netdev - Re: [PATCH] ipv4: avoid undefined behavior in do_ip

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Message-ID: <50A0244F.1070302@gmail.com>
Date:	Sun, 11 Nov 2012 17:18:55 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: avoid undefined behavior in do_ip_setsockopt()

On 11/11/12 5:02 PM, David Miller wrote:
> 
> This code is a fast bit test on purpose.  You're making the
> code slower.

No, it's the opposite.  All modern compilers optimize switch cases
into a fast bit test.  The original "smarter" code, however, hinders
the compiler determining the mask for a fast bit test.  With this
patch, GCC is able to compute a better mask.  You can check the
assembly.

- xi
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