code: def fast(self):
          
          if self.sorting == TraceSortingFormat.INLINE_SORTING:
              return self.iline
          elif self.sorting == TraceSortingFormat.CROSSLINE_SORTING:
              return self.xline
          else:
              raise RuntimeError("Unknown sorting.")
docs: Access the 'fast' dimension
  
          This mode yields iline or xline mode, depending on which one is laid
          out `faster`, i.e. the line with linear disk layout. Use this mode if
          the inline/crossline distinction isn't as interesting as traversing in
          a fast manner (typically when you want to apply a function to the whole
          file, line-by-line).
  
          Returns
          -------
          fast : Line
              line addressing mode
  
          Notes
          -----
          .. versionadded:: 1.1