linux-kernel - [PATCH] log2.h: Define order_base

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Date:	Sat, 10 Nov 2007 22:53:36 -0500 (EST)
From:	"Robert P. J. Day" <rpjday@...shcourse.ca>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
cc:	Andrew Morton <akpm@...l.org>
Subject: [PATCH] log2.h: Define order_base_2() macro for convenience.

Given a number of places in the tree that need to calculate this value
explicitly, might as well just create a macro for it.

Signed-off-by: Robert P. J. Day <rpjday@...shcourse.ca>

---

  run-time tested for the first several values.  note that this macro
is defined strictly in terms of rounding *up* -- i've seen no places
in the tree that require this expression to be rounded down, so i'm
not drawing that distinction.

diff --git a/include/linux/log2.h b/include/linux/log2.h
index c8cf5e8..ed121c0 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -190,4 +190,20 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
 	__rounddown_pow_of_two(n)		\
  )

+/**
+ * order_base_2 - calculate the (rounded up) base 2 order of the argument
+ * @n - parameter
+ *
+ * The first few values calculated by this routine:
+ *  ob2(0) = 0
+ *  ob2(1) = 0
+ *  ob2(2) = 1
+ *  ob2(3) = 2
+ *  ob2(4) = 2
+ *  ob2(5) = 3
+ *  ... and so on.
+ */
+
+#define order_base_2(n) ilog2(roundup_pow_of_two(n))
+
 #endif /* _LINUX_LOG2_H */

-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http://crashcourse.ca
========================================================================
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