GNU科学库，幂函数效率

Question

I was going through GSL library. I am pasting the function they used for finding the power of a double number.

double gsl_pow_int(double x, int n)
{
  double value = 1.0;

  if(n < 0) {
    x = 1.0/x;
    n = -n;
  }

  /* repeated squaring method 
   * returns 0.0^0 = 1.0, so continuous in x
   */
  do {
     if(n & 1) value *= x;  /* for n odd */
     n >>= 1;
     x *= x;
  } while (n);

  return value;
}

But wouldn't it be more efficient if they use?

double gsl_pow_int(double x, int n)
    {
      double value = 1.0;

      if(n < 0) {
        x = 1.0/x;
        n = -n;
      }

      /* repeated squaring method 
       * returns 0.0^0 = 1.0, so continuous in x
       */
      do{
        if(--n)value*=x;
    }while(n);
    return value;
 }

Answer 1

Your code doesn't even properly handle negative powers! How can you claim that your code is optimised.

Also,next,just decreasing space from your program doesn't make your code more-optimised.Their code has got more readability and more proper indentation than yours!!! Their code is proper for negative powers too and much more optimised!

Also,next, bitwise logical operations like & and right shifting >> is considered more efficient than multiplying as what you have done.