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[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>
This commit is contained in:
David Howells 2006-12-08 02:37:51 -08:00 committed by Linus Torvalds
parent f0d1b0b30d
commit 312a0c1709
2 changed files with 26 additions and 6 deletions
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6
include/linux/kernel.h
View File

@ -158,12 +158,6 @@ static inline int printk(const char *s, ...) { return 0; }
unsigned long int_sqrt(unsigned long); 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(void);
extern int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst); extern int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst);
extern bool printk_timed_ratelimit(unsigned long *caller_jiffies, extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,

26
include/linux/log2.h
View File

@ -43,6 +43,15 @@ int __ilog2_u64(u64 n)
} }
#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);
}
/** /**
* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
* @n - parameter * @n - parameter
@ -128,4 +137,21 @@ int __ilog2_u64(u64 n)
__ilog2_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 */ #endif /* _LINUX_LOG2_H */