[Summary view] [Print] [Text view]

   1  <?php
   2  
   3  /**
   4   * 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\BCMath;
  15  
  16  use phpseclib3\Math\BigInteger\Engines\BCMath;
  17  
  18  /**
  19   * Sliding Window Exponentiation Engine
  20   *
  21   * @author  Jim Wigginton <terrafrost@php.net>
  22   */
  23  abstract class Base extends BCMath
  24  {
  25      /**
  26       * Cache constants
  27       *
  28       * $cache[self::VARIABLE] tells us whether or not the cached data is still valid.
  29       *
  30       */
  31      const VARIABLE = 0;
  32      /**
  33       * $cache[self::DATA] contains the cached data.
  34       *
  35       */
  36      const DATA = 1;
  37  
  38      /**
  39       * Test for engine validity
  40       *
  41       * @return bool
  42       */
  43      public static function isValidEngine()
  44      {
  45          return static::class != __CLASS__;
  46      }
  47  
  48      /**
  49       * Performs modular exponentiation.
  50       *
  51       * @param BCMath $x
  52       * @param BCMath $e
  53       * @param BCMath $n
  54       * @param string $class
  55       * @return BCMath
  56       */
  57      protected static function powModHelper(BCMath $x, BCMath $e, BCMath $n, $class)
  58      {
  59          if (empty($e->value)) {
  60              $temp = new $class();
  61              $temp->value = '1';
  62              return $x->normalize($temp);
  63          }
  64  
  65          return $x->normalize(static::slidingWindow($x, $e, $n, $class));
  66      }
  67  
  68      /**
  69       * Modular reduction preparation
  70       *
  71       * @param string $x
  72       * @param string $n
  73       * @param string $class
  74       * @see self::slidingWindow()
  75       * @return string
  76       */
  77      protected static function prepareReduce($x, $n, $class)
  78      {
  79          return static::reduce($x, $n);
  80      }
  81  
  82      /**
  83       * Modular multiply
  84       *
  85       * @param string $x
  86       * @param string $y
  87       * @param string $n
  88       * @param string $class
  89       * @see self::slidingWindow()
  90       * @return string
  91       */
  92      protected static function multiplyReduce($x, $y, $n, $class)
  93      {
  94          return static::reduce(bcmul($x, $y), $n);
  95      }
  96  
  97      /**
  98       * Modular square
  99       *
 100       * @param string $x
 101       * @param string $n
 102       * @param string $class
 103       * @see self::slidingWindow()
 104       * @return string
 105       */
 106      protected static function squareReduce($x, $n, $class)
 107      {
 108          return static::reduce(bcmul($x, $x), $n);
 109      }
 110  }