How fast can one compute the power of a number?

Let $x \in \mathbb{R}$ and $k \in \mathbb{Z}^+ \cup \{0\}$ then how fast can one compute $x^k$?

If $x, k \in \mathbb{Z}$ then I guess this previous discussion already settled that, How many operations at maximum needed to compute powering of a number, i.e. $N^k$?

• What is your model of real computation? – Yuval Filmus Apr 26 '16 at 16:27
• Those are the things that are not clear to me :) It would be great if you could kindly explain! For a specific purpose I have in mind you can as well assume that $x$ is being obtained as the inner product of two d-dimensional real vectors of bounded norm. – gradstudent Apr 26 '16 at 16:34
• I suggest you do some reading first on the area. There are at least two or three different models. If I remember correctly there is a list somewhere on cstheory. – Yuval Filmus Apr 26 '16 at 16:37

If both $x,k \in \mathbb{R}$, then you can compute $x^k$ as $e^{k \log x}$ as there are somewhat efficient algorithms for $e^x$ and $\log x$.