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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 4B0E8C432C0 for ; Fri, 22 Nov 2019 08:56:46 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 1578220708 for ; Fri, 22 Nov 2019 08:56:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hnNKIpWz" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1578220708 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48686 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iY4k9-0003uE-AO for qemu-devel@archiver.kernel.org; Fri, 22 Nov 2019 03:56:45 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48549) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iY4jG-0002lt-QM for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:55:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iY4jF-00045y-Ra for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:55:50 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:42458 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iY4jF-00045l-No for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:55:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574412949; h=from:from:reply-to: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=zbJikIq9CKwSEcHz6wGPv04ne3C9Kf0INkPOFcOtJ+s=; b=hnNKIpWzX+vS50XKwv1U8fAeMAmkmYbzx/oh7dv8x0WNAJEthmMP/Umi89bBvpf92VRJQ0 AHibxwpdUZJ3ZPFBRwk2hpCxMr6sPUulyrXwdnO+cO2VA8SSU7/RO66D2MSOwcGTheqhcb 9pBHpajlfzWXtFhTGbQFLqv7XjqckBU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-387-vbFU01wAOTKLVHCURmOqHA-1; Fri, 22 Nov 2019 03:55:46 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0D0C9800054; Fri, 22 Nov 2019 08:55:45 +0000 (UTC) Received: from redhat.com (unknown [10.36.118.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 96C0A67660; Fri, 22 Nov 2019 08:55:44 +0000 (UTC) From: Juan Quintela To: Markus Armbruster Subject: Re: [PATCH v3 2/2] util/cutils: Fix incorrect integer->float conversion caught by clang In-Reply-To: <20191122080039.12771-3-armbru@redhat.com> (Markus Armbruster's message of "Fri, 22 Nov 2019 09:00:39 +0100") References: <20191122080039.12771-1-armbru@redhat.com> <20191122080039.12771-3-armbru@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) Date: Fri, 22 Nov 2019 09:55:42 +0100 Message-ID: <87v9rci92p.fsf@trasno.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: vbFU01wAOTKLVHCURmOqHA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: quintela@redhat.com Cc: Fangrui Song , richard.henderson@linaro.org, qemu-devel@nongnu.org, dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Markus Armbruster wrote: > From: Fangrui Song > > Clang does not like do_strtosz()'s code to guard against overflow: > > qemu/util/cutils.c:245:23: error: implicit conversion from 'unsigned = long' to 'double' changes value from 18446744073709550592 to 18446744073709= 551616 [-Werror,-Wimplicit-int-float-conversion] > > The warning will be enabled by default in clang 10. It is not > available for clang <=3D 9. > > val * mul >=3D 0xfffffffffffffc00 is indeed wrong. 0xfffffffffffffc00 > is not representable exactly as double. It's half-way between the > representable values 0xfffffffffffff800 and 0x10000000000000000. > Which one we get is implementation-defined. Bad. > > We want val * mul > (the largest uint64_t exactly representable as > double). That's 0xfffffffffffff800. Write it as nextafter(0x1p64, 0) > with a suitable comment. > > Signed-off-by: Fangrui Song > Reviewed-by: Markus Armbruster > [Patch split, commit message improved] > Signed-off-by: Markus Armbruster Reviewed-by: Juan Quintela Learning this *new* C99 float format O:-)