220 20058 article Path: news.gmane.org!not-for-mail From: Myriachan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Should GCD/LCM take variable numbers of arguments? Date: Wed, 26 Aug 2015 12:42:35 -0700 (PDT) Lines: 123 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5977_1731344511.1440618155833" X-Trace: ger.gmane.org 1440618171 21227 80.91.229.3 (26 Aug 2015 19:42:51 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 26 Aug 2015 19:42:51 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDKLT4PURQHRBLFN7CXAKGQEZRAJTVI@isocpp.org Wed Aug 26 21:42:41 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f198.google.com ([209.85.220.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZUgak-0001EZ-Kz for gclcip-std-proposals@m.gmane.org; Wed, 26 Aug 2015 21:42:38 +0200 Original-Received: by qkcu126 with SMTP id u126sf3649643qkc.0 for ; Wed, 26 Aug 2015 12:42:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=b0iSP7n5xHhv75KOzfz9Nr/erqn/Sp9iXeXoR+EBYjw=; b=SXpEObs7u7fVz1ZhZ/ZlWeLOFviFMPu6QSmE01PVhSfL+KmcU1pQBNwHDVlxWSH9wJ wP307xN5iOkhSBxN+vOp3f3bv3KwNGBUryF0mU60+2TnQiG7AKD84tQulO1OwmxCgdxx 3MAJfCUTkOI5MqRH9DtJCE4tdADWmP9z8y1f17ZaWxDiiARUWEW6oe3wMqz7h/vWjjxi J8Lfh101XQa9xTN/M3DIM5crULbg3Ol1QkhMtWAFc/dbsCu0KH9RS2+tAaipEAeFLafz clo6jhdGrhsTHkGPs3ALxht0BUzFN1dwDGPTTIH7b9NCf1KjcFhVn736xon30dAvsS6X ROtw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=b0iSP7n5xHhv75KOzfz9Nr/erqn/Sp9iXeXoR+EBYjw=; b=TBSZtWBNjXfiN2p3HAQZxoLZF2eMcz3kFRuq+GCtMphmbyqTtxcmlK5AuIiVy5DGon D6+8WO7wFTq8Ek9ACcobU2DGjGPdTOSyCYrLD050lzNFzYIBkbtQ6S26NfxtCbXNP4mx N7SUiwXUVvybPorMT3VuL5w5vz/K2HQ6F7TTJI9zglDxKEZjEPLBgshb4f2SvrSQ0TWC fB+vZQLw5aq1zUno0lsj5Xxyo4B3iI8Tl9zUTaCrIe/Q3MeOIx55Otgg3xGrasZyEjSl 7QgQSyMcfqtdEoswD0lyGGuuq+Hkukkw7XsW4qTlfpdd2eXo/PWp5b6GlBP2hzwc0d/7 k9xQ== X-Gm-Message-State: ALoCoQmm2cq2+nObMct8kqKI7eZhTlTDPPC/bvMYs+eD50nYa2au/476Rkdb4YuDPMvUS6bv5g2c X-Received: by 10.13.225.206 with SMTP id k197mr132722ywe.40.1440618157683; Wed, 26 Aug 2015 12:42:37 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.49.72 with SMTP id s8ls258203ign.22.gmail; Wed, 26 Aug 2015 12:42:36 -0700 (PDT) X-Received: by 10.50.30.197 with SMTP id u5mr85381igh.5.1440618156628; Wed, 26 Aug 2015 12:42:36 -0700 (PDT) In-Reply-To: X-Original-Sender: myriachan@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:20058 Archived-At: ------=_Part_5977_1731344511.1440618155833 Content-Type: multipart/alternative; boundary="----=_Part_5978_1705726041.1440618155834" ------=_Part_5978_1705726041.1440618155834 Content-Type: text/plain; charset=UTF-8 On Saturday, August 22, 2015 at 9:51:09 PM UTC-7, Daryle Walker wrote: > > I recently saw descriptions of GCD and LCM as part of the Library > Fundamentals v2 paper (N4529), the original paper (N4601), and > cppreference.com. I'm wondering if those functions should take variable > numbers of arguments. I mean like: > > > constexpr T gcd(T x); // returns |x| > > constexpr common_type_t gcd(T x, U y); // current definition > > constexpr common_type_t gcd(T x, U y, V z, W ...a); // > returns gcd(x, gcd(y, z, a...)) > > > // And similar for "lcm" > > > Good idea?... > > That seems reasonable; implementations could potentially have a faster version for multiple inputs if they wanted. I'm wondering about what the return type ought to be, though. gcd(INT_MIN, 0) == -INT_MIN, which would be undefined if the return type is int. Perhaps make_unsigned_t> ? I don't know whether it's worthwhile, but we could define gcd and lcm for zero and one parameter as well. gcd() == 0, lcm() == 1 I suppose; gcd(x) == x and lcm(x) == x, obviously. Melissa -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_5978_1705726041.1440618155834 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Saturday, August 22, 2015 at 9:51:09 PM UTC-7, Daryle Walker wrote:
I recently saw des= criptions of GCD and LCM as part of the Library Fundamentals v2 paper (N452= 9), the original paper (N4601), and cppreference.com. I'm wondering if those functions should take v= ariable numbers of arguments. I mean like:

<typename T>
constexpr T gcd(T= x); =C2=A0// returns |x|
<typename= T, typename U= >
conste= xpr common_type_t<T, U> gcd(T x, U y); =C2=A0// = current definition
<typename= T, typename U, typename V, typename... W>
constexpr comm= on_type_t<T, U, V,= W...> gcd(= T x, U y, V z, W ...a); =C2=A0// returns gcd(x, gcd(y, z, a...))

// And similar for "lcm"

<= br>
Good idea?...

That seems reasonable; implementations could potentially have a faster ver= sion for multiple inputs if they wanted.

I'm wondering about wha= t the return type ought to be, though.=C2=A0 gcd(INT_MIN, 0) =3D=3D -INT_MI= N, which would be undefined if the return type is int.=C2=A0 Perhaps make_u= nsigned_t<common_type_t<T, U, V, W...>> ?

I don't kn= ow whether it's worthwhile, but we could define gcd and lcm for zero an= d one parameter as well.=C2=A0 gcd() =3D=3D 0, lcm() =3D=3D 1 I suppose; gc= d(x) =3D=3D x and lcm(x) =3D=3D x, obviously.

Melissa

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