presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/addFieldValueDate
class DateTimeFunctions:    @Description("add the specified amount of date to the given date")
    @LiteralParameters("x")
    @ScalarFunction("date_add")
    @SqlType(StandardTypes.DATE)
    public static long addFieldValueDate(ConnectorSession session, @SqlType("varchar(x)") Slice unit, @SqlType(StandardTypes.BIGINT) long value, @SqlType(StandardTypes.DATE) long date)
    {
        long millis = getDateField(UTC_CHRONOLOGY, unit).add(DAYS.toMillis(date), toIntExact(value));
        return MILLISECONDS.toDays(millis);
    }