Integer to/from Base62 in PHP

base62.php

<?php
// Author: Gonçalo Baltazar <[email protected]>
// I place this code in the public domain.

/**
 * Functions to encode/decode an integer to/from base62.
 * It is limited to positive integers up to BASE62_MAX to make sure it works on
 * 32-bit systems.
 */

// You can change BASE62_CHARS but keep it 62 characters long.
define('BASE62_CHARS', '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');
define('BASE62_MAX', 2147483647);
define('BASE62_MAX_5CHARS', 916132831);

/**
 * Encode int to base62.
 * By default it returns a string padded to 5 characters. If encoding a number
 * bigger than BASE62_MAX_5CHARS the string will have 6 characters.
 * Change the default padding with $pad.
 */
function int_to_base62($num, $pad=5) {
	$n = (int) $num;
	if ($num != $n || $n < 0 || $n > BASE62_MAX) {
		// invalid int
		return null;
	}
	$chars = BASE62_CHARS;
	$str = '';
	do {
		$str = $chars[$n%62] . $str;
		$n = floor($n/62);
	} while ($n > 0);
	return ($pad && $pad > 0 ? str_pad($str, ($pad > 6 ? 6 : $pad), '0', STR_PAD_LEFT) : $str);
}

/**
 * Decode int from base62.
 * If $strict == true only strings with 5 or 6 characters are considered valid.
 * Change it to false if a $pad other than 5 or 6 was used to encode.
 */
function int_from_base62($str, $strict=true) {
	$str = (string) $str;
	$l = strlen($str);
	if ($strict && $l != 6 && $l != 5 || !$strict && ($l < 1 || $l > 6)) {
		return null;
	}
	$powers = array(1, 62, 3844, 238328, 14776336, 916132832);
	$n = 0;
	for ($i = 0; $i < $l; ++$i) {
		$v = strpos(BASE62_CHARS, $str[$l - $i - 1]);
		if ($v === false) {
			// invalid char
			return null;
		}
		$n += $v * $powers[$i];
		if ($n > BASE62_MAX || is_float($n)) {
			// in PHP, int "overflows to float"
			return null;
		}
	}
	return $n;
}

?>