gcc/ada/libgnat/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) 1996-2017, 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_Warning;
  33
  34 with System;                 use System;
  35 with System.Unsigned_Types;  use System.Unsigned_Types;
  36
  37 with Ada.Exceptions;         use Ada.Exceptions;
  38 with Ada.Unchecked_Conversion;
  39
  40 package body System.Bit_Ops is
  41
  42    subtype Bits_Array is System.Unsigned_Types.Packed_Bytes1 (Positive);
  43    --  Dummy array type used to interpret the address values. We use the
  44    --  unaligned version always, since this will handle both the aligned and
  45    --  unaligned cases, and we always do these operations by bytes anyway.
  46    --  Note: we use a ones origin array here so that the computations of the
  47    --  length in bytes work correctly (give a non-negative value) for the
  48    --  case of zero length bit strings). Note that we never allocate any
  49    --  objects of this type (we can't because they would be absurdly big).
  50
  51    type Bits is access Bits_Array;
  52    --  This is the actual type into which address values are converted
  53
  54    function To_Bits is new Ada.Unchecked_Conversion (Address, Bits);
  55
  56    LE : constant := Standard'Default_Bit_Order;
  57    --  Static constant set to 0 for big-endian, 1 for little-endian
  58
  59    --  The following is an array of masks used to mask the final byte, either
  60    --  at the high end (big-endian case) or the low end (little-endian case).
  61
  62    Masks : constant array (1 .. 7) of Packed_Byte := (
  63      (1 - LE) * 2#1000_0000# + LE * 2#0000_0001#,
  64      (1 - LE) * 2#1100_0000# + LE * 2#0000_0011#,
  65      (1 - LE) * 2#1110_0000# + LE * 2#0000_0111#,
  66      (1 - LE) * 2#1111_0000# + LE * 2#0000_1111#,
  67      (1 - LE) * 2#1111_1000# + LE * 2#0001_1111#,
  68      (1 - LE) * 2#1111_1100# + LE * 2#0011_1111#,
  69      (1 - LE) * 2#1111_1110# + LE * 2#0111_1111#);
  70
  71    -----------------------
  72    -- Local Subprograms --
  73    -----------------------
  74
  75    procedure Raise_Error;
  76    pragma No_Return (Raise_Error);
  77    --  Raise Constraint_Error, complaining about unequal lengths
  78
  79    -------------
  80    -- Bit_And --
  81    -------------
  82
  83    procedure Bit_And
  84      (Left   : Address;
  85       Llen   : Natural;
  86       Right  : Address;
  87       Rlen   : Natural;
  88       Result : Address)
  89    is
  90       LeftB   : constant Bits := To_Bits (Left);
  91       RightB  : constant Bits := To_Bits (Right);
  92       ResultB : constant Bits := To_Bits (Result);
  93
  94    begin
  95       if Llen /= Rlen then
  96          Raise_Error;
  97       end if;
  98
  99       for J in 1 .. (Rlen + 7) / 8 loop
 100          ResultB (J) := LeftB (J) and RightB (J);
 101       end loop;
 102    end Bit_And;
 103
 104    ------------
 105    -- Bit_Eq --
 106    ------------
 107
 108    function Bit_Eq
 109      (Left  : Address;
 110       Llen  : Natural;
 111       Right : Address;
 112       Rlen  : Natural) return Boolean
 113    is
 114       LeftB  : constant Bits := To_Bits (Left);
 115       RightB : constant Bits := To_Bits (Right);
 116
 117    begin
 118       if Llen /= Rlen then
 119          return False;
 120
 121       else
 122          declare
 123             BLen : constant Natural := Llen / 8;
 124             Bitc : constant Natural := Llen mod 8;
 125
 126          begin
 127             if LeftB (1 .. BLen) /= RightB (1 .. BLen) then
 128                return False;
 129
 130             elsif Bitc /= 0 then
 131                return
 132                  ((LeftB (BLen + 1) xor RightB (BLen + 1))
 133                    and Masks (Bitc)) = 0;
 134
 135             else -- Bitc = 0
 136                return True;
 137             end if;
 138          end;
 139       end if;
 140    end Bit_Eq;
 141
 142    -------------
 143    -- Bit_Not --
 144    -------------
 145
 146    procedure Bit_Not
 147      (Opnd   : System.Address;
 148       Len    : Natural;
 149       Result : System.Address)
 150    is
 151       OpndB   : constant Bits := To_Bits (Opnd);
 152       ResultB : constant Bits := To_Bits (Result);
 153
 154    begin
 155       for J in 1 .. (Len + 7) / 8 loop
 156          ResultB (J) := not OpndB (J);
 157       end loop;
 158    end Bit_Not;
 159
 160    ------------
 161    -- Bit_Or --
 162    ------------
 163
 164    procedure Bit_Or
 165      (Left   : Address;
 166       Llen   : Natural;
 167       Right  : Address;
 168       Rlen   : Natural;
 169       Result : Address)
 170    is
 171       LeftB   : constant Bits := To_Bits (Left);
 172       RightB  : constant Bits := To_Bits (Right);
 173       ResultB : constant Bits := To_Bits (Result);
 174
 175    begin
 176       if Llen /= Rlen then
 177          Raise_Error;
 178       end if;
 179
 180       for J in 1 .. (Rlen + 7) / 8 loop
 181          ResultB (J) := LeftB (J) or RightB (J);
 182       end loop;
 183    end Bit_Or;
 184
 185    -------------
 186    -- Bit_Xor --
 187    -------------
 188
 189    procedure Bit_Xor
 190      (Left   : Address;
 191       Llen   : Natural;
 192       Right  : Address;
 193       Rlen   : Natural;
 194       Result : Address)
 195    is
 196       LeftB   : constant Bits := To_Bits (Left);
 197       RightB  : constant Bits := To_Bits (Right);
 198       ResultB : constant Bits := To_Bits (Result);
 199
 200    begin
 201       if Llen /= Rlen then
 202          Raise_Error;
 203       end if;
 204
 205       for J in 1 .. (Rlen + 7) / 8 loop
 206          ResultB (J) := LeftB (J) xor RightB (J);
 207       end loop;
 208    end Bit_Xor;
 209
 210    -----------------
 211    -- Raise_Error --
 212    -----------------
 213
 214    procedure Raise_Error is
 215    begin
 216       Raise_Exception
 217         (Constraint_Error'Identity, "operand lengths are unequal");
 218    end Raise_Error;
 219
 220 end System.Bit_Ops;