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Diffstat (limited to 'src/include/c.h')
| -rw-r--r-- | src/include/c.h | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/src/include/c.h b/src/include/c.h index 5847ecda839..7fe083c3afb 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -332,6 +332,33 @@ #endif /* + * Define a compiler-independent macro for determining if an expression is a + * compile-time integer const. We don't define this macro to return 0 when + * unsupported due to the risk of users of the macro misbehaving if we return + * 0 when the expression *is* an integer constant. Callers may check if this + * macro is defined by checking if HAVE_PG_BUILTIN_INTEGER_CONSTANT_P is + * defined. + */ +#if defined(HAVE__BUILTIN_CONSTANT_P) + +/* When __builtin_const_p() is available, use it. */ +#define pg_builtin_integer_constant_p(x) __builtin_constant_p(x) +#define HAVE_PG_BUILTIN_INTEGER_CONSTANT_P +#elif defined(_MSC_VER) && defined(__STDC_VERSION__) + +/* + * With MSVC we can use a trick with _Generic to make this work. This has + * been borrowed from: + * https://stackoverflow.com/questions/49480442/detecting-integer-constant-expressions-in-macros + * and only works with integer constants. Compilation will fail if given a + * constant or variable of any type other than an integer. + */ +#define pg_builtin_integer_constant_p(x) \ + _Generic((1 ? ((void *) ((x) * (uintptr_t) 0)) : &(int) {1}), int *: 1, void *: 0) +#define HAVE_PG_BUILTIN_INTEGER_CONSTANT_P +#endif + +/* * pg_assume(expr) states that we assume `expr` to evaluate to true. In assert * enabled builds pg_assume() is turned into an assertion, in optimized builds * we try to clue the compiler into the fact that `expr` is true. |