rand/rngs/
mock.rs

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//! Mock random number generator
10
11#![allow(deprecated)]
12
13use rand_core::{impls, RngCore};
14
15#[cfg(feature = "serde")]
16use serde::{Deserialize, Serialize};
17
18/// A mock generator yielding very predictable output
19///
20/// This generates an arithmetic sequence (i.e. adds a constant each step)
21/// over a `u64` number, using wrapping arithmetic. If the increment is 0
22/// the generator yields a constant.
23///
24/// Other integer types (64-bit and smaller) are produced via cast from `u64`.
25///
26/// Other types are produced via their implementation of [`Rng`](crate::Rng) or
27/// [`Distribution`](crate::distr::Distribution).
28/// Output values may not be intuitive and may change in future releases but
29/// are considered
30/// [portable](https://rust-random.github.io/book/portability.html).
31/// (`bool` output is true when bit `1u64 << 31` is set.)
32///
33/// # Example
34///
35/// ```
36/// # #![allow(deprecated)]
37/// use rand::Rng;
38/// use rand::rngs::mock::StepRng;
39///
40/// let mut my_rng = StepRng::new(2, 1);
41/// let sample: [u64; 3] = my_rng.random();
42/// assert_eq!(sample, [2, 3, 4]);
43/// ```
44#[derive(Debug, Clone, PartialEq, Eq)]
45#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
46#[deprecated(since = "0.9.2", note = "Deprecated without replacement")]
47pub struct StepRng {
48    v: u64,
49    a: u64,
50}
51
52impl StepRng {
53    /// Create a `StepRng`, yielding an arithmetic sequence starting with
54    /// `initial` and incremented by `increment` each time.
55    pub fn new(initial: u64, increment: u64) -> Self {
56        StepRng {
57            v: initial,
58            a: increment,
59        }
60    }
61}
62
63impl RngCore for StepRng {
64    #[inline]
65    fn next_u32(&mut self) -> u32 {
66        self.next_u64() as u32
67    }
68
69    #[inline]
70    fn next_u64(&mut self) -> u64 {
71        let res = self.v;
72        self.v = self.v.wrapping_add(self.a);
73        res
74    }
75
76    #[inline]
77    fn fill_bytes(&mut self, dst: &mut [u8]) {
78        impls::fill_bytes_via_next(self, dst)
79    }
80}
rand/rngs/mock.rs

rand/rngs/
mock.rs
