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mod bigcollatz{
    use num_bigint::{BigUint};
    use num_traits::{Zero, One};
    use std::ops::{Add, Mul, Div};
    use num_bigint::ToBigUint;

    pub struct BigCollatz {
        curr: BigUint,
        done: bool,
        pub start : BigUint,
        pub steps: u32,
    }

    pub struct CollatzStep{
        pub step: u32,
        pub curr: BigUint,
    }

    impl BigCollatz {
        pub fn new(ini: BigUint) -> BigCollatz {
            BigCollatz {
                start: ini.clone(),
                curr: ini.clone(),
                steps: 0,
                done: false,
            }
        }
    }

    impl Iterator for BigCollatz {
        type Item = CollatzStep;

        fn next(&mut self) -> Option<CollatzStep> {
            if self.done { return None };

            let one: BigUint = BigUint::one();
            let zero: BigUint = BigUint::zero();
            let two: BigUint = BigUint::from(2u32);
            let three: BigUint = BigUint::from(3u32);

            let curr = &self.curr;
            let result = curr.clone();

            if curr % &two ==  zero{
                self.curr = curr.div(&two);
            }else{
                self.curr = curr.mul(&three).add(&one);
            }
            if self.curr <= one{
                self.done = true
            }
            self.steps +=1;

            Some( CollatzStep{
                step: self.steps,
                curr: result
            })
        }
    }

    #[test]
    fn it_works() {
        let c = BigCollatz::new(100.to_biguint().unwrap() );
        for x in c{
            println!("n:{}, step:{}", x.curr, x.step);
            assert_eq!( x.curr > BigUint::one(), true );
        }
    }

}