From 664443126819168348 X-Google-Thread: f78e5,9ea02bfab7bc90f,start X-Google-NewGroupId: yes X-Google-Attributes: gid7894ca11fe,domainid0,public,usenet X-Google-Language: ENGLISH,UTF8 Path: g2news2.google.com!news2.google.com!news.glorb.com!news.alt.net!frodo.cs.rpi.edu!not-for-mail From: David Krauss Newsgroups: comp.std.c++ Subject: Defect Report: is_iec559 should be defined in terms of binary format Date: Sat, 27 Mar 2010 12:41:34 CST Organization: unknown Lines: 45 Sender: cppmods@cs.rpi.edu Approved: stephen.clamage@sun.com Message-ID: <71C0DB7F-160E-4393-A3AE-39C1AC6B6C7D@mac.com> NNTP-Posting-Host: netlab.cs.rpi.edu Content-Type: text/plain; charset=windows-1252 To: (Usenet) Return-Path: X-Original-Date: Fri, 26 Mar 2010 23:42:13 -0500 X-Submission-Address: std-c++@netlab.cs.rpi.edu Xref: g2news2.google.com comp.std.c++:2322 My implementation reports numeric_limits::is_iec559 == true for the Intel 80-bit format. Intel 80 is not defined by or related to IEC 559; an alternative 128-bit format is. Perhaps one source of this issue is the grandfather clause in C99 §F.2/1 footnote 307: ‘‘Extended’’ is IEC 60559’s double-extended data format. Extended refers to both the common 80-bit and quadruple 128-bit IEC 60559 formats. This would seem to be trying to change the very content of IEC 559! However, to put this in context, note that C99 provides the user with much less information about the implementation. From §F.1/1: An implementation that defines _ _STDC_IEC_559_ _ shall conform to the specifications in this annex. There is one macro and no other compliance information. If Intel 80 were considered non-compliant, it would preclude its use entirely on IEC 559 compliant C implementations. C++ does not have this issue: the user queries FP types for compliance individually. I believe this justifies an exception to the trend of deferring numeric decisions to the C spec. Moreover, no C++ standard explicitly refers to C FP at all. The definition of is_iec559, §18.2.1.2/52, says simply 52 True if and only if the type adheres to IEC 559 standard. This is ambiguous enough to allow Intel 80 if you consider IEC 559's provision for arbitrary formats adhering to the principles and features of the explicitly defined formats. But that interpretation would make is_iec559 meaningless: other members of numeric_traits<> already describe the features of a FP type that would contribute to compliance besides binary format. So there is really no other information for it to convey. - Cheers, David -- [ 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 ]