I am a newbie. I want to code a chinese chess engine, and I want to modify Stockfish source code to do so. But the Stockfish source code is too hard to understand. There are no document to explain everything. I don't know where to start. For example, today I try to understand the bitbase.cpp file. This line of code in this file is not well documented:
constexpr unsigned MAX_INDEX = 2*24*64*64; // stm * psq * wksq * bksq = 196608
I really don't know where to ask questions about these kind of things. It's open source but it seem to be understanded by only few people. Please give me suggestions to understand the source code better. Thanks!