HyperLogLog is a probabilistic algorithm for estimating the number of distinct elements (cardinality) of a multiset. Several variations of the original algorithm, described by P. Flajolet et al., have been proposed.

The following implementations are provided:

• HyperLogLog
• HyperLogLog++

Add to Cargo.toml:

[dependencies]
hyperloglogplus = "*"

With Rust compiler version 1.45.0 or higher consider enabling the const-loop feature for better performance, see here for more details.

[dependencies]
hyperloglogplus = { version = "*", features = ["const-loop"] }

A simple example using HyperLogLog++ implementation:

use std::collections::hash_map::RandomState;
use hyperloglogplus::{HyperLogLog, HyperLogLogPlus};

let mut hllp: HyperLogLogPlus<u32, _> =
    HyperLogLogPlus::new(16, RandomState::new()).unwrap();

hllp.insert(&12345);
hllp.insert(&23456);

assert_eq!(hllp.count().trunc() as u32, 2);

Here you can find figures and discussion on experimental evaluation.