220 30781 article Path: news.gmane.org!.POSTED!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: safe integrals comparison Date: Sun, 5 Feb 2017 16:10:15 +0100 Lines: 106 Approved: news@gmane.org Message-ID: References: <66f9bab2-7220-4bf1-afb7-77c5efa1bac3@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1486307418 22897 195.159.176.226 (5 Feb 2017 15:10:18 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 5 Feb 2017 15:10:18 +0000 (UTC) User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBWMA3XCAKGQE6CIFHQQ@isocpp.org Sun Feb 05 16:10:13 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f72.google.com ([209.85.215.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1caOSD-0005gy-DO for gclcip-std-proposals@m.gmane.org; Sun, 05 Feb 2017 16:10:13 +0100 Original-Received: by mail-lf0-f72.google.com with SMTP id z134sf25786739lff.5 for ; Sun, 05 Feb 2017 07:10:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=TApxkF4gDA0D0qmNYSQq0WLgyl8ychhBGpHGtHPWvlw=; b=Ih9ZXC8HHA+0UML4azj+lBWSQ4ebv+RHzOEvIsnLA0xzC8Ohej7OEJxRd0WgC8on9p +H6r4BgRG2y2VxP3ljPeJE/utAixxgmxyuFhCMS+ybQXPz0lGUVdUeX9/nmVQYv5ok19 meCw50s16DwjH0kFfOybPkFa/mSJoqkyNEpmsdsul392Tso/fMydb2RkB7JsJ0lxLeLM xceOCJjzvWL/hFqEZHRDeQDe5fzky+G4tsbXCBZM97Jb1Acaa1UDNMuweEsNY11lOXna YqkJJndTRUX9zzg3WAYMsY6/m40T9rjWZNrg4Ur2R0OQIMf3iPanuyLqsAxa3sxkxCyI X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=TApxkF4gDA0D0qmNYSQq0WLgyl8ychhBGpHGtHPWvlw=; b=ZStIyNFtncmR6gCIQhh2vUL9RvpBMPUguKMBX7PPrp3lWlssX7cPIY7eo8/7dPUOzq a3kwxrt3iqcymIKijVGtn8cjmtypzY1lEwgpe0fHdKHvZGMgZeOh5stutggfkMsicWB7 aX+XcEPBAaPGO/2jDXCu9LHSC7KnIktviMC/p90meGxl67bIqydyPT28rAUKYIupzDIy LS03T1SP7Keufpg67yJRHMxkBc5FUblo4p/SjjqAqWkq/epBD2h98/5UdMArt7t4O/jW Sr2cF2OpX3BnWd4cfDFPhUc+BIYgZf3BW4gy0w5InEW8Vf1R9BEiFbYYVMzv5cCudBsA X-Gm-Message-State: AIkVDXKLqUMlztuyVjGsK3yCGj18On3cyLf7Fi17r9fGsptmdC9Xo5YTRwTpNUyZ4haD7Q== X-Received: by 10.46.80.86 with SMTP id v22mr557434ljd.22.1486307418394; Sun, 05 Feb 2017 07:10:18 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.159.195 with SMTP id i186ls806775wme.12.canary-gmail; Sun, 05 Feb 2017 07:10:17 -0800 (PST) X-Received: by 10.28.19.207 with SMTP id 198mr4869169wmt.70.1486307417251; Sun, 05 Feb 2017 07:10:17 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp13.smtpout.orange.fr. [80.12.242.135]) by mx.google.com with ESMTPS id 140si4604234wmt.40.2017.02.05.07.10.17 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 05 Feb 2017 07:10:17 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.135 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.135; Original-Received: from imac-de-vicente-botet-escriba.home ([2.11.72.89]) by mwinf5d75 with ME id h3AF1u00R1vahZu033AGQW; Sun, 05 Feb 2017 16:10:17 +0100 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sun, 05 Feb 2017 16:10:17 +0100 X-ME-IP: 2.11.72.89 In-Reply-To: <66f9bab2-7220-4bf1-afb7-77c5efa1bac3@isocpp.org> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.135 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:30781 Archived-At: Le 20/01/2017 =C3=A0 17:31, federico.kircheis@gmail.com a =C3=A9crit : > Hello to everyone, this is my first proposal, I hope you'll find it=20 > interesting, give me some feedback and help to improve my=20 > idea/implementation/proposal. > > > > > My proposal would be to add four templated functions which work only=20 > for integral types (bool excluded). > > The first function would be: > > template constexpr bool in_range(const T t)=20 > noexcept; > > Usage > size_t i =3D=3D ... > if(in_range(i)){ > // safe to convert i to a DWORD value, parameter... > } else { > // not possible to represent i as a DWORD > } > There si something related in GSL narrow/narrow_cast. Your function=20 could be named can_be_narrowed(i). There could also be template bool can_be_narrowed(U); template optional try_to_narrow(U); > The second function would be: > > template constexpr bool cmp_equal(const T t,=20 > const U u) noexcept; > > Usage > size_t i =3D=3D ... > DWORD j =3D=3D ... > if(cmp_equal(i,j)){ > // i and j represent the same quantity > } else { > // i and j represents different quantities > } > > Currently we are going more towards 3-value comparisons (p0100r2). There=20 will surely be an additional operator <=3D>. It would be better to start=20 by defining some kind of safe_3compare. Have you considered defining a wrapper that has this safe semantic. if( safe(i) =3D=3D safe(j) ){ > > > The fourth function I would like to add is: > > template constexpr std::size_t precision() noexcept; > > > The reasons are described here: > > https://www.securecoding.cert.org/confluence/display/c/INT35-C.+Use+corre= ct+integer+precisions > > Quote: > "Integer types in C have both a size and a precision. The size=20 > indicates the number of bytes used by an object and can be retrieved=20 > for any object or type using the sizeof operator. The precision of an=20 > integer type is the number of bits it uses to represent values,=20 > excluding any sign and padding bits. > > Padding bits contribute to the integer's size, but not to its=20 > precision. Consequently, inferring the precision of an integer type=20 > from its size may result in too large a value, which can then lead to=20 > incorrect assumptions about the numeric range of these types. =20 > Programmers should use correct integer precisions in their code, and=20 > in particular, should not use the sizeof operator to compute the=20 > precision of an integer type on architectures that use padding bits or=20 > in strictly conforming (that is, portable) programs." > > > The function precision is used internally (by cmp_equal, cmp_less and=20 > in_range) for verifying which type is bigger, in order to safely cast=20 > before comparing the types. I also think, that this function should be=20 > part of the API, since it is very handy. Wondering if you shouldn't use std::numeric_limits, and if there is=20 not enough information there to request the addition of a trait? Vicente --=20 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 e= mail 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/a734e3fd-d203-1ed6-d605-bf54f6a6e1e9%40wanadoo.f= r. .