docs: def next_fat(self, current):
          """
          Helper gives you seekable position of next FAT sector. Should not be
          called from external code.
          """
          sector_size = self.header.sector_size // 4
          block = current // sector_size
          difat_position = 76
  
          if block >= 109:
              block -= 109
              sector = self.header.difat_sector_start
  
              while block >= sector_size:
                  position = (sector + 1) << self.header.sector_shift
                  position += self.header.sector_size - 4
                  sector = self.get_long(position)
                  block -= sector_size - 1
  
              difat_position = (sector + 1) << self.header.sector_shift
          fat_sector = self.get_long(difat_position + block * 4)
  
          fat_position = (fat_sector + 1) << self.header.sector_shift
          fat_position += (current % sector_size) * 4
  
          return self.get_long(fat_position)