1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                I N T E R F A C E S . C . P O I N T E R S                 --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 1992-2015, Free Software Foundation, Inc.         --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32with Interfaces.C.Strings; use Interfaces.C.Strings;
33with System;               use System;
34
35with Ada.Unchecked_Conversion;
36
37package body Interfaces.C.Pointers is
38
39   type Addr is mod 2 ** System.Parameters.ptr_bits;
40
41   function To_Pointer is new Ada.Unchecked_Conversion (Addr,      Pointer);
42   function To_Addr    is new Ada.Unchecked_Conversion (Pointer,   Addr);
43   function To_Addr    is new Ada.Unchecked_Conversion (ptrdiff_t, Addr);
44   function To_Ptrdiff is new Ada.Unchecked_Conversion (Addr,      ptrdiff_t);
45
46   Elmt_Size : constant ptrdiff_t :=
47                 (Element_Array'Component_Size
48                   + Storage_Unit - 1) / Storage_Unit;
49
50   subtype Index_Base is Index'Base;
51
52   ---------
53   -- "+" --
54   ---------
55
56   function "+" (Left : Pointer; Right : ptrdiff_t) return Pointer is
57   begin
58      if Left = null then
59         raise Pointer_Error;
60      end if;
61
62      return To_Pointer (To_Addr (Left) + To_Addr (Elmt_Size * Right));
63   end "+";
64
65   function "+" (Left : ptrdiff_t; Right : Pointer) return Pointer is
66   begin
67      if Right = null then
68         raise Pointer_Error;
69      end if;
70
71      return To_Pointer (To_Addr (Elmt_Size * Left) + To_Addr (Right));
72   end "+";
73
74   ---------
75   -- "-" --
76   ---------
77
78   function "-" (Left : Pointer; Right : ptrdiff_t) return Pointer is
79   begin
80      if Left = null then
81         raise Pointer_Error;
82      end if;
83
84      return To_Pointer (To_Addr (Left) - To_Addr (Right * Elmt_Size));
85   end "-";
86
87   function "-" (Left : Pointer; Right : Pointer) return ptrdiff_t is
88   begin
89      if Left = null or else Right = null then
90         raise Pointer_Error;
91      end if;
92
93      return To_Ptrdiff (To_Addr (Left) - To_Addr (Right)) / Elmt_Size;
94   end "-";
95
96   ----------------
97   -- Copy_Array --
98   ----------------
99
100   procedure Copy_Array
101     (Source  : Pointer;
102      Target  : Pointer;
103      Length  : ptrdiff_t)
104   is
105      T : Pointer;
106      S : Pointer;
107
108   begin
109      if Source = null or else Target = null then
110         raise Dereference_Error;
111
112      --  Forward copy
113
114      elsif To_Addr (Target) <= To_Addr (Source) then
115         T := Target;
116         S := Source;
117         for J in 1 .. Length loop
118            T.all := S.all;
119            Increment (T);
120            Increment (S);
121         end loop;
122
123      --  Backward copy
124
125      else
126         T := Target + Length;
127         S := Source + Length;
128         for J in 1 .. Length loop
129            Decrement (T);
130            Decrement (S);
131            T.all := S.all;
132         end loop;
133      end if;
134   end Copy_Array;
135
136   ---------------------------
137   -- Copy_Terminated_Array --
138   ---------------------------
139
140   procedure Copy_Terminated_Array
141     (Source     : Pointer;
142      Target     : Pointer;
143      Limit      : ptrdiff_t := ptrdiff_t'Last;
144      Terminator : Element := Default_Terminator)
145   is
146      L : ptrdiff_t;
147      S : Pointer := Source;
148
149   begin
150      if Source = null or Target = null then
151         raise Dereference_Error;
152      end if;
153
154      --  Compute array limited length (including the terminator)
155
156      L := 0;
157      while L < Limit loop
158         L := L + 1;
159         exit when S.all = Terminator;
160         Increment (S);
161      end loop;
162
163      Copy_Array (Source, Target, L);
164   end Copy_Terminated_Array;
165
166   ---------------
167   -- Decrement --
168   ---------------
169
170   procedure Decrement (Ref : in out Pointer) is
171   begin
172      Ref := Ref - 1;
173   end Decrement;
174
175   ---------------
176   -- Increment --
177   ---------------
178
179   procedure Increment (Ref : in out Pointer) is
180   begin
181      Ref := Ref + 1;
182   end Increment;
183
184   -----------
185   -- Value --
186   -----------
187
188   function Value
189     (Ref        : Pointer;
190      Terminator : Element := Default_Terminator) return Element_Array
191   is
192      P : Pointer;
193      L : constant Index_Base := Index'First;
194      H : Index_Base;
195
196   begin
197      if Ref = null then
198         raise Dereference_Error;
199
200      else
201         H := L;
202         P := Ref;
203
204         loop
205            exit when P.all = Terminator;
206            H := Index_Base'Succ (H);
207            Increment (P);
208         end loop;
209
210         declare
211            subtype A is Element_Array (L .. H);
212
213            type PA is access A;
214            for PA'Size use System.Parameters.ptr_bits;
215            function To_PA is new Ada.Unchecked_Conversion (Pointer, PA);
216
217         begin
218            return To_PA (Ref).all;
219         end;
220      end if;
221   end Value;
222
223   function Value
224     (Ref    : Pointer;
225      Length : ptrdiff_t) return Element_Array
226   is
227      L : Index_Base;
228      H : Index_Base;
229
230   begin
231      if Ref = null then
232         raise Dereference_Error;
233
234      --  For length zero, we need to return a null slice, but we can't make
235      --  the bounds of this slice Index'First, since this could cause a
236      --  Constraint_Error if Index'First = Index'Base'First.
237
238      elsif Length <= 0 then
239         declare
240            pragma Warnings (Off); -- kill warnings since X not assigned
241            X : Element_Array (Index'Succ (Index'First) .. Index'First);
242            pragma Warnings (On);
243
244         begin
245            return X;
246         end;
247
248      --  Normal case (length non-zero)
249
250      else
251         L := Index'First;
252         H := Index'Val (Index'Pos (Index'First) + Length - 1);
253
254         declare
255            subtype A is Element_Array (L .. H);
256
257            type PA is access A;
258            for PA'Size use System.Parameters.ptr_bits;
259            function To_PA is new Ada.Unchecked_Conversion (Pointer, PA);
260
261         begin
262            return To_PA (Ref).all;
263         end;
264      end if;
265   end Value;
266
267   --------------------
268   -- Virtual_Length --
269   --------------------
270
271   function Virtual_Length
272     (Ref        : Pointer;
273      Terminator : Element := Default_Terminator) return ptrdiff_t
274   is
275      P : Pointer;
276      C : ptrdiff_t;
277
278   begin
279      if Ref = null then
280         raise Dereference_Error;
281
282      else
283         C := 0;
284         P := Ref;
285
286         while P.all /= Terminator loop
287            C := C + 1;
288            Increment (P);
289         end loop;
290
291         return C;
292      end if;
293   end Virtual_Length;
294
295end Interfaces.C.Pointers;
296