vendor/rand-0.7.3/src/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 use rand_core::{impls, Error, RngCore};
  12
  13 /// A simple implementation of `RngCore` for testing purposes.
  14 ///
  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.
  18 ///
  19 /// ```
  20 /// use rand::Rng;
  21 /// use rand::rngs::mock::StepRng;
  22 ///
  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 {
  37         StepRng {
  38             v: initial,
  39             a: increment,
  40         }
  41     }
  42 }
  43
  44 impl RngCore for StepRng {
  45     #[inline]
  46     fn next_u32(&mut self) -> u32 {
  47         self.next_u64() as u32
  48     }
  49
  50     #[inline]
  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
  57     #[inline]
  58     fn fill_bytes(&mut self, dest: &mut [u8]) {
  59         impls::fill_bytes_via_next(self, dest);
  60     }
  61
  62     #[inline]
  63     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
  64         self.fill_bytes(dest);
  65         Ok(())
  66     }
  67 }