сортировка слиянием

#include <vector>
 
template <typename T>
inline void swap( T & arg1, T & arg2)
{
    T temp = arg1;
    arg1 = arg2;
    arg2 = temp;
};
template <typename T>
inline void merge( std::vector<T> & vArray, std::vector<T> & vTemp, int head, int middle, int tail)
{
    int tmp = 0, lower = head, upper = middle+1;
 
    while (lower <= middle && upper <= tail)
    {
        if (vArray[lower] < vArray[upper])
        {   vTemp[tmp++] = vArray[lower++]; }
        else
        {   vTemp[tmp++] = vArray[upper++]; }
    }
 
    if (lower <= middle)
    {
        for(; lower <= middle; vTemp[tmp++] = vArray[lower++]);
    }
    else
    {
        for(; upper <= tail; vTemp[tmp++] = vArray[upper++]);
    }
 
    int arrayPointer = head;
    for (tmp = 0; arrayPointer <= tail; vArray[arrayPointer++] = vTemp[tmp++]);
}
template <typename T>
inline void merge_sort_helper( std::vector<T> & vArray, std::vector<T> & vTemp, int head, int tail)
{
    if(head == tail) 
    {   return; }
 
    int middle = (head+tail)/2;
 
    merge_sort_helper( vArray, vTemp, head, middle);
    merge_sort_helper( vArray, vTemp, middle+1, tail);
 
    merge( vArray, vTemp, head, middle, tail);
}
 
template <typename T>
void merge_sort( std::vector<T> & vArray)
{
    std::vector<T> v(vArray.size(), 0);
    merge_sort_helper( vArray, v, 0, vArray.size()-1);
}