220 35618 <1971370.BddXmUsGWe@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 12:42:10 -0800 Lines: 48 Approved: news@gmane.org Message-ID: <1971370.BddXmUsGWe@tjmaciei-mobl1> References: <69593098-e2cc-487e-bd14-9001b27aa7c1@isocpp.org> <1660240.TqYmd56DvC@tjmaciei-mobl1> <659853f7-4d67-4cbc-4632-1a7cfc532f44@gmail.com> 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 1511988131 16241 195.159.176.226 (29 Nov 2017 20:42:11 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 29 Nov 2017 20:42:11 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBJFX7TIAKGQEHGBA7EI@isocpp.org Wed Nov 29 21:42:07 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f199.google.com ([209.85.220.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eK9BF-0003nw-I4 for gclcip-std-proposals@m.gmane.org; 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[2001:19f0:5:2221::1:3]) by mx.google.com with ESMTPS id 41si2033118qtu.188.2017.11.29.12.42.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 29 Nov 2017 12:42:11 -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 9006A2E08 for ; Wed, 29 Nov 2017 12:42:11 -0800 (PST) In-Reply-To: <659853f7-4d67-4cbc-4632-1a7cfc532f44@gmail.com> 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:35618 Archived-At: On Wednesday, 29 November 2017 12:36:22 PST Andrey Semashev wrote: > On 11/29/17 22:41, Thiago Macieira wrote: > > On Wednesday, 29 November 2017 11:08:38 PST Matthew Woehlke wrote: > >> I can already hear people screaming that they don't *want* the compiler > >> to optimize. Well... go write in assembly, if that's what you want. > > > > Just use unsigned if you really meant to have the overflow semantics. > > Unsigned is unsigned, why would you have to convert to unsigned integers > to handle signed overflow? Because you can. a = b = INT_MAX; UB: c = a + b; Totally valid: c = int(unsigned(a) + unsigned(b)); Since the conversion back from unsigned to signed is IB, you can compare against a and verify if it's smaller. if (a + 1 > a) // constant true if (a + 1U > a) // comparison remains > > Converting from unsigned to signed is completely defined if the result is > > in the positive range of the signed type, and IB if it's outside. Since > > it's IB, you can rely on the result being the same across compiler > > versions and optimisation flags. > > Implementation-specific behavior is not portable, it cannot be relied upon. Indeed, but that's what Hyman wants: well-behaved but implementation-specific behaviour. -- 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/1971370.BddXmUsGWe%40tjmaciei-mobl1. .