Crate ranged_set [] [src]

Space efficient storage using ranges

When should you use RangedSet?

RangedSet is designed for use cases where a large number of values that are contiguous need storage and fast lookup. The inspiration came from implementing a cache lookup for a program that worked out converging number sequences for the Collatz conjecture. Using a HashSet became very slow after caching about 3 million u64s. (A smaller, incorrect version of this program is given below. It is incorrect in that it automatically caches values before knowing that the sequence converges. It can do this because all the values below 256 are known to converge.)


use ranged_set::RangedSet;

fn collatz(number: u64) -> u64 {
   match number % 2 == 0 {
       false => 3 * number + 1,
       true => number / 2,

fn main() {
    let mut cache = RangedSet::new();

    for i in 1..256 {
        let mut current = i;
        print!("{}: ", current);

        loop {
            println!("{} -> ", current);

            if cache.contains(&current) {
            } else {
                current = collatz(current);



A set that stores values in contiguous ranges