presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/addFieldValueTimestampWithTimeZone
class DateTimeFunctions:    @Description("add the specified amount of time to the given timestamp")
    @LiteralParameters("x")
    @ScalarFunction("date_add")
    @SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE)
    public static long addFieldValueTimestampWithTimeZone(
            @SqlType("varchar(x)") Slice unit,
            @SqlType(StandardTypes.BIGINT) long value,
            @SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE) long timestampWithTimeZone)
    {
        long millis = getTimestampField(unpackChronology(timestampWithTimeZone), unit).add(unpackMillisUtc(timestampWithTimeZone), toIntExact(value));
        return updateMillisUtc(millis, timestampWithTimeZone);
    }