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