Fix PR ada/111813 (Inconsistent limit in Ada.Calendar.Formatting)

The description of the second Value function (returning Duration) (ARM 9.6.1(87)
doesn't place any limitation on the Elapsed_Time parameter's value, beyond
"Constraint_Error is raised if the string is not formatted as described for Image, or
the function cannot interpret the given string as a Duration value".

It would seem reasonable that Value and Image should be consistent, in that any
string produced by Image should be accepted by Value. Since Image must produce
a two-digit representation of the Hours, there's an implication that its
Elapsed_Time parameter should be less than 100.0 hours (the ARM merely says
that in that case the result is implementation-defined).

The current implementation of Value raises Constraint_Error if the Elapsed_Time
parameter is greater than or equal to 24 hours.

This patch removes the restriction, so that the Elapsed_Time parameter must only
be less than 100.0 hours.

2023-10-15 Simon Wright <simon@pushface.org>

	PR ada/111813
gcc/ada/
	* libgnat/a-calfor.adb (Value (2)): Allow values of
	parameter Elapsed_Time greater than or equal to 24 hours, by doing
	the hour calculations in Natural rather than Hour_Number (0 ..
	23). Calculate the result directly rather than by using Seconds_Of
	(whose Hour parameter is of type Hour_Number).
	If an exception occurs of type Constraint_Error, re-raise it
	rather than raising a new CE.

gcc/testsuite/
	* gnat.dg/calendar_format_value.adb: New test.

2 files changed, 34 insertions, 3 deletions

diff --git a/gcc/ada/libgnat/a-calfor.adb b/gcc/ada/libgnat/a-calfor.adb
index 18f4e73..493728b 100644
--- a/gcc/ada/libgnat/a-calfor.adb
+++ b/gcc/ada/libgnat/a-calfor.adb
@@ -777,7 +777,7 @@ package body Ada.Calendar.Formatting is
 
    function Value (Elapsed_Time : String) return Duration is
       D          : String (1 .. 11);
-      Hour       : Hour_Number;
+      Hour       : Natural;
       Minute     : Minute_Number;
       Second     : Second_Number;
       Sub_Second : Second_Duration := 0.0;
@@ -817,7 +817,7 @@ package body Ada.Calendar.Formatting is
 
       --  Value extraction
 
-      Hour   := Hour_Number   (Hour_Number'Value   (D (1 .. 2)));
+      Hour   := Natural       (Natural'Value       (D (1 .. 2)));
       Minute := Minute_Number (Minute_Number'Value (D (4 .. 5)));
       Second := Second_Number (Second_Number'Value (D (7 .. 8)));
 
@@ -837,9 +837,14 @@ package body Ada.Calendar.Formatting is
          raise Constraint_Error;
       end if;
 
-      return Seconds_Of (Hour, Minute, Second, Sub_Second);
+      return Duration (Hour * 3600)
+        + Duration (Minute * 60)
+        + Duration (Second)
+        + Sub_Second;
 
    exception
+      --  CE is mandated, but preserve trace if CE already.
+      when Constraint_Error => raise;
       when others => raise Constraint_Error;
    end Value;
 
diff --git a/gcc/testsuite/gnat.dg/calendar_format_value.adb b/gcc/testsuite/gnat.dg/calendar_format_value.adb
new file mode 100644
index 0000000..e98e496
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/calendar_format_value.adb
@@ -0,0 +1,26 @@
+-- { dg-do run }
+-- { dg-options "-O2" }
+
+with Ada.Calendar.Formatting;
+
+procedure Calendar_Format_Value is
+   Limit : constant Duration
+     := 99 * 3600.0 + 59 * 60.0 + 59.0;
+begin
+   declare
+      Image : constant String := Ada.Calendar.Formatting .Image (Limit);
+      Image_Error : exception;
+   begin
+      if Image /= "99:59:59" then
+         raise Image_Error with "image: " & Image;
+      end if;
+      declare
+         Value : constant Duration := Ada.Calendar.Formatting.Value (Image);
+         Value_Error : exception;
+      begin
+         if Value /= Limit then
+            raise Value_Error with "duration: " & Value'Image;
+         end if;
+      end;
+   end;
+end Calendar_Format_Value;