Math class from Taylor Otwell. Thanks to @brad (captain_jim1@yahoo.com) for the class content.

Math.php

<?php

class Math {

        /**
         * The base.
         *
         * @var string
         */
        private static $base = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

        /**
         * Convert a from a given base to base 10.
         *
         * @param  string  $value
         * @param  int     $base
         * @return int
         */
        public static function to_base_10($value, $b = 62)
        {
                $limit = strlen($value);
                $result = strpos(static::$base, $value[0]);

                for($i = 1; $i < $limit; $i++)
                {
                        $result = $b * $result + strpos(static::$base, $value[$i]);
                }

                return $result;
        }

        /**
         * Convert from base 10 to another base.
         *
         * @param  int     $value
         * @param  int     $base
         * @return string
         */
        public static function to_base($value, $b = 62)
        {
                $r = $value  % $b;
                $result = static::$base[$r];
                $q = floor($value / $b);

                while ($q)
                {
                        $r = $q % $b;
                        $q = floor($q / $b);
                        $result = static::$base[$r].$result;
                }

                return $result;
        }

}