From owner-svn-src-head@FreeBSD.ORG  Sun Oct 19 12:03:13 2014
Return-Path: <owner-svn-src-head@FreeBSD.ORG>
Delivered-To: svn-src-head@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 9B188A8E;
 Sun, 19 Oct 2014 12:03:13 +0000 (UTC)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
 by mx1.freebsd.org (Postfix) with ESMTP id 426A7E16;
 Sun, 19 Oct 2014 12:03:11 +0000 (UTC)
Received: from porto.starpoint.kiev.ua (porto-e.starpoint.kiev.ua
 [212.40.38.100])
 by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id PAA06395;
 Sun, 19 Oct 2014 15:03:04 +0300 (EEST)
 (envelope-from avg@FreeBSD.org)
Received: from localhost ([127.0.0.1])
 by porto.starpoint.kiev.ua with esmtp (Exim 4.34 (FreeBSD))
 id 1XfpCR-000P9z-QS; Sun, 19 Oct 2014 15:03:03 +0300
Message-ID: <5443A83F.5090807@FreeBSD.org>
Date: Sun, 19 Oct 2014 15:02:07 +0300
From: Andriy Gapon <avg@FreeBSD.org>
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64;
 rv:31.0) Gecko/20100101 Thunderbird/31.1.2
MIME-Version: 1.0
To: "Alexander V. Chernikov" <melifaro@FreeBSD.org>,
 src-committers@FreeBSD.org, svn-src-all@FreeBSD.org,
 svn-src-head@FreeBSD.org
Subject: Re: svn commit: r273274 - head/sys/netpfil/ipfw
References: <201410191115.s9JBFJxA058370@svn.freebsd.org>
In-Reply-To: <201410191115.s9JBFJxA058370@svn.freebsd.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
 <svn-src-head.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head/>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 19 Oct 2014 12:03:13 -0000

On 19/10/2014 14:15, Alexander V. Chernikov wrote:
> +static uint32_t
> +roundup2p(uint32_t v)
> +{
> +
> +	v--;
> +	v |= v >> 1;
> +	v |= v >> 2;
> +	v |= v >> 4;
> +	v |= v >> 8;
> +	v |= v >> 16;
> +	v++;
> +
> +	return (v);
> +}

I think that on platforms where an optimized version of fls() is available that
would work faster than this cool piece of bit magic.

-- 
Andriy Gapon