Re: Calendar_Utilities package (long posting)

[mfeldman@seas.gwu.edu (Michael Feldman)]

Dave Emery's calendar utilities package is really nice. A quick scan of it 
reveals a small flaw that has bitten me and my students more than once: in
extracting the integer part of Calendar.Seconds(Calendar.Time) the package
is converting to predefined integer. This is not portable, because if it's
late in the day and integer'size = 16 (as is the case on PC's, usually),
the conversion will raise constraint_error. "Mainframe" Ada's generally use
32-bit integer, which is clearly bigger than 86400.0, but Meridian and
Janus both use 16-bit integer. Bad news here. My hack is to convert to
float first. I'm not sure what accuracy problems this might present if
you're working in fractions of a second, but you all get the idea.

Anybody got a cleaner hack than mine? Have a look at this code:
(obviously My_Int_IO is the usual instantiation for predefined integer).
I've tested on both Unix and PC Ada's.
(Please don't flame about the simple-minded repetitive calculations;
I broke it out so the novice could easily understand it).

WITH Text_IO;
WITH My_Int_IO;
WITH Calendar;
PROCEDURE TimeOfDay IS

  CurrentTime :      Calendar.Time;
  SecsPastMidnight : Calendar.Day_Duration;
  MinsPastMidnight : Natural;
  Secs :             Natural;
  Mins :             Natural;
  Hrs :              Natural;

BEGIN -- show time as hh:mm:ss, 24-hr time

  CurrentTime := Calendar.Clock;
  SecsPastMidnight := Calendar.Seconds(CurrentTime);
  MinsPastMidnight := Natural(Float(SecsPastMidnight)/60.0 - 0.5);
  Secs :=  Natural(Float(SecsPastMidnight) - 60.0 * Float(MinsPastMidnight));
  Mins :=             MinsPastMidnight REM 60;
  Hrs :=              MinsPastMidnight / 60;

  My_Int_IO.Put (Item => Hrs, Width => 1);
  Text_IO.Put (Item => ':');
  IF Mins < 10 THEN
     Text_IO.Put (Item => '0');
  END IF;
  My_Int_IO.Put (Item => Mins, Width => 1);
  Text_IO.Put (Item => ':');
  IF Secs < 10 THEN
     Text_IO.Put (Item => '0');
  END IF;
  My_Int_IO.Put (Item => Secs, Width => 1);
  Text_IO.New_Line;

END TimeOfDay;