From: Antti Palosaari <crope@iki.fi>
To: Peter Rosin <peda@lysator.liu.se>
Cc: linux-media@vger.kernel.org,
Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
linux-kernel@vger.kernel.org
Subject: Re: m88ds3103: Undefined division
Date: Fri, 19 Feb 2016 12:46:42 +0200 [thread overview]
Message-ID: <56C6F292.3090508@iki.fi> (raw)
In-Reply-To: <56C6EA14.7080405@lysator.liu.se>
On 02/19/2016 12:10 PM, Peter Rosin wrote:
> Hi!
>
> I'm looking at this code in drivers/media/dvb-frontends/m88ds3103.c in
> the m88ds3103_set_frontend() function, line 600 (give or take):
>
> s32tmp = 0x10000 * (tuner_frequency - c->frequency);
> s32tmp = DIV_ROUND_CLOSEST(s32tmp, priv->mclk_khz);
> if (s32tmp < 0)
> s32tmp += 0x10000;
>
> There is code that tries to handle negative s32tmp, so I assume that
> negative s32tmp is a possibility. Further, priv->mclk_khz is an unsigned
> type as far as I can tell. But then we have this comment for the
> DIV_ROUND_CLOSEST macro:
>
> /*
> * Divide positive or negative dividend by positive divisor and round
> * to closest integer. Result is undefined for negative divisors and
> * for negative dividends if the divisor variable type is unsigned.
> */
> #define DIV_ROUND_CLOSEST(x, divisor)( \
>
> I don't know how bad this is, and what the consequences of garbage are,
> but from here it looks like a problem waiting to happen...
Divisor type (mclk) needs to be changed signed then somehow...
regards
Antti
--
http://palosaari.fi/
prev parent reply other threads:[~2016-02-19 10:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-19 10:10 Peter Rosin
2016-02-19 10:46 ` Antti Palosaari [this message]
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