1 files changed, 123 insertions, 0 deletions
diff --git a/rand/src/read.rs b/rand/src/read.rs
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+++ b/rand/src/read.rs
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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.
+
+use std::io::{self, Read};
+use std::mem;
+use 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.
+///
+/// # Example
+///
+/// ```rust
+/// use rand::{read, Rng};
+///
+/// let data = vec![1, 2, 3, 4, 5, 6, 7, 8];
+/// let mut rng = read::ReadRng::new(&data[..]);
+/// println!("{:x}", rng.gen::<u32>());
+/// ```
+#[derive(Debug)]
+pub struct ReadRng<R> {
+    reader: R
+}
+
+impl<R: Read> ReadRng<R> {
+    /// Create a new `ReadRng` from a `Read`.
+    pub fn new(r: R) -> ReadRng<R> {
+        ReadRng {
+            reader: r
+        }
+    }
+}
+
+impl<R: Read> Rng for ReadRng<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 buf = [0; 4];
+        fill(&mut self.reader, &mut buf).unwrap();
+        unsafe { *(buf.as_ptr() as *const u32) }
+    }
+    fn next_u64(&mut self) -> u64 {
+        // see above for explanation.
+        let mut buf = [0; 8];
+        fill(&mut self.reader, &mut buf).unwrap();
+        unsafe { *(buf.as_ptr() as *const u64) }
+    }
+    fn fill_bytes(&mut self, v: &mut [u8]) {
+        if v.len() == 0 { return }
+        fill(&mut self.reader, v).unwrap();
+    }
+}
+
+fn fill(r: &mut Read, mut buf: &mut [u8]) -> io::Result<()> {
+    while buf.len() > 0 {
+        match try!(r.read(buf)) {
+            0 => return Err(io::Error::new(io::ErrorKind::Other,
+                                           "end of file reached")),
+            n => buf = &mut mem::replace(&mut buf, &mut [])[n..],
+        }
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod test {
+    use super::ReadRng;
+    use Rng;
+
+    #[test]
+    fn test_reader_rng_u64() {
+        // transmute from the target to avoid endianness concerns.
+        let v = vec![0u8, 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 = ReadRng::new(&v[..]);
+
+        assert_eq!(rng.next_u64(), 1_u64.to_be());
+        assert_eq!(rng.next_u64(), 2_u64.to_be());
+        assert_eq!(rng.next_u64(), 3_u64.to_be());
+    }
+    #[test]
+    fn test_reader_rng_u32() {
+        let v = vec![0u8, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3];
+        let mut rng = ReadRng::new(&v[..]);
+
+        assert_eq!(rng.next_u32(), 1_u32.to_be());
+        assert_eq!(rng.next_u32(), 2_u32.to_be());
+        assert_eq!(rng.next_u32(), 3_u32.to_be());
+    }
+    #[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 = ReadRng::new(&v[..]);
+        rng.fill_bytes(&mut w);
+
+        assert!(v == w);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_reader_rng_insufficient_bytes() {
+        let mut rng = ReadRng::new(&[][..]);
+        let mut v = [0u8; 3];
+        rng.fill_bytes(&mut v);
+    }
+}