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

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Date:	Wed, 03 Feb 2010 19:47:55 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	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>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Wed, 2010-02-03 at 19:14 +0100, Borislav Petkov wrote:

> alternative("call hweightXX", "popcnt", X86_FEATURE_POPCNT)

Make sure to apply a 0xff bitmask to the popcnt r16 call for hweight8(),
and hweight64() needs a bit of magic for 32bit, but yes, something like
that ought to work nicely.

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