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authorRobert P. J. Day <rpjday@mindspring.com>2007-10-16 23:29:32 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 08:42:56 -0700
commitb311e921b385b5a848f0806df16276aca1ecae07 (patch)
tree957947e319b23150ddbbf7db52f9bdd24b6cdba5
parentd9aacccf457d07d729cfc7bf20ff0c7428357a9f (diff)
Add a "rounddown_pow_of_two" routine to log2.h
To go along with the existing "roundup_pow_of_two" routine, add one for rounding down since that operation appears to crop up on a regular basis in the source tree. [m.kozlowski@tuxland.pl: fix unbalanced parentheses] Signed-off-by: Robert P. J. Day <rpjday@mindspring.com> Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/log2.h25
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 1b8a2c1cb0e3..c8cf5e8ef171 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -63,6 +63,15 @@ unsigned long __roundup_pow_of_two(unsigned long n)
return 1UL << fls_long(n - 1);
}
+/*
+ * round down to nearest power of two
+ */
+static inline __attribute__((const))
+unsigned long __rounddown_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
@@ -165,4 +174,20 @@ unsigned long __roundup_pow_of_two(unsigned long n)
__roundup_pow_of_two(n) \
)
+/**
+ * rounddown_pow_of_two - round the given value down to nearest power of two
+ * @n - parameter
+ *
+ * round the given value down 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 rounddown_pow_of_two(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ (n == 1) ? 0 : \
+ (1UL << ilog2(n))) : \
+ __rounddown_pow_of_two(n) \
+ )
+
#endif /* _LINUX_LOG2_H */