A base56 implementation

gistfile1.aw

<?php

class Base56
{
	/**
	 * Base56 alphabet. Technically, this component will do arbitrary encoding
	 * depending upon the alphabet, but whatevs!
	 * @var string
	 */
	private static $_alphabet = '23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz';

	/**
	 * The encoded maximum addressible number.
	 * @var string
	 */
	private static $_max = 'yqWeWeMYeK9';

	/**
	 * Encodes an integer to a base-56 representation.
	 * @param integer $number
	 * @return string
	 */
	public static function encode($number)
	{
		$base = strlen(self::$_alphabet);
		$data = '';

		while($number > 0)
		{
			$remainder = $number % $base;
			$number = (int) (($number - $remainder) / $base);
			$data .= self::$_alphabet[$remainder];
		}

		return strrev($data);
	}

	/**
	 * Decodes an integer from its base-56 representation.
	 * @param string $data
	 * @return integer
	 */
	public static function decode($data)
	{
		// Allow 0 to be used as a padding character for fixed-length representations
		$data = str_replace('0', '', $data);

		$base = strlen(self::$_alphabet);
		$valueMap = array_flip(str_split(self::$_alphabet));

		$number = 0;

		if(strspn($data, self::$_alphabet) !== strlen($data) || $data > self::$_max)
		{
			throw new Exception('Invalid Base56 string');
		}

		$data = strrev($data);
		for($i = 0, $j = strlen($data); $i < $j; ++$i)
		{
			// Retrieves the numeric representation for this character and then
			// performs what is effectively a shift
			$number += $valueMap[$data[$i]] * pow($base, $i);
		}

		return $number;
	}
}