g-calend.adb (Has_53_Weeks): Rename to Last_Year_Has_53_Weeks.

2007-09-26  Hristian Kirtchev  <kirtchev@adacore.com>

	* g-calend.adb (Has_53_Weeks): Rename to Last_Year_Has_53_Weeks. Add a
	call to Jan_1_Day _Of_Week to optimize its performance.
	(Is_Leap): Move the routine to the scope of Week_In_Year.
	(Jan_1_Day_Of_Week): New routine in Week_In_Year which calculates the
	weekday on which January 1 falls of Year - 1 and Year + 1. This function
	avoids calling Time_Of and Split, thus making it more efficent.
	(Week_In_Year): Reimplemented in oder to follow ISO 8601.

	* g-calend.ads (Week_In_Year): Change comment to reflect new
	implementation.

From-SVN: r128790

gcc/ada/g-calend.ads

@@ -6,7 +6,7 @@
 --                                                                          --
 --                                 S p e c                                  --
 --                                                                          --
---          Copyright (C) 1999-2006, Free Software Foundation, Inc.         --
+--          Copyright (C) 1999-2007, Free Software Foundation, Inc.         --
 --                                                                          --
 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
 -- terms of the  GNU General Public License as published  by the Free Soft- --
@@ -72,7 +72,13 @@ package GNAT.Calendar is
    --  December is day 365 or 366 for leap year).
 
    function Week_In_Year (Date : Ada.Calendar.Time) return Week_In_Year_Number;
-   --  Returns the week number in the year with Monday as first day of week
+   --  Returns the week number as defined in ISO 8601. A week always starts on
+   --  a Monday and the first week of a particular year is the one containing
+   --  the first Thursday. A year may have 53 weeks when January 1st is a
+   --  Wednesday and the year is leap or January 1st is a Thursday. Note that
+   --  the last days of December may belong to the first week on the next year
+   --  and conversely, the first days of January may belong to the last week
+   --  of the last year.
 
    procedure Split
      (Date       : Ada.Calendar.Time;