linux-kernel - Re: [PATCH net-next] ether_addr_equal: Optimize implementation, remove unused compare_ether

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Date:	Thu, 05 Dec 2013 15:36:55 -0800
From:	Joe Perches <joe@...ches.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	netdev@...r.kernel.org, Rob Landley <rob@...dley.net>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] ether_addr_equal: Optimize implementation,
 remove unused compare_ether_addr

On Thu, 2013-12-05 at 15:32 -0800, Stephen Hemminger wrote:
> On Thu,  5 Dec 2013 14:54:38 -0800
> Joe Perches <joe@...ches.com> wrote:
> 
> > +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> > +	u32 fold = ((*(const u32 *)addr1) ^ (*(const u32 *)addr2)) |
> > +		   ((*(const u16 *)(addr1 + 4)) ^ (*(const u16 *)(addr2 + 4)));
> > +
> > +	return fold == 0;
> 
> Why the temporary variable.

It's cost free and I think a bit more readable.

>  You can just do:
> 	return ((*(const u32 *)addr1) ^ (*(const u32 *)addr2)) |
> 	       ((*(const u16 *)(addr1 + 4)) ^ (*(const u16 *)(addr2 + 4))) != 0;

== 0

> Or
> 	return !!((*(const u32 *)addr1) ^ (*(const u32 *)addr2)) |
> 	         ((*(const u16 *)(addr1 + 4)) ^ (*(const u16 *)(addr2 + 4))));

!!!? :)


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