linux-kernel - RE: [RFC V5 3/3] arm64:add bitrev.h file to support rbit instruction

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Date:	Fri, 31 Oct 2014 10:03:27 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Will Deacon' <will.deacon@....com>
CC:	'Rob Herring' <robherring2@...il.com>,
	'Joe Perches' <joe@...ches.com>,
	'Russell King - ARM Linux' <linux@....linux.org.uk>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'akinobu.mita@...il.com'" <akinobu.mita@...il.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [RFC V5 3/3] arm64:add bitrev.h file to support rbit instruction

> From: Will Deacon [mailto:will.deacon@....com]
> Sent: Thursday, October 30, 2014 8:01 PM
> To: Wang, Yalin
> Cc: 'Rob Herring'; 'Joe Perches'; 'Russell King - ARM Linux'; 'linux-
> kernel@...r.kernel.org'; 'akinobu.mita@...il.com'; 'linux-mm@...ck.org';
> 'linux-arm-kernel@...ts.infradead.org'
> Subject: Re: [RFC V5 3/3] arm64:add bitrev.h file to support rbit
> instruction
> 
> > +static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
> > +{
> > +	if (__builtin_constant_p(x)) {
> > +		x = (x >> 16) | (x << 16);
> > +		x = ((x & 0xFF00FF00) >> 8) | ((x & 0x00FF00FF) << 8);
> > +		x = ((x & 0xF0F0F0F0) >> 4) | ((x & 0x0F0F0F0F) << 4);
> > +		x = ((x & 0xCCCCCCCC) >> 2) | ((x & 0x33333333) << 2);
> > +		return ((x & 0xAAAAAAAA) >> 1) | ((x & 0x55555555) << 1);
> 
> Shouldn't this part be in the generic code?

Good  idea, I will change this part into linux/bitrev.h .
Thanks
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