I have the following code which, when given a number n, calculates the nth Fibonacci number.

pub fn fibonacci(n: i64) -> i64 {
   fib_iter(1, 0, 0, 1, n)
}


fn fib_iter(a: i64, b: i64, p: i64, q: i64, count: i64) -> i64 {
   if count == 0 {
      return b;
   }

   if is_even(count) {
      return fib_iter(a, b, p*p + q*q, 2*p*q + q*q, count / 2);
   }

   fib_iter(b*q + a*q + a*p, b*p + a*q, p, q, count - 1)
}

The problem is it only works for i64 while I would like it to be generic, so it works for any integral type.

I tried using the Integer trait from the num crate to make it generic:

pub fn fibonacci<T: Integer>(n: T) -> T {
   fib_iter(1, 0, 0, 1, n)
}

fn fib_iter<T: Integer>(a: T, b: T, p: T, q: T, count: T) -> T {
   if count.is_zero() {
      return b;
   }

   if count.is_even() {
      return fib_iter(a, b, p*p + q*q, 2*p*q + q*q, count / 2);
   }

   fib_iter(b*q + a*q + a*p, b*p + a*q, p, q, count - 1)
}

But it doesn’t like the use of any integer literals, for example:

66 |       return fib_iter(a, b, p*p + q*q, 2*p*q + q*q, count / 2);
   |                                         ^ no implementation for `{integer} * T`

...


69 |    fib_iter(b*q + a*q + a*p, b*p + a*q, p, q, count - 1)
   |                                                       ^ expected type parameter `T`, found integer

I also tried doing something like the following:

let two: T = 2;

But same problem.
And same if I try using traits Mul, Div, Add, Sub etc.