From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21475 invoked by alias); 15 Jan 2015 13:43:26 -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: 34289 Received: (qmail 23143 invoked from network); 15 Jan 2015 13:43:23 -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: Thu, 15 Jan 2015 14:34:21 +0100 From: Vincent Lefevre To: "zsh-workers@zsh.org" Subject: Re: Math expression evaluation error? Message-ID: <20150115133421.GA30651@ypig.lip.ens-lyon.fr> Mail-Followup-To: "zsh-workers@zsh.org" References: <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> <20150114144752.GA23984@ypig.lip.ens-lyon.fr> <363741421271463@web10o.yandex.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <363741421271463@web10o.yandex.ru> X-Mailer-Info: http://www.vinc17.net/mutt/ User-Agent: Mutt/1.5.23-6396-vl-r76280 (2015-01-15) On 2015-01-15 00:37:43 +0300, ZyX wrote: > 14.01.2015, 17:48, "Vincent Lefevre" : > > 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. > > No. The context explicitly says that signed long integers or doubles > should be used. Context of the ISO C standard obviously does not say > anything like this. Wrong. The context of $((...)) is signed long arithmetic. If a shell wants to use double's (such as 1.0), that's only an extension. > > 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. > > Nope, it cannot ever be conforming. POSIX does this by saying that > semantic of operation is the same as in C, Only for what it specifies. > except that only signed long integers and doubles are allowed. No, POSIX says "As an extension, the shell may recognize arithmetic expressions beyond those listed." and does not specify anything on such expressions. $((1.0/2)) is such an arithmetic expression beyond those listed. In particular, it does *not* say that "only signed long integers and doubles are allowed". A shell could implement other types (number fields or whatever), and specific operators. And note that in such an expression, "/" is not necessarily an operator, but could be part of a constant. -- Vincent Lefčvre - Web: 100% accessible validated (X)HTML - Blog: Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)