220 31542 <58C2D210.6080900@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Math constants Date: Fri, 10 Mar 2017 11:19:28 -0500 Lines: 58 Approved: news@gmane.org Message-ID: <58C2D210.6080900@gmail.com> References: <6bccd7e5-82ad-4c59-9f72-f7fb6639c0ca@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1489162807 1890 195.159.176.226 (10 Mar 2017 16:20:07 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 10 Mar 2017 16:20:07 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBE5ERPDAKGQEZI5W6ZY@isocpp.org Fri Mar 10 17:19:59 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f200.google.com ([209.85.217.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cmNGl-0007nH-Iz for gclcip-std-proposals@m.gmane.org; Fri, 10 Mar 2017 17:19:55 +0100 Original-Received: by mail-ua0-f200.google.com with SMTP id f54sf101625388uaa.5 for ; Fri, 10 Mar 2017 08:20:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding: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=k3SVxDPkCtu27CTUvhCEnBSb3e5Lt00FDKaQ5d7NSQc=; b=h1cbJU3TXWql8FsDNHh9MCNhtztnifUmcR2yI1aVurv5qduIu9sHJ/PZKnqZ1EK65m Nk1J+FVFgnFSQ+ekXXAm6cvxHmzTkyz0qi9BKH4BFD64+e2IR400e0a4hKeCaGOuCBgk KiRFTvFvbwWVmMDnPCiE+bMgw0NIfmKx6zO2maqYUwOnUegQlEwgEdeAf26ToSTN7QFR +tEdZYD+feKMYMTvgWyAEhcA90cnsXv5c7u76yOcsOx/h9rrDG67TsoJ3geozY7++h2M +IriuvvLiX3AByFZdNzW6poTtXlMWypiw2vcLNO/w5vXUsicgG7nULXmZ1CmfDELSJJv X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :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=k3SVxDPkCtu27CTUvhCEnBSb3e5Lt00FDKaQ5d7NSQc=; b=i7LLmsUvyKtiwh0dtnXeRxdVy4q9y0ziyz+6OKzIn28X+KPfhCn2pmJU8rdzPcuOhq eHxQOon80oc5AMIQ7VQOIxi+eTS5vphKOeQXdh7867kW2V6B+iIqd2ocMvZSlD0trbUQ Wx4tGAV/B/unchxqyzD4IRSNXolhwguCz576n9Mh8g5G1SwRFSUzccGsP0ATHCS3VapS wEG97h6mHksH0YBm1juy2FdtD80cab5soVAM75ZbbX/P1Zinh9PUdszFHtpdr9cOxLfq wmJ0SAwhz+agxZHBnM2TrR8OR+rKOhSYZujnPKXIGlP8vux6SfvoyjSs5SGcMis65swM X-Gm-Message-State: AMke39nPvlNeLbZJAC9e5+zbGX0V/uT5W83kSEsHuaku4H5eZ/nZcNEyD1gpe+Q+pp1mZA== X-Received: by 10.200.36.104 with SMTP id d37mr3554503qtd.56.1489162773464; Fri, 10 Mar 2017 08:19:33 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.129.81 with SMTP id c78ls2717910iod.28.gmail; Fri, 10 Mar 2017 08:19:30 -0800 (PST) X-Received: by 10.36.185.16 with SMTP id w16mr3036627ite.118.1489162770867; Fri, 10 Mar 2017 08:19:30 -0800 (PST) Original-Received: from mail-it0-x241.google.com (mail-it0-x241.google.com. [2607:f8b0:4001:c0b::241]) by mx.google.com with ESMTPS id k201si2543021itk.102.2017.03.10.08.19.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 10 Mar 2017 08:19:30 -0800 (PST) Received-SPF: pass (google.com: domain of mwoehlke.floss@gmail.com designates 2607:f8b0:4001:c0b::241 as permitted sender) client-ip=2607:f8b0:4001:c0b::241; Original-Received: by mail-it0-x241.google.com with SMTP id w185so1762624ita.3 for ; Fri, 10 Mar 2017 08:19:30 -0800 (PST) X-Received: by 10.36.107.202 with SMTP id v193mr2770348itc.21.1489162770479; Fri, 10 Mar 2017 08:19:30 -0800 (PST) Original-Received: from [192.168.1.176] (tripoint.kitware.com. [66.194.253.20]) by smtp.googlemail.com with ESMTPSA id l33sm4546307iod.8.2017.03.10.08.19.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 10 Mar 2017 08:19:29 -0800 (PST) In-Reply-To: <6bccd7e5-82ad-4c59-9f72-f7fb6639c0ca@isocpp.org> X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 2607:f8b0:4001:c0b::241 as permitted sender) smtp.mailfrom=mwoehlke.floss@gmail.com; dmarc=pass (p=NONE sp=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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:31542 Archived-At: On 2017-03-09 17:44, 3dw4rd@verizon.net wrote: > I think that this could devolve into endless bikeshed discussions and wha= t=20 > constants to include.=20 template class pi_helper { static constexpr value =3D 3.14159...; constexpr operator T() { return value; } template constexpr T times() { return numerator * value / denominator; } } template inline constexpr pi_helper pi; ....and as QOI, implementations can provide explicit specializations of any of `times()` that make sense. This way the namespace isn't polluted by bunches of `pi_1_3` and so forth, and it's clearer what value you are asking for. For roots, I think something like: template extern T sqrt; ....makes sense. We should specify that at least a particular set of these must be available, but this would provide a hook where compilers can provide an intrinsic such that any square root is available as a constexpr. (This would also permit compilers to choose to provide them via an intrinsic that can always compute them, but e.g. using a variable-precision algorithm that ensures the result is always accurate within the limits of the requested type.) We can do something similar for logarithm constants. I don't think we should have constants for 180/pi and pi/180; having constexpr functions for these operations will I think lead to better code. Otherwise, we should definitely have Euler's constant, on principle if nothing else, but I don't think I've ever used the golden ratio or anything involving square roots and pi. (When are those useful? When is pi=C2=B2/6 useful?) --=20 Matthew --=20 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 e= mail 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/58C2D210.6080900%40gmail.com. .