On Sun, Jan 09, 2022 at 09:20:09PM +0100, Peter Rosin wrote:
> Hi!
>
> On 2022-01-09 13:48, Andy Shevchenko wrote:
> > On Sat, Jan 8, 2022 at 10:53 PM Liam Beguin <liambeguin@xxxxxxxxx> 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?
>
> This feels a bit excessive when the "problem" is two extra abs calls.
> I don't think the code will get any easier to read by changing
> abs(rescale->denominator) into fract.denominator and with my maintainer
> hat on, I vote for just letting the compiler exercise its CSE engine.
I agree with Peter here, and would rather keep it as is.
Liam
> Cheers,
> Peter
