From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3ACE1C433F5 for ; Fri, 11 Feb 2022 15:42:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238786AbiBKPmG (ORCPT ); Fri, 11 Feb 2022 10:42:06 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:53856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231338AbiBKPmG (ORCPT ); Fri, 11 Feb 2022 10:42:06 -0500 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B50B13A; Fri, 11 Feb 2022 07:42:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1644594125; x=1676130125; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=T3ef5F65PJmfBcchWNRaBxXxdQ77ulKuIvsCxJQZ99I=; b=bVKeKt28Y6DD5975ETB7oi+mvVF0r3Ik06C3lwQRmhAvmiK9nGWaoDVK jF9Yra0BpEZQ2TUnevCQty8DkB3FNtHotwc7V7brfe1ozV02sSoWHubcp qd9kWQC9DbJbubhN9tHYxAH6dSj3ImNsMWenWg2uLuglr7K/S73sc/68j quLG47Yjh4PaGXyO3VdYnhlVFG1cFvTnsq1II71Y1uxlDzeXzQ9tqEVeH e7pixcBtzp0fdw0Q0Z0ANOp2UOqr8fjclZzSD5NfbX/MmTdrHylHW+LxZ OkLW23uSVR8Vc3Rup2cog/Fd9wmk2/olsy0bM0sjV1VGvzJuSUi9H++pu g==; X-IronPort-AV: E=McAfee;i="6200,9189,10254"; a="247344181" X-IronPort-AV: E=Sophos;i="5.88,361,1635231600"; d="scan'208";a="247344181" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Feb 2022 07:42:04 -0800 X-IronPort-AV: E=Sophos;i="5.88,361,1635231600"; d="scan'208";a="488056186" Received: from smile.fi.intel.com ([10.237.72.61]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Feb 2022 07:42:01 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.95) (envelope-from ) id 1nIY2i-003UaW-0O; Fri, 11 Feb 2022 17:41:04 +0200 Date: Fri, 11 Feb 2022 17:41:03 +0200 From: Andy Shevchenko To: Jani Nikula Cc: Thomas Zimmermann , Javier Martinez Canillas , linux-fbdev@vger.kernel.org, David Airlie , Daniel Vetter , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Noralf =?iso-8859-1?Q?Tr=F8nnes?= , Geert Uytterhoeven , Maxime Ripard , Sam Ravnborg Subject: Re: [PATCH v4 1/6] drm/format-helper: Add drm_fb_xrgb8888_to_gray8_line() Message-ID: References: <20220211091927.2988283-1-javierm@redhat.com> <20220211091927.2988283-2-javierm@redhat.com> <4fa465d9-4fac-4199-9a04-d8e09d164308@redhat.com> <7560cd10-0a7c-3fda-da83-9008833e3901@suse.de> <87pmnt7gm3.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87pmnt7gm3.fsf@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org On Fri, Feb 11, 2022 at 02:05:56PM +0200, Jani Nikula wrote: > On Fri, 11 Feb 2022, Thomas Zimmermann wrote: > > Am 11.02.22 um 12:12 schrieb Andy Shevchenko: > >> On Fri, Feb 11, 2022 at 11:40:13AM +0100, Javier Martinez Canillas wrote: > >>> On 2/11/22 11:28, Andy Shevchenko wrote: > >>>> On Fri, Feb 11, 2022 at 10:19:22AM +0100, Javier Martinez Canillas wrote: ... > >>>>> +static void drm_fb_xrgb8888_to_gray8_line(u8 *dst, const u32 *src, unsigned int pixels) > >>>>> +{ > >>>>> + unsigned int x; > >>>>> + > >>>>> + for (x = 0; x < pixels; x++) { > >>>>> + u8 r = (*src & 0x00ff0000) >> 16; > >>>>> + u8 g = (*src & 0x0000ff00) >> 8; > >>>>> + u8 b = *src & 0x000000ff; > >>>>> + > >>>>> + /* ITU BT.601: Y = 0.299 R + 0.587 G + 0.114 B */ > >>>>> + *dst++ = (3 * r + 6 * g + b) / 10; > >>>>> + src++; > >>>>> + } > >>>> > >>>> Can be done as > >>>> > >>>> while (pixels--) { > >>>> ... > >>>> } > >>>> > >>>> or > >>>> > >>>> do { > >>>> ... > >>>> } while (--pixels); > >>>> > >>> > >>> I don't see why a while loop would be an improvement here TBH. > >> > >> Less letters to parse when reading the code. > > > > It's a simple refactoring of code that has worked well so far. Let's > > leave it as-is for now. > > IMO *always* prefer a for loop over while or do-while. > > The for (i = 0; i < N; i++) is such a strong paradigm in C. You > instantly know how many times you're going to loop, at a glance. Not so > with with the alternatives, which should be used sparingly. while () {} _is_ a paradigm, for-loop is syntax sugar on top of it. > And yes, the do-while suggested above is buggy, and you actually need to > stop and think to see why. It depends if pixels can be 0 or not and if it's not, then does it contain last or number. The do {} while (--pixels); might be buggy iff pixels may be 0. -- With Best Regards, Andy Shevchenko