diff options
Diffstat (limited to 'gl/verify.h')
| -rw-r--r-- | gl/verify.h | 41 |
1 files changed, 32 insertions, 9 deletions
diff --git a/gl/verify.h b/gl/verify.h index bcd3f5a0..4ad780c8 100644 --- a/gl/verify.h +++ b/gl/verify.h @@ -69,13 +69,14 @@ 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__); + #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. + 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 @@ -103,20 +104,41 @@ 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 GCC does not warn about the last declaration mentioned above. If a future version of GCC introduces a warning for this, the problem could be worked around - by using code specialized to GCC, e.g.,: + by using code specialized to GCC, just as __COUNTER__ is already + being used if available. #if 4 <= __GNUC__ - # define verify(R) \ - extern int (* verify_function__ (void)) \ - [__builtin_constant_p (R) && (R) ? 1 : -1] + # define verify(R) [another version to keep GCC happy] #endif * 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. Return 1. */ @@ -135,6 +157,7 @@ template <int w> /* Verify requirement R at compile-time, as a declaration without a trailing ';'. */ -# define verify(R) extern int (* verify_function__ (void)) [verify_true (R)] +# define verify(R) \ + extern int (* _GL_GENSYM (verify_function) (void)) [verify_true (R)] #endif |