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<?php
/**
* Modular Exponentiation Engine
*
* PHP version 5 and 7
*
* @category Math
* @package BigInteger
* @author Jim Wigginton <terrafrost@php.net>
* @copyright 2017 Jim Wigginton
* @license http://www.opensource.org/licenses/mit-license.html MIT License
* @link http://pear.php.net/package/Math_BigInteger
*/
namespace phpseclib3\Math\BigInteger\Engines\BCMath;
use phpseclib3\Math\BigInteger\Engines\BCMath;
/**
* Sliding Window Exponentiation Engine
*
* @package PHP
* @author Jim Wigginton <terrafrost@php.net>
* @access public
*/
abstract class Base extends BCMath
{
/**
* Cache constants
*
* $cache[self::VARIABLE] tells us whether or not the cached data is still valid.
*
* @access private
*/
const VARIABLE = 0;
/**
* $cache[self::DATA] contains the cached data.
*
* @access private
*/
const DATA = 1;
/**
* Test for engine validity
*
* @return bool
*/
public static function isValidEngine()
{
return static::class != __CLASS__;
}
/**
* Performs modular exponentiation.
*
* @param \phpseclib3\Math\BigInteger\Engines\BCMath $x
* @param \phpseclib3\Math\BigInteger\Engines\BCMath $e
* @param \phpseclib3\Math\BigInteger\Engines\BCMath $n
* @param string $class
* @return \phpseclib3\Math\BigInteger\Engines\BCMath
*/
protected static function powModHelper(BCMath $x, BCMath $e, BCMath $n, $class)
{
if (empty($e->value)) {
$temp = new $class();
$temp->value = '1';
return $x->normalize($temp);
}
return $x->normalize(static::slidingWindow($x, $e, $n, $class));
}
/**
* Modular reduction preparation
*
* @param string $x
* @param string $n
* @param string $class
* @see self::slidingWindow()
* @return string
*/
protected static function prepareReduce($x, $n, $class)
{
return static::reduce($x, $n);
}
/**
* Modular multiply
*
* @param string $x
* @param string $y
* @param string $n
* @param string $class
* @see self::slidingWindow()
* @return string
*/
protected static function multiplyReduce($x, $y, $n, $class)
{
return static::reduce(bcmul($x, $y), $n);
}
/**
* Modular square
*
* @param string $x
* @param string $n
* @param string $class
* @see self::slidingWindow()
* @return string
*/
protected static function squareReduce($x, $n, $class)
{
return static::reduce(bcmul($x, $x), $n);
}
}
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