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0731742a | 1 | // Copyright 2018 Developers of the Rand project. |
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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 | ||
dfeec247 | 11 | use rand_core::{impls, Error, RngCore}; |
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12 | |
13 | /// A simple implementation of `RngCore` for testing purposes. | |
dfeec247 | 14 | /// |
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15 | /// This generates an arithmetic sequence (i.e. adds a constant each step) |
16 | /// over a `u64` number, using wrapping arithmetic. If the increment is 0 | |
17 | /// the generator yields a constant. | |
dfeec247 | 18 | /// |
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19 | /// ``` |
20 | /// use rand::Rng; | |
21 | /// use rand::rngs::mock::StepRng; | |
dfeec247 | 22 | /// |
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23 | /// let mut my_rng = StepRng::new(2, 1); |
24 | /// let sample: [u64; 3] = my_rng.gen(); | |
25 | /// assert_eq!(sample, [2, 3, 4]); | |
26 | /// ``` | |
27 | #[derive(Debug, Clone)] | |
28 | pub struct StepRng { | |
29 | v: u64, | |
30 | a: u64, | |
31 | } | |
32 | ||
33 | impl StepRng { | |
34 | /// Create a `StepRng`, yielding an arithmetic sequence starting with | |
35 | /// `initial` and incremented by `increment` each time. | |
36 | pub fn new(initial: u64, increment: u64) -> Self { | |
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37 | StepRng { |
38 | v: initial, | |
39 | a: increment, | |
40 | } | |
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41 | } |
42 | } | |
43 | ||
44 | impl RngCore for StepRng { | |
416331ca | 45 | #[inline] |
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46 | fn next_u32(&mut self) -> u32 { |
47 | self.next_u64() as u32 | |
48 | } | |
49 | ||
416331ca | 50 | #[inline] |
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51 | fn next_u64(&mut self) -> u64 { |
52 | let result = self.v; | |
53 | self.v = self.v.wrapping_add(self.a); | |
54 | result | |
55 | } | |
56 | ||
416331ca | 57 | #[inline] |
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58 | fn fill_bytes(&mut self, dest: &mut [u8]) { |
59 | impls::fill_bytes_via_next(self, dest); | |
60 | } | |
61 | ||
416331ca | 62 | #[inline] |
b7449926 | 63 | fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { |
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64 | self.fill_bytes(dest); |
65 | Ok(()) | |
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66 | } |
67 | } |