At Fri, 11 Mar 2011 12:04:15 -0800, Simonson, Lucanus J wrote:
More seriously, I fail to see an vector operation that is "limited by the language". I have very eager to see the one you speak about.
If you have the same variable in more than one place in an expression
sometimes called "aliasing"
you can map that expression to different/fewer instructions than if they were all different variables in different places. There is no way to perform that mapping using expression templates because it cannot be detected in template metaprogramming which varaibles are the same, only that they have the same type. Therefor you cannot map expression to the optimal instructions using template metaprogramming.
I beg to differ, at least most of the time. You can detect aliasing at runtime and choose an optimal implementation on that basis, and when the sameness of the two variables is information available to the compiler (as it often is), constant-folding and dead-code-elimination will throw away the test and the dead branch, leaving only the optimal code. -- Dave Abrahams BoostPro Computing http://www.boostpro.com