linux-kernel - Re: [PATCH v11 08/15] iio: afe: rescale: fix accuracy for small fractional scales

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Message-ID: <CAHp75VdonriGKBQz=pnJboPZ=HPfuYSakEGCorBath5iBxfX_Q@mail.gmail.com>
Date:   Wed, 22 Dec 2021 14:27:01 +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 08/15] iio: afe: rescale: fix accuracy for small
 fractional scales

On Wed, Dec 22, 2021 at 5:47 AM Liam Beguin <liambeguin@...il.com> wrote:
>
> From: Liam Beguin <lvb@...hos.com>
>
> The approximation caused by integer divisions can be costly on smaller
> scale values since the decimal part is significant compared to the
> integer part. Switch to an IIO_VAL_INT_PLUS_NANO scale type in such
> cases to maintain accuracy.

...

> -               tmp = div_s64(tmp, 1000000000LL);
> +
> +               tmp = div_s64_rem(tmp, 1000000000LL, &rem);
>                 *val = tmp;

> -               return scale_type;
> +

It seems you may add this blank line to one of the previous patches, may you?

> +               if (!rem)
> +                       return scale_type;

-- 
With Best Regards,
Andy Shevchenko