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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 Reader to treat it as an RNG.
use container::Container;
use option::{Some, None};
use io::Reader;
use rand::Rng;
/// An RNG that reads random bytes straight from a `Reader`. This will
/// work best with an infinite reader, but this is not required.
///
/// It will fail if it there is insufficient data to fulfill a request.
///
/// # Example
///
/// ```rust
/// use std::rand::{reader, Rng};
/// use std::io::mem;
///
/// let mut rng = reader::ReaderRng::new(mem::MemReader::new(~[1,2,3,4,5,6,7,8]));
/// println!("{:x}", rng.gen::<uint>());
/// ```
pub struct ReaderRng<R> {
priv reader: R
}
impl<R: Reader> ReaderRng<R> {
/// Create a new `ReaderRng` from a `Reader`.
pub fn new(r: R) -> ReaderRng<R> {
ReaderRng {
reader: r
}
}
}
impl<R: Reader> 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.
if cfg!(target_endian="little") {
self.reader.read_le_u32()
} else {
self.reader.read_be_u32()
}
}
fn next_u64(&mut self) -> u64 {
// see above for explanation.
if cfg!(target_endian="little") {
self.reader.read_le_u64()
} else {
self.reader.read_be_u64()
}
}
fn fill_bytes(&mut self, v: &mut [u8]) {
if v.len() == 0 { return }
match self.reader.read(v) {
Some(n) if n == v.len() => return,
Some(n) => fail!("ReaderRng.fill_bytes could not fill buffer: \
read {} out of {} bytes.", n, v.len()),
None => fail!("ReaderRng.fill_bytes reached eof.")
}
}
}
#[cfg(test)]
mod test {
use super::*;
use io::mem::MemReader;
use cast;
use rand::*;
use prelude::*;
#[test]
fn test_reader_rng_u64() {
// transmute from the target to avoid endianness concerns.
let v = ~[1u64, 2u64, 3u64];
let bytes: ~[u8] = unsafe {cast::transmute(v)};
let mut rng = ReaderRng::new(MemReader::new(bytes));
assert_eq!(rng.next_u64(), 1);
assert_eq!(rng.next_u64(), 2);
assert_eq!(rng.next_u64(), 3);
}
#[test]
fn test_reader_rng_u32() {
// transmute from the target to avoid endianness concerns.
let v = ~[1u32, 2u32, 3u32];
let bytes: ~[u8] = unsafe {cast::transmute(v)};
let mut rng = ReaderRng::new(MemReader::new(bytes));
assert_eq!(rng.next_u32(), 1);
assert_eq!(rng.next_u32(), 2);
assert_eq!(rng.next_u32(), 3);
}
#[test]
fn test_reader_rng_fill_bytes() {
let v = [1u8, 2, 3, 4, 5, 6, 7, 8];
let mut w = [0u8, .. 8];
let mut rng = ReaderRng::new(MemReader::new(v.to_owned()));
rng.fill_bytes(w);
assert_eq!(v, w);
}
#[test]
#[should_fail]
fn test_reader_rng_insufficient_bytes() {
let mut rng = ReaderRng::new(MemReader::new(~[]));
let mut v = [0u8, .. 3];
rng.fill_bytes(v);
}
}
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