SimdHash

A high-performance SIMD-accelerated hashing library that computes multiple hashes in parallel using CPU vector instructions.

SimdHash processes multiple input buffers simultaneously by packing them into SIMD lanes, achieving significant throughput improvements over scalar implementations.

Supported Algorithms

Algorithm	SIMD Parallel	Scalar Fallback
MD4	✓
MD5	✓
SHA-1	✓
SHA-256	✓
SHA-384		✓ (OpenSSL)
SHA-512		✓ (OpenSSL)
NTLM	✓
FNV-1 32	✓
FNV-1a 32	✓
FNV-1 64	✓
FNV-1a 64	✓

Supported SIMD Instruction Sets

• AVX-512 — 16 lanes (512-bit)
• AVX2 — 8 lanes (256-bit)
• SSE4.2 — 4 lanes (128-bit)
• SSSE3 — 4 lanes (128-bit)
• SSE2 — 4 lanes (128-bit)
• ARM NEON — 4 lanes (128-bit)

By default, the build auto-detects the best instruction set for the host CPU via -march=native.

Dependencies

• Clang (C/C++ compiler)
• CMake ≥ 3.14
• OpenSSL (libcrypto) — for SHA-384/SHA-512 and test verification
• ICU (libicuuc) — for Unicode/NTLM support

Building

mkdir -p build && cd build
cmake ..
make

Specifying a SIMD level

Use the SIMD variable to target a specific instruction set instead of auto-detecting:

cmake -DSIMD=avx512 ..   # AVX-512
cmake -DSIMD=avx256 ..   # AVX2
cmake -DSIMD=sse42 ..    # SSE4.2
cmake -DSIMD=ssse3 ..    # SSSE3
cmake -DSIMD=sse2 ..     # SSE2

Build types

cmake -DCMAKE_BUILD_TYPE=Release ..   # (default) optimized
cmake -DCMAKE_BUILD_TYPE=Debug ..     # debug + AddressSanitizer

Usage

C API

#include "simdhash.h"

// Hash a single buffer
uint8_t digest[MD5_SIZE];
SimdHashSingle(HashAlgorithmMD5, length, buffer, digest);

// Hash multiple buffers in parallel (one per SIMD lane)
SimdHashContext ctx;
SimdHashInit(&ctx, HashAlgorithmSHA256);
SimdHashUpdate(&ctx, lengths, buffers);
SimdHashFinalize(&ctx);
// Digests are interleaved in ctx.H[]

C++ API

#include "SimdHash.hpp"
#include "SimdHashBuffer.hpp"

// Single hash
std::array<uint8_t, SHA256_SIZE> digest;
simdhash::SimdHashSingle(HashAlgorithmSHA256, input, digest);

// Batched hashing with SimdHashBuffer
SimdHashBuffer buf(MAX_BUFFER_SIZE);
buf.Set(0, "hello");
buf.Set(1, "world");
// ...
SimdHashContext ctx;
SimdHashInit(&ctx, HashAlgorithmMD5);
SimdHashUpdate(&ctx, buf.GetLengths(), buf.ConstBuffers());
SimdHashFinalize(&ctx);

Testing

Tests use Google Test (fetched automatically by CMake).

cd build
make                # build library + tests
ctest               # run all tests

License

Copyright © 2020–2025 Gareth Evans. All rights reserved.