64 lines
1.4 KiB
Rust
64 lines
1.4 KiB
Rust
// Copyright (c) Facebook, Inc. and its affiliates.
|
|
//
|
|
// This source code is licensed under the MIT license found in the
|
|
// LICENSE file in the root directory of this source tree.
|
|
|
|
use rand::{CryptoRng, Error, RngCore};
|
|
use std::cmp::min;
|
|
|
|
/// A simple implementation of `RngCore` for testing purposes.
|
|
///
|
|
/// This generates a cyclic sequence (i.e. cycles over an initial buffer)
|
|
///
|
|
///
|
|
#[derive(Debug, Clone)]
|
|
pub struct CycleRng {
|
|
v: Vec<u8>,
|
|
}
|
|
|
|
impl CycleRng {
|
|
/// Create a `CycleRng`, yielding a sequence starting with
|
|
/// `initial` and looping thereafter
|
|
pub fn new(initial: Vec<u8>) -> Self {
|
|
CycleRng { v: initial }
|
|
}
|
|
}
|
|
|
|
fn rotate_left<T>(data: &mut [T], steps: usize) {
|
|
if data.is_empty() {
|
|
return;
|
|
}
|
|
let steps = steps % data.len();
|
|
|
|
data[..steps].reverse();
|
|
data[steps..].reverse();
|
|
data.reverse();
|
|
}
|
|
|
|
impl RngCore for CycleRng {
|
|
fn next_u32(&mut self) -> u32 {
|
|
unimplemented!()
|
|
}
|
|
|
|
#[inline]
|
|
fn next_u64(&mut self) -> u64 {
|
|
unimplemented!()
|
|
}
|
|
|
|
#[inline]
|
|
fn fill_bytes(&mut self, dest: &mut [u8]) {
|
|
let len = min(self.v.len(), dest.len());
|
|
(&mut dest[..len]).copy_from_slice(&self.v[..len]);
|
|
rotate_left(&mut self.v, len);
|
|
}
|
|
|
|
#[inline]
|
|
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
|
|
self.fill_bytes(dest);
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
// This is meant for testing only
|
|
impl CryptoRng for CycleRng {}
|