}

  /** Returns {@code true} if {@code x} represents a power of two. */
  public static boolean isPowerOfTwo(BigInteger x) {
    checkNotNull(x);
    return x.signum() > 0 && x.getLowestSetBit() == x.bitLength() - 1;
  }

  /**
   * Returns the base-2 logarithm of {@code x}, rounded according to the specified rounding mode.
   *
   * @throws IllegalArgumentException if {@code x <= 0}

    BigDecimal bigMean = new BigDecimal(bigX.add(bigY)).divide(two, RoundingMode.FLOOR);
    return bigMean.intValueExact();
  }

  private static boolean fitsInInt(BigInteger big) {
    return big.bitLength() <= 31;
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNullPointers() {
    NullPointerTester tester = new NullPointerTester();
    tester.setDefault(int.class, 1);

    BigDecimal bigMean = new BigDecimal(bigX.add(bigY)).divide(two, RoundingMode.FLOOR);
    return bigMean.longValueExact();
  }

  private static boolean fitsInLong(BigInteger big) {
    return big.bitLength() <= 63;
  }

  private static final BigInteger MAX_LONG = BigInteger.valueOf(Long.MAX_VALUE);
  private static final BigInteger MIN_LONG = BigInteger.valueOf(Long.MIN_VALUE);