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------------------------------------------------------------------------------
--                                                                          --
--                         GNAT LIBRARY COMPONENTS                          --
--                                                                          --
--    A D A . C O N T A I N E R S . I N D E F I N I T E _ V E C T O R S     --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 2004-2005, Free Software Foundation, Inc.         --
--                                                                          --
-- This specification is derived from the Ada Reference Manual for use with --
-- GNAT. The copyright notice above, and the license provisions that follow --
-- apply solely to the  contents of the part following the private keyword. --
--                                                                          --
-- 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- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
-- Boston, MA 02110-1301, USA.                                              --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- This unit has originally being developed by Matthew J Heaney.            --
------------------------------------------------------------------------------
 
with Ada.Containers.Generic_Array_Sort;
with Ada.Unchecked_Deallocation;
with System;  use type System.Address;
 
package body Ada.Containers.Indefinite_Vectors is
 
   type Int is range System.Min_Int .. System.Max_Int;
 
   procedure Free is
     new Ada.Unchecked_Deallocation (Elements_Type, Elements_Access);
 
   procedure Free is
     new Ada.Unchecked_Deallocation (Element_Type, Element_Access);
 
   ---------
   -- "&" --
   ---------
 
   function "&" (Left, Right : Vector) return Vector is
      LN : constant Count_Type := Length (Left);
      RN : constant Count_Type := Length (Right);
 
   begin
      if LN = 0 then
         if RN = 0 then
            return Empty_Vector;
         end if;
 
         declare
            RE : Elements_Type renames
                   Right.Elements (Index_Type'First .. Right.Last);
 
            Elements : Elements_Access :=
                         new Elements_Type (RE'Range);
 
         begin
            for I in Elements'Range loop
               begin
                  if RE (I) /= null then
                     Elements (I) := new Element_Type'(RE (I).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            return (Controlled with Elements, Right.Last, 0, 0);
         end;
 
      end if;
 
      if RN = 0 then
         declare
            LE : Elements_Type renames
                   Left.Elements (Index_Type'First .. Left.Last);
 
            Elements : Elements_Access :=
                         new Elements_Type (LE'Range);
 
         begin
            for I in Elements'Range loop
               begin
                  if LE (I) /= null then
                     Elements (I) := new Element_Type'(LE (I).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            return (Controlled with Elements, Left.Last, 0, 0);
         end;
      end if;
 
      declare
         Last_As_Int : constant Int'Base :=  -- TODO: handle overflow
                         Int (Index_Type'First) + Int (LN) + Int (RN) - 1;
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         declare
            Last : constant Index_Type := Index_Type (Last_As_Int);
 
            LE : Elements_Type renames
                   Left.Elements (Index_Type'First .. Left.Last);
 
            RE : Elements_Type renames
                   Right.Elements (Index_Type'First .. Right.Last);
 
            Elements : Elements_Access :=
                         new Elements_Type (Index_Type'First .. Last);
 
            I : Index_Type'Base := No_Index;
 
         begin
            for LI in LE'Range loop
               I := I + 1;
 
               begin
                  if LE (LI) /= null then
                     Elements (I) := new Element_Type'(LE (LI).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            for RI in RE'Range loop
               I := I + 1;
 
               begin
                  if RE (RI) /= null then
                     Elements (I) := new Element_Type'(RE (RI).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            return (Controlled with Elements, Last, 0, 0);
         end;
      end;
   end "&";
 
   function "&" (Left : Vector; Right : Element_Type) return Vector is
      LN : constant Count_Type := Length (Left);
 
   begin
      if LN = 0 then
         declare
            subtype Elements_Subtype is
              Elements_Type (Index_Type'First .. Index_Type'First);
 
            Elements : Elements_Access := new Elements_Subtype;
 
         begin
            begin
               Elements (Elements'First) := new Element_Type'(Right);
            exception
               when others =>
                  Free (Elements);
                  raise;
            end;
 
            return (Controlled with Elements, Index_Type'First, 0, 0);
         end;
      end if;
 
      declare
         Last_As_Int : constant Int'Base :=
                         Int (Index_Type'First) + Int (LN);
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         declare
            Last : constant Index_Type := Index_Type (Last_As_Int);
 
            LE : Elements_Type renames
                   Left.Elements (Index_Type'First .. Left.Last);
 
            Elements : Elements_Access :=
                        new Elements_Type (Index_Type'First .. Last);
 
         begin
            for I in LE'Range loop
               begin
                  if LE (I) /= null then
                     Elements (I) := new Element_Type'(LE (I).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            begin
               Elements (Elements'Last) := new Element_Type'(Right);
            exception
               when others =>
                  for J in Index_Type'First .. Elements'Last - 1 loop
                     Free (Elements (J));
                  end loop;
 
                  Free (Elements);
                  raise;
            end;
 
            return (Controlled with Elements, Last, 0, 0);
         end;
      end;
   end "&";
 
   function "&" (Left : Element_Type; Right : Vector) return Vector is
      RN : constant Count_Type := Length (Right);
 
   begin
      if RN = 0 then
         declare
            subtype Elements_Subtype is
              Elements_Type (Index_Type'First .. Index_Type'First);
 
            Elements : Elements_Access := new Elements_Subtype;
 
         begin
            begin
               Elements (Elements'First) := new Element_Type'(Left);
            exception
               when others =>
                  Free (Elements);
                  raise;
            end;
 
            return (Controlled with Elements, Index_Type'First, 0, 0);
         end;
      end if;
 
      declare
         Last_As_Int : constant Int'Base :=
                         Int (Index_Type'First) + Int (RN);
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         declare
            Last : constant Index_Type := Index_Type (Last_As_Int);
 
            RE : Elements_Type renames
                   Right.Elements (Index_Type'First .. Right.Last);
 
            Elements : Elements_Access :=
                         new Elements_Type (Index_Type'First .. Last);
 
            I : Index_Type'Base := Index_Type'First;
 
         begin
            begin
               Elements (I) := new Element_Type'(Left);
            exception
               when others =>
                  Free (Elements);
                  raise;
            end;
 
            for RI in RE'Range loop
               I := I + 1;
 
               begin
                  if RE (RI) /= null then
                     Elements (I) := new Element_Type'(RE (RI).all);
                  end if;
               exception
                  when others =>
                     for J in Index_Type'First .. I - 1 loop
                        Free (Elements (J));
                     end loop;
 
                     Free (Elements);
                     raise;
               end;
            end loop;
 
            return (Controlled with Elements, Last, 0, 0);
         end;
      end;
   end "&";
 
   function "&" (Left, Right : Element_Type) return Vector is
   begin
      if Index_Type'First >= Index_Type'Last then
         raise Constraint_Error;
      end if;
 
      declare
         Last : constant Index_Type := Index_Type'First + 1;
 
         subtype ET is Elements_Type (Index_Type'First .. Last);
 
         Elements : Elements_Access := new ET;
      begin
         begin
            Elements (Elements'First) := new Element_Type'(Left);
         exception
            when others =>
               Free (Elements);
               raise;
         end;
 
         begin
            Elements (Elements'Last) := new Element_Type'(Right);
         exception
            when others =>
               Free (Elements (Elements'First));
               Free (Elements);
               raise;
         end;
 
         return (Controlled with Elements, Elements'Last, 0, 0);
      end;
   end "&";
 
   ---------
   -- "=" --
   ---------
 
   function "=" (Left, Right : Vector) return Boolean is
   begin
      if Left'Address = Right'Address then
         return True;
      end if;
 
      if Left.Last /= Right.Last then
         return False;
      end if;
 
      for J in Index_Type'First .. Left.Last loop
         if Left.Elements (J) = null then
            if Right.Elements (J) /= null then
               return False;
            end if;
 
         elsif Right.Elements (J) = null then
            return False;
 
         elsif Left.Elements (J).all /= Right.Elements (J).all then
            return False;
         end if;
      end loop;
 
      return True;
   end "=";
 
   ------------
   -- Adjust --
   ------------
 
   procedure Adjust (Container : in out Vector) is
   begin
      if Container.Last = No_Index then
         Container.Elements := null;
         return;
      end if;
 
      declare
         E : Elements_Type renames Container.Elements.all;
         L : constant Index_Type := Container.Last;
 
      begin
         Container.Elements := null;
         Container.Last := No_Index;
         Container.Busy := 0;
         Container.Lock := 0;
 
         Container.Elements := new Elements_Type (Index_Type'First .. L);
 
         for I in Container.Elements'Range loop
            if E (I) /= null then
               Container.Elements (I) := new Element_Type'(E (I).all);
            end if;
 
            Container.Last := I;
         end loop;
      end;
   end Adjust;
 
   ------------
   -- Append --
   ------------
 
   procedure Append (Container : in out Vector; New_Item : Vector) is
   begin
      if Is_Empty (New_Item) then
         return;
      end if;
 
      if Container.Last = Index_Type'Last then
         raise Constraint_Error;
      end if;
 
      Insert
        (Container,
         Container.Last + 1,
         New_Item);
   end Append;
 
   procedure Append
     (Container : in out Vector;
      New_Item  : Element_Type;
      Count     : Count_Type := 1)
   is
   begin
      if Count = 0 then
         return;
      end if;
 
      if Container.Last = Index_Type'Last then
         raise Constraint_Error;
      end if;
 
      Insert
        (Container,
         Container.Last + 1,
         New_Item,
         Count);
   end Append;
 
   --------------
   -- Capacity --
   --------------
 
   function Capacity (Container : Vector) return Count_Type is
   begin
      if Container.Elements = null then
         return 0;
      end if;
 
      return Container.Elements'Length;
   end Capacity;
 
   -----------
   -- Clear --
   -----------
 
   procedure Clear (Container : in out Vector) is
   begin
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      while Container.Last >= Index_Type'First loop
         declare
            X : Element_Access := Container.Elements (Container.Last);
         begin
            Container.Elements (Container.Last) := null;
            Container.Last := Container.Last - 1;
            Free (X);
         end;
      end loop;
   end Clear;
 
   --------------
   -- Contains --
   --------------
 
   function Contains
     (Container : Vector;
      Item      : Element_Type) return Boolean
   is
   begin
      return Find_Index (Container, Item) /= No_Index;
   end Contains;
 
   ------------
   -- Delete --
   ------------
 
   procedure Delete
     (Container : in out Vector;
      Index     : Extended_Index;
      Count     : Count_Type := 1)
   is
   begin
      if Index < Index_Type'First then
         raise Constraint_Error;
      end if;
 
      if Index > Container.Last then
         if Index > Container.Last + 1 then
            raise Constraint_Error;
         end if;
 
         return;
      end if;
 
      if Count = 0 then
         return;
      end if;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      declare
         Index_As_Int    : constant Int := Int (Index);
         Old_Last_As_Int : constant Int := Int (Container.Last);
 
         --  TODO: somewhat vestigial...fix ???
         Count1 : constant Int'Base := Int (Count);
         Count2 : constant Int'Base := Old_Last_As_Int - Index_As_Int + 1;
         N      : constant Int'Base := Int'Min (Count1, Count2);
 
         J_As_Int : constant Int'Base := Index_As_Int + N;
         E        : Elements_Type renames Container.Elements.all;
 
      begin
         if J_As_Int > Old_Last_As_Int then
            while Container.Last >= Index loop
               declare
                  K : constant Index_Type := Container.Last;
                  X : Element_Access := E (K);
 
               begin
                  E (K) := null;
                  Container.Last := K - 1;
                  Free (X);
               end;
            end loop;
 
         else
            declare
               J : constant Index_Type := Index_Type (J_As_Int);
 
               New_Last_As_Int : constant Int'Base := Old_Last_As_Int - N;
               New_Last        : constant Index_Type :=
                                   Index_Type (New_Last_As_Int);
 
            begin
               for K in Index .. J - 1 loop
                  declare
                     X : Element_Access := E (K);
                  begin
                     E (K) := null;
                     Free (X);
                  end;
               end loop;
 
               E (Index .. New_Last) := E (J .. Container.Last);
               Container.Last := New_Last;
            end;
         end if;
      end;
   end Delete;
 
   procedure Delete
     (Container : in out Vector;
      Position  : in out Cursor;
      Count     : Count_Type := 1)
   is
   begin
      if Position.Container = null then
         raise Constraint_Error;
      end if;
 
      if Position.Container /= Container'Unchecked_Access
        or else Position.Index > Container.Last
      then
         raise Program_Error;
      end if;
 
      Delete (Container, Position.Index, Count);
 
      Position := No_Element;  -- See comment in a-convec.adb
   end Delete;
 
   ------------------
   -- Delete_First --
   ------------------
 
   procedure Delete_First
     (Container : in out Vector;
      Count     : Count_Type := 1)
   is
   begin
      if Count = 0 then
         return;
      end if;
 
      if Count >= Length (Container) then
         Clear (Container);
         return;
      end if;
 
      Delete (Container, Index_Type'First, Count);
   end Delete_First;
 
   -----------------
   -- Delete_Last --
   -----------------
 
   procedure Delete_Last
     (Container : in out Vector;
      Count     : Count_Type := 1)
   is
      N : constant Count_Type := Length (Container);
 
   begin
      if Count = 0
        or else N = 0
      then
         return;
      end if;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      declare
         E : Elements_Type renames Container.Elements.all;
 
      begin
         for Indx in 1 .. Count_Type'Min (Count, N) loop
            declare
               J : constant Index_Type := Container.Last;
               X : Element_Access := E (J);
 
            begin
               E (J) := null;
               Container.Last := J - 1;
               Free (X);
            end;
         end loop;
      end;
   end Delete_Last;
 
   -------------
   -- Element --
   -------------
 
   function Element
     (Container : Vector;
      Index     : Index_Type) return Element_Type
   is
   begin
      if Index > Container.Last then
         raise Constraint_Error;
      end if;
 
      declare
         EA : constant Element_Access := Container.Elements (Index);
 
      begin
         if EA = null then
            raise Constraint_Error;
         end if;
 
         return EA.all;
      end;
   end Element;
 
   function Element (Position : Cursor) return Element_Type is
   begin
      if Position.Container = null then
         raise Constraint_Error;
      end if;
 
      return Element (Position.Container.all, Position.Index);
   end Element;
 
   --------------
   -- Finalize --
   --------------
 
   procedure Finalize (Container : in out Vector) is
   begin
      Clear (Container);
 
      declare
         X : Elements_Access := Container.Elements;
      begin
         Container.Elements := null;
         Free (X);
      end;
   end Finalize;
 
   ----------
   -- Find --
   ----------
 
   function Find
     (Container : Vector;
      Item      : Element_Type;
      Position  : Cursor := No_Element) return Cursor
   is
   begin
      if Position.Container /= null
        and then (Position.Container /= Container'Unchecked_Access
                    or else Position.Index > Container.Last)
      then
         raise Program_Error;
      end if;
 
      for J in Position.Index .. Container.Last loop
         if Container.Elements (J) /= null
           and then Container.Elements (J).all = Item
         then
            return (Container'Unchecked_Access, J);
         end if;
      end loop;
 
      return No_Element;
   end Find;
 
   ----------------
   -- Find_Index --
   ----------------
 
   function Find_Index
     (Container : Vector;
      Item      : Element_Type;
      Index     : Index_Type := Index_Type'First) return Extended_Index
   is
   begin
      for Indx in Index .. Container.Last loop
         if Container.Elements (Indx) /= null
           and then Container.Elements (Indx).all = Item
         then
            return Indx;
         end if;
      end loop;
 
      return No_Index;
   end Find_Index;
 
   -----------
   -- First --
   -----------
 
   function First (Container : Vector) return Cursor is
   begin
      if Is_Empty (Container) then
         return No_Element;
      end if;
 
      return (Container'Unchecked_Access, Index_Type'First);
   end First;
 
   -------------------
   -- First_Element --
   -------------------
 
   function First_Element (Container : Vector) return Element_Type is
   begin
      return Element (Container, Index_Type'First);
   end First_Element;
 
   -----------------
   -- First_Index --
   -----------------
 
   function First_Index (Container : Vector) return Index_Type is
      pragma Unreferenced (Container);
   begin
      return Index_Type'First;
   end First_Index;
 
   ---------------------
   -- Generic_Sorting --
   ---------------------
 
   package body Generic_Sorting is
 
      -----------------------
      -- Local Subprograms --
      -----------------------
 
      function Is_Less (L, R : Element_Access) return Boolean;
      pragma Inline (Is_Less);
 
      -------------
      -- Is_Less --
      -------------
 
      function Is_Less (L, R : Element_Access) return Boolean is
      begin
         if L = null then
            return R /= null;
         elsif R = null then
            return False;
         else
            return L.all < R.all;
         end if;
      end Is_Less;
 
      ---------------
      -- Is_Sorted --
      ---------------
 
      function Is_Sorted (Container : Vector) return Boolean is
      begin
         if Container.Last <= Index_Type'First then
            return True;
         end if;
 
         declare
            E : Elements_Type renames Container.Elements.all;
         begin
            for I in Index_Type'First .. Container.Last - 1 loop
               if Is_Less (E (I + 1), E (I)) then
                  return False;
               end if;
            end loop;
         end;
 
         return True;
      end Is_Sorted;
 
      -----------
      -- Merge --
      -----------
 
      procedure Merge (Target, Source : in out Vector) is
         I : Index_Type'Base := Target.Last;
         J : Index_Type'Base;
 
      begin
         if Target.Last < Index_Type'First then
            Move (Target => Target, Source => Source);
            return;
         end if;
 
         if Target'Address = Source'Address then
            return;
         end if;
 
         if Source.Last < Index_Type'First then
            return;
         end if;
 
         if Source.Busy > 0 then
            raise Program_Error;
         end if;
 
         Target.Set_Length (Length (Target) + Length (Source));
 
         J := Target.Last;
         while Source.Last >= Index_Type'First loop
            if I < Index_Type'First then
               declare
                  Src : Elements_Type renames
                    Source.Elements (Index_Type'First .. Source.Last);
 
               begin
                  Target.Elements (Index_Type'First .. J) := Src;
                  Src := (others => null);
               end;
 
               Source.Last := No_Index;
               return;
            end if;
 
            declare
               Src : Element_Access renames Source.Elements (Source.Last);
               Tgt : Element_Access renames Target.Elements (I);
 
            begin
               if Is_Less (Src, Tgt) then
                  Target.Elements (J) := Tgt;
                  Tgt := null;
                  I := I - 1;
 
               else
                  Target.Elements (J) := Src;
                  Src := null;
                  Source.Last := Source.Last - 1;
               end if;
            end;
 
            J := J - 1;
         end loop;
      end Merge;
 
      ----------
      -- Sort --
      ----------
 
      procedure Sort (Container : in out Vector)
      is
         procedure Sort is
            new Generic_Array_Sort
             (Index_Type   => Index_Type,
              Element_Type => Element_Access,
              Array_Type   => Elements_Type,
              "<"          => Is_Less);
 
      --  Start of processing for Sort
 
      begin
         if Container.Last <= Index_Type'First then
            return;
         end if;
 
         if Container.Lock > 0 then
            raise Program_Error;
         end if;
 
         Sort (Container.Elements (Index_Type'First .. Container.Last));
      end Sort;
 
   end Generic_Sorting;
 
   -----------------
   -- Has_Element --
   -----------------
 
   function Has_Element (Position : Cursor) return Boolean is
   begin
      if Position.Container = null then
         return False;
      end if;
 
      return Position.Index <= Position.Container.Last;
   end Has_Element;
 
   ------------
   -- Insert --
   ------------
 
   procedure Insert
     (Container : in out Vector;
      Before    : Extended_Index;
      New_Item  : Element_Type;
      Count     : Count_Type := 1)
   is
      N : constant Int := Int (Count);
 
      New_Last_As_Int : Int'Base;
      New_Last        : Index_Type;
 
      Dst : Elements_Access;
 
   begin
      if Before < Index_Type'First then
         raise Constraint_Error;
      end if;
 
      if Before > Container.Last
        and then Before > Container.Last + 1
      then
         raise Constraint_Error;
      end if;
 
      if Count = 0 then
         return;
      end if;
 
      declare
         Old_Last_As_Int : constant Int := Int (Container.Last);
 
      begin
         New_Last_As_Int := Old_Last_As_Int + N;
 
         if New_Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         New_Last := Index_Type (New_Last_As_Int);
      end;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      if Container.Elements = null then
         Container.Elements :=
           new Elements_Type (Index_Type'First .. New_Last);
 
         Container.Last := No_Index;
 
         for J in Container.Elements'Range loop
            Container.Elements (J) := new Element_Type'(New_Item);
            Container.Last := J;
         end loop;
 
         return;
      end if;
 
      if New_Last <= Container.Elements'Last then
         declare
            E : Elements_Type renames Container.Elements.all;
         begin
            if Before <= Container.Last then
               declare
                  Index_As_Int : constant Int'Base :=
                                   Index_Type'Pos (Before) + N;
 
                  Index : constant Index_Type := Index_Type (Index_As_Int);
 
                  J : Index_Type'Base := Before;
 
               begin
                  E (Index .. New_Last) := E (Before .. Container.Last);
                  Container.Last := New_Last;
 
                  while J < Index loop
                     E (J) := new Element_Type'(New_Item);
                     J := J + 1;
                  end loop;
               exception
                  when others =>
                     E (J .. Index - 1) := (others => null);
                     raise;
               end;
 
            else
               for J in Before .. New_Last loop
                  E (J) := new Element_Type'(New_Item);
                  Container.Last := J;
               end loop;
            end if;
         end;
 
         return;
      end if;
 
      declare
         First    : constant Int := Int (Index_Type'First);
         New_Size : constant Int'Base := New_Last_As_Int - First + 1;
         Size     : Int'Base := Int'Max (1, Container.Elements'Length);
 
      begin
         while Size < New_Size loop
            if Size > Int'Last / 2 then
               Size := Int'Last;
               exit;
            end if;
 
            Size := 2 * Size;
         end loop;
 
         --  TODO: The following calculations aren't quite right, since
         --  there will be overflow if Index_Type'Range is very large
         --  (e.g. this package is instantiated with a 64-bit integer).
         --  END TODO.
 
         declare
            Max_Size : constant Int'Base := Int (Index_Type'Last) - First + 1;
         begin
            if Size > Max_Size then
               Size := Max_Size;
            end if;
         end;
 
         declare
            Dst_Last : constant Index_Type := Index_Type (First + Size - 1);
         begin
            Dst := new Elements_Type (Index_Type'First .. Dst_Last);
         end;
      end;
 
      if Before <= Container.Last then
         declare
            Index_As_Int : constant Int'Base :=
                             Index_Type'Pos (Before) + N;
 
            Index : constant Index_Type := Index_Type (Index_As_Int);
 
            Src : Elements_Access := Container.Elements;
 
         begin
            Dst (Index_Type'First .. Before - 1) :=
              Src (Index_Type'First .. Before - 1);
 
            Dst (Index .. New_Last) := Src (Before .. Container.Last);
 
            Container.Elements := Dst;
            Container.Last := New_Last;
            Free (Src);
 
            for J in Before .. Index - 1 loop
               Dst (J) := new Element_Type'(New_Item);
            end loop;
         end;
 
      else
         declare
            Src : Elements_Access := Container.Elements;
 
         begin
            Dst (Index_Type'First .. Container.Last) :=
              Src (Index_Type'First .. Container.Last);
 
            Container.Elements := Dst;
            Free (Src);
 
            for J in Before .. New_Last loop
               Dst (J) := new Element_Type'(New_Item);
               Container.Last := J;
            end loop;
         end;
      end if;
   end Insert;
 
   procedure Insert
     (Container : in out Vector;
      Before    : Extended_Index;
      New_Item  : Vector)
   is
      N : constant Count_Type := Length (New_Item);
 
   begin
      if Before < Index_Type'First then
         raise Constraint_Error;
      end if;
 
      if Before > Container.Last
        and then Before > Container.Last + 1
      then
         raise Constraint_Error;
      end if;
 
      if N = 0 then
         return;
      end if;
 
      Insert_Space (Container, Before, Count => N);
 
      declare
         Dst_Last_As_Int : constant Int'Base :=
                             Int'Base (Before) + Int'Base (N) - 1;
 
         Dst_Last : constant Index_Type := Index_Type (Dst_Last_As_Int);
 
         Dst : Elements_Type renames
                 Container.Elements (Before .. Dst_Last);
 
         Dst_Index : Index_Type'Base := Before - 1;
 
      begin
         if Container'Address /= New_Item'Address then
            declare
               Src : Elements_Type renames
                       New_Item.Elements (Index_Type'First .. New_Item.Last);
 
            begin
               for Src_Index in Src'Range loop
                  Dst_Index := Dst_Index + 1;
 
                  if Src (Src_Index) /= null then
                     Dst (Dst_Index) := new Element_Type'(Src (Src_Index).all);
                  end if;
               end loop;
            end;
 
            return;
         end if;
 
         declare
            subtype Src_Index_Subtype is Index_Type'Base range
              Index_Type'First .. Before - 1;
 
            Src : Elements_Type renames
                    Container.Elements (Src_Index_Subtype);
 
         begin
            for Src_Index in Src'Range loop
               Dst_Index := Dst_Index + 1;
 
               if Src (Src_Index) /= null then
                  Dst (Dst_Index) := new Element_Type'(Src (Src_Index).all);
               end if;
            end loop;
         end;
 
         if Dst_Last = Container.Last then
            return;
         end if;
 
         declare
            subtype Src_Index_Subtype is Index_Type'Base range
              Dst_Last + 1 .. Container.Last;
 
            Src : Elements_Type renames
                    Container.Elements (Src_Index_Subtype);
 
         begin
            for Src_Index in Src'Range loop
               Dst_Index := Dst_Index + 1;
 
               if Src (Src_Index) /= null then
                  Dst (Dst_Index) := new Element_Type'(Src (Src_Index).all);
               end if;
            end loop;
         end;
      end;
   end Insert;
 
   procedure Insert
     (Container : in out Vector;
      Before    : Cursor;
      New_Item  : Vector)
   is
      Index : Index_Type'Base;
 
   begin
      if Before.Container /= null
        and then Before.Container /= Container'Unchecked_Access
      then
         raise Program_Error;
      end if;
 
      if Is_Empty (New_Item) then
         return;
      end if;
 
      if Before.Container = null
        or else Before.Index > Container.Last
      then
         if Container.Last = Index_Type'Last then
            raise Constraint_Error;
         end if;
 
         Index := Container.Last + 1;
 
      else
         Index := Before.Index;
      end if;
 
      Insert (Container, Index, New_Item);
   end Insert;
 
   procedure Insert
     (Container : in out Vector;
      Before    : Cursor;
      New_Item  : Vector;
      Position  : out Cursor)
   is
      Index : Index_Type'Base;
 
   begin
      if Before.Container /= null
        and then Before.Container /= Vector_Access'(Container'Unchecked_Access)
      then
         raise Program_Error;
      end if;
 
      if Is_Empty (New_Item) then
         if Before.Container = null
           or else Before.Index > Container.Last
         then
            Position := No_Element;
         else
            Position := (Container'Unchecked_Access, Before.Index);
         end if;
 
         return;
      end if;
 
      if Before.Container = null
        or else Before.Index > Container.Last
      then
         if Container.Last = Index_Type'Last then
            raise Constraint_Error;
         end if;
 
         Index := Container.Last + 1;
 
      else
         Index := Before.Index;
      end if;
 
      Insert (Container, Index, New_Item);
 
      Position := Cursor'(Container'Unchecked_Access, Index);
   end Insert;
 
   procedure Insert
     (Container : in out Vector;
      Before    : Cursor;
      New_Item  : Element_Type;
      Count     : Count_Type := 1)
   is
      Index : Index_Type'Base;
 
   begin
      if Before.Container /= null
        and then Before.Container /= Vector_Access'(Container'Unchecked_Access)
      then
         raise Program_Error;
      end if;
 
      if Count = 0 then
         return;
      end if;
 
      if Before.Container = null
        or else Before.Index > Container.Last
      then
         if Container.Last = Index_Type'Last then
            raise Constraint_Error;
         end if;
 
         Index := Container.Last + 1;
 
      else
         Index := Before.Index;
      end if;
 
      Insert (Container, Index, New_Item, Count);
   end Insert;
 
   procedure Insert
     (Container : in out Vector;
      Before    : Cursor;
      New_Item  : Element_Type;
      Position  : out Cursor;
      Count     : Count_Type := 1)
   is
      Index : Index_Type'Base;
 
   begin
      if Before.Container /= null
        and then Before.Container /= Vector_Access'(Container'Unchecked_Access)
      then
         raise Program_Error;
      end if;
 
      if Count = 0 then
         if Before.Container = null
           or else Before.Index > Container.Last
         then
            Position := No_Element;
         else
            Position := (Container'Unchecked_Access, Before.Index);
         end if;
 
         return;
      end if;
 
      if Before.Container = null
        or else Before.Index > Container.Last
      then
         if Container.Last = Index_Type'Last then
            raise Constraint_Error;
         end if;
 
         Index := Container.Last + 1;
 
      else
         Index := Before.Index;
      end if;
 
      Insert (Container, Index, New_Item, Count);
 
      Position := (Container'Unchecked_Access, Index);
   end Insert;
 
   ------------------
   -- Insert_Space --
   ------------------
 
   procedure Insert_Space
     (Container : in out Vector;
      Before    : Extended_Index;
      Count     : Count_Type := 1)
   is
      N : constant Int := Int (Count);
 
      New_Last_As_Int : Int'Base;
      New_Last        : Index_Type;
 
      Dst : Elements_Access;
 
   begin
      if Before < Index_Type'First then
         raise Constraint_Error;
      end if;
 
      if Before > Container.Last
        and then Before > Container.Last + 1
      then
         raise Constraint_Error;
      end if;
 
      if Count = 0 then
         return;
      end if;
 
      declare
         Old_Last_As_Int : constant Int := Int (Container.Last);
 
      begin
         New_Last_As_Int := Old_Last_As_Int + N;
 
         if New_Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         New_Last := Index_Type (New_Last_As_Int);
      end;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      if Container.Elements = null then
         Container.Elements :=
           new Elements_Type (Index_Type'First .. New_Last);
 
         Container.Last := New_Last;
         return;
      end if;
 
      if New_Last <= Container.Elements'Last then
         declare
            E : Elements_Type renames Container.Elements.all;
 
         begin
            if Before <= Container.Last then
               declare
                  Index_As_Int : constant Int'Base :=
                                   Index_Type'Pos (Before) + N;
 
                  Index : constant Index_Type := Index_Type (Index_As_Int);
 
               begin
                  E (Index .. New_Last) := E (Before .. Container.Last);
                  E (Before .. Index - 1) := (others => null);
               end;
            end if;
         end;
 
         Container.Last := New_Last;
         return;
      end if;
 
      declare
         First    : constant Int := Int (Index_Type'First);
         New_Size : constant Int'Base := New_Last_As_Int - First + 1;
         Size     : Int'Base := Int'Max (1, Container.Elements'Length);
 
      begin
         while Size < New_Size loop
            if Size > Int'Last / 2 then
               Size := Int'Last;
               exit;
            end if;
 
            Size := 2 * Size;
         end loop;
 
         --  TODO: The following calculations aren't quite right, since
         --  there will be overflow if Index_Type'Range is very large
         --  (e.g. this package is instantiated with a 64-bit integer).
         --  END TODO.
 
         declare
            Max_Size : constant Int'Base := Int (Index_Type'Last) - First + 1;
         begin
            if Size > Max_Size then
               Size := Max_Size;
            end if;
         end;
 
         declare
            Dst_Last : constant Index_Type := Index_Type (First + Size - 1);
         begin
            Dst := new Elements_Type (Index_Type'First .. Dst_Last);
         end;
      end;
 
      declare
         Src : Elements_Access := Container.Elements;
 
      begin
         if Before <= Container.Last then
            declare
               Index_As_Int : constant Int'Base :=
                                Index_Type'Pos (Before) + N;
 
               Index : constant Index_Type := Index_Type (Index_As_Int);
 
            begin
               Dst (Index_Type'First .. Before - 1) :=
                 Src (Index_Type'First .. Before - 1);
 
               Dst (Index .. New_Last) := Src (Before .. Container.Last);
            end;
 
         else
            Dst (Index_Type'First .. Container.Last) :=
              Src (Index_Type'First .. Container.Last);
         end if;
 
         Container.Elements := Dst;
         Container.Last := New_Last;
         Free (Src);
      end;
   end Insert_Space;
 
   procedure Insert_Space
     (Container : in out Vector;
      Before    : Cursor;
      Position  : out Cursor;
      Count     : Count_Type := 1)
   is
      Index : Index_Type'Base;
 
   begin
      if Before.Container /= null
        and then Before.Container /= Vector_Access'(Container'Unchecked_Access)
      then
         raise Program_Error;
      end if;
 
      if Count = 0 then
         if Before.Container = null
           or else Before.Index > Container.Last
         then
            Position := No_Element;
         else
            Position := (Container'Unchecked_Access, Before.Index);
         end if;
 
         return;
      end if;
 
      if Before.Container = null
        or else Before.Index > Container.Last
      then
         if Container.Last = Index_Type'Last then
            raise Constraint_Error;
         end if;
 
         Index := Container.Last + 1;
 
      else
         Index := Before.Index;
      end if;
 
      Insert_Space (Container, Index, Count);
 
      Position := Cursor'(Container'Unchecked_Access, Index);
   end Insert_Space;
 
   --------------
   -- Is_Empty --
   --------------
 
   function Is_Empty (Container : Vector) return Boolean is
   begin
      return Container.Last < Index_Type'First;
   end Is_Empty;
 
   -------------
   -- Iterate --
   -------------
 
   procedure Iterate
     (Container : Vector;
      Process   : not null access procedure (Position : in Cursor))
   is
      V : Vector renames Container'Unrestricted_Access.all;
      B : Natural renames V.Busy;
 
   begin
      B := B + 1;
 
      begin
         for Indx in Index_Type'First .. Container.Last loop
            Process (Cursor'(Container'Unchecked_Access, Indx));
         end loop;
      exception
         when others =>
            B := B - 1;
            raise;
      end;
 
      B := B - 1;
   end Iterate;
 
   ----------
   -- Last --
   ----------
 
   function Last (Container : Vector) return Cursor is
   begin
      if Is_Empty (Container) then
         return No_Element;
      end if;
 
      return (Container'Unchecked_Access, Container.Last);
   end Last;
 
   ------------------
   -- Last_Element --
   ------------------
 
   function Last_Element (Container : Vector) return Element_Type is
   begin
      return Element (Container, Container.Last);
   end Last_Element;
 
   ----------------
   -- Last_Index --
   ----------------
 
   function Last_Index (Container : Vector) return Extended_Index is
   begin
      return Container.Last;
   end Last_Index;
 
   ------------
   -- Length --
   ------------
 
   function Length (Container : Vector) return Count_Type is
      L : constant Int := Int (Container.Last);
      F : constant Int := Int (Index_Type'First);
      N : constant Int'Base := L - F + 1;
 
   begin
      if N > Count_Type'Pos (Count_Type'Last) then
         raise Constraint_Error;
      end if;
 
      return Count_Type (N);
   end Length;
 
   ----------
   -- Move --
   ----------
 
   procedure Move
     (Target : in out Vector;
      Source : in out Vector)
   is
   begin
      if Target'Address = Source'Address then
         return;
      end if;
 
      if Source.Busy > 0 then
         raise Program_Error;
      end if;
 
      Clear (Target);
 
      declare
         Target_Elements : constant Elements_Access := Target.Elements;
      begin
         Target.Elements := Source.Elements;
         Source.Elements := Target_Elements;
      end;
 
      Target.Last := Source.Last;
      Source.Last := No_Index;
   end Move;
 
   ----------
   -- Next --
   ----------
 
   function Next (Position : Cursor) return Cursor is
   begin
      if Position.Container = null then
         return No_Element;
      end if;
 
      if Position.Index < Position.Container.Last then
         return (Position.Container, Position.Index + 1);
      end if;
 
      return No_Element;
   end Next;
 
   ----------
   -- Next --
   ----------
 
   procedure Next (Position : in out Cursor) is
   begin
      if Position.Container = null then
         return;
      end if;
 
      if Position.Index < Position.Container.Last then
         Position.Index := Position.Index + 1;
      else
         Position := No_Element;
      end if;
   end Next;
 
   -------------
   -- Prepend --
   -------------
 
   procedure Prepend (Container : in out Vector; New_Item : Vector) is
   begin
      Insert (Container, Index_Type'First, New_Item);
   end Prepend;
 
   procedure Prepend
     (Container : in out Vector;
      New_Item  : Element_Type;
      Count     : Count_Type := 1)
   is
   begin
      Insert (Container,
              Index_Type'First,
              New_Item,
              Count);
   end Prepend;
 
   --------------
   -- Previous --
   --------------
 
   procedure Previous (Position : in out Cursor) is
   begin
      if Position.Container = null then
         return;
      end if;
 
      if Position.Index > Index_Type'First then
         Position.Index := Position.Index - 1;
      else
         Position := No_Element;
      end if;
   end Previous;
 
   function Previous (Position : Cursor) return Cursor is
   begin
      if Position.Container = null then
         return No_Element;
      end if;
 
      if Position.Index > Index_Type'First then
         return (Position.Container, Position.Index - 1);
      end if;
 
      return No_Element;
   end Previous;
 
   -------------------
   -- Query_Element --
   -------------------
 
   procedure Query_Element
     (Container : Vector;
      Index     : Index_Type;
      Process   : not null access procedure (Element : in Element_Type))
   is
      V : Vector renames Container'Unrestricted_Access.all;
      B : Natural renames V.Busy;
      L : Natural renames V.Lock;
 
   begin
      if Index > Container.Last then
         raise Constraint_Error;
      end if;
 
      if V.Elements (Index) = null then
         raise Constraint_Error;
      end if;
 
      B := B + 1;
      L := L + 1;
 
      begin
         Process (V.Elements (Index).all);
      exception
         when others =>
            L := L - 1;
            B := B - 1;
            raise;
      end;
 
      L := L - 1;
      B := B - 1;
   end Query_Element;
 
   procedure Query_Element
     (Position : Cursor;
      Process  : not null access procedure (Element : in Element_Type))
   is
   begin
      if Position.Container = null then
         raise Constraint_Error;
      end if;
 
      Query_Element (Position.Container.all, Position.Index, Process);
   end Query_Element;
 
   ----------
   -- Read --
   ----------
 
   procedure Read
     (Stream    : access Root_Stream_Type'Class;
      Container : out Vector)
   is
      Length : Count_Type'Base;
      Last   : Index_Type'Base := Index_Type'Pred (Index_Type'First);
 
      B : Boolean;
 
   begin
      Clear (Container);
 
      Count_Type'Base'Read (Stream, Length);
 
      if Length > Capacity (Container) then
         Reserve_Capacity (Container, Capacity => Length);
      end if;
 
      for J in Count_Type range 1 .. Length loop
         Last := Last + 1;
 
         Boolean'Read (Stream, B);
 
         if B then
            Container.Elements (Last) :=
              new Element_Type'(Element_Type'Input (Stream));
         end if;
 
         Container.Last := Last;
      end loop;
   end Read;
 
   procedure Read
     (Stream   : access Root_Stream_Type'Class;
      Position : out Cursor)
   is
   begin
      raise Program_Error;
   end Read;
 
   ---------------------
   -- Replace_Element --
   ---------------------
 
   procedure Replace_Element
     (Container : in out Vector;
      Index     : Index_Type;
      New_Item  : Element_Type)
   is
   begin
      if Index > Container.Last then
         raise Constraint_Error;
      end if;
 
      if Container.Lock > 0 then
         raise Program_Error;
      end if;
 
      declare
         X : Element_Access := Container.Elements (Index);
      begin
         Container.Elements (Index) := new Element_Type'(New_Item);
         Free (X);
      end;
   end Replace_Element;
 
   procedure Replace_Element
     (Container : in out Vector;
      Position  : Cursor;
      New_Item  : Element_Type)
   is
   begin
      if Position.Container = null then
         raise Constraint_Error;
      end if;
 
      if Position.Container /= Container'Unrestricted_Access then
         raise Program_Error;
      end if;
 
      Replace_Element (Container, Position.Index, New_Item);
   end Replace_Element;
 
   ----------------------
   -- Reserve_Capacity --
   ----------------------
 
   procedure Reserve_Capacity
     (Container : in out Vector;
      Capacity  : Count_Type)
   is
      N : constant Count_Type := Length (Container);
 
   begin
      if Capacity = 0 then
         if N = 0 then
            declare
               X : Elements_Access := Container.Elements;
            begin
               Container.Elements := null;
               Free (X);
            end;
 
         elsif N < Container.Elements'Length then
            if Container.Busy > 0 then
               raise Program_Error;
            end if;
 
            declare
               subtype Array_Index_Subtype is Index_Type'Base range
                 Index_Type'First .. Container.Last;
 
               Src : Elements_Type renames
                       Container.Elements (Array_Index_Subtype);
 
               subtype Array_Subtype is
                 Elements_Type (Array_Index_Subtype);
 
               X : Elements_Access := Container.Elements;
 
            begin
               Container.Elements := new Array_Subtype'(Src);
               Free (X);
            end;
         end if;
 
         return;
      end if;
 
      if Container.Elements = null then
         declare
            Last_As_Int : constant Int'Base :=
                            Int (Index_Type'First) + Int (Capacity) - 1;
 
         begin
            if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
               raise Constraint_Error;
            end if;
 
            declare
               Last : constant Index_Type := Index_Type (Last_As_Int);
 
               subtype Array_Subtype is
                 Elements_Type (Index_Type'First .. Last);
 
            begin
               Container.Elements := new Array_Subtype;
            end;
         end;
 
         return;
      end if;
 
      if Capacity <= N then
         if N < Container.Elements'Length then
            if Container.Busy > 0 then
               raise Program_Error;
            end if;
 
            declare
               subtype Array_Index_Subtype is Index_Type'Base range
                 Index_Type'First .. Container.Last;
 
               Src : Elements_Type renames
                       Container.Elements (Array_Index_Subtype);
 
               subtype Array_Subtype is
                 Elements_Type (Array_Index_Subtype);
 
               X : Elements_Access := Container.Elements;
 
            begin
               Container.Elements := new Array_Subtype'(Src);
               Free (X);
            end;
         end if;
 
         return;
      end if;
 
      if Capacity = Container.Elements'Length then
         return;
      end if;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      declare
         Last_As_Int : constant Int'Base :=
                         Int (Index_Type'First) + Int (Capacity) - 1;
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         declare
            Last : constant Index_Type := Index_Type (Last_As_Int);
 
            subtype Array_Subtype is
              Elements_Type (Index_Type'First .. Last);
 
            X : Elements_Access := Container.Elements;
 
         begin
            Container.Elements := new Array_Subtype;
 
            declare
               Src : Elements_Type renames
                       X (Index_Type'First .. Container.Last);
 
               Tgt : Elements_Type renames
                       Container.Elements (Index_Type'First .. Container.Last);
 
            begin
               Tgt := Src;
            end;
 
            Free (X);
         end;
      end;
   end Reserve_Capacity;
 
   ----------------------
   -- Reverse_Elements --
   ----------------------
 
   procedure Reverse_Elements (Container : in out Vector) is
   begin
      if Container.Length <= 1 then
         return;
      end if;
 
      if Container.Lock > 0 then
         raise Program_Error;
      end if;
 
      declare
         I : Index_Type := Index_Type'First;
         J : Index_Type := Container.Last;
         E : Elements_Type renames Container.Elements.all;
 
      begin
         while I < J loop
            declare
               EI : constant Element_Access := E (I);
 
            begin
               E (I) := E (J);
               E (J) := EI;
            end;
 
            I := I + 1;
            J := J - 1;
         end loop;
      end;
   end Reverse_Elements;
 
   ------------------
   -- Reverse_Find --
   ------------------
 
   function Reverse_Find
     (Container : Vector;
      Item      : Element_Type;
      Position  : Cursor := No_Element) return Cursor
   is
      Last : Index_Type'Base;
 
   begin
      if Position.Container /= null
        and then Position.Container /= Container'Unchecked_Access
      then
         raise Program_Error;
      end if;
 
      if Position.Container = null
        or else Position.Index > Container.Last
      then
         Last := Container.Last;
      else
         Last := Position.Index;
      end if;
 
      for Indx in reverse Index_Type'First .. Last loop
         if Container.Elements (Indx) /= null
           and then Container.Elements (Indx).all = Item
         then
            return (Container'Unchecked_Access, Indx);
         end if;
      end loop;
 
      return No_Element;
   end Reverse_Find;
 
   ------------------------
   -- Reverse_Find_Index --
   ------------------------
 
   function Reverse_Find_Index
     (Container : Vector;
      Item      : Element_Type;
      Index     : Index_Type := Index_Type'Last) return Extended_Index
   is
      Last : Index_Type'Base;
 
   begin
      if Index > Container.Last then
         Last := Container.Last;
      else
         Last := Index;
      end if;
 
      for Indx in reverse Index_Type'First .. Last loop
         if Container.Elements (Indx) /= null
           and then Container.Elements (Indx).all = Item
         then
            return Indx;
         end if;
      end loop;
 
      return No_Index;
   end Reverse_Find_Index;
 
   ---------------------
   -- Reverse_Iterate --
   ---------------------
 
   procedure Reverse_Iterate
     (Container : Vector;
      Process   : not null access procedure (Position : in Cursor))
   is
      V : Vector renames Container'Unrestricted_Access.all;
      B : Natural renames V.Busy;
 
   begin
      B := B + 1;
 
      begin
         for Indx in reverse Index_Type'First .. Container.Last loop
            Process (Cursor'(Container'Unchecked_Access, Indx));
         end loop;
      exception
         when others =>
            B := B - 1;
            raise;
      end;
 
      B := B - 1;
   end Reverse_Iterate;
 
   ----------------
   -- Set_Length --
   ----------------
 
   procedure Set_Length
     (Container : in out Vector;
      Length    : Count_Type)
   is
      N : constant Count_Type := Indefinite_Vectors.Length (Container);
 
   begin
      if Length = N then
         return;
      end if;
 
      if Container.Busy > 0 then
         raise Program_Error;
      end if;
 
      if Length < N then
         for Index in 1 .. N - Length loop
            declare
               J : constant Index_Type := Container.Last;
               X : Element_Access := Container.Elements (J);
 
            begin
               Container.Elements (J) := null;
               Container.Last := J - 1;
               Free (X);
            end;
         end loop;
 
         return;
      end if;
 
      if Length > Capacity (Container) then
         Reserve_Capacity (Container, Capacity => Length);
      end if;
 
      declare
         Last_As_Int : constant Int'Base :=
                         Int (Index_Type'First) + Int (Length) - 1;
 
      begin
         Container.Last := Index_Type (Last_As_Int);
      end;
   end Set_Length;
 
   ----------
   -- Swap --
   ----------
 
   procedure Swap
     (Container : in out Vector;
      I, J      : Index_Type)
   is
   begin
      if I > Container.Last
        or else J > Container.Last
      then
         raise Constraint_Error;
      end if;
 
      if I = J then
         return;
      end if;
 
      if Container.Lock > 0 then
         raise Program_Error;
      end if;
 
      declare
         EI : Element_Access renames Container.Elements (I);
         EJ : Element_Access renames Container.Elements (J);
 
         EI_Copy : constant Element_Access := EI;
 
      begin
         EI := EJ;
         EJ := EI_Copy;
      end;
   end Swap;
 
   procedure Swap
     (Container : in out Vector;
      I, J      : Cursor)
   is
   begin
      if I.Container = null
        or else J.Container = null
      then
         raise Constraint_Error;
      end if;
 
      if I.Container /= Container'Unrestricted_Access
        or else J.Container /= Container'Unrestricted_Access
      then
         raise Program_Error;
      end if;
 
      Swap (Container, I.Index, J.Index);
   end Swap;
 
   ---------------
   -- To_Cursor --
   ---------------
 
   function To_Cursor
     (Container : Vector;
      Index     : Extended_Index) return Cursor
   is
   begin
      if Index not in Index_Type'First .. Container.Last then
         return No_Element;
      end if;
 
      return Cursor'(Container'Unchecked_Access, Index);
   end To_Cursor;
 
   --------------
   -- To_Index --
   --------------
 
   function To_Index (Position : Cursor) return Extended_Index is
   begin
      if Position.Container = null then
         return No_Index;
      end if;
 
      if Position.Index <= Position.Container.Last then
         return Position.Index;
      end if;
 
      return No_Index;
   end To_Index;
 
   ---------------
   -- To_Vector --
   ---------------
 
   function To_Vector (Length : Count_Type) return Vector is
   begin
      if Length = 0 then
         return Empty_Vector;
      end if;
 
      declare
         First       : constant Int := Int (Index_Type'First);
         Last_As_Int : constant Int'Base := First + Int (Length) - 1;
         Last        : Index_Type;
         Elements    : Elements_Access;
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         Last := Index_Type (Last_As_Int);
         Elements := new Elements_Type (Index_Type'First .. Last);
 
         return (Controlled with Elements, Last, 0, 0);
      end;
   end To_Vector;
 
   function To_Vector
     (New_Item : Element_Type;
      Length   : Count_Type) return Vector
   is
   begin
      if Length = 0 then
         return Empty_Vector;
      end if;
 
      declare
         First       : constant Int := Int (Index_Type'First);
         Last_As_Int : constant Int'Base := First + Int (Length) - 1;
         Last        : Index_Type'Base;
         Elements    : Elements_Access;
 
      begin
         if Last_As_Int > Index_Type'Pos (Index_Type'Last) then
            raise Constraint_Error;
         end if;
 
         Last := Index_Type (Last_As_Int);
         Elements := new Elements_Type (Index_Type'First .. Last);
 
         Last := Index_Type'First;
 
         begin
            loop
               Elements (Last) := new Element_Type'(New_Item);
               exit when Last = Elements'Last;
               Last := Last + 1;
            end loop;
         exception
            when others =>
               for J in Index_Type'First .. Last - 1 loop
                  Free (Elements (J));
               end loop;
 
               Free (Elements);
               raise;
         end;
 
         return (Controlled with Elements, Last, 0, 0);
      end;
   end To_Vector;
 
   --------------------
   -- Update_Element --
   --------------------
 
   procedure Update_Element
     (Container : in out Vector;
      Index     : Index_Type;
      Process   : not null access procedure (Element : in out Element_Type))
   is
      B : Natural renames Container.Busy;
      L : Natural renames Container.Lock;
 
   begin
      if Index > Container.Last then
         raise Constraint_Error;
      end if;
 
      if Container.Elements (Index) = null then
         raise Constraint_Error;
      end if;
 
      B := B + 1;
      L := L + 1;
 
      begin
         Process (Container.Elements (Index).all);
      exception
         when others =>
            L := L - 1;
            B := B - 1;
            raise;
      end;
 
      L := L - 1;
      B := B - 1;
   end Update_Element;
 
   procedure Update_Element
     (Container : in out Vector;
      Position  : Cursor;
      Process   : not null access procedure (Element : in out Element_Type))
   is
   begin
      if Position.Container = null then
         raise Constraint_Error;
      end if;
 
      if Position.Container /= Container'Unrestricted_Access then
         raise Program_Error;
      end if;
 
      Update_Element (Container, Position.Index, Process);
   end Update_Element;
 
   -----------
   -- Write --
   -----------
 
   procedure Write
     (Stream    : access Root_Stream_Type'Class;
      Container : Vector)
   is
      N : constant Count_Type := Length (Container);
 
   begin
      Count_Type'Base'Write (Stream, N);
 
      if N = 0 then
         return;
      end if;
 
      declare
         E : Elements_Type renames Container.Elements.all;
 
      begin
         for Indx in Index_Type'First .. Container.Last loop
 
            --  There's another way to do this.  Instead a separate
            --  Boolean for each element, you could write a Boolean
            --  followed by a count of how many nulls or non-nulls
            --  follow in the array.
 
            if E (Indx) = null then
               Boolean'Write (Stream, False);
            else
               Boolean'Write (Stream, True);
               Element_Type'Output (Stream, E (Indx).all);
            end if;
         end loop;
      end;
   end Write;
 
   procedure Write
     (Stream   : access Root_Stream_Type'Class;
      Position : Cursor)
   is
   begin
      raise Program_Error;
   end Write;
 
end Ada.Containers.Indefinite_Vectors;