Random Number Generation - II

Given a function rand5() which generates values between 0-5 with equal probablities, how would you create another function rand7() which generates values between 0-7?

For that matter given a function randM() which generates numbers between 0-M, how would you create another function randN() which generates numbers between 0-N with equal probabilities? Is it possible for every value of M,N?

PS: I'm calling this "Random Number Generation - II" because we already have another version of this problem here.

Think in terms of possible values being generated by the given randX() function and map to all the possible values to be generated by the target randY() function