| /* Compile-time assert-like macros. |
| |
| Copyright (C) 2005-2006, 2009-2016 Free Software Foundation, Inc. |
| |
| This program is free software: you can redistribute it and/or modify |
| it under the terms of the GNU Lesser General Public License as published by |
| the Free Software Foundation; either version 2.1 of the License, or |
| (at your option) any later version. |
| |
| This program is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public License |
| along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| |
| /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ |
| |
| #ifndef _GL_VERIFY_H |
| #define _GL_VERIFY_H |
| |
| |
| /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11. |
| This is supported by GCC 4.6.0 and later, in C mode, and its use |
| here generates easier-to-read diagnostics when verify (R) fails. |
| |
| Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11. |
| This will likely be supported by future GCC versions, in C++ mode. |
| |
| Use this only with GCC. If we were willing to slow 'configure' |
| down we could also use it with other compilers, but since this |
| affects only the quality of diagnostics, why bother? */ |
| #if (4 < __GNUC__ + (6 <= __GNUC_MINOR__) \ |
| && (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \ |
| && !defined __cplusplus) |
| # define _GL_HAVE__STATIC_ASSERT 1 |
| #endif |
| /* The condition (99 < __GNUC__) is temporary, until we know about the |
| first G++ release that supports static_assert. */ |
| #if (99 < __GNUC__) && defined __cplusplus |
| # define _GL_HAVE_STATIC_ASSERT 1 |
| #endif |
| |
| /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other |
| system headers, defines a conflicting _Static_assert that is no |
| better than ours; override it. */ |
| #ifndef _GL_HAVE_STATIC_ASSERT |
| # include <stddef.h> |
| # undef _Static_assert |
| #endif |
| |
| /* Each of these macros verifies that its argument R is nonzero. To |
| be portable, R should be an integer constant expression. Unlike |
| assert (R), there is no run-time overhead. |
| |
| If _Static_assert works, verify (R) uses it directly. Similarly, |
| _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct |
| that is an operand of sizeof. |
| |
| The code below uses several ideas for C++ compilers, and for C |
| compilers that do not support _Static_assert: |
| |
| * The first step is ((R) ? 1 : -1). Given an expression R, of |
| integral or boolean or floating-point type, this yields an |
| expression of integral type, whose value is later verified to be |
| constant and nonnegative. |
| |
| * Next this expression W is wrapped in a type |
| struct _gl_verify_type { |
| unsigned int _gl_verify_error_if_negative: W; |
| }. |
| If W is negative, this yields a compile-time error. No compiler can |
| deal with a bit-field of negative size. |
| |
| One might think that an array size check would have the same |
| effect, that is, that the type struct { unsigned int dummy[W]; } |
| would work as well. However, inside a function, some compilers |
| (such as C++ compilers and GNU C) allow local parameters and |
| variables inside array size expressions. With these compilers, |
| an array size check would not properly diagnose this misuse of |
| the verify macro: |
| |
| void function (int n) { verify (n < 0); } |
| |
| * For the verify macro, the struct _gl_verify_type will need to |
| somehow be embedded into a declaration. To be portable, this |
| declaration must declare an object, a constant, a function, or a |
| typedef name. If the declared entity uses the type directly, |
| such as in |
| |
| struct dummy {...}; |
| typedef struct {...} dummy; |
| extern struct {...} *dummy; |
| extern void dummy (struct {...} *); |
| extern struct {...} *dummy (void); |
| |
| two uses of the verify macro would yield colliding declarations |
| if the entity names are not disambiguated. A workaround is to |
| attach the current line number to the entity name: |
| |
| #define _GL_CONCAT0(x, y) x##y |
| #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
| extern struct {...} * _GL_CONCAT (dummy, __LINE__); |
| |
| But this has the problem that two invocations of verify from |
| within the same macro would collide, since the __LINE__ value |
| would be the same for both invocations. (The GCC __COUNTER__ |
| macro solves this problem, but is not portable.) |
| |
| A solution is to use the sizeof operator. It yields a number, |
| getting rid of the identity of the type. Declarations like |
| |
| extern int dummy [sizeof (struct {...})]; |
| extern void dummy (int [sizeof (struct {...})]); |
| extern int (*dummy (void)) [sizeof (struct {...})]; |
| |
| can be repeated. |
| |
| * Should the implementation use a named struct or an unnamed struct? |
| Which of the following alternatives can be used? |
| |
| extern int dummy [sizeof (struct {...})]; |
| extern int dummy [sizeof (struct _gl_verify_type {...})]; |
| extern void dummy (int [sizeof (struct {...})]); |
| extern void dummy (int [sizeof (struct _gl_verify_type {...})]); |
| extern int (*dummy (void)) [sizeof (struct {...})]; |
| extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; |
| |
| In the second and sixth case, the struct type is exported to the |
| outer scope; two such declarations therefore collide. GCC warns |
| about the first, third, and fourth cases. So the only remaining |
| possibility is the fifth case: |
| |
| extern int (*dummy (void)) [sizeof (struct {...})]; |
| |
| * GCC warns about duplicate declarations of the dummy function if |
| -Wredundant-decls is used. GCC 4.3 and later have a builtin |
| __COUNTER__ macro that can let us generate unique identifiers for |
| each dummy function, to suppress this warning. |
| |
| * This implementation exploits the fact that older versions of GCC, |
| which do not support _Static_assert, also do not warn about the |
| last declaration mentioned above. |
| |
| * GCC warns if -Wnested-externs is enabled and verify() is used |
| within a function body; but inside a function, you can always |
| arrange to use verify_expr() instead. |
| |
| * In C++, any struct definition inside sizeof is invalid. |
| Use a template type to work around the problem. */ |
| |
| /* Concatenate two preprocessor tokens. */ |
| #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
| #define _GL_CONCAT0(x, y) x##y |
| |
| /* _GL_COUNTER is an integer, preferably one that changes each time we |
| use it. Use __COUNTER__ if it works, falling back on __LINE__ |
| otherwise. __LINE__ isn't perfect, but it's better than a |
| constant. */ |
| #if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
| # define _GL_COUNTER __COUNTER__ |
| #else |
| # define _GL_COUNTER __LINE__ |
| #endif |
| |
| /* Generate a symbol with the given prefix, making it unique if |
| possible. */ |
| #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
| |
| /* Verify requirement R at compile-time, as an integer constant expression |
| that returns 1. If R is false, fail at compile-time, preferably |
| with a diagnostic that includes the string-literal DIAGNOSTIC. */ |
| |
| #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
| (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) |
| |
| #ifdef __cplusplus |
| # if !GNULIB_defined_struct__gl_verify_type |
| template <int w> |
| struct _gl_verify_type { |
| unsigned int _gl_verify_error_if_negative: w; |
| }; |
| # define GNULIB_defined_struct__gl_verify_type 1 |
| # endif |
| # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| _gl_verify_type<(R) ? 1 : -1> |
| #elif defined _GL_HAVE__STATIC_ASSERT |
| # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| struct { \ |
| _Static_assert (R, DIAGNOSTIC); \ |
| int _gl_dummy; \ |
| } |
| #else |
| # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
| struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } |
| #endif |
| |
| /* Verify requirement R at compile-time, as a declaration without a |
| trailing ';'. If R is false, fail at compile-time, preferably |
| with a diagnostic that includes the string-literal DIAGNOSTIC. |
| |
| Unfortunately, unlike C11, this implementation must appear as an |
| ordinary declaration, and cannot appear inside struct { ... }. */ |
| |
| #ifdef _GL_HAVE__STATIC_ASSERT |
| # define _GL_VERIFY _Static_assert |
| #else |
| # define _GL_VERIFY(R, DIAGNOSTIC) \ |
| extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
| [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] |
| #endif |
| |
| /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ |
| #ifdef _GL_STATIC_ASSERT_H |
| # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert |
| # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC) |
| # endif |
| # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert |
| # define static_assert _Static_assert /* C11 requires this #define. */ |
| # endif |
| #endif |
| |
| /* @assert.h omit start@ */ |
| |
| /* Each of these macros verifies that its argument R is nonzero. To |
| be portable, R should be an integer constant expression. Unlike |
| assert (R), there is no run-time overhead. |
| |
| There are two macros, since no single macro can be used in all |
| contexts in C. verify_true (R) is for scalar contexts, including |
| integer constant expression contexts. verify (R) is for declaration |
| contexts, e.g., the top level. */ |
| |
| /* Verify requirement R at compile-time, as an integer constant expression. |
| Return 1. This is equivalent to verify_expr (R, 1). |
| |
| verify_true is obsolescent; please use verify_expr instead. */ |
| |
| #define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")") |
| |
| /* Verify requirement R at compile-time. Return the value of the |
| expression E. */ |
| |
| #define verify_expr(R, E) \ |
| (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) |
| |
| /* Verify requirement R at compile-time, as a declaration without a |
| trailing ';'. */ |
| |
| #define verify(R) _GL_VERIFY (R, "verify (" #R ")") |
| |
| #ifdef __has_builtin |
| # define _GL_MACRO__has_builtin __has_builtin |
| #else |
| # define _GL_MACRO__has_builtin(x) 0 |
| #endif |
| |
| /* Assume that R always holds. This lets the compiler optimize |
| accordingly. R should not have side-effects; it may or may not be |
| evaluated. Behavior is undefined if R is false. */ |
| |
| #if (_GL_MACRO__has_builtin (__builtin_unreachable) \ |
| || 4 < __GNUC__ + (5 <= __GNUC_MINOR__)) |
| # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |
| #elif 1200 <= _MSC_VER |
| # define assume(R) __assume (R) |
| #elif (defined lint \ |
| && (_GL_MACRO__has_builtin (__builtin_trap) \ |
| || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)))) |
| /* Doing it this way helps various packages when configured with |
| --enable-gcc-warnings, which compiles with -Dlint. It's nicer |
| when 'assume' silences warnings even with older GCCs. */ |
| # define assume(R) ((R) ? (void) 0 : __builtin_trap ()) |
| #else |
| # define assume(R) ((void) (0 && (R))) |
| #endif |
| |
| /* @assert.h omit end@ */ |
| |
| #endif |