size(int decimal, int length, int i)
-{
-	if (decimal <= 0)
-		i++;
-	while (decimal)
-	{
-		decimal /= length;
-		i++;
-	}
-	return (i);
-}
+/*
+** check :
+** -if the base has no characters that appear more than one time
+** -if the signes '-' and '+' are not part of the set
+** -if there are no invisible characters (inferior to 32 or equal to 127)
+*/
 
-static char	*ft_decimal_to_base(int decimal, char *base, char *res, int size)
+int
+	is_valid_base(char *base)
 {
-	long	nb;
-	int		i;
+	int	i;
+	int	j;
 
-	nb = decimal;
 	i = 0;
 	while (base[i])
-		i++;
-	if (nb < 0)
-		nb = -nb;
-	while (--size >= 0)
 	{
-		res[size] = base[nb % i];
-		nb /= i;
+		j = i + 1;
+		while (base[j])
+			if (base[i] == base[j++])
+				return (0);
+		if (base[i] == '-' || base[i] == '+' || base[i] < 33 || base[i] == 127)
+			return (0);
+		i++;
 	}
-	return (res);
+	if (i >= 2)
+		return (1);
+	return (0);
 }
 
-static int	ft_base_to_decimal(char *nbr, char *base, int length, int i)
+/*
+** check :
+** -if base is valid
+** -if nbr contain characters
+** -if nbr is made of elements of base only
+*/
+
+int
+	is_valid_nbr(char *nbr, char *base)
 {
-	long	decimal;
-	int		j;
+	int	i;
+	int	j;
+
+	i = 0;
+	if (!is_valid_base(base))
+		return (0);
+	while (nbr[i])
+	{
+		j = 0;
+		while (base[j] && nbr[i] != base[j])
+			j++;
+		if (base[j] == '\0')
+			return (0);
+		i++;
+	}
+	if (i == 0)
+		return (0);
+	return (1);
+}
+
+/*
+** -transform a nbr written as a string into a decimal nbr
+** -it's an unsigned nbr because the negativity is managed elsewhere
+** -if the number is bigger than the max unsigned long int it's false
+*/
+
+unsigned long int
+	base_to_decimal(char *nbr, char *base)
+{
+	unsigned long int	decimal;
+	int					i;
+	int					j;
+	int					length;
 
 	decimal = 0;
-	if (nbr[i] == '-')
-		i++;
+	i = 0;
+	length = 0;
+	while (base[length])
+		length++;
 	while (nbr[i])
 	{
 		j = 0;
 		while (nbr[i] != base[j] && base[j])
 			j++;
+		if ((18446744073709551615U - j) / length > decimal)
+			return (0);
 		decimal = (decimal * length) + j;
 		i++;
 	}
-	if (nbr[0] == '-')
-		decimal = -decimal;
 	return (decimal);
 }
 
-char		*ft_convertbase(char *nbr, char *base_from, char *base_to)
+char
+	*decimal_to_base(unsigned long int decimal, char *base, int malloc_size)
 {
-	int		length;
-	int		size;
-	int		decimal;
-	char	*res;
+	int		base_size;
+	int		neg;
+	char	*result;
+	unsigned long int nb;
 
-	res = 0;
-	length = 0;
-	while (base_from[length])
-		length++;
-	decimal = ft_base_to_decimal(nbr, base_from, length, 0);
-	length = 0;
-	while (base_to[length])
-		length++;
-	size = ft_malloc_size(decimal, length, 0);
-	res = (char *)malloc(sizeof(char) * (size + 1));
-	res[size] = '\0';
-	return (ft_decimal_to_base(decimal, base_to, res, size));
+	neg = malloc_size;
+	base_size = 0;
+	while (base[base_size])
+		base_size++;
+	nb = decimal;
+	while (nb /= base_size)
+		malloc_size++;
+	result = (char *)malloc(sizeof(char) * (malloc_size + 2));
+	result[malloc_size + 1] = '\0';
+	if (neg)
+		result[0] = '-';
+	while (malloc_size >= 0)
+	{
+		result[malloc_size--] = base[decimal % base_size];
+		decimal /= base_size;
+	}
+	return (result);
+}
+
+char
+	*ft_convertbase(char *nbr, char *base_from, char *base_to)
+{
+	int					length;
+	unsigned long int	decimal;
+
+	length = 0;
+	if (nbr[0] == '-')
+	{
+		nbr++;
+		length = 1;
+	}
+	if (!is_valid_nbr(nbr, base_from) || !is_valid_base(base_to))
+		return (NULL);
+	if ((decimal = base_to_decimal(nbr, base_from)) == 0)
+		return (NULL);
+	return (decimal_to_base(decimal, base_to, length));
 }