pub struct LaggedFibonacciPRNG {

    circular_buffer: [u32; 64],

    index: usize,

}

impl LaggedFibonacciPRNG {

    fn new(init_values: &[u8]) -> Self {

        let mut buf = [0xa98765 + 68; 64];

        for i in 0..std::cmp::min(init_values.len(), 54) {

            buf[i] = init_values[i] as u32;

        }

        let mut prng = Self {

            circular_buffer: buf,

            index: 54,

        };

        for i in 0..2048 {

            prng.get_next();

        }

        prng

    }

    #[inline]

    fn get_next(&mut self) -> u32 {

        self.index = (self.index + 1) & 0x3f;

        self.circular_buffer[self.index] = (self.circular_buffer[(self.index + 40) & 0x3f]

            + self.circular_buffer[(self.index + 9) & 0x3f])

            & 0x7fffffff;

        self.circular_buffer[self.index]

    }

    #[inline]

    fn get_random(&mut self, modulo: u32) -> u32 {

        self.get_next();

        self.get_next() % modulo

    }

    #[inline]

    fn add_randomness(&mut self, value: u32) {

        self.index = (self.index + 1) & 0x3f;

        self.circular_buffer[self.index] ^= value;

    }

}

impl Iterator for LaggedFibonacciPRNG {

    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {

        self.get_next();

        Some(self.get_next())

    }

}

#[cfg(test)]

#[test]

fn compatibility() {

    let mut prng = LaggedFibonacciPRNG::new("{052e2aee-ce41-4720-97bd-559a413bf866}".as_bytes());

    assert_eq!(prng.get_random(1000), 418);

    assert_eq!(prng.get_random(1000000), 554064);

    assert_eq!(prng.get_random(0xffffffff), 239515837);

    prng.add_randomness(123);

    for i in 0..=100000 {

        prng.get_random(2);

    }

    assert_eq!(prng.get_random(0xffffffff), 525333582);

}