Struct xorf::Fuse32[−][src]

pub struct Fuse32 {
    pub seed: u64,
    pub segment_length: usize,
    pub fingerprints: Box<[u32]>,
}

Expand description

Xor filter using 32-bit fingerprints in a fuse graph. Requires less space than an Xor32.

A Fuse32 filter uses <36.404 bits per entry of the set is it constructed from, and has a false positive rate of effectively zero (1/2^32 =~ 1/4 billion). As with other probabilistic filters, a higher number of entries decreases the bits per entry but increases the false positive rate.

A Fuse32 filter uses less space and is faster to construct than an Xor32 filter, but requires a large number of keys to be constructed. Experimentally, this number is somewhere >100_000. For smaller key sets, prefer the Xor32 filter. A Fuse32 filter may fail to be constructed.

A Fuse32 is constructed from a set of 64-bit unsigned integers and is immutable.

use xorf::{Filter, Fuse32};
use core::convert::TryFrom;

const SAMPLE_SIZE: usize = 1_000_000;
let keys: Vec<u64> = (0..SAMPLE_SIZE).map(|_| rng.gen()).collect();
let filter = Fuse32::try_from(&keys).unwrap();

// no false negatives
for key in keys {
    assert!(filter.contains(&key));
}

// bits per entry
let bpe = (filter.len() as f64) * 32.0 / (SAMPLE_SIZE as f64);
assert!(bpe < 36.404, "Bits per entry is {}", bpe);

// false positive rate
let false_positives: usize = (0..SAMPLE_SIZE)
    .map(|_| rng.gen())
    .filter(|n| filter.contains(n))
    .count();
let fp_rate: f64 = (false_positives * 100) as f64 / SAMPLE_SIZE as f64;
assert!(fp_rate < 0.0000000000000001, "False positive rate is {}", fp_rate);

Serializing and deserializing Fuse32 filters can be enabled with the serde feature.

Fields

seed: u64

The seed for the filter

segment_length: usize

The number of blocks in the filter

fingerprints: Box<[u32]>

The fingerprints for the filter

Struct xorf::Fuse32[−][src]

Fields

Trait Implementations

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