[libvirt] [RFC PATCH] maint: let MIN/MAX evaluate only once, on modern compilers
We might as well take advantage of gcc's extensions for a safer
MIN()/MAX() macro.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
RFC because we could also try to fall back to older gcc's typeof(a)_a=(a)
when the newer __auto_type _a=(a) is not present, and because I don't
know how to properly probe for __auto_type and/or typeof support in
clang (I know that clang added __auto_type in 2015, per
https://reviews.llvm.org/D12686); I also don't know if we have officially
stated that we require gcc/clang (because of attribute((cleanup)), which
really cannot be emulated without extensions), or if we still try to
allow compilation with other compilers; if we have, I don't know if we
have declared a minimum compiler version that we demand (qemu has recently
demanded gcc 4.8 or clang 3.4 [branded 5.1 on Apple]).
src/util/virutil.h | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/src/util/virutil.h b/src/util/virutil.h
index 908d8920ec..364e354bcb 100644
--- a/src/util/virutil.h
+++ b/src/util/virutil.h
@@ -28,10 +28,26 @@
# include <sys/types.h>
# ifndef MIN
-# define MIN(a, b) ((a) < (b) ? (a) : (b))
+# if __GNUC_PREREQ(4, 9)
+# define MIN(a, b) ({ \
+ __auto_type _a = (a); \
+ __auto_type _b = (b); \
+ _a < _b ? _a : _b; \
+ })
+# else
+# define MIN(a, b) ((a) < (b) ? (a) : (b))
+# endif
# endif
# ifndef MAX
-# define MAX(a, b) ((a) > (b) ? (a) : (b))
+# if __GNUC_PREREQ(4, 9)
+# define MAX(a, b) ({ \
+ __auto_type _a = (a); \
+ __auto_type _b = (b); \
+ _a > _b ? _a : _b; \
+ })
+# else
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+# endif
# endif
--
2.20.1