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 | use rand_core::{impls, Error, RngCore}; |
12 | |
13 | #[cfg (feature = "serde1" )] |
14 | use serde::{Serialize, Deserialize}; |
15 | |
16 | /// A simple implementation of `RngCore` for testing purposes. |
17 | /// |
18 | /// This generates an arithmetic sequence (i.e. adds a constant each step) |
19 | /// over a `u64` number, using wrapping arithmetic. If the increment is 0 |
20 | /// the generator yields a constant. |
21 | /// |
22 | /// ``` |
23 | /// use rand::Rng; |
24 | /// use rand::rngs::mock::StepRng; |
25 | /// |
26 | /// let mut my_rng = StepRng::new(2, 1); |
27 | /// let sample: [u64; 3] = my_rng.gen(); |
28 | /// assert_eq!(sample, [2, 3, 4]); |
29 | /// ``` |
30 | #[derive(Debug, Clone, PartialEq, Eq)] |
31 | #[cfg_attr (feature = "serde1" , derive(Serialize, Deserialize))] |
32 | pub struct StepRng { |
33 | v: u64, |
34 | a: u64, |
35 | } |
36 | |
37 | impl StepRng { |
38 | /// Create a `StepRng`, yielding an arithmetic sequence starting with |
39 | /// `initial` and incremented by `increment` each time. |
40 | pub fn new(initial: u64, increment: u64) -> Self { |
41 | StepRng { |
42 | v: initial, |
43 | a: increment, |
44 | } |
45 | } |
46 | } |
47 | |
48 | impl RngCore for StepRng { |
49 | #[inline ] |
50 | fn next_u32(&mut self) -> u32 { |
51 | self.next_u64() as u32 |
52 | } |
53 | |
54 | #[inline ] |
55 | fn next_u64(&mut self) -> u64 { |
56 | let result = self.v; |
57 | self.v = self.v.wrapping_add(self.a); |
58 | result |
59 | } |
60 | |
61 | #[inline ] |
62 | fn fill_bytes(&mut self, dest: &mut [u8]) { |
63 | impls::fill_bytes_via_next(self, dest); |
64 | } |
65 | |
66 | #[inline ] |
67 | fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { |
68 | self.fill_bytes(dest); |
69 | Ok(()) |
70 | } |
71 | } |
72 | |
73 | #[cfg (test)] |
74 | mod tests { |
75 | #[test] |
76 | #[cfg (feature = "serde1" )] |
77 | fn test_serialization_step_rng() { |
78 | use super::StepRng; |
79 | |
80 | let some_rng = StepRng::new(42, 7); |
81 | let de_some_rng: StepRng = |
82 | bincode::deserialize(&bincode::serialize(&some_rng).unwrap()).unwrap(); |
83 | assert_eq!(some_rng.v, de_some_rng.v); |
84 | assert_eq!(some_rng.a, de_some_rng.a); |
85 | |
86 | } |
87 | } |
88 | |