gcc/ada/s-bitops.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
   4 --                                                                          --
   5 --                       S Y S T E M . B I T _ O P S                        --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --         Copyright (C) 1996-2009, 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 pragma Compiler_Unit;
  33
  34 with System;                 use System;
  35 with System.Unsigned_Types;  use System.Unsigned_Types;
  36
  37 with Ada.Unchecked_Conversion;
  38
  39 package body System.Bit_Ops is
  40
  41    subtype Bits_Array is System.Unsigned_Types.Packed_Bytes1 (Positive);
  42    --  Dummy array type used to interpret the address values. We use the
  43    --  unaligned version always, since this will handle both the aligned and
  44    --  unaligned cases, and we always do these operations by bytes anyway.
  45    --  Note: we use a ones origin array here so that the computations of the
  46    --  length in bytes work correctly (give a non-negative value) for the
  47    --  case of zero length bit strings). Note that we never allocate any
  48    --  objects of this type (we can't because they would be absurdly big).
  49
  50    type Bits is access Bits_Array;
  51    --  This is the actual type into which address values are converted
  52
  53    function To_Bits is new Ada.Unchecked_Conversion (Address, Bits);
  54
  55    LE : constant := Standard'Default_Bit_Order;
  56    --  Static constant set to 0 for big-endian, 1 for little-endian
  57
  58    --  The following is an array of masks used to mask the final byte, either
  59    --  at the high end (big-endian case) or the low end (little-endian case).
  60
  61    Masks : constant array (1 .. 7) of Packed_Byte := (
  62      (1 - LE) * 2#1000_0000# + LE * 2#0000_0001#,
  63      (1 - LE) * 2#1100_0000# + LE * 2#0000_0011#,
  64      (1 - LE) * 2#1110_0000# + LE * 2#0000_0111#,
  65      (1 - LE) * 2#1111_0000# + LE * 2#0000_1111#,
  66      (1 - LE) * 2#1111_1000# + LE * 2#0001_1111#,
  67      (1 - LE) * 2#1111_1100# + LE * 2#0011_1111#,
  68      (1 - LE) * 2#1111_1110# + LE * 2#0111_1111#);
  69
  70    -----------------------
  71    -- Local Subprograms --
  72    -----------------------
  73
  74    procedure Raise_Error;
  75    --  Raise Constraint_Error, complaining about unequal lengths
  76
  77    -------------
  78    -- Bit_And --
  79    -------------
  80
  81    procedure Bit_And
  82      (Left   : Address;
  83       Llen   : Natural;
  84       Right  : Address;
  85       Rlen   : Natural;
  86       Result : Address)
  87    is
  88       LeftB   : constant Bits := To_Bits (Left);
  89       RightB  : constant Bits := To_Bits (Right);
  90       ResultB : constant Bits := To_Bits (Result);
  91
  92    begin
  93       if Llen /= Rlen then
  94          Raise_Error;
  95       end if;
  96
  97       for J in 1 .. (Rlen + 7) / 8 loop
  98          ResultB (J) := LeftB (J) and RightB (J);
  99       end loop;
 100    end Bit_And;
 101
 102    ------------
 103    -- Bit_Eq --
 104    ------------
 105
 106    function Bit_Eq
 107      (Left  : Address;
 108       Llen  : Natural;
 109       Right : Address;
 110       Rlen  : Natural) return Boolean
 111    is
 112       LeftB  : constant Bits := To_Bits (Left);
 113       RightB : constant Bits := To_Bits (Right);
 114
 115    begin
 116       if Llen /= Rlen then
 117          return False;
 118
 119       else
 120          declare
 121             BLen : constant Natural := Llen / 8;
 122             Bitc : constant Natural := Llen mod 8;
 123
 124          begin
 125             if LeftB (1 .. BLen) /= RightB (1 .. BLen) then
 126                return False;
 127
 128             elsif Bitc /= 0 then
 129                return
 130                  ((LeftB (BLen + 1) xor RightB (BLen + 1))
 131                    and Masks (Bitc)) = 0;
 132
 133             else -- Bitc = 0
 134                return True;
 135             end if;
 136          end;
 137       end if;
 138    end Bit_Eq;
 139
 140    -------------
 141    -- Bit_Not --
 142    -------------
 143
 144    procedure Bit_Not
 145      (Opnd   : System.Address;
 146       Len    : Natural;
 147       Result : System.Address)
 148    is
 149       OpndB   : constant Bits := To_Bits (Opnd);
 150       ResultB : constant Bits := To_Bits (Result);
 151
 152    begin
 153       for J in 1 .. (Len + 7) / 8 loop
 154          ResultB (J) := not OpndB (J);
 155       end loop;
 156    end Bit_Not;
 157
 158    ------------
 159    -- Bit_Or --
 160    ------------
 161
 162    procedure Bit_Or
 163      (Left   : Address;
 164       Llen   : Natural;
 165       Right  : Address;
 166       Rlen   : Natural;
 167       Result : Address)
 168    is
 169       LeftB   : constant Bits := To_Bits (Left);
 170       RightB  : constant Bits := To_Bits (Right);
 171       ResultB : constant Bits := To_Bits (Result);
 172
 173    begin
 174       if Llen /= Rlen then
 175          Raise_Error;
 176       end if;
 177
 178       for J in 1 .. (Rlen + 7) / 8 loop
 179          ResultB (J) := LeftB (J) or RightB (J);
 180       end loop;
 181    end Bit_Or;
 182
 183    -------------
 184    -- Bit_Xor --
 185    -------------
 186
 187    procedure Bit_Xor
 188      (Left   : Address;
 189       Llen   : Natural;
 190       Right  : Address;
 191       Rlen   : Natural;
 192       Result : Address)
 193    is
 194       LeftB   : constant Bits := To_Bits (Left);
 195       RightB  : constant Bits := To_Bits (Right);
 196       ResultB : constant Bits := To_Bits (Result);
 197
 198    begin
 199       if Llen /= Rlen then
 200          Raise_Error;
 201       end if;
 202
 203       for J in 1 .. (Rlen + 7) / 8 loop
 204          ResultB (J) := LeftB (J) xor RightB (J);
 205       end loop;
 206    end Bit_Xor;
 207
 208    -----------------
 209    -- Raise_Error --
 210    -----------------
 211
 212    procedure Raise_Error is
 213    begin
 214       raise Constraint_Error;
 215    end Raise_Error;
 216
 217 end System.Bit_Ops;