linux-kernel - Re: [PATCH] thermal: Fix KELVIN_TO

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Message-ID: <1395635132.13968.40.camel@joe-AO722>
Date:	Sun, 23 Mar 2014 21:25:32 -0700
From:	Joe Perches <joe@...ches.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <eduardo.valentin@...com>
Subject: Re: [PATCH] thermal: Fix KELVIN_TO_CELSIUS macro

On Sun, 2014-03-23 at 21:14 -0700, Guenter Roeck wrote:
> It is always a good idea to use paranthesis around macro parameters
> to avoid undesired side effects.
> 
> In this specific case, KELVIN_TO_CELSIUS() is used in
> drivers/platform/x86/asus-wmi.c with parameter "value & 0xFFFF",
> which due to operator evaluation order causes more or less random
> results.

Maybe it's better to use a statement expression to avoid
multiple calculations of t

Maybe;

#define KELVIN_TO_CELSIUS(t)				\
({							\
	long _t = (long)(t) - 2732;			\
	_t >= 0 ? (_t + 5) / 10 : (_t - 5) / 10;	\
})


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