linux-kernel - Re: [PATCH] lib/checksum.c: optimize do

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Date:	Thu, 07 Jul 2011 04:36:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	abbotti@....co.uk
Cc:	ian.abbott@....co.uk, netdev@...r.kernel.org, arnd@...db.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/checksum.c: optimize do_csum a bit

From: Ian Abbott <abbotti@....co.uk>
Date: Thu, 7 Jul 2011 12:32:45 +0100

> On 07/07/11 12:29, David Miller wrote:
>> From: Ian Abbott <abbotti@....co.uk>
>> Date: Thu, 7 Jul 2011 12:18:49 +0100
>> 
>>> Reduce the number of variables modified by the loop in do_csum() by 1,
>>> which seems like a good idea.  On Nios II (a RISC CPU with 3-operand
>>> instruction set) it reduces the loop from 7 to 6 instructions, including
>>> the conditional branch.
>>>
>>> Signed-off-by: Ian Abbott <abbotti@....co.uk>
>> 
>> I think you'll overshoot past the end of the buffer when there are
>> trailing bytes to handle.
>> 
>> The whole reason we need the count variable is to handle those
>> kinds of cases.
> 
> I don't think it does.  That's what the & ~3 was for.

Aha, yes that indeed makes it work.
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