abs(double ) is wrong

    /**
     * Returns the absolute value of a <code>double</code> value.
     * If the argument is not negative, the argument is returned.
     * If the argument is negative, the negation of the argument is returned.
     *
     * @param a a <code>double</code> value.
     * @return the absolute value of the argument.
     * @since JDK1.0
     */

    public static double abs(double a)
    {
      return (a < 0 || a == -0.0D) ? -a :a;
    }


In floating point, 0.0 == -0.0, so abs(+0.0) will return -0.0.

The best thing is to recode this as:
 return a <= 0.0 ? 0.0 - a :a;

because 0.0 - 0.0 = 0.0, 0.0 - (-0.0) = 0.0

This is probably more efficient than coding an extra comparison, or
a doubleToLongBits operation.