linux-kernel - Re: [PATCH v12 07/16] iio: afe: rescale: add INT_PLUS

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Date:   Sun, 9 Jan 2022 14:48:46 +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 v12 07/16] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

On Sat, Jan 8, 2022 at 10:53 PM Liam Beguin <liambeguin@...il.com> wrote:
>
> Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types.
> Add support for these to allow using the iio-rescaler with them.

...

> +               mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA;
> +
> +               /*
> +                * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if either *val
> +                * OR *val2 is negative the schan scale is negative, i.e.
> +                * *val = 1 and *val2 = -0.5 yields -1.5 not -0.5.
> +                */
> +               neg = *val < 0 || *val2 < 0;
> +
> +               tmp = (s64)abs(*val) * abs(rescale->numerator);
> +               *val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
> +
> +               tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
> +               tmp = div_s64(tmp, abs(rescale->denominator));

Isn't it too many repetitive abs() calls?

What about

// Create a macro and use for u16 (struct rn5t618_channel_ratios), s16
(struct twl4030_prescale_divider_ratios), s32 (can be reused in struct
rescale)
struct u32_fract {
  u32 numerator;
  u32 denominator;
};
// (potential reuse in struct hclge_ptp_cycle) and so on...

  struct u32_fract fract = {
    .numerator = abs(rescale->numerator),
    .denominator = abs(rescale->denominator),
  };

// obviously we can add a macro/inliner to abs() the fract struct and
return original sign

and reuse fract.numerator, fract.denominator?

> +               *val += div_s64_rem(tmp, mult, val2);
> +
> +               /*
> +                * If only one of the rescaler elements or the schan scale is
> +                * negative, the combined scale is negative.
> +                */
> +               if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
> +                       if (*val)
> +                               *val = -*val;
> +                       else
> +                               *val2 = -*val2;
> +               }


--
With Best Regards,
Andy Shevchenko