kevy-hash

A non-cryptographic hash (FxHasher + fmix64) for single-trust-domain keyspaces — pure Rust, zero dependencies.

FxHasher is FxHash's mixing function followed by an fmix64 finalizer (the finalizer from MurmurHash3). The combination gets avalanche on the low bits that FxHash alone misses, while staying 3.7–7× faster than std::collections's SipHash on short keys.

Part of kevy — kevy is a single-process server with no untrusted clients within a shard, so DoS-resistant SipHash is unnecessary overhead.

use kevy_hash::FxHasher;
use std::hash::Hasher;

let mut h = FxHasher::default();
h.write(b"foo");
let hash: u64 = h.finish();

For drop-in HashMap use, the crate provides a BuildHasher + ready-made type aliases:

use kevy_hash::{FxBuildHasher, FxHashMap};

let mut m: FxHashMap<&str, i32> = FxHashMap::default();
m.insert("x", 1);

// equivalent, more explicit:
use std::collections::HashMap;
let mut m2: HashMap<&str, i32, FxBuildHasher> = HashMap::default();
m2.insert("y", 2);

For callers that don't need the Hasher state machine, the KevyHash trait gives a stateless one-shot:

use kevy_hash::KevyHash;
let h: u64 = b"hello"[..].kevy_hash();

Trust model

⚠️ FxHasher is not DoS-resistant. Do not feed it adversary-controlled keys without rate-limiting or per-shard isolation first. For kevy this is fine — one shard = one trust domain.

License

MIT OR Apache-2.0