From: "Ray Lee" <ray@madrabbit.org>
To: "Soumyadip Das Mahapatra" <dip_kernel@yahoo.co.in>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Improved Swaping Method In sort.c
Date: Wed, 30 Apr 2008 11:19:31 -0700 [thread overview]
Message-ID: <2c0942db0804301119r430b3b86t880437da1f7ce513@mail.gmail.com> (raw)
In-Reply-To: <191572.86791.qm@web94110.mail.in2.yahoo.com>
On Wed, Apr 30, 2008 at 11:09 AM, Soumyadip Das Mahapatra
<dip_kernel@yahoo.co.in> wrote:
> Thanks Jan,
> Actually it should be
> static void u32_swap(void *a, void *b)
> {
> *(u32 *)b ^= *(u32 *)a;
> *(u32 *)a ^= *(u32 *)b;
> *(u32 *)b ^= *(u32 *)a;
> }
> But this code saves memory equaling two integers. What about that ?
The above prevents gcc from storing the intermediary in a register. So
you're trading fast register access for slow memory access.
Really, you shouldn't be prosing optimizations unless you do two
things: check the output of gcc (on at least one platform, but really
should be several), and include timings of before/after.
prev parent reply other threads:[~2008-04-30 18:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-30 18:09 Soumyadip Das Mahapatra
2008-04-30 18:17 ` Andi Kleen
2008-04-30 18:19 ` Ray Lee [this message]
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