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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]:40170 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lLfr0-0008Jx-BA for qemu-devel@archiver.kernel.org; Mon, 15 Mar 2021 01:33:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42736) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lLfq5-0007tD-Iz for qemu-devel@nongnu.org; Mon, 15 Mar 2021 01:32:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:33600) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lLfq3-0001CU-7n for qemu-devel@nongnu.org; Mon, 15 Mar 2021 01:32:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615786341; 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=mRB4+vM3plksvateWx4pZqHvzVltYM8Gt0FO6PUa3vI=; b=SkSXynzvmZKH0Fn7fZNln1Qtwn88V7zC+ef7lqmpyCvFfBePB+F8BGKmAYzdQoNRZbUBPh WkkKHuS4VOX9Henfr1dPfLBfVXOsyAvRiwvhaL6Hf7tudkoja8iC3x1Xpy3yrAnAhpKhnw 0nYjsq/HAjJfC2c+nJVU6914VdGpbtc= 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-190-XXFPYbvdNRudmcecyVLBcw-1; Mon, 15 Mar 2021 01:32:19 -0400 X-MC-Unique: XXFPYbvdNRudmcecyVLBcw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7D931363A8; Mon, 15 Mar 2021 05:32:18 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-72.ams2.redhat.com [10.36.112.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6FE1C46; Mon, 15 Mar 2021 05:32:17 +0000 (UTC) Subject: Re: [PATCH] utils: Use fma in qemu_strtosz To: Richard Henderson , qemu-devel@nongnu.org References: <20210314234821.1954428-1-richard.henderson@linaro.org> From: Thomas Huth Message-ID: <8422f58c-743b-e028-a116-b7c3b507e3c9@redhat.com> Date: Mon, 15 Mar 2021 06:32:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210314234821.1954428-1-richard.henderson@linaro.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.25, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: peter.maydell@linaro.org, berrange@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 15/03/2021 00.48, Richard Henderson wrote: > Use fma to simulatneously scale and round up fraction. > > The libm function will always return a properly rounded double precision > value, which will eliminate any extra precision the x87 co-processor may > give us, which will keep the output predictable vs other hosts. > > Adding DBL_EPSILON while scaling should help with fractions like > 12.345, where the closest representable number is actually 12.3449*. > > Signed-off-by: Richard Henderson > --- > util/cutils.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/util/cutils.c b/util/cutils.c > index d89a40a8c3..f7f8e48a68 100644 > --- a/util/cutils.c > +++ b/util/cutils.c > @@ -342,7 +342,7 @@ static int do_strtosz(const char *nptr, const char **end, > retval = -ERANGE; > goto out; > } > - *result = val * mul + (uint64_t) (fraction * mul); > + *result = val * mul + (uint64_t)fma(fraction, mul, DBL_EPSILON); > retval = 0; > > out: Will this fix the failure that we're currently seeing with 32-bit builds? ( https://gitlab.com/qemu-project/qemu/-/jobs/1096980112#L3258 for example ) Reviewed-by: Thomas Huth