| // Copyright 2018 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // https://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! Mock random number generator |
| |
| use rand_core::{RngCore, Error, impls}; |
| |
| /// A simple implementation of `RngCore` for testing purposes. |
| /// |
| /// This generates an arithmetic sequence (i.e. adds a constant each step) |
| /// over a `u64` number, using wrapping arithmetic. If the increment is 0 |
| /// the generator yields a constant. |
| /// |
| /// ``` |
| /// use rand::Rng; |
| /// use rand::rngs::mock::StepRng; |
| /// |
| /// let mut my_rng = StepRng::new(2, 1); |
| /// let sample: [u64; 3] = my_rng.gen(); |
| /// assert_eq!(sample, [2, 3, 4]); |
| /// ``` |
| #[derive(Debug, Clone)] |
| pub struct StepRng { |
| v: u64, |
| a: u64, |
| } |
| |
| impl StepRng { |
| /// Create a `StepRng`, yielding an arithmetic sequence starting with |
| /// `initial` and incremented by `increment` each time. |
| pub fn new(initial: u64, increment: u64) -> Self { |
| StepRng { v: initial, a: increment } |
| } |
| } |
| |
| impl RngCore for StepRng { |
| fn next_u32(&mut self) -> u32 { |
| self.next_u64() as u32 |
| } |
| |
| fn next_u64(&mut self) -> u64 { |
| let result = self.v; |
| self.v = self.v.wrapping_add(self.a); |
| result |
| } |
| |
| fn fill_bytes(&mut self, dest: &mut [u8]) { |
| impls::fill_bytes_via_next(self, dest); |
| } |
| |
| fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { |
| Ok(self.fill_bytes(dest)) |
| } |
| } |