Feistel Hash

feistel.php

<?php

    /**
     * This function computes a hash of an integer. This can be used to not expose values to a customer, such as
     * not giving them the id value for passing them to URLs. This algorithm is a bidirectional encryption (Feistel cipher) that maps
     * the integer space onto itself. 
     * 
     * @link http://wiki.postgresql.org/wiki/Pseudo_encrypt Algorithm used
     * @link http://en.wikipedia.org/wiki/Feistel_cipher Wikipedia page about Feistel ciphers
     * @param int $value
     * @return int
     * @author Baldur Rensch <[email protected]>
     */
    private static function computeHash($value) 
    {
        $l1 = ($value >> 16) & 65535;
        $r1 = $value & 65535;
        for ($i = 0; $i < 3; $i++) {
            $l2 = $r1;
            $r2 = $l1 ^ (int) ((((1366 * $r1 + 150889) % 714025) / 714025) * 32767);
            $l1 = $l2;
            $r1 = $r2;
        }
        return ($r1 << 16) + $l1;
    }