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| author | David Herrmann <dh.herrmann@gmail.com> | 2014-08-15 16:54:52 +0200 |
|---|---|---|
| committer | David Herrmann <dh.herrmann@gmail.com> | 2014-08-15 16:59:09 +0200 |
| commit | 7242d7420b04132f93f1426ec713f9b09bdeba54 (patch) | |
| tree | 79937cb4843d701f1f7c6fdb6b954a9c9a720925 /src/shared | |
| parent | fdcba430aeae442ab0ea12a08d96cfc3d13f57ef (diff) | |
macro: add CONST_MAX() macro
The CONST_MAX() macro is similar to MAX(), but verifies that both
arguments have the same type and are constant expressions. Furthermore,
the result of CONST_MAX() is again a constant-expression.
CONST_MAX() avoids any statement-expressions and other non-trivial
expression-types. This avoids rather arbitrary restrictions in both GCC
and LLVM, which both either fail with statement-expressions inside
type-declarations or statement-expressions inside static-const
initializations.
If anybody knows how to circumvent this, please feel free to unify
CONST_MAX() and MAX().
Diffstat (limited to 'src/shared')
| -rw-r--r-- | src/shared/macro.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/shared/macro.h b/src/shared/macro.h index 11bd8b3a93..179b24c983 100644 --- a/src/shared/macro.h +++ b/src/shared/macro.h @@ -140,6 +140,15 @@ static inline unsigned long ALIGN_POWER2(unsigned long u) { _a > _b ? _a : _b; \ }) +/* evaluates to (void) if _A or _B are not constant or of different types */ +#define CONST_MAX(_A, _B) \ + __extension__ (__builtin_choose_expr( \ + __builtin_constant_p(_A) && \ + __builtin_constant_p(_B) && \ + __builtin_types_compatible_p(typeof(_A), typeof(_B)), \ + ((_A) > (_B)) ? (_A) : (_B), \ + (void)0)) + #define MAX3(x,y,z) \ __extension__ ({ \ const typeof(x) _c = MAX(x,y); \ |