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   1  <?php
   2  
   3  /**
   4   * PHP Power of Two Modular Exponentiation Engine
   5   *
   6   * PHP version 5 and 7
   7   *
   8   * @author    Jim Wigginton <terrafrost@php.net>
   9   * @copyright 2017 Jim Wigginton
  10   * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  11   * @link      http://pear.php.net/package/Math_BigInteger
  12   */
  13  
  14  namespace phpseclib3\Math\BigInteger\Engines\PHP\Reductions;
  15  
  16  use phpseclib3\Math\BigInteger\Engines\PHP\Base;
  17  
  18  /**
  19   * PHP Power Of Two Modular Exponentiation Engine
  20   *
  21   * @author  Jim Wigginton <terrafrost@php.net>
  22   */
  23  abstract class PowerOfTwo extends Base
  24  {
  25      /**
  26       * Prepare a number for use in Montgomery Modular Reductions
  27       *
  28       * @param array $x
  29       * @param array $n
  30       * @param string $class
  31       * @return array
  32       */
  33      protected static function prepareReduce(array $x, array $n, $class)
  34      {
  35          return self::reduce($x, $n, $class);
  36      }
  37  
  38      /**
  39       * Power Of Two Reduction
  40       *
  41       * @param array $x
  42       * @param array $n
  43       * @param string $class
  44       * @return array
  45       */
  46      protected static function reduce(array $x, array $n, $class)
  47      {
  48          $lhs = new $class();
  49          $lhs->value = $x;
  50          $rhs = new $class();
  51          $rhs->value = $n;
  52  
  53          $temp = new $class();
  54          $temp->value = [1];
  55  
  56          $result = $lhs->bitwise_and($rhs->subtract($temp));
  57          return $result->value;
  58      }
  59  }