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 X-Spam-Level: X-Spam-Status: No, score=-7.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F108C49EAB for ; Fri, 25 Jun 2021 17:44:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 813C161879 for ; Fri, 25 Jun 2021 17:44:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229906AbhFYRrN (ORCPT ); Fri, 25 Jun 2021 13:47:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:58864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229531AbhFYRrM (ORCPT ); Fri, 25 Jun 2021 13:47:12 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0A0BC6157E; Fri, 25 Jun 2021 17:44:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624643091; bh=OtC2yHps4Gx+4TrmMrLMl5zOxwe81NfKarp7uzkjwAE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nYYpRXzLYtG50IJPZ9h6GR6iiH9qLv/987IdlIdK5dKrh21BIZ+L9nZMW5wmsXkCj bkUCxO6poe0/XjIdqzeMhQUJ02SikvRfoluA2b6j3zcVhcWy8WQkESoMv1CEmoTmRf zvSm7MgsEl7hsV4kfl2c2VGwTLvBWFcABJdyNLzV5PmWWc5O80dWaq8zbdkSs05jhx GpL/nHSdwHT5MVeB5wCK9WIUjmSBtYNzh3geb6VS8EMzDIVIWVzQNv8kPueBPLv9q2 9SCT6wbXxcTWntCFYGb3TwaibrE+PetCqMeofXd+cAlAs+iRV4eyCSarQKU8lYJfyq Jz4kJvGKRbPiA== Received: by pali.im (Postfix) id 97367A7D; Fri, 25 Jun 2021 19:44:48 +0200 (CEST) Date: Fri, 25 Jun 2021 19:44:48 +0200 From: Pali =?utf-8?B?Um9ow6Fy?= To: Geert Uytterhoeven Cc: Willy Tarreau , Michael Turquette , Stephen Boyd , Rob Herring , Greg Kroah-Hartman , Andrew Lunn , Gregory Clement , Sebastian Hesselbarth , Vladimir Vid , Marek =?utf-8?B?QmVow7pu?= , linux-clk , "open list:SERIAL DRIVERS" , Linux Kernel Mailing List , Linux ARM Subject: Re: [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Message-ID: <20210625174448.kje4pvg5ixpu3vaw@pali> References: <20210624224909.6350-1-pali@kernel.org> <20210625143617.12826-1-pali@kernel.org> <20210625143617.12826-8-pali@kernel.org> <20210625153803.u6uesckcqyvvo7dl@pali> <20210625155008.GB16901@1wt.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 25 June 2021 19:39:10 Geert Uytterhoeven wrote: > Hi Willy, > > On Fri, Jun 25, 2021 at 5:50 PM Willy Tarreau wrote: > > On Fri, Jun 25, 2021 at 05:38:03PM +0200, Pali Rohár wrote: > > > On Friday 25 June 2021 17:22:31 Geert Uytterhoeven wrote: > > > > > +/* > > > > > + * DIV_U64_ROUND_CLOSEST - unsigned 64bit divide with 32bit divisor rounded to nearest integer > > > > > + * @dividend: unsigned 64bit dividend > > > > > + * @divisor: unsigned 32bit divisor > > > > > + * > > > > > + * Divide unsigned 64bit dividend by unsigned 32bit divisor > > > > > + * and round to closest integer. > > > > > + * > > > > > + * Return: dividend / divisor rounded to nearest integer > > > > > + */ > > > > > +#define DIV_U64_ROUND_CLOSEST(dividend, divisor) \ > > > > > + ({ u32 _tmp = (divisor); div_u64((u64)(dividend) + _tmp / 2, _tmp); }) > > > > > > > > Given "dividend" should already be an unsigned 64-bit value, I don't > > > > think the cast to "u64" is needed. Similar macros in this file also > > > > don't have the cast. > > > > > > It is just to ensure that plus operation between dividend and _tmp is > > > evaluated in 64-bit context to prevent overflow. Just a case when user > > > calls this macro with 32-bit dividend param. As it is a macro (and not > > > inline function) type is not automatically enforced. > > > > I agree, a large u32 argument added to _tmp/2 could overflow and remain > > 32 bits, yielding an incorrect result. The cast is mandatory here (and > > will either emit no code, or be useful). > > Fair enough. > So we want to add a cast to DIV64_U64_ROUND_CLOSEST() above, too? For DIV64_U64_ROUND_CLOSEST() it is not needed. divisor is copied into u64 _tmp variable and therefore "(dividend) + _tmp / 2" is already evaluated in 64-bit context even when dividend is only 32-bit. The only trap is that negative value as written below. > > The only trap I'm seeing is if a negative signed int is passed in dividend, > > it will be sign-extended and will give a large u64 value. A preliminary > > u32 cast could avoid this but would break valid u64 arguments, and I'd > > claim we never know what the user wants if this happens in the first place. > > Yep. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds 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 X-Spam-Level: X-Spam-Status: No, score=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4AA9C2B9F4 for ; Fri, 25 Jun 2021 17:46:37 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6E24661864 for ; Fri, 25 Jun 2021 17:46:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E24661864 Authentication-Results: mail.kernel.org; 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Fri, 25 Jun 2021 19:44:48 +0200 (CEST) Date: Fri, 25 Jun 2021 19:44:48 +0200 From: Pali =?utf-8?B?Um9ow6Fy?= To: Geert Uytterhoeven Cc: Willy Tarreau , Michael Turquette , Stephen Boyd , Rob Herring , Greg Kroah-Hartman , Andrew Lunn , Gregory Clement , Sebastian Hesselbarth , Vladimir Vid , Marek =?utf-8?B?QmVow7pu?= , linux-clk , "open list:SERIAL DRIVERS" , Linux Kernel Mailing List , Linux ARM Subject: Re: [PATCH v2 07/11] math64: New DIV_U64_ROUND_CLOSEST helper Message-ID: <20210625174448.kje4pvg5ixpu3vaw@pali> References: <20210624224909.6350-1-pali@kernel.org> <20210625143617.12826-1-pali@kernel.org> <20210625143617.12826-8-pali@kernel.org> <20210625153803.u6uesckcqyvvo7dl@pali> <20210625155008.GB16901@1wt.eu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210625_104451_897225_EA542755 X-CRM114-Status: GOOD ( 33.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org T24gRnJpZGF5IDI1IEp1bmUgMjAyMSAxOTozOToxMCBHZWVydCBVeXR0ZXJob2V2ZW4gd3JvdGU6 Cj4gSGkgV2lsbHksCj4gCj4gT24gRnJpLCBKdW4gMjUsIDIwMjEgYXQgNTo1MCBQTSBXaWxseSBU YXJyZWF1IDx3QDF3dC5ldT4gd3JvdGU6Cj4gPiBPbiBGcmksIEp1biAyNSwgMjAyMSBhdCAwNToz ODowM1BNICswMjAwLCBQYWxpIFJvaMOhciB3cm90ZToKPiA+ID4gT24gRnJpZGF5IDI1IEp1bmUg MjAyMSAxNzoyMjozMSBHZWVydCBVeXR0ZXJob2V2ZW4gd3JvdGU6Cj4gPiA+ID4gPiArLyoKPiA+ ID4gPiA+ICsgKiBESVZfVTY0X1JPVU5EX0NMT1NFU1QgLSB1bnNpZ25lZCA2NGJpdCBkaXZpZGUg d2l0aCAzMmJpdCBkaXZpc29yIHJvdW5kZWQgdG8gbmVhcmVzdCBpbnRlZ2VyCj4gPiA+ID4gPiAr ICogQGRpdmlkZW5kOiB1bnNpZ25lZCA2NGJpdCBkaXZpZGVuZAo+ID4gPiA+ID4gKyAqIEBkaXZp c29yOiB1bnNpZ25lZCAzMmJpdCBkaXZpc29yCj4gPiA+ID4gPiArICoKPiA+ID4gPiA+ICsgKiBE aXZpZGUgdW5zaWduZWQgNjRiaXQgZGl2aWRlbmQgYnkgdW5zaWduZWQgMzJiaXQgZGl2aXNvcgo+ ID4gPiA+ID4gKyAqIGFuZCByb3VuZCB0byBjbG9zZXN0IGludGVnZXIuCj4gPiA+ID4gPiArICoK PiA+ID4gPiA+ICsgKiBSZXR1cm46IGRpdmlkZW5kIC8gZGl2aXNvciByb3VuZGVkIHRvIG5lYXJl c3QgaW50ZWdlcgo+ID4gPiA+ID4gKyAqLwo+ID4gPiA+ID4gKyNkZWZpbmUgRElWX1U2NF9ST1VO RF9DTE9TRVNUKGRpdmlkZW5kLCBkaXZpc29yKSAgICAgICBcCj4gPiA+ID4gPiArICAgICAgICh7 IHUzMiBfdG1wID0gKGRpdmlzb3IpOyBkaXZfdTY0KCh1NjQpKGRpdmlkZW5kKSArIF90bXAgLyAy LCBfdG1wKTsgfSkKPiA+ID4gPgo+ID4gPiA+IEdpdmVuICJkaXZpZGVuZCIgc2hvdWxkIGFscmVh ZHkgYmUgYW4gdW5zaWduZWQgNjQtYml0IHZhbHVlLCBJIGRvbid0Cj4gPiA+ID4gdGhpbmsgdGhl IGNhc3QgdG8gInU2NCIgaXMgbmVlZGVkLiBTaW1pbGFyIG1hY3JvcyBpbiB0aGlzIGZpbGUgYWxz bwo+ID4gPiA+IGRvbid0IGhhdmUgdGhlIGNhc3QuCj4gPiA+Cj4gPiA+IEl0IGlzIGp1c3QgdG8g ZW5zdXJlIHRoYXQgcGx1cyBvcGVyYXRpb24gYmV0d2VlbiBkaXZpZGVuZCBhbmQgX3RtcCBpcwo+ ID4gPiBldmFsdWF0ZWQgaW4gNjQtYml0IGNvbnRleHQgdG8gcHJldmVudCBvdmVyZmxvdy4gSnVz dCBhIGNhc2Ugd2hlbiB1c2VyCj4gPiA+IGNhbGxzIHRoaXMgbWFjcm8gd2l0aCAzMi1iaXQgZGl2 aWRlbmQgcGFyYW0uIEFzIGl0IGlzIGEgbWFjcm8gKGFuZCBub3QKPiA+ID4gaW5saW5lIGZ1bmN0 aW9uKSB0eXBlIGlzIG5vdCBhdXRvbWF0aWNhbGx5IGVuZm9yY2VkLgo+ID4KPiA+IEkgYWdyZWUs IGEgbGFyZ2UgdTMyIGFyZ3VtZW50IGFkZGVkIHRvIF90bXAvMiBjb3VsZCBvdmVyZmxvdyBhbmQg cmVtYWluCj4gPiAzMiBiaXRzLCB5aWVsZGluZyBhbiBpbmNvcnJlY3QgcmVzdWx0LiBUaGUgY2Fz dCBpcyBtYW5kYXRvcnkgaGVyZSAoYW5kCj4gPiB3aWxsIGVpdGhlciBlbWl0IG5vIGNvZGUsIG9y IGJlIHVzZWZ1bCkuCj4gCj4gRmFpciBlbm91Z2guCj4gU28gd2Ugd2FudCB0byBhZGQgYSBjYXN0 IHRvIERJVjY0X1U2NF9ST1VORF9DTE9TRVNUKCkgYWJvdmUsIHRvbz8KCkZvciBESVY2NF9VNjRf Uk9VTkRfQ0xPU0VTVCgpIGl0IGlzIG5vdCBuZWVkZWQuIGRpdmlzb3IgaXMgY29waWVkIGludG8K dTY0IF90bXAgdmFyaWFibGUgYW5kIHRoZXJlZm9yZSAiKGRpdmlkZW5kKSArIF90bXAgLyAyIiBp cyBhbHJlYWR5CmV2YWx1YXRlZCBpbiA2NC1iaXQgY29udGV4dCBldmVuIHdoZW4gZGl2aWRlbmQg aXMgb25seSAzMi1iaXQuCgpUaGUgb25seSB0cmFwIGlzIHRoYXQgbmVnYXRpdmUgdmFsdWUgYXMg d3JpdHRlbiBiZWxvdy4KCj4gPiBUaGUgb25seSB0cmFwIEknbSBzZWVpbmcgaXMgaWYgYSBuZWdh dGl2ZSBzaWduZWQgaW50IGlzIHBhc3NlZCBpbiBkaXZpZGVuZCwKPiA+IGl0IHdpbGwgYmUgc2ln bi1leHRlbmRlZCBhbmQgd2lsbCBnaXZlIGEgbGFyZ2UgdTY0IHZhbHVlLiBBIHByZWxpbWluYXJ5 Cj4gPiB1MzIgY2FzdCBjb3VsZCBhdm9pZCB0aGlzIGJ1dCB3b3VsZCBicmVhayB2YWxpZCB1NjQg YXJndW1lbnRzLCBhbmQgSSdkCj4gPiBjbGFpbSB3ZSBuZXZlciBrbm93IHdoYXQgdGhlIHVzZXIg d2FudHMgaWYgdGhpcyBoYXBwZW5zIGluIHRoZSBmaXJzdCBwbGFjZS4KPiAKPiBZZXAuCj4gCj4g R3J7b2V0amUsZWV0aW5nfXMsCj4gCj4gICAgICAgICAgICAgICAgICAgICAgICAgR2VlcnQKPiAK PiAtLSAKPiBHZWVydCBVeXR0ZXJob2V2ZW4gLS0gVGhlcmUncyBsb3RzIG9mIExpbnV4IGJleW9u ZCBpYTMyIC0tIGdlZXJ0QGxpbnV4LW02OGsub3JnCj4gCj4gSW4gcGVyc29uYWwgY29udmVyc2F0 aW9ucyB3aXRoIHRlY2huaWNhbCBwZW9wbGUsIEkgY2FsbCBteXNlbGYgYSBoYWNrZXIuIEJ1dAo+ IHdoZW4gSSdtIHRhbGtpbmcgdG8gam91cm5hbGlzdHMgSSBqdXN0IHNheSAicHJvZ3JhbW1lciIg b3Igc29tZXRoaW5nIGxpa2UgdGhhdC4KPiAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAg IC0tIExpbnVzIFRvcnZhbGRzCgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fXwpsaW51eC1hcm0ta2VybmVsIG1haWxpbmcgbGlzdApsaW51eC1hcm0ta2VybmVs QGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcvbWFpbG1hbi9s aXN0aW5mby9saW51eC1hcm0ta2VybmVsCg==