220 26351 article Path: news.gmane.org!not-for-mail From: John McFarlane Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: On P0037 - Fixed-Point Real Numbers Date: Mon, 20 Jun 2016 13:17:02 -0700 Lines: 127 Approved: news@gmane.org Message-ID: References: <201606200924.36959.marc.mutz@kdab.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=94eb2c128ec233d31c0535bb630b X-Trace: ger.gmane.org 1466453837 5475 80.91.229.3 (20 Jun 2016 20:17:17 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jun 2016 20:17:17 +0000 (UTC) Cc: std-proposals@isocpp.org, Robert Ramey , mcfarlane.john+fixed-point@gmail.com To: Marc Mutz Original-X-From: std-proposals+bncBDS7B7WQUYOBBP46UG5QKGQEPMOJQZI@isocpp.org Mon Jun 20 22:17:10 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bF5d3-0006BI-7I for gclcip-std-proposals@m.gmane.org; Mon, 20 Jun 2016 22:17:05 +0200 Original-Received: by mail-yw0-f198.google.com with SMTP id v77sf46995083ywg.1 for ; Mon, 20 Jun 2016 13:17:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc: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=IS8BRrRNWpVJ8PZOSqkuYweDV/5Ft9eeo2agtAksRF4=; b=ZvXFTXbp1mRA28qlrJuktJCtt6gjs25xXkrJ6GVT+ldxklvbj3EpvvWSdcFU/j2mLb 05Yb3ob0ANHXCmIC5U3Ll77aObpGa6rvfy22+VC7lWz8wlpwT/jzvvofsHA5e1xexo5I IXec6pL3S/Lupc2Y1u3vc1ybQmtzmdUI4uKLvmz1oLeiAwXmVCUzvx7X1H6MUcEMvXs8 PzCDUSIc6u3dd3WBJ6Da2B8g16DWTZH7rz21ZOj142TSawYNBFT86Z2OIFI+uXlaTYgC DFbc2Q54kdGmM/6VQhmbNV409wY9Zp9cDfwuToWJqauXEzhf/cn6Nju+MP7PvtTx588K M8LQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc: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=IS8BRrRNWpVJ8PZOSqkuYweDV/5Ft9eeo2agtAksRF4=; b=hiYqMX/ZtjXg67r8tLLl00kZfbkEmlkDpzhZutcckMmxhHq8xhKv26/xH1kF428vSq k0uywsLf+RC2/ZPxVxPzQgNjiw9G8Olol9FUbRWbh/O0sC1KLelVyabMpDk4rrxtTUEZ 4Z6YUZJJb0h2VKsz2rj99wDp45+UlpF2JPYMVOXjtAHNds5VVQqT36Z6Lrr5pfGO4w1L S2Ar4kp/HxRNtFu3k32kZ8rAq4cjoW7rEo+PGM7sBQhOFexOBn2GeOjUwSGM8Jwk5wKH Clg3DxtE+uyFrUgiTaH3CIx3j1iyr5emaGBQaNFPZB0xd1E0IJKEkixWVxJt0Y/X7ZET rnOg== X-Gm-Message-State: ALyK8tK0JhPDQOeuAt5qV+Al0PFuvFDb07T/F5xsaqpM8y0zsmJYYjyPxgtqifBIhOXCRA== X-Received: by 10.237.36.121 with SMTP id s54mr20872092qtc.12.1466453824200; Mon, 20 Jun 2016 13:17:04 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.43.181 with SMTP id u50ls2794957ota.58.gmail; Mon, 20 Jun 2016 13:17:03 -0700 (PDT) X-Received: by 10.129.109.147 with SMTP id i141mr2268121ywc.220.1466453823250; Mon, 20 Jun 2016 13:17:03 -0700 (PDT) Original-Received: from mail-yw0-x22e.google.com (mail-yw0-x22e.google.com. [2607:f8b0:4002:c05::22e]) by mx.google.com with ESMTPS id a5si7083453ywg.369.2016.06.20.13.17.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Jun 2016 13:17:03 -0700 (PDT) Received-SPF: pass (google.com: domain of mcfarlane.john@gmail.com designates 2607:f8b0:4002:c05::22e as permitted sender) client-ip=2607:f8b0:4002:c05::22e; Original-Received: by mail-yw0-x22e.google.com with SMTP id b72so22956842ywa.3 for ; Mon, 20 Jun 2016 13:17:03 -0700 (PDT) X-Received: by 10.129.164.145 with SMTP id b139mr10706087ywh.171.1466453823047; Mon, 20 Jun 2016 13:17:03 -0700 (PDT) Original-Received: by 10.37.15.133 with HTTP; Mon, 20 Jun 2016 13:17:02 -0700 (PDT) In-Reply-To: <201606200924.36959.marc.mutz@kdab.com> X-Original-Sender: mcfarlane.john@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of mcfarlane.john@gmail.com designates 2607:f8b0:4002:c05::22e as permitted sender) smtp.mailfrom=mcfarlane.john@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.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:26351 Archived-At: --94eb2c128ec233d31c0535bb630b Content-Type: text/plain; charset=UTF-8 If `fixed_point` took a `ratio` object, its range would be reduced to the range of `maxint_t`. Here's an example of functionality what would not be possible with such a limitation: [ https://github.com/johnmcfarlane/fixed_point/blob/5d1a016b865ecbcf8479059fdabae9406cff984a/src/test/index.cpp#L94 ]. On Mon, Jun 20, 2016 at 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 > -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CABPJVnRchMhpJ31FjGo9NW5tvwJUP8KuExBRtc_yXNJGsqU7hA%40mail.gmail.com. --94eb2c128ec233d31c0535bb630b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
If `= fixed_point` took a `ratio` object, its range would be reduced to the range= of `maxint_t`. Here's an example of functionality what would not be po= ssible with such a limitation: [https://github.com/johnmcfarlane/fixed_point/blob/5d1a016b865ecbcf8= 479059fdabae9406cff984a/src/test/index.cpp#L94].

On Mon, Jun 20, 2016 at 12:24 AM, Marc Mutz <marc.mutz@= kdab.com> 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 anyth= ing about
<ratio>.

So I'd like to ask why a fixed_point is represented by an exponent, and= not a
std::ratio object:

=C2=A0 =C2=A0using dollars =3D fixed_point<int, ratio<1,100>>; = // in units of cents

Though maybe then the fixed_point name is no longer so good, and something<= br> 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<= br> form 2^-N for some N.

Thanks,
Marc

--
Marc Mutz <marc.mutz@kdab.com&= gt; | Senior Software Engineer
KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company
Tel: +49-30-521= 325470
KDAB - Qt, C++ and OpenGL Experts

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