unordered_map thousand time slower than the vc++ 2010 version by badre429

it tried this code in both version visual c++ 2010 and visual studio 11 developer preview
and the i was shoked by the result
vs 11 TIME = 100 * vs2010 TIME
//______________________________________________
#include<iostream>
#include<unordered_map>
#include<Windows.h>
using namespace std;

double DoubleRand()
{
    return (double(rand())*double(rand())*double(rand())+double(rand())*double(rand())*double(rand())+double(rand())*double(rand())*double(rand()))/(double(rand())*double(rand())*double(rand())+double(rand())*double(rand())*double(rand()));
}
void print(double x)
{
cout    <<x<<endl;
}

int main()
{
    int _time=GetTickCount();
    srand(_time);
    int tableLenght=1000000;
    unordered_map<double ,int> maptab;
    
    double * tab=new double[tableLenght];
    for (int i = 0; i <tableLenght ; i++)
    {
        tab[i]=DoubleRand();
    }

    for (int i = 0; i <tableLenght ; i++)
    {
        maptab[tab[i]]=i;
    }
    double somme=0;
    for (int i = 0; i < 10; i++)
    {
        for (int k = 0; k < tableLenght; k++)
        {
            somme+=maptab[tab[k]];
        }
    }
    int somme2=0;

     for (int i = 0; i < tableLenght; i++)
                {
                    somme2 += i;
                 }
    print(maptab.size());
    print(somme);
    print(somme2*10);
    print(GetTickCount()- _time );
    system("pause");
}