From: Andrew Morton <akpm@linux-foundation.org>
To: Jani Nikula <jani.nikula@intel.com>
Cc: linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org,
dri-devel@lists.freedesktop.org,
"Christian König" <christian.koenig@amd.com>,
"David Gow" <davidgow@google.com>
Subject: Re: [PATCH 0/4] log2: make is_power_of_2() more generic
Date: Thu, 30 Mar 2023 12:50:41 -0700 [thread overview]
Message-ID: <20230330125041.83b0f39fa3a4ec1a42dfd95f@linux-foundation.org> (raw)
In-Reply-To: <20230330104243.2120761-1-jani.nikula@intel.com>
On Thu, 30 Mar 2023 13:42:39 +0300 Jani Nikula <jani.nikula@intel.com> wrote:
> is_power_of_2() only works for types <= sizeof(unsigned long) and it's
> also not a constant expression. There are a number of places in kernel
> where is_power_of_2() is called on u64, which fails on 32-bit
> builds. Try to remedy that. While at it, make it a constant expression
> when possible.
Yes, the current `is_power_of_2(unsigned long n)' isn't very general.
But wouldn't all these issues be addressed by simply doing
#define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
?
(With suitable tweaks to avoid evaluating `n' more than once)
next prev parent reply other threads:[~2023-03-30 19:50 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-30 10:42 [PATCH 0/4] log2: make is_power_of_2() more generic Jani Nikula
2023-03-30 10:42 ` [PATCH 1/4] log2: add helper __IS_POWER_OF_2() Jani Nikula
2023-03-30 10:42 ` [PATCH 2/4] log2: have is_power_of_2() support bigger types than unsigned long Jani Nikula
2023-03-30 10:42 ` [PATCH 3/4] log2: allow use of is_power_of_2() in constant expressions Jani Nikula
2023-03-30 10:42 ` [PATCH 4/4] drm/i915/reg: use is_power_of_2() from log2.h Jani Nikula
2023-03-30 10:59 ` [PATCH 0/4] log2: make is_power_of_2() more generic Christian König
2023-03-30 19:50 ` Andrew Morton [this message]
2023-03-30 21:53 ` David Laight
2023-03-30 22:18 ` Andrew Morton
2023-03-31 7:33 ` David Laight
2023-03-31 8:31 ` Jani Nikula
2023-04-05 15:27 ` Steven Price
2024-04-12 10:01 ` Jani Nikula
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