From -4569831299143315144 X-Google-Thread: f78e5,9ea02bfab7bc90f X-Google-NewGroupId: yes X-Google-Attributes: gid7894ca11fe,domainid0,public,usenet X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news2.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: Fri, 02 Apr 2010 11:40:02 -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: Thu, 1 Apr 2010 14:02:47 -0700 (PDT) X-Submission-Address: std-c++@netlab.cs.rpi.edu Date: Fri, 2 Apr 2010 11:33:55 CST Lines: 45 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-kg6XY8/7drGj1+Dakqxf3YO03SCUTcDvE8YCuk2CgpPv/2XHchobPDPAzHkzypPgIfvUfCqwMvDxRc0!+JGB9s90MLSG/jh9lGVASidlogLftlCIUZkQjFPeBnFaxu52v1q+fwfSKz14jvvHhh8l9M8hkYG3!emH5j0JYWNebYD6JXQkQ8VTGjec= 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: g2news1.google.com comp.std.c++:2361 On Mar 31, 9:51 pm, Potatoswatter wrote: > It would also correctly return true if double implemented extended- > single Rightly so. > GNU simply sets "is_iec559 = has_infinity && has_quiet_NaN && > has_denorm == denorm_present." As specified, is_iec559 is redundant > and misleading. If the GNU tools indeed define is_iec559 that way for all formats on all machines, I would argue that there is bug in the GNU implementation; IEC559 places requirements not only on the available values in a format, but also requires that operations are correctly rounded, that the four basic rounding modes are supported, that edge cases produce specified results, and that certain means to handle exceptional conditions are provided. For example, the somewhat obscure 16 byte "double-double" (or "dirty-double") head-tail format should not have is_iec559 == true despite the fact that it has encodings for infinity, quiet NaN and denormals, as operations are not correctly rounded (in typical implementations). > If it were restricted to basic types, it would usefully identify encodings. As I understand it, the intent is not to uniquely identify encodings, but rather to indicate that a type supports all the standardized IEC559 features to allow users to take advantage of them in a more portable fashion. If you want unique type identifiers, I think you really want the standard to define a header like that provides typenames along the lines of "float32_t", "float64_t" and "float128_t" that are explicitly bound to the IEEE-754 (2008) binary32, binary64, and binary128 types (and probably names for the new decimal floating-point types as well). -- [ 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 ]