Hi everyone ! I read the excellent "C++ Templates - The Complete Guide", and their chapter about expression templates sounded really really great about performance, and because it was extremly interesting, I decided to write my own 3D vector class by imitating their "Array" class, by adding some functions... Maybe their implementation isn't the best, because it looks really complicated, and I'm sure there are manners to do it simpler, I'll try later, but first I'd like to understand well what I'm doing and make some tests about performance. By now, it works really good. Comparing to a "naïv" class template, when I make a lot of operations, mine can be more than 10 times quicker than the normal one, only if I make a lot of operations (let's say 1 million A = B + C for exemple)... But only on GCC (my version is 3.1.2 or something like this). Because with Visual C++ Express 2005, performances are REALLY REALLY bad ! This is the way I take the measures :

struct Trial
{
   Trial () {T = 0;}
   double T;
   double temp;

   double GetTime ()
   {
      LARGE_INTEGER Clock;
      LARGE_INTEGER ClockFreq;
      QueryPerformanceCounter  ( &Clock );
      QueryPerformanceFrequency( &ClockFreq );
      return (Clock.QuadPart) / (double)(ClockFreq.QuadPart);
   }

    void Start ()
    {
        temp = GetTime();
    }

    void End ()
    {
        temp = GetTime() - temp;
        T += temp;
    }
};

int main()
{	
	{
   Trial maStructure;
   maStructure.Start ();
   Vec3 <double> A (1.0, 1.0, 1.0);
   Vec3 <double> B (2.0, 2.0, 2.0);
   Vec3 <double> C (3.0, 3.0, 3.0);

   for (size_t i = 0 ; i != 10000000 ; ++i)
      A = B+C+A;

   maStructure.End ();
   std::cout << "Implémentation Michaël " << maStructure.T;
	}

Maybe it's not the best way to do that, but with a lot of operations, I can do it with a watch or a chrono ! And with Visual Express C++ 2005 it's a lot more fast with the normal way of doing a vector class. for (size_t i = 0 ; i != 10000000 ; ++i) A = B+C+A; With Code::Blocks (GCC 3.1.2) : 0.0710791 (it appears immediatly). With Visual : 0.353937 (I have to wait a little before this appears). All is compiled in released mode, with all the optimizations applied in both compilers... I really don't know why it doesn't work good, because those expressions templates seems really interesting and I really would like to use them later in games, maybe it could boost performance ! Here is the code: http://membres.lycos.fr/hl2connection/VectorClass.7z I know that that kind of programming is really hard to read, but if someone could get a look, or tell me some advices... PS : I can't read ASM, it's like Chinese for me, so don't answer me : "look at the ASM code :nerd:". Thanks !

- Configuration Options
- C/C++
- Code Generation
- Floating Point Model: Fast (/fp:fast)

Your running time should be now identical to that of gcc. In my case it's even 10% faster.

Hej !

Thanks for your answer, but it's not really better. It's a quite the same result (around 5 times faster on GCC than Visual).

EDIT :
- Configuration Options
- C/C++
- Advanced
- Convention d'appel (in fact mine is in French :p Don't know how to say that in english) : __fastcall instead of __cdecl, it's a little faster (around 0.25 instead of 0.35, but still far away from GCC :/.)

ASM is Chinese, I can read it but don't understand nothing.

For Visual Express C++ 2005 :

/O2 /Ob1 /Oi /Ot /Oy /GT /GL /FD /EHsc /MT /Gy /arch:SSE /fp:fast /Fo"Release\\" /Fd"Release\vc80.pdb" /W2 /nologo /c /Gr /TP /errorReport:prompt

For GCC :

Optimize fully (O3), Expensive Optimizations (-fexpensive-optimizations)
and a CPU architecture tuning (-march=athlon-xp)

Ok, just for test I set the warning level to the max (4), and I had some strange warnings (I tried to translate the warnings in English between parenthesis):

warning C4512: 'A_Add<T,OP1,OP2>' : l'opérateur d'assignation n'a pas pu être généré ('A_Add<T,OP1,OP2>' : the assigment operator couldn't be generated)
with
[
T=double,
OP1=SVec3<double>,
OP2=SVec3<double>
]

voir la référence à l'instanciation de la classe modèle 'A_Add<T,OP1,OP2>' en cours de compilation (see the reference at the instanciation of the template class 'A_Add<T, OP1, OP2>' while it's compilating)
with
[
T=double,
OP1=SVec3<double>,
OP2=SVec3<double>
]

voir la référence à l'instanciation de la classe modèle 'Vec3<T,Expr>' en cours de compilation (see the reference at the instanciation of the template class 'Vec3<T, Expr>' while it's compilating)
with
[
T=double,
Expr=A_Add<double,SVec3<double>,SVec3<double>>
]

warning C4512: 'A_Add<T,OP1,OP2>' : l'opérateur d'assignation n'a pas pu être généré ('A_Add<T,OP1,OP2>' : the assigment operator couldn't be generated)
with
[
T=double,
OP1=A_Add<double,SVec3<double>,SVec3<double>>,
OP2=SVec3<double>
]

voir la référence à l'instanciation de la classe modèle 'A_Add<T,OP1,OP2>' en cours de compilation (see the reference at the instanciation of the template class 'A_Add<T, OP1, OP2>' while it's compilating)
with
[
T=double,
OP1=A_Add<double,SVec3<double>,SVec3<double>>,
OP2=SVec3<double>
]

voir la référence à l'instanciation de la classe modèle 'Vec3<T,Expr>' en cours de compilation (see the reference at the instanciation of the template class 'Vec3<T, Expr>' while it's compilating)
with
[
T=double,
Expr=A_Add<double,A_Add<double,SVec3<double>,SVec3<double>>,SVec3<double>>
]

I found a solution about the warnings, Visual just needed the operator= for the class A_Add. I added it but it changes simply nothing for the performance :/.

[Edited by - Bakura on June 11, 2007 3:13:44 PM]