1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
/* nbdkit
* Copyright Red Hat
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Red Hat nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef NBDKIT_COMPILER_MACROS_H
#define NBDKIT_COMPILER_MACROS_H
#ifndef __cplusplus
/* BUILD_BUG_UNLESS_TRUE(1) => 0
* BUILD_BUG_UNLESS_TRUE(0) => compile-time failure
*
* It works by constructing a struct which has an impossible
* (negative-sized) bitfield in the false case. Anonymous bitfields
* are permitted in C99 and above.
*
* The Linux kernel calls this BUILD_BUG_ON_ZERO(!cond) which is a
* confusing name. It has the same semantics except cond is negated.
*/
#define BUILD_BUG_STRUCT_SIZE(cond) \
(sizeof (struct { int: (cond) ? 1 : -1; }))
#define BUILD_BUG_UNLESS_TRUE(cond) \
(BUILD_BUG_STRUCT_SIZE (cond) - BUILD_BUG_STRUCT_SIZE (cond))
/* Each of TYPE_IS_POINTER() and TYPE_IS_ARRAY() produces a build failure if it
* is invoked with an object that has neither pointer-to-object type nor array
* type.
*
* C99 6.5.2.1 constrains one of the operands of the subscript operator to have
* pointer-to-object type, and the other operand to have integer type. In the
* replacement text of TYPE_IS_POINTER(), we use [0] as subscript (providing the
* integer operand), therefore the macro argument (p) is constrained to have
* pointer-to-object type.
*
* If TYPE_IS_POINTER() is invoked with a pointer that has pointer-to-object
* type, the constraint is directly satisfied, and TYPE_IS_POINTER() evaluates,
* at compile time, to 1.
*
* If TYPE_IS_POINTER() is invoked with an array, the constraint of the
* subscript operator is satisfied again -- because the array argument "decays"
* to a pointer to the array's initial element (C99 6.3.2p3) --, and
* TYPE_IS_POINTER() evaluates, at compile time, to 0.
*
* If TYPE_IS_POINTER() is invoked with an argument having any other type, then
* the subscript operator constraint is not satisfied, and C99 5.1.1.3p1
* requires the emission of a diagnostic message -- the build breaks. Therefore,
* TYPE_IS_ARRAY() can be defined simply as the logical negation of
* TYPE_IS_POINTER().
*/
#define TYPE_IS_POINTER(p) \
(__builtin_types_compatible_p (typeof (p), typeof (&(p)[0])))
#define TYPE_IS_ARRAY(a) (!TYPE_IS_POINTER (a))
#else /* __cplusplus */
#define BUILD_BUG_UNLESS_TRUE(cond) 0
#define TYPE_IS_POINTER(p) 1
#define TYPE_IS_ARRAY(a) 1
#endif /* __cplusplus */
#endif /* NBDKIT_COMPILER_MACROS_H */
|
