Base-encoding/decoding with arbitrary radix.

xbase.php

<?php
/**
 * Base-encoding/decoding with arbitrary radix.
 * @see http://stackoverflow.com/questions/1119722/base-62-conversion-in-python#answer-1119769
 */
define('BASE_64_ALPHABET', '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');

function xbase_encode($number, $alphabet = BASE_64_ALPHABET) {
    if ($number == 0)
        return $alphabet[0];
	else if ($number < 0)
		$number = abs($number);
	$encoded = '';
    $base = strlen($alphabet);
    while ($number) {
        $reminder = $number % $base;
		$number = floor(($number - $reminder) / $base);
        $encoded .= $alphabet[$reminder];
	}
    return strrev($encoded);
}


function xbase_decode($string, $alphabet = BASE_64_ALPHABET) {
    $base = strlen($alphabet);
    $length = strlen($string);
    $decoded = 0;
	for ($split = str_split($string), $i = 0; $i < count($split); $i++)
		$decoded += strpos($alphabet, $split[$i]) * pow($base, $length - $i - 1);
	return $decoded;
}