linux-kernel - [PATCH 1/2] lib/lcm.c: Ensure correct result whenever it fits

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Message-Id: <1387291572-12348-1-git-send-email-linux@rasmusvillemoes.dk>
Date:	Tue, 17 Dec 2013 15:46:11 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	linux-kernel@...r.kernel.org
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH 1/2] lib/lcm.c: Ensure correct result whenever it fits

Ensure that lcm(a,b) returns the mathematically correct result,
provided it fits in an unsigned long. The current version returns
garbage if a*b overflows, even if the final result would fit.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
There are of course still plenty of cases where the return value is
wrong.

 lib/lcm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/lcm.c b/lib/lcm.c
index b9c8de4..01b3aa9 100644
--- a/lib/lcm.c
+++ b/lib/lcm.c
@@ -7,7 +7,7 @@
 unsigned long lcm(unsigned long a, unsigned long b)
 {
 	if (a && b)
-		return (a * b) / gcd(a, b);
+		return (a / gcd(a, b)) * b;
 	else if (b)
 		return b;
 
-- 
1.8.4.rc3.2.g61bff3f

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