linux-kernel - Re: [PATCH V3] blackfin: optimize ffz, __ffs, ffs, _

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Date:	Fri, 15 Apr 2016 09:08:34 -0700
From:	Joe Perches <joe@...ches.com>
To:	zengzhaoxiu@....com, linux-kernel@...r.kernel.org
Cc:	Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>,
	Steven Miao <realmz6@...il.com>,
	adi-buildroot-devel@...ts.sourceforge.net
Subject: Re: [PATCH V3] blackfin: optimize ffz, __ffs, ffs, __fls, and fls
 functions

On Fri, 2016-04-15 at 23:20 +0800, zengzhaoxiu@....com wrote:
> From: Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>
> 
> blackfin has popcount instruction (ONES), we can do the efficient
> computing (ffz, __ffs, ffs, __fls, and fls) use this instruction.
[]
> diff --git a/arch/blackfin/include/asm/bitops.h b/arch/blackfin/include/asm/bitops.h
[]
> +static inline unsigned int __arch_hweight64(__u64 w)
> +{
> +	return __arch_hweight32((unsigned int)(w >> 32)) +
> +	       __arch_hweight32((unsigned int)w);
> +}

trivia:  perhaps this is more readable as:

	return __arch_hweight32(upper_32_bits(w)) +
	       __arch_hweight32(lower_32_bits(w));