fcfish

fcfish is a C17 port of the Stockfish chess engine, written against C17 so the whole tree parses under Frama-C. The goal is a bit-exact 1:1 clone: the same bench node signature, the same bestmove, NNUE evaluation, Syzygy tablebases and Lazy-SMP threading. Like Stockfish, it is a UCI engine, not a GUI.

It is a Lazy-SMP engine with NNUE evaluation that is bit-exact with upstream — ./build.sh signature benches the same node count Stockfish produces — with Syzygy tablebases, Lazy-SMP threading and NUMA wired into build.sh's SOURCES and driven by the search.

How it was ported

Stockfish's C++ leans on templates, classes, RAII, operator overloading and exceptions, none of which map onto C17 without re-deciding the design. The port makes those decisions once and decomposes the engine into small single-responsibility modules.

../Stockfish remains the golden: it defines correct behaviour, and the differential gate compares against a pristine upstream build. Where fcfish and Stockfish disagree, Stockfish wins.

Build

Requires clang with C17 support and bash. No build system, no dependencies.

./build.sh              # build the engine (-O3) -> build/fcfish
./build.sh test         # unit + property suite, ASan+UBSan
./build.sh bench        # run the benchmark and print the node signature
./build.sh parity       # the full in-repo gate battery
./build.sh help         # every step

Documentation

• docs/ — the architecture, each subsystem, the C17 patterns.
• CONTRIBUTING.md — the gates and the workflow.

License

fcfish is a derivative of Stockfish and is distributed under the GNU General Public License v3 — see Copying.txt. All chess strength and the NNUE networks come from the Stockfish project; see AUTHORS. The networks are trained on Leela Chess Zero data under the ODbL.