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 2549EEB64DB for ; Wed, 14 Jun 2023 20:34:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236542AbjFNUee (ORCPT ); Wed, 14 Jun 2023 16:34:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236739AbjFNUe3 (ORCPT ); Wed, 14 Jun 2023 16:34:29 -0400 Received: from relay2-d.mail.gandi.net (relay2-d.mail.gandi.net [217.70.183.194]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 724C02684; Wed, 14 Jun 2023 13:34:23 -0700 (PDT) X-GND-Sasl: herve.codina@bootlin.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1686774861; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yZm6YcC6DcFVvhOCrWE7tXXzeBzGgryfSQmR/S4llfA=; b=nQ7IcnTL8O0E6kwDyNu6kT3yKmiODt5kIbcs4yQzM21QJqc0CQKBJIc3UrH/URxks21i4Q 9JDF6iwAmNyudNKKRcD0kHBCsZ3QewttgXr+j9xOz+MIl9aAXdhVsdLtpuij47spr3wHhP oiFNRk5+jJKlfQrXTBEqUn2ZGP6BHOFo5zPXwmIznrIvw5LV4kJRgivyTBcLIKcP2G1I4C g6EaUm43GYdJ7VH+I5IkZJw/S6qTZq51RC8aJ0SDC8Iwzr16gbEqI2w17H8ooobPKogxQ8 eXkxHWcDGFL7R9vQx9kUmhtAykgtUQX3buafDqQ0A5OKsiSwUBLg0djxY9Hn3g== X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com X-GND-Sasl: herve.codina@bootlin.com Received: by mail.gandi.net (Postfix) with ESMTPSA id 9A02040005; Wed, 14 Jun 2023 20:34:19 +0000 (UTC) Date: Wed, 14 Jun 2023 22:34:18 +0200 From: Herve Codina To: Andy Shevchenko Cc: Liam Girdwood , Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Jonathan Cameron , Lars-Peter Clausen , Jaroslav Kysela , Takashi Iwai , Kuninori Morimoto , alsa-devel@alsa-project.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, Christophe Leroy , Thomas Petazzoni Subject: Re: [PATCH v4 07/13] minmax: Introduce {min,max}_array() Message-ID: <20230614223418.0d7e355d@bootlin.com> In-Reply-To: References: <20230614074904.29085-1-herve.codina@bootlin.com> <20230614074904.29085-8-herve.codina@bootlin.com> <20230614114214.1371485e@bootlin.com> Organization: Bootlin X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andy, On Wed, 14 Jun 2023 14:51:43 +0300 Andy Shevchenko wrote: > On Wed, Jun 14, 2023 at 12:42 PM Herve Codina wrote: > > On Wed, 14 Jun 2023 12:02:57 +0300 > > Andy Shevchenko wrote: > > > On Wed, Jun 14, 2023 at 10:49 AM Herve Codina wrote: > > ... > > > > > + typeof(__array[0] + 0) __element = __array[--__len]; \ > > > > > > Do we need the ' + 0' part? > > > > Yes. > > > > __array can be an array of const items and it is legitimate to get the > > minimum value from const items. > > > > typeof(__array[0]) keeps the const qualifier but we need to assign __element > > in the loop. > > One way to drop the const qualifier is to get the type from a rvalue computed > > from __array[0]. This rvalue has to have the exact same type with only the const > > dropped. > > '__array[0] + 0' was a perfect canditate. > > Seems like this also deserves a comment. But if the series is accepted > as is, it may be done as a follow up. > Finally not so simple ... I did some deeper tests and the macros need to be fixed. I hope this one (with comments added) is correct: --- 8 --- /* * Do not check the array parameter using __must_be_array(). * In the following legit use-case where the "array" passed is a simple pointer, * __must_be_array() will return a failure. * --- 8< --- * int *buff * ... * min = min_array(buff, nb_items); * --- 8< --- * * The first typeof(&(array)[0]) is needed in order to support arrays of both * 'int *buff' and 'int buf[N]' types. * * typeof(__array[0] + 0) used for __element is needed as the array can be an * array of const items. * In order to discard the const qualifier use an arithmetic operation (rvalue). * This arithmetic operation discard the const but also can lead to an integer * promotion. For instance, a const s8 __array[0] lead to an int __element due * to the promotion. * In this case, simple min() or max() operation fails (type mismatch). * Use min_t() or max_t() (op_t parameter) enforcing the type in order to avoid * the min() or max() failure. */ #define __minmax_array(op_t, array, len) ({ \ typeof(&(array)[0]) __array = (array); \ typeof(len) __len = (len); \ typeof(__array[0] + 0) __element = __array[--__len]; \ while (__len--) \ __element = op_t(typeof(__array[0]), __element, __array[__len]); \ __element; }) /** * min_array - return minimum of values present in an array * @array: array * @len: array length * * Note that @len must not be zero (empty array). */ #define min_array(array, len) __minmax_array(min_t, array, len) /** * max_array - return maximum of values present in an array * @array: array * @len: array length * * Note that @len must not be zero (empty array). */ #define max_array(array, len) __minmax_array(max_t, array, len) --- 8< --- Tested ok from user-space on my x86_64 using the following types for *buff and buff[N]: - signed/unsigned char - signed/unsigned short - signed/unsigned int - signed/unsigned long - signed/unsigned long long - float, double, long double (even if not used in the kernel) Can you give me your feedback on this last version ? If you are ok, it will be present in the next iteration of the series. Otherwise, as a last ressort, I will drop the {min,max}_array() and switch back to the specific min/max computation in IIO inkern.c Sorry for this back and forth and this last minute detected bug. Best regards, Hervé -- Hervé Codina, Bootlin Embedded Linux and Kernel engineering https://bootlin.com