From: Avi Kivity <avi@redhat.com>
To: Markus Armbruster <armbru@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>,
Peter Maydell <peter.maydell@linaro.org>,
qemu-devel@nongnu.org, Jia Liu <proljc@gmail.com>,
patches@linaro.org
Subject: Re: [Qemu-devel] [PATCH] bitops.h: Add field32() and field64() functions to extract bitfields
Date: Sun, 08 Jul 2012 14:37:56 +0300 [thread overview]
Message-ID: <4FF97114.1050507@redhat.com> (raw)
In-Reply-To: <m3r4t0565f.fsf@blackfin.pond.sub.org>
On 06/28/2012 08:58 AM, Markus Armbruster wrote:
>>>
>>> Better code is an argument only if the effect can be demonstrated.
>>
>> I don't know even for which compilers or CPUs this is true so it's
>> unlikely I could demonstrate it. However, googling finds a few
>> articles in defense of this.
>
> Hearsay. Your honor, I rest my case :)
On x86_64, conversion from unsigned to unsigned long takes zero
instructions, but conversion from int to long takes one instruction. So
expressions like a[i] are one instruction shorter if the index is unsigned.
unsigned is also slightly safer from a security perspective, since you
only need to consider overflow, not underflow.
I used to be an int fan but I have been converted. My fingers still
prefer int though.
--
error compiling committee.c: too many arguments to function
next parent reply other threads:[~2012-07-08 11:38 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
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2012-07-08 11:37 ` Avi Kivity [this message]
2012-07-08 11:45 ` [Qemu-devel] [PATCH] bitops.h: Add field32() and field64() functions to extract bitfields Blue Swirl
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