QuickPHF

QuickPHF is a Rust crate that allows you to use static compile-time generated hash maps and hash sets using PTHash perfect hash functions.

This crate only contains the runtime code required for using such structures. To generate them, look at the quickphf_codegen crate instead.

The minimum supported Rust version is 1.56. This crate is #![no_std] and #![forbid(unsafe_code)].

Features

• Provides 3 perfect hash function-backed data structures: PhfMap and PhfSet, which, for ease of use, mimic the immutable part of the interface of the standard library HashMap and HashSet; and RawPhfMap, which is a hash map that does not store its keys.
• About twice as fast as phf at lookup, and more than 10 times faster at construction.
• Uses a Rust implementation of Wang Yi's wyhash algorithm for hashing.
• Uses the quickdiv crate to speed up modulo computations.
• Very low memory usage: no unused capacity and less than a byte of overhead per entry.

Example

use quickphf::examples::*;

// You can use `PhfMap` or `PhfSet` just like `HashMap` or `HashSet`.
assert_eq!(FOURTH_POWERS_TO_ROOTS.get(&4096), Some(&8));
assert_eq!(FOURTH_POWERS_TO_ROOTS.get(&17), None);

assert!(PRIME_DIGITS.contains(&3));
assert_eq!(PRIME_DIGITS.len(), 4);

// With a `RawPhfMap` you would mostly use the `get` method. Note
// that it directly returns a &T instead of an Option<&T>.
assert_eq!(HOLIDAYS_PER_MONTH.get("jul"), &1);

// If you query for an invalid key, it will silently return an
// arbitrary answer.
let valid_reference = HOLIDAYS_PER_MONTH.get("purple");

Performance

In general, quickphf is about twice as fast as phf at lookup, with RawPhfMap being faster than PhfMap, especially for larger hash maps.

License

Licensed under any of:

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)
• zlib License (LICENSE-ZLIB or https://opensource.org/license/zlib/)

at your choice.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be multi-licensed as above, without any additional terms or conditions.