[tz] Is there a high-level conversion process description available?

Willy at willylorenzo.com Willy at willylorenzo.com
Sun Oct 23 21:01:43 UTC 2011

I was wondering if there exists a high-level description of the process of converting a wall-time from one zone into UTC (and vice-versa) that describes the conversion using the text based zone information (the rules and zones) rather than referencing the binary files.  If conversions simply can’t be done that way because they require additional data that’s produced by zic, then I’d like to know that too.  

I’m attempting an implementation of the TZ database in a system called Lotus Notes, which uses a BASIC like language for programming called LotusScript.  So I pretty much have to build everything from scratch...which is fine.  I’m going through the archives and I’ve already found good info there from the recent "Time zone confusion and implementation hints" thread back in July (don’t know why Yves Goergen didn’t want to install Cygwin...5 minutes after reading that message I had Cygwin installed and was reviewing those tzinfo files!)  But I’m still looking for (what seems to be) basic information, such as can the tz code convert 2011-11-06 1:30 AM America/New_York? That date seems to gets different results based on which converter I use online, as it would appear that you have to know the DST status in order to get the DST status to convert to UTC.

I know nothing about Unix or the c/c++/java languages so I know have a steep learning curve if I want to understand the existing tz code...but I’m hoping that if I can understand the zone conversion process then I can write the necessary code.   I’ve got the nearly 5300 lines of rules, zones, leaps, and links stored in a Notes db for easier manipulation, and I can take a zone UNTIL or a rule and year and produce a date from it.  So it’s a start.


Willy Lorenzo

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