linux-kernel - Re: [PATCH 2/5] bitops: compile time optimization for hweight

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Date:	Thu, 04 Feb 2010 17:04:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Thu, 2010-02-04 at 16:54 +0100, Borislav Petkov wrote:
> On Thu, Feb 04, 2010 at 04:13:52PM +0100, Peter Zijlstra wrote:
> > hweight_long() isn't an arch primitive, only __arch_hweight{8,16,32,64}
> > are.
> 
> Yeah, I'm still looking for the proper location. hweight_long() is the
> generic version so do we want to do the
> 
> #ifndef __HAVE_ARCH_POPCNT
> static inline unsigned long hweight_long(unsigned long w)
> ....
> 
> #endif
> 
> thing and define a x86-specific version? 

No, just don't touch hweight_long(), simply provide
__arch_hweight{8,16,32,64} and all will be well.

hweight_long() is provided by <include/linux.h> and is constructed from
height32() and hweight64() depending on the actual word size.

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