1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--              A D A . C A L E N D A R . A R I T H M E T I C               --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--         Copyright (C) 2005-2008, Free Software Foundation, Inc.          --
10--                                                                          --
11-- This specification is derived from the Ada Reference Manual for use with --
12-- GNAT.  In accordance with the copyright of that document, you can freely --
13-- copy and modify this specification,  provided that if you redistribute a --
14-- modified version,  any changes that you have made are clearly indicated. --
15--                                                                          --
16------------------------------------------------------------------------------
17
18--  This package provides arithmetic operations of time values using days
19--  and leap seconds. Ada.Calendar.Arithmetic is defined in the Ada 2005
20--  RM (9.6.1).
21
22package Ada.Calendar.Arithmetic is
23
24   --  Arithmetic on days:
25
26   --  Rough estimate on the number of days over the range of Ada time
27
28   type Day_Count is range
29     -(366 * (1 + Year_Number'Last - Year_Number'First))
30        ..
31     +(366 * (1 + Year_Number'Last - Year_Number'First));
32
33   subtype Leap_Seconds_Count is Integer range -2047 .. 2047;
34   --  Count of leap seconds. Negative leap seconds occur whenever the
35   --  astronomical time is faster than the atomic time or as a result of
36   --  Difference when Left < Right.
37
38   procedure Difference
39     (Left         : Time;
40      Right        : Time;
41      Days         : out Day_Count;
42      Seconds      : out Duration;
43      Leap_Seconds : out Leap_Seconds_Count);
44   --  Returns the difference between Left and Right. Days is the number of
45   --  days of difference, Seconds is the remainder seconds of difference
46   --  excluding leap seconds, and Leap_Seconds is the number of leap seconds.
47   --  If Left < Right, then Seconds <= 0.0, Days <= 0, and Leap_Seconds <= 0,
48   --  otherwise all values are nonnegative. The absolute value of Seconds is
49   --  always less than 86_400.0. For the returned values, if Days = 0, then
50   --  Seconds + Duration (Leap_Seconds) = Calendar."-" (Left, Right)
51
52   function "+" (Left : Time;      Right : Day_Count) return Time;
53   function "+" (Left : Day_Count; Right : Time)      return Time;
54   --  Adds a number of days to a time value. Time_Error is raised if the
55   --  result is not representable as a value of type Time.
56
57   function "-" (Left : Time;      Right : Day_Count) return Time;
58   --  Subtracts a number of days from a time value. Time_Error is raised if
59   --  the result is not representable as a value of type Time.
60
61   function "-" (Left : Time;      Right : Time)      return Day_Count;
62   --  Subtracts two time values, and returns the number of days between them.
63   --  This is the same value that Difference would return in Days.
64
65end Ada.Calendar.Arithmetic;
66