Created
January 7, 2020 03:28
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basic Bloom Filter with 4 hashing functions
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use bit_vec::BitVec; | |
use std::hash::{Hash, Hasher}; | |
// use 4 hash functions | |
use ahash::AHasher; | |
use fnv::FnvHasher; | |
use metrohash::MetroHash64; | |
use siphasher::sip::SipHasher; | |
pub struct BloomFilter { | |
bits: BitVec, | |
k: usize, | |
hash_builders: Vec<fn() -> Box<dyn Hasher>>, | |
} | |
fn builder1() -> Box<dyn Hasher> { | |
Box::new(FnvHasher::default()) | |
} | |
fn builder2() -> Box<dyn Hasher> { | |
Box::new(SipHasher::new()) | |
} | |
fn builder3() -> Box<dyn Hasher> { | |
Box::new(AHasher::default()) | |
} | |
fn builder4() -> Box<dyn Hasher> { | |
Box::new(MetroHash64::new()) | |
} | |
impl BloomFilter { | |
pub fn with_capacity(k: usize) -> Self { | |
BloomFilter { | |
k, | |
bits: BitVec::from_elem(k, false), | |
hash_builders: vec![builder1, builder2, builder3, builder4], | |
} | |
} | |
pub fn insert<T: Hash>(&mut self, val: T) { | |
for h in self.hash_builders.iter() { | |
let mut hasher = h(); | |
val.hash(&mut hasher); | |
self.bits.set((hasher.finish() as usize) % self.k, true); | |
} | |
} | |
pub fn test<T: Hash>(&self, val: T) -> bool { | |
let mut membership = true; | |
for h in self.hash_builders.iter() { | |
let mut hasher = h(); | |
val.hash(&mut hasher); | |
membership &= self.bits.get((hasher.finish() as usize) % self.k).unwrap(); | |
if !membership { | |
return membership; | |
} | |
} | |
membership | |
} | |
} | |
#[cfg(test)] | |
mod tests { | |
use super::*; | |
#[test] | |
fn basic_insert() { | |
let mut bm = BloomFilter::with_capacity(10); | |
let val = "hello world"; | |
bm.insert(val); | |
assert!(bm.test(val)); | |
} | |
} |
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