Ada package for dates prior to 1900?

Ret_Build_Engineer · December 18, 2023, 3:11am

Hi;

How does one do calendar, date and time, calculations in Ada if the dates are prior to 1900? I’m sure that this is a real problem that has been encountered previously. I’ve never seen anything that does this. Do people just make a foreign call to Perl or UNIX cal program?

Thanks,
Ken Wolcott

JeremyGrosser · December 18, 2023, 4:10am

The Matreshka League library looks like it has fairly comprehensive support for date/time operations using a base time in 1582 AD.

github.com

godunko/matreshka/blob/39f896135df653999895eeca8420b7cfdc1da89c/source/league/matreshka-internals-calendars.ads#L55


      
          
          package Matreshka.Internals.Calendars is
          
             pragma Preelaborate;
          
             --  Universal Time Coordinated (UTC) representation from the X/Open DCE Time
             --  Service is used as internal representation. It is defined as follows:
             --
             --     Time units          100 nanoseconds (10-7 seconds)
             --
             --     Base time           15 October 1582 00:00:00.
             --
             --     Approximate range   AD 30,000
             --
             --  UTC time in this implementation always refers to time in Greenwich Time
             --  Zone.
          
             type Absolute_Time is new Interfaces.Integer_64;
          
             --  The corresponding internal representations of relative time is the same
             --  one as for absolute time, and hence with similar characteristics:

Generally speaking, if you’re regularly working with dates prior to January 1, 1970, you should consider parsing the “backzone” file from the tzdata distribution and doing the math yourself rather than relying on a library. There are a lot of cases that are open to interpretation depending on your project’s goals. The comments in backzone may be helpful context.

JC001 · December 18, 2023, 1:30pm

What operations do you need?

Ret_Build_Engineer · December 18, 2023, 11:36pm

Hi;

I’lol take a look at the Matreshka League library.

No need at all; just significant curiosity that such a thing didn’t (apparently) exist.

Thanks,
Ken

JC001 · December 19, 2023, 11:21pm

PragmARC.Date_Handler can do formatting, day-of-week, leap-year, and days-in-month for any year CE in Positive, if that’s of any interest.