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

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Date:	Tue, 29 Mar 2016 10:27:36 +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,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 01/31] bitops: add parity functions

在 2016年03月28日 14:51, Sam Ravnborg 写道:
>> diff --git a/include/asm-generic/bitops/arch_parity.h b/include/asm-generic/bitops/arch_parity.h
>> new file mode 100644
>> index 0000000..cddc555
>> --- /dev/null
>> +++ b/include/asm-generic/bitops/arch_parity.h
>> @@ -0,0 +1,39 @@
>> +#ifndef _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
>> +#define _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
>> +
>> +#include <asm/types.h>
>> +
>> +/*
>> + * Refrence to 'https://graphics.stanford.edu/~seander/bithacks.html#ParityParallel'.
>> + */
>> +
>> +static inline unsigned int __arch_parity4(unsigned int w)
>> +{
>> +	w &= 0xf;
>> +	return (0x6996 >> w) & 1;
>> +}
>> +
>> +static inline unsigned int __arch_parity8(unsigned int w)
>> +{
>> +	w ^= w >> 4;
>> +	return __arch_parity4(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity16(unsigned int w)
>> +{
>> +	w ^= w >> 8;
>> +	return __arch_parity8(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity32(unsigned int w)
>> +{
>> +	w ^= w >> 16;
>> +	return __arch_parity16(w);
>> +}
>> +
>> +static inline unsigned int __arch_parity64(__u64 w)
>> +{
>> +	return __arch_parity32((unsigned int)(w >> 32) ^ (unsigned int)w);
>> +}
> Defining these as static inlines in asm-generic prevent an architecture
> from selecting between a more optimal asm version or the generic version
> at run-time.
> sparc would benefit from this as only some sparc chips supports popc.
> See how this is done for hweight*
>
> 	Sam

Thanks. I will try.