gcc/ada/libgnat/i-cpoint.adb

   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) 1992-2023, 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
  32 with Interfaces.C.Strings;    use Interfaces.C.Strings;
  33 with System.Storage_Elements; use System.Storage_Elements;
  34 with System;                  use System;
  35
  36 with Ada.Unchecked_Conversion;
  37
  38 package body Interfaces.C.Pointers is
  39
  40    subtype Offset is Storage_Offset;
  41
  42    function To_Pointer is new Ada.Unchecked_Conversion (Address,   Pointer);
  43    function To_Addr    is new Ada.Unchecked_Conversion (Pointer,   Address);
  44    function To_Offset  is new Ada.Unchecked_Conversion (ptrdiff_t, Offset);
  45    function To_Ptrdiff is new Ada.Unchecked_Conversion (Offset,    ptrdiff_t);
  46
  47    Elmt_Size : constant ptrdiff_t :=
  48                  (Element_Array'Component_Size
  49                    + Storage_Unit - 1) / Storage_Unit;
  50
  51    subtype Index_Base is Index'Base;
  52
  53    ---------
  54    -- "+" --
  55    ---------
  56
  57    function "+" (Left : Pointer; Right : ptrdiff_t) return Pointer is
  58    begin
  59       if Left = null then
  60          raise Pointer_Error;
  61       end if;
  62
  63       return To_Pointer (To_Addr (Left) + To_Offset (Elmt_Size * Right));
  64    end "+";
  65
  66    function "+" (Left : ptrdiff_t; Right : Pointer) return Pointer is
  67    begin
  68       if Right = null then
  69          raise Pointer_Error;
  70       end if;
  71
  72       return To_Pointer (To_Offset (Elmt_Size * Left) + To_Addr (Right));
  73    end "+";
  74
  75    ---------
  76    -- "-" --
  77    ---------
  78
  79    function "-" (Left : Pointer; Right : ptrdiff_t) return Pointer is
  80    begin
  81       if Left = null then
  82          raise Pointer_Error;
  83       end if;
  84
  85       return To_Pointer (To_Addr (Left) - To_Offset (Right * Elmt_Size));
  86    end "-";
  87
  88    function "-" (Left : Pointer; Right : Pointer) return ptrdiff_t is
  89    begin
  90       if Left = null or else Right = null then
  91          raise Pointer_Error;
  92       end if;
  93
  94       return To_Ptrdiff (To_Addr (Left) - To_Addr (Right)) / Elmt_Size;
  95    end "-";
  96
  97    ----------------
  98    -- Copy_Array --
  99    ----------------
 100
 101    procedure Copy_Array
 102      (Source  : Pointer;
 103       Target  : Pointer;
 104       Length  : ptrdiff_t)
 105    is
 106       T : Pointer;
 107       S : Pointer;
 108
 109    begin
 110       if Source = null or else Target = null then
 111          raise Dereference_Error;
 112
 113       --  Forward copy
 114
 115       elsif To_Addr (Target) <= To_Addr (Source) then
 116          T := Target;
 117          S := Source;
 118          for J in 1 .. Length loop
 119             T.all := S.all;
 120             Increment (T);
 121             Increment (S);
 122          end loop;
 123
 124       --  Backward copy
 125
 126       else
 127          T := Target + Length;
 128          S := Source + Length;
 129          for J in 1 .. Length loop
 130             Decrement (T);
 131             Decrement (S);
 132             T.all := S.all;
 133          end loop;
 134       end if;
 135    end Copy_Array;
 136
 137    ---------------------------
 138    -- Copy_Terminated_Array --
 139    ---------------------------
 140
 141    procedure Copy_Terminated_Array
 142      (Source     : Pointer;
 143       Target     : Pointer;
 144       Limit      : ptrdiff_t := ptrdiff_t'Last;
 145       Terminator : Element := Default_Terminator)
 146    is
 147       L : ptrdiff_t;
 148       S : Pointer := Source;
 149
 150    begin
 151       if Source = null or Target = null then
 152          raise Dereference_Error;
 153       end if;
 154
 155       --  Compute array limited length (including the terminator)
 156
 157       L := 0;
 158       while L < Limit loop
 159          L := L + 1;
 160          exit when S.all = Terminator;
 161          Increment (S);
 162       end loop;
 163
 164       Copy_Array (Source, Target, L);
 165    end Copy_Terminated_Array;
 166
 167    ---------------
 168    -- Decrement --
 169    ---------------
 170
 171    procedure Decrement (Ref : in out Pointer) is
 172    begin
 173       Ref := Ref - 1;
 174    end Decrement;
 175
 176    ---------------
 177    -- Increment --
 178    ---------------
 179
 180    procedure Increment (Ref : in out Pointer) is
 181    begin
 182       Ref := Ref + 1;
 183    end Increment;
 184
 185    -----------
 186    -- Value --
 187    -----------
 188
 189    function Value
 190      (Ref        : Pointer;
 191       Terminator : Element := Default_Terminator) return Element_Array
 192    is
 193       P : Pointer;
 194       L : constant Index_Base := Index'First;
 195       H : Index_Base;
 196
 197    begin
 198       if Ref = null then
 199          raise Dereference_Error;
 200
 201       else
 202          H := L;
 203          P := Ref;
 204
 205          loop
 206             exit when P.all = Terminator;
 207             H := Index_Base'Succ (H);
 208             Increment (P);
 209          end loop;
 210
 211          declare
 212             subtype A is Element_Array (L .. H);
 213
 214             type PA is access A;
 215             for PA'Size use System.Parameters.ptr_bits;
 216             function To_PA is new Ada.Unchecked_Conversion (Pointer, PA);
 217
 218          begin
 219             return To_PA (Ref).all;
 220          end;
 221       end if;
 222    end Value;
 223
 224    function Value
 225      (Ref    : Pointer;
 226       Length : ptrdiff_t) return Element_Array
 227    is
 228       L : Index_Base;
 229       H : Index_Base;
 230
 231    begin
 232       if Ref = null then
 233          raise Dereference_Error;
 234
 235       --  For length zero, we need to return a null slice, but we can't make
 236       --  the bounds of this slice Index'First, since this could cause a
 237       --  Constraint_Error if Index'First = Index'Base'First.
 238
 239       elsif Length <= 0 then
 240          declare
 241             pragma Warnings (Off); -- kill warnings since X not assigned
 242             X : Element_Array (Index'Succ (Index'First) .. Index'First);
 243             pragma Warnings (On);
 244
 245          begin
 246             return X;
 247          end;
 248
 249       --  Normal case (length non-zero)
 250
 251       else
 252          L := Index'First;
 253          H := Index'Val (Index'Pos (Index'First) + Length - 1);
 254
 255          declare
 256             subtype A is Element_Array (L .. H);
 257
 258             type PA is access A;
 259             for PA'Size use System.Parameters.ptr_bits;
 260             function To_PA is new Ada.Unchecked_Conversion (Pointer, PA);
 261
 262          begin
 263             return To_PA (Ref).all;
 264          end;
 265       end if;
 266    end Value;
 267
 268    --------------------
 269    -- Virtual_Length --
 270    --------------------
 271
 272    function Virtual_Length
 273      (Ref        : Pointer;
 274       Terminator : Element := Default_Terminator) return ptrdiff_t
 275    is
 276       P : Pointer;
 277       C : ptrdiff_t;
 278
 279    begin
 280       if Ref = null then
 281          raise Dereference_Error;
 282
 283       else
 284          C := 0;
 285          P := Ref;
 286
 287          while P.all /= Terminator loop
 288             C := C + 1;
 289             Increment (P);
 290          end loop;
 291
 292          return C;
 293       end if;
 294    end Virtual_Length;
 295
 296 end Interfaces.C.Pointers;