code: public function getContext()
      {
          $s = '';
          foreach (['a', 'b', 'c', 'd'] as $i) {
              $v = $this->{$i};
              $s .= chr($v & 0xff);
              $s .= chr(($v >> 8) & 0xff);
              $s .= chr(($v >> 16) & 0xff);
              $s .= chr(($v >> 24) & 0xff);
          }
  
          return $s;
      }
docs: Get MD5 stream context.
  
  @return string