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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 D89B4C43331 for ; Sat, 28 Mar 2020 16:14:45 +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 A961F20716 for ; Sat, 28 Mar 2020 16:14:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A961F20716 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=c-sky.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54736 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jIE6e-000127-T8 for qemu-devel@archiver.kernel.org; Sat, 28 Mar 2020 12:14:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44565) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jIE5v-0000MD-PT for qemu-devel@nongnu.org; Sat, 28 Mar 2020 12:14:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jIE5t-0002yW-Fq for qemu-devel@nongnu.org; Sat, 28 Mar 2020 12:13:58 -0400 Received: from smtp2200-217.mail.aliyun.com ([121.197.200.217]:60513) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jIE5s-0002rb-Vp; Sat, 28 Mar 2020 12:13:57 -0400 X-Alimail-AntiSpam: AC=CONTINUE; BC=0.2579638|-1; CH=green; DM=|CONTINUE|false|; DS=CONTINUE|ham_regular_dialog|0.0190046-0.000301582-0.980694; FP=0|0|0|0|0|-1|-1|-1; HT=e02c03312; MF=zhiwei_liu@c-sky.com; NM=1; PH=DS; RN=9; RT=9; SR=0; TI=SMTPD_---.H6ju01._1585412024; Received: from 192.168.3.18(mailfrom:zhiwei_liu@c-sky.com fp:SMTPD_---.H6ju01._1585412024) by smtp.aliyun-inc.com(10.147.42.253); Sun, 29 Mar 2020 00:13:45 +0800 Subject: Re: [PATCH v6 18/61] target/riscv: vector single-width integer multiply instructions To: Richard Henderson , alistair23@gmail.com, chihmin.chao@sifive.com, palmer@dabbelt.com References: <20200317150653.9008-1-zhiwei_liu@c-sky.com> <20200317150653.9008-19-zhiwei_liu@c-sky.com> <1a5900d9-dc26-04f2-74b2-0bada246a0e7@linaro.org> <8be612c0-4345-c1f2-3b82-73a9a1ea4133@c-sky.com> <53209745-9b54-00b3-2b1f-1271f0843021@linaro.org> From: LIU Zhiwei Message-ID: <5dabf936-6a4f-5d76-0d16-ff357d1ee376@c-sky.com> Date: Sun, 29 Mar 2020 00:13:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <53209745-9b54-00b3-2b1f-1271f0843021@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 121.197.200.217 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: , Cc: guoren@linux.alibaba.com, wenmeng_zhang@c-sky.com, qemu-riscv@nongnu.org, qemu-devel@nongnu.org, wxy194768@alibaba-inc.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/3/28 23:47, Richard Henderson wrote: > On 3/28/20 8:17 AM, LIU Zhiwei wrote: >>> Missed the improvement here.  See tcg_gen_mulsu2_i64. >> Though I have not gotten the principle, the code in tcg_gen_mulsu2_i64 is much >> tidier. > Let A = signed operand, > B = unsigned operand > P = unsigned product > > If the sign bit A is set, then P is too large. > In that case we subtract 2**64 * B to fix that: > > HI_P -= (A < 0 ? B : 0) > > where the conditional is computed as (A >> 63) & B. I think I get it. LET  A = 2 ** 64  - X THEN X = 2 ** 64 - A SIGNED_P = -X * B if (A * B == P) then (2 ** 64  - X) * B == P 2 **64 * B - X * B == P -X *B == P - 2**64*B HI_P -= (A < 0 ? B ：0） Zhiwei > > r~