From mboxrd@z Thu Jan  1 00:00:00 1970
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From: tmoran@bix.com
Subject: Re: Conversion to UNIX time
Date: 2000/07/20
Message-ID: <noxd5.305$5l.149364@news.pacbell.net>#1/1
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References: <u4s5lop1z.fsf@gsfc.nasa.gov>
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X-Trace: news.pacbell.net 964076179 206.170.2.244 (Wed,
 19 Jul 2000 23:56:19 PDT)
Organization: SBC Internet Services
NNTP-Posting-Date: Wed, 19 Jul 2000 23:56:19 PDT
Newsgroups: comp.lang.ada
Date: 2000-07-20T00:00:00+00:00
List-Id: <comp.lang.ada>

>If you can convert time to an unsigned integer, you're all set.
  Here's code to produce the a day number, with 1 being January 1,
in Ada.Calendar.Year_Number'first.
(Julian_Day(A_Time) - Julian_Day(First_Unix_Date))*24*60*60+Ada.Calendar.Seconds
with appropriate type conversions should give you a (large) unsigned integer.

type Day_Count is range
  -366*(1+Ada.Calendar.Year_Number'last - Ada.Calendar.Year_Number'first)
  ..
  366*(1+Ada.Calendar.Year_Number'last - Ada.Calendar.Year_Number'first);

subtype Is_Leap_Year is Boolean;
Days_Before : constant array(Is_Leap_Year, Ada.Calendar.Month_Number) of Day_Count
    := (False => (0,31,59,90,120,151,181,212,243,273,304,334),
        True  => (0,31,60,91,121,152,182,213,244,274,305,335));

subtype Day_Number_In_Era is Day_Count range 1 .. Day_Count'last;
    --   1 => 1/1/Ada.Calendar.Year_Number'first

function Julian_Day(T : Ada.Calendar.Time) return Day_Number_In_Era is
    This_Year : constant Integer := Integer(Ada.Calendar.Year(T));
    Base_Year : constant Integer := Integer(Ada.Calendar.Year_Number'first);
    Leap_Year : constant Boolean :=
        (This_Year mod 4) = 0
         and ((This_Year mod 400) = 0 or (not (This_Year mod 100 = 0)));
begin
    return Day_Count(This_Year - Base_Year)*365
         + Day_Count((This_Year-1)/4 - (Base_Year-1)/4)
         - Day_Count((This_Year-1)/100 - (Base_Year-1)/100)
         + Day_Count((This_Year-1)/400 - (Base_Year-1)/400)
         + Day_Count(Ada.Calendar.Day(T))
         + Days_Before(Leap_Year, Ada.Calendar.Month(T));
end Julian_Day;