4ku is an a C++ chess engine designed to fit into 4,096 bytes. Source code is minified, compressed, and then appended to a script. The script decompresses the source, compiles it, and then runs the executable. The script and source combination fits into the size limits, while the resulting executable does not.

4ku can be built normally, but it won't fit into the size restriction:

git clone https://github.com/kz04px/4ku
mkdir 4ku/build
cd 4ku/build
cmake ..
cmake --build .

To build the small version of 4ku on Linux, run build-mini.sh located in the root directory:

sh build-mini.sh

No small version of 4ku is currently available on Windows.

3,586 bytes

• Linux
• A C++ compiler
• python3
• lzma

The build script, launch scripts, and compression tool (lzma) are all specific to Linux and would need replacing for 4ku to run on Windows. The code itself should be portable.

The minifier requires Python 3 to run. It's fragile and will not handle arbitrary C++ code. If better solutions are found in the future it can be replaced.

Points of note:

• Variable name substitutions are hard coded
• Erroneous substitutions may happen
• Multiple passes required

Removed:

• Whitespace
• Single line comments
• Block comments
• const
• noexcept
• Attributes: nodiscard, maybe_unused

The UCI protocol isn't strictly followed in the interests of space:

• The first line of input after startup will be interpreted as "uci" even if it isn't.
• "stop" is unsupported.
• Both "position fen [fen]" and "position startpos" are ignored.
• Only wtime and btime are supported.