src/libstd/rand/reader.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A wrapper around any Read to treat it as an RNG.
  12
  13 #![allow(dead_code)]
  14
  15 use io::prelude::*;
  16 use rand::Rng;
  17
  18 /// An RNG that reads random bytes straight from a `Read`. This will
  19 /// work best with an infinite reader, but this is not required.
  20 ///
  21 /// # Panics
  22 ///
  23 /// It will panic if it there is insufficient data to fulfill a request.
  24 pub struct ReaderRng<R> {
  25     reader: R
  26 }
  27
  28 impl<R: Read> ReaderRng<R> {
  29     /// Create a new `ReaderRng` from a `Read`.
  30     pub fn new(r: R) -> ReaderRng<R> {
  31         ReaderRng {
  32             reader: r
  33         }
  34     }
  35 }
  36
  37 impl<R: Read> Rng for ReaderRng<R> {
  38     fn next_u32(&mut self) -> u32 {
  39         // This is designed for speed: reading a LE integer on a LE
  40         // platform just involves blitting the bytes into the memory
  41         // of the u32, similarly for BE on BE; avoiding byteswapping.
  42         let mut bytes = [0; 4];
  43         self.fill_bytes(&mut bytes);
  44         unsafe { *(bytes.as_ptr() as *const u32) }
  45     }
  46     fn next_u64(&mut self) -> u64 {
  47         // see above for explanation.
  48         let mut bytes = [0; 8];
  49         self.fill_bytes(&mut bytes);
  50         unsafe { *(bytes.as_ptr() as *const u64) }
  51     }
  52     fn fill_bytes(&mut self, mut v: &mut [u8]) {
  53         while !v.is_empty() {
  54             let t = v;
  55             match self.reader.read(t) {
  56                 Ok(0) => panic!("ReaderRng.fill_bytes: EOF reached"),
  57                 Ok(n) => v = t.split_at_mut(n).1,
  58                 Err(e) => panic!("ReaderRng.fill_bytes: {}", e),
  59             }
  60         }
  61     }
  62 }
  63
  64 #[cfg(test)]
  65 mod tests {
  66     use super::ReaderRng;
  67     use rand::Rng;
  68
  69     #[test]
  70     fn test_reader_rng_u64() {
  71         // transmute from the target to avoid endianness concerns.
  72         let v = &[0, 0, 0, 0, 0, 0, 0, 1,
  73                   0, 0, 0, 0, 0, 0, 0, 2,
  74                   0, 0, 0, 0, 0, 0, 0, 3][..];
  75         let mut rng = ReaderRng::new(v);
  76
  77         assert_eq!(rng.next_u64(), 1u64.to_be());
  78         assert_eq!(rng.next_u64(), 2u64.to_be());
  79         assert_eq!(rng.next_u64(), 3u64.to_be());
  80     }
  81     #[test]
  82     fn test_reader_rng_u32() {
  83         let v = &[0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3][..];
  84         let mut rng = ReaderRng::new(v);
  85
  86         assert_eq!(rng.next_u32(), 1u32.to_be());
  87         assert_eq!(rng.next_u32(), 2u32.to_be());
  88         assert_eq!(rng.next_u32(), 3u32.to_be());
  89     }
  90     #[test]
  91     fn test_reader_rng_fill_bytes() {
  92         let v = [1, 2, 3, 4, 5, 6, 7, 8];
  93         let mut w = [0; 8];
  94
  95         let mut rng = ReaderRng::new(&v[..]);
  96         rng.fill_bytes(&mut w);
  97
  98         assert!(v == w);
  99     }
 100
 101     #[test]
 102     #[should_panic]
 103     fn test_reader_rng_insufficient_bytes() {
 104         let mut rng = ReaderRng::new(&[][..]);
 105         let mut v = [0; 3];
 106         rng.fill_bytes(&mut v);
 107     }
 108 }