Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()

Andy Shevchenko
2025-10-31T12:52:06Z

On Fri, Oct 31, 2025 at 12:45:30PM +0000, David Laight wrote:
> On Fri, 31 Oct 2025 11:54:30 +0200
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > On Fri, Oct 31, 2025 at 09:43:36AM +0000, David Laight wrote:
> > > On Fri, 31 Oct 2025 08:45:00 +0100
> > > Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

...

> > > > tstamp_scale = sensor->sensor_info->tstamp_scale +
> > > > - const_ilog2(NSEC_PER_SEC) / const_ilog2(10);
> > > > + ilog2(NSEC_PER_SEC) / ilog2(10);
> > >
> > > Is that just a strange way of writing 9 ?
> >
> > Why? It's correct way of writing log¹⁰(NSEC_PER_SEC), the problem here is that
> > "i" people do not think about :-)
>
> Even without the "i" the division could easily give 8.999999.
> So you'd be relying on rounding to get the required integral value.
>
> > But we have intlog10(), I completely forgot about it.
>
> And it isn't the function the code is looking for.
> (The result is shifted left 24 and it doesn't have an optimisation
> for constants.)

Do you have an idea how to improve that?

--
With Best Regards,
Andy Shevchenko