Reminder of the division of x to the power y by z.
Precondition: z > 0
assert(pow(3, 5, 7) == 5); assert(pow(2, 2, 1) == 0); assert(pow(3, 3, 3) == 0); assert(pow(7, 4, 2) == 1); assert(pow(53, 0, 2) == 1); assert(pow(53, 1, 3) == 2); assert(pow(53, 2, 5) == 4); assert(pow(0, 0, 5) == 1); assert(pow(0, 5, 5) == 0);
Computes x to the power y modulo z.