From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 19265 invoked by alias); 14 Jan 2015 14:48:02 -0000 Mailing-List: contact zsh-workers-help@zsh.org; run by ezmlm Precedence: bulk X-No-Archive: yes List-Id: Zsh Workers List List-Post: List-Help: X-Seq: 34278 Received: (qmail 29188 invoked from network); 14 Jan 2015 14:47:58 -0000 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on f.primenet.com.au X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham version=3.3.2 Date: Wed, 14 Jan 2015 15:47:52 +0100 From: Vincent Lefevre To: "zsh-workers@zsh.org" Subject: Re: Math expression evaluation error? Message-ID: <20150114144752.GA23984@ypig.lip.ens-lyon.fr> Mail-Followup-To: "zsh-workers@zsh.org" References: <150110085320.ZM28012@torch.brasslantern.com> <54B173ED.20301@eastlink.ca> <150110111445.ZM21328@torch.brasslantern.com> <54B1A5EC.2080202@eastlink.ca> <150110175103.ZM21764@torch.brasslantern.com> <54B205B8.4080208@eastlink.ca> <20150112091737.GB27773@xvii.vinc17.org> <1518701421079502@web12g.yandex.ru> <20150113160031.GA12079@ypig.lip.ens-lyon.fr> <2295541421190213@web9j.yandex.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2295541421190213@web9j.yandex.ru> X-Mailer-Info: http://www.vinc17.net/mutt/ User-Agent: Mutt/1.5.23-6392-vl-r75100 (2015-01-06) On 2015-01-14 02:03:33 +0300, ZyX wrote: > 13.01.2015, 19:01, "Vincent Lefevre" : > > In POSIX, it is always an integer division. > > What?! > > 1. How POSIX is related? Zsh is not a POSIX shell and it is not emulation mode that is being discussed here. Zsh is partly based on POSIX for compatibility. The big difference is the lack of word splitting (unless SH_WORD_SPLIT is set). Otherwise I think that one should expect similar behavior, unless there is a good reason. > 2. If this standard is correct: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html#tagtcjh_15 then it references ISO C standard. [...] > Where do you see a requirement for `/` to be integer division? The context is an integer arithmetic. Thus / is necessarily an integer division, like in C with integer types. > 3. POSIX (http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04) says that “Only signed long integer arithmetic is required.” And the section referenced there talks about signed long or double. Signed long integer arithmetic is *required* to be in there, but signed long integer arithmetics is *not required* to be the *only* arithmetics present in POSIX shell. It says: "as long as it does not affect the results in cases where there is no overflow" If $((1/2)) gave 0.5 in some shells, I fear this would break various scripts. So, if a real-floating type is used, then for "/", I suppose that the implementation should do a floor() after the division if the context has operands recognized as integers, which is here equivalent to the integer division despite the two roundings (proved in http://www.vinc17.net/research/papers/rr_intdiv). But POSIX doesn't specify the arithmetic evaluation on expressions other than signed long integer arithmetic. An implementation that decides that $((1.0/2)) gives 17 "as an extension" could still be conforming. -- Vincent Lefèvre - Web: 100% accessible validated (X)HTML - Blog: Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)