Re: Ada.Calendar and NTP (and Unix Epoch)

[Adam Beneschan <adam@irvine.com>]

On Monday, July 23, 2012 2:42:32 PM UTC-7, erlo wrote:
> The following code raises an ADA.CALENDAR.TIME_ERROR exception:
> 
> with Calendar;
> with Calendar.Conversions;
> with Calendar.Arithmetic;
> with Calendar.Formatting;
> with Text_IO;
> with Ada.Exceptions;
> 
> use Calendar;
> use Text_IO;
> 
> 
> procedure Main is
>     AdaTid : Time;
> begin
>     AdaTid := Conversions.To_Ada_Time(tm_year  => 00,
>                                       tm_mon   => 00,
>                                       tm_day   => 01,
>                                       tm_hour  => 0,
>                                       tm_min   => 0,
>                                       tm_sec   => 0,
>                                       tm_isdst => 0); -- raises exception
> 
> 
>     put_line(Formatting.Image(Date                  => AdaTid,
>                               Include_Time_Fraction => False,
>                               Time_Zone             => 0));
> 
> end Main;
> 
> This is because Ada.Calendar starts at 1-1-1901. But NTP starts at 
> 1-1-1900, so how can I work my way around this issue?

My gut feeling is that if NTP gives you a time in the range 1-1-1900 to 12-31-1900, something is pretty wrong because computers didn't exist during that time period.  So I'm not really sure what the issue is.  I think you need to be more specific about what you're trying to do.  What kind of value is your program using for an "NTP time"--is it an integer, and if so, what does it represent (seconds since 1-1-1900, nanoseconds since 1-1-1900, or what)?  Are you trying to see if an NTP time is less than or greater than a value of Ada.Calendar.Time, or compute the difference in seconds (or something else) between an NTP time value and an Ada.Calendar.Time value, or what?  

                        -- Adam