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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--              A D A . C A L E N D A R . A R I T H M E T I C               --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--         Copyright (C) 2005-2008, Free Software Foundation, Inc.          --

--                                                                          --

-- This specification is derived from the Ada Reference Manual for use with --

-- GNAT.  In accordance with the copyright of that document, you can freely --

-- copy and modify this specification,  provided that if you redistribute a --

-- modified version,  any changes that you have made are clearly indicated. --

--                                                                          --

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--  This package provides arithmetic operations of time values using days

--  and leap seconds. Ada.Calendar.Arithmetic is defined in the Ada 2005

--  RM (9.6.1).

package Ada.Calendar.Arithmetic is

   --  Arithmetic on days:

   --  Rough estimate on the number of days over the range of Ada time

   type Day_Count is range

     -(366 * (1 + Year_Number'Last - Year_Number'First))

        ..

     +(366 * (1 + Year_Number'Last - Year_Number'First));

   subtype Leap_Seconds_Count is Integer range -2047 .. 2047;

   --  Count of leap seconds. Negative leap seconds occur whenever the

   --  astronomical time is faster than the atomic time or as a result of

   --  Difference when Left < Right.

   procedure Difference

     (Left         : Time;

      Right        : Time;

      Days         : out Day_Count;

      Seconds      : out Duration;

      Leap_Seconds : out Leap_Seconds_Count);

   --  Returns the difference between Left and Right. Days is the number of

   --  days of difference, Seconds is the remainder seconds of difference

   --  excluding leap seconds, and Leap_Seconds is the number of leap seconds.

   --  If Left < Right, then Seconds <= 0.0, Days <= 0, and Leap_Seconds <= 0,

   --  otherwise all values are nonnegative. The absolute value of Seconds is

   --  always less than 86_400.0. For the returned values, if Days = 0, then

   --  Seconds + Duration (Leap_Seconds) = Calendar."-" (Left, Right)

   function "+" (Left : Time;      Right : Day_Count) return Time;

   function "+" (Left : Day_Count; Right : Time)      return Time;

   --  Adds a number of days to a time value. Time_Error is raised if the

   --  result is not representable as a value of type Time.

   function "-" (Left : Time;      Right : Day_Count) return Time;

   --  Subtracts a number of days from a time value. Time_Error is raised if

   --  the result is not representable as a value of type Time.

   function "-" (Left : Time;      Right : Time)      return Day_Count;

   --  Subtracts two time values, and returns the number of days between them.

   --  This is the same value that Difference would return in Days.

end Ada.Calendar.Arithmetic;