title: Power of 2 approximation in fixed point
body: <p>Currently, I am using a small lookup table and linear interpolation which is quite fast and also accurate enough (max error is less than 0.001). However I was wondering if there is an approximation which is even faster.</p>
  
  <p>Since the integer part of the exponent can be extracted and calculated by bitshifts, the approximation just needs to work in the range [-1,1]
  I have tried to find a chebyshev polynomial, but could not achieve a good accuracy for polynomials of low order. I could live with a max error around 0.01 I guess, but I did not get near that number. Higher order polynomials are not an option, since they are much less efficient than my current lookup table based solution.</p>