220 26346 <201606201758.41906.marc.mutz@kdab.com> article Path: news.gmane.org!not-for-mail From: Marc Mutz Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: On P0037 - Fixed-Point Real Numbers Date: Mon, 20 Jun 2016 17:58:39 +0200 Organization: KDAB Lines: 62 Approved: news@gmane.org Message-ID: <201606201758.41906.marc.mutz@kdab.com> References: <201606200924.36959.marc.mutz@kdab.com> <0e429c80-84d9-4c6e-93ff-6c5dcb26c9d4@rrsd.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1466438287 14043 80.91.229.3 (20 Jun 2016 15:58:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jun 2016 15:58:07 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCRPXDOU7ECRBAFFUC5QKGQERBKV6DA@isocpp.org Mon Jun 20 17:57:54 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f72.google.com ([74.125.82.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bF1aE-0001va-C2 for gclcip-std-proposals@m.gmane.org; Mon, 20 Jun 2016 17:57:54 +0200 Original-Received: by mail-wm0-f72.google.com with SMTP id a66sf30738331wme.1 for ; Mon, 20 Jun 2016 08:57:54 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:from:organization:to:subject:date :references:in-reply-to:mime-version:content-transfer-encoding :message-id:x-original-sender:x-original-authentication-results :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=0rvLYP6XfsNGEKzKkvRSihIMTaVZKT+acwEB9qFV6nE=; b=D1hviIzG+E0n4slomRldyty9hhc/0z6e8DgjDcTj7eLx8Nphtln0bkGq4AYRQpF2s1 kdirTXtclcjxMdfqTlf3VmVPfMAJFNO6tnnGe3b6JnkwMzCwg/bybmp59A7EQMIYxxWa +zcIF6EG0dBrRO6zoeumWE6WdY12reBfFXET3QC+plxwzVV10+sRonmZ4DEGZTXJwPKr c3cdTHNyW/cCnjudlHsLxQyoNXbsjLwLVQQKAJWroB7U20+gULnkyPXEJf+7WyAroWnZ tt0r4wSdcrBQvcDJJvZbddYuEELee4hZEvfsIoMug83eu+b/6ZPIJYxB+D7uc X-Gm-Message-State: ALyK8tJO+7LFmnpRpQsI3q2Ql4WOgdYAyqlUtLUywx0n5vqb9CEwCQHZn6n4RNxwL7++ew== X-Received: by 10.25.169.76 with SMTP id s73mr2011013lfe.5.1466438273747; Mon, 20 Jun 2016 08:57:53 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.158.19 with SMTP id h19ls413784wme.49.gmail; Mon, 20 Jun 2016 08:57:52 -0700 (PDT) X-Received: by 10.28.152.202 with SMTP id a193mr12105704wme.98.1466438272429; Mon, 20 Jun 2016 08:57:52 -0700 (PDT) Original-Received: from mail.kdab.com (mail.kdab.com. [176.9.126.58]) by mx.google.com with ESMTPS id fi5si30117290wjb.85.2016.06.20.08.57.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Jun 2016 08:57:52 -0700 (PDT) Received-SPF: pass (google.com: domain of marc.mutz@kdab.com designates 176.9.126.58 as permitted sender) client-ip=176.9.126.58; X-Virus-Scanned: amavisd-new at kdab.com Original-Sender: marc@kdab.com In-Reply-To: <0e429c80-84d9-4c6e-93ff-6c5dcb26c9d4@rrsd.com> X-Original-Sender: marc.mutz@kdab.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of marc.mutz@kdab.com designates 176.9.126.58 as permitted sender) smtp.mailfrom=marc.mutz@kdab.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:26346 Archived-At: On Monday 20 June 2016 16:45:11 Robert Ramey wrote: > Obviously you're absolutely correct on this. It seems that the whole > job is aready done - and in the most general way. > > But one thing bothers me - with std::ratio I can't specify the > underlying value type. One of the fixed_binary use cases is to use it > for a pixel > > fixed_binary // or something like that > > how could std::ration be used to address this? The same way as std::chrono::duration does. Ratio is just that: a ratio. The underlying type is another template argument: template > class duration; template /2>> class fixed_point; http://en.cppreference.com/w/cpp/chrono/duration Thanks, Marc > Robert Ramey > > On 6/20/16 12:24 AM, Marc Mutz wrote: > > On Sunday 28 February 2016 23:49:04 Robert Ramey wrote: > >> integer part + fractional part where fraction part is any integer. > > > > ... or a std::ratio<>. I don't quite like that we'll have two independent > > fixed-point implementations in the standard: duration and fixed_point. > > > > I'm sure this has been discussed, but P0037R2 doesn't contain anything > > about . > > > > So I'd like to ask why a fixed_point is represented by an exponent, and > > not a > > > > std::ratio object: > > using dollars = fixed_point>; // in units of cents > > > > Though maybe then the fixed_point name is no longer so good, and > > something containing "discrete" might be better. > > > > If the answer is "we want to restrict to an integer number of bits for > > performance", then the counter-argument would be that that can be done > > using specialisation of the operations based on whether the std::ratio > > is of the form 2^-N for some N. > > > > Thanks, > > Marc -- Marc Mutz | Senior Software Engineer KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company Tel: +49-30-521325470 KDAB - Qt, C++ and OpenGL Experts .