88 lines
2.3 KiB
Rust
88 lines
2.3 KiB
Rust
// 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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//! Mock random number generator
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use rand_core::{impls, Error, RngCore};
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#[cfg(feature = "serde1")]
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use serde::{Serialize, Deserialize};
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/// A simple implementation of `RngCore` for testing purposes.
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///
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/// This generates an arithmetic sequence (i.e. adds a constant each step)
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/// over a `u64` number, using wrapping arithmetic. If the increment is 0
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/// the generator yields a constant.
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///
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/// ```
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/// use rand::Rng;
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/// use rand::rngs::mock::StepRng;
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///
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/// let mut my_rng = StepRng::new(2, 1);
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/// let sample: [u64; 3] = my_rng.gen();
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/// assert_eq!(sample, [2, 3, 4]);
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/// ```
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#[derive(Debug, Clone, PartialEq, Eq)]
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#[cfg_attr(feature = "serde1", derive(Serialize, Deserialize))]
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pub struct StepRng {
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v: u64,
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a: u64,
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}
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impl StepRng {
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/// Create a `StepRng`, yielding an arithmetic sequence starting with
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/// `initial` and incremented by `increment` each time.
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pub fn new(initial: u64, increment: u64) -> Self {
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StepRng {
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v: initial,
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a: increment,
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}
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}
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}
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impl RngCore for StepRng {
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#[inline]
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fn next_u32(&mut self) -> u32 {
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self.next_u64() as u32
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}
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#[inline]
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fn next_u64(&mut self) -> u64 {
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let result = self.v;
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self.v = self.v.wrapping_add(self.a);
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result
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}
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#[inline]
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fn fill_bytes(&mut self, dest: &mut [u8]) {
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impls::fill_bytes_via_next(self, dest);
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}
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#[inline]
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fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
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self.fill_bytes(dest);
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Ok(())
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}
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}
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#[cfg(test)]
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mod tests {
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#[test]
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#[cfg(feature = "serde1")]
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fn test_serialization_step_rng() {
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use super::StepRng;
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let some_rng = StepRng::new(42, 7);
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let de_some_rng: StepRng =
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bincode::deserialize(&bincode::serialize(&some_rng).unwrap()).unwrap();
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assert_eq!(some_rng.v, de_some_rng.v);
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assert_eq!(some_rng.a, de_some_rng.a);
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}
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}
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