Turning an integer into random string and back again

Question

what I'm wanting is to convert an integer into a string. For example, 123456789 may become 8GFsah93r ... you know like Youtube, Pastebin and what not. I then want to convert it back.

I'm working with large integers, for example: 131569877435989900

Take a look at this link: http://codepad.viper-7.com/wHKOMi

This is my attempt using a function I found on the web, obviously... it's not correctly converting back to integer. I'm needing something that does this realiably.

Thanks

Answer 1

Ok, one of the ideas is to use a character array as a representation of a numeric system. Then you can convert from base 10 to base x and vica-versa. The value will be shorter and less readable (altought, you should encrypt it with a two-way crypter if it must be secure).

A solution:

final class UrlShortener {

    private static $charfeed = Array(
    'a','A','b','B','c','C','d','D','e','E','f','F','g','G','h','H','i','I','j','J','k','K','l','L','m',
    'M','n','N','o','O','p','P','q','Q','r','R','s','S','t','T','u','U','v','V','w','W','x','X','y','Y',
    'z','Z','0','1','2','3','4','5','6','7','8','9');

    public static function intToShort($number) {
        $need = count(self::$charfeed);
        $s = '';

        do {
            $s .= self::$charfeed[$number%$need];
            $number = floor($number/$need);
        } while($number > 0);

        return $s;
    }

    public static function shortToInt($string) {
        $num = 0;
        $need = count(self::$charfeed);
        $length = strlen($string);

        for($x = 0; $x < $length; $x++) {
            $key = array_search($string[$x], self::$charfeed);
            $value = $key * pow($need, $x);
            $num += $value;
        }

        return $num;
    }
}

Then you can use:

UrlShortener::intToShort(2);
UrlShortener::shortToInt("b"); 

EDIT

with large numbers, it does not work. You should use this version (with bcmath http://www.php.net/manual/en/book.bc.php ) with very large numbers:

final class UrlShortener {

    private static $charfeed = Array(
    'a','A','b','B','c','C','d','D','e','E','f','F','g','G','h','H','i','I','j','J','k','K','l','L','m',
    'M','n','N','o','O','p','P','q','Q','r','R','s','S','t','T','u','U','v','V','w','W','x','X','y','Y',
    'z','Z','0','1','2','3','4','5','6','7','8','9');

    public static function intToShort($number) {
        $need = count(self::$charfeed);
        $s = '';

        do {
            $s .= self::$charfeed[bcmod($number, $need)];
            $number = floor($number/$need);
        } while($number > 0);

        return $s;
    }

    public static function shortToInt($string) {
        $num = 0;
        $need = count(self::$charfeed);
        $length = strlen($string);

        for($x = 0; $x < $length; $x++) {
            $key = array_search($string[$x], self::$charfeed);
            $value = $key * bcpow($need, $x);
            $num += $value;
        }

        return $num;
    }
}
$original = 131569877435989900;
$short = UrlShortener::intToShort($original);
echo $short;
echo '<br/>';
$result = UrlShortener::shortToInt($short);
echo $result;
echo '<br/>';
echo bccomp($original, $result);

If something missing from here, please let me know, because it's only a snippet from my library (I don't wanna insert the whole thing here)

negra

Answer 2

check base64 encoding: http://php.net/manual/en/function.base64-encode.php http://php.net/manual/en/function.base64-decode.php

If you want a shorter string first encode it into an 8bit string then encode. You can do this with % 256 and / 256.

Or you could manually do what base64 does, get the first 6bits and encode it to a char.