220 30842 <24bee7ba-de92-49e5-b5c0-e033f4b86f89@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: rhalbersma@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Detecting compile-time evaluation Date: Thu, 9 Feb 2017 11:29:26 -0800 (PST) Lines: 71 Approved: news@gmane.org Message-ID: <24bee7ba-de92-49e5-b5c0-e033f4b86f89@isocpp.org> References: <86a47916-27c3-4e29-862f-9b4e1f105c1c@isocpp.org> <12459132.29Ej4iibtf@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_379_666786968.1486668566476" X-Trace: blaine.gmane.org 1486668569 7443 195.159.176.226 (9 Feb 2017 19:29:29 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 9 Feb 2017 19:29:29 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCMYZKMJV4IRBF4G6PCAKGQEBRURNKY@isocpp.org Thu Feb 09 20:29:23 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f199.google.com ([209.85.213.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cbuPC-0001ae-PC for gclcip-std-proposals@m.gmane.org; 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Thu, 09 Feb 2017 11:29:28 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.9.200 with SMTP id 8ls21112180otz.48.gmail; Thu, 09 Feb 2017 11:29:27 -0800 (PST) X-Received: by 10.157.56.117 with SMTP id r50mr383830otd.12.1486668567294; Thu, 09 Feb 2017 11:29:27 -0800 (PST) In-Reply-To: <12459132.29Ej4iibtf@tjmaciei-mobl1> X-Original-Sender: rhalbersma@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:30842 Archived-At: ------=_Part_379_666786968.1486668566476 Content-Type: multipart/alternative; boundary="----=_Part_380_391178010.1486668566476" ------=_Part_380_391178010.1486668566476 Content-Type: text/plain; charset=UTF-8 On Thursday, February 9, 2017 at 7:12:40 PM UTC+1, Thiago Macieira wrote: > > > We used to have this problem with Clang: for example, > qCountTrailingZeroBits > wasn't constexpr with Clang until 3.8, because we couldn't use > __builtin_ctz > in a constexpr context. > That is inaccurate: builtin bit-twiddling in constexpr contexts has been supported since Clang 3.4. int main() { static_assert(__builtin_ctz(0x8) == 3, ""); } http://melpon.org/wandbox/permlink/atER2z2uVzSPxzjA -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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On Thursday, February 9, 2017 at 7:12:40 PM UTC+1, Thiago = Macieira wrote:

We used to = have this problem with Clang: for example, qCountTrailingZeroBits=20
wasn't constexpr with Clang until 3.8, because we couldn't use = __builtin_ctz=20
in a constexpr context.

That is inaccurate: builtin bit-twiddl= ing in constexpr contexts has been supported since Clang 3.4.=C2=A0

int main()
{
=C2=A0 =C2=A0 static_ass= ert(__builtin_ctz(0x8) =3D=3D 3, "");
}

<= /div>
http://melpon.org/wandbox/permlink/atER2z2uVzSPxzjA=C2=A0

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