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279 lines
11 KiB
279 lines
11 KiB
/* Compile-time assert-like macros. |
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Copyright (C) 2005-2006, 2009-2017 Free Software Foundation, Inc. |
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This program is free software: you can redistribute it and/or modify |
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it under the terms of the GNU General Public License as published by |
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the Free Software Foundation; either version 3 of the License, or |
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(at your option) any later version. |
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This program is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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GNU General Public License for more details. |
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You should have received a copy of the GNU General Public License |
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along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
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/* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ |
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#ifndef _GL_VERIFY_H |
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#define _GL_VERIFY_H |
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/* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11. |
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This is supported by GCC 4.6.0 and later, in C mode, and its use |
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here generates easier-to-read diagnostics when verify (R) fails. |
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Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11. |
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This will likely be supported by future GCC versions, in C++ mode. |
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Use this only with GCC. If we were willing to slow 'configure' |
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down we could also use it with other compilers, but since this |
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affects only the quality of diagnostics, why bother? */ |
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#if (4 < __GNUC__ + (6 <= __GNUC_MINOR__) \ |
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&& (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \ |
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&& !defined __cplusplus) |
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# define _GL_HAVE__STATIC_ASSERT 1 |
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#endif |
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/* The condition (99 < __GNUC__) is temporary, until we know about the |
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first G++ release that supports static_assert. */ |
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#if (99 < __GNUC__) && defined __cplusplus |
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# define _GL_HAVE_STATIC_ASSERT 1 |
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#endif |
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/* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other |
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system headers, defines a conflicting _Static_assert that is no |
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better than ours; override it. */ |
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#ifndef _GL_HAVE_STATIC_ASSERT |
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# include <stddef.h> |
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# undef _Static_assert |
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#endif |
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/* Each of these macros verifies that its argument R is nonzero. To |
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be portable, R should be an integer constant expression. Unlike |
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assert (R), there is no run-time overhead. |
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If _Static_assert works, verify (R) uses it directly. Similarly, |
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_GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct |
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that is an operand of sizeof. |
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The code below uses several ideas for C++ compilers, and for C |
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compilers that do not support _Static_assert: |
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* The first step is ((R) ? 1 : -1). Given an expression R, of |
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integral or boolean or floating-point type, this yields an |
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expression of integral type, whose value is later verified to be |
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constant and nonnegative. |
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* Next this expression W is wrapped in a type |
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struct _gl_verify_type { |
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unsigned int _gl_verify_error_if_negative: W; |
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}. |
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If W is negative, this yields a compile-time error. No compiler can |
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deal with a bit-field of negative size. |
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One might think that an array size check would have the same |
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effect, that is, that the type struct { unsigned int dummy[W]; } |
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would work as well. However, inside a function, some compilers |
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(such as C++ compilers and GNU C) allow local parameters and |
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variables inside array size expressions. With these compilers, |
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an array size check would not properly diagnose this misuse of |
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the verify macro: |
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void function (int n) { verify (n < 0); } |
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* For the verify macro, the struct _gl_verify_type will need to |
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somehow be embedded into a declaration. To be portable, this |
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declaration must declare an object, a constant, a function, or a |
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typedef name. If the declared entity uses the type directly, |
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such as in |
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struct dummy {...}; |
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typedef struct {...} dummy; |
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extern struct {...} *dummy; |
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extern void dummy (struct {...} *); |
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extern struct {...} *dummy (void); |
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two uses of the verify macro would yield colliding declarations |
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if the entity names are not disambiguated. A workaround is to |
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attach the current line number to the entity name: |
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#define _GL_CONCAT0(x, y) x##y |
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#define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
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extern struct {...} * _GL_CONCAT (dummy, __LINE__); |
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But this has the problem that two invocations of verify from |
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within the same macro would collide, since the __LINE__ value |
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would be the same for both invocations. (The GCC __COUNTER__ |
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macro solves this problem, but is not portable.) |
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A solution is to use the sizeof operator. It yields a number, |
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getting rid of the identity of the type. Declarations like |
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extern int dummy [sizeof (struct {...})]; |
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extern void dummy (int [sizeof (struct {...})]); |
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extern int (*dummy (void)) [sizeof (struct {...})]; |
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can be repeated. |
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* Should the implementation use a named struct or an unnamed struct? |
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Which of the following alternatives can be used? |
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extern int dummy [sizeof (struct {...})]; |
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extern int dummy [sizeof (struct _gl_verify_type {...})]; |
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extern void dummy (int [sizeof (struct {...})]); |
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extern void dummy (int [sizeof (struct _gl_verify_type {...})]); |
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extern int (*dummy (void)) [sizeof (struct {...})]; |
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extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; |
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In the second and sixth case, the struct type is exported to the |
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outer scope; two such declarations therefore collide. GCC warns |
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about the first, third, and fourth cases. So the only remaining |
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possibility is the fifth case: |
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extern int (*dummy (void)) [sizeof (struct {...})]; |
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* GCC warns about duplicate declarations of the dummy function if |
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-Wredundant-decls is used. GCC 4.3 and later have a builtin |
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__COUNTER__ macro that can let us generate unique identifiers for |
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each dummy function, to suppress this warning. |
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* This implementation exploits the fact that older versions of GCC, |
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which do not support _Static_assert, also do not warn about the |
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last declaration mentioned above. |
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* GCC warns if -Wnested-externs is enabled and verify() is used |
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within a function body; but inside a function, you can always |
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arrange to use verify_expr() instead. |
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* In C++, any struct definition inside sizeof is invalid. |
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Use a template type to work around the problem. */ |
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/* Concatenate two preprocessor tokens. */ |
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#define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
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#define _GL_CONCAT0(x, y) x##y |
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/* _GL_COUNTER is an integer, preferably one that changes each time we |
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use it. Use __COUNTER__ if it works, falling back on __LINE__ |
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otherwise. __LINE__ isn't perfect, but it's better than a |
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constant. */ |
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#if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
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# define _GL_COUNTER __COUNTER__ |
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#else |
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# define _GL_COUNTER __LINE__ |
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#endif |
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/* Generate a symbol with the given prefix, making it unique if |
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possible. */ |
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#define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
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/* Verify requirement R at compile-time, as an integer constant expression |
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that returns 1. If R is false, fail at compile-time, preferably |
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with a diagnostic that includes the string-literal DIAGNOSTIC. */ |
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#define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
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(!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) |
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#ifdef __cplusplus |
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# if !GNULIB_defined_struct__gl_verify_type |
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template <int w> |
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struct _gl_verify_type { |
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unsigned int _gl_verify_error_if_negative: w; |
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}; |
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# define GNULIB_defined_struct__gl_verify_type 1 |
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# endif |
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# define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
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_gl_verify_type<(R) ? 1 : -1> |
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#elif defined _GL_HAVE__STATIC_ASSERT |
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# define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
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struct { \ |
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_Static_assert (R, DIAGNOSTIC); \ |
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int _gl_dummy; \ |
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} |
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#else |
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# define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
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struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } |
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#endif |
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/* Verify requirement R at compile-time, as a declaration without a |
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trailing ';'. If R is false, fail at compile-time, preferably |
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with a diagnostic that includes the string-literal DIAGNOSTIC. |
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Unfortunately, unlike C11, this implementation must appear as an |
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ordinary declaration, and cannot appear inside struct { ... }. */ |
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#ifdef _GL_HAVE__STATIC_ASSERT |
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# define _GL_VERIFY _Static_assert |
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#else |
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# define _GL_VERIFY(R, DIAGNOSTIC) \ |
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extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
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[_GL_VERIFY_TRUE (R, DIAGNOSTIC)] |
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#endif |
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/* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ |
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#ifdef _GL_STATIC_ASSERT_H |
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# if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert |
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# define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC) |
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# endif |
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# if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert |
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# define static_assert _Static_assert /* C11 requires this #define. */ |
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# endif |
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#endif |
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/* @assert.h omit start@ */ |
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/* Each of these macros verifies that its argument R is nonzero. To |
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be portable, R should be an integer constant expression. Unlike |
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assert (R), there is no run-time overhead. |
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There are two macros, since no single macro can be used in all |
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contexts in C. verify_true (R) is for scalar contexts, including |
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integer constant expression contexts. verify (R) is for declaration |
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contexts, e.g., the top level. */ |
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/* Verify requirement R at compile-time, as an integer constant expression. |
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Return 1. This is equivalent to verify_expr (R, 1). |
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verify_true is obsolescent; please use verify_expr instead. */ |
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#define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")") |
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/* Verify requirement R at compile-time. Return the value of the |
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expression E. */ |
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#define verify_expr(R, E) \ |
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(_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) |
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/* Verify requirement R at compile-time, as a declaration without a |
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trailing ';'. */ |
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#define verify(R) _GL_VERIFY (R, "verify (" #R ")") |
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#ifndef __has_builtin |
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# define __has_builtin(x) 0 |
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#endif |
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/* Assume that R always holds. This lets the compiler optimize |
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accordingly. R should not have side-effects; it may or may not be |
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evaluated. Behavior is undefined if R is false. */ |
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#if (__has_builtin (__builtin_unreachable) \ |
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|| 4 < __GNUC__ + (5 <= __GNUC_MINOR__)) |
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# define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |
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#elif 1200 <= _MSC_VER |
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# define assume(R) __assume (R) |
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#elif ((defined GCC_LINT || defined lint) \ |
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&& (__has_builtin (__builtin_trap) \ |
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|| 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)))) |
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/* Doing it this way helps various packages when configured with |
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--enable-gcc-warnings, which compiles with -Dlint. It's nicer |
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when 'assume' silences warnings even with older GCCs. */ |
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# define assume(R) ((R) ? (void) 0 : __builtin_trap ()) |
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#else |
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# define assume(R) ((void) (0 && (R))) |
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#endif |
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/* @assert.h omit end@ */ |
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#endif
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