code: private function readBIFF5CellRangeAddressFixed($subData)
      {
          // offset: 0; size: 2; index to first row
          $fr = self::getUInt2d($subData, 0) + 1;
  
          // offset: 2; size: 2; index to last row
          $lr = self::getUInt2d($subData, 2) + 1;
  
          // offset: 4; size: 1; index to first column
          $fc = ord($subData[4]);
  
          // offset: 5; size: 1; index to last column
          $lc = ord($subData[5]);
  
          // check values
          if ($fr > $lr || $fc > $lc) {
              throw new Exception('Not a cell range address');
          }
  
          // column index to letter
          $fc = Coordinate::stringFromColumnIndex($fc + 1);
          $lc = Coordinate::stringFromColumnIndex($lc + 1);
  
          if ($fr == $lr and $fc == $lc) {
              return "$fc$fr";
          }
  
          return "$fc$fr:$lc$lr";
      }
docs: Reads a cell range address in BIFF5 e.g. 'A2:B6' or 'A1'
  always fixed range
  section 2.5.14.
  
  @param string $subData
  
  @throws Exception
  
  @return string