gcc/ada/s-bitops.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA RUNTIME 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 --                                                                          --
  10 --         Copyright (C) 1996-2000 Free Software Foundation, Inc.           --
  11 --                                                                          --
  12 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNAT was originally developed  by the GNAT team at  New York University. --
  31 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 with GNAT.Exceptions;       use GNAT.Exceptions;
  36 with System;                use System;
  37 with System.Unsigned_Types; use System.Unsigned_Types;
  38 with Unchecked_Conversion;
  39
  40 package body System.Bit_Ops is
  41
  42    subtype Bits_Array is System.Unsigned_Types.Packed_Bytes1 (Positive);
  43    --  Unconstrained array used to interprete 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).
  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 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    -----------------------
  72    -- Local Subprograms --
  73    -----------------------
  74
  75    procedure Raise_Error;
  76    --  Raise Constraint_Error, complaining about unequal lengths
  77
  78    -------------
  79    -- Bit_And --
  80    -------------
  81
  82    procedure Bit_And
  83      (Left   : Address;
  84       Llen   : Natural;
  85       Right  : Address;
  86       Rlen   : Natural;
  87       Result : Address)
  88    is
  89       LeftB   : constant Bits := To_Bits (Left);
  90       RightB  : constant Bits := To_Bits (Right);
  91       ResultB : constant Bits := To_Bits (Result);
  92
  93    begin
  94       if Llen /= Rlen then
  95          Raise_Error;
  96       end if;
  97
  98       for J in 1 .. (Rlen + 7) / 8 loop
  99          ResultB (J) := LeftB (J) and RightB (J);
 100       end loop;
 101    end Bit_And;
 102
 103    ------------
 104    -- Bit_Eq --
 105    ------------
 106
 107    function Bit_Eq
 108      (Left  : Address;
 109       Llen  : Natural;
 110       Right : Address;
 111       Rlen  : Natural)
 112       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 Llen /= Rlen then
 128                return False;
 129
 130             elsif LeftB (1 .. BLen) /= RightB (1 .. BLen) then
 131                return False;
 132
 133             elsif Bitc /= 0 then
 134                return
 135                  ((LeftB (BLen + 1) xor RightB (BLen + 1))
 136                    and Masks (Bitc)) = 0;
 137
 138             else -- Bitc = 0
 139                return True;
 140             end if;
 141          end;
 142       end if;
 143    end Bit_Eq;
 144
 145    -------------
 146    -- Bit_Not --
 147    -------------
 148
 149    procedure Bit_Not
 150      (Opnd   : System.Address;
 151       Len    : Natural;
 152       Result : System.Address)
 153    is
 154       OpndB   : constant Bits := To_Bits (Opnd);
 155       ResultB : constant Bits := To_Bits (Result);
 156
 157    begin
 158       for J in 1 .. (Len + 7) / 8 loop
 159          ResultB (J) := not OpndB (J);
 160       end loop;
 161    end Bit_Not;
 162
 163    ------------
 164    -- Bit_Or --
 165    ------------
 166
 167    procedure Bit_Or
 168      (Left   : Address;
 169       Llen   : Natural;
 170       Right  : Address;
 171       Rlen   : Natural;
 172       Result : Address)
 173    is
 174       LeftB   : constant Bits := To_Bits (Left);
 175       RightB  : constant Bits := To_Bits (Right);
 176       ResultB : constant Bits := To_Bits (Result);
 177
 178    begin
 179       if Llen /= Rlen then
 180          Raise_Error;
 181       end if;
 182
 183       for J in 1 .. (Rlen + 7) / 8 loop
 184          ResultB (J) := LeftB (J) or RightB (J);
 185       end loop;
 186    end Bit_Or;
 187
 188    -------------
 189    -- Bit_Xor --
 190    -------------
 191
 192    procedure Bit_Xor
 193      (Left   : Address;
 194       Llen   : Natural;
 195       Right  : Address;
 196       Rlen   : Natural;
 197       Result : Address)
 198    is
 199       LeftB   : constant Bits := To_Bits (Left);
 200       RightB  : constant Bits := To_Bits (Right);
 201       ResultB : constant Bits := To_Bits (Result);
 202
 203    begin
 204       if Llen /= Rlen then
 205          Raise_Error;
 206       end if;
 207
 208       for J in 1 .. (Rlen + 7) / 8 loop
 209          ResultB (J) := LeftB (J) xor RightB (J);
 210       end loop;
 211    end Bit_Xor;
 212
 213    -----------------
 214    -- Raise_Error --
 215    -----------------
 216
 217    procedure Raise_Error is
 218    begin
 219       Raise_Exception (CE, "unequal lengths in logical operation");
 220    end Raise_Error;
 221
 222 end System.Bit_Ops;