[PATCH 2/4] LOG2: Alter roundup_pow_of_two() so that it can use a ilog2() on a constant [try #4]

David Howells
2006-10-06T13:35:00Z

From: David Howells <dhowells@redhat.com>

Alter roundup_pow_of_two() so that it can make use of ilog2() 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 | 26 ++++++++++++++++++++++++++
2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 473101a..67ca3ad 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -156,12 +156,6 @@ #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 3979c60..d02e1a5 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -43,6 +43,15 @@ int __ilog2_u64(u64 n)
}
#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);
+}
+
/**
* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
* @n - parameter
@@ -128,4 +137,21 @@ ( \
__ilog2_u64(n) \
)

+/**
+ * roundup_pow_of_two - round the given value up to nearest power of two
+ * @n - parameter
+ *
+ * round the given balue up to the 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 << (ilog2((n) - 1) + 1)) \
+ ) : \
+ __roundup_pow_of_two(n) \
+ )
+
#endif /* _LINUX_LOG2_H */