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authorRoland Dreier <rdreier@cisco.com>2010-01-15 17:01:22 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-01-16 12:15:39 -0800
commitcc8ef6eb21e964b1c5eb97b2d0e8ac9893e1bf86 (patch)
treec30758f4f980a71acd662f55006af80c8a11b27f /include
parentd2dbe08ddceb4ba2b274abb84326d7e69d454e5c (diff)
downloadlinux-linaro-android-cc8ef6eb21e964b1c5eb97b2d0e8ac9893e1bf86.tar.gz
kernel.h: add BUILD_BUG_ON_NOT_POWER_OF_2()
Add BUILD_BUG_ON_NOT_POWER_OF_2() When code relies on a constant being a power of 2: #define FOO 512 /* must be a power of 2 */ it would be nice to be able to do: BUILD_BUG_ON(!is_power_of_2(FOO)); However applying an inline function does not result in a compile-time constant that can be used with BUILD_BUG_ON(), so trying that gives results in: error: bit-field '<anonymous>' width not an integer constant As suggested by akpm, rather than monkeying around with is_power_of_2() and risking gcc warts about constant expressions, just create a macro BUILD_BUG_ON_NOT_POWER_OF_2() to encapsulate this common requirement. Signed-off-by: Roland Dreier <rolandd@cisco.com> Cc: Bart Van Assche <bvanassche@acm.org> Cc: David Dillow <dave@thedillows.org> Cc: "Robert P. J. Day" <rpjday@crashcourse.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/kernel.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3fc9f5aab5f..328bca609b9 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -734,6 +734,10 @@ struct sysinfo {
/* Force a compilation error if condition is constant and true */
#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
+/* Force a compilation error if a constant expression is not a power of 2 */
+#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \
+ BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
+
/* Force a compilation error if condition is true, but also produce a
result (of value 0 and type size_t), so the expression can be used
e.g. in a structure initializer (or where-ever else comma expressions