URL shortener

bijective.php

<?php

class Bijective
{
	public $dictionary = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

	public function __construct()
	{
		$this->dictionary = str_split($this->dictionary);
	}

	function encode($i)
	{
		if ($i == 0)
		return $this->dictionary[0];

		$result = '';
		$base = count($this->dictionary);

		while ($i > 0)
		{
			$result[] = $this->dictionary[($i % $base)];
			$i = floor($i / $base);
		}

		$result = array_reverse($result);

		return join("", $result);
	}

	function decode($input)
	{
		$i = 0;
		$base = count($this->dictionary);

		$input = str_split($input);

		foreach($input as $char)
		{
			$pos = array_search($char, $this->dictionary);

			$i = $i * $base + $pos;
		}

		return $i;
	}
}

// Sample usage
$Bijective = new Bijective();

header('Content-Type: text/plain');

print $Bijective->encode(123654). "\n\n";

print $Bijective->decode($Bijective->encode(123654)). "\n\n";

If you don't worry about a custom dictionary (most people don't), the native base_convert() functiona is the way to go:

<?php

$fromBase = 10;
$toBase = 36;
print base_convert(123654, $fromBase, $toBase);

@alganet, actually it's even better than that using the GMP extension: gmp_strval(gmp_init($number, 10), 62);