code: private static double copysign(double x, double y) {
          return fromhilo((hi(x) & 0x7fffffff) | (hi(y) & 0x80000000), lo(x));
      }
docs: copysign(double x, double y) <BR>
  copysign(x,y) returns a value with the magnitude of x and
  with the sign bit of y.