How to call a function when bytes of an array changes?

If have a very large array, Arr [255]. I'm writing a function which should perform a task whenever any one or more byte in this array has been updated by other functions. Could you help me with the best possible method?

For any change in first 3 bytes of Arr, I can call the function Task() like the following.

int main (void)
{
   while (1)
   {
       CheckArrayUpdated ();
   }
}

void CheckArrayUpdated (void)
{
    static char ArrPre [3];

    if (
       (ArrPre [0] != Arr [0]) ||
       (ArrPre [1] != Arr [1]) ||
       (ArrPre [2] != Arr [2]) 
       )
    {
        Task ();

        ArrPre [0] = Arr [0];
        ArrPre [1] = Arr [1];
        ArrPre [2] = Arr [2];
    }
    else;
}

How can I do this for the entire array, without consuming much of processing time and increasing the length and size of code?