958 lines
31 KiB
Rust
958 lines
31 KiB
Rust
// Copyright 2019-2020 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// TODO(ia0): Remove when the module is used.
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#![allow(dead_code)]
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use crate::bitfield::*;
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use crate::{Storage, StorageIndex, StoreError, StoreResult};
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use alloc::vec::Vec;
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use core::cmp::min;
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type WORD = u32;
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/// Size of a word in bytes.
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///
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/// Currently, the store only supports storages where a word is 4 bytes.
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const WORD_SIZE: usize = core::mem::size_of::<WORD>();
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/// Minimum number of words per page.
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///
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/// Currently, the store only supports storages where pages have at least 8 words.
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const MIN_NUM_WORDS_PER_PAGE: usize = 8;
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/// Maximum size of a page in bytes.
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///
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/// Currently, the store only supports storages where pages are between 8 and 1024 [words].
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///
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/// [words]: constant.WORD_SIZE.html
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const MAX_PAGE_SIZE: usize = 4096;
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/// Maximum number of erase cycles.
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///
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/// Currently, the store only supports storages where the maximum number of erase cycles fits on 16
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/// bits.
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const MAX_ERASE_CYCLE: usize = 65535;
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/// Minimum number of pages.
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///
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/// Currently, the store only supports storages with at least 3 pages.
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const MIN_NUM_PAGES: usize = 3;
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/// Maximum page index.
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///
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/// Thus the maximum number of pages is one more than this number. Currently, the store only
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/// supports storages where the number of pages is between 3 and 64.
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const MAX_PAGE_INDEX: usize = 63;
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/// Maximum key index.
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///
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/// Thus the number of keys is one more than this number. Currently, the store only supports 4096
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/// keys.
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const MAX_KEY_INDEX: usize = 4095;
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/// Maximum length in bytes of a user payload.
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///
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/// Currently, the store only supports values smaller than 1024 bytes.
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const MAX_VALUE_LEN: usize = 1023;
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/// Maximum number of updates per transaction.
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///
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/// Currently, the store only supports transactions with at most 31 updates.
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const MAX_UPDATES: usize = 31;
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/// Maximum number of words per virtual page.
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const MAX_VIRT_PAGE_SIZE: usize = div_ceil(MAX_PAGE_SIZE, WORD_SIZE) - CONTENT_WORD;
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/// Word with all bits set to one.
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const ERASED_WORD: WORD = !(0 as WORD);
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/// Helpers for a given storage configuration.
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#[derive(Clone, Debug)]
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pub struct Format {
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/// The size in bytes of a page in the storage.
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///
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/// # Invariant
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///
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/// - Words divide a page evenly.
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/// - There are at least 8 words in a page.
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/// - There are at most `MAX_PAGE_SIZE` bytes in a page.
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page_size: usize,
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/// The number of pages in the storage.
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///
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/// # Invariant
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///
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/// - There are at least 3 pages.
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/// - There are at most `MAX_PAGE_INDEX + 1` pages.
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num_pages: usize,
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/// The maximum number of times a page can be erased.
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///
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/// # Invariant
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///
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/// - A page can be erased at most `MAX_ERASE_CYCLE` times.
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max_page_erases: usize,
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}
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impl Format {
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/// Extracts the format from a storage.
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///
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/// Returns `None` if the storage is not [supported].
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///
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/// [supported]: struct.Format.html#method.is_storage_supported
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pub fn new<S: Storage>(storage: &S) -> Option<Format> {
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if Format::is_storage_supported(storage) {
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Some(Format {
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page_size: storage.page_size(),
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num_pages: storage.num_pages(),
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max_page_erases: storage.max_page_erases(),
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})
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} else {
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None
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}
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}
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/// Returns whether a storage is supported.
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///
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/// A storage is supported if the following conditions hold:
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/// - The size of a word is [`WORD_SIZE`] bytes.
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/// - The size of a word evenly divides the size of a page.
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/// - A page contains at least [`MIN_NUM_WORDS_PER_PAGE`] words.
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/// - A page contains at most [`MAX_PAGE_SIZE`] bytes.
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/// - There are at least [`MIN_NUM_PAGES`] pages.
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/// - There are at most [`MAX_PAGE_INDEX`]` + 1` pages.
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/// - A word can be written at least twice between erase cycles.
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/// - The maximum number of erase cycles is at most [`MAX_ERASE_CYCLE`].
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///
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/// [`WORD_SIZE`]: constant.WORD_SIZE.html
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/// [`MIN_NUM_WORDS_PER_PAGE`]: constant.MIN_NUM_WORDS_PER_PAGE.html
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/// [`MAX_PAGE_SIZE`]: constant.MAX_PAGE_SIZE.html
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/// [`MIN_NUM_PAGES`]: constant.MIN_NUM_PAGES.html
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/// [`MAX_PAGE_INDEX`]: constant.MAX_PAGE_INDEX.html
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/// [`MAX_ERASE_CYCLE`]: constant.MAX_ERASE_CYCLE.html
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fn is_storage_supported<S: Storage>(storage: &S) -> bool {
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let word_size = storage.word_size();
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let page_size = storage.page_size();
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let num_pages = storage.num_pages();
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let max_word_writes = storage.max_word_writes();
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let max_page_erases = storage.max_page_erases();
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word_size == WORD_SIZE
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&& page_size % word_size == 0
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&& (MIN_NUM_WORDS_PER_PAGE * word_size <= page_size && page_size <= MAX_PAGE_SIZE)
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&& (MIN_NUM_PAGES <= num_pages && num_pages <= MAX_PAGE_INDEX + 1)
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&& max_word_writes >= 2
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&& max_page_erases <= MAX_ERASE_CYCLE
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}
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/// The size of a word in bytes.
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pub fn word_size(&self) -> usize {
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WORD_SIZE
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}
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/// The size of a page in bytes.
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///
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/// We have `MIN_NUM_WORDS_PER_PAGE * self.word_size() <= self.page_size() <= MAX_PAGE_SIZE`.
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pub fn page_size(&self) -> usize {
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self.page_size
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}
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/// The number of pages in the storage, denoted by `N`.
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///
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/// We have `MIN_NUM_PAGES <= N <= MAX_PAGE_INDEX + 1`.
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pub fn num_pages(&self) -> usize {
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self.num_pages
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}
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/// The maximum page index.
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///
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/// We have `2 <= self.max_page() <= MAX_PAGE_INDEX`.
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pub fn max_page(&self) -> usize {
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self.num_pages - 1
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}
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/// The maximum number of times a page can be erased, denoted by `E`.
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///
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/// We have `E <= MAX_ERASE_CYCLE`.
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pub fn max_page_erases(&self) -> usize {
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self.max_page_erases
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}
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/// The maximum key.
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pub fn max_key(&self) -> usize {
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MAX_KEY_INDEX
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}
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/// The maximum number of updates per transaction.
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pub fn max_updates(&self) -> usize {
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MAX_UPDATES
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}
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/// The size of a virtual page in words, denoted by `Q`.
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///
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/// A virtual page is stored in a physical page after the page header.
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///
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/// We have `MIN_NUM_WORDS_PER_PAGE - 2 <= Q <= MAX_VIRT_PAGE_SIZE`.
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pub fn virt_page_size(&self) -> usize {
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self.page_size() / self.word_size() - CONTENT_WORD
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}
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/// The maximum length in bytes of a user payload.
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///
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/// We have `(MIN_NUM_WORDS_PER_PAGE - 3) * self.word_size() <= self.max_value_len() <=
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/// MAX_VALUE_LEN`.
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pub fn max_value_len(&self) -> usize {
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min(
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(self.virt_page_size() - 1) * self.word_size(),
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MAX_VALUE_LEN,
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)
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}
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/// The maximum prefix length in words, denoted by `M`.
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///
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/// A prefix is the first words of a virtual page that belong to the last entry of the previous
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/// virtual page. This happens because entries may overlap up to 2 virtual pages.
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///
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/// We have `MIN_NUM_WORDS_PER_PAGE - 3 <= M < Q`.
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pub fn max_prefix_len(&self) -> usize {
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self.bytes_to_words(self.max_value_len())
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}
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/// The total virtual capacity in words, denoted by `V`.
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///
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/// We have `V = (N - 1) * (Q - 1) - M`.
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///
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/// We can show `V >= (N - 2) * (Q - 1)` with the following steps:
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/// - `M <= Q - 1` from `M < Q` from [`M`] definition
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/// - `-M >= -(Q - 1)` from above
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/// - `V >= (N - 1) * (Q - 1) - (Q - 1)` from `V` definition
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///
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/// [`M`]: struct.Format.html#method.max_prefix_len
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pub fn virt_size(&self) -> usize {
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(self.num_pages() - 1) * (self.virt_page_size() - 1) - self.max_prefix_len()
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}
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/// The total user capacity in words, denoted by `C`.
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///
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/// We have `C = V - N = (N - 1) * (Q - 2) - M - 1`.
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///
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/// We can show `C >= (N - 2) * (Q - 2) - 2` with the following steps:
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/// - `V >= (N - 2) * (Q - 1)` from [`V`] definition
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/// - `C >= (N - 2) * (Q - 1) - N` from `C` definition
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/// - `(N - 2) * (Q - 1) - N = (N - 2) * (Q - 2) - 2` by calculus
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///
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/// [`V`]: struct.Format.html#method.virt_size
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pub fn total_capacity(&self) -> usize {
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// From the virtual capacity, we reserve N - 1 words for `Erase` entries and 1 word for a
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// `Clear` entry.
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self.virt_size() - self.num_pages()
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}
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/// The total virtual lifetime in words, denoted by `L`.
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///
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/// We have `L = (E * N + N - 1) * Q`.
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pub fn total_lifetime(&self) -> Position {
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Position::new(self, self.max_page_erases(), self.num_pages() - 1, 0)
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}
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/// Returns the word position of the first entry of a page.
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///
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/// The init info of the page must be provided to know where the first entry of the page
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/// starts.
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pub fn page_head(&self, init: InitInfo, page: usize) -> Position {
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Position::new(self, init.cycle, page, init.prefix)
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}
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/// Returns the storage index of the init info of a page.
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pub fn index_init(&self, page: usize) -> StorageIndex {
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let byte = INIT_WORD * self.word_size();
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StorageIndex { page, byte }
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}
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/// Parses the init info of a page from its storage representation.
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pub fn parse_init(&self, word: WORD) -> StoreResult<WordState<InitInfo>> {
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Ok(if word == ERASED_WORD {
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WordState::Erased
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} else if WORD_CHECKSUM.get(word)? != 0 {
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WordState::Partial
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} else {
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let cycle = INIT_CYCLE.get(word);
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let prefix = INIT_PREFIX.get(word);
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if cycle > self.max_page_erases() || prefix > self.max_prefix_len() {
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return Err(StoreError::InvalidStorage);
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}
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WordState::Valid(InitInfo { cycle, prefix })
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})
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}
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/// Builds the storage representation of an init info.
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pub fn build_init(&self, init: InitInfo) -> [u8; WORD_SIZE] {
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let mut word = ERASED_WORD;
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INIT_CYCLE.set(&mut word, init.cycle);
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INIT_PREFIX.set(&mut word, init.prefix);
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WORD_CHECKSUM.set(&mut word, 0);
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word.to_ne_bytes()
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}
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/// Returns the storage index of the compact info of a page.
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pub fn index_compact(&self, page: usize) -> StorageIndex {
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let byte = COMPACT_WORD * self.word_size();
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StorageIndex { page, byte }
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}
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/// Parses the compact info of a page from its storage representation.
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pub fn parse_compact(&self, word: WORD) -> StoreResult<WordState<CompactInfo>> {
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Ok(if word == ERASED_WORD {
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WordState::Erased
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} else if WORD_CHECKSUM.get(word)? != 0 {
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WordState::Partial
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} else {
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let tail = COMPACT_TAIL.get(word);
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if tail > self.virt_size() + self.max_prefix_len() {
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return Err(StoreError::InvalidStorage);
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}
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WordState::Valid(CompactInfo { tail })
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})
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}
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/// Builds the storage representation of a compact info.
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pub fn build_compact(&self, compact: CompactInfo) -> [u8; WORD_SIZE] {
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let mut word = ERASED_WORD;
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COMPACT_TAIL.set(&mut word, compact.tail);
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WORD_CHECKSUM.set(&mut word, 0);
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word.to_ne_bytes()
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}
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/// Builds the storage representation of an internal entry.
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pub fn build_internal(&self, internal: InternalEntry) -> [u8; WORD_SIZE] {
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let mut word = ERASED_WORD;
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match internal {
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InternalEntry::Erase { page } => {
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ID_ERASE.set(&mut word);
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ERASE_PAGE.set(&mut word, page);
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}
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InternalEntry::Clear { min_key } => {
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ID_CLEAR.set(&mut word);
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CLEAR_MIN_KEY.set(&mut word, min_key);
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}
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InternalEntry::Marker { count } => {
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ID_MARKER.set(&mut word);
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MARKER_COUNT.set(&mut word, count);
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}
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InternalEntry::Remove { key } => {
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ID_REMOVE.set(&mut word);
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REMOVE_KEY.set(&mut word, key);
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}
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}
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WORD_CHECKSUM.set(&mut word, 0);
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word.to_ne_bytes()
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}
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/// Parses the first word of an entry from its storage representation.
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pub fn parse_word(&self, word: WORD) -> StoreResult<WordState<ParsedWord>> {
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let valid = if ID_PADDING.check(word) {
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ParsedWord::Padding(Padding { length: 0 })
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} else if ID_HEADER.check(word) {
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if HEADER_DELETED.get(word) {
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let length = HEADER_LENGTH.get(word);
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if length > self.max_value_len() {
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return Err(StoreError::InvalidStorage);
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}
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let length = self.bytes_to_words(length);
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ParsedWord::Padding(Padding { length })
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} else {
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let flipped = HEADER_FLIPPED.get(word);
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let length = HEADER_LENGTH.get(word);
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let key = HEADER_KEY.get(word);
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let checksum = HEADER_CHECKSUM.get(word)?;
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ParsedWord::Header(Header {
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flipped,
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length,
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key,
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checksum,
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})
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}
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} else if ID_ERASE.check(word) {
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let page = ERASE_PAGE.get(word);
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ParsedWord::Internal(InternalEntry::Erase { page })
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} else if ID_CLEAR.check(word) {
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let min_key = CLEAR_MIN_KEY.get(word);
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ParsedWord::Internal(InternalEntry::Clear { min_key })
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} else if ID_MARKER.check(word) {
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let count = MARKER_COUNT.get(word);
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ParsedWord::Internal(InternalEntry::Marker { count })
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} else if ID_REMOVE.check(word) {
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let key = REMOVE_KEY.get(word);
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ParsedWord::Internal(InternalEntry::Remove { key })
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} else if word == ERASED_WORD {
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return Ok(WordState::Erased);
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} else {
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return Ok(WordState::Partial);
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};
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if let ParsedWord::Internal(internal) = &valid {
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if WORD_CHECKSUM.get(word)? != 0 {
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return Ok(WordState::Partial);
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}
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let invalid = match internal {
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InternalEntry::Erase { page } => *page > self.max_page(),
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InternalEntry::Clear { min_key } => *min_key > self.max_key(),
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InternalEntry::Marker { count } => *count > MAX_UPDATES,
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InternalEntry::Remove { key } => *key > self.max_key(),
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};
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if invalid {
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return Err(StoreError::InvalidStorage);
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}
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}
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Ok(WordState::Valid(valid))
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}
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/// Builds the storage representation of a user entry.
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pub fn build_user(&self, key: usize, value: &[u8]) -> Vec<u8> {
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let length = value.len();
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let word_size = self.word_size();
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let footer = self.bytes_to_words(length);
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let mut result = vec![0xff; (1 + footer) * word_size];
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result[word_size..][..length].copy_from_slice(value);
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let mut word = ERASED_WORD;
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ID_HEADER.set(&mut word);
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if footer > 0 && is_erased(&result[footer * word_size..]) {
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HEADER_FLIPPED.set(&mut word);
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*result.last_mut().unwrap() = 0x7f;
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}
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HEADER_LENGTH.set(&mut word, length);
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HEADER_KEY.set(&mut word, key);
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HEADER_CHECKSUM.set(&mut word, count_zeros(&result[footer * word_size..]));
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result[..word_size].copy_from_slice(&word.to_ne_bytes());
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result
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}
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/// Sets the padding bit in the first word of a user entry.
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pub fn set_padding(&self, word: &mut WORD) {
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ID_PADDING.set(word);
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}
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/// Sets the deleted bit in the first word of a user entry.
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pub fn set_deleted(&self, word: &mut WORD) {
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HEADER_DELETED.set(word);
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}
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/// Returns the minimum number of words to represent a given number of bytes.
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///
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/// # Preconditions
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///
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/// - `bytes + self.word_size()` does not overflow.
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pub fn bytes_to_words(&self, bytes: usize) -> usize {
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div_ceil(bytes, self.word_size())
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}
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}
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/// The word index of the init info in a page.
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const INIT_WORD: usize = 0;
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/// The word index of the compact info in a page.
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const COMPACT_WORD: usize = 1;
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/// The word index of the content of a page.
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///
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/// Since a page is at least 8 words, there is always at least 6 words of content.
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const CONTENT_WORD: usize = 2;
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/// The checksum for a single word.
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///
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/// Since checksums are the number of bits set to zero and a word is 32 bits, we need 5 bits to
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/// store numbers between 0 and 27 (which is 32 - 5).
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const WORD_CHECKSUM: Checksum = Checksum {
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field: Field { pos: 27, len: 5 },
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};
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|
|
|
// The fields of the init info of a page.
|
|
bitfield! {
|
|
/// The number of times the page has been erased.
|
|
INIT_CYCLE: Field <= MAX_ERASE_CYCLE,
|
|
|
|
/// The word index of the first entry in this virtual page.
|
|
INIT_PREFIX: Field <= div_ceil(MAX_VALUE_LEN, WORD_SIZE),
|
|
|
|
#[cfg(test)]
|
|
LEN_INIT: Length,
|
|
}
|
|
|
|
// The fields of the compact info of a page.
|
|
bitfield! {
|
|
/// The distance in words between head and tail at compaction.
|
|
///
|
|
/// In particular, compaction copies non-deleted user entries from the head to the tail as long
|
|
/// as entries span the page to be compacted.
|
|
COMPACT_TAIL: Field <= MAX_VIRT_PAGE_SIZE * MAX_PAGE_INDEX,
|
|
|
|
#[cfg(test)]
|
|
LEN_COMPACT: Length,
|
|
}
|
|
|
|
// Overview of the first word of the different kind of entries.
|
|
//
|
|
// Each column represents a bit of the word. The first 2 lines give the position in hexadecimal of
|
|
// the bit in the word (the exponent of 2 when the word is written in binary). Each entry starts
|
|
// with the sequence of bits of its identifier. The dots following the identifier are the number of
|
|
// bits necessary to hold the information of the entry (including the checksum). The remaining free
|
|
// bits after the dots are not used by the entry.
|
|
//
|
|
// 0 1
|
|
// 0123456789abcdef0123456789abcdef
|
|
// padding 0
|
|
// header 10..............................
|
|
// erase 11000...........
|
|
// clear 11001.................
|
|
// marker 11010..........
|
|
// remove 11011.................
|
|
//
|
|
// NOTE: We could pad the internal entries to the right by extending their identifier. This permits
|
|
// to free some space for shorter identifier for future kind of entries.
|
|
|
|
// The fields of a padding entry.
|
|
bitfield! {
|
|
/// The identifier for padding entries.
|
|
ID_PADDING: ConstField = [0],
|
|
}
|
|
|
|
// The fields of a user entry.
|
|
bitfield! {
|
|
/// The identifier for user entries.
|
|
ID_HEADER: ConstField = [1 0],
|
|
|
|
/// Whether the user entry is deleted.
|
|
HEADER_DELETED: Bit,
|
|
|
|
/// Whether the last bit of the user data is flipped.
|
|
HEADER_FLIPPED: Bit,
|
|
|
|
/// The length in bytes of the user data.
|
|
// NOTE: It is possible to support values of length 1024 by having a separate kind of entries
|
|
// when the value is empty. We could then subtract one from the length here.
|
|
HEADER_LENGTH: Field <= MAX_VALUE_LEN,
|
|
|
|
/// The key of the user entry.
|
|
HEADER_KEY: Field <= MAX_KEY_INDEX,
|
|
|
|
/// The checksum of the user entry.
|
|
///
|
|
/// This counts the number of bits set to zero in both the first and last words of the user
|
|
/// entry, except in the checksum itself. So it needs 6 bits to store numbers between 0 and 58.
|
|
// NOTE: It may be possible to save one bit by storing:
|
|
// - the footer checksum (as a field) if the value is not empty
|
|
// - the header checksum (as a checksum) if the value is empty
|
|
HEADER_CHECKSUM: Checksum <= 58,
|
|
|
|
#[cfg(test)]
|
|
LEN_HEADER: Length,
|
|
}
|
|
|
|
// The fields of an erase entry.
|
|
bitfield! {
|
|
/// The identifier for erase entries.
|
|
ID_ERASE: ConstField = [1 1 0 0 0],
|
|
|
|
/// The page to be erased.
|
|
ERASE_PAGE: Field <= MAX_PAGE_INDEX,
|
|
|
|
#[cfg(test)]
|
|
LEN_ERASE: Length,
|
|
}
|
|
|
|
// The fields of a clear entry.
|
|
bitfield! {
|
|
/// The identifier for clear entries.
|
|
ID_CLEAR: ConstField = [1 1 0 0 1],
|
|
|
|
/// The minimum key to be cleared.
|
|
///
|
|
/// All entries with a key below this limit are not cleared. All other entries are deleted.
|
|
CLEAR_MIN_KEY: Field <= MAX_KEY_INDEX,
|
|
|
|
#[cfg(test)]
|
|
LEN_CLEAR: Length,
|
|
}
|
|
|
|
// The fields of a marker entry.
|
|
bitfield! {
|
|
/// The identifier for marker entries.
|
|
ID_MARKER: ConstField = [1 1 0 1 0],
|
|
|
|
/// The number of updates in this transaction.
|
|
///
|
|
/// The update entries follow this marker entry.
|
|
MARKER_COUNT: Field <= MAX_UPDATES,
|
|
|
|
#[cfg(test)]
|
|
LEN_MARKER: Length,
|
|
}
|
|
|
|
// The fields of a remove entry.
|
|
bitfield! {
|
|
/// The identifier for remove entries.
|
|
ID_REMOVE: ConstField = [1 1 0 1 1],
|
|
|
|
/// The key of the user entry to be removed.
|
|
REMOVE_KEY: Field <= MAX_KEY_INDEX,
|
|
|
|
#[cfg(test)]
|
|
LEN_REMOVE: Length,
|
|
}
|
|
|
|
/// The position of a word in the virtual storage.
|
|
///
|
|
/// With the notations defined in `Format`, let:
|
|
/// - `w` a virtual word offset in a page which is between `0` and `Q - 1`
|
|
/// - `p` a page offset which is between `0` and `N - 1`
|
|
/// - `c` the number of erase cycles of a page which is between `0` and `E`
|
|
///
|
|
/// Then the position of a word is `(c*N + p)*Q + w`. This position monotonically increases and
|
|
/// represents the consumed lifetime of the storage.
|
|
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
|
|
pub struct Position(usize);
|
|
|
|
impl core::ops::Add<usize> for Position {
|
|
type Output = Position;
|
|
|
|
fn add(self, delta: usize) -> Position {
|
|
Position(self.0 + delta)
|
|
}
|
|
}
|
|
|
|
impl core::ops::Sub<Position> for Position {
|
|
type Output = usize;
|
|
|
|
fn sub(self, base: Position) -> usize {
|
|
self.0 - base.0
|
|
}
|
|
}
|
|
|
|
impl core::ops::AddAssign<usize> for Position {
|
|
fn add_assign(&mut self, delta: usize) {
|
|
self.0 += delta;
|
|
}
|
|
}
|
|
|
|
impl Position {
|
|
/// Create a word position given its coordinates.
|
|
///
|
|
/// The coordinates of a word are:
|
|
/// - Its word index in its page.
|
|
/// - Its page index in the storage.
|
|
/// - The number of times that page was erased.
|
|
pub fn new(format: &Format, cycle: usize, page: usize, word: usize) -> Position {
|
|
Position((cycle * format.num_pages() + page) * format.virt_page_size() + word)
|
|
}
|
|
|
|
/// Accesses the underlying position as a natural number.
|
|
pub fn get(self) -> usize {
|
|
self.0
|
|
}
|
|
|
|
/// Returns the associated storage index.
|
|
pub fn index(self, format: &Format) -> StorageIndex {
|
|
let page = self.page(format);
|
|
let word = CONTENT_WORD + self.word(format);
|
|
let byte = word * format.word_size();
|
|
StorageIndex { page, byte }
|
|
}
|
|
|
|
/// Returns the beginning of the current virtual page.
|
|
pub fn page_begin(self, format: &Format) -> Position {
|
|
let virt_page_size = format.virt_page_size();
|
|
Position((self.0 / virt_page_size) * virt_page_size)
|
|
}
|
|
|
|
/// Returns the beginning of the next virtual page.
|
|
pub fn next_page(self, format: &Format) -> Position {
|
|
let virt_page_size = format.virt_page_size();
|
|
Position((self.0 / virt_page_size + 1) * virt_page_size)
|
|
}
|
|
|
|
/// Returns the number of times the current page was erased.
|
|
pub fn cycle(self, format: &Format) -> usize {
|
|
(self.0 / format.virt_page_size()) / format.num_pages()
|
|
}
|
|
|
|
/// Returns the current page index.
|
|
pub fn page(self, format: &Format) -> usize {
|
|
(self.0 / format.virt_page_size()) % format.num_pages()
|
|
}
|
|
|
|
/// Returns the current word index in the page.
|
|
pub fn word(self, format: &Format) -> usize {
|
|
self.0 % format.virt_page_size()
|
|
}
|
|
}
|
|
|
|
/// Possible states of some storage representation as a word.
|
|
pub enum WordState<T> {
|
|
/// The word is still erased.
|
|
Erased,
|
|
|
|
/// The word is partially written.
|
|
Partial,
|
|
|
|
/// Holds the decoded version of a valid word.
|
|
Valid(T),
|
|
}
|
|
|
|
/// Information for an initialized page.
|
|
pub struct InitInfo {
|
|
/// The number of times this page has been erased.
|
|
pub cycle: usize,
|
|
|
|
/// The word index of the first entry in this virtual page.
|
|
pub prefix: usize,
|
|
}
|
|
|
|
/// Information for a page being compacted.
|
|
pub struct CompactInfo {
|
|
/// The distance in words between head and tail at compaction.
|
|
pub tail: usize,
|
|
}
|
|
|
|
/// The first word of an entry.
|
|
#[derive(Debug)]
|
|
pub enum ParsedWord {
|
|
/// Padding entry.
|
|
Padding(Padding),
|
|
|
|
/// Header of a user entry.
|
|
Header(Header),
|
|
|
|
/// Internal entry.
|
|
Internal(InternalEntry),
|
|
}
|
|
|
|
/// Padding entry.
|
|
#[derive(Debug)]
|
|
pub struct Padding {
|
|
/// The number of following padding words after the first word of the padding entry.
|
|
pub length: usize,
|
|
}
|
|
|
|
/// Header of a user entry.
|
|
#[derive(Debug)]
|
|
pub struct Header {
|
|
/// Whether the last bit of the user data is flipped.
|
|
pub flipped: bool,
|
|
|
|
/// The length in bytes of the user data.
|
|
pub length: usize,
|
|
|
|
/// The key of the user entry.
|
|
pub key: usize,
|
|
|
|
/// The checksum of the user entry.
|
|
pub checksum: usize,
|
|
}
|
|
|
|
impl Header {
|
|
/// Checks the validity of a user entry.
|
|
///
|
|
/// If the user entry has no payload, the `footer` must be set to `None`. Otherwise it should be
|
|
/// the last word of the entry.
|
|
pub fn check(&self, footer: Option<&[u8]>) -> bool {
|
|
footer.map_or(0, count_zeros) == self.checksum
|
|
}
|
|
}
|
|
|
|
/// Internal entry.
|
|
#[derive(Debug)]
|
|
pub enum InternalEntry {
|
|
/// Indicates that a page should be erased.
|
|
Erase {
|
|
/// The page to be erased.
|
|
page: usize,
|
|
},
|
|
|
|
/// Indicates that user entries with high key should be deleted.
|
|
Clear {
|
|
/// The minimum key a user entry should have to be deleted.
|
|
min_key: usize,
|
|
},
|
|
|
|
/// Marks the start of a transaction.
|
|
///
|
|
/// The marker is followed by a given number of updates, which are either user entries or remove
|
|
/// entries.
|
|
Marker {
|
|
/// The number of updates in the transaction.
|
|
count: usize,
|
|
},
|
|
|
|
/// Indicates that a user entry should be removed.
|
|
///
|
|
/// This is only useful (and valid) as part of a transaction, since removing a single entry is
|
|
/// already atomic.
|
|
Remove {
|
|
/// The key of the user entry to be removed.
|
|
key: usize,
|
|
},
|
|
}
|
|
|
|
/// Returns whether a slice has all bits equal to one.
|
|
pub fn is_erased(slice: &[u8]) -> bool {
|
|
slice.iter().all(|&x| x == 0xff)
|
|
}
|
|
|
|
/// Divides then takes ceiling.
|
|
///
|
|
/// Returns `ceil(x / m)` in mathematical notations (not Rust code).
|
|
///
|
|
/// # Preconditions
|
|
///
|
|
/// - `x + m` does not overflow.
|
|
const fn div_ceil(x: usize, m: usize) -> usize {
|
|
(x + m - 1) / m
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
|
|
#[test]
|
|
fn size_of_format() {
|
|
assert_eq!(std::mem::size_of::<Format>(), 24);
|
|
}
|
|
|
|
#[test]
|
|
fn checksum_ok() {
|
|
let Field { pos, len } = WORD_CHECKSUM.field;
|
|
// There is enough bits to represents the number of zeros preceding the checksum.
|
|
assert_eq!(len, num_bits(pos));
|
|
// The checksum is the last field of a word.
|
|
assert_eq!(pos + len, 8 * WORD_SIZE);
|
|
// The data of words using the checksum don't overlap the checksum.
|
|
let words = &[
|
|
&LEN_INIT,
|
|
&LEN_COMPACT,
|
|
&LEN_ERASE,
|
|
&LEN_CLEAR,
|
|
&LEN_MARKER,
|
|
&LEN_REMOVE,
|
|
];
|
|
for word in words {
|
|
assert!(word.pos < pos);
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn init_ok() {
|
|
assert_eq!(INIT_CYCLE.pos, 0);
|
|
assert_eq!(INIT_CYCLE.len, 16);
|
|
assert_eq!(INIT_PREFIX.pos, 16);
|
|
assert_eq!(INIT_PREFIX.len, 9);
|
|
assert_eq!(LEN_INIT.pos, 25);
|
|
}
|
|
|
|
#[test]
|
|
fn compact_ok() {
|
|
assert_eq!(COMPACT_TAIL.pos, 0);
|
|
assert_eq!(COMPACT_TAIL.len, 16);
|
|
assert_eq!(LEN_COMPACT.pos, 16);
|
|
}
|
|
|
|
#[test]
|
|
fn header_ok() {
|
|
assert_eq!(ID_HEADER.field.pos, 0);
|
|
assert_eq!(ID_HEADER.field.len, 2);
|
|
assert_eq!(ID_HEADER.value, 0b01);
|
|
assert_eq!(HEADER_DELETED.pos, 2);
|
|
assert_eq!(HEADER_FLIPPED.pos, 3);
|
|
assert_eq!(HEADER_LENGTH.pos, 4);
|
|
assert_eq!(HEADER_LENGTH.len, 10);
|
|
assert_eq!(HEADER_KEY.pos, 14);
|
|
assert_eq!(HEADER_KEY.len, 12);
|
|
assert_eq!(HEADER_CHECKSUM.field.pos, 26);
|
|
assert_eq!(HEADER_CHECKSUM.field.len, 6);
|
|
assert_eq!(LEN_HEADER.pos, 32);
|
|
}
|
|
|
|
#[test]
|
|
fn erase_ok() {
|
|
assert_eq!(ID_ERASE.field.pos, 0);
|
|
assert_eq!(ID_ERASE.field.len, 5);
|
|
assert_eq!(ID_ERASE.value, 0b00011);
|
|
assert_eq!(ERASE_PAGE.pos, 5);
|
|
assert_eq!(ERASE_PAGE.len, 6);
|
|
assert_eq!(LEN_ERASE.pos, 11);
|
|
}
|
|
|
|
#[test]
|
|
fn clear_ok() {
|
|
assert_eq!(ID_CLEAR.field.pos, 0);
|
|
assert_eq!(ID_CLEAR.field.len, 5);
|
|
assert_eq!(ID_CLEAR.value, 0b10011);
|
|
assert_eq!(CLEAR_MIN_KEY.pos, 5);
|
|
assert_eq!(CLEAR_MIN_KEY.len, 12);
|
|
assert_eq!(LEN_CLEAR.pos, 17);
|
|
}
|
|
|
|
#[test]
|
|
fn marker_ok() {
|
|
assert_eq!(ID_MARKER.field.pos, 0);
|
|
assert_eq!(ID_MARKER.field.len, 5);
|
|
assert_eq!(ID_MARKER.value, 0b01011);
|
|
assert_eq!(MARKER_COUNT.pos, 5);
|
|
assert_eq!(MARKER_COUNT.len, 5);
|
|
assert_eq!(LEN_MARKER.pos, 10);
|
|
}
|
|
|
|
#[test]
|
|
fn remove_ok() {
|
|
assert_eq!(ID_REMOVE.field.pos, 0);
|
|
assert_eq!(ID_REMOVE.field.len, 5);
|
|
assert_eq!(ID_REMOVE.value, 0b11011);
|
|
assert_eq!(REMOVE_KEY.pos, 5);
|
|
assert_eq!(REMOVE_KEY.len, 12);
|
|
assert_eq!(LEN_REMOVE.pos, 17);
|
|
}
|
|
|
|
#[test]
|
|
fn is_erased_ok() {
|
|
assert!(is_erased(&[]));
|
|
assert!(is_erased(&[0xff]));
|
|
assert!(is_erased(&[0xff, 0xff]));
|
|
assert!(!is_erased(&[0x00]));
|
|
assert!(!is_erased(&[0xff, 0xfe]));
|
|
assert!(!is_erased(&[0x7f, 0xff]));
|
|
}
|
|
|
|
#[test]
|
|
fn div_ceil_ok() {
|
|
assert_eq!(div_ceil(0, 1), 0);
|
|
assert_eq!(div_ceil(1, 1), 1);
|
|
assert_eq!(div_ceil(2, 1), 2);
|
|
assert_eq!(div_ceil(0, 2), 0);
|
|
assert_eq!(div_ceil(1, 2), 1);
|
|
assert_eq!(div_ceil(2, 2), 1);
|
|
assert_eq!(div_ceil(3, 2), 2);
|
|
}
|
|
|
|
#[test]
|
|
fn positions_fit_in_a_word() {
|
|
// All reachable positions are smaller than this value, which is one past the last position.
|
|
// It is simply the total number of virtual words, i.e. the number of words per virtual page
|
|
// times the number of virtual pages times the number of times a virtual page can be used
|
|
// (one more than the number of times it can be erased since we can write before the first
|
|
// erase cycle and after the last erase cycle).
|
|
assert_eq!(
|
|
(MAX_ERASE_CYCLE + 1) * (MAX_PAGE_INDEX + 1) * MAX_VIRT_PAGE_SIZE,
|
|
0xff800000
|
|
);
|
|
}
|
|
}
|