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

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Message-ID: <87y52i94aw.fsf@rasmusvillemoes.dk>
Date:	Tue, 14 Jan 2014 12:43:51 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib/lcm.c: Ensure correct result whenever it fits

Rasmus Villemoes <linux@...musvillemoes.dk> writes:

Ping...

> 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;

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