android/guava/src/com/google/common/primitives/UnsignedLong.java
public BigInteger bigIntegerValue() {
    BigInteger bigInt = BigInteger.valueOf(value & UNSIGNED_MASK);
    if (value < 0) {
      bigInt = bigInt.setBit(Long.SIZE - 1);
    }
    return bigInt;
  }
public BigInteger bigIntegerValue() {
    BigInteger bigInt = BigInteger.valueOf(value & UNSIGNED_MASK);
    if (value < 0) {
      bigInt = bigInt.setBit(Long.SIZE - 1);
    }
    return bigInt;
  }
Returns the value of this {@code UnsignedLong} as a {@link BigInteger}.