The GEAR hashing function is a fast, rolling hash function that is well suited for content defined chunking.

In particular, this function is used as a building block for the FastCDC algorithm.

The implementation provided in this crate consists of both a simple, scalar variant, as well as optimized versions for the SSE4.2 and AVX2 instruction sets.

use gearhash::Hasher;

// set up initial state
let mut chunks = vec![];
let mut offset = 0;

// create new hasher
let mut hasher = Hasher::default();

// loop through all matches, and push the corresponding chunks
while let Some(boundary) = hasher.next_match(&buf[offset..], MASK) {
    chunks.push(&buf[offset..offset + boundary]);
    offset += boundary;
}

// push final chunk
chunks.push(&buf[offset..]);

To ensure memory safety of the unsafe SIMD code in this crate, we use cargo-fuzz.

You can find the fuzzing targets under fuzz/fuzz_targets, which can be run using cargo fuzz run <target>.

This project is licensed under either of

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

at your option.

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