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// Copyright 2021-2023 Protocol Labs
// Copyright 2019-2022 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT
//! # RLE+ Bitset Encoding
//!
//! (from https://github.com/filecoin-project/specs/blob/master/src/listings/data_structures.md)
//!
//! RLE+ is a lossless compression format based on [RLE](https://en.wikipedia.org/wiki/Run-length_encoding).
//! Its primary goal is to reduce the size in the case of many individual bits, where RLE breaks down quickly,
//! while keeping the same level of compression for large sets of contiguous bits.
//!
//! In tests it has shown to be more compact than RLE iteself, as well as [Concise](https://arxiv.org/pdf/1004.0403.pdf) and [Roaring](https://roaringbitmap.org/).
//!
//! ## Format
//!
//! The format consists of a header, followed by a series of blocks, of which there are three different types.
//!
//! The format can be expressed as the following [BNF](https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form) grammar.
//!
//! ```text
//! <encoding> ::= <header> <blocks>
//! <header> ::= <version> <bit>
//! <version> ::= "00"
//! <blocks> ::= <block> <blocks> | ""
//! <block> ::= <block_single> | <block_short> | <block_long>
//! <block_single> ::= "1"
//! <block_short> ::= "01" <bit> <bit> <bit> <bit>
//! <block_long> ::= "00" <unsigned_varint>
//! <bit> ::= "0" | "1"
//! ```
//!
//! An `<unsigned_varint>` is defined as specified [here](https://github.com/multiformats/unsigned-varint).
//!
//! ### Header
//!
//! The header indiciates the very first bit of the bit vector to encode. This means the first bit is always
//! the same for the encoded and non encoded form.
//!
//! ### Blocks
//!
//! The blocks represent how many bits, of the current bit type there are. As `0` and `1` alternate in a bit vector
//! the inital bit, which is stored in the header, is enough to determine if a length is currently referencing
//! a set of `0`s, or `1`s.
//!
//! #### Block Single
//!
//! If the running length of the current bit is only `1`, it is encoded as a single set bit.
//!
//! #### Block Short
//!
//! If the running length is less than `16`, it can be encoded into up to four bits, which a short block
//! represents. The length is encoded into a 4 bits, and prefixed with `01`, to indicate a short block.
//!
//! #### Block Long
//!
//! If the running length is `16` or larger, it is encoded into a varint, and then prefixed with `00` to indicate
//! a long block.
//!
//!
//! > **Note:** The encoding is unique, so no matter which algorithm for encoding is used, it should produce
//! > the same encoding, given the same input.
//!
mod error;
mod reader;
mod writer;
use std::borrow::Cow;
#[cfg(feature = "enable-arbitrary")]
use arbitrary::{size_hint, Arbitrary, Unstructured};
pub use error::Error;
use fvm_ipld_encoding::strict_bytes;
pub use reader::BitReader;
use serde::{Deserialize, Deserializer, Serialize, Serializer};
pub use writer::BitWriter;
use super::BitField;
use crate::{RangeSize, MAX_ENCODED_SIZE};
impl Serialize for BitField {
fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
where
S: Serializer,
{
let bytes = self.to_bytes();
if bytes.len() > MAX_ENCODED_SIZE {
return Err(serde::ser::Error::custom(format!(
"encoded bitfield was too large {}",
bytes.len()
)));
}
strict_bytes::serialize(&bytes, serializer)
}
}
impl<'de> Deserialize<'de> for BitField {
fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
where
D: Deserializer<'de>,
{
let bytes: Cow<'de, [u8]> = strict_bytes::deserialize(deserializer)?;
if bytes.len() > MAX_ENCODED_SIZE {
return Err(serde::de::Error::custom(format!(
"encoded bitfield was too large {}",
bytes.len()
)));
}
Self::from_bytes(&bytes).map_err(serde::de::Error::custom)
}
}
#[cfg(feature = "enable-arbitrary")]
impl<'a> Arbitrary<'a> for BitField {
fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
let mut next_value: bool = bool::arbitrary(u)?;
let mut ranges = Vec::new();
let mut index = 0u64;
let mut total_len: u64 = 0;
let size = u.arbitrary_len::<(u64, u8)>()?;
for _ in 0..size {
// 3 line crappy "power-law" distribution
let len = u64::arbitrary(u)?;
let shift = u.int_in_range(0..=63)?;
let len = (len & (u64::MAX >> shift)).saturating_add(1);
let (new_total_len, ovf) = total_len.overflowing_add(len);
if ovf {
break;
}
total_len = new_total_len;
let start = index;
index += len;
let end = index;
if next_value {
ranges.push(start..end);
}
next_value = !next_value;
}
Ok(Self {
ranges,
..Default::default()
})
}
fn size_hint(depth: usize) -> (usize, Option<usize>) {
size_hint::and(<usize as Arbitrary>::size_hint(depth), (0, None))
}
}
impl BitField {
/// Decodes RLE+ encoded bytes into a bit field.
pub fn from_bytes(bytes: &[u8]) -> Result<Self, Error> {
let mut reader = BitReader::new(bytes)?;
let version = reader.read(2);
if version != 0 {
return Err(Error::UnsupportedVersion);
}
let mut next_value = reader.read(1) == 1;
let mut ranges = Vec::new();
let mut index = 0u64;
let mut total_len: u64 = 0;
while let Some(len) = reader.read_len()? {
let (new_total_len, ovf) = total_len.overflowing_add(len);
if ovf {
return Err(Error::RLEOverflow);
}
total_len = new_total_len;
let start = index;
index += len;
let end = index;
if next_value {
ranges.push(start..end);
}
next_value = !next_value;
}
// next_value equal true means we just read a run of zeros
// which means that there is a trailing run of zeros
if next_value {
return Err(Error::NotMinimal);
}
Ok(Self {
ranges,
..Default::default()
})
}
/// Turns a bit field into its RLE+ encoded form.
pub fn to_bytes(&self) -> Vec<u8> {
let mut iter = self.ranges();
let first_range = match iter.next() {
Some(range) => range,
None => return Default::default(),
};
let mut writer = BitWriter::new();
writer.write(0, 2); // version 00
if first_range.start == 0 {
writer.write(1, 1); // the first bit is a 1
} else {
writer.write(0, 1); // the first bit is a 0
writer.write_len(first_range.start); // the number of leading 0s
}
writer.write_len(first_range.size());
let mut index = first_range.end;
// for each range of 1s we first encode the number of 0s that came prior
// before encoding the number of 1s
for range in iter {
writer.write_len(range.start - index); // zeros
writer.write_len(range.size()); // ones
index = range.end;
}
writer.finish()
}
}
#[cfg(test)]
mod tests {
use rand::{Rng, SeedableRng};
use rand_xorshift::XorShiftRng;
use super::super::{bitfield, ranges_from_bits};
use super::{BitField, BitWriter, Error};
use crate::iter::Ranges;
#[test]
fn test() {
for (i, (bits, expected)) in [
(vec![], Ok(bitfield![])),
(
vec![
1, 0, // incorrect version
1, // starts with 1
0, 1, // fits into 4 bits
0, 0, 0, 1, // 8 - 1
],
Err(Error::UnsupportedVersion),
),
(
vec![
0, 0, // version
1, // starts with 1
0, 1, // fits into 4 bits
0, 0, 0, 1, // 8 - 1
],
Ok(bitfield![1, 1, 1, 1, 1, 1, 1, 1]),
),
(
vec![
0, 0, // version
1, // starts with 1
0, 1, // fits into 4 bits
0, 0, 1, 0, // 4 - 1
1, // 1 - 0
0, 1, // fits into 4 bits
1, 1, 0, 0, // 3 - 1
],
Ok(bitfield![1, 1, 1, 1, 0, 1, 1, 1]),
),
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // does not fit into 4 bits
1, 0, 0, 1, 1, 0, 0, 0, // 25 - 1
],
Ok(bitfield![
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
]),
),
// Trailing garbage.
(
vec![
0, 0, // version
1, // starts with 1
1, // 1 - 1
0, 1, // fits into 4 bits
0, 0, 0, 0, // 0 - 0
1, // 1 - 1
],
Err(Error::NotMinimal),
),
// Trailing garbage.
(
vec![
0, 0, // version
1, // starts with 1
1, // 1 - 1
0, 0, // fits into a varint
0, 0, 0, 0, 0, 0, 0, 0, // 0 - 0
1, // 1 - 1
],
Err(Error::NotMinimal),
),
// when the last byte is zero, this should fail
(
vec![
0, 0, // version
1, // starts with 1
0, 1, // fits into 4 bits
1, 0, 1, // 5 - 1
0, 0, 0, 0, 0, 0, 0, 0,
],
Err(Error::NotMinimal),
),
// a valid varint
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 0, 0, 0, 1, 0, 0, 0, // 17 - 1
0, 0, 0,
],
Ok(bitfield![1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]),
),
// a varint that is not minimally encoded
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 1, 0, 0, 0, 0, 0, 1, // 3 - 1
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1,
],
Err(Error::InvalidVarint),
),
// a varint must allow 9 bytes plus 1 bit, or 0..u64::MAX
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 1, 1, 1, 1, 1, 1, 1, // 1 - 1
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0,
],
Ok(BitField::from_ranges(Ranges::new(std::iter::once(
0..u64::MAX,
)))),
),
// Now overflow by 1.
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
0, 0, 0, 0, 0, 0, 0, 1, // 1 - 1
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0,
0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0,
0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0,
],
Err(Error::InvalidVarint),
),
// total running length should not overflow
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 1, 1, 1, 1, 1, 1, 1, // 9223372036854775807 - 1
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, // fits into a varint
1, 1, 1, 1, 1, 1, 1, 1, // 9223372036854775807 - 0
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, // fits into 4 bits
0, 1, 0, 0, // 2 - 1
],
Err(Error::RLEOverflow),
),
// block_long that could have fit on block_short.
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 1, 0, 0, 0, 0, 0, 0, // 3 - 1
1, 1, 1,
],
Err(Error::NotMinimal),
),
// block_long that could have fit on block_single.
(
vec![
0, 0, // version
1, // starts with 1
0, 0, // fits into a varint
1, 0, 0, 0, 0, 0, 0, 0, // 1 - 1
1, 1, 1,
],
Err(Error::NotMinimal),
),
// block_short that could have fit on block_single.
(
vec![
0, 0, // version
1, // starts with 1
0, 1, // fits into 4 bits
1, 0, 0, 0, // 1 - 1
1, 1, 1, 1, 1, 1, 1,
],
Err(Error::NotMinimal),
),
// tailing runs of zeros
(
vec![
0, 0, // version
0, // starts with 0
1, // run of one
],
Err(Error::NotMinimal),
),
(
vec![
0, 0, // version
0, // starts with 0
0, 1, // fits into 4 bits
0, 0, 1, 0,
],
Err(Error::NotMinimal),
),
(
vec![
0, 0, // version
1, // starts with 1
0, 1, // fits into 4 bits
0, 0, 1, 0, // 2
1, // trailing run of zeros
],
Err(Error::NotMinimal),
),
(
vec![
0, 0, // version
0, // starts with 1
1, //run of one
0, 1, // fits into 4 bits
0, 0, 1, 0, // 2
0, 1, 0, 0, 1, 0, // 2 trailing zeros
],
Err(Error::NotMinimal),
),
]
.into_iter()
.enumerate()
{
let mut writer = BitWriter::new();
for bit in bits {
writer.write(bit, 1);
}
let res = BitField::from_bytes(&writer.finish_test());
assert_eq!(res, expected, "test {} failed", i);
}
}
#[test]
fn roundtrip() {
let mut rng = XorShiftRng::seed_from_u64(1);
for _i in 0..1000 {
let len: u64 = rng.gen_range(0..1000);
let bits: Vec<_> = (0..len).filter(|_| rng.gen::<bool>()).collect();
let ranges: Vec<_> = ranges_from_bits(bits.clone()).collect();
let bf = BitField::from_ranges(ranges_from_bits(bits));
assert_eq!(bf.ranges().collect::<Vec<_>>(), ranges);
}
}
#[test]
fn iter_last() {
// Create RLE with 2**64-2 set bits- tests timeout on the `let max` line with last
let rle: Vec<u8> = vec![
0xE4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x2F, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0x7F,
];
let max = BitField::from_bytes(&rle).unwrap().last().unwrap();
assert_eq!(max, 18446744073709551614);
}
#[test]
fn test_unset_last() {
// Create a bitfield first 3 set bits
let ranges: Vec<u64> = vec![0, 1, 2, 3];
let iter = ranges_from_bits(ranges);
let mut bf = BitField::from_ranges(iter);
// Unset bit at pos 3
bf.unset(3);
let last = bf.last().unwrap();
assert_eq!(2, last);
}
#[test]
fn test_unset_max() {
// Create any bitfield
let ranges: Vec<u64> = vec![0, 1, 2, 3];
let iter = ranges_from_bits(ranges);
let mut bf = BitField::from_ranges(iter);
// Unset u64::MAX
bf.unset(u64::MAX);
let last = bf.ranges().last().unwrap();
assert_eq!(0..4, last);
}
#[test]
fn test_zero_last() {
let mut bf = BitField::new();
bf.set(0);
let last = bf.last().unwrap();
assert_eq!(0, last);
}
}