1use rand_chacha::{ChaCha8Rng, rand_core::SeedableRng};
 2use rand_core::RngCore;
 3
 4const MAXF64: f64 = 9007199254740992.0;
 5
 6pub struct Source {
 7    source: ChaCha8Rng,
 8}
 9
10impl Source {
11    pub fn new(seed: [u8; 32]) -> Source {
12        Source {
13            source: ChaCha8Rng::from_seed(seed),
14        }
15    }
16
17    pub fn branch(&mut self) -> ([u8; 32], Self) {
18        let mut seed = [0; 32];
19        self.source.fill_bytes(&mut seed);
20        (seed, Source::new(seed))
21    }
22
23    #[inline(always)]
24    pub fn next_u64n(&mut self, max: u64, mask: u64) -> u64 {
25        let mut x: u64 = self.next_u64() & mask;
26        while x >= max {
27            x = self.next_u64() & mask;
28        }
29        x
30    }
31
32    #[inline(always)]
33    pub fn next_f64(&mut self, min: f64, max: f64) -> f64 {
34        min + ((self.next_u64() << 11 >> 11) as f64) / MAXF64 * (max - min)
35    }
36
37    pub fn next_i64(&mut self) -> i64 {
38        self.next_u64() as i64
39    }
40}
41
42impl RngCore for Source {
43    #[inline(always)]
44    fn next_u32(&mut self) -> u32 {
45        self.source.next_u32()
46    }
47
48    #[inline(always)]
49    fn next_u64(&mut self) -> u64 {
50        self.source.next_u64()
51    }
52
53    #[inline(always)]
54    fn fill_bytes(&mut self, bytes: &mut [u8]) {
55        self.source.fill_bytes(bytes)
56    }
57}