Fastest square root algorithm

Question

I was looking for a fast algorythm for integer square roots and I found this one http://medialab.freaknet.org/martin/src/sqrt/.
The algorithm comes from a book by Mr C. Woo on how to do maths on an abacus.
I post the javaized version here in case anyone finds it interesting.
I believe this is the fastest square root function in existance for integers (and in game programming much of the time you aren't interested in fractions)
/* Fast interger square root adapted from algorithm by Martin Guy @ UKC, June 1985.
    *   Origonally from a book on programming abaci by Mr C. Woo.
   public static int fastSqrt2(int n)
      int op, res, one;
      op = n;
      res = 0;
      /* "one" starts at the highest power of four <= than the argument. */
      one = 1 << 30;   /* second-to-top bit set */
      while (one > op) one >>= 2;
      while (one != 0)
         if (op >= res + one)
            op = op - (res + one);
            res = res +  (one<<1);
         res >>= 1;
         one >>= 2;
      return(res);
   }

Answer 1

public static double sqrt(double a){
  if(a<0) throw new IllegalArgumentException("number<0");
  double precision=0.001;
  double x_nMinus1 = -1;
  double x_n = 1;
  while( Math.abs(x_n - x_nMinus1) > precision ) {
    x_nMinus1 = x_n;
    x_n = (x_nMinus1 * x_nMinus1 + a) / (2*x_nMinus1);          
  return x_n;           
}