Ada.Calendar."+" gives peculiar result (Gnat 3.13)

Ada.Calendar."+" gives peculiar result (Gnat 3.13)

[Charles Darcy]

Hello,

	I've been using the Ada.Calendar.Time type to represent dates in my
program, and have struck a problem.

	Within a loop, I add (7 * Ada.Calendar.Day_Duration'Last) to an
Ada.Calendar.Time object, at the end of each iteration. I expected this
to advance the time by 1 week, and so it does initially. After a number
of loop iterations, however, the addition seems to advance the time by 1
week and 1 hour.

	Below is code which demonstrates the problem:


      declare
         use Ada.Text_IO;
         use Ada.Calendar;
         The_Year    : Year_Number;
         The_Month   : Month_Number;
         The_Day     : Day_Number;
         The_Seconds : Day_Duration;
         The_Date    : Time        := Time_Of (1995, 12, 2);
      begin
         for Count in 1 .. 100 loop
            Put_Line ("");
            Put_Line ("Iteration: " & Integer'Image (Count));

            Split (The_Date, The_Year, The_Month, The_Day, The_Seconds);
            Put_Line ("The_Date:");
            Put_Line ("  year:    " & Year_Number'Image (The_Year));
            Put_Line ("  month:   " & Month_Number'Image (The_Month));
            Put_Line ("  day:     " & Day_Number'Image (The_Day));
            Put_Line ("  seconds: " & Day_Duration'Image (The_Seconds));

            The_Date := The_Date + 7 * Ada.Calendar.Day_Duration'Last;
         end loop;
      end;


	The output begins with ...

Iteration:  1
The_Date:
  year:     1995
  month:    12
  day:      2
  seconds:  0.000000000

Iteration:  2
The_Date:
  year:     1995
  month:    12
  day:      9
  seconds:  0.000000000

Iteration:  3
The_Date:
  year:     1995
  month:    12
  day:      16
  seconds:  0.000000000


	... which is as I expected. However, later on ...


Iteration:  19
The_Date:
  year:     1996
  month:    4
  day:      6
  seconds:  0.000000000

Iteration:  20
The_Date:
  year:     1996
  month:    4
  day:      13
  seconds:  3600.000000000

Iteration:  21
The_Date:
  year:     1996
  month:    4
  day:      20
  seconds:  3600.000000000


	... an additional hour (the 3600 seconds) seems to have been added.
Still later, the additional hour disappears ...


Iteration:  48
The_Date:
  year:     1996
  month:    10
  day:      26
  seconds:  3600.000000000

Iteration:  49
The_Date:
  year:     1996
  month:    11
  day:      2
  seconds:  0.000000000

Iteration:  50
The_Date:
  year:     1996
  month:    11
  day:      9
  seconds:  0.000000000



	Any ideas as to what is going on ? In case its relevant, I'm using Gnat
3.13p under Linux.


regards,

Charles.


P.S.	Can anyone recommend a good Date package ?

Re: Ada.Calendar."+" gives peculiar result (Gnat 3.13)

[Ian Wild]

Charles Darcy wrote:
> 
> Hello,
> 
>         I've been using the Ada.Calendar.Time type to represent dates in my
> program, and have struck a problem.
> 
>         Within a loop, I add (7 * Ada.Calendar.Day_Duration'Last) to an
> Ada.Calendar.Time object, at the end of each iteration. I expected this
> to advance the time by 1 week, and so it does initially. After a number
> of loop iterations, however, the addition seems to advance the time by 1
> week and 1 hour.

Daylight savings time?

Odd thing is, it seems to be using US rules, and
you're posting from .au, so I'd've expected the
anomalies to happen in the opposite order.

Re: Ada.Calendar."+" gives peculiar result (Gnat 3.13)

[Charles Darcy]

Ian Wild wrote:
> 
> Charles Darcy wrote:
> >
> > Hello,
> >
> >         I've been using the Ada.Calendar.Time type to represent dates in my
> > program, and have struck a problem.
> >
> >         Within a loop, I add (7 * Ada.Calendar.Day_Duration'Last) to an
> > Ada.Calendar.Time object, at the end of each iteration. I expected this
> > to advance the time by 1 week, and so it does initially. After a number
> > of loop iterations, however, the addition seems to advance the time by 1
> > week and 1 hour.
> 
> Daylight savings time?

	Yes, the problem seems related to Daylight Savings Time. The dates on
which the extra hour appears and disappears, correspond to DST begin/end
dates.

> 
> Odd thing is, it seems to be using US rules, and
> you're posting from .au, so I'd've expected the
> anomalies to happen in the opposite order.


	I've just checked the Linux system time zone and found it set to
Abidjan, Africa. I set the correct zone (NSW, Australia), re-run the
test, and found that the additional hour has disappeared altogether. The
time now advances one week exactly, irrespective of whether daylight
savings time is in effect.

Re: Ada.Calendar."+" gives peculiar result (Gnat 3.13)

[Karel Thönissen]

Charles Darcy schreef:
> 
> Hello,
> 
>         I've been using the Ada.Calendar.Time type to represent dates in my
> program, and have struck a problem.
> 
>         Within a loop, I add (7 * Ada.Calendar.Day_Duration'Last) to an
> Ada.Calendar.Time object, at the end of each iteration. I expected this
> to advance the time by 1 week, and so it does initially. After a number
> of loop iterations, however, the addition seems to advance the time by 1
> week and 1 hour.

[code snipped]

>         Any ideas as to what is going on ? In case its relevant, I'm using Gnat
> 3.13p under Linux.

Daylight-saving / summertime.

-- 

Groeten, Karel Th�nissen

Hello Technologies develops high-integrity software for complex systems

Re: Ada.Calendar."+" gives peculiar result (Gnat 3.13)

[Charles Darcy]

Karel Th�nissen wrote:
> 
> Charles Darcy schreef:
> >
> > Hello,
> >
> >         I've been using the Ada.Calendar.Time type to represent dates in my
> > program, and have struck a problem.
> >
> >         Within a loop, I add (7 * Ada.Calendar.Day_Duration'Last) to an
> > Ada.Calendar.Time object, at the end of each iteration. I expected this
> > to advance the time by 1 week, and so it does initially. After a number
> > of loop iterations, however, the addition seems to advance the time by 1
> > week and 1 hour.
> 
> [code snipped]
> 
> >         Any ideas as to what is going on ? In case its relevant, I'm using Gnat
> > 3.13p under Linux.
> 
> Daylight-saving / summertime.


	Of course. Thanks (and sorry for being dense).