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.


f :: Num a => a -> Int -> a
f a b | b == 2 = a2
      | b == 3 = a3
      | b == 4 = a4
      | b == 5 = a4 * a
      | b == 6 = a3 * a3
      | b == 7 = a3 * a3 * a
      | b == 8 = a4 * a4
      | b == 9 = a4 * a4 * a
      | True   = a4 * a4 * a2
      where a2 = a  * a
            a3 = a2 * a
            a4 = a2 * a2