1 /* -*- buffer-read-only: t -*- vi: set ro: */ 2 /* DO NOT EDIT! GENERATED AUTOMATICALLY! */ 3 /* Compile-time assert-like macros. 4 5 Copyright (C) 2005-2006, 2009-2019 Free Software Foundation, Inc. 6 7 This program is free software: you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 3 of the License, or 10 (at your option) any later version. 11 12 This program is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 19 20 /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ 21 22 #ifndef _GL_VERIFY_H 23 #define _GL_VERIFY_H 24 25 26 /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11. 27 This is supported by GCC 4.6.0 and later, in C mode, and its use 28 here generates easier-to-read diagnostics when verify (R) fails. 29 30 Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11. 31 This is supported by GCC 6.1.0 and later, in C++ mode. 32 33 Use this only with GCC. If we were willing to slow 'configure' 34 down we could also use it with other compilers, but since this 35 affects only the quality of diagnostics, why bother? */ 36 #if (4 < __GNUC__ + (6 <= __GNUC_MINOR__) \ 37 && (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \ 38 && !defined __cplusplus) 39 # define _GL_HAVE__STATIC_ASSERT 1 40 #endif 41 #if (6 <= __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 #ifdef __GNUC__ 252 # define verify(R) _GL_VERIFY (R, "verify (" #R ")") 253 #else 254 /* PGI barfs if R is long. Play it safe. */ 255 # define verify(R) _GL_VERIFY (R, "verify (...)") 256 #endif 257 258 #ifndef __has_builtin 259 # define __has_builtin(x) 0 260 #endif 261 262 /* Assume that R always holds. This lets the compiler optimize 263 accordingly. R should not have side-effects; it may or may not be 264 evaluated. Behavior is undefined if R is false. */ 265 266 #if (__has_builtin (__builtin_unreachable) \ 267 || 4 < __GNUC__ + (5 <= __GNUC_MINOR__)) 268 # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) 269 #elif 1200 <= _MSC_VER 270 # define assume(R) __assume (R) 271 #elif ((defined GCC_LINT || defined lint) \ 272 && (__has_builtin (__builtin_trap) \ 273 || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)))) 274 /* Doing it this way helps various packages when configured with 275 --enable-gcc-warnings, which compiles with -Dlint. It's nicer 276 when 'assume' silences warnings even with older GCCs. */ 277 # define assume(R) ((R) ? (void) 0 : __builtin_trap ()) 278 #else 279 /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */ 280 # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0) 281 #endif 282 283 /* @assert.h omit end@ */ 284 285 #endif 286