[PATCH 6/6] Alter roundup_pow_of_two() so that it can make use of long_log2() on a constant

David Howells
2006-09-13T13:03:10Z

From: David Howells <dhowells@redhat.com>

Alter roundup_pow_of_two() so that it can make use of long_log2() on a constant
to produce a constant value, retaining the ability for an arch to override it
in the non-const case.

This permits the function to be used to initialise variables.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

include/linux/kernel.h | 6 ------
include/linux/log2.h | 23 +++++++++++++++++++++++
2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e8c6c66..e5947fb 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -155,12 +155,6 @@ #endif

unsigned long int_sqrt(unsigned long);

-static inline unsigned long
-__attribute_const__ roundup_pow_of_two(unsigned long x)
-{
- return 1UL << fls_long(x - 1);
-}
-
extern int printk_ratelimit(void);
extern int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst);

diff --git a/include/linux/log2.h b/include/linux/log2.h
index a2f6858..2b55af0 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -74,6 +74,15 @@ #endif
#endif

/*
+ * round up to nearest power of two
+ */
+static inline __attribute__((const))
+unsigned long __roundup_pow_of_two(unsigned long n)
+{
+ return 1UL << fls_long(n - 1);
+}
+
+/*
* constant-capable 32-bit log of base 2 calculation
* - this can be used to initialise global variables from constant data, hence
* the massive ternary operator construction
@@ -218,4 +227,18 @@ ( \
__get_order(n, PAGE_SHIFT) \
)

+/*
+ * round up to nearest power of two
+ * - the result is undefined when n == 0
+ * - this can be used to initialise global variables from constant data
+ */
+#define roundup_pow_of_two(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ (n == 1) ? 0 : \
+ (1UL << (long_log2((n) - 1) + 1)) \
+ ) : \
+ __roundup_pow_of_two(n) \
+ )
+
#endif /* _LINUX_LOG2_H */