Incorrect comment on bit order in class BitBoard?

[rhalbersma]

In bitboard.h, for class BoardSquare the comment on line 43/44 states:

// As a single number, 0 to 63, bottom to top, left to right.
// 0 is a1, 8 is a2, 63 is h8.

In contrast, for the class BitBoard the comment on line 88/89 states:

// Bit enumeration goes from bottom to top, from left to right:
// Square a1 is bit 0, square a8 is bit 7, square b1 is bit 8.

However, the subsequent BitBoard member functions set, reset etc. take a BoardSquare parameter. So in fact BitBoard has the same ordering as BoardSquare.

Should this comment in class BitBoard be updated?

[mooskagh]

Yeah initially it was wrong in both places, but then fixed in one but apparently not another.

[rhalbersma]

There are some other improvements possible in bitboard.h. E.g. BitBoard::Mirror() could use the compiler intrinsics _byteswap_uint64 (MSVC) or __builtin_bswap64 (gcc/clang). This should reduce the current 15 instructions to 1 on modern architectures.

And ReverseBitsInBytes from mcts/node.cc could be moved to be a member function of BitBoard, and renamed MirrorVertical e.g. (and Mirror be renamed to MirrorHorizontal).

I also don’t quite understand the rationale to vertically mirror the inputs for training, could you explain?

I could send a PR later. What do you think?

[mooskagh]

Those are good suggestsions, PR will be appreciated!

[TesseractA]

Still Relevant?

[mooskagh]

Yes, I've just check, still wrong (the comments issue in the very first comment). :)