code: public static boolean equalsIncludingNaN(double x, double y, double eps) {
          return equalsIncludingNaN(x, y) || (FastMath.abs(y - x) <= eps);
      }
docs: Returns true if both arguments are NaN or are equal or within the range
  of allowed error (inclusive).
  
  @param x first value
  @param y second value
  @param eps the amount of absolute error to allow.
  @return {@code true} if the values are equal or within range of each other,
  or both are NaN.
  @since 2.2