2. [4 Here is an algorithm that calculates and returns % m Note: math.floor is a function that returns the floor of a given number (i.e. returns the largest integer not greater than r) 1 def rec mod (x, n, m): Pre: ??? Post: ??? 6 if n== 0: return 1 elif n % 2-0: 10 return rec-mod (x , n/2, m)-*2 % m else: 12 return ((rec-mod (x , math . floor (n/2), m)*+2 % m) (x % m)) % m * State preconditions and postconditions for this function. Then, prove that this algorithm is correct according to your specifications. Hint: The Inultiplication property of modular arith1n(tic states that (a *b) % Tn (a % m * b % m %m