netdev - Re: [TCP] IPV6 : Change a divide into a right shift in tcp_v6_send

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Message-Id: <20071221.155030.131184865.yoshfuji@linux-ipv6.org>
Date:	Fri, 21 Dec 2007 15:50:30 +0900 (JST)
From:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>
To:	dada1@...mosbay.com
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	yoshfuji@...ux-ipv6.org
Subject: Re: [TCP] IPV6 : Change a divide into a right shift in
 tcp_v6_send_ack()

In article <476B574E.80601@...mosbay.com> (at Fri, 21 Dec 2007 07:03:58 +0100), Eric Dumazet <dada1@...mosbay.com> says:

> Because tot_len is signed in tcp_v6_send_ack(), tot_len/4 forces compiler
> to emit an integer divide, while we can help it to use a right shift,
> less expensive.

Are you really sure?
At least, gcc-4.1.2-20061115 (debian) does not make any difference.

And, IMHO, because shift for signed variable is fragile, so we should
avoid using it.

--yoshfuji
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