URL shortening - make your own URL shortener

If you ever thought about URL shortening, you've probably already figured out, how it works.

Those random letters and numbers which serve as a key (in hashtable data structures) are basically encoded integers, which are AUTO_INCREMENT values in the database.

Here are the encoding and decoding functions:

const ALLOWED_CHARS = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

function id2short($integer, $base = self::ALLOWED_CHARS) {
	$out = '';
	$length = strlen($base);
	while($integer > $length-1) {
		$out = $base[fmod($integer, $length)].$out;
		$integer = floor( $integer / $length);
	}
	return $base[$integer].$out;
}

function short2id($string, $base = self::ALLOWED_CHARS) {
	$length = strlen($base);
	$size = strlen($string)-1;
	$string = str_split($string);
	$out = strpos($base, array_pop($string));
	foreach($string as $i=>$char) {
		$out += strpos($base, $char) * pow($length, $size - $i);
	}
	return $out;
}

Full code here.