220 37486 article Path: news.gmane.org!.POSTED!not-for-mail From: Bo Persson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allowing std::complex's magic permission for other types Date: Tue, 27 Mar 2018 02:03:20 +0200 Lines: 31 Approved: news@gmane.org Message-ID: References: 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 X-Trace: blaine.gmane.org 1522108885 18478 195.159.176.226 (27 Mar 2018 00:01:25 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 27 Mar 2018 00:01:25 +0000 (UTC) User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCZ6RLW3UIKBBUEU43KQKGQE543XJDA@isocpp.org Tue Mar 27 02:01:21 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f0c3F-0004ib-J6 for gclcip-std-proposals@m.gmane.org; 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Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1f0c3C-0004ed-1E for std-proposals@isocpp.org; Tue, 27 Mar 2018 02:01:18 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 24 Original-X-Complaints-To: usenet@blaine.gmane.org In-Reply-To: Content-Language: sv X-Original-Sender: gclcip-std-proposals@m.gmane.org X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) smtp.mailfrom=gclcip-std-proposals@m.gmane.org 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:37486 Archived-At: On 2018-03-26 22:26, Myriachan wrote: > I would like to propose that C++ get a mechanism by which the magical > ability of std::complex * to be reinterpret_cast to T * could be > allowed for other classes. > > A simple case of this is a vector4 type: > > struct vector3 { float x; float y; float z; float w; }; > > The performance difference is strong enough that our project actually > gets a much larger performance /increase/ from using > -fno-strict-aliasing versus -fstrict-aliasing with the changes required > for compliance. > This is not what the std::complex magic requires from the compiler. At least one implementation (MSVC) instead stores a two element array, which does away with any potential padding and also makes pointer arithmetic reasonable. Bo Persson -- 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/p9c1k7%24h28%241%40blaine.gmane.org. .