static double bigToDouble(BigInteger x) {
    // This is an extremely fast implementation of BigInteger.doubleValue(). JDK patch pending.
    BigInteger absX = x.abs();
    int exponent = absX.bitLength() - 1;
    // exponent == floor(log2(abs(x)))
    if (exponent < Long.SIZE - 1) {
      return x.longValue();
    } else if (exponent > MAX_EXPONENT) {
      return x.signum() * POSITIVE_INFINITY;
    }

    /*

  private static final double[] doubleInLongRange = new double[ARRAY_SIZE];
  private static final double[] positiveDoubles = new double[ARRAY_SIZE];

  @Param({"DOWN", "UP", "FLOOR", "CEILING", "HALF_EVEN", "HALF_UP", "HALF_DOWN"})
  RoundingMode mode;

  @BeforeExperiment
  void setUp() {
    for (int i = 0; i < ARRAY_SIZE; i++) {
      doubleInIntRange[i] = randomDouble(Integer.SIZE - 2);

      nonzero[i] = randomNonZeroBigInteger(Integer.SIZE - 2).intValue();
      ints[i] = RANDOM_SOURCE.nextInt();
    }
  }

  @Param({"DOWN", "UP", "FLOOR", "CEILING", "HALF_EVEN", "HALF_UP", "HALF_DOWN"})
  RoundingMode mode;

  @Benchmark
  int log2(int reps) {
    int tmp = 0;
    for (int i = 0; i < reps; i++) {
      int j = i & ARRAY_MASK;

    @Override
    @CheckForNull
    public E lower(@ParametricNullness E e) {
      return getElementOrNull(multiset().headMultiset(e, OPEN).lastEntry());
    }

    @Override
    @CheckForNull
    public E floor(@ParametricNullness E e) {
      return getElementOrNull(multiset().headMultiset(e, CLOSED).lastEntry());
    }

    @Override
    @CheckForNull
    public E ceiling(@ParametricNullness E e) {

      return standardSubSet(fromElement, toElement);
    }

    @Override
    public @Nullable T lower(T e) {
      return standardLower(e);
    }

    @Override
    public @Nullable T floor(T e) {
      return standardFloor(e);
    }

    @Override
    public @Nullable T ceiling(T e) {
      return standardCeiling(e);
    }

    @Override
    public @Nullable T higher(T e) {

      }
    }
  }

  // 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);

        NavigableSet<Integer> unfiltered = createUnfiltered(filtered);
        for (int i = 0; i < 10; i++) {
          assertEquals(unfiltered.lower(i), filtered.lower(i));
          assertEquals(unfiltered.floor(i), filtered.floor(i));
          assertEquals(unfiltered.ceiling(i), filtered.ceiling(i));
          assertEquals(unfiltered.higher(i), filtered.higher(i));
        }
      }
    }
  }

    @CheckForNull
    public V lower(@ParametricNullness V v) {
      return getSortedSetDelegate().lower(v);
    }

    @Override
    @CheckForNull
    public V floor(@ParametricNullness V v) {
      return getSortedSetDelegate().floor(v);
    }

    @Override
    @CheckForNull
    public V ceiling(@ParametricNullness V v) {
      return getSortedSetDelegate().ceiling(v);
    }

    @Override

    assertThat(set.floor("f")).isNull();
  }

  public void testFloor_elementPresent() {
    ImmutableSortedSet<String> set =
        ImmutableSortedSet.copyOf(new String[] {"e", "a", "e", "f", "b", "i", "d", "a", "c", "k"});
    assertThat(set.floor("f")).isEqualTo("f");
    assertThat(set.floor("j")).isEqualTo("i");
    assertThat(set.floor("q")).isEqualTo("k");
  }

  private static final double[] doubleInLongRange = new double[ARRAY_SIZE];
  private static final double[] positiveDoubles = new double[ARRAY_SIZE];

  @Param({"DOWN", "UP", "FLOOR", "CEILING", "HALF_EVEN", "HALF_UP", "HALF_DOWN"})
  RoundingMode mode;

  @BeforeExperiment
  void setUp() {
    for (int i = 0; i < ARRAY_SIZE; i++) {
      doubleInIntRange[i] = randomDouble(Integer.SIZE - 2);