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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A wrapper around any Read to treat it as an RNG.
#![allow(dead_code)]
use prelude::v1::*;
use io::prelude::*;
use rand::Rng;
/// An RNG that reads random bytes straight from a `Read`. This will
/// work best with an infinite reader, but this is not required.
///
/// # Panics
///
/// It will panic if it there is insufficient data to fulfill a request.
pub struct ReaderRng<R> {
reader: R
}
impl<R: Read> ReaderRng<R> {
/// Create a new `ReaderRng` from a `Read`.
pub fn new(r: R) -> ReaderRng<R> {
ReaderRng {
reader: r
}
}
}
impl<R: Read> Rng for ReaderRng<R> {
fn next_u32(&mut self) -> u32 {
// This is designed for speed: reading a LE integer on a LE
// platform just involves blitting the bytes into the memory
// of the u32, similarly for BE on BE; avoiding byteswapping.
let mut bytes = [0; 4];
self.fill_bytes(&mut bytes);
unsafe { *(bytes.as_ptr() as *const u32) }
}
fn next_u64(&mut self) -> u64 {
// see above for explanation.
let mut bytes = [0; 8];
self.fill_bytes(&mut bytes);
unsafe { *(bytes.as_ptr() as *const u64) }
}
fn fill_bytes(&mut self, mut v: &mut [u8]) {
while !v.is_empty() {
let t = v;
match self.reader.read(t) {
Ok(0) => panic!("ReaderRng.fill_bytes: EOF reached"),
Ok(n) => v = t.split_at_mut(n).1,
Err(e) => panic!("ReaderRng.fill_bytes: {}", e),
}
}
}
}
#[cfg(test)]
mod tests {
use prelude::v1::*;
use super::ReaderRng;
use rand::Rng;
#[test]
fn test_reader_rng_u64() {
// transmute from the target to avoid endianness concerns.
let v = &[0, 0, 0, 0, 0, 0, 0, 1,
0 , 0, 0, 0, 0, 0, 0, 2,
0, 0, 0, 0, 0, 0, 0, 3][..];
let mut rng = ReaderRng::new(v);
assert_eq!(rng.next_u64(), 1u64.to_be());
assert_eq!(rng.next_u64(), 2u64.to_be());
assert_eq!(rng.next_u64(), 3u64.to_be());
}
#[test]
fn test_reader_rng_u32() {
let v = &[0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3][..];
let mut rng = ReaderRng::new(v);
assert_eq!(rng.next_u32(), 1u32.to_be());
assert_eq!(rng.next_u32(), 2u32.to_be());
assert_eq!(rng.next_u32(), 3u32.to_be());
}
#[test]
fn test_reader_rng_fill_bytes() {
let v = [1, 2, 3, 4, 5, 6, 7, 8];
let mut w = [0; 8];
let mut rng = ReaderRng::new(&v[..]);
rng.fill_bytes(&mut w);
assert!(v == w);
}
#[test]
#[should_panic]
fn test_reader_rng_insufficient_bytes() {
let mut rng = ReaderRng::new(&[][..]);
let mut v = [0; 3];
rng.fill_bytes(&mut v);
}
}
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