rand/rngs/
std.rs

Help
1// Copyright 2018 Developers of the Rand project.
2//
3// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
5// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
6// option. This file may not be copied, modified, or distributed
7// except according to those terms.
8
9//! The standard RNG
10
11use crate::{CryptoRng, Error, RngCore, SeedableRng};
12
13pub(crate) use rand_chacha::ChaCha12Core as Core;
14
15use rand_chacha::ChaCha12Rng as Rng;
16
17/// The standard RNG. The PRNG algorithm in `StdRng` is chosen to be efficient
18/// on the current platform, to be statistically strong and unpredictable
19/// (meaning a cryptographically secure PRNG).
20///
21/// The current algorithm used is the ChaCha block cipher with 12 rounds. Please
22/// see this relevant [rand issue] for the discussion. This may change as new 
23/// evidence of cipher security and performance becomes available.
24///
25/// The algorithm is deterministic but should not be considered reproducible
26/// due to dependence on configuration and possible replacement in future
27/// library versions. For a secure reproducible generator, we recommend use of
28/// the [rand_chacha] crate directly.
29///
30/// [rand_chacha]: https://crates.io/crates/rand_chacha
31/// [rand issue]: https://github.com/rust-random/rand/issues/932
32#[cfg_attr(doc_cfg, doc(cfg(feature = "std_rng")))]
33#[derive(Clone, Debug, PartialEq, Eq)]
34pub struct StdRng(Rng);
35
36impl RngCore for StdRng {
37    #[inline(always)]
38    fn next_u32(&mut self) -> u32 {
39        self.0.next_u32()
40    }
41
42    #[inline(always)]
43    fn next_u64(&mut self) -> u64 {
44        self.0.next_u64()
45    }
46
47    #[inline(always)]
48    fn fill_bytes(&mut self, dest: &mut [u8]) {
49        self.0.fill_bytes(dest);
50    }
51
52    #[inline(always)]
53    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
54        self.0.try_fill_bytes(dest)
55    }
56}
57
58impl SeedableRng for StdRng {
59    type Seed = <Rng as SeedableRng>::Seed;
60
61    #[inline(always)]
62    fn from_seed(seed: Self::Seed) -> Self {
63        StdRng(Rng::from_seed(seed))
64    }
65
66    #[inline(always)]
67    fn from_rng<R: RngCore>(rng: R) -> Result<Self, Error> {
68        Rng::from_rng(rng).map(StdRng)
69    }
70}
71
72impl CryptoRng for StdRng {}
73
74
75#[cfg(test)]
76mod test {
77    use crate::rngs::StdRng;
78    use crate::{RngCore, SeedableRng};
79
80    #[test]
81    fn test_stdrng_construction() {
82        // Test value-stability of StdRng. This is expected to break any time
83        // the algorithm is changed.
84        #[rustfmt::skip]
85        let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
86                    0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
87
88        let target = [10719222850664546238, 14064965282130556830];
89
90        let mut rng0 = StdRng::from_seed(seed);
91        let x0 = rng0.next_u64();
92
93        let mut rng1 = StdRng::from_rng(rng0).unwrap();
94        let x1 = rng1.next_u64();
95
96        assert_eq!([x0, x1], target);
97    }
98}
rand/rngs/std.rs

rand/rngs/
std.rs
