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| 1 /* Compile-time assert-like macros. |
| 2 |
| 3 Copyright (C) 2005-2006, 2009-2012 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__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__)) && !defined __cplu
splus |
| 35 # define _GL_HAVE__STATIC_ASSERT 1 |
| 36 # endif |
| 37 /* The condition (99 < __GNUC__) is temporary, until we know about the |
| 38 first G++ release that supports static_assert. */ |
| 39 # if (99 < __GNUC__) && defined __cplusplus |
| 40 # define _GL_HAVE_STATIC_ASSERT 1 |
| 41 # endif |
| 42 |
| 43 /* Each of these macros verifies that its argument R is nonzero. To |
| 44 be portable, R should be an integer constant expression. Unlike |
| 45 assert (R), there is no run-time overhead. |
| 46 |
| 47 If _Static_assert works, verify (R) uses it directly. Similarly, |
| 48 _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct |
| 49 that is an operand of sizeof. |
| 50 |
| 51 The code below uses several ideas for C++ compilers, and for C |
| 52 compilers that do not support _Static_assert: |
| 53 |
| 54 * The first step is ((R) ? 1 : -1). Given an expression R, of |
| 55 integral or boolean or floating-point type, this yields an |
| 56 expression of integral type, whose value is later verified to be |
| 57 constant and nonnegative. |
| 58 |
| 59 * Next this expression W is wrapped in a type |
| 60 struct _gl_verify_type { |
| 61 unsigned int _gl_verify_error_if_negative: W; |
| 62 }. |
| 63 If W is negative, this yields a compile-time error. No compiler can |
| 64 deal with a bit-field of negative size. |
| 65 |
| 66 One might think that an array size check would have the same |
| 67 effect, that is, that the type struct { unsigned int dummy[W]; } |
| 68 would work as well. However, inside a function, some compilers |
| 69 (such as C++ compilers and GNU C) allow local parameters and |
| 70 variables inside array size expressions. With these compilers, |
| 71 an array size check would not properly diagnose this misuse of |
| 72 the verify macro: |
| 73 |
| 74 void function (int n) { verify (n < 0); } |
| 75 |
| 76 * For the verify macro, the struct _gl_verify_type will need to |
| 77 somehow be embedded into a declaration. To be portable, this |
| 78 declaration must declare an object, a constant, a function, or a |
| 79 typedef name. If the declared entity uses the type directly, |
| 80 such as in |
| 81 |
| 82 struct dummy {...}; |
| 83 typedef struct {...} dummy; |
| 84 extern struct {...} *dummy; |
| 85 extern void dummy (struct {...} *); |
| 86 extern struct {...} *dummy (void); |
| 87 |
| 88 two uses of the verify macro would yield colliding declarations |
| 89 if the entity names are not disambiguated. A workaround is to |
| 90 attach the current line number to the entity name: |
| 91 |
| 92 #define _GL_CONCAT0(x, y) x##y |
| 93 #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
| 94 extern struct {...} * _GL_CONCAT (dummy, __LINE__); |
| 95 |
| 96 But this has the problem that two invocations of verify from |
| 97 within the same macro would collide, since the __LINE__ value |
| 98 would be the same for both invocations. (The GCC __COUNTER__ |
| 99 macro solves this problem, but is not portable.) |
| 100 |
| 101 A solution is to use the sizeof operator. It yields a number, |
| 102 getting rid of the identity of the type. Declarations like |
| 103 |
| 104 extern int dummy [sizeof (struct {...})]; |
| 105 extern void dummy (int [sizeof (struct {...})]); |
| 106 extern int (*dummy (void)) [sizeof (struct {...})]; |
| 107 |
| 108 can be repeated. |
| 109 |
| 110 * Should the implementation use a named struct or an unnamed struct? |
| 111 Which of the following alternatives can be used? |
| 112 |
| 113 extern int dummy [sizeof (struct {...})]; |
| 114 extern int dummy [sizeof (struct _gl_verify_type {...})]; |
| 115 extern void dummy (int [sizeof (struct {...})]); |
| 116 extern void dummy (int [sizeof (struct _gl_verify_type {...})]); |
| 117 extern int (*dummy (void)) [sizeof (struct {...})]; |
| 118 extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; |
| 119 |
| 120 In the second and sixth case, the struct type is exported to the |
| 121 outer scope; two such declarations therefore collide. GCC warns |
| 122 about the first, third, and fourth cases. So the only remaining |
| 123 possibility is the fifth case: |
| 124 |
| 125 extern int (*dummy (void)) [sizeof (struct {...})]; |
| 126 |
| 127 * GCC warns about duplicate declarations of the dummy function if |
| 128 -Wredundant_decls is used. GCC 4.3 and later have a builtin |
| 129 __COUNTER__ macro that can let us generate unique identifiers for |
| 130 each dummy function, to suppress this warning. |
| 131 |
| 132 * This implementation exploits the fact that older versions of GCC, |
| 133 which do not support _Static_assert, also do not warn about the |
| 134 last declaration mentioned above. |
| 135 |
| 136 * In C++, any struct definition inside sizeof is invalid. |
| 137 Use a template type to work around the problem. */ |
| 138 |
| 139 /* Concatenate two preprocessor tokens. */ |
| 140 # define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
| 141 # define _GL_CONCAT0(x, y) x##y |
| 142 |
| 143 /* _GL_COUNTER is an integer, preferably one that changes each time we |
| 144 use it. Use __COUNTER__ if it works, falling back on __LINE__ |
| 145 otherwise. __LINE__ isn't perfect, but it's better than a |
| 146 constant. */ |
| 147 # if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
| 148 # define _GL_COUNTER __COUNTER__ |
| 149 # else |
| 150 # define _GL_COUNTER __LINE__ |
| 151 # endif |
| 152 |
| 153 /* Generate a symbol with the given prefix, making it unique if |
| 154 possible. */ |
| 155 # define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
| 156 |
| 157 /* Verify requirement R at compile-time, as an integer constant expression |
| 158 that returns 1. If R is false, fail at compile-time, preferably |
| 159 with a diagnostic that includes the string-literal DIAGNOSTIC. */ |
| 160 |
| 161 # define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
| 162 (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) |
| 163 |
| 164 # ifdef __cplusplus |
| 165 # if !GNULIB_defined_struct__gl_verify_type |
| 166 template <int w> |
| 167 struct _gl_verify_type { |
| 168 unsigned int _gl_verify_error_if_negative: w; |
| 169 }; |
| 170 # define GNULIB_defined_struct__gl_verify_type 1 |
| 171 # endif |
| 172 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| 173 _gl_verify_type<(R) ? 1 : -1> |
| 174 # elif defined _GL_HAVE__STATIC_ASSERT |
| 175 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| 176 struct { \ |
| 177 _Static_assert (R, DIAGNOSTIC); \ |
| 178 int _gl_dummy; \ |
| 179 } |
| 180 # else |
| 181 # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| 182 struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } |
| 183 # endif |
| 184 |
| 185 /* Verify requirement R at compile-time, as a declaration without a |
| 186 trailing ';'. If R is false, fail at compile-time, preferably |
| 187 with a diagnostic that includes the string-literal DIAGNOSTIC. |
| 188 |
| 189 Unfortunately, unlike C11, this implementation must appear as an |
| 190 ordinary declaration, and cannot appear inside struct { ... }. */ |
| 191 |
| 192 # ifdef _GL_HAVE__STATIC_ASSERT |
| 193 # define _GL_VERIFY _Static_assert |
| 194 # else |
| 195 # define _GL_VERIFY(R, DIAGNOSTIC) \ |
| 196 extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
| 197 [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] |
| 198 # endif |
| 199 |
| 200 /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ |
| 201 # ifdef _GL_STATIC_ASSERT_H |
| 202 # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert |
| 203 # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC) |
| 204 # endif |
| 205 # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert |
| 206 # define static_assert _Static_assert /* C11 requires this #define. */ |
| 207 # endif |
| 208 # endif |
| 209 |
| 210 /* @assert.h omit start@ */ |
| 211 |
| 212 /* Each of these macros verifies that its argument R is nonzero. To |
| 213 be portable, R should be an integer constant expression. Unlike |
| 214 assert (R), there is no run-time overhead. |
| 215 |
| 216 There are two macros, since no single macro can be used in all |
| 217 contexts in C. verify_true (R) is for scalar contexts, including |
| 218 integer constant expression contexts. verify (R) is for declaration |
| 219 contexts, e.g., the top level. */ |
| 220 |
| 221 /* Verify requirement R at compile-time, as an integer constant expression. |
| 222 Return 1. This is equivalent to verify_expr (R, 1). |
| 223 |
| 224 verify_true is obsolescent; please use verify_expr instead. */ |
| 225 |
| 226 # define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")") |
| 227 |
| 228 /* Verify requirement R at compile-time. Return the value of the |
| 229 expression E. */ |
| 230 |
| 231 # define verify_expr(R, E) \ |
| 232 (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) |
| 233 |
| 234 /* Verify requirement R at compile-time, as a declaration without a |
| 235 trailing ';'. */ |
| 236 |
| 237 # define verify(R) _GL_VERIFY (R, "verify (" #R ")") |
| 238 |
| 239 /* @assert.h omit end@ */ |
| 240 |
| 241 #endif |
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