linux-kernel - Re: [PATCH] Introduce a boolean "single_bit

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Message-Id: <1246299311.7698.19.camel@nathan.suse.cz>
Date:	Mon, 29 Jun 2009 20:15:11 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Robert P. J. Day" <rpjday@...shcourse.ca>,
	David Daney <ddaney@...iumnetworks.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Introduce a boolean "single_bit_set" function.

Andrew Morton píše v Pá 24. 04. 2009 v 10:46 -0700:
> On Fri, 24 Apr 2009 06:40:39 -0400 (EDT) "Robert P. J. Day" <rpjday@...shcourse.ca> wrote:
> 
> >   so it would be a simple matter to define the bit set boolean in
> > terms of hweight_long(), yes?  so what about, in bitops.h:
> > 
> >   static inline bool
> >   exactly_one_bit_set(unsigned long w)
> >   {
> > 	return hweight_long(w) == 1;
> >   }
> > 
> >   static inline bool
> >   more_than_one_bit_set(unsigned long w)
> >   {
> > 	return hweight_long(w) > 1;
> >   }
> > 

Andrew, you must be kidding! Are you seriously suggesting to replace a
simple and instruction with a call to an extern library function with 17
instructions (not including the call and ret)?

I'd better check the use of hweight in the kernel to eradicate as many
calls to it as possible...

Petr Tesarik


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