From -3758659439026482573 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,94e9c2bbb0060b48 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-07-30 16:57:01 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!kibo.news.demon.net!news.demon.co.uk!demon!mail2news.demon.co.uk!not-for-mail From: Allan_W@my-dejanews.com (Allan W) Newsgroups: comp.std.c++ Subject: Re: Proposals for small vectors? Date: Tue, 30 Jul 2002 23:56:50 GMT Organization: http://groups.google.com/ Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <23b84d65.0207301527.38062bdd@posting.google.com> References: <87wurryywb.fsf@grue.ucsd.edu> <3D38FB4F.1020909@animats.com> <3D3CB3C6.20106@animats.com> X-Trace: mail2news.demon.co.uk 1028073415 mail2news:11363 mail2news mail2news.demon.co.uk X-Complaints-To: abuse@demon.net X-Mail2News-Path: news.demon.net!mulga.cs.mu.oz.au X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit NNTP-Posting-Date: 30 Jul 2002 23:27:51 GMT X-MailScanner: Passed Lines: 51 Xref: archiver1.google.com comp.std.c++:12904 John Nagle wrote > "valmatrix" would support N x M matrices, with > the size defined at template instantiation. The > underlying representation would be guaranteed to > be a built-in array of the specified element type, > and the underlying representation data would be > accessable from the outside if needed. > (There are many APIs in existence that use such > a representation; this allows efficient C++ > use or encapsulation of them.) > > Both row-major and column-major representations > would be supported, again, determined at template > instantiation time. (OpenGL and Direct-X use 4x4 > matrices of different direction, so we must > support both.) I'm worried that a less-than-careful implementation could cause major code bloat. If my program a 4x4, 4x8, 8x4, and 8x8 valmatrixes, would a lot of code be instanciated four times? If I have both row-major and column-major representations, would this grow to 8 times? Judicious use of inheritance can drastically reduce the amount of code generated from a template instanciation -- but in some circumstances this can provide a (very modest) performance penalty. Most code wouldn't even notice the performance difference, but I suppose that video updates very well could -- and that could make this type of code factoring inappropriate for graphics. > Like "valarray", the implementation would be > optimized for performance, not generality. If > generality is needed, Boost's "Matrix" class > is probably more appropriate. I'm not a graphics programmer. Maybe it's reasonable to say, "this is only appropriate for a graphics app where 'optimize' means 'optimize for speed, burn as much memory as you need'." But I'd want that to be VERY explicit -- maybe in the class name (i.e. GraphicsQuickValMatrix). Among C++ novices, templates already have an (undeserved) reputation for code bloat. If valmatrix ends up using a lot of code space, this will be the first place that people point to "prove" this allegation. --- [ 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://www.jamesd.demon.co.uk/csc/faq.html ]