220 37517 article Path: news.gmane.org!.POSTED!not-for-mail From: Viacheslav Usov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allowing std::complex's magic permission for other types Date: Wed, 28 Mar 2018 12:34:59 +0200 Lines: 62 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: multipart/alternative; boundary="000000000000235d610568768f78" X-Trace: blaine.gmane.org 1522233179 7623 195.159.176.226 (28 Mar 2018 10:32:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 28 Mar 2018 10:32:59 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBDU6VRPKW4BBBVO75XKQKGQEBMGDRWY@isocpp.org Wed Mar 28 12:32:55 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f199.google.com ([209.85.192.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f18Nz-0001tL-0e for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id d21-v6sor208814plr.67.2018.03.28.03.35.00 for (Google Transport Security); Wed, 28 Mar 2018 03:35:00 -0700 (PDT) Received-SPF: pass (google.com: domain of via.usov@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a17:902:680c:: with SMTP id h12-v6mr3378777plk.46.1522233300441; Wed, 28 Mar 2018 03:35:00 -0700 (PDT) Original-Received: by 10.236.175.138 with HTTP; Wed, 28 Mar 2018 03:34:59 -0700 (PDT) In-Reply-To: X-Original-Sender: via.usov@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=OgmSDcOP; spf=pass (google.com: domain of via.usov@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=via.usov@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE 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:37517 Archived-At: --000000000000235d610568768f78 Content-Type: text/plain; charset="UTF-8" On Wed, Mar 28, 2018 at 1:17 AM, Myriachan wrote: > The C++ Standard rules state that you can treat an array of std::complex as an array of float of double the number of elements. That is, you can do pointer arithmetic on a float * that crosses complex objects. That cannot be done other than with compiler magic. Only "if a is an expression of type cv complex* and the expression a[i] is well-defined for an integer expression i", which has to mean that we have an array of complex objects. Given that each is required to be layout compatible with T[2], reinterpreting the bigger array as T[2 * (i + 1)] does not need any more magic. Cheers, V. -- 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/CAA7YVg2n1N_QrxC09Er4vLr%2BebwQ5GhkD-3isND76d4YJHwC0g%40mail.gmail.com. --000000000000235d610568768f78 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On W= ed, Mar 28, 2018 at 1:17 AM, Myriachan <myriachan@gmail.com> wrote:

> The C++ Standard rules state that you= can treat an array of std::complex<float> as an array of float of do= uble the number of elements.=C2=A0 That is, you can do pointer arithmetic o= n a float * that crosses complex<float> objects.=C2=A0 That cannot be= done other than with compiler magic.

Only "i= f a is an expression of type cv complex<T>* and the expression a[i] i= s well-defined for an integer expression i", which has to mean that we= have an array of complex objects. Given that each is required to be layout= compatible with T[2], reinterpreting the bigger array as T[2 * (i + 1)] do= es not need any more magic.

Cheers,
V.

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