1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554
//! The fastest bloom filter in Rust. No accuracy compromises. Use any hasher.
//!
//! ## Background
//! Bloom filters are space efficient approximate membership set data structure. False positives from `contains` are possible, but false negatives
//! are not, i.e. `contains` for all items in the set is guaranteed to return true, while `contains` for all items not in the set probably return false.
//!
//! Blocked bloom filters are supported by an underlying bit vector, chunked into 512, 256, 128, or 64 bit "blocks", to track item membership.
//! To insert, a number of bits, based on the item's hash, are set in the underlying bit vector. To check membership, a number of bits, based on the item's hash, are checked in the underlying bit vector.
//!
//! Once constructed, neither the bloom filter's underlying memory usage nor number of bits per item change.
//!
//! ## Implementation
//! `b100m-filter` is blazingly fast because it uses L1 cache friendly blocks and efficiently derives many index bits from only one hash per value. Compared to traditional implementations, `b100m-filter` is 2-5 times faster for small sets of items, and hundreds of times faster for larger item sets. In all cases, `b100m-filter` maintains competitive false positive rates.
//!
//! # Examples
//! Basic usage:
//! ```
//! use b100m_filter::BloomFilter;
//!
//! let num_blocks = 4; // by default, each block is 512 bits
//!
//! let filter = BloomFilter::builder(num_blocks).items(["42", "🦀"].iter());
//! assert!(filter.contains("42"));
//! assert!(filter.contains("🦀"));
//! ```
//! Use any hasher:
//! ```
//! use b100m_filter::BloomFilter;
//! use ahash::RandomState;
//!
//! let num_blocks = 4; // by default, each block is 512 bits
//!
//! let filter = BloomFilter::builder(num_blocks)
//! .hasher(RandomState::default())
//! .items(["42", "🦀"].iter());
//! ```
//!
//! ## References
//! - [Bloom Filter](https://brilliant.org/wiki/bloom-filter/)
//! - [Less hashing, same performance: Building a better Bloom filter](https://dl.acm.org/doi/10.5555/1400123.1400125)
//! - [A fast alternative to the modulo reduction](https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/)
use std::hash::{BuildHasher, Hash, Hasher};
mod hasher;
use hasher::DefaultHasher;
mod builder;
pub use builder::Builder;
mod bit_vector;
use bit_vector::BlockedBitVec;
/// Produces a new hash efficiently from two orignal hashes and a seed.
///
/// Modified from <https://dl.acm.org/doi/10.5555/1400123.1400125>.
#[inline]
fn seeded_hash_from_hashes(h1: &mut u64, h2: &mut u64, seed: u64) -> u64 {
*h1 = h1.wrapping_add(*h2).rotate_left(5);
*h2 = h2.wrapping_add(seed);
*h1
}
/// A space efficient approximate membership set data structure.
/// False positives from `contains` are possible, but false negatives
/// are not, i.e. `contains` for all items in the set is guaranteed to return
/// true, while `contains` for all items not in the set probably return false.
///
/// `BloomFilter` is supported by an underlying bit vector, chunked into 512, 256, 128, or 64 bit "blocks", to track item membership.
/// To insert, a number of bits, based on the item's hash, are set in the underlying bit vector.
/// To check membership, a number of bits, based on the item's hash, are checked in the underlying bit vector.
///
/// Once constructed, neither the bloom filter's underlying memory usage nor number of bits per item change.
///
/// # Examples
/// Basic usage:
/// ```
/// use b100m_filter::BloomFilter;
///
/// let num_blocks = 4; // by default, each block is 512 bits
///
/// let filter = BloomFilter::builder(num_blocks).items(["42", "🦀"].iter());
/// assert!(filter.contains("42"));
/// assert!(filter.contains("🦀"));
/// ```
/// Use any hasher:
/// ```
/// use b100m_filter::BloomFilter;
/// use ahash::RandomState;
///
/// let num_blocks = 4; // by default, each block is 512 bits
///
/// let filter = BloomFilter::builder(num_blocks)
/// .hasher(RandomState::default())
/// .items(["42", "🦀"].iter());
/// ```
#[derive(Debug, Clone)]
pub struct BloomFilter<const BLOCK_SIZE_BITS: usize = 512, S = DefaultHasher> {
bits: BlockedBitVec<BLOCK_SIZE_BITS>,
num_hashes: u64,
hasher: S,
}
impl BloomFilter {
pub(crate) fn new_builder<const BLOCK_SIZE_BITS: usize>(
num_blocks: usize,
) -> Builder<BLOCK_SIZE_BITS> {
Builder::<BLOCK_SIZE_BITS> {
num_blocks,
hasher: Default::default(),
}
}
/// Creates a new instance of `Builder` to construct a `BloomFilter`
/// with `num_blocks` number of blocks for tracking item membership.
/// **Each block is 512 bits of memory.**
///
/// Use `builder256`, `builder128`, or `builder64` for more speed
/// but slightly higher false positive rates.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder(16).hashes(4);
/// ```
pub fn builder(num_blocks: usize) -> Builder<512> {
Self::builder512(num_blocks)
}
/// Creates a new instance of `Builder` to construct a `BloomFilter`
/// with `num_blocks` number of blocks for tracking item membership.
/// **Each block is 512 bits of memory.**
///
/// Use `builder256`, `builder128`, or `builder64` for more speed
/// but slightly higher false positive rates.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder512(16).hashes(4);
/// ```
pub fn builder512(num_blocks: usize) -> Builder<512> {
Self::new_builder::<512>(num_blocks)
}
/// Creates a new instance of `Builder` to construct a `BloomFilter`
/// with `num_blocks` number of blocks for tracking item membership.
/// **Each block is 256 bits of memory.**
///
/// `Builder<256>` is faster but less accurate than `Builder<512>`.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder256(16).hashes(4);
/// ```
pub fn builder256(num_blocks: usize) -> Builder<256> {
Self::new_builder::<256>(num_blocks)
}
/// Creates a new instance of `Builder` to construct a `BloomFilter`
/// with `num_blocks` number of blocks for tracking item membership.
/// **Each block is 128 bits of memory.**
///
/// `Builder<128>` is faster but less accurate than `Builder<256>`.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder128(16).hashes(8);
/// ```
pub fn builder128(num_blocks: usize) -> Builder<128> {
Self::new_builder::<128>(num_blocks)
}
/// Creates a new instance of `Builder` to construct a `BloomFilter`
/// with `num_blocks` number of blocks for tracking item membership.
/// **Each block is 64 bits of memory.**
///
/// `Builder<64>` is faster but less accurate than `Builder<128>`.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder64(16).hashes(8);
/// ```
pub fn builder64(num_blocks: usize) -> Builder<64> {
Self::new_builder::<64>(num_blocks)
}
}
impl<const BLOCK_SIZE_BITS: usize, S: BuildHasher> BloomFilter<BLOCK_SIZE_BITS, S> {
const BIT_INDEX_MASK_LEN: u32 = u32::ilog2(BLOCK_SIZE_BITS as u32);
/// Used to grab the last N bits from a hash.
const BIT_INDEX_MASK: u64 = (1 << Self::BIT_INDEX_MASK_LEN) - 1;
/// Number of coordinates (i.e. bits in our bloom filter) that can be derived by one hash.
/// One hash is u64 bits, and we only need 9 bits (LOG2_U64_BITS + LOG2_BLOCK_SIZE) from
/// the hash for a bit index. For more runtime performance we can cheaply copy an index
/// from the hash, instead of computing the next hash.
///
/// From experiments, powers of 2 coordinates from the hash provides the best performance
/// for `contains` for existing and non-existing values.
const NUM_COORDS_PER_HASH: u32 = 2u32.pow(u32::ilog2(64 / Self::BIT_INDEX_MASK_LEN));
#[inline]
fn floor_round(x: f64) -> u64 {
let floored = x.floor() as u64;
let thresh = Self::NUM_COORDS_PER_HASH as u64;
if floored < thresh {
thresh
} else {
floored - (floored % thresh)
}
}
/// The optimal number of hashes to perform for an item given the expected number of items to be contained in one block.
/// Proof under "False Positives Analysis": <https://brilliant.org/wiki/bloom-filter/>
#[inline]
fn optimal_hashes(num_items: usize) -> u64 {
let m = BLOCK_SIZE_BITS as f64;
let n = std::cmp::max(num_items, 1) as f64;
let num_hashes = m / n * f64::ln(2.0f64);
Self::floor_round(num_hashes)
}
/// Returns a the block index for an item's hash.
/// The block index must be in the range `0..self.bits.num_blocks()`.
/// This implementation is a more performant alternative to `hash % self.bits.num_blocks()`:
/// <https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/>
#[inline]
fn block_index(&self, hash: u64) -> usize {
(((hash >> 32) as usize * self.bits.num_blocks()) >> 32) as usize
}
/// Return the bit indexes within a block for an item's two orginal hashes.
///
/// First, a seeded hash is derived from two orginal hashes, `hash1` and `hash2`.
/// Second, `Self::NUM_COORDS_PER_HASH` bit indexes are returned, each `Self::BIT_INDEX_MASK_LEN`
/// consecutive sections of the hash bits.
#[inline]
fn bit_indexes(hash1: &mut u64, hash2: &mut u64, seed: u64) -> impl Iterator<Item = usize> {
let h = seeded_hash_from_hashes(hash1, hash2, seed);
(0..Self::NUM_COORDS_PER_HASH).map(move |j| {
let mut bit_index = h.wrapping_shr(j * Self::BIT_INDEX_MASK_LEN); // remove right bits from previous bit index (j - 1)
bit_index &= Self::BIT_INDEX_MASK; // remove left bits to keep bit index in range of a block's bit size
bit_index as usize
})
}
/// Returns all seeds that should be used by the hasher
#[inline]
fn hash_seeds(size: u64) -> impl Iterator<Item = u64> {
(0..size).step_by(Self::NUM_COORDS_PER_HASH as usize)
}
/// Adds a value to the bloom filter.
///
/// # Examples
/// ```
/// use b100m_filter::BloomFilter;
///
/// let mut bloom = BloomFilter::builder(4).hashes(4);
/// bloom.insert(&2);
/// assert!(bloom.contains(&2));
/// ```
#[inline]
pub fn insert(&mut self, val: &(impl Hash + ?Sized)) {
let [mut h1, mut h2] = self.get_orginal_hashes(val);
let block = &mut self.bits.get_block_mut(self.block_index(h1));
for i in Self::hash_seeds(self.num_hashes) {
BlockedBitVec::<BLOCK_SIZE_BITS>::set_all_for_block(
block,
Self::bit_indexes(&mut h1, &mut h2, i),
);
}
}
/// Returns `false` if the bloom filter definitely does not contain a value.
/// Returns `true` if the bloom filter may contain a value, with a degree of certainty.
///
/// # Examples
///
/// ```
/// use b100m_filter::BloomFilter;
///
/// let bloom = BloomFilter::builder(4).items([1, 2, 3].iter());
/// assert!(bloom.contains(&1));
/// ```
#[inline]
pub fn contains(&self, val: &(impl Hash + ?Sized)) -> bool {
let [mut h1, mut h2] = self.get_orginal_hashes(val);
let block = &self.bits.get_block(self.block_index(h1));
Self::hash_seeds(self.num_hashes).into_iter().all(|i| {
BlockedBitVec::<BLOCK_SIZE_BITS>::check_all_for_block(
block,
Self::bit_indexes(&mut h1, &mut h2, i),
)
})
}
/// Returns the effective number of hashes per item. In other words,
/// the number of bits derived per item.
///
/// For performance reasons, the number of bits is rounded to down to a power of 2, depending on `BLOCK_SIZE_BITS`.
#[inline]
pub fn num_hashes(&self) -> u64 {
self.num_hashes
}
/// The first two hashes of the value to be inserted or checked.
///
/// Subsequent hashes are efficiently derived from these two using `seeded_hash_from_hashes`,
/// generating many "seeded hashes" values for the single value.
#[inline]
fn get_orginal_hashes(&self, val: &(impl Hash + ?Sized)) -> [u64; 2] {
let mut state = self.hasher.build_hasher();
val.hash(&mut state);
let hash = state.finish();
[hash, hash.wrapping_shr(32)]
}
}
impl<T, const BLOCK_SIZE_BITS: usize, S: BuildHasher> Extend<T> for BloomFilter<BLOCK_SIZE_BITS, S>
where
T: Hash,
{
#[inline]
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
for val in iter {
self.insert(&val);
}
}
}
impl PartialEq for BloomFilter {
fn eq(&self, other: &Self) -> bool {
self.bits == other.bits && self.num_hashes == other.num_hashes
}
}
impl Eq for BloomFilter {}
#[cfg(test)]
mod tests {
use super::*;
use rand::{rngs::StdRng, Rng, SeedableRng};
use std::collections::HashSet;
fn random_strings(num: usize, min_repeat: u32, max_repeat: u32, seed: u64) -> Vec<String> {
let mut rng = StdRng::seed_from_u64(seed);
let gen = rand_regex::Regex::compile(r"[a-zA-Z]+", max_repeat).unwrap();
(&mut rng)
.sample_iter(&gen)
.filter(|s: &String| s.len() >= min_repeat as usize)
.take(num)
.collect()
}
#[test]
fn random_inserts_always_contained() {
fn random_inserts_always_contained_<const N: usize>() {
for mag in 1..6 {
let size = 10usize.pow(mag);
for bloom_size_mag in 6..10 {
let num_blocks_bytes = 1 << bloom_size_mag;
let sample_vals = random_strings(size, 16, 32, 52323);
let num_blocks = num_blocks_bytes / (N >> 3);
let filter =
BloomFilter::new_builder::<N>(num_blocks).items(sample_vals.iter());
for x in &sample_vals {
assert!(filter.contains(x));
}
}
}
}
random_inserts_always_contained_::<512>();
random_inserts_always_contained_::<256>();
random_inserts_always_contained_::<128>();
random_inserts_always_contained_::<64>();
}
#[test]
fn seeded_is_same() {
let mag = 3;
let size = 10usize.pow(mag);
let bloom_size_bytes = 1 << 10;
let sample_vals = random_strings(size, 16, 32, 53226);
let block_size = bloom_size_bytes / 64;
for x in 0u8..4 {
let seed = [x; 16];
let filter1 = BloomFilter::builder(block_size)
.seed(&seed)
.items(sample_vals.iter());
let filter2 = BloomFilter::builder(block_size)
.seed(&seed)
.items(sample_vals.iter());
assert_eq!(filter1, filter2);
}
}
fn false_pos_rate<const N: usize>(filter: &BloomFilter<N>, control: &HashSet<String>) -> f64 {
let sample_anti_vals = random_strings(1000, 16, 32, 11);
let mut total = 0;
let mut false_positives = 0;
for x in &sample_anti_vals {
if !control.contains(x) {
total += 1;
if filter.contains(x) {
false_positives += 1;
}
}
}
(false_positives as f64) / (total as f64)
}
#[test]
fn false_pos_decrease_with_size() {
for mag in 1..5 {
let size = 10usize.pow(mag);
let mut prev_fp = 1.0;
let mut prev_prev_fp = 1.0;
for bloom_size_mag in 6..18 {
let bloom_size_bytes = 1 << bloom_size_mag;
let num_blocks = bloom_size_bytes / 64;
let sample_vals = random_strings(size, 16, 32, 5234);
let filter = BloomFilter::builder512(num_blocks)
.seed(&[1u8; 16])
.items(sample_vals.iter());
let control: HashSet<String> = sample_vals.into_iter().collect();
let fp = false_pos_rate(&filter, &control);
println!(
"{:?}, {:?}, {:.6}, {:?}",
size,
bloom_size_bytes,
fp,
filter.num_hashes(),
);
assert!(fp <= prev_fp || prev_fp <= prev_prev_fp); // allows 1 data point to be higher
prev_prev_fp = prev_fp;
prev_fp = fp;
}
}
}
#[test]
fn test_floor_round() {
fn assert_floor_round<const N: usize>() {
let hashes = BloomFilter::<N>::NUM_COORDS_PER_HASH;
for i in 0..hashes {
assert_eq!(hashes as u64, BloomFilter::<N>::floor_round(i as f64));
}
for i in (hashes as u64..100).step_by(hashes as usize) {
for j in 0..(hashes as u64) {
let x = (i + j) as f64;
assert_eq!(i, BloomFilter::<N>::floor_round(x));
assert_eq!(i, BloomFilter::<N>::floor_round(x + 0.9999));
assert_eq!(i, BloomFilter::<N>::floor_round(x + 0.0001));
}
}
}
assert_floor_round::<512>();
assert_floor_round::<256>();
assert_floor_round::<128>();
assert_floor_round::<64>();
}
fn assert_even_distribution(distr: &[u64], err: f64) {
assert!(err > 0.0 && err < 1.0);
let expected: i64 = (distr.iter().sum::<u64>() / (distr.len() as u64)) as i64;
let thresh = (expected as f64 * err) as i64;
for x in distr {
let diff = (*x as i64 - expected).abs();
assert!(diff <= thresh, "{x:?} deviates from {expected:?}");
}
}
#[test]
fn block_hash_distribution() {
fn block_hash_distribution_<const N: usize>(filter: BloomFilter<N>) {
let mut rng = StdRng::seed_from_u64(1);
let iterations = 1000000;
let mut buckets = vec![0; filter.bits.num_blocks()];
for _ in 0..iterations {
let h1 = (&mut rng).gen_range(0..u64::MAX);
buckets[filter.block_index(h1)] += 1;
}
assert_even_distribution(&buckets, 0.05);
}
let num_blocks = 100;
let seed = [0; 16];
block_hash_distribution_::<512>(BloomFilter::builder512(num_blocks).seed(&seed).hashes(1));
block_hash_distribution_::<256>(BloomFilter::builder256(num_blocks).seed(&seed).hashes(1));
block_hash_distribution_::<128>(BloomFilter::builder128(num_blocks).seed(&seed).hashes(1));
block_hash_distribution_::<64>(BloomFilter::builder64(num_blocks).seed(&seed).hashes(1));
}
#[test]
fn test_seeded_hash_from_hashes() {
let mut rng = StdRng::seed_from_u64(524323);
let mut h1 = (&mut rng).gen_range(0..u64::MAX);
let mut h2 = (&mut rng).gen_range(0..u64::MAX);
let size = 1000;
let mut seeded_hash_counts = vec![0; size];
let iterations = 10000000;
for i in 0..iterations {
let hi = seeded_hash_from_hashes(&mut h1, &mut h2, i);
seeded_hash_counts[(hi as usize) % size] += 1;
}
assert_even_distribution(&seeded_hash_counts, 0.05);
}
#[test]
fn index_hash_distribution() {
fn index_hash_distribution_<const N: usize>(filter: BloomFilter<N>, thresh_pct: f64) {
let [mut h1, mut h2] = filter.get_orginal_hashes("qwerty");
let mut counts = vec![0; N];
let iterations = 100000;
for i in 0..iterations {
for bit_index in BloomFilter::<N>::bit_indexes(&mut h1, &mut h2, i) {
let index = bit_index as usize % N;
counts[index] += 1;
}
}
assert_even_distribution(&counts, thresh_pct);
}
let seed = [0; 16];
index_hash_distribution_::<512>(BloomFilter::builder512(1).seed(&seed).hashes(1), 0.2);
index_hash_distribution_::<256>(BloomFilter::builder256(1).seed(&seed).hashes(1), 0.05);
index_hash_distribution_::<128>(BloomFilter::builder128(1).seed(&seed).hashes(1), 0.05);
index_hash_distribution_::<64>(BloomFilter::builder64(1).seed(&seed).hashes(1), 0.05);
}
#[test]
fn test_debug() {
let filter = BloomFilter::builder64(1).hashes(1);
assert!(!format!("{:?}", filter).is_empty());
}
#[test]
fn test_clone() {
let filter = BloomFilter::builder(4).hashes(4);
assert_eq!(filter, filter.clone());
}
}