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<?php
namespace ls\mersenne;
/**
* Set seed for this response
* If there is no seed, create a new one
* Also inits the twister.
* @param int $surveyid
* @param null|\Survey $survey (for testing purposes))
* @return void
*/
function setSeed($surveyid, $survey = null)
{
/* In started survey : get seed from response table */
if (isset($_SESSION['responses_' . $surveyid]['srid'])) {
$oResponse = \Response::model($surveyid)->findByPk($_SESSION['responses_' . $surveyid]['srid']);
$seed = $oResponse->seed;
/* fix empty seed, this allow broken seed (not number) */
if (empty($seed)) {
$seed = mt_rand();
$oResponse->seed = $seed;
$oResponse->save();
}
} else {
$seed = mt_rand();
/* On activated (but not started) survey : set seed in startingValues */
if (!$survey) {
$survey = \Survey::model()->findByPk($surveyid);
}
if ($survey->getIsActive()) {
$table = \Yii::app()->db->schema->getTable('{{responses_' . $surveyid . '}}');
if (isset($table->columns['seed'])) {
$_SESSION['responses_' . $surveyid]['startingValues']['seed'] = $seed;
}
}
}
MersenneTwister::init($seed);
}
/**
* Shuffle an array using MersenneTwister
* Argument NOT called by reference!
* @param array $arr
* @return array
*/
function shuffle(array $arr)
{
$mt = MersenneTwister::getInstance();
return $mt->shuffle($arr);
}
/**
* Custom random algorithm to get consistent behaviour between PHP versions.
*
* Copied from: http://www.dr-chuck.com/csev-blog/2015/09/a-mersenne_twister-implementation-in-php/
*/
class MersenneTwister
{
private $state = array();
private $index = 0;
/**
* Singleton variable
* @var MersenneTwister
*/
private static $instance = null;
/**
* @param int $seed
* @return void
*/
public static function init($seed)
{
self::$instance = new MersenneTwister($seed);
}
/**
* @return MersenneTwister
*/
public static function getInstance()
{
if (empty(self::$instance)) {
throw new \Exception('Must init MersenneTwister before use. Should be done in randomizationGroupsAndQuestions.');
}
return self::$instance;
}
/**
* Shuffle with seed
* @param array $arr
* @param $seed
* @return array
*/
public function shuffle($arr)
{
$mt = self::$instance;
$new = $arr;
for ($i = count($new) - 1; $i > 0; $i--) {
$j = $mt->getNext(0, $i);
$tmp = $new[$i];
$new[$i] = $new[$j];
$new[$j] = $tmp;
}
return $new;
}
/**
* @param integer $seed
*/
public function __construct($seed = null)
{
if ($seed === null) {
$seed = mt_rand();
}
$this->setSeed($seed);
}
/**
* @param integer $seed
*/
public function setSeed($seed)
{
$this->state[0] = $seed & 0xffffffff;
for ($i = 1; $i < 624; $i++) {
$this->state[$i] = (((0x6c078965 * ($this->state[$i - 1] ^ ($this->state[$i - 1] >> 30))) + $i)) & 0xffffffff;
}
$this->index = 0;
}
private function generateTwister()
{
for ($i = 0; $i < 624; $i++) {
$y = (($this->state[$i] & 0x1) + ($this->state[$i] & 0x7fffffff)) & 0xffffffff;
$this->state[$i] = ($this->state[($i + 397) % 624] ^ ($y >> 1)) & 0xffffffff;
if (($y % 2) == 1) {
$this->state[$i] = ($this->state[$i] ^ 0x9908b0df) & 0xffffffff;
}
}
}
/**
* @param integer $min
* @param integer $max
*/
public function getNext($min = null, $max = null)
{
if (($min === null && $max !== null) || ($min !== null && $max === null)) {
throw new \Exception('Invalid arguments');
}
if ($this->index === 0) {
$this->generateTwister();
}
$y = $this->state[$this->index];
$y = ($y ^ ($y >> 11)) & 0xffffffff;
$y = ($y ^ (($y << 7) & 0x9d2c5680)) & 0xffffffff;
$y = ($y ^ (($y << 15) & 0xefc60000)) & 0xffffffff;
$y = ($y ^ ($y >> 18)) & 0xffffffff;
$this->index = ($this->index + 1) % 624;
if ($min === null && $max === null) {
return $y;
}
$range = abs($max - $min);
return min($min, $max) + ($y % ($range + 1));
}
}