InstagramShortUrl encoding/decoding service

InstagramShortUrl.php

<?php

namespace Smittn\InstagramBundle\Services;
	
class InstagramShortUrl {

	private $alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_';
	
	public function __construct() {
		
	}
	
	function encode($num) {
	
		$base_count = strlen($this->alphabet);
		$encoded = '';

		while ($num >= $base_count) {
			$div = $num/$base_count;
			$mod = ($num-($base_count*intval($div)));
			$encoded = $this->alphabet[$mod] . $encoded;
			$num = intval($div);
		}

		if ($num) {
			$encoded = $this->alphabet[$num] . $encoded;
		}

		return $encoded;
	
	}

	function decode($num) {
		
		$decoded = 0;
		$multi = 1;
		while (strlen($num) > 0) {
			$digit = $num[strlen($num)-1];
			$decoded += $multi * strpos($this->alphabet, $digit);
			$multi = $multi * strlen($this->alphabet);
			$num = substr($num, 0, -1);
		}

		return $decoded;
	
	}	
	
}