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<?php
/**
* @copyright Copyright (c) 2017 Matthias Held <matthias.held@uni-konstanz.de>
* @author Matthias Held <matthias.held@uni-konstanz.de>
* @license GNU AGPL version 3 or any later version
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
namespace OCA\RansomwareDetection\Entropy;
use OCP\ILogger;
class Entropy
{
/** @var ILogger */
private $logger;
/**
* @param IConfig $config
*/
public function __construct(
ILogger $logger
) {
$this->logger = $logger;
}
/**
* Calculates the entropy of data.
*
* @param string $data
*
* @return float
*/
public function calculateEntropy($data)
{
$entropy = 0;
$size = strlen($data);
foreach (count_chars($data, 1) as $value) {
$p = $value / $size;
$entropy -= $p * log($p) / log(2);
}
return $entropy;
}
/**
* Calculates the standard deviation.
*
* @param array $array
*
* @return float
*/
public function sd($array)
{
if (is_array($array) && count($array) > 0) {
// square root of sum of squares devided by N-1
return sqrt(array_sum(array_map(
function ($x, $mean) {
return pow($x - $mean, 2);
},
$array,
array_fill(
0,
count($array),
(array_sum($array) / count($array))
)
)) / (count($array) - 1));
}
return 0.0;
}
}
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