linux-kernel - Re: [PATCH 2/3] x86/hash: swap parameters of crc32

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Date:	Wed, 26 Feb 2014 09:29:51 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<davem@...emloft.net>, <mingo@...e.hu>, <tglx@...utronix.de>,
	"Daniel Borkmann" <dborkman@...hat.com>, <ffusco@...hat.com>,
	<tgraf@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] x86/hash: swap parameters of crc32_u32()

>>> On 25.02.14 at 21:37, "H. Peter Anvin" <hpa@...or.com> wrote:
> On 02/25/2014 12:34 PM, Daniel Borkmann wrote:
>> On 02/25/2014 09:26 PM, H. Peter Anvin wrote:
>>> On 02/21/2014 02:33 AM, Jan Beulich wrote:
>>>> ... to match its two callers (i.e. the alternative would have been to
>>>> swap the arguments at the call sites).
>>>>
>>>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>>> Cc: Francesco Fusco <ffusco@...hat.com>
>>>> Cc: Daniel Borkmann <dborkman@...hat.com>
>>>> Cc: Thomas Graf <tgraf@...hat.com>
>>>> Cc: David S. Miller <davem@...emloft.net>
>>>> ---
>>>>   arch/x86/lib/hash.c |    2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> Jan, do you want to do an updated version of this patch?  Daniel, I
>>> presume you are going to push this patch?
>> 
>> Good point. I'm fine if this is going to be picked up
>> by x86 maintainers. Feel free to add my ...
>> 
>> Acked-by: Daniel Borkmann <dborkman@...hat.com>
>> 
>> ... if you want to do an updated version that also
>> includes our recent findings/discussion, Jan.
>> 
> 
> Well, I don't want to change the names of the arguments in the inline
> function unless we also change the their functions and actually reverse
> the order of the operands as used.

So I'm confused now: Whether we change the function's
parameters or the callers' argument order has the same net effect:
It's either (with the current patch)

static inline u32 crc32_u32(u32 val, u32 crc)
		seed = crc32_u32(*p32++, seed);
		seed = crc32_u32(tmp, seed);
		seed = crc32_u32(*p32++, seed);

or it would be (with parameter order kept and argument order
swapped)

static inline u32 crc32_u32(u32 crc, u32 val)
		seed = crc32_u32(seed, *p32++);
		seed = crc32_u32(seed, tmp);
		seed = crc32_u32(seed, *p32++);

I.e. it is precisely the case that their names and functions disagree
in the current (unpatched) version.

Jan

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