From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B2B0B2080E9 for ; Thu, 6 Mar 2025 09:13:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741252385; cv=none; b=WG7/cZ9iNrgqtaTJdk+uMzMDYRlu356nsj47VvJ9b/pRtX2uvR5G4BfTyVgWVYi6AwyJp5831rPZ7rWPH9fVe6JD4Q2fagD9K/S/hI1zl4y0/hrcncbix/HUvrD9bwEqDIHmmySKeB21hB32G/LR2awVp0DQrWKKeZ3DAgCjON0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741252385; c=relaxed/simple; bh=Fa3khYTsYb65t1eGIqtFP/8//326/NxcLm3FoWFgUpE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Pw9Jx6q1DxHt0NwxEx8hvboVvYJNeO9X95ZxKIj7+GLOt+l1fZGQDNoZkXz2BWwMaJJfkAvBPWU8p66stsyPjfYRhjl/iwwYa2piqHsWhN2HU2vtuZK24yLRvkBoH4XVqmwXtTraV0q8yFHWRQ/cctTn3O+7GM0QjuwpuW888LY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=UqK9OTqB; arc=none smtp.client-ip=198.175.65.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="UqK9OTqB" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1741252383; x=1772788383; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=Fa3khYTsYb65t1eGIqtFP/8//326/NxcLm3FoWFgUpE=; b=UqK9OTqBXybm3lubgYz/+rXvESEwAO6+QGWdKuz1tKcpjTFFPuhYatSW EpPBf+vIXGOVtb9qy+SZP5BW7YNclJUFJJWwd/w0Lf3eztZUqOqtxYO95 49TFCnJmqElJ2yBa0y9fC46V3I6jOzbfAz+zJTUeEB14I6uOkRLbAWj4W Y3yBq8P97rgCdGOZarhHRNEt9vGD2351h9zVe1Xjc1WeuGPmNii24zWdK kdA4xV7ApKRIzP1Q4PCVuTc8Whk0xOnfnJ1i6igZOh8fy8wzAcBUfNjUF Xr4yvCWYsqfjlHNob8lrEunLBas47fZljnc9ms+nOCUk/vUdv0pOmb/26 A==; X-CSE-ConnectionGUID: ctX8oUVVRNSIICPquwAnYg== X-CSE-MsgGUID: Bknri0uiQECKrnlX+O3GOQ== X-IronPort-AV: E=McAfee;i="6700,10204,11363"; a="53235047" X-IronPort-AV: E=Sophos;i="6.14,225,1736841600"; d="scan'208";a="53235047" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2025 01:13:03 -0800 X-CSE-ConnectionGUID: dFBNRtAfSS6CGP6FLmnZ9w== X-CSE-MsgGUID: mAS1kDNERQ6UBT2LTMCvdw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,224,1728975600"; d="scan'208";a="156189644" Received: from smile.fi.intel.com ([10.237.72.58]) by orviesa001.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Mar 2025 01:12:58 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.98) (envelope-from ) id 1tq7Hi-000000004PZ-41p3; Thu, 06 Mar 2025 11:12:54 +0200 Date: Thu, 6 Mar 2025 11:12:54 +0200 From: Andy Shevchenko To: David Laight Cc: Vincent Mailhol , Yury Norov , Lucas De Marchi , Rasmus Villemoes , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Andrew Morton , linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Andi Shyti , David Laight , Dmitry Baryshkov , Jani Nikula Subject: Re: [PATCH v4 4/8] bits: introduce fixed-type BIT Message-ID: References: <20250305-fixed-type-genmasks-v4-0-1873dcdf6723@wanadoo.fr> <20250305-fixed-type-genmasks-v4-4-1873dcdf6723@wanadoo.fr> <824dc1d1-14f0-433e-aa3f-679527b87077@wanadoo.fr> <20250305215027.5d9be1fa@pumpkin> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250305215027.5d9be1fa@pumpkin> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo On Wed, Mar 05, 2025 at 09:50:27PM +0000, David Laight wrote: > On Wed, 5 Mar 2025 21:56:22 +0200 > Andy Shevchenko wrote: > > On Thu, Mar 06, 2025 at 02:17:18AM +0900, Vincent Mailhol wrote: > > > On 06/03/2025 at 00:48, Andy Shevchenko wrote: > > > > On Wed, Mar 05, 2025 at 11:48:10PM +0900, Vincent Mailhol wrote: > > > >> On 05/03/2025 at 23:33, Andy Shevchenko wrote: > > > >>> On Wed, Mar 05, 2025 at 10:00:16PM +0900, Vincent Mailhol via B4 Relay wrote: ... > > > >>>> +#define BIT_U8(b) (BIT_INPUT_CHECK(u8, b) + (unsigned int)BIT(b)) > > > >>>> +#define BIT_U16(b) (BIT_INPUT_CHECK(u16, b) + (unsigned int)BIT(b)) > > > >>> > > > >>> Why not u8 and u16? This inconsistency needs to be well justified. > > > >> > > > >> Because of the C integer promotion rules, if casted to u8 or u16, the > > > >> expression will immediately become a signed integer as soon as it is get > > > >> used. For example, if casted to u8 > > > >> > > > >> BIT_U8(0) + BIT_U8(1) > > > >> > > > >> would be a signed integer. And that may surprise people. > > > > > > > > Yes, but wouldn't be better to put it more explicitly like > > > > > > > > #define BIT_U8(b) (BIT_INPUT_CHECK(u8, b) + (u8)BIT(b) + 0 + UL(0)) // + ULL(0) ? > > > > > > OK, the final result would be unsigned. But, I do not follow how this is > > > more explicit. > > > > > > Also, why doing: > > > > > > (u8)BIT(b) + 0 + UL(0) > > > > > > and not just: > > > > > > (u8)BIT(b) + UL(0) > > > > > > ? > > > > > > What is that intermediary '+ 0' for? > > > > > > I am sorry, but I am having a hard time understanding how casting to u8 > > > and then doing an addition with an unsigned long is more explicit than > > > directly doing a cast to the desired type. > > > > Reading this again, I think we don't need it at all. u8, aka unsigned char, > > will be promoted to int, but it will be int with a value < 256, can't be signed > > as far as I understand this correctly. > > The value can't be negative, but the type will be a signed one. Yes, that's what I mentioned above: "int with the value < 256". > Anything comparing types (and there are a few) will treat it as signed. > It really is bad practise to even pretend you can have an expression > (rather that a variable) that has a type smaller than 'int'. > It wouldn't surprise me if even an 'a = b' assignment promotes 'b' to int. We have tons of code with u8/u16, what you are proposing here is like "let's get rid of those types and replace all of them by int/unsigned int". We have ISAs that are byte-oriented despite being 32- or 64-bit platforms. > So it is even questionable whether BIT8() and BIT16() should even exist at all. The point is to check the boundaries and not in the returned value per se. > There can be reasons to return 'unsigned int' rather than 'unsigned long'. > But with the type definitions that Linux uses (and can't really be changed) > you can have BIT32() that is 'unsigned int' and BIT64() that is 'unsigned long > long'. These are then the same on 32bit and 64bit. -- With Best Regards, Andy Shevchenko