code: private function _readData($bl)
      {
          $block = $bl;
          $data = '';
  
          while ($block != -2) {
              $pos = ($block + 1) * self::BIG_BLOCK_SIZE;
              $data .= substr($this->data, $pos, self::BIG_BLOCK_SIZE);
              $block = self::getInt4d($this->bigBlockChain, $block * 4);
          }
  
          return $data;
      }
docs: Read a standard stream (by joining sectors using information from SAT).
  
  @param int $bl Sector ID where the stream starts
  
  @return string Data for standard stream