linux-kernel - [PATCH] Optimize is_power_of

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Message-Id: <1181926602.25193.5.camel@grianne>
Date:	Fri, 15 Jun 2007 18:56:42 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] Optimize is_power_of_2().

From: Vegard Nossum <vegard@...tkore.net>
Date: Fri, 15 Jun 2007 18:35:49 +0200
Subject: [PATCH] Optimize is_power_of_2().

Rationale: Removes one conditional branch and reduces icache footprint.
Proof: If n is false, the product of n and any value is false. If n is
true, the truth of (n * x) is the truth of x.

Signed-off-by: Vegard Nossum <vegard@...tkore.net>
---
 include/linux/log2.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 1b8a2c1..56196b1 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -51,7 +51,7 @@ int __ilog2_u64(u64 n)
 static inline __attribute__((const))
 bool is_power_of_2(unsigned long n)
 {
-	return (n != 0 && ((n & (n - 1)) == 0));
+	return n * !(n & (n - 1));
 }

 /*
-- 
1.5.0.6

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