presto-spi/src/main/java/io/prestosql/spi/type/UnscaledDecimal128Arithmetic.java/UnscaledDecimal128Arithmetic/addWithOverflow
class UnscaledDecimal128Arithmetic:    public static long addWithOverflow(Slice left, Slice right, Slice result)
    {
        boolean leftNegative = isNegative(left);
        boolean rightNegative = isNegative(right);
        long overflow = 0;
        if (leftNegative == rightNegative) {
            // either both negative or both positive
            overflow = addUnsignedReturnOverflow(left, right, result, leftNegative);
            if (leftNegative) {
                overflow = -overflow;
            }
        }
        else {
            int compare = compareAbsolute(left, right);
            if (compare > 0) {
                subtractUnsigned(left, right, result, leftNegative);
            }
            else if (compare < 0) {
                subtractUnsigned(right, left, result, !leftNegative);
            }
            else {
                setToZero(result);
            }
        }
        return overflow;
    }