GIF89a; EcchiShell v1.0
//proc/self/root/usr/share/gettext/, 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