191     cache: VecDeque<ZVec>,  field
201         let mut cache: VecDeque<ZVec> = VecDeque::new();  in new()  localVariable
202         cache.push_back(level_zero_key);  in new()
203         Self { current: 0, cache }  in new()
211         boot_level >= self.current && !self.cache.is_empty()  in level_accessible()
222         let first_not_cached = self.current + self.cache.len();  in get_hkdf_key()
228             let highest_key = self.cache.back().unwrap();  in get_hkdf_key()
231             self.cache.push_back(next_key);  in get_hkdf_key()
235         Ok(Some(self.cache.get(boot_level - self.current).unwrap()))  in get_hkdf_key()
246                 self.cache.len()  in advance_boot_level()
257         self.cache = self.cache.split_off(new_boot_level - self.current);  in advance_boot_level()
269         self.cache.clear();  in finish()