}
  }

  public void testCeilingPowerOfTwoZero() {
    assertThrows(
        IllegalArgumentException.class, () -> BigIntegerMath.ceilingPowerOfTwo(BigInteger.ZERO));
  }

  public void testFloorPowerOfTwoZero() {
    assertThrows(
        IllegalArgumentException.class, () -> BigIntegerMath.floorPowerOfTwo(BigInteger.ZERO));
  }

   * checkedPow(2, log2(x, FLOOR))}.
   *
   * @throws IllegalArgumentException if {@code x <= 0}
   * @since 20.0
   */
  public static long floorPowerOfTwo(long x) {
    checkPositive("x", x);

    // Long.highestOneBit was buggy on GWT.  We've fixed it, but I'm not certain when the fix will
    // be released.