punktfunk/crates/punktfunk-core/vendor/fec-rs

fec-rs

A pure Rust Reed-Solomon erasure coding library with runtime SIMD acceleration.

Features

• Pure Rust — No C/C++ dependencies or FFI. Everything is implemented in safe Rust (with targeted unsafe for SIMD intrinsics).
• Runtime SIMD detection — Automatically uses the fastest available instruction set via std::is_x86_feature_detected!. A single binary works on all x86_64 systems.
• GF(2^8) — Operates over the Galois field GF(2^8) with generating polynomial 29 (0x1D), compatible with the Moonlight streaming protocol.
• Shard-by-shard encoding — Incremental encoding via ShardByShard for streaming use cases.
• Reconstruction — Reconstruct missing data and/or parity shards from any sufficient subset.

SIMD Acceleration

On x86_64, the library automatically detects CPU features at runtime and uses the best available instruction set:

• GFNI + AVX2 — Single-instruction GF multiply on 32 bytes (Intel Alder Lake+, AMD Zen 4+)
• AVX2 — VPSHUFB split-table nibble lookup on 32 bytes
• GFNI + SSE — Single-instruction GF multiply on 16 bytes
• SSSE3 — VPSHUFB split-table nibble lookup on 16 bytes
• Scalar — Lookup table fallback

Parallel Encoding

Enable the parallel feature for optional rayon-based parallel encoding:

fec-rs = { version = "0.1", features = ["parallel"] }

When enabled, large encode workloads automatically distribute parity shard computation across threads. Small workloads use the sequential path to avoid overhead.

Usage

use fec_rs::ReedSolomon;

let rs = ReedSolomon::new(4, 2).unwrap();

let mut shards: Vec<Vec<u8>> = vec![
    vec![0, 1, 2, 3],
    vec![4, 5, 6, 7],
    vec![8, 9, 10, 11],
    vec![12, 13, 14, 15],
    vec![0, 0, 0, 0], // parity shard 1
    vec![0, 0, 0, 0], // parity shard 2
];

// Encode parity
rs.encode(&mut shards).unwrap();

// Verify
assert!(rs.verify(&shards).unwrap());

// Simulate loss of shard 0
let mut recovery: Vec<Option<Vec<u8>>> = shards.into_iter().map(Some).collect();
recovery[0] = None;

// Reconstruct
rs.reconstruct(&mut recovery).unwrap();

License: BSD-2-Clause