1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . B I T _ O P S --
9 -- Copyright (C) 1996-2005 Free Software Foundation, Inc. --
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 2, 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. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
32 ------------------------------------------------------------------------------
34 with System; use System;
35 with System.Pure_Exceptions; use System.Pure_Exceptions;
36 with System.Unsigned_Types; use System.Unsigned_Types;
38 with Unchecked_Conversion;
40 package body System.Bit_Ops is
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).
51 type Bits is access Bits_Array;
52 -- This is the actual type into which address values are converted
54 function To_Bits is new Unchecked_Conversion (Address, Bits);
56 LE : constant := Standard'Default_Bit_Order;
57 -- Static constant set to 0 for big-endian, 1 for little-endian
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).
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#);
71 -----------------------
72 -- Local Subprograms --
73 -----------------------
75 procedure Raise_Error;
76 -- Raise Constraint_Error, complaining about unequal lengths
89 LeftB : constant Bits := To_Bits (Left);
90 RightB : constant Bits := To_Bits (Right);
91 ResultB : constant Bits := To_Bits (Result);
98 for J in 1 .. (Rlen + 7) / 8 loop
99 ResultB (J) := LeftB (J) and RightB (J);
111 Rlen : Natural) return Boolean
113 LeftB : constant Bits := To_Bits (Left);
114 RightB : constant Bits := To_Bits (Right);
122 BLen : constant Natural := Llen / 8;
123 Bitc : constant Natural := Llen mod 8;
126 if LeftB (1 .. BLen) /= RightB (1 .. BLen) then
131 ((LeftB (BLen + 1) xor RightB (BLen + 1))
132 and Masks (Bitc)) = 0;
146 (Opnd : System.Address;
148 Result : System.Address)
150 OpndB : constant Bits := To_Bits (Opnd);
151 ResultB : constant Bits := To_Bits (Result);
154 for J in 1 .. (Len + 7) / 8 loop
155 ResultB (J) := not OpndB (J);
170 LeftB : constant Bits := To_Bits (Left);
171 RightB : constant Bits := To_Bits (Right);
172 ResultB : constant Bits := To_Bits (Result);
179 for J in 1 .. (Rlen + 7) / 8 loop
180 ResultB (J) := LeftB (J) or RightB (J);
195 LeftB : constant Bits := To_Bits (Left);
196 RightB : constant Bits := To_Bits (Right);
197 ResultB : constant Bits := To_Bits (Result);
204 for J in 1 .. (Rlen + 7) / 8 loop
205 ResultB (J) := LeftB (J) xor RightB (J);
213 procedure Raise_Error is
215 Raise_Exception (CE, "unequal lengths in logical operation");