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 $value
 * @return int
 * @author Baldur Rensch <[email protected]>
 */
function computeHash($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;
}

// Test Run

$numbers = array(
	-PHP_INT_MAX,
	-56578,
	-232,
	-34,
	-1,
	0,
	1,
	34,
	232,
	56578,
	9999999999,
	PHP_INT_MAX,
	9999999999999999999999999999, // "0"
);

foreach($numbers as $number)
{
	print $number . ' = ' . computeHash($number). "\n";
}