From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Aring Subject: Re: [PATCH net-next v4 2/8] 6lowpan: add uncompress header size function Date: Wed, 26 Feb 2014 19:32:11 +0100 Message-ID: <20140226183209.GA31268@omega> References: <1393430712-11298-1-git-send-email-alex.aring@gmail.com> <1393430712-11298-3-git-send-email-alex.aring@gmail.com> <063D6719AE5E284EB5DD2968C1650D6D0F6CBBCA@AcuExch.aculab.com> <1393439085.407.31.camel@joe-AO722> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: "netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-zigbee-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org" , David Laight , "davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org" To: Joe Perches Return-path: Content-Disposition: inline In-Reply-To: <1393439085.407.31.camel@joe-AO722> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-zigbee-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: netdev.vger.kernel.org On Wed, Feb 26, 2014 at 10:24:45AM -0800, Joe Perches wrote: > On Wed, 2014-02-26 at 16:10 +0000, David Laight wrote: > > From: Alexander Aring > [] > > > diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h > [] > > > +static inline u8 lowpan_addr_mode_size(const u8 addr_mode) > > > +{ > > > + switch (addr_mode) { > > > + case LOWPAN_IPHC_ADDR_00: > > > + return 16; > > > + case LOWPAN_IPHC_ADDR_01: > > > + return 8; > > > + case LOWPAN_IPHC_ADDR_02: > > > + return 2; > > > + default: > > > + return 0; > > > + } > > > +} > > > > The compiler will generate much better code if you index an array instead > > of using a switch statement. > > Are you sure of that? > > Perhaps the compiler would inline the assignment > anyway if addr_mode is __builtin_constant_p > > gcc 4.8 here does the same thing with: > > static inline unsigned char f1(unsigned char a) > { > switch (a) { > case 0: return 16; > case 1: return 8; > case 2: return 2; > default: return 0; > } > } > > static inline unsigned char f2(unsigned char a) > { > static const unsigned char rtns[] = { 16, 8, 2, 0 }; > > return rtns[a & 3]; > } to make a mask with & 3 is already done, so we don't need that. I am not sure what I should do now, change or not change? :-) - Alex ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk