Re: Ada.Calendar.Formatting.Image (or Time_Of) changing the time

["Randy Brukardt" <randy@rrsoftware.com>]

"Simon Wright" <simon@pushface.org> wrote in message 
news:lyv9nl8p6w.fsf@pushface.org...
...
> There was a conversation on Ada-Comment in June last year, in which it
> turned out that compiler implementers may have have been misinterpreting
> the ARM. It was quite confusing.

Not just a conversation, but also a Binding Interpretation AI (which 
therefore applies to Ada 2012 compilers), AI12-0336-1.

Essentially, the formal definition of Time_Offset, and the way it was 
actually implemented by every compiler except mine, was completely 
different. We decided to match practice, especially as that matches the way 
the Internet uses time offsets. So that part of the RM was rewritten.

As Dmitry says, the default Time_Offset on GNAT gives one UTC. If you want 
CST or CDT (my time zones, which change on this coming Sunday), one needs to 
use -360 or -300. We've added a new renaming Local_Time_Image to make this 
relatively easy (dunno if GNAT has it yet).

The advantage of this definition is that the base UTC time doesn't jump 
during the year, but if you are interested in local time, you have to 
determine the offset based on the time-of-year.

Your example suggests that GNAT is doing something weird with times that are 
far away from today. That's certainly not intended, sounds like a bug to me. 
Certainly is a bug with the rewritten rules for Time_Image.

                                                   Randy.