.setExpectation(nextDown(-Math.pow(2, 53)), FLOOR, UP, HALF_UP)
        .roundUnnecessaryShouldThrow()
        .test();
  }

  public void testRoundToDouble_negativeTwoToThe54MinusOne() {
    new RoundToDoubleTester(BigDecimal.valueOf((-1L << 54) - 1))
        .setExpectation(-Math.pow(2, 54), DOWN, CEILING, HALF_DOWN, HALF_UP, HALF_EVEN)
        .setExpectation(nextDown(-Math.pow(2, 54)), FLOOR, UP)
        .roundUnnecessaryShouldThrow()

        .setExpectation(nextDown(-Math.pow(2, 53)), FLOOR, UP, HALF_UP)
        .roundUnnecessaryShouldThrow()
        .test();
  }

  public void testRoundToDouble_negativeTwoToThe54MinusOne() {
    new RoundToDoubleTester(BigDecimal.valueOf((-1L << 54) - 1))
        .setExpectation(-Math.pow(2, 54), DOWN, CEILING, HALF_DOWN, HALF_UP, HALF_EVEN)
        .setExpectation(nextDown(-Math.pow(2, 54)), FLOOR, UP)
        .roundUnnecessaryShouldThrow()

  // Relies on the correctness of sqrt(BigInteger, FLOOR).
  @GwtIncompatible // TODO
  public void testSqrtExact() {
    for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
      BigInteger floor = BigIntegerMath.sqrt(x, FLOOR);
      // We only expect an exception if x was not a perfect square.
      boolean isPerfectSquare = floor.pow(2).equals(x);
      try {
        assertEquals(floor, BigIntegerMath.sqrt(x, UNNECESSARY));

      }
    }
  }

  // Relies on the correctness of log10(long, FLOOR) and of pow(long, int).
  @GwtIncompatible // TODO
  public void testLog10Exact() {
    for (long x : POSITIVE_LONG_CANDIDATES) {
      int floor = LongMath.log10(x, FLOOR);
      boolean expectedSuccess = LongMath.pow(10, floor) == x;
      try {
        assertEquals(floor, LongMath.log10(x, UNNECESSARY));
        assertTrue(expectedSuccess);

            }
            roundFloor = toX(roundFloorAsDouble, RoundingMode.FLOOR);
          }

          X deltaToFloor = minus(x, roundFloor);
          X deltaToCeiling = minus(roundCeiling, x);
          int diff = deltaToFloor.compareTo(deltaToCeiling);
          if (diff < 0) { // closer to floor
            return roundFloorAsDouble;
          } else if (diff > 0) { // closer to ceiling

     * can narrow the possible floor(log10(x)) values to two. For example, if floor(log2(x)) is 6,
     * then 64 <= x < 128, so floor(log10(x)) is either 1 or 2.
     */
    int y = maxLog10ForLeadingZeros[Integer.numberOfLeadingZeros(x)];
    /*
     * y is the higher of the two possible values of floor(log10(x)). If x < 10^y, then we want the

     * can narrow the possible floor(log10(x)) values to two. For example, if floor(log2(x)) is 6,
     * then 64 <= x < 128, so floor(log10(x)) is either 1 or 2.
     */
    int y = maxLog10ForLeadingZeros[Long.numberOfLeadingZeros(x)];
    /*
     * y is the higher of the two possible values of floor(log10(x)). If x < 10^y, then we want the

    /*
     * Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
     * guaranteed to be either exact or one less than the correct value. This follows from fact that
     * floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not quite
     * trivial.
     */
    long quotient = ((dividend >>> 1) / divisor) << 1;
    long rem = dividend - quotient * divisor;

  }

  @Override
  public @Nullable E lower(E element) {
    return forward.higher(element);
  }

  @Override
  public @Nullable E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  public @Nullable E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  public @Nullable E higher(E element) {
    return forward.lower(element);
  }

  @Override

  }

  @Override
  public @Nullable E lower(E element) {
    return forward.higher(element);
  }

  @Override
  public @Nullable E floor(E element) {
    return forward.ceiling(element);
  }

  @Override
  public @Nullable E ceiling(E element) {
    return forward.floor(element);
  }

  @Override
  public @Nullable E higher(E element) {
    return forward.lower(element);
  }

  @Override