Re: [TCP] IPV6 : Change a divide into a right shift in tcp_v6_send_ack()

From: Jeff Garzik <redacted>
Date: Fri, 21 Dec 2007 06:26:48 -0500

YOSHIFUJI Hideaki / 吉藤英明 wrote:

quoted

In article [ref] (at Fri, 21 Dec 2007 07:03:58 +0100), Eric Dumazet [off-list ref] says:

quoted

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.

Quite true -- thus it is a matter of taste to the programmer.

Not true, the code output does change, check your optimize-for-size
kernel config setting.

This was discussed and explained later in this thread, and I also
explained it to you on IRC Jeff ;-)