fn genBishopAttacks() [@typeInfo(Square).Enum.fields.len]BoardType {
    const moves = [_][2]i2{
        .{ -1, -1 },
        .{ -1, 1 },
        .{ 1, -1 },
        .{ 1, 1 },
    };
    var ret: [64]BoardType = [_]BoardType{0} ** 64;
    for (std.enums.values(Square)) |square| {
        const rank = @intCast(isize, SIZE - square.int() / SIZE);
        const file = @intCast(isize, square.int() % SIZE);
        var attacks: BoardType = 0;
        var step: i5 = 1;
        while (step < SIZE - 1) : (step += 1) {
            for (moves) |m| {
                const dr = rank + m[0] * step;
                const df = file + m[1] * step;
                if (dr < 2 or dr > 7) continue;
                if (df < 1 or df > 7) continue;
                const s = @intCast(u6, (SIZE - dr) * SIZE + df);
                attacks |= @intCast(BoardType, @as(BoardType, 1) << s);
            }
        }
        ret[@enumToInt(square)] = attacks;
    }
    return ret;
}
test "BishopAttacks" {
    const ba = genBishopAttacks();
    {
        var bb: BitBoard = .{};
        var set = [_]Square{ .b2, .c3, .d4, .e5, .f6, .g7 };
        bb.setSlice(&set);
        try std.testing.expectEqual(
            bb.board,
            ba[@enumToInt(Square.a1)],
        );
    }
}