Module ahash

Expand description

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

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 resistence 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 (t is primarly 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);
}

Modules§

random_state

Structs§

AHashMap: A HashMap using RandomState to hash the items. (Requires the std feature to be enabled.)
AHashSet: A HashSet using RandomState to hash the items. (Requires the std feature to be enabled.)
AHasher: A Hasher for hashing an arbitrary stream of bytes.
RandomState: Provides a Hasher factory. This is typically used (e.g. by HashMap) to create AHashers in order to hash the keys of the map. See build_hasher below.

Traits§

HashMapExt: A convenience trait that can be used together with the type aliases defined to get access to the new() and with_capacity() methods for the HashMap type alias.
HashSetExt: A convenience trait that can be used together with the type aliases defined to get access to the new() and with_capacity() methods for the HashSet type aliases.

Type Aliases§