Fast positive integer power function

I'm trying to figure out how to compute an integer power of a double efficiently with as little overhead as possible (trying to avoid loops and recursion to minimize the amount of calls and jumps). Calculation speed is the priority.
So far I got this trivial piece of code:

double f(double a,char b){
if(b==2)return a*a;
if(b==3)return a*a*a;
if(b==4)return a*a*a*a;
if(b==5)return a*a*a*a*a;
if(b==6)return a*a*a*a*a*a;
if(b==7)return a*a*a*a*a*a*a;
if(b==8)return a*a*a*a*a*a*a*a;
if(b==9)return a*a*a*a*a*a*a*a*a;
        return a*a*a*a*a*a*a*a*a*a;
}

...which of course assumes the exponent is at most 10. The code can easily be expanded if higher exponents are needed.
I'm thinking this is probably optimal, but I know you /prog/riders have some magic tricks up your sleeve, so hit me with them.

a²ⁿ = (a²)ⁿ

double pow(double x, int n) {
  double x2;
  if (n == -1) return 1 / x;
  if (n < 0) return 1 / pow(x, -n);
  if (n == 0) return 1;
  if (n == 1) return x;
  x2 = x * x;
  if (n == 2) return x2;
  if (n % 2 == 0) return pow(x2, n / 2);
  return x * pow(x2, (n - 1) / 2);
}

This seems O(log n).