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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                I N T E R F A C E S . C . P O I N T E R S                 --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--          Copyright (C) 1992-2004 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- --

-- 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.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

with Interfaces.C.Strings; use Interfaces.C.Strings;

with System;               use System;

with Unchecked_Conversion;

package body Interfaces.C.Pointers is

   type Addr is mod Memory_Size;

   function To_Pointer is new Unchecked_Conversion (Addr,      Pointer);

   function To_Addr    is new Unchecked_Conversion (Pointer,   Addr);

   function To_Addr    is new Unchecked_Conversion (ptrdiff_t, Addr);

   function To_Ptrdiff is new Unchecked_Conversion (Addr,      ptrdiff_t);

   Elmt_Size : constant ptrdiff_t :=

                 (Element_Array'Component_Size

                   + Storage_Unit - 1) / Storage_Unit;

   subtype Index_Base is Index'Base;

   ---------

   -- "+" --

   ---------

   function "+" (Left : Pointer; Right : ptrdiff_t) return Pointer is

   begin

      if Left = null then

         raise Pointer_Error;

      end if;

      return To_Pointer (To_Addr (Left) + To_Addr (Elmt_Size * Right));

   end "+";

   function "+" (Left : ptrdiff_t; Right : Pointer) return Pointer is

   begin

      if Right = null then

         raise Pointer_Error;

      end if;

      return To_Pointer (To_Addr (Elmt_Size * Left) + To_Addr (Right));

   end "+";

   ---------

   -- "-" --

   ---------

   function "-" (Left : Pointer; Right : ptrdiff_t) return Pointer is

   begin

      if Left = null then

         raise Pointer_Error;

      end if;

      return To_Pointer (To_Addr (Left) - To_Addr (Right * Elmt_Size));

   end "-";

   function "-" (Left : Pointer; Right : Pointer) return ptrdiff_t is

   begin

      if Left = null or else Right = null then

         raise Pointer_Error;

      end if;

      return To_Ptrdiff (To_Addr (Left) - To_Addr (Right)) / Elmt_Size;

   end "-";

   ----------------

   -- Copy_Array --

   ----------------

   procedure Copy_Array

     (Source  : Pointer;

      Target  : Pointer;

      Length  : ptrdiff_t)

   is

      T : Pointer := Target;

      S : Pointer := Source;

   begin

      if S = null or else T = null then

         raise Dereference_Error;

      else

         for J in 1 .. Length loop

            T.all := S.all;

            Increment (T);

            Increment (S);

         end loop;

      end if;

   end Copy_Array;

   ---------------------------

   -- Copy_Terminated_Array --

   ---------------------------

   procedure Copy_Terminated_Array

     (Source     : Pointer;

      Target     : Pointer;

      Limit      : ptrdiff_t := ptrdiff_t'Last;

      Terminator : Element := Default_Terminator)

   is

      S : Pointer   := Source;

      T : Pointer   := Target;

      L : ptrdiff_t := Limit;

   begin

      if S = null or else T = null then

         raise Dereference_Error;

      else

         while L > 0 loop

            T.all := S.all;

            exit when T.all = Terminator;

            Increment (T);

            Increment (S);

            L := L - 1;

         end loop;

      end if;

   end Copy_Terminated_Array;

   ---------------

   -- Decrement --

   ---------------

   procedure Decrement (Ref : in out Pointer) is

   begin

      Ref := Ref - 1;

   end Decrement;

   ---------------

   -- Increment --

   ---------------

   procedure Increment (Ref : in out Pointer) is

   begin

      Ref := Ref + 1;

   end Increment;

   -----------

   -- Value --

   -----------

   function Value

     (Ref        : Pointer;

      Terminator : Element := Default_Terminator) return Element_Array

   is

      P : Pointer;

      L : constant Index_Base := Index'First;

      H : Index_Base;

   begin

      if Ref = null then

         raise Dereference_Error;

      else

         H := L;

         P := Ref;

         loop

            exit when P.all = Terminator;

            H := Index_Base'Succ (H);

            Increment (P);

         end loop;

         declare

            subtype A is Element_Array (L .. H);

            type PA is access A;

            function To_PA is new Unchecked_Conversion (Pointer, PA);

         begin

            return To_PA (Ref).all;

         end;

      end if;

   end Value;

   function Value

     (Ref    : Pointer;

      Length : ptrdiff_t) return Element_Array

   is

      L : Index_Base;

      H : Index_Base;

   begin

      if Ref = null then

         raise Dereference_Error;

      --  For length zero, we need to return a null slice, but we can't make

      --  the bounds of this slice Index'First, since this could cause a

      --  Constraint_Error if Index'First = Index'Base'First.

      elsif Length <= 0 then

         declare

            pragma Warnings (Off); -- kill warnings since X not assigned

            X : Element_Array (Index'Succ (Index'First) .. Index'First);

            pragma Warnings (On);

         begin

            return X;

         end;

      --  Normal case (length non-zero)

      else

         L := Index'First;

         H := Index'Val (Index'Pos (Index'First) + Length - 1);

         declare

            subtype A is Element_Array (L .. H);

            type PA is access A;

            function To_PA is new Unchecked_Conversion (Pointer, PA);

         begin

            return To_PA (Ref).all;

         end;

      end if;

   end Value;

   --------------------

   -- Virtual_Length --

   --------------------

   function Virtual_Length

     (Ref        : Pointer;

      Terminator : Element := Default_Terminator) return ptrdiff_t

   is

      P : Pointer;

      C : ptrdiff_t;

   begin

      if Ref = null then

         raise Dereference_Error;

      else

         C := 0;

         P := Ref;

         while P.all /= Terminator loop

            C := C + 1;

            Increment (P);

         end loop;

         return C;

      end if;

   end Virtual_Length;

end Interfaces.C.Pointers;