From: William Lee Irwin III <wli@holomorphy.com>
To: linux-ia64@vger.kernel.org
Subject: Re: free bootmem feedback patch
Date: Fri, 16 Jul 2004 00:11:41 +0000 [thread overview]
Message-ID: <20040716001141.GA3411@holomorphy.com> (raw)
In-Reply-To: <40F46962.4090604@sgi.com>
On Thu, Jul 15, 2004 at 04:16:38PM -0700, William Lee Irwin III wrote:
>> Unfortunately no. It would be nice to have one.
On Fri, Jul 16, 2004 at 12:34:20AM +0100, Matthew Wilcox wrote:
> #define log2(x) (ffs(x) - 1)
> (ffs returns a value from 0 to 32 whereas log2 wants to return -1 to 31)
> Obviously it rounds down, but that's entirely consistent with the behaviour
> of, say, 7/4 in C.
The kernel uses __ffs(), which returns from 0 to 31 and is undefined on 0.
Its rounding behavior is wrong for log2(). Anyhow, we happen to know it's
a power of 2 and that __ffs() will do.
-- wli
next prev parent reply other threads:[~2004-07-16 0:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-13 22:59 free bootmem feedback patch Joshua Aas
2004-07-13 23:14 ` Luck, Tony
2004-07-13 23:52 ` Joshua Aas
2004-07-14 8:44 ` Andi Kleen
2004-07-14 9:17 ` William Lee Irwin III
2004-07-14 9:19 ` William Lee Irwin III
2004-07-14 16:17 ` Joshua Aas
2004-07-14 18:34 ` Luck, Tony
2004-07-14 22:12 ` William Lee Irwin III
2004-07-15 19:11 ` Luck, Tony
2004-07-15 19:31 ` Matthew Wilcox
2004-07-15 20:21 ` David Mosberger
2004-07-15 23:16 ` William Lee Irwin III
2004-07-15 23:34 ` Matthew Wilcox
2004-07-15 23:53 ` Luck, Tony
2004-07-16 0:09 ` David Mosberger
2004-07-16 0:11 ` William Lee Irwin III [this message]
2004-07-16 0:18 ` Matthew Wilcox
2004-07-16 0:18 ` William Lee Irwin III
2004-08-03 17:53 ` Josh Aas
2004-08-03 23:53 ` William Lee Irwin III
2004-08-06 14:11 ` Josh Aas
2004-08-06 14:17 ` William Lee Irwin III
2004-08-06 17:58 ` Luck, Tony
2004-08-06 18:27 ` Josh Aas
2004-08-06 20:09 ` Luck, Tony
2004-08-06 20:51 ` William Lee Irwin III
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