// Checks for a single bit set.
      boolean expected = x.signum() > 0 & x.and(x.subtract(ONE)).equals(ZERO);
      assertEquals(expected, BigIntegerMath.isPowerOfTwo(x));
    }
  }

  public void testLog2ZeroAlwaysThrows() {
    for (RoundingMode mode : ALL_ROUNDING_MODES) {
      assertThrows(IllegalArgumentException.class, () -> BigIntegerMath.log2(ZERO, mode));
    }
  }

  public void testLog2NegativeAlwaysThrows() {

      BigInteger bigX = BigInteger.valueOf(x);
      boolean expected = (bigX.signum() > 0) && (bigX.bitCount() == 1);
      assertEquals(expected, IntMath.isPowerOfTwo(x));
    }
  }

  public void testLog2ZeroAlwaysThrows() {
    for (RoundingMode mode : ALL_ROUNDING_MODES) {
      assertThrows(IllegalArgumentException.class, () -> IntMath.log2(0, mode));
    }
  }

  public void testLog2NegativeAlwaysThrows() {