1 files changed, 108 insertions, 0 deletions
diff --git a/ctr-std/src/rand/reader.rs b/ctr-std/src/rand/reader.rs
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+++ b/ctr-std/src/rand/reader.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.
+
+#![allow(dead_code)]
+
+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 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);
+    }
+}