"Geoffrey Irving" <irving@cs.stanford.edu> wrote in message news:20060909180645.GC20743@lie.Stanford.EDU...
On Sat, Sep 09, 2006 at 06:27:40PM +0800, Joel de Guzman wrote:
Andy Little wrote:
You must've missed this: Dan wrote me an email a while back. He says: "Interestingly using fusion::fold to do maths on boost::arrays, I'm finding that with vc8.0 fusion significantly outperforms the standard library equivalent code, presumably as it has more information available at compile time, and with inlining it effectively unrolls the entire loops."
I asked Dan to add his tests to libs/fusion/example to showcase this favorable "phenomena" :-).
I can't find that, but I am probably looking in the wrong place. Do you mean Boost CVS?
Sorry, you'll have to wait a bit more. Dan says he'll do it over the weekend.
I think the main reason for this is that inlining a fusion loop means that the compiler has obeyed an explicit programmer suggestion (inline), whereas unrolling a constant size array loop is loop unrolling, which is impossible to suggest to the compiler (and typically requires higher -O levels, etc.). A while back when I implemented a vector type with constant size for loops, it slowed down the whole application by 30%.
I'm very curious to see how much better fusion can do. Andy: is your fusion code in an easily accessible place where I could grab it and stick some of it into our vector class to test it in a (probably) larger example?
The code is in quan CVS. Heres the info page: http://sourceforge.net/cvs/?group_id=170593 The module name is quan-trunk Unfortunately there are quite a few dependencies on the rest of the Quan stuff. To use it direct you will need to download everything and point the compiler at the quan directory. The dot_product is implemented in <quan-trunk/quan/fusion/dot_product.hpp> OTOH You could however just download that header and replace the functors quan::operator_plus, quan::operator_plus_equals, and quan::operator_multiplies ( and swap_args) with your own versions which *should* remove the dependencies, but you will need to look at the <quan/fusion/swap_args.hpp> header to get the boost::reference_wrapper signatures for assignment There is an example use in <quan-matters/examples/fusion/dot_product.cpp>. regards Andy Little