File : 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) 1996-2013, 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 -- --
19 -- --
20 -- --
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;