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Ruthless

A UCI chess engine written in Rust.

The design is heavily inspired by Reckless, which I read through a lot while writing mine.

What's inside

  • Bitboards with magic bitboard move generation
  • Alpha-beta search (PVS, null move pruning, LMR)
  • Quiescence search
  • Transposition table, Zobrist hashing
  • NNUE eval, the net is ruthless.bin
  • UCI protocol

The net was trained on vondele's master-binpacks_relabel.

Building

You need a recent Rust toolchain (edition 2024, so up to date stable).

cargo build --release

Binary ends up in target/release/. On Windows it's Ruthless.exe.

The default build targets x86-64-v2 (SSE4.2 + POPCNT), so the binary runs on any x86-64 machine. target-cpu=native is intentionally not the default: such binaries fail with illegal instruction on hosts that lack one of the build machine's ISA extensions.

For releases, build one binary per microarchitecture level and ship them separately:

RUSTFLAGS="-C target-cpu=x86-64-v2" cargo build --release  # baseline
RUSTFLAGS="-C target-cpu=x86-64-v3" cargo build --release  # AVX2, BMI2, FMA
RUSTFLAGS="-C target-cpu=x86-64-v4" cargo build --release  # AVX-512

make release-v2 / release-v3 / release-v4 do the same on Unix shells.

Slider move generation picks PEXT or magic bitboards at startup: PEXT is used when BMI2 is available and the CPU is not an AMD Zen 1/2 (family 0x17), where PEXT is microcoded and slower than a magic multiply-shift.

Running

It only speaks UCI, so you'll want a GUI like Cute Chess, Nibbler or Banksia. You can also poke it by hand in the terminal:

./target/release/Ruthless
uci
isready
position startpos moves e2e4 e7e5
go movetime 1000

License

MIT