diff options
Diffstat (limited to 'include/qemu')
| -rw-r--r-- | include/qemu/osdep.h | 57 |
1 files changed, 47 insertions, 10 deletions
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index ff7c17b857..0d26a1b9bd 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -236,18 +236,55 @@ extern int daemon(int, int); #define SIZE_MAX ((size_t)-1) #endif -#ifndef MIN -#define MIN(a, b) (((a) < (b)) ? (a) : (b)) -#endif -#ifndef MAX -#define MAX(a, b) (((a) > (b)) ? (a) : (b)) -#endif +/* + * Two variations of MIN/MAX macros. The first is for runtime use, and + * evaluates arguments only once (so it is safe even with side + * effects), but will not work in constant contexts (such as array + * size declarations) because of the '{}'. The second is for constant + * expression use, where evaluating arguments twice is safe because + * the result is going to be constant anyway, but will not work in a + * runtime context because of a void expression where a value is + * expected. Thus, both gcc and clang will fail to compile if you use + * the wrong macro (even if the error may seem a bit cryptic). + * + * Note that neither form is usable as an #if condition; if you truly + * need to write conditional code that depends on a minimum or maximum + * determined by the pre-processor instead of the compiler, you'll + * have to open-code it. + */ +#undef MIN +#define MIN(a, b) \ + ({ \ + typeof(1 ? (a) : (b)) _a = (a), _b = (b); \ + _a < _b ? _a : _b; \ + }) +#define MIN_CONST(a, b) \ + __builtin_choose_expr( \ + __builtin_constant_p(a) && __builtin_constant_p(b), \ + (a) < (b) ? (a) : (b), \ + ((void)0)) +#undef MAX +#define MAX(a, b) \ + ({ \ + typeof(1 ? (a) : (b)) _a = (a), _b = (b); \ + _a > _b ? _a : _b; \ + }) +#define MAX_CONST(a, b) \ + __builtin_choose_expr( \ + __builtin_constant_p(a) && __builtin_constant_p(b), \ + (a) > (b) ? (a) : (b), \ + ((void)0)) -/* Minimum function that returns zero only iff both values are zero. - * Intended for use with unsigned values only. */ +/* + * Minimum function that returns zero only if both values are zero. + * Intended for use with unsigned values only. + */ #ifndef MIN_NON_ZERO -#define MIN_NON_ZERO(a, b) ((a) == 0 ? (b) : \ - ((b) == 0 ? (a) : (MIN(a, b)))) +#define MIN_NON_ZERO(a, b) \ + ({ \ + typeof(1 ? (a) : (b)) _a = (a), _b = (b); \ + _a == 0 ? _b : (_b == 0 || _b > _a) ? _a : _b; \ + }) #endif /* Round number down to multiple */ |