linux-kernel - Re: [PATCH 01/31] bitops: add parity functions

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Date:	Mon, 28 Mar 2016 10:15:24 +0800
From:	Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Kepplinger <martink@...teo.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Yury Norov <yury.norov@...il.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 01/31] bitops: add parity functions

On 2016年03月27日 21:38, zhaoxiu.zeng wrote:
> On 2016/3/27 20:44, Sam Ravnborg wrote:
>> Hi Zeng.
>>
>> Looking through the arch specific implementations of __arch_parity().
>> Some architectures uses #defines, other uses inline static functions.
>>
>> Any particular reason that you select one approach over the other
>> in the different cases?
>>
>> ia64:
>> +#define __arch_parity32(x) ((unsigned int) __arch_parity64((x) & 0xfffffffful))
>> +#define __arch_parity16(x) ((unsigned int) __arch_parity64((x) & 0xfffful))
>> +#define __arch_parity8(x)  ((unsigned int) __arch_parity64((x) & 0xfful))
>> +#define __arch_parity4(x)  ((unsigned int) __arch_parity64((x) & 0xful))
>>
>> tile:
>> +static inline unsigned int __arch_parity32(unsigned int w)
>> +{
>> +	return __builtin_popcount(w) & 1;
>> +}
>> +
>> +static inline unsigned int __arch_parity16(unsigned int w)
>> +{
>> +	return __arch_parity32(w & 0xffff);
>> +}
>> +
>> +static inline unsigned int __arch_parity8(unsigned int w)
>> +{
>> +	return __arch_parity32(w & 0xff);
>> +}
>> +
>> +static inline unsigned int __arch_parity4(unsigned int w)
>> +{
>> +	return __arch_parity32(w & 0xf);
>> +}
>>
> No particular reason, just like the architecture's __arch_hweightN.
>
>> Just two examples.
>>
>> Adding the parity helpers seems like veny nice simplifications.
>>
>> A few comments to some of those I looked at.
>> (I am not subscribed to lkml, so you get it as comments here)
>>
> I think the conversion is simple and readable.
>
>> [PATCH 21/31] mtd: use parity16 in ssfdc.c
>> The original code semes to check that the parity equals the
>> value of first bit in the address.
>> This seems lost after the conversion.
>>
> The original get_parity return 1 if the number is even, so
> if block_address is valid, "block_address & 0x7ff" must be odd.
Make corrections:

The original get_parity return 1 if hweight of the input number is even, so
if block_address is valid, hweight of "block_address & 0x7ff" must be odd.

>
>> [PATCH 20/31] scsi: use parity32 in isci/phy.c
>> +	if (parity32(phy_cap.all))
>>   		phy_cap.parity = 1;
>> Could be written like this - simpler IMO:
>> 	phy_cap.parity = parity32(phy_cap.all);
>>
>>
>> 	Sam
>>
> Yes. Thanks!
>