Maximum element in all AXB sub matrices of NXM matrix

I was trying to find maximum element of any sub matrix AXB from a matrix NXM. I implemented sparse tree method. But I was unable to optimise this. Actually I need to solve range queries, so I need to optimize the code. On doing pre-computation, for any N,M values it takes O(NMlog(N)log(M)) time complexity. How can I improve this to (N*M). Here is my code for precomputation

for(int i=0; i<n;i++)
  for(int j=0; j<m;j++)
        cin>>arr[i][j];

for(int i=0; pow(2,i) <= n; i++)
        for(int j=0; pow(2,j) <= m; j++)
            for(int x=0; x + pow(2,i)-1 < n; x++)
                for(int y = 0; y + pow(2,j) -1 < m; y++)
                {
                    i=(int)i;
                    j=(int)j;
                    if (i == 0 && j == 0)
                            M[x][y][i][j] = arr[x][y]; 
                    else if (i == 0)
                            M[x][y][i][j] = maxi(2,M[x][y][i][j-1], M[x][(int)(y+pow(2,(j-1)))][i][j-1]);
                    else if (j == 0)
                            M[x][y][i][j] = maxi(2,M[x][y][i-1][j], M[(int)(x+ pow(2,(i-1)))][y][i-1][j]);
                    else 
                            M[x][y][i][j] = maxi(4,M[x][y][i-1][j-1], M[(int)(x + pow(2,(i-1)))][y][i-1][j-1], M[x][(int)(y+pow(2,(j-1)))][i-1][j-1], M[(int)(x + pow(2,(i-1)))][(int)(y+pow(2,(j-1)))][i-1][j-1]);
                }

For input x,y,x1,y1

 k = log(x1 - x + 1);
 l = log(y1 - y + 1);
 int max_element = max(4,M[x][y][k][l], M[(int)(x1 - pow(2,k) + 1)][y][k][l], M[x][(int)(y1 - pow(2,l) + 1)][k][l], M[(int)(x1 - pow(2,k) + 1)][(int)(y1 - pow(2,l) + 1)][k][l]);

How can Improve performance of this code. Please help.