Body language is not a criteria that interviewers should seriously be looking at unless you are hiring someone that will be representing the company publicly or it's a high-level position: PR, executives, marketing, etc.
Everyone (for large values of most people) thinks that they are normal, and that everyone they interact with has a comparable, rational evaluation mechanism.
Disabusing this notion - and providing some simple ideas to consider when interacting with people who don't know you, but from whom you seek favour - is one of the more useful aspects of articles like this.
How do i prepare for that :\ ?
If I were put on the spot with those constraints I'd suggest a lookup table.
I'm currently looking for a new job, however I tend to ask about the process upfront, if it sounds like a wanky anal probe type of interview I simply withdraw from the process. Which is sad, as some of the jobs I'd really like.
The only way to "prepare" for situations like these is to go in with a willingness to trust one's own gut - and to simply break off the interview once you start to feel you're not being treated professionally, and that the questions you're being asked are, like the above, completely out of line.†
† Okay, maybe if you were applying for the job of chairing some IEEE committee on numerical standards or something, thiis particular question might be. But I somehow doubt that was the case with this particular role.
I know how bitwise operators works and have a CS degree... But even with googling I couldn't find a straight forward way to implement a general exponential operator using only bit operations.
Then, you need to code a multiply(x, y) method using some more bit shifting cleverness and your new add method.
Then, do repeated squaring using your new multiply method.
Aside from having to port an algorithm, I'm pretty sure the last time I used a bitwise operator seriously in 10 years was back in uni.
Unless this problem is for a job working on calculations on hardware that only supplies bitwise ops, it's a math trivia problem disguised as a coding interview question.