public BigInteger toBigIntegerSlow() {
    BigInteger bigInt = this.mag.toBigIntegerSlow();
    return this.negative ? bigInt.negate() : bigInt;
  }
Convert this object to {@link BigInteger}. Do not use this method in a
performance sensitive place.

@return BigInteger to represent this object
common/src/java/org/apache/hadoop/hive/common/type/SignedInt128.java