ChibiHash-rs

Rust port of N-R-K/ChibiHash. See the article ChibiHash: A small, fast 64-bit hash function for more information.

All credit for the algorithm goes to N-R-K.

Versioning

Since crate version 0.4.0 the crate offers two versions of the algorithm:

• v1 is the original implementation and the default one.
• v2 is a new implementation with better performance and passes all tests in smhasher3.

If you import the crate without any version specifier, the v1 version is used. The v1 version can also be explicitly selected by importing chibihash::v1::* instead.

If you want the latest and greatest version, you can import chibihash::v2::*.

The v2 version will be the default in the next major version.

Features

• 64-bit hash function
• Deterministic
• Fast
• No dependencies
• no-std compatible
• Multiple ways to use ChibiHash:
  1. Direct Hashing: One-shot hashing using chibi_hash64()
  2. Simple Hasher: Basic implementation using ChibiHasher (implements std::hash::Hasher)
  3. Streaming Hasher: Memory-efficient streaming with StreamingChibiHasher (implements std::hash::Hasher) - currently only available in v1
  4. BuildHasher: ChibiHasher implements BuildHasher. This allows using ChibiHash as the default hasher for std::collections::HashMap and std::collections::HashSet. Use ChibiHashMap and ChibiHashSet types.

Example

use chibihash::{chibi_hash64, ChibiHasher, StreamingChibiHasher, ChibiHashMap, ChibiHashSet};
use std::hash::Hasher;

fn main() {
    // Method 1: Direct hashing
    let hash = chibi_hash64(b"yellow world", 42);
    println!("Direct hash: {:016x}", hash);

    // Method 2: Using Hasher trait
    let mut hasher = ChibiHasher::new(42);
    hasher.write(b"yellow world");
    println!("Hasher trait: {:016x}", hasher.finish());

    // Method 3: Streaming hashing
    let mut hasher = StreamingChibiHasher::new(0);
    hasher.update(b"yellow ");
    hasher.update(b"world");
    println!("Streaming: {:016x}", hasher.finalize());

    // Method 4: BuildHasher for HashMap
    let mut map: ChibiHashMap<String, i32> = ChibiHashMap::default();
    map.insert("hello".to_string(), 42);
    println!("BuildHasher HashMap: {:?}", map.get("hello"));

    // Method 5: BuildHasher for HashSet
    let mut set: ChibiHashSet<String> = ChibiHashSet::default();
    set.insert("hello".to_string());
    println!("BuildHasher HashSet: {}", set.contains("hello"));

}

Tests

Run cargo test to see the tests.

Benchmarks

Run cargo bench to see the benchmarks. See target/criterion/report/index.html for the HTML report.

The repository also contains a benchmark comparing the Rust implementation to the C implementation. Run cargo bench --features ffi to see the benchmark. The C version can be found from the csrc directory. The benchmark utilises FFI to call the C version.

Based on limited testing, the pure Rust implementation is faster than the C version when the input sizes are small (below 1024 bytes). With larger input sizes they are equal. Possibly due to the overhead of the FFI interface itself.

When not to use ChibiHash

Copy-paste from the original repository. Same applies here.

Here are some reasons to avoid using this:

• For cryptographic purposes.
• For protecting against collision attacks (SipHash is the recommended one for this purpose).
• When you need very strong probability against collisions: ChibiHash does very minimal amount of mixing compared to other hashes (e.g xxhash64). And so chances of collision should in theory be higher.

License

MIT. The original C version is under the Unlicense.