Why is valarray so slow?

Question

I am trying to use valarray since it is much like MATLAB while operating vector and matrices. I first did some performance check and found that valarray cannot achieve the p

Answer 1

I just tried it on a Linux x86-64 system (Sandy Bridge CPU):

gcc 4.5.0:

double operator* 9.64185 ms
valarray operator* 9.36987 ms
valarray[i] operator* 9.35815 ms

Intel ICC 12.0.2:

double operator* 7.76757 ms
valarray operator* 9.60208 ms
valarray[i] operator* 7.51409 ms

In both cases I just used -O3 and no other optimisation-related flags.

It looks like the MS C++ compiler and/or valarray implementation suck.

---

Here's the OP's code modified for Linux:

#include 
#include 
#include 
#include 

using namespace std ;

double gettime_hp();

int main()
{
    enum { N = 5*1024*1024 };
    valarray a(N), b(N), c(N) ;
    int i,j;
    for(  j=0 ; j<8 ; ++j )
    {
        for(  i=0 ; i