linux-kernel - Re: [PATCH 10/31] Add sparc-specific parity functions

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Date:	Mon, 28 Mar 2016 11:29:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	zhaoxiu.zeng@...il.com
Cc:	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH 10/31] Add sparc-specific parity functions

From: Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>
Date: Mon, 28 Mar 2016 13:44:03 +0800

> 在 2016年03月28日 10:43, David Miller 写道:
>> From: "zhaoxiu.zeng" <zhaoxiu.zeng@...il.com>
>> Date: Sun, 27 Mar 2016 14:43:10 +0800
>>
>>> +
>>> +/*
>>> + * parityN: returns the parity of a N-bit word,
>>> + * i.e. the number of 1-bits in x modulo 2.
>>> + */
>>> +
>>> +#define __arch_parity4(w)	(__arch_hweight8((w) & 0xf) & 1)
>>> +#define __arch_parity8(w)	(__arch_hweight8(w) & 1)
>>> +#define __arch_parity16(w)	(__arch_hweight16(w) & 1)
>>> +#define __arch_parity32(w)	(__arch_hweight32(w) & 1)
>>> +#define __arch_parity64(w)	((unsigned int)__arch_hweight64(w) & 1)
>> This looks like asm-generic/ material to me.
> 
> This is generic for the architectures which have popcount instruction,
> but more higher costs than asm-generic/ for others.

Which is why said stanza's in the asm-generic header should be triggered
by a CPP define or similar.