[PATCH] LOG2: Alter roundup_pow_of_two() so that it can use a ilog2() on a constant

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>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3710cce16642fd9e04464a463d912363e2560f7f..e8bfac34d2ba1cdd6192b5c270ef9d41159df883 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -158,12 +158,6 @@ static inline int printk(const char *s, ...) { return 0; }
 
 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);
 extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 3979c60325ffabb9df953ac02bb8e24986608dc2..d02e1a547a7e9deb1e8bc21857780bdc2c7693c0 100644 (file)
--- 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 @@ int __ilog2_u64(u64 n)
        __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 */