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, included by 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
# 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
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 ")")
#ifndef __has_builtin
# define __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 (__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 \
&& (__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