Module ahash

A fast and DOS-resistent hash function, for use in HashMaps.

• Crate ::ahash.
• docs.rs
• crates.io
• GitHub

The Rust standard HashMap (and HashSet) use a pluggable hash function defined by the standard Hasher trait. The default hasher used by Rust's HashMap is SipHash 1-3, which provides strong resistance to denial-of-service (DOS) attacks against hash maps.

SipHash is relatively slow though, particularly for small keys like integers, so it is common for programs to use a different implementation of Hasher.

ahash is both DOS-resistent, and fast enough for almost all uses of hash maps.

It comes with tradeoffs though, which is probably why it is not used in the standard library.

ahash does not have a fixed hash function - it is version- and platform-specific, so it is only suitable for use in-memory, and not for making stable comparisons across systems (it is primarily for use in Rust's HashMap and HashSet). On x86 it makes use of AES-NI instructions for performance.

Although ahash can be used in no-std contexts, the standard Rust HashMap cannot, as it lives in the std crate. For no-std hash maps use the hashbrown crate.

Examples

Construct a standard HashMap with an AHasher by using the AHashMap type alias.

use ahash::AHashMap;

fn main() {
    let mut map: AHashMap<i32, i32> = AHashMap::new();
    map.insert(12, 34);
    map.insert(56, 78);
}