Divide and conquer

Please look again at the pseudocode from our theory. It calculates the sum of an array using the divide and conquer paradigm.

function f(array, left, right):
    if left == right then:
        return 0    
    if left == right-1 then:
        return array[left]
    middle = int((left + right) / 2)
    left = f(array, left, middle)
    right = f(array, middle, right)
    return left + right

Here $int()$ function returns the largest integer less than the given number, for example, $int(4.5)$ will return 4.

Can you please distinguish the base cases, the divide and conquer, and the combining portion of the code?