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 --                            $Revision: 1.1 $
  10 --                                                                          --
  11 --         Copyright (C) 1996-2000 Free Software Foundation, Inc.           --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNAT was originally developed  by the GNAT team at  New York University. --
  32 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with GNAT.Exceptions;       use GNAT.Exceptions;
  37 with System;                use System;
  38 with System.Unsigned_Types; use System.Unsigned_Types;
  39 with Unchecked_Conversion;
  40
  41 package body System.Bit_Ops is
  42
  43    subtype Bits_Array is System.Unsigned_Types.Packed_Bytes1 (Positive);
  44    --  Unconstrained array used to interprete the address values. We use the
  45    --  unaligned version always, since this will handle both the aligned and
  46    --  unaligned cases, and we always do these operations by bytes anyway.
  47    --  Note: we use a ones origin array here so that the computations of the
  48    --  length in bytes work correctly (give a non-negative value) for the
  49    --  case of zero length bit strings).
  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 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    -----------------------
  73    -- Local Subprograms --
  74    -----------------------
  75
  76    procedure 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)
 113       return  Boolean
 114    is
 115       LeftB  : constant Bits := To_Bits (Left);
 116       RightB : constant Bits := To_Bits (Right);
 117
 118    begin
 119       if Llen /= Rlen then
 120          return False;
 121
 122       else
 123          declare
 124             BLen : constant Natural := Llen / 8;
 125             Bitc : constant Natural := Llen mod 8;
 126
 127          begin
 128             if Llen /= Rlen then
 129                return False;
 130
 131             elsif LeftB (1 .. BLen) /= RightB (1 .. BLen) then
 132                return False;
 133
 134             elsif Bitc /= 0 then
 135                return
 136                  ((LeftB (BLen + 1) xor RightB (BLen + 1))
 137                    and Masks (Bitc)) = 0;
 138
 139             else -- Bitc = 0
 140                return True;
 141             end if;
 142          end;
 143       end if;
 144    end Bit_Eq;
 145
 146    -------------
 147    -- Bit_Not --
 148    -------------
 149
 150    procedure Bit_Not
 151      (Opnd   : System.Address;
 152       Len    : Natural;
 153       Result : System.Address)
 154    is
 155       OpndB   : constant Bits := To_Bits (Opnd);
 156       ResultB : constant Bits := To_Bits (Result);
 157
 158    begin
 159       for J in 1 .. (Len + 7) / 8 loop
 160          ResultB (J) := not OpndB (J);
 161       end loop;
 162    end Bit_Not;
 163
 164    ------------
 165    -- Bit_Or --
 166    ------------
 167
 168    procedure Bit_Or
 169      (Left   : Address;
 170       Llen   : Natural;
 171       Right  : Address;
 172       Rlen   : Natural;
 173       Result : Address)
 174    is
 175       LeftB   : constant Bits := To_Bits (Left);
 176       RightB  : constant Bits := To_Bits (Right);
 177       ResultB : constant Bits := To_Bits (Result);
 178
 179    begin
 180       if Llen /= Rlen then
 181          Raise_Error;
 182       end if;
 183
 184       for J in 1 .. (Rlen + 7) / 8 loop
 185          ResultB (J) := LeftB (J) or RightB (J);
 186       end loop;
 187    end Bit_Or;
 188
 189    -------------
 190    -- Bit_Xor --
 191    -------------
 192
 193    procedure Bit_Xor
 194      (Left   : Address;
 195       Llen   : Natural;
 196       Right  : Address;
 197       Rlen   : Natural;
 198       Result : Address)
 199    is
 200       LeftB   : constant Bits := To_Bits (Left);
 201       RightB  : constant Bits := To_Bits (Right);
 202       ResultB : constant Bits := To_Bits (Result);
 203
 204    begin
 205       if Llen /= Rlen then
 206          Raise_Error;
 207       end if;
 208
 209       for J in 1 .. (Rlen + 7) / 8 loop
 210          ResultB (J) := LeftB (J) xor RightB (J);
 211       end loop;
 212    end Bit_Xor;
 213
 214    -----------------
 215    -- Raise_Error --
 216    -----------------
 217
 218    procedure Raise_Error is
 219    begin
 220       Raise_Exception (CE, "unequal lengths in logical operation");
 221    end Raise_Error;
 222
 223 end System.Bit_Ops;