A5Hash.Sharp

High-performance, AI-assisted C# port of the original a5hash family of hash functions by Aleksey Vaneev.

• Upstream repo: https://github.com/avaneev/a5hash
• Upstream author: Aleksey Vaneev (2025), MIT licensed

This library provides:

• new A5Hash(seed, options) instance API (recommended)
• A5Hash.Hash / A5Hash.Hash32 / A5Hash.Hash128 static convenience APIs

a5hash is a fast non-cryptographic hash intended for hash tables / bloom filters (not a cryptographic primitive).

Install

NuGet

dotnet add package A5Hash.Sharp

Source

Copy src/A5Hash/A5Hash.cs into your project and enable AllowUnsafeBlocks.

Usage

using A5Hash;

ReadOnlySpan<byte> bytes = "Hello, World!"u8;
ReadOnlySpan<char> chars = "Hello, World!";

// Recommended: instance API (seed configured once)
var hasher = new A5Hash(seed: 0xDEADBEEFCAFEBABE);

ulong h64Bytes = hasher.Hash(bytes);
uint  h32Bytes = hasher.Hash32(bytes);
var (lowBytes, highBytes) = hasher.Hash128(bytes);

ulong h64Chars = hasher.Hash(chars);
uint  h32Chars = hasher.Hash32(chars);
var (lowChars, highChars) = hasher.Hash128(chars);

// Optional: disable intrinsics/SIMD (for diagnostics/portability)
var scalarHasher = new A5Hash(seed: 0xDEADBEEFCAFEBABE, options: new A5HashOptions { UseIntrinsics = false });

// Static convenience API still available
ulong seeded = A5Hash.Hash(chars, seed: 0xDEADBEEFCAFEBABE);

Hashing a slice (zero allocations)

byte[] buffer = new byte[1024];
var hasher = new A5Hash(seed: 0);
ulong hash = hasher.Hash(buffer.AsSpan(0, 256));

Benchmarks (short)

Full tables are in benchmarks.md and include:

1. Native C vs C# (same algorithm)

Highlights from the latest run (see benchmarks.md for details):

• 64-bit throughput (1MB): ~5.9 GB/s (C#) vs ~5.6 GB/s (native C)
• 4-byte throughput (ops/s): a5hash32 ~368M ops/s

Requirements

• Targets net8.0 and net10.0
• AllowUnsafeBlocks=true

Credits

• Original algorithm + C implementation: https://github.com/avaneev/a5hash by Aleksey Vaneev
• This repo: AI-assisted port + performance work

License

MIT — see LICENSE.