}
}
fn genKnightAttacks() [@typeInfo(Square).Enum.fields.len]BoardType {
    var ret: [64]BoardType = [_]BoardType{0} ** 64;
    var bb: BitBoard = .{};
    for (std.enums.values(Square)) |square| {
        bb.board = 0;
        bb.set(square);
        // upward
        if (bb.board & Square.fileBits('a') == 0)
            ret[@enumToInt(square)] |= bb.board >> 17;
        if (bb.board & Square.fileBits('h') == 0)
            ret[@enumToInt(square)] |= bb.board >> 15;
        if (bb.board & (Square.fileBits('a') | Square.fileBits('b')) == 0)
            ret[@enumToInt(square)] |= bb.board >> 10;
        if (bb.board & (Square.fileBits('h') | Square.fileBits('g')) == 0)
            ret[@enumToInt(square)] |= bb.board >> 6;
        // downward
        if (bb.board & Square.fileBits('h') == 0)
            ret[@enumToInt(square)] |= bb.board << 17;
        if (bb.board & Square.fileBits('a') == 0)
            ret[@enumToInt(square)] |= bb.board << 15;
        if (bb.board & (Square.fileBits('h') | Square.fileBits('g')) == 0)
            ret[@enumToInt(square)] |= bb.board << 10;
        if (bb.board & (Square.fileBits('a') | Square.fileBits('b')) == 0)
            ret[@enumToInt(square)] |= bb.board << 6;

    return ret;

test "KnightAttacks" {
    const ka = genKnightAttacks();
    { // full move
        var bb: BitBoard = .{};
        bb.set(.c7);
        bb.set(.e7);
        bb.set(.b6);
        bb.set(.f6);
        bb.set(.c3);
        bb.set(.e3);
        bb.set(.b4);
        bb.set(.f4);
        try std.testing.expectEqual(
            bb.board,
            ka[@enumToInt(Square.d5)],
        );
    }
    { // only 6 move
        var bb: BitBoard = .{};
        bb.set(.f7);
        bb.set(.h7);
        bb.set(.e6);
        bb.set(.e4);
        bb.set(.f3);
        bb.set(.h3);
        try std.testing.expectEqual(
            bb.board,
            ka[@enumToInt(Square.g5)],
        );
    }
    { // only 4 move
        var bb: BitBoard = .{};
        bb.set(.b7);
        bb.set(.c6);
        bb.set(.c4);
        bb.set(.b3);
        try std.testing.expectEqual(
            bb.board,
            ka[@enumToInt(Square.a5)],
        );
    }
}