Shuffle effectiveness testing

// (C) 2012 Tim Gurto

#include <iostream>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <list>

double correlation(int *xData, int *yData, int size){
   assert(size > 0);

   //calculate means
   double xMean = 0, yMean = 0;
   for (int i = 0; i != size; ++i){
      xMean += xData[i];
      yMean += yData[i];
   }
   xMean /= size;
   yMean /= size;

   //calculate sums
   double
      sumXX = 0,
      sumYY = 0,
      sumXY = 0;
   for (int i = 0; i != size; ++i){
      double
         xDiff = xData[i] - xMean,
         yDiff = yData[i] - yMean;
      sumXX += xDiff * xDiff;
      sumYY += yDiff * yDiff;
      sumXY += xDiff * yDiff;
   }

   return sumXY / sqrt(sumXX * sumYY);
}

void bubbleShuffle(int *data, int size){
   for (int i = 0; i != size-1; ++i)
      for (int j = 0; j != size-1-i; ++j)
         if (rand() % 2){
            int temp = data[j];
            data[j] = data[j+1];
            data[j+1] = temp;
         }
}

void selectionShuffle(int *data, int size){

   //copy into list
   std::list<int> list;
   for (int i = 0; i != size; ++i)
      list.push_back(data[i]);

   //select back to array
   for (int i = 0; i != size; ++i){
      //navigate to random element
      int n = rand() % list.size();
      std::list<int>::const_iterator it = list.begin();
      while (n-- > 0)
         ++it;
      data[i] = *it;
      list.erase(it);
   }

}

double testShuffle(void (*shuffleFun)(int *data, int size)){
   const static int SIZE = 1000;
   const static int TESTS = 100;
   int data[SIZE];
   for (int i = 0; i != SIZE; ++i)
      data[i] = i;

   //tests
   double averageCorrelation = 0;
   for (int testNum = 0; testNum != TESTS; ++testNum){

      //shuffle
      int shuffledData[SIZE];
      for (int i = 0; i != SIZE; ++i)
         shuffledData[i] = i;
      shuffleFun(data, SIZE);

      //add correlation
     averageCorrelation += correlation(data, shuffledData, SIZE);
   }

   //average and return
   averageCorrelation /= TESTS;
   return 1 - abs(averageCorrelation);
}

int main(){
   srand(time(0));
   std::cout << "   Bubble shuffle: " << testShuffle(bubbleShuffle) << std::endl;
   std::cout << "Selection shuffle: " << testShuffle(selectionShuffle) << std::endl;
}