From -113911901717061605 X-Google-Thread: f78e5,9ea02bfab7bc90f X-Google-NewGroupId: yes X-Google-Attributes: gid7894ca11fe,domainid0,public,usenet X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news1.google.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 29 Mar 2010 13:20:17 -0500 Return-Path: To: (Usenet) From: Steve Newsgroups: comp.std.c++ Subject: Re: Defect Report: is_iec559 should be defined in terms of binary format Organization: http://groups.google.com Sender: cppmods@cs.rpi.edu Approved: austern@google.com Message-ID: References: <71C0DB7F-160E-4393-A3AE-39C1AC6B6C7D@mac.com> Content-Type: text/plain; charset=ISO-8859-1 X-Original-Date: Sun, 28 Mar 2010 14:18:20 -0700 (PDT) X-Submission-Address: std-c++@netlab.cs.rpi.edu Date: Mon, 29 Mar 2010 13:12:48 CST Lines: 35 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-2JHR9+bKP+Pihk+ecxjQQpfeFU0SGbNtThQpWrVQ9sdj6U0n89+3tXFS+eHeK2Y5J1iIi+6rCNJ1aab!/uJVDq5KPXkDHifpvNGe2YJTxfyU2vAakPHFMTf+4Kx6JzLTIPpmKuTT2uaQaKdmUDhO6iAtkLCC!zLw4wLuV3+EnkFHzRtncMU0kIw== X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Xref: g2news2.google.com comp.std.c++:2332 >From the IEEE-754 (1985) / IEC559 (1989) spec: "3.3. Extended Formats The single extended and double extended formats encode in an implementation-dependent way the sets of values in 3.1 subject to the constraints of Table 1." Those requirements actually boil down to: precision of at least 64 bits, exponent range of at least [-16382, +16383], exponent width of at least 15 bits, and a total encoding width of at least 79 bits. These requirements are obviously satisfied by the Intel 80 bit format (indeed, the standard was written with that format in mind). The standard further requires that correctly rounded basic operations be provided for any arithmetic type. The x87 FPU hardware provides said operations for the 80-bit (with some library support for certain conversions). The C++ spec says that is_iec559 is "true if and only if the type adheres to IEC 559 standard." It does *not* say "is a basic format of the IEC559 standard". The 80-bit type adheres to the IEC 559 standard as an extended type, and therefor is_iec559 correctly returns true for that type. Note that none of this changes in the 2008 revision of the IEEE-754 document. The 80-bit format satisfies the requirements of an extended format associated with the binary64 format, and as such "adheres to the standard". -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]