220 35617 <2409200.B6bFol9Gvi@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Rotational shift operator Date: Wed, 29 Nov 2017 12:38:52 -0800 Lines: 83 Approved: news@gmane.org Message-ID: <2409200.B6bFol9Gvi@tjmaciei-mobl1> References: <69593098-e2cc-487e-bd14-9001b27aa7c1@isocpp.org> <1660240.TqYmd56DvC@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1511987939 1405 195.159.176.226 (29 Nov 2017 20:38:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 29 Nov 2017 20:38:59 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBXVV7TIAKGQEXMZQGJY@isocpp.org Wed Nov 29 21:38:53 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f199.google.com ([209.85.216.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eK984-00089C-LZ for gclcip-std-proposals@m.gmane.org; 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[2001:19f0:5:2221::1:3]) by mx.google.com with ESMTPS id z81si2770884qkz.106.2017.11.29.12.38.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 29 Nov 2017 12:38:54 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 2001:19f0:5:2221::1:3 as permitted sender) client-ip=2001:19f0:5:2221::1:3; Original-Received: from tjmaciei-mobl1.localnet (fmdmzpr04-ext.fm.intel.com [192.55.54.39]) by smtp.macieira.info (Postfix) with ESMTPSA id 030712E02 for ; Wed, 29 Nov 2017 12:38:54 -0800 (PST) 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 2001:19f0:5:2221::1:3 as permitted sender) smtp.mailfrom=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:35617 Archived-At: On Wednesday, 29 November 2017 12:10:22 PST Hyman Rosen wrote: > On Wed, Nov 29, 2017 at 6:57 AM, David Brown wrote: > > 1. int arithmetic is no longer associative and distributive. > > 2. Multiply and divide (when there is no remainder) are no longer > > inverses. > > 3. Basic identities like "if you add a positive number to an integer, it > > gets bigger" no longer hold. > > 4. Division by a known constant can't always be done by multiplication. > > If you want specific algebraic structures, create classes that implement > them. > C++ fundamental types are not those. They are a language reflection of the > underlying CPU behavior. That's where you're wrong. They are not. The C++ language is defined on top of an abstract machine and the primitive types are types in *that* machine. Not specifically your CPU. Besides, doing what you're proposing is close to impossible. We can't reorder instructions in classes like the compiler can. But they can insert extra checks or simply perform operations in unsigned types, converting to signed as needed. > > The mistake some people make is to think that a C (or C++) "int" is > > > > just > > > > > a signed type matching the cpu's registers. > > > > > > The mistake some people make is to think that it's not. > > > > You are wrong. Totally wrong. > > No, you are :-) Hyman, considering the people behind the language text say you are wrong. the chances are that you're wrong. I understand you want to change that. But right now, you're in the wrong. > > You are confusing implementation defined behaviour (which compilers have > > to define and document) and undefined behaviour (which compilers do not > > have to define). > > I'm not confusing them. I'm saying that it's wrong for the standards to > make > behavior undefined when it could be unspecified, implementation-defined, or > fully specified (e.g., left-to-right order of evaluation). We agree to disagree. > > I can't think of /any/ circumstances in which it would have been useful > > for > > signed integer overflow to wrap around. > > People use it for overflow checks after the fact. It's easier. What's the > correct > rewrite of the following? > if (b > 0 && a + b < a) // > *overflow* if (b > INT_MAX - a) > When something is behaving intentionally badly, that is not a > misunderstanding > on my part, that's a difference of opinion on priorities. Authorities get > to chime > in on what should be a priority; that's what authorities are *for*. In our case, they are called "the ISO C++ Standard Committee". I think they've made their ruling known. -- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center -- 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/2409200.B6bFol9Gvi%40tjmaciei-mobl1. .