From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from eggs.gnu.org (eggs.gnu.org [IPv6:2001:470:142:3::10]) by sourceware.org (Postfix) with ESMTPS id B344D3858D20 for ; Mon, 9 Jan 2023 13:25:03 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org B344D3858D20 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=nexgo.de Authentication-Results: sourceware.org; spf=fail smtp.mailfrom=nexgo.de Received: from mr6.vodafonemail.de ([145.253.228.166]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pEs93-0006UX-Sr for gcc@gnu.org; Mon, 09 Jan 2023 08:25:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nexgo.de; s=vfde-smtpout-mb-15sep; t=1673270694; bh=vD4ybRgnaZniyMu8XVJJm5rBh4lImnzcT5xAujbrHyc=; h=Message-ID:From:To:References:In-Reply-To:Subject:Date: Content-Type:X-Mailer:From; b=HoDq5EFhNLPTjaLcSQYd89id5NfPulXElqgdCndmclo22sXUqtaP0Yxs4DSRoHwAs 1r1bGhUvQbJjUxMT84V4w5wDTdN5HkKmfSPpyZBlsi0fQR6HXfnuFA7UZdrbuGRXCK EVNKQ3BlRAAp6f4gFiqn9b6ojx3Y6cS7WCIF7VO0= Received: from smtp.vodafone.de (unknown [10.0.0.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by mr6.vodafonemail.de (Postfix) with ESMTPS id 4NrF6Z2b7sz1ytr; Mon, 9 Jan 2023 13:24:54 +0000 (UTC) Received: from H270 (p5de6d091.dip0.t-ipconnect.de [93.230.208.145]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by smtp.vodafone.de (Postfix) with ESMTPSA id 4NrF6Q310KzKm4L; Mon, 9 Jan 2023 13:24:40 +0000 (UTC) Message-ID: From: "Stefan Kanthak" To: , "LIU Hao" References: <554A1354252F43BB8915A74129C41BE3@H270> In-Reply-To: Subject: Re: Widening multiplication, but no narrowing division [i386/AMD64] Date: Mon, 9 Jan 2023 14:19:45 +0100 Organization: Me, myself & IT MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.24158 X-purgate-type: clean X-purgate: clean X-purgate-size: 482 X-purgate-ID: 155817::1673270689-AFFD64F8-C796E62F/0/0 Received-SPF: pass client-ip=145.253.228.166; envelope-from=stefan.kanthak@nexgo.de; helo=mr6.vodafonemail.de X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9,DKIM_SIGNED=0.1,DKIM_VALID=-0.1,DKIM_VALID_AU=-0.1,DKIM_VALID_EF=-0.1,RCVD_IN_DNSWL_LOW=-0.7,RCVD_IN_MSPIKE_H2=-0.001,RCVD_IN_VALIDITY_RPBL=1.31,SPF_HELO_NONE=0.001,SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-Spam-Status: No, score=-0.6 required=5.0 tests=BAYES_20,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_FAIL,SPF_HELO_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: LIU Hao wrote: >在 2023/1/9 20:20, Stefan Kanthak 写道: >> Hi, >> >> GCC (and other C compilers too) support the widening multiplication >> of i386/AMD64 processors, but DON'T support their narrowing division: >> >> > > QWORD-DWORD division would change the behavior of your program. [...] > If DIV was used, it would effect an exception: Guess why I use "schoolbook" division? Please read the end of my post until you understand the code. regards Stefan