linux-kernel - Re: [PATCH] ds2760: fix integer overflow for time_to_empty

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Message-ID: <20090730140041.GA25759@oksana.dev.rtsoft.ru>
Date:	Thu, 30 Jul 2009 18:00:41 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Daniel Mack <daniel@...aq.de>
Cc:	linux-kernel@...r.kernel.org,
	Szabolcs Gyurko <szabolcs.gyurko@....hu>,
	Matt Reimer <mreimer@...p.net>, Anton Vorontsov <cbou@...l.ru>
Subject: Re: [PATCH] ds2760: fix integer overflow for time_to_empty_now

On Fri, Jul 24, 2009 at 03:19:33PM +0200, Daniel Mack wrote:
> On the device we're currently developing, battery sizes of ~2.8Ah and
> current flow of ~600mA are typical.
> 
> With that values, the life_sec computation overflows due to the
> multiplication by 3600.
> 
> Signed-off-by: Daniel Mack <daniel@...aq.de>
> Cc: Szabolcs Gyurko <szabolcs.gyurko@....hu>
> Cc: Matt Reimer <mreimer@...p.net>
> Cc: Anton Vorontsov <cbou@...l.ru>
> 
> Signed-off-by: Daniel Mack <daniel@...aq.de>
> ---
>  drivers/power/ds2760_battery.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/ds2760_battery.c b/drivers/power/ds2760_battery.c
> index d545fee..5d30dc0 100644
> --- a/drivers/power/ds2760_battery.c
> +++ b/drivers/power/ds2760_battery.c
> @@ -212,8 +212,8 @@ static int ds2760_battery_read_status(struct ds2760_device_info *di)
>  		di->rem_capacity = 100;
>  
>  	if (di->current_uA)
> -		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) *
> -				 3600L) / di->current_uA;
> +		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) * 36L)
> +					/ (di->current_uA / 100L);

Hm... "(di->current_uA / 100L)" might result to 0, so you'll get
div by zero. Removing the parenthesis will help.

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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