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authorDavid Herrmann <dh.herrmann@gmail.com>2014-08-15 16:54:52 +0200
committerDavid Herrmann <dh.herrmann@gmail.com>2014-08-15 16:59:09 +0200
commit7242d7420b04132f93f1426ec713f9b09bdeba54 (patch)
tree79937cb4843d701f1f7c6fdb6b954a9c9a720925 /src/shared
parentfdcba430aeae442ab0ea12a08d96cfc3d13f57ef (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.h9
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); \