dhcpd-pools  2.28
ISC dhcpd lease usage analyser
verify.h
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1 /* Compile-time assert-like macros.
2 
3  Copyright (C) 2005-2006, 2009-2015 Free Software Foundation, Inc.
4 
5  This program is free software: you can redistribute it and/or modify
6  it under the terms of the GNU General Public License as published by
7  the Free Software Foundation; either version 3 of the License, or
8  (at your option) any later version.
9 
10  This program is distributed in the hope that it will be useful,
11  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  GNU General Public License for more details.
14 
15  You should have received a copy of the GNU General Public License
16  along with this program. If not, see <http://www.gnu.org/licenses/>. */
17 
18 /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */
19 
20 #ifndef _GL_VERIFY_H
21 #define _GL_VERIFY_H
22 
23 
24 /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11.
25  This is supported by GCC 4.6.0 and later, in C mode, and its use
26  here generates easier-to-read diagnostics when verify (R) fails.
27 
28  Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11.
29  This will likely be supported by future GCC versions, in C++ mode.
30 
31  Use this only with GCC. If we were willing to slow 'configure'
32  down we could also use it with other compilers, but since this
33  affects only the quality of diagnostics, why bother? */
34 #if (4 < __GNUC__ + (6 <= __GNUC_MINOR__) \
35  && (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \
36  && !defined __cplusplus)
37 # define _GL_HAVE__STATIC_ASSERT 1
38 #endif
39 /* The condition (99 < __GNUC__) is temporary, until we know about the
40  first G++ release that supports static_assert. */
41 #if (99 < __GNUC__) && defined __cplusplus
42 # define _GL_HAVE_STATIC_ASSERT 1
43 #endif
44 
45 /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
46  system headers, defines a conflicting _Static_assert that is no
47  better than ours; override it. */
48 #ifndef _GL_HAVE_STATIC_ASSERT
49 # include <stddef.h>
50 # undef _Static_assert
51 #endif
52 
53 /* Each of these macros verifies that its argument R is nonzero. To
54  be portable, R should be an integer constant expression. Unlike
55  assert (R), there is no run-time overhead.
56 
57  If _Static_assert works, verify (R) uses it directly. Similarly,
58  _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct
59  that is an operand of sizeof.
60 
61  The code below uses several ideas for C++ compilers, and for C
62  compilers that do not support _Static_assert:
63 
64  * The first step is ((R) ? 1 : -1). Given an expression R, of
65  integral or boolean or floating-point type, this yields an
66  expression of integral type, whose value is later verified to be
67  constant and nonnegative.
68 
69  * Next this expression W is wrapped in a type
70  struct _gl_verify_type {
71  unsigned int _gl_verify_error_if_negative: W;
72  }.
73  If W is negative, this yields a compile-time error. No compiler can
74  deal with a bit-field of negative size.
75 
76  One might think that an array size check would have the same
77  effect, that is, that the type struct { unsigned int dummy[W]; }
78  would work as well. However, inside a function, some compilers
79  (such as C++ compilers and GNU C) allow local parameters and
80  variables inside array size expressions. With these compilers,
81  an array size check would not properly diagnose this misuse of
82  the verify macro:
83 
84  void function (int n) { verify (n < 0); }
85 
86  * For the verify macro, the struct _gl_verify_type will need to
87  somehow be embedded into a declaration. To be portable, this
88  declaration must declare an object, a constant, a function, or a
89  typedef name. If the declared entity uses the type directly,
90  such as in
91 
92  struct dummy {...};
93  typedef struct {...} dummy;
94  extern struct {...} *dummy;
95  extern void dummy (struct {...} *);
96  extern struct {...} *dummy (void);
97 
98  two uses of the verify macro would yield colliding declarations
99  if the entity names are not disambiguated. A workaround is to
100  attach the current line number to the entity name:
101 
102  #define _GL_CONCAT0(x, y) x##y
103  #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
104  extern struct {...} * _GL_CONCAT (dummy, __LINE__);
105 
106  But this has the problem that two invocations of verify from
107  within the same macro would collide, since the __LINE__ value
108  would be the same for both invocations. (The GCC __COUNTER__
109  macro solves this problem, but is not portable.)
110 
111  A solution is to use the sizeof operator. It yields a number,
112  getting rid of the identity of the type. Declarations like
113 
114  extern int dummy [sizeof (struct {...})];
115  extern void dummy (int [sizeof (struct {...})]);
116  extern int (*dummy (void)) [sizeof (struct {...})];
117 
118  can be repeated.
119 
120  * Should the implementation use a named struct or an unnamed struct?
121  Which of the following alternatives can be used?
122 
123  extern int dummy [sizeof (struct {...})];
124  extern int dummy [sizeof (struct _gl_verify_type {...})];
125  extern void dummy (int [sizeof (struct {...})]);
126  extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
127  extern int (*dummy (void)) [sizeof (struct {...})];
128  extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})];
129 
130  In the second and sixth case, the struct type is exported to the
131  outer scope; two such declarations therefore collide. GCC warns
132  about the first, third, and fourth cases. So the only remaining
133  possibility is the fifth case:
134 
135  extern int (*dummy (void)) [sizeof (struct {...})];
136 
137  * GCC warns about duplicate declarations of the dummy function if
138  -Wredundant-decls is used. GCC 4.3 and later have a builtin
139  __COUNTER__ macro that can let us generate unique identifiers for
140  each dummy function, to suppress this warning.
141 
142  * This implementation exploits the fact that older versions of GCC,
143  which do not support _Static_assert, also do not warn about the
144  last declaration mentioned above.
145 
146  * GCC warns if -Wnested-externs is enabled and verify() is used
147  within a function body; but inside a function, you can always
148  arrange to use verify_expr() instead.
149 
150  * In C++, any struct definition inside sizeof is invalid.
151  Use a template type to work around the problem. */
152 
153 /* Concatenate two preprocessor tokens. */
154 #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
155 #define _GL_CONCAT0(x, y) x##y
156 
157 /* _GL_COUNTER is an integer, preferably one that changes each time we
158  use it. Use __COUNTER__ if it works, falling back on __LINE__
159  otherwise. __LINE__ isn't perfect, but it's better than a
160  constant. */
161 #if defined __COUNTER__ && __COUNTER__ != __COUNTER__
162 # define _GL_COUNTER __COUNTER__
163 #else
164 # define _GL_COUNTER __LINE__
165 #endif
166 
167 /* Generate a symbol with the given prefix, making it unique if
168  possible. */
169 #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
170 
171 /* Verify requirement R at compile-time, as an integer constant expression
172  that returns 1. If R is false, fail at compile-time, preferably
173  with a diagnostic that includes the string-literal DIAGNOSTIC. */
174 
175 #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \
176  (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC)))
177 
178 #ifdef __cplusplus
179 # if !GNULIB_defined_struct__gl_verify_type
180 template <int w>
181  struct _gl_verify_type {
182  unsigned int _gl_verify_error_if_negative: w;
183  };
184 # define GNULIB_defined_struct__gl_verify_type 1
185 # endif
186 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
187  _gl_verify_type<(R) ? 1 : -1>
188 #elif defined _GL_HAVE__STATIC_ASSERT
189 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
190  struct { \
191  _Static_assert (R, DIAGNOSTIC); \
192  int _gl_dummy; \
193  }
194 #else
195 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
196  struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; }
197 #endif
198 
199 /* Verify requirement R at compile-time, as a declaration without a
200  trailing ';'. If R is false, fail at compile-time, preferably
201  with a diagnostic that includes the string-literal DIAGNOSTIC.
202 
203  Unfortunately, unlike C11, this implementation must appear as an
204  ordinary declaration, and cannot appear inside struct { ... }. */
205 
206 #ifdef _GL_HAVE__STATIC_ASSERT
207 # define _GL_VERIFY _Static_assert
208 #else
209 # define _GL_VERIFY(R, DIAGNOSTIC) \
210  extern int (*_GL_GENSYM (_gl_verify_function) (void)) \
211  [_GL_VERIFY_TRUE (R, DIAGNOSTIC)]
212 #endif
213 
214 /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */
215 #ifdef _GL_STATIC_ASSERT_H
216 # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert
217 # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC)
218 # endif
219 # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert
220 # define static_assert _Static_assert /* C11 requires this #define. */
221 # endif
222 #endif
223 
224 /* @assert.h omit start@ */
225 
226 /* Each of these macros verifies that its argument R is nonzero. To
227  be portable, R should be an integer constant expression. Unlike
228  assert (R), there is no run-time overhead.
229 
230  There are two macros, since no single macro can be used in all
231  contexts in C. verify_true (R) is for scalar contexts, including
232  integer constant expression contexts. verify (R) is for declaration
233  contexts, e.g., the top level. */
234 
235 /* Verify requirement R at compile-time, as an integer constant expression.
236  Return 1. This is equivalent to verify_expr (R, 1).
237 
238  verify_true is obsolescent; please use verify_expr instead. */
239 
240 #define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")")
241 
242 /* Verify requirement R at compile-time. Return the value of the
243  expression E. */
244 
245 #define verify_expr(R, E) \
246  (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E))
247 
248 /* Verify requirement R at compile-time, as a declaration without a
249  trailing ';'. */
250 
251 #define verify(R) _GL_VERIFY (R, "verify (" #R ")")
252 
253 #ifndef __has_builtin
254 # define __has_builtin(x) 0
255 #endif
256 
257 /* Assume that R always holds. This lets the compiler optimize
258  accordingly. R should not have side-effects; it may or may not be
259  evaluated. Behavior is undefined if R is false. */
260 
261 #if (__has_builtin (__builtin_unreachable) \
262  || 4 < __GNUC__ + (5 <= __GNUC_MINOR__))
263 # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
264 #elif 1200 <= _MSC_VER
265 # define assume(R) __assume (R)
266 #elif (defined lint \
267  && (__has_builtin (__builtin_trap) \
268  || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__))))
269  /* Doing it this way helps various packages when configured with
270  --enable-gcc-warnings, which compiles with -Dlint. It's nicer
271  when 'assume' silences warnings even with older GCCs. */
272 # define assume(R) ((R) ? (void) 0 : __builtin_trap ())
273 #else
274 # define assume(R) ((void) (0 && (R)))
275 #endif
276 
277 /* @assert.h omit end@ */
278 
279 #endif