nnue-jsontobin

A little utility for converting from Marlinflow's NNUE JSON format into a binary NNUE for embedding into chess engine executables. Currently supports relative networks and HalfKA networks.

Usage

Most typical usage is to convert a JSON file into a unified binary file, with an 8-bit output weight array. This is achieved by running the following command:

nnue-jsontobin INPUT.json --output OUTPUT.bin

This will produce a binary file with the following structure:

in C++:

struct alignas(64) NetworkWeights {
    std::array<std::int16_t, 768 * NEURONS * BUCKETS> feature_weights;
    std::array<std::int16_t, NEURONS>                 feature_biases;
    std::array<std::int8_t , NEURONS * 2>             output_weights;
    std::int16_t                                      output_bias;
}

or, in Rust:

#[repr(C, align(64))]
struct NetworkWeights {
    feature_weights: [i16; 768 * NEURONS * BUCKETS],
    feature_biases:  [i16; NEURONS],
    output_weights:  [i8; NEURONS * 2],
    output_bias:     i16,
}

Binary files will be aligned to 64 bytes (size is a multiple of 64 bytes), and so will be padded with trailing zeros if necessary.

For backwards compatibility, you can also produce a binary file with a 16-bit output weight array, by adding the --big-out flag.

nnue-jsontobin performs quantisation of the network weights during the conversion process, and by default uses 255 and 64 as the quantisation factors.

These factors are configurable with the --qa and --qb flags, respectively.

Building

nnue-jsontobin is written in Rust, and can be built with cargo build --release.

License

nnue-jsontobin is licensed under the MIT license.