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use crate::buckets::Buckets;
use crate::hash::compute_k_num;
use crate::{BloomFilter, BuildHashKernels, HashKernels};
use rand::random;
use std::hash::Hash;
pub struct Filter<BHK: BuildHashKernels> {
buckets: Buckets, hash_kernels: BHK::HK, p: usize, }
impl<BHK: BuildHashKernels> Filter<BHK> {
pub fn new(m: usize, d: u8, fp_rate: f64, build_hash_kernels: BHK) -> Self {
let mut k = compute_k_num(fp_rate);
if k > m {
k = m
} else if k == 0 {
k = 1
}
let buckets = Buckets::new(m, d);
let hash_kernels = build_hash_kernels.with_k(k, buckets.len());
Self {
buckets,
hash_kernels,
p: compute_p_num(m, k, d, fp_rate),
}
}
fn decrement(&mut self) {
let r: usize = random();
(0..self.p).for_each(|i| {
let bucket = (r + i) % self.buckets.len();
self.buckets.increment(bucket, -1)
})
}
}
fn compute_p_num(m: usize, k: usize, d: u8, fp_rate: f64) -> usize {
let (m, k, d) = (m as f64, k as f64, f64::from(d));
let max = 2f64.powf(d) - 1.0;
let sub_denom = (1.0 - fp_rate.powf(1.0 / k)).powf(1.0 / max);
let denom = (1.0 / sub_denom - 1.0) * (1.0 / k - 1.0 / m);
let p = (1.0 / denom).ceil();
if p <= 0.0 {
1
} else {
p as usize
}
}
impl<BHK: BuildHashKernels> BloomFilter for Filter<BHK> {
fn insert<T: Hash>(&mut self, item: &T) {
self.decrement();
let max = self.buckets.max_value();
self.hash_kernels.hash_iter(item).for_each(|i| self.buckets.set(i, max))
}
fn contains<T: Hash>(&self, item: &T) -> bool {
self.hash_kernels.hash_iter(item).all(|i| self.buckets.get(i) > 0)
}
fn reset(&mut self) {
self.buckets.reset()
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::hash::DefaultBuildHashKernels;
use proptest::{collection::size_range, prelude::any_with, proptest, proptest_helper};
use rand::random;
use std::collections::hash_map::RandomState;
fn _contains(items: &[usize]) {
let mut filter = Filter::new(100, 3, 0.03, DefaultBuildHashKernels::new(random(), RandomState::new()));
assert!(items.iter().all(|i| !filter.contains(i)));
items.iter().for_each(|i| filter.insert(i));
assert!(items.iter().all(|i| filter.contains(i)));
}
proptest! {
#[test]
fn contains(ref items in any_with::<Vec<usize>>(size_range(7).lift())) {
_contains(items)
}
}
}