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authorDavid Howells2006-12-08 11:37:51 +0100
committerLinus Torvalds2006-12-08 17:28:51 +0100
commit312a0c170945b49f319960afd2e492c05f9dd551 (patch)
treef3c122cc65d18bc647b45d89b3a8d0fb8492422b /include/linux/log2.h
parent[PATCH] LOG2: Implement a general integer log2 facility in the kernel (diff)
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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>
Diffstat (limited to 'include/linux/log2.h')
-rw-r--r--include/linux/log2.h26
1 files changed, 26 insertions, 0 deletions
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 3979c60325ff..d02e1a547a7e 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 @@ 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 */