220 34698 article Path: news.gmane.org!.POSTED!not-for-mail From: David Brown Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Constexpr maths functions Date: Sun, 8 Oct 2017 12:45:06 +0200 Lines: 48 Approved: news@gmane.org Message-ID: References: <01e6fcdd-3250-4017-b53a-cea48f869817@isocpp.org> <8c572022-0abd-6677-4b50-788651354e1e@westcontrol.com> <79697376-5ccd-470a-b197-ab717ae1d64a@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"; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1507459510 27963 195.159.176.226 (8 Oct 2017 10:45:10 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 8 Oct 2017 10:45:10 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 To: Niall Douglas , ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDP6R2XHXIARBMUD5DHAKGQEQWRZMBQ@isocpp.org Sun Oct 08 12:45:05 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e194v-0006E5-6Y for gclcip-std-proposals@m.gmane.org; Sun, 08 Oct 2017 12:45:01 +0200 Original-Received: by mail-lf0-f70.google.com with SMTP id p195sf6383806lfd.18 for ; Sun, 08 Oct 2017 03:45:08 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1507459508; cv=pass; d=google.com; s=arc-20160816; b=e4gMuWCMOk4+B19oUAjRB7j7HHcvV63m+uDyHK0tmtXYiAfWUd2hudm7j1SzBTV/rM 3/T6p5UQUCUIbbMwmCiVJkuNsMW1tekiXQPKBlAeIzfUtKugCx5DA8+CKZnujKEYZSHJ 9Zr4+f91n41eHcTQCx4IGu0KI6lpQcVR5PsOVvX+9nJLZCwKTXzOHwDYMRGKN8BO15+B PLL0i6kJe6GS/MZyU8aFy5M8pNSKnSwFnqdb5G9VjZEbZyY1Kul1bZftK0N2aZFns9f4 C6ljdbfCy3riZR85vz4yoHLzata3dvbFnwM6Q906Ffu+sTAr0lIubk5V3zmEVTKccYN3 0MpQ== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:reply-to:content-transfer-encoding :content-language:in-reply-to:mime-version:user-agent:date :message-id:from:references:to:subject:arc-authentication-results :arc-message-signature:dkim-signature:arc-authentication-results; bh=NUj69IZBM5nHPsS/RvKDF8QnlWFZm7bsvQ/4CQTzqCA=; b=gmWJ/lVQ0eG0rh07s9U707EUgEE1nodK1JsHRDgUk6gvHJ8QCuVM5y14GjTQz4HLHT DDWNZOUX1zCaX+7Dhw7uNsF/03azQTXab9SJD81LSGdwsWpR8LN7TCrgR0GfAsJWt7Ei BJl9Sz4s/o7a+zX3HALwNXDQ8XV2MmbQUN/rY6y0Nv4keesOFTkVt8bxhZ9FjrDRnnnp vj2vzzNYIVYG+xg6DZ1DDkKLS+QpShievFuEr2NmVNlBgUWaHLCijy1OEvARC/Wba6Re Viq6QipnYDsryIbXyoOmHpCTRdgRSi/PwDA+IPKJ3T+0qaHrrrwupIfnHPv2+b ARC-Authentication-Results: i=2; mx.google.com; spf=pass (google.com: domain of david@westcontrol.com designates 213.162.250.26 as permitted sender) smtp.mailfrom=david@westcontrol.com 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-language:content-transfer-encoding :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=NUj69IZBM5nHPsS/RvKDF8QnlWFZm7bsvQ/4CQTzqCA=; b=fi7TnH1HlVb9hJEMrzh8eWYACcmjLB0F6huY/tIGmDXPYesxHoSfjpodahE7GeO0YY HCMM/IjpN7l8ubj+ZCvJKXHxXrFsilp6WTgXCT0TjZdkpANTOFG2iHA3NCBvZFIj4skT DxOzX5dK9xdCcvRdUSPS0y9yiKyvYmRhXdi3xksLmOozo1kVvKIqmDV/KsnnW3uMN6Cu KwsrQSouyAsfgah11+M1csekU13fzgSbS+5QA04+NUQcSGCt7Th//J3v2ftkQeDrDi4V iVptNNRovmxmGcmz5HzEdcmeoAwHFI1tiPLfjSkIHDmk5QKT/ogvI5rL84wAZO/WqniY Ur+ 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-language :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=NUj69IZBM5nHPsS/RvKDF8QnlWFZm7bsvQ/4CQTzqCA=; b=pdES+/5DYwso/nrsWFqGtRfFj72cHX0N2LLqIEe0A0xGZryU7OBqE76482mR1CGoL6 wbanBLHvNTj25qDPScC8ym6eVaV8Vh7deJzzeIpK9T89bKtRs7HSq1hG31c0PsiJfVvC eYWjt6HW9johnnyPuI4d29cZqXp3wRqjaW7n4PJJJfVMqi9wlDeXKGiFs0n1WMNomAIc ETinaDd71fymP+2SbpbVHpLRkKl/xyMkaFkqudTSWmuol4HGNL2u/sq2qtAvZm3BtJay uYe0D9tZA+yY6gpMcm5WNsReebQ8g4mdAKB90xYh3CU X-Gm-Message-State: AMCzsaUtTeEs8iKyP9zbmzkBFEmrVUIcDAvc9C/vbkSya2s1NyqYZUid C3KBGAREGllRkoYOiBDNR0friw== X-Google-Smtp-Source: AOwi7QAOy9KaBCh0TV/jTnHU1FfdC4jSik1UOORVnrMD/zXibMB6L2U23VE3Mw6L5ZKnjS0LToA13g== X-Received: by 10.25.35.87 with SMTP id j84mr166923lfj.23.1507459508343; Sun, 08 Oct 2017 03:45:08 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.46.48.26 with SMTP id w26ls330098ljw.6.gmail; Sun, 08 Oct 2017 03:45:06 -0700 (PDT) X-Received: by 10.46.75.2 with SMTP id y2mr3111650lja.91.1507459506455; Sun, 08 Oct 2017 03:45:06 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1507459506; cv=none; d=google.com; s=arc-20160816; b=c6Mj6WHqWr3hSe7Q/RQfXE4G/HMbz9hdSMuhHpBk6guidADqyOWSyw6jFuWtBLUtxt ph+3oqXB2OJwersY64pBgb2U6mpb2IKaompSd7sIO2hfw3knYEJQ31WnvvUXFfetug4r UEh23KRYtGjNUXxuM5Ui8haBimVt9GG1wfU5bs9hIWIsBETg9knYrvbhJqMS6rB4B1KZ OAb1TPEBRxZEKln3wRHDsz1prcqEBmeQd//29O4N97hVHD6rDkTIBjHjbaOjAgPclQCv BsCXPrqWV+DpF4m/AXONse98urJYxwldB6MK7XJZvUcqMKmqakPs5IjhBTPQRvjsaux8 SLYg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:to:subject :arc-authentication-results; bh=0ZV3c+Tjq5+nSslP+zHc44U/x7QXig2SF8ycIb4VRsE=; b=XeqaYD7fU9h/GpQMtJOl0fBSzWB9CGeZCxuIK/UzKvEyVntA3zxs7qe7TD1jsvQpHi cQcaEa1wcVRkGmWThwCsqg5KobjCPoyFHq2bSFebMBxy3IwRWfB1Jio1+Hnst/4cgCMv CU8TuzlDt4fUDB0IoBD27kRAtdrUnKV3CrVUJdNPD1YN29evug6T5w1qH9+zEU8Z1r9d v5H7sRrXw5W1leDJCg31XlViuky09mIdyM6me3c9XSX1gdqIuiE+DqsB0X9PcQxD4iuZ CZgOI/3Kn/PGGNhmBtef4OoaiqO6nh4LOt4PvIrOP+Lzs/oSuVJ6nZM7Q9LKPoFrWXrw qp/Q== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of david@westcontrol.com designates 213.162.250.26 as permitted sender) smtp.mailfrom=david@westcontrol.com Original-Received: from mailfilter04.hatteland.com (mailfilter04.hatteland.com. [213.162.250.26]) by mx.google.com with ESMTPS id s139si2496557lfs.649.2017.10.08.03.45.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 08 Oct 2017 03:45:06 -0700 (PDT) Received-SPF: pass (google.com: domain of david@westcontrol.com designates 213.162.250.26 as permitted sender) client-ip=213.162.250.26; Original-Received: from localhost (localhost [127.0.0.1]) by mailfilter04.hatteland.com (Postfix) with ESMTP id 91BB7109501; Sun, 8 Oct 2017 12:45:14 +0200 (CEST) X-Virus-Scanned: by SpamTitan at hatteland.com Original-Received: from mailfilter04.hatteland.com (localhost [127.0.0.1]) by mailfilter04.hatteland.com (Postfix) with ESMTP id CAA66109383; Sun, 8 Oct 2017 12:45:13 +0200 (CEST) Original-Received: from JHSVMHUB01.netsentral.no (unknown [172.21.1.101]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mailfilter04.hatteland.com (Postfix) with ESMTPS id C506510928A; Sun, 8 Oct 2017 12:45:13 +0200 (CEST) Original-Received: from [192.168.4.245] (172.21.20.100) by e2010.hatteland.com (172.21.1.25) with Microsoft SMTP Server (TLS) id 14.3.224.2; Sun, 8 Oct 2017 12:45:05 +0200 In-Reply-To: <79697376-5ccd-470a-b197-ab717ae1d64a@isocpp.org> Content-Language: en-GB X-Originating-IP: [172.21.20.100] X-Original-Sender: david@westcontrol.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@westcontrol.com designates 213.162.250.26 as permitted sender) smtp.mailfrom=david@westcontrol.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:34698 Archived-At: On 08/10/17 01:01, Niall Douglas wrote: > On Saturday, October 7, 2017 at 1:24:46 AM UTC+1, David Brown wrote: >=20 >=20 > On 06/10/17 17:48, Niall Douglas wrote: > > > > =C2=A0 =C2=A0 Is there any reason why this could not be supported = in the C++ > > =C2=A0 =C2=A0 standards? > > > > Breaks compatibility with C I would imagine. > > >=20 > That would be a reasonable (but not great) justification - though I > don't see how it would. =C2=A0Perhaps errno support would be the prob= lem? >=20 >=20 > It's not even that. >=20 > A very common use case for C++ is to compile straight-C programs for the= =20 > improved optimisation. >=20 > Thus a C program must run exactly the same in C++ as it would in C.=20 > Making the cmath functions go constexpr in C++ breaks that, badly. >=20 /What/ would break? In all the code I have written, there is nothing=20 about "sin" or other functions that cannot be pre-calculated.=20 "sin(x)" gives the same result for compile-time constant x whether it is=20 done at run time or at compile time. You sound so convinced that it=20 would "break badly" to do this calculation at run time (though compilers=20 certainly /do/ handle this at compile time - gcc has no problem with=20 using sin() in constexpr functions and initialisation). What am I missing? --=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/d170ed43-361a-c5df-ff46-157240760a97%40westcontr= ol.com. .