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   1  <?php
   2  // +----------------------------------------------------------------------+

   3  // | PHP Version 4                                                        |

   4  // +----------------------------------------------------------------------+

   5  // | Copyright (c) 1997-2004 The PHP Group                                |

   6  // +----------------------------------------------------------------------+

   7  // | This source file is subject to version 3.0 of the PHP license,       |

   8  // | that is bundled with this package in the file LICENSE, and is        |

   9  // | available at through the world-wide-web at                           |

  10  // | http://www.php.net/license/3_0.txt.                                  |

  11  // | If you did not receive a copy of the PHP license and are unable to   |

  12  // | obtain it through the world-wide-web, please send a note to          |

  13  // | license@php.net so we can mail you a copy immediately.               |

  14  // +----------------------------------------------------------------------+

  15  // | Authors: Aidan Lister <aidan@php.net>                                |

  16  // +----------------------------------------------------------------------+

  17  //

  18  // $Id: bcpowmod.php,v 1.2 2005/11/22 20:24:45 aidan Exp $

  19  
  20  
  21  /**

  22   * Replace bcpowmod()

  23   *

  24   * @category    PHP

  25   * @package     PHP_Compat

  26   * @link        http://php.net/function.bcpowmod

  27   * @author      Sara Golemon <pollita@php.net>

  28   * @version     $Revision: 1.2 $

  29   * @since       PHP 5.0.0

  30   * @require     PHP 4.0.0 (user_error)

  31   */
  32  if (!function_exists('bcpowmod')) {
  33      function bcpowmod($x, $y, $modulus, $scale)
  34      {
  35          // Sanity check

  36          if (!is_scalar($x)) {
  37              user_error('bcpowmod() expects parameter 1 to be string, ' .
  38                  gettype($x) . ' given', E_USER_WARNING);
  39              return false;
  40          }
  41  
  42          if (!is_scalar($y)) {
  43              user_error('bcpowmod() expects parameter 2 to be string, ' .
  44                  gettype($y) . ' given', E_USER_WARNING);
  45              return false;
  46          }
  47  
  48          if (!is_scalar($modulus)) {
  49              user_error('bcpowmod() expects parameter 3 to be string, ' .
  50                  gettype($modulus) . ' given', E_USER_WARNING);
  51              return false;
  52          }
  53  
  54          if (!is_scalar($scale)) {
  55              user_error('bcpowmod() expects parameter 4 to be integer, ' .
  56                  gettype($scale) . ' given', E_USER_WARNING);
  57              return false;
  58          }
  59  
  60          $t = '1';
  61          while (bccomp($y, '0')) {
  62              if (bccomp(bcmod($y, '2'), '0')) {
  63                  $t = bcmod(bcmul($t, $x), $modulus);
  64                  $y = bcsub($y, '1');
  65              }
  66  
  67              $x = bcmod(bcmul($x, $x), $modulus);
  68              $y = bcdiv($y, '2');
  69          }
  70  
  71          return $t;
  72      }
  73  }
  74  
  75  ?>