Re: [Boost-users] [operators] loss of performance

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2006-05-08 09:27:34

At 23:05 2006-05-07, you wrote:
>Hi all -
>
>I just tried out the operators library for the first time today.  I
>was quite happy with how easily it helped me implement my test class.
>Unfortunately, I'm running into some performance issues, in particular
>with operator +.
>
>The interesting thing is that the new operator += is actually faster
>than my old += by about a factor of 2, but my operator + is slower
>than my old + by a factor of nearly 10!
>
>I'm new here, and not really sure how much code is appropriate to post
>to the list, so here's a minimal rundown:
>
>--------------------------------------------------------------------------
>Old code:
>
>template<typename real>
>Vector3<real> operator + (const Vector3<real> &a, const Vector3<real> &b);
>
>template<typename real>
>class Vector3 {
>protected:
>     real m_v[3];
>..
>..
>     friend Vector3 operator +<> (const Vector3 &a, const Vector3 &b);
>};
>
>template<typename real>
>inline Vector3<real> operator + (const Vector3<real> &a, const
>Vector3<real> &b){
>     Vector3<real> t;
>     t[0] = a[0] + b[0];
>     t[1] = a[1] + b[1];
>     t[2] = a[2] + b[2];
>     return t;
>}
>
>-------------------------------------------------------------------------------------------------
>New code (note that the new code is templatized on size, and that my
>instantiations
>were of size 3 to match the above code):
>
>template<typename T, unsigned int S>
>class vec
>     : boost::additive< vec<T, S>
>     , boost::multiplicative< vec<T, S>, T
>       > >
>{
>private:
>     typedef unsigned int uint;
>     typedef const T &const_reference;
>     typedef T &reference;
>
>private:
>     boost::array<T,S> m_v;
>
>     template<typename U>
>     vec &operator += (const vec<U,S> &t){
>         for(uint i = 0; i < S; ++i){
>             m_v[i] += t.m_v[i];
>         }
>         return *this;
>     }
>};
>
>Any ideas how to increase the performance of the new code here?  A
>factor of 10 makes it seem like I am just missing something important.

you showed us the code that you claim is faster, what do you want us to do?

>Thanks,
>   Brian
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"