220 15609 <14072581.09eDfPqFOs@tjmaciei-mobl4> article Path: news.gmane.org!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Library support for relaxed constexpr Date: Mon, 12 Jan 2015 14:43:32 -0800 Lines: 65 Approved: news@gmane.org Message-ID: <14072581.09eDfPqFOs@tjmaciei-mobl4> References: <5ccd3d6e-859c-4b66-b61c-317b704647f2@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1421103253 4353 80.91.229.3 (12 Jan 2015 22:54:13 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 12 Jan 2015 22:54:13 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBD5B2GSQKGQEFIEICQY@isocpp.org Mon Jan 12 23:54:08 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f72.google.com ([209.85.215.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YAns8-0007Cv-Gv for gclcip-std-proposals@m.gmane.org; Mon, 12 Jan 2015 23:54:08 +0100 Original-Received: by mail-la0-f72.google.com with SMTP id gq15sf14801119lab.3 for ; Mon, 12 Jan 2015 14:54:08 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:user-agent :in-reply-to:references:mime-version:content-type: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=0CZwPWH8+iwHu/wsKXfdZjlzWz0T2Rz9F/D8ACrR54g=; b=l7hqS3rWUtpZRp/thMjGpvhhM6nw2mio+Rhr/i5bVaS7LeJ6gH5l1wGovlK8wtvMIf npg4/S+g4Dl+iEtMAph+utEZfg9W28Q/6V3VSWmRtadpIM4EouruytMS4Ppl2KcgWtB6 IybmA3LECWp2ADqVAWmhAdzd0L5s1yvS4RkV34dP5q+DBouLfAYLuJztNcA33zSRwl+a ILTUWYa+mJZN+b/DqilFlbFc9WAH8OdXvkN7KvEr4juGTOgoT35XyMZvVREg/FsAEzLZ F3ZTBgZvbo43IAtQyN72a/IVq4RjOWNr2bcqpHQZita7m+WWlthT442iaxZUgJ0oKzg+ ykNQ== X-Gm-Message-State: ALoCoQnCl/DZw7wnhMy9hOUnbtPPqGY5vOQRrRPwWPSfye03389QE3mtpCGcxzgwLNKmfMRvDGXl X-Received: by 10.112.141.232 with SMTP id rr8mr4046508lbb.0.1421103247978; Mon, 12 Jan 2015 14:54:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.181.13.116 with SMTP id ex20ls694618wid.21.canary; Mon, 12 Jan 2015 14:54:06 -0800 (PST) X-Received: by 10.181.12.17 with SMTP id em17mr34769053wid.45.1421103246821; Mon, 12 Jan 2015 14:54:06 -0800 (PST) Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [2a01:4f8:d13:f81:21c:14ff:fe01:12a3]) by mx.google.com with ESMTP id ei5si16822551wid.4.2015.01.12.14.54.06 for ; Mon, 12 Jan 2015 14:54:06 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) client-ip=2a01:4f8:d13:f81:21c:14ff:fe01:12a3; Original-Received: from tjmaciei-mobl4.localnet (jfdmzpr03-ext.jf.intel.com [134.134.139.72]) by gondolin.macieira.info (Postfix) with ESMTPSA id 47B9C11A770 for ; Mon, 12 Jan 2015 14:54:06 -0800 (PST) User-Agent: KMail/4.14.3 (Linux/3.11.10-21-desktop; KDE/4.14.3; x86_64; ; ) In-Reply-To: X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) smtp.mail=thiago@macieira.org 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:15609 Archived-At: On Monday 12 January 2015 16:39:29 Matthew Woehlke wrote: > On 2015-01-12 15:56, rhalbersma@gmail.com wrote: > > [...] it is perhaps time to introduce this feature > > into the Standard Library. > > > > I write "introduce" rather than "update" because AFAICS, there is > > currently > > *zero* usage of relaxed constexpr (e.g. non-const but constexpr member > > functions) in the current Draft Standard. > > Some implementations have apparently started adding constexpr anyway. > > If a concerted effort is made to 'fix' this, please don't forget places > like , , etc. (I had to change some code that was > originally written against libstdc++ because libc++ does not have > constexpr of e.g. ldexp. Having constexpr of basic math functions and > number manipulation functions seems like a no-brainer...) Note that the difference is whether the intrinsic functions are considered constexpr or not. For GCC, __builtin_ldexp is constexpr but isn't for Clang: $ cat test.cpp constexpr int f() { return __builtin_ldexp(1, 2); } $ gcc -c test.cpp $ clang -c test.cpp test.cpp:1:15: error: constexpr function never produces a constant expression [-Winvalid-constexpr] constexpr int f() { return __builtin_ldexp(1, 2); } ^ test.cpp:1:28: note: subexpression not valid in a constant expression constexpr int f() { return __builtin_ldexp(1, 2); } ^ libstdc++ is written specifically for GCC, so it makes use of that fact. template inline _GLIBCXX_CONSTEXPR typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, double>::__type ldexp(_Tp __x, int __exp) { return __builtin_ldexp(__x, __exp); } Not so with libc++, which supports multiple compilers and thus doesn't use the intrinsic but instead calls the libm function: template inline _LIBCPP_INLINE_VISIBILITY typename enable_if::value, double>::type ldexp(_A1 __x, int __e) _NOEXCEPT {return ldexp((double)__x, __e);} -- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center PGP/GPG: 0x6EF45358; fingerprint: E067 918B B660 DBD1 105C 966C 33F5 F005 6EF4 5358 -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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