1 pub struct LaggedFibonacciPRNG {

     2     circular_buffer: [u32; 64],

     3     index: usize,

     4 }

     5 

     6 impl LaggedFibonacciPRNG {

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

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

     9 

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

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

    12         }

    13 

    14         let mut prng = Self {

    15             circular_buffer: buf,

    16             index: 54,

    17         };

    18 

    19         for i in 0..2048 {

    20             prng.get_next();

    21         }

    22 

    23         prng

    24     }

    25 

    26     #[inline]

    27     fn get_next(&mut self) -> u32 {

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

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

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

    31             & 0x7fffffff;

    32 

    33         self.circular_buffer[self.index]

    34     }

    35 

    36     #[inline]

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

    38         self.get_next();

    39         self.get_next() % modulo

    40     }

    41 

    42     #[inline]

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

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

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

    46     }

    47 }

    48 

    49 #[cfg(test)]

    50 #[test]

    51 fn compatibility() {

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

    53 

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

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

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

    57 

    58     prng.add_randomness(123);

    59 

    60     for i in 0..=100000 {

    61         prng.get_random(2);

    62     }

    63 

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

    65 }