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// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Mock random number generator
use rand_core::{impls, Error, RngCore};
#[cfg(feature = "serde1")]
use serde::{Serialize, Deserialize};
/// A simple implementation of `RngCore` for testing purposes.
///
/// This generates an arithmetic sequence (i.e. adds a constant each step)
/// over a `u64` number, using wrapping arithmetic. If the increment is 0
/// the generator yields a constant.
///
/// ```
/// use rand::Rng;
/// use rand::rngs::mock::StepRng;
///
/// let mut my_rng = StepRng::new(2, 1);
/// let sample: [u64; 3] = my_rng.gen();
/// assert_eq!(sample, [2, 3, 4]);
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde1", derive(Serialize, Deserialize))]
pub struct StepRng {
v: u64,
a: u64,
}
impl StepRng {
/// Create a `StepRng`, yielding an arithmetic sequence starting with
/// `initial` and incremented by `increment` each time.
pub fn new(initial: u64, increment: u64) -> Self {
StepRng {
v: initial,
a: increment,
}
}
}
impl RngCore for StepRng {
#[inline]
fn next_bool(&mut self) -> bool {
(self.next_u64() & 1) == 1
}
#[inline]
fn next_u32(&mut self) -> u32 {
self.next_u64() as u32
}
#[inline]
fn next_u64(&mut self) -> u64 {
let result = self.v;
self.v = self.v.wrapping_add(self.a);
result
}
#[inline]
fn fill_bytes(&mut self, dest: &mut [u8]) {
impls::fill_bytes_via_next(self, dest);
}
#[inline]
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
self.fill_bytes(dest);
Ok(())
}
}
#[cfg(test)]
mod tests {
#[test]
#[cfg(feature = "serde1")]
fn test_serialization_step_rng() {
use super::StepRng;
let some_rng = StepRng::new(42, 7);
let de_some_rng: StepRng =
bincode::deserialize(&bincode::serialize(&some_rng).unwrap()).unwrap();
assert_eq!(some_rng.v, de_some_rng.v);
assert_eq!(some_rng.a, de_some_rng.a);
}
}