ASDF encoder

asdf_encoder.class.php

<?php
class ASDF{
        private static $r = 10000000;
        private static $d = 10001;
        private static $f = 0;

        public static function encode($x) {
                $x %= (self::$r - self::$r % self::$d);
                return floor(self::$r / self::$d) * (($x + self::$f) % self::$d) + floor($x / self::$d);
        }

        public static function decode($y) {
                $m = floor(self::$r / self::$d);
                return (floor($y / $m)+(self::$d - self::$f % self::$d)) % self::$d + ($y % $m) * self::$d;
        }
}