Reverse breaking changes

Likely most of these will happen with the next minor version bump

Author: dhardy

src/lib.rs

@@ -338,7 +338,14 @@ pub trait Rng {
     fn next_u32(&mut self) -> u32;
 
     /// Return the next random u64.
-    fn next_u64(&mut self) -> u64;
+    /// 
+    /// This function has a default implementation  of `next_u32`. The
+    /// default implementation should not be used in wrapper types since the
+    /// wrapped RNG may have its own implementation which may be more efficient
+    /// or even produce different results.
+    fn next_u64(&mut self) -> u64 {
+        impls::next_u64_via_u32(self)
+    }
 
     /// Return the next random f32 selected from the half-open
     /// interval `[0, 1)`.
@@ -393,6 +400,11 @@ pub trait Rng {
     }
 
     /// Fill `dest` with random data.
+    /// 
+    /// This function has a default implementation in terms of `next_u64`. The
+    /// default implementation should not be used in wrapper types since the
+    /// wrapped RNG may have its own implementation which may be more efficient
+    /// or even produce different results.
     ///
     /// This method does *not* have a requirement to bear any fixed
     /// relationship to the other methods, for example, it does *not*
@@ -414,7 +426,9 @@ pub trait Rng {
     /// thread_rng().fill_bytes(&mut v);
     /// println!("{:?}", &v[..]);
     /// ```
-    fn fill_bytes(&mut self, dest: &mut [u8]);
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        impls::fill_bytes_via_u64(self, dest)
+    }
 
     /// Return a random value of a `Rand` type.
     ///
@@ -726,7 +740,7 @@ pub struct Closed01<F>(pub F);
 
 /// The standard RNG. This is designed to be efficient on the current
 /// platform.
-#[derive(Clone, Debug)]
+#[derive(Copy, Clone, Debug)]
 pub struct StdRng {
     rng: IsaacWordRng,
 }

src/prng/chacha.rs

@@ -27,7 +27,7 @@ const CHACHA_ROUNDS: u32 = 20; // Cryptographically secure from 8 upwards as of
 ///
 /// [1]: D. J. Bernstein, [*ChaCha, a variant of
 /// Salsa20*](http://cr.yp.to/chacha.html)
-#[derive(Clone)]
+#[derive(Copy, Clone)]
 pub struct ChaChaRng {
     buffer:  [u32; STATE_WORDS], // Internal buffer of output
     state:   [u32; STATE_WORDS], // Initial state

src/prng/isaac.rs

@@ -87,6 +87,7 @@ const RAND_SIZE: usize = 1 << RAND_SIZE_LEN;
 ///
 /// [3]: Jean-Philippe Aumasson, [*On the pseudo-random generator ISAAC*]
 ///      (http://eprint.iacr.org/2006/438)
+#[derive(Copy)]
 pub struct IsaacRng {
     rsl: [u32; RAND_SIZE],
     mem: [w32; RAND_SIZE],
@@ -119,6 +120,12 @@ impl fmt::Debug for IsaacRng {
 }
 
 impl IsaacRng {
+    /// Create an ISAAC random number generator using the default
+    /// fixed seed.
+    pub fn new_unseeded() -> IsaacRng {
+        Self::new_from_u64(0)
+    }
+    
     /// Creates an ISAAC random number generator using an u64 as seed.
     /// If `seed == 0` this will produce the same stream of random numbers as
     /// the reference implementation when used unseeded.

src/prng/isaac64.rs

@@ -71,6 +71,7 @@ const RAND_SIZE: usize = 1 << RAND_SIZE_LEN;
 ///
 /// [1]: Bob Jenkins, [*ISAAC and RC4*]
 ///      (http://burtleburtle.net/bob/rand/isaac.html)
+#[derive(Copy)]
 pub struct Isaac64Rng {
     rsl: [u64; RAND_SIZE],
     mem: [w64; RAND_SIZE],
@@ -103,6 +104,12 @@ impl fmt::Debug for Isaac64Rng {
 }
 
 impl Isaac64Rng {
+    /// Create a 64-bit ISAAC random number generator using the
+    /// default fixed seed.
+    pub fn new_unseeded() -> Isaac64Rng {
+        Self::new_from_u64(0)
+    }
+    
     /// Creates an ISAAC-64 random number generator using an u64 as seed.
     /// If `seed == 0` this will produce the same stream of random numbers as
     /// the reference implementation when used unseeded.