linux-kernel - Re: [PATCH v11 09/15] iio: afe: rescale: reduce risk of integer overflow

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Message-ID: <CAHp75Vc0aWrFtNK1ZkHkwP62zNXQJaDcn9pc8Uhfq0kOnWzmJg@mail.gmail.com>
Date:   Wed, 22 Dec 2021 14:29:04 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Liam Beguin <liambeguin@...il.com>
Cc:     Peter Rosin <peda@...ntia.se>, Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v11 09/15] iio: afe: rescale: reduce risk of integer overflow

On Wed, Dec 22, 2021 at 5:47 AM Liam Beguin <liambeguin@...il.com> wrote:
>
> From: Liam Beguin <lvb@...hos.com>
>
> Reduce the risk of integer overflow by doing the scale calculation on
> a 64-bit integer. Since the rescaling is only performed on *val, reuse
> the IIO_VAL_FRACTIONAL_LOG2 case.

...

> -               tmp = 1 << *val2;

At some point this should be BIT()
Rule of thumb (in accordance with C standard), always use unsigned
value as left operand of the _left_ shift.

> +               if (scale_type == IIO_VAL_FRACTIONAL)
> +                       tmp = *val2;
> +               else
> +                       tmp = 1 << *val2;


-- 
With Best Regards,
Andy Shevchenko