def read r
      if @m
        res = @m[r]
        return res if res
        
        # Falling back on IO.read - mmap failed"
        @m = nil
      end
      
      @io.sysseek(r.first, IO::SEEK_SET)
      return @io.sysread(r.last-r.first+1)
    end
def read r
      if @m
        res = @m[r]
        return res if res
        
        # Falling back on IO.read - mmap failed"
        @m = nil
      end
      
      @io.sysseek(r.first, IO::SEEK_SET)
      return @io.sysread(r.last-r.first+1)
    end
Warning: This will be very slow if not mmap'd