linux-kernel - Re: [PATCH] drivers:iio:dac make expression evaluation 64-bit

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Date:   Wed, 22 Dec 2021 20:49:26 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Mihail Chindris <mihail.chindris@...log.com>,
        "open list:IIO SUBSYSTEM AND DRIVERS" <linux-iio@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        kernel-janitors <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] drivers:iio:dac make expression evaluation 64-bit

On Wed, Dec 22, 2021 at 5:59 PM Muhammad Usama Anjum
<usama.anjum@...labora.com> wrote:
>
> Two 32-bit values are being evaluated using 32-bit arithmetic and then
> passed to s64 type. It is wrong. Expression should be evaluated using
> 64-bit arithmetic and then passed.

...

>         dac->ch_data[ch].scale_dec = DIV_ROUND_CLOSEST((s64)rem * 1000000,
>                                                         65536);

Shouldn't the above be fixed as well? Has anybody tried to compile on
32-bit arch this?

> -       dac->ch_data[ch].offset_int = div_s64_rem(v_min * 65536, span, &rem);
> +       dac->ch_data[ch].offset_int = div_s64_rem(v_min * 65536L, span, &rem);
>         tmp = (s64)rem * 1000000;
>         dac->ch_data[ch].offset_dec = div_s64(tmp, span);
>  }

-- 
With Best Regards,
Andy Shevchenko