From: Eric Blake <eblake@redhat.com>
To: Richard Henderson <rth@twiddle.net>
Cc: Alex Williamson <alex.williamson@redhat.com>,
lersek@redhat.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2] exec: Fix non-power-of-2 sized accesses
Date: Fri, 16 Aug 2013 14:04:06 -0600 [thread overview]
Message-ID: <520E85B6.3070004@redhat.com> (raw)
In-Reply-To: <520E817B.3010105@twiddle.net>
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On 08/16/2013 01:46 PM, Richard Henderson wrote:
> On 08/16/2013 08:37 AM, Alex Williamson wrote:
>> On Fri, 2013-08-16 at 08:27 -0700, Richard Henderson wrote:
>>> On 08/16/2013 05:50 AM, Alex Williamson wrote:
>>>> + /* Size must be a power of 2 */
>>>> + if (l & (l - 1)) {
>>>> + while (l & (access_size_max - 1)) {
>>>> + access_size_max >>= 1;
>>>> + }
>>>> + }
>>>> +
>>>
>>> Why the loop at all? x & -x extracts the lsb of x.
>>
>> l = 5, we want 4, not 1. Thanks,
>
> It still doesn't require a loop.
>
> l = 1 << (31 - clz32(l));
or even pow2floor() declared in qemu-common.h and implemented in
cutils.c. No need to reinvent what we already have.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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prev parent reply other threads:[~2013-08-16 20:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-16 12:50 [Qemu-devel] [PATCH v2] exec: Fix non-power-of-2 sized accesses Alex Williamson
2013-08-16 13:37 ` Laszlo Ersek
2013-08-16 15:27 ` Richard Henderson
2013-08-16 15:37 ` Alex Williamson
2013-08-16 15:43 ` Alex Williamson
2013-08-16 15:46 ` Alex Williamson
2013-08-16 19:46 ` Richard Henderson
2013-08-16 20:04 ` Eric Blake [this message]
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