From -209429405833209023 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,7b33df5790e7ad92 X-Google-Attributes: gidf78e5,public From: Gabriel Dos_Reis Subject: Re: complex design flaw (#1) Date: 1999/03/18 Message-ID: #1/1 X-Deja-AN: 455996104 Content-Transfer-Encoding: 8bit Approved: Fergus Henderson References: <01be6e30$aeae59e0$7d9cd4c7@danielp.interlog.com> <01be6faa$cbf35d40$7d9cd4c7@danielp.interlog.com> X-Original-Date: 18 Mar 1999 04:15:05 +0100 Content-Type: text/plain; charset=iso-8859-1 X-Complaints-To: news@news.unimelb.edu.au X-Trace: izvestia.its.unimelb.edu.au 921733562 12659 128.250.29.17 (18 Mar 1999 05:06:02 GMT) Organization: I.N.R.I.A Sophia-Antipolis (France) X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANvCJpeEDnX0m9pzZAQElwgF/RO7sbcJQ87AB6h1VJMDFekXXH4TpP9wv 0d/809VG2fTa9P/C2qO7pQU0OVcimfy7 =g8j+ Mime-Version: 1.0 NNTP-Posting-Date: 18 Mar 1999 05:06:02 GMT Newsgroups: comp.std.c++ "Daniel Parker" writes: | Jerry Coffin wrote in article | ... | > | > In article <01be6e30$aeae59e0$7d9cd4c7@danielp.interlog.com>, | > danielp@no_spam.com says... | > | > > double x = 0.0; | > > double y; | > > | > > memset( &y, 0, sizeof(double) ); | > > | > > x == y ? | > > memcmp( &x, &y, sizeof(double) ) == 0 ? | > | > No, to both questions. If you were restricting things to IEEE | > floating point, I _believe_ (though I'd have to do some looking to be | > sure) that setting all bits to zero will result in a value of zero. | | OK, but in the spirit of Gabriel Dos_Reis's post, would it be sensible | (stupid?) to do the following. In the system dependency library (that's | the - hopefully small - one with all the #ifdef's) provide an | implementation of an allocator such that if one were to write something | like | | SquareMatrix< std::complex > A(10000); | | on systems that supported IEEE, the allocation of the data would proceed as | follows: allocate 10000*10000*sizeof(std::complex) of raw memory, | memset it to zero, and skip the step of calling placement new. There is nothing wrong with it. That is in essence what I was saying: an implementation is free to do that optimization. In fact, I would expect amoderatly mature C++ implementation to perform similar optimization. -- Gabriel Dos Reis, dosreis@cmla.ens-cachan.fr --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]