Converting timestamps from local timezone to UTC with RPG and SQL

When timestamps are stored in a database table, they are often stored in local time. This is not bad at all, but if you have to compare or coordinate timestamps of different time zones, it quickly gets complicated due to different time offsets, different daylight saving time rules and so on. So it would be nice, to convert timestamps from local time to UTC and back. We will create a RPG procedure to do that, and make it available as a SQL user defined function (UDF).