}
    return x;
  }

  @CanIgnoreReturnValue
  static double checkNonNegative(String role, double x) {
    if (!(x >= 0)) { // not x < 0, to work with NaN.
      throw new IllegalArgumentException(role + " (" + x + ") must be >= 0");
    }
    return x;
  }

  static void checkRoundingUnnecessary(boolean condition) {
    if (!condition) {