From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: "Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
"Jyoti Bhayana" <jbhayana@google.com>,
"Jonathan Cameron" <jic23@kernel.org>,
"David Lechner" <dlechner@baylibre.com>,
"Nuno Sá" <nuno.sa@analog.com>,
"Andy Shevchenko" <andy@kernel.org>
Subject: Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
Date: Fri, 31 Oct 2025 11:54:30 +0200 [thread overview]
Message-ID: <aQSHVsWGXzigTEMe@smile.fi.intel.com> (raw)
In-Reply-To: <20251031094336.6f352b4f@pumpkin>
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 :-) But we have intlog10(), I completely forgot
about it.
> Mathematically log2(x)/log2(10) is log10(x) - which would be 9.
> The code does seem to be 'in luck' though.
> NSEC_PER_SEC is 10^9 or 0x3b9aca00, so ilog2(NSEC_PER_SEC) is 29.
> ilog2(10) is 3, and 29/3 is 9.
>
> Do the same for 10^10 and you get 11.
That code looks like working by luck entirely, TBH. I just took the scope of
the patch to start dropping const_ilog2() usages.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2025-10-31 9:54 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-31 7:45 [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2() Andy Shevchenko
2025-10-31 9:43 ` David Laight
2025-10-31 9:54 ` Andy Shevchenko [this message]
2025-10-31 12:45 ` David Laight
2025-10-31 12:51 ` Andy Shevchenko
2025-10-31 16:13 ` David Laight
2025-11-03 8:30 ` Andy Shevchenko
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