openethereum/util/bloom/src/lib.rs
2016-10-21 11:57:30 +02:00

252 lines
7.0 KiB
Rust

// Copyright 2015, 2016 Ethcore (UK) Ltd.
// This file is part of Parity.
// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Parity. If not, see <http://www.gnu.org/licenses/>.
extern crate siphasher;
use std::cmp;
use std::mem;
use std::f64;
use std::hash::{Hash, Hasher};
use std::collections::HashSet;
use siphasher::sip::SipHasher;
// TODO [ToDr] Both hashers are exactly the same - no point to keep two.
const NUMBER_OF_HASHERS: usize = 2;
/// BitVec structure with journalling
/// Every time any of the blocks is getting set it's index is tracked
/// and can be then drained by `drain` method
struct BitVecJournal {
elems: Vec<u64>,
journal: HashSet<usize>,
}
impl BitVecJournal {
pub fn new(size: usize) -> BitVecJournal {
let extra = if size % 8 > 0 { 1 } else { 0 };
BitVecJournal {
elems: vec![0u64; size / 8 + extra],
journal: HashSet::new(),
}
}
pub fn from_parts(parts: &[u64]) -> BitVecJournal {
BitVecJournal {
elems: parts.to_vec(),
journal: HashSet::new(),
}
}
pub fn set(&mut self, index: usize) {
let e_index = index / 64;
let bit_index = index % 64;
let val = self.elems.get_mut(e_index).unwrap();
*val |= 1u64 << bit_index;
self.journal.insert(e_index);
}
pub fn get(&self, index: usize) -> bool {
let e_index = index / 64;
let bit_index = index % 64;
self.elems[e_index] & (1 << bit_index) != 0
}
pub fn drain(&mut self) -> Vec<(usize, u64)> {
let journal = mem::replace(&mut self.journal, HashSet::new()).into_iter();
journal.map(|idx| (idx, self.elems[idx])).collect::<Vec<(usize, u64)>>()
}
pub fn saturation(&self) -> f64 {
self.elems.iter().fold(0u64, |acc, e| acc + e.count_ones() as u64) as f64 / (self.elems.len() * 64) as f64
}
}
/// Bloom filter structure
pub struct Bloom {
bitmap: BitVecJournal,
bitmap_bits: u64,
k_num: u32,
// TODO [ToDr] Both hashers are exactly the same - no point to keep two.
sips: [SipHasher; NUMBER_OF_HASHERS],
}
impl Bloom {
/// Create a new bloom filter structure.
/// bitmap_size is the size in bytes (not bits) that will be allocated in memory
/// items_count is an estimation of the maximum number of items to store.
pub fn new(bitmap_size: usize, items_count: usize) -> Bloom {
assert!(bitmap_size > 0 && items_count > 0);
let bitmap_bits = (bitmap_size as u64) * 8u64;
let k_num = Bloom::optimal_k_num(bitmap_bits, items_count);
let bitmap = BitVecJournal::new(bitmap_bits as usize);
let sips = [SipHasher::new(), SipHasher::new()];
Bloom {
bitmap: bitmap,
bitmap_bits: bitmap_bits,
k_num: k_num,
sips: sips,
}
}
/// Initializes bloom filter from saved state
pub fn from_parts(parts: &[u64], k_num: u32) -> Bloom {
let bitmap_size = parts.len() * 8;
let bitmap_bits = (bitmap_size as u64) * 8u64;
let bitmap = BitVecJournal::from_parts(parts);
let sips = [SipHasher::new(), SipHasher::new()];
Bloom {
bitmap: bitmap,
bitmap_bits: bitmap_bits,
k_num: k_num,
sips: sips,
}
}
/// Create a new bloom filter structure.
/// items_count is an estimation of the maximum number of items to store.
/// fp_p is the wanted rate of false positives, in ]0.0, 1.0[
pub fn new_for_fp_rate(items_count: usize, fp_p: f64) -> Bloom {
let bitmap_size = Bloom::compute_bitmap_size(items_count, fp_p);
Bloom::new(bitmap_size, items_count)
}
/// Compute a recommended bitmap size for items_count items
/// and a fp_p rate of false positives.
/// fp_p obviously has to be within the ]0.0, 1.0[ range.
pub fn compute_bitmap_size(items_count: usize, fp_p: f64) -> usize {
assert!(items_count > 0);
assert!(fp_p > 0.0 && fp_p < 1.0);
let log2 = f64::consts::LN_2;
let log2_2 = log2 * log2;
((items_count as f64) * f64::ln(fp_p) / (-8.0 * log2_2)).ceil() as usize
}
/// Records the presence of an item.
pub fn set<T>(&mut self, item: T)
where T: Hash
{
let mut hashes = [0u64, 0u64];
for k_i in 0..self.k_num {
let bit_offset = (self.bloom_hash(&mut hashes, &item, k_i) % self.bitmap_bits) as usize;
self.bitmap.set(bit_offset);
}
}
/// Check if an item is present in the set.
/// There can be false positives, but no false negatives.
pub fn check<T>(&self, item: T) -> bool
where T: Hash
{
let mut hashes = [0u64, 0u64];
for k_i in 0..self.k_num {
let bit_offset = (self.bloom_hash(&mut hashes, &item, k_i) % self.bitmap_bits) as usize;
if !self.bitmap.get(bit_offset) {
return false;
}
}
true
}
/// Return the number of bits in the filter
pub fn number_of_bits(&self) -> u64 {
self.bitmap_bits
}
/// Return the number of hash functions used for `check` and `set`
pub fn number_of_hash_functions(&self) -> u32 {
self.k_num
}
fn optimal_k_num(bitmap_bits: u64, items_count: usize) -> u32 {
let m = bitmap_bits as f64;
let n = items_count as f64;
let k_num = (m / n * f64::ln(2.0f64)).ceil() as u32;
cmp::max(k_num, 1)
}
fn bloom_hash<T>(&self, hashes: &mut [u64; NUMBER_OF_HASHERS], item: &T, k_i: u32) -> u64
where T: Hash
{
if k_i < NUMBER_OF_HASHERS as u32 {
let mut sip = self.sips[k_i as usize].clone();
item.hash(&mut sip);
let hash = sip.finish();
hashes[k_i as usize] = hash;
hash
} else {
hashes[0].wrapping_add((k_i as u64).wrapping_mul(hashes[1]) % 0xffffffffffffffc5)
}
}
/// Drains the bloom journal returning the updated bloom part
pub fn drain_journal(&mut self) -> BloomJournal {
BloomJournal {
entries: self.bitmap.drain(),
hash_functions: self.k_num,
}
}
/// Returns the ratio of set bits in the bloom filter to the total bits
pub fn saturation(&self) -> f64 {
self.bitmap.saturation()
}
}
/// Bloom journal
/// Returns the tuple of (bloom part index, bloom part value) where each one is representing
/// an index of bloom parts that was updated since the last drain
pub struct BloomJournal {
pub hash_functions: u32,
pub entries: Vec<(usize, u64)>,
}
#[cfg(test)]
mod tests {
use super::Bloom;
#[test]
fn get_set() {
let mut bloom = Bloom::new(10, 80);
let key = vec![115u8, 99];
assert!(!bloom.check(&key));
bloom.set(&key);
assert!(bloom.check(&key));
}
#[test]
fn journalling() {
let initial = vec![0u64; 8];
let mut bloom = Bloom::from_parts(&initial, 3);
bloom.set(&vec![5u8, 4]);
let drain = bloom.drain_journal();
assert_eq!(2, drain.entries.len())
}
#[test]
fn saturation() {
let initial = vec![0u64; 8];
let mut bloom = Bloom::from_parts(&initial, 3);
bloom.set(&vec![5u8, 4]);
let full = bloom.saturation();
// 2/8/64 = 0.00390625
assert!(full >= 0.0039f64 && full <= 0.004f64);
}
}