Coverage Report

Created: 2025-05-07 06:59

/rust/registry/src/index.crates.io-6f17d22bba15001f/rand-0.8.5/src/rngs/std.rs
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// Copyright 2018 Developers of the Rand project.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! The standard RNG
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use crate::{CryptoRng, Error, RngCore, SeedableRng};
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pub(crate) use rand_chacha::ChaCha12Core as Core;
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use rand_chacha::ChaCha12Rng as Rng;
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/// The standard RNG. The PRNG algorithm in `StdRng` is chosen to be efficient
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/// on the current platform, to be statistically strong and unpredictable
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/// (meaning a cryptographically secure PRNG).
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///
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/// The current algorithm used is the ChaCha block cipher with 12 rounds. Please
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/// see this relevant [rand issue] for the discussion. This may change as new 
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/// evidence of cipher security and performance becomes available.
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///
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/// The algorithm is deterministic but should not be considered reproducible
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/// due to dependence on configuration and possible replacement in future
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/// library versions. For a secure reproducible generator, we recommend use of
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/// the [rand_chacha] crate directly.
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///
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/// [rand_chacha]: https://crates.io/crates/rand_chacha
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/// [rand issue]: https://github.com/rust-random/rand/issues/932
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#[cfg_attr(doc_cfg, doc(cfg(feature = "std_rng")))]
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct StdRng(Rng);
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impl RngCore for StdRng {
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    #[inline(always)]
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    fn next_u32(&mut self) -> u32 {
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        self.0.next_u32()
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    }
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    #[inline(always)]
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    fn next_u64(&mut self) -> u64 {
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        self.0.next_u64()
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    }
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    #[inline(always)]
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    fn fill_bytes(&mut self, dest: &mut [u8]) {
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        self.0.fill_bytes(dest);
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    }
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    #[inline(always)]
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    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
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        self.0.try_fill_bytes(dest)
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    }
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}
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impl SeedableRng for StdRng {
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    type Seed = <Rng as SeedableRng>::Seed;
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    #[inline(always)]
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    fn from_seed(seed: Self::Seed) -> Self {
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        StdRng(Rng::from_seed(seed))
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    }
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    #[inline(always)]
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    fn from_rng<R: RngCore>(rng: R) -> Result<Self, Error> {
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        Rng::from_rng(rng).map(StdRng)
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    }
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}
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impl CryptoRng for StdRng {}
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#[cfg(test)]
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mod test {
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    use crate::rngs::StdRng;
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    use crate::{RngCore, SeedableRng};
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    #[test]
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    fn test_stdrng_construction() {
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        // Test value-stability of StdRng. This is expected to break any time
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        // the algorithm is changed.
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        #[rustfmt::skip]
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        let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
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                    0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
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        let target = [10719222850664546238, 14064965282130556830];
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        let mut rng0 = StdRng::from_seed(seed);
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        let x0 = rng0.next_u64();
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        let mut rng1 = StdRng::from_rng(rng0).unwrap();
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        let x1 = rng1.next_u64();
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        assert_eq!([x0, x1], target);
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    }
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}