Fast SQRT

fast_sqrt

static double fast_sqrt( const double number )
{
   const double f = 1.5;

   const double x = number * 0.5;
   double y = number;
   union 
   {
      double *double_repr;
      long long *long_long_repr;
   } sqrt_union;

   sqrt_union.double_repr = &y;
   long long i = *(sqrt_union.long_long_repr);

   // for floats use:
   // i = 0x5f3759df - (i >> 1);
   i = 0x5fe6eb50c7b537a9LL - (i >> 1);  
   sqrt_union.long_long_repr = &i;
   y = *(sqrt_union.double_repr);
   y = y * (f - (x * y * y));
   y = y * (f - (x * y * y));
   return (number * y);
   //0x5fe6eb50c7b537a9
}