Update nitrokey crate to 0.3.3

This change updates the nitrokey crate to version 0.3.3. Along with that
change we update rand to 0.6.4 because rand 0.6.1 does not yet contain a
publicly accessible rand_os. Note that we no longer require all
crates in rand's workspace, but only rand_os and rand_core, which is a
significant reduction in the number of lines of code compiled.

Import subrepo nitrokey/:nitrokey at 7cf747d56ddc0b7eeedc3caf36dcc909907a171c
Import subrepo rand/:rand at 4336232dda03323634b10ec72ddf27914aebc3a2

13 files changed, 68 insertions, 1580 deletions

diff --git a/rand/src/deprecated.rs b/rand/src/deprecated.rs
index 985ae61..88eb09f 100644
--- a/rand/src/deprecated.rs
+++ b/rand/src/deprecated.rs
@@ -151,12 +151,12 @@ impl SeedableRng for ChaChaRng {
 }
 
 impl ChaChaRng {
-    #[cfg(rust_1_26)]
+    #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
     pub fn get_word_pos(&self) -> u128 {
         self.0.get_word_pos()
     }
 
-    #[cfg(rust_1_26)]
+    #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
     pub fn set_word_pos(&mut self, word_offset: u128) {
         self.0.set_word_pos(word_offset)
     }
@@ -291,45 +291,12 @@ impl SeedableRng for StdRng {
 impl CryptoRng for StdRng {}
 
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
+#[cfg(feature="rand_os")]
 #[derive(Clone, Debug)]
 #[deprecated(since="0.6.0", note="import with rand::rngs::OsRng instead")]
 pub struct OsRng(rngs::OsRng);
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
-#[cfg(feature="std")]
+#[cfg(feature="rand_os")]
 impl RngCore for OsRng {
     #[inline(always)]
     fn next_u32(&mut self) -> u32 {
@@ -352,48 +319,14 @@ impl RngCore for OsRng {
     }
 }
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
-#[cfg(feature="std")]
+#[cfg(feature="rand_os")]
 impl OsRng {
     pub fn new() -> Result<Self, Error> {
         rngs::OsRng::new().map(OsRng)
     }
 }
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
-#[cfg(feature="std")]
+#[cfg(feature="rand_os")]
 impl CryptoRng for OsRng {}
 
 
diff --git a/rand/src/distributions/integer.rs b/rand/src/distributions/integer.rs
index 4e6604d..7e408db 100644
--- a/rand/src/distributions/integer.rs
+++ b/rand/src/distributions/integer.rs
@@ -45,7 +45,7 @@ impl Distribution<u64> for Standard {
     }
 }
 
-#[cfg(rust_1_26)]
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
 impl Distribution<u128> for Standard {
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u128 {
@@ -85,7 +85,7 @@ impl_int_from_uint! { i8, u8 }
 impl_int_from_uint! { i16, u16 }
 impl_int_from_uint! { i32, u32 }
 impl_int_from_uint! { i64, u64 }
-#[cfg(rust_1_26)] impl_int_from_uint! { i128, u128 }
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))] impl_int_from_uint! { i128, u128 }
 impl_int_from_uint! { isize, usize }
 
 #[cfg(feature="simd_support")]
@@ -147,7 +147,7 @@ mod tests {
         rng.sample::<i16, _>(Standard);
         rng.sample::<i32, _>(Standard);
         rng.sample::<i64, _>(Standard);
-        #[cfg(rust_1_26)]
+        #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
         rng.sample::<i128, _>(Standard);
         
         rng.sample::<usize, _>(Standard);
@@ -155,7 +155,7 @@ mod tests {
         rng.sample::<u16, _>(Standard);
         rng.sample::<u32, _>(Standard);
         rng.sample::<u64, _>(Standard);
-        #[cfg(rust_1_26)]
+        #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
         rng.sample::<u128, _>(Standard);
     }
 }
diff --git a/rand/src/distributions/mod.rs b/rand/src/distributions/mod.rs
index 160cd31..5e879cb 100644
--- a/rand/src/distributions/mod.rs
+++ b/rand/src/distributions/mod.rs
@@ -182,7 +182,7 @@
 //! [`Weibull`]: struct.Weibull.html
 //! [`WeightedIndex`]: struct.WeightedIndex.html
 
-#[cfg(any(rust_1_26, features="nightly"))]
+#[cfg(any(rustc_1_26, features="nightly"))]
 use core::iter;
 use Rng;
 
@@ -316,7 +316,7 @@ impl<'a, D, R, T> Iterator for DistIter<'a, D, R, T>
     }
 }
 
-#[cfg(rust_1_26)]
+#[cfg(rustc_1_26)]
 impl<'a, D, R, T> iter::FusedIterator for DistIter<'a, D, R, T>
     where D: Distribution<T>, R: Rng + 'a {}
 
@@ -328,7 +328,7 @@ impl<'a, D, R, T> iter::TrustedLen for DistIter<'a, D, R, T>
 /// A generic random value distribution, implemented for many primitive types.
 /// Usually generates values with a numerically uniform distribution, and with a
 /// range appropriate to the type.
-/// 
+///
 /// ## Built-in Implementations
 ///
 /// Assuming the provided `Rng` is well-behaved, these implementations
diff --git a/rand/src/distributions/uniform.rs b/rand/src/distributions/uniform.rs
index 5fb89e3..ceed77d 100644
--- a/rand/src/distributions/uniform.rs
+++ b/rand/src/distributions/uniform.rs
@@ -111,7 +111,7 @@
 
 #[cfg(feature = "std")]
 use std::time::Duration;
-#[cfg(all(not(feature = "std"), rust_1_25))]
+#[cfg(all(not(feature = "std"), rustc_1_25))]
 use core::time::Duration;
 
 use Rng;
@@ -277,7 +277,7 @@ impl<X: SampleUniform> From<::core::ops::Range<X>> for Uniform<X> {
     }
 }
 
-#[cfg(rust_1_27)]
+#[cfg(rustc_1_27)]
 impl<X: SampleUniform> From<::core::ops::RangeInclusive<X>> for Uniform<X> {
     fn from(r: ::core::ops::RangeInclusive<X>) -> Uniform<X> {
         Uniform::new_inclusive(r.start(), r.end())
@@ -452,8 +452,9 @@ macro_rules! uniform_int_impl {
                         let ints_to_reject = (unsigned_max - range + 1) % range;
                         unsigned_max - ints_to_reject
                     } else {
-                        // conservative but fast approximation
-                       range << range.leading_zeros()
+                        // conservative but fast approximation. `- 1` is necessary to allow the
+                        // same comparison without bias.
+                        (range << range.leading_zeros()).wrapping_sub(1)
                     };
 
                 loop {
@@ -472,7 +473,7 @@ uniform_int_impl! { i8, i8, u8, i32, u32 }
 uniform_int_impl! { i16, i16, u16, i32, u32 }
 uniform_int_impl! { i32, i32, u32, i32, u32 }
 uniform_int_impl! { i64, i64, u64, i64, u64 }
-#[cfg(rust_1_26)]
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
 uniform_int_impl! { i128, i128, u128, u128, u128 }
 uniform_int_impl! { isize, isize, usize, isize, usize }
 uniform_int_impl! { u8, i8, u8, i32, u32 }
@@ -480,7 +481,7 @@ uniform_int_impl! { u16, i16, u16, i32, u32 }
 uniform_int_impl! { u32, i32, u32, i32, u32 }
 uniform_int_impl! { u64, i64, u64, i64, u64 }
 uniform_int_impl! { usize, isize, usize, isize, usize }
-#[cfg(rust_1_26)]
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
 uniform_int_impl! { u128, u128, u128, i128, u128 }
 
 #[cfg(all(feature = "simd_support", feature = "nightly"))]
@@ -835,14 +836,14 @@ uniform_float_impl! { f64x8, u64x8, f64, u64, 64 - 52 }
 ///
 /// [`UniformSampler`]: trait.UniformSampler.html
 /// [`Uniform`]: struct.Uniform.html
-#[cfg(any(feature = "std", rust_1_25))]
+#[cfg(any(feature = "std", rustc_1_25))]
 #[derive(Clone, Copy, Debug)]
 pub struct UniformDuration {
     mode: UniformDurationMode,
     offset: u32,
 }
 
-#[cfg(any(feature = "std", rust_1_25))]
+#[cfg(any(feature = "std", rustc_1_25))]
 #[derive(Debug, Copy, Clone)]
 enum UniformDurationMode {
     Small {
@@ -859,12 +860,12 @@ enum UniformDurationMode {
     }
 }
 
-#[cfg(any(feature = "std", rust_1_25))]
+#[cfg(any(feature = "std", rustc_1_25))]
 impl SampleUniform for Duration {
     type Sampler = UniformDuration;
 }
 
-#[cfg(any(feature = "std", rust_1_25))]
+#[cfg(any(feature = "std", rustc_1_25))]
 impl UniformSampler for UniformDuration {
     type X = Duration;
 
@@ -989,7 +990,7 @@ mod tests {
     fn test_integers() {
         use core::{i8, i16, i32, i64, isize};
         use core::{u8, u16, u32, u64, usize};
-        #[cfg(rust_1_26)]
+        #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
         use core::{i128, u128};
 
         let mut rng = ::test::rng(251);
@@ -1053,7 +1054,7 @@ mod tests {
         }
         t!(i8, i16, i32, i64, isize,
            u8, u16, u32, u64, usize);
-        #[cfg(rust_1_26)]
+        #[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
         t!(i128, u128);
 
         #[cfg(all(feature = "simd_support", feature = "nightly"))]
@@ -1208,11 +1209,11 @@ mod tests {
 
 
     #[test]
-    #[cfg(any(feature = "std", rust_1_25))]
+    #[cfg(any(feature = "std", rustc_1_25))]
     fn test_durations() {
         #[cfg(feature = "std")]
         use std::time::Duration;
-        #[cfg(all(not(feature = "std"), rust_1_25))]
+        #[cfg(all(not(feature = "std"), rustc_1_25))]
         use core::time::Duration;
 
         let mut rng = ::test::rng(253);
@@ -1283,7 +1284,7 @@ mod tests {
         assert_eq!(r.inner.scale, 5.0);
     }
 
-    #[cfg(rust_1_27)]
+    #[cfg(rustc_1_27)]
     #[test]
     fn test_uniform_from_std_range_inclusive() {
         let r = Uniform::from(2u32..=6);
diff --git a/rand/src/distributions/unit_circle.rs b/rand/src/distributions/unit_circle.rs
index abb36dc..01ab76a 100644
--- a/rand/src/distributions/unit_circle.rs
+++ b/rand/src/distributions/unit_circle.rs
@@ -29,27 +29,26 @@ use distributions::{Distribution, Uniform};
 ///       NBS Appl. Math. Ser., No. 12. Washington, DC: U.S. Government Printing
 ///       Office, pp. 36-38.
 #[derive(Clone, Copy, Debug)]
-pub struct UnitCircle {
-    uniform: Uniform<f64>,
-}
+pub struct UnitCircle;
 
 impl UnitCircle {
     /// Construct a new `UnitCircle` distribution.
     #[inline]
     pub fn new() -> UnitCircle {
-        UnitCircle { uniform: Uniform::new(-1., 1.) }
+        UnitCircle
     }
 }
 
 impl Distribution<[f64; 2]> for UnitCircle {
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [f64; 2] {
+        let uniform = Uniform::new(-1., 1.);
         let mut x1;
         let mut x2;
         let mut sum;
         loop {
-            x1 = self.uniform.sample(rng);
-            x2 = self.uniform.sample(rng);
+            x1 = uniform.sample(rng);
+            x2 = uniform.sample(rng);
             sum = x1*x1 + x2*x2;
             if sum < 1. {
                 break;
diff --git a/rand/src/distributions/unit_sphere.rs b/rand/src/distributions/unit_sphere.rs
index 61cbda5..37de88b 100644
--- a/rand/src/distributions/unit_sphere.rs
+++ b/rand/src/distributions/unit_sphere.rs
@@ -28,23 +28,22 @@ use distributions::{Distribution, Uniform};
 ///       Sphere.*](https://doi.org/10.1214/aoms/1177692644)
 ///       Ann. Math. Statist. 43, no. 2, 645--646.
 #[derive(Clone, Copy, Debug)]
-pub struct UnitSphereSurface {
-    uniform: Uniform<f64>,
-}
+pub struct UnitSphereSurface;
 
 impl UnitSphereSurface {
     /// Construct a new `UnitSphereSurface` distribution.
     #[inline]
     pub fn new() -> UnitSphereSurface {
-        UnitSphereSurface { uniform: Uniform::new(-1., 1.) }
+        UnitSphereSurface
     }
 }
 
 impl Distribution<[f64; 3]> for UnitSphereSurface {
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> [f64; 3] {
+        let uniform = Uniform::new(-1., 1.);
         loop {
-            let (x1, x2) = (self.uniform.sample(rng), self.uniform.sample(rng));
+            let (x1, x2) = (uniform.sample(rng), uniform.sample(rng));
             let sum = x1*x1 + x2*x2;
             if sum >= 1. {
                 continue;
diff --git a/rand/src/distributions/utils.rs b/rand/src/distributions/utils.rs
index a2112fd..d4d3642 100644
--- a/rand/src/distributions/utils.rs
+++ b/rand/src/distributions/utils.rs
@@ -61,7 +61,7 @@ macro_rules! wmul_impl {
 wmul_impl! { u8, u16, 8 }
 wmul_impl! { u16, u32, 16 }
 wmul_impl! { u32, u64, 32 }
-#[cfg(rust_1_26)]
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
 wmul_impl! { u64, u128, 64 }
 
 // This code is a translation of the __mulddi3 function in LLVM's
@@ -125,9 +125,9 @@ macro_rules! wmul_impl_large {
         )+
     };
 }
-#[cfg(not(rust_1_26))]
+#[cfg(not(all(rustc_1_26, not(target_os = "emscripten"))))]
 wmul_impl_large! { u64, 32 }
-#[cfg(rust_1_26)]
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))]
 wmul_impl_large! { u128, 64 }
 
 macro_rules! wmul_impl_usize {
diff --git a/rand/src/lib.rs b/rand/src/lib.rs
index d364bd1..ca231b5 100644
--- a/rand/src/lib.rs
+++ b/rand/src/lib.rs
@@ -13,7 +13,7 @@
 //! useful types and distributions, and some randomness-related algorithms.
 //!
 //! # Quick Start
-//! 
+//!
 //! To get you started quickly, the easiest and highest-level way to get
 //! a random value is to use [`random()`]; alternatively you can use
 //! [`thread_rng()`]. The [`Rng`] trait provides a useful API on all RNGs, while
@@ -22,7 +22,7 @@
 //!
 //! ```
 //! use rand::prelude::*;
-//! 
+//!
 //! if rand::random() { // generates a boolean
 //!     // Try printing a random unicode code point (probably a bad idea)!
 //!     println!("char: {}", rand::random::<char>());
@@ -36,7 +36,7 @@
 //! ```
 //!
 //! # The Book
-//! 
+//!
 //! For the user guide and futher documentation, please read
 //! [The Rust Rand Book](https://rust-random.github.io/book).
 //!
@@ -58,19 +58,14 @@
 #![cfg_attr(not(feature="std"), no_std)]
 #![cfg_attr(all(feature="alloc", not(feature="std")), feature(alloc))]
 #![cfg_attr(all(feature="simd_support", feature="nightly"), feature(stdsimd))]
-#![cfg_attr(feature = "stdweb", recursion_limit="128")]
 
 #[cfg(feature = "std")] extern crate core;
 #[cfg(all(feature = "alloc", not(feature="std")))] #[macro_use] extern crate alloc;
 
 #[cfg(feature="simd_support")] extern crate packed_simd;
 
-#[cfg(all(target_arch="wasm32", not(target_os="emscripten"), feature="stdweb"))]
-#[macro_use]
-extern crate stdweb;
-
-#[cfg(all(target_arch = "wasm32", feature = "wasm-bindgen"))]
-extern crate wasm_bindgen;
+#[cfg(feature = "rand_os")]
+extern crate rand_os;
 
 extern crate rand_core;
 extern crate rand_isaac;    // only for deprecations
@@ -119,23 +114,7 @@ pub mod seq;
 #[cfg(feature="std")] #[doc(hidden)] pub use deprecated::EntropyRng;
 
 #[allow(deprecated)]
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
+#[cfg(feature="rand_os")]
 #[doc(hidden)]
 pub use deprecated::OsRng;
 
@@ -152,23 +131,7 @@ pub mod jitter {
     pub use rngs::TimerError;
 }
 #[allow(deprecated)]
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
+#[cfg(feature="rand_os")]
 #[doc(hidden)]
 pub mod os {
     pub use deprecated::OsRng;
@@ -549,13 +512,13 @@ macro_rules! impl_as_byte_slice {
 impl_as_byte_slice!(u16);
 impl_as_byte_slice!(u32);
 impl_as_byte_slice!(u64);
-#[cfg(rust_1_26)] impl_as_byte_slice!(u128);
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))] impl_as_byte_slice!(u128);
 impl_as_byte_slice!(usize);
 impl_as_byte_slice!(i8);
 impl_as_byte_slice!(i16);
 impl_as_byte_slice!(i32);
 impl_as_byte_slice!(i64);
-#[cfg(rust_1_26)] impl_as_byte_slice!(i128);
+#[cfg(all(rustc_1_26, not(target_os = "emscripten")))] impl_as_byte_slice!(i128);
 impl_as_byte_slice!(isize);
 
 macro_rules! impl_as_byte_slice_arrays {
@@ -712,61 +675,6 @@ pub fn random<T>() -> T where Standard: Distribution<T> {
     thread_rng().gen()
 }
 
-// Due to rustwasm/wasm-bindgen#201 this can't be defined in the inner os
-// modules, so hack around it for now and place it at the root.
-#[cfg(all(feature = "wasm-bindgen", target_arch = "wasm32"))]
-#[doc(hidden)]
-#[allow(missing_debug_implementations)]
-pub mod __wbg_shims {
-
-    // `extern { type Foo; }` isn't supported on 1.22 syntactically, so use a
-    // macro to work around that.
-    macro_rules! rust_122_compat {
-        ($($t:tt)*) => ($($t)*)
-    }
-
-    rust_122_compat! {
-        extern crate wasm_bindgen;
-
-        pub use wasm_bindgen::prelude::*;
-
-        #[wasm_bindgen]
-        extern "C" {
-            pub type Function;
-            #[wasm_bindgen(constructor)]
-            pub fn new(s: &str) -> Function;
-            #[wasm_bindgen(method)]
-            pub fn call(this: &Function, self_: &JsValue) -> JsValue;
-
-            pub type This;
-            #[wasm_bindgen(method, getter, structural, js_name = self)]
-            pub fn self_(me: &This) -> JsValue;
-            #[wasm_bindgen(method, getter, structural)]
-            pub fn crypto(me: &This) -> JsValue;
-
-            #[derive(Clone, Debug)]
-            pub type BrowserCrypto;
-
-            // TODO: these `structural` annotations here ideally wouldn't be here to
-            // avoid a JS shim, but for now with feature detection they're
-            // unavoidable.
-            #[wasm_bindgen(method, js_name = getRandomValues, structural, getter)]
-            pub fn get_random_values_fn(me: &BrowserCrypto) -> JsValue;
-            #[wasm_bindgen(method, js_name = getRandomValues, structural)]
-            pub fn get_random_values(me: &BrowserCrypto, buf: &mut [u8]);
-
-            #[wasm_bindgen(js_name = require)]
-            pub fn node_require(s: &str) -> NodeCrypto;
-
-            #[derive(Clone, Debug)]
-            pub type NodeCrypto;
-
-            #[wasm_bindgen(method, js_name = randomFillSync, structural)]
-            pub fn random_fill_sync(me: &NodeCrypto, buf: &mut [u8]);
-        }
-    }
-}
-
 #[cfg(test)]
 mod test {
     use rngs::mock::StepRng;
diff --git a/rand/src/rngs/entropy.rs b/rand/src/rngs/entropy.rs
index 8736324..372b4d7 100644
--- a/rand/src/rngs/entropy.rs
+++ b/rand/src/rngs/entropy.rs
@@ -191,43 +191,11 @@ impl EntropySource for NoSource {
 }
 
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
+#[cfg(feature="rand_os")]
 #[derive(Clone, Debug)]
 pub struct Os(rngs::OsRng);
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
+#[cfg(feature="rand_os")]
 impl EntropySource for Os {
     fn new_and_fill(dest: &mut [u8]) -> Result<Self, Error> {
         let mut rng = rngs::OsRng::new()?;
@@ -240,23 +208,7 @@ impl EntropySource for Os {
     }
 }
 
-#[cfg(not(all(feature="std",
-              any(target_os = "linux", target_os = "android",
-                  target_os = "netbsd",
-                  target_os = "dragonfly",
-                  target_os = "haiku",
-                  target_os = "emscripten",
-                  target_os = "solaris",
-                  target_os = "cloudabi",
-                  target_os = "macos", target_os = "ios",
-                  target_os = "freebsd",
-                  target_os = "openbsd", target_os = "bitrig",
-                  target_os = "redox",
-                  target_os = "fuchsia",
-                  windows,
-                  all(target_arch = "wasm32", feature = "stdweb"),
-                  all(target_arch = "wasm32", feature = "wasm-bindgen"),
-))))]
+#[cfg(not(feature="std"))]
 type Os = NoSource;
 
 
diff --git a/rand/src/rngs/mod.rs b/rand/src/rngs/mod.rs
index 70c4506..847fc94 100644
--- a/rand/src/rngs/mod.rs
+++ b/rand/src/rngs/mod.rs
@@ -178,40 +178,5 @@ pub use self::small::SmallRng;
 pub use self::std::StdRng;
 #[cfg(feature="std")] pub use self::thread::ThreadRng;
 
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
-mod os;
-
-#[cfg(all(feature="std",
-          any(target_os = "linux", target_os = "android",
-              target_os = "netbsd",
-              target_os = "dragonfly",
-              target_os = "haiku",
-              target_os = "emscripten",
-              target_os = "solaris",
-              target_os = "cloudabi",
-              target_os = "macos", target_os = "ios",
-              target_os = "freebsd",
-              target_os = "openbsd", target_os = "bitrig",
-              target_os = "redox",
-              target_os = "fuchsia",
-              windows,
-              all(target_arch = "wasm32", feature = "stdweb"),
-              all(target_arch = "wasm32", feature = "wasm-bindgen"),
-)))]
-pub use self::os::OsRng;
+#[cfg(feature="rand_os")]
+pub use rand_os::OsRng;
diff --git a/rand/src/rngs/os.rs b/rand/src/rngs/os.rs
deleted file mode 100644
index e609c50..0000000
--- a/rand/src/rngs/os.rs
+++ /dev/null
@@ -1,1275 +0,0 @@
-// Copyright 2018 Developers of the Rand project.
-// Copyright 2013-2015 The Rust Project Developers.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! Interface to the random number generator of the operating system.
-
-use std::fmt;
-use rand_core::{CryptoRng, RngCore, Error, impls};
-
-/// A random number generator that retrieves randomness straight from the
-/// operating system.
-///
-/// This is the preferred external source of entropy for most applications.
-/// Commonly it is used to initialize a user-space RNG, which can then be used
-/// to generate random values with much less overhead than `OsRng`.
-///
-/// You may prefer to use [`EntropyRng`] instead of `OsRng`. It is unlikely, but
-/// not entirely theoretical, for `OsRng` to fail. In such cases [`EntropyRng`]
-/// falls back on a good alternative entropy source.
-///
-/// `OsRng::new()` is guaranteed to be very cheap (after the first successful
-/// call), and will never consume more than one file handle per process.
-///
-/// # Platform sources
-///
-/// | OS               | interface
-/// |------------------|---------------------------------------------------------
-/// | Linux, Android   | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after reading from `/dev/random` once
-/// | Windows          | [`RtlGenRandom`][3]
-/// | macOS, iOS       | [`SecRandomCopyBytes`][4]
-/// | FreeBSD          | [`kern.arandom`][5]
-/// | OpenBSD, Bitrig  | [`getentropy`][6]
-/// | NetBSD           | [`/dev/urandom`][7] after reading from `/dev/random` once
-/// | Dragonfly BSD    | [`/dev/random`][8]
-/// | Solaris, illumos | [`getrandom`][9] system call if available, otherwise [`/dev/random`][10]
-/// | Fuchsia OS       | [`cprng_draw`][11]
-/// | Redox            | [`rand:`][12]
-/// | CloudABI         | [`random_get`][13]
-/// | Haiku            | `/dev/random` (identical to `/dev/urandom`)
-/// | Web browsers     | [`Crypto.getRandomValues`][14] (see [Support for WebAssembly and ams.js][14])
-/// | Node.js          | [`crypto.randomBytes`][15] (see [Support for WebAssembly and ams.js][16])
-///
-/// Rand doesn't have a blanket implementation for all Unix-like operating
-/// systems that reads from `/dev/urandom`. This ensures all supported operating
-/// systems are using the recommended interface and respect maximum buffer
-/// sizes.
-///
-/// ## Support for WebAssembly and ams.js
-///
-/// The three Emscripten targets `asmjs-unknown-emscripten`,
-/// `wasm32-unknown-emscripten` and `wasm32-experimental-emscripten` use
-/// Emscripten's emulation of `/dev/random` on web browsers and Node.js.
-///
-/// The bare Wasm target `wasm32-unknown-unknown` tries to call the javascript
-/// methods directly, using either `stdweb` in combination with `cargo-web` or
-/// `wasm-bindgen` depending on what features are activated for this crate.
-///
-/// ## Early boot
-///
-/// It is possible that early in the boot process the OS hasn't had enough time
-/// yet to collect entropy to securely seed its RNG, especially on virtual
-/// machines.
-///
-/// Some operating systems always block the thread until the RNG is securely
-/// seeded. This can take anywhere from a few seconds to more than a minute.
-/// Others make a best effort to use a seed from before the shutdown and don't
-/// document much.
-///
-/// A few, Linux, NetBSD and Solaris, offer a choice between blocking, and
-/// getting an error. With `try_fill_bytes` we choose to get the error
-/// ([`ErrorKind::NotReady`]), while the other methods use a blocking interface.
-///
-/// On Linux (when the `genrandom` system call is not available) and on NetBSD
-/// reading from `/dev/urandom` never blocks, even when the OS hasn't collected
-/// enough entropy yet. As a countermeasure we try to do a single read from
-/// `/dev/random` until we know the OS RNG is initialized (and store this in a
-/// global static).
-///
-/// # Panics
-///
-/// `OsRng` is extremely unlikely to fail if `OsRng::new()`, and one read from
-/// it, where succesfull. But in case it does fail, only [`try_fill_bytes`] is
-/// able to report the cause. Depending on the error the other [`RngCore`]
-/// methods will retry several times, and panic in case the error remains.
-///
-/// [`EntropyRng`]: struct.EntropyRng.html
-/// [`RngCore`]: ../trait.RngCore.html
-/// [`try_fill_bytes`]: ../trait.RngCore.html#method.tymethod.try_fill_bytes
-/// [`ErrorKind::NotReady`]: ../enum.ErrorKind.html#variant.NotReady
-///
-/// [1]: http://man7.org/linux/man-pages/man2/getrandom.2.html
-/// [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
-/// [3]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa387694.aspx
-/// [4]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
-/// [5]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
-/// [6]: https://man.openbsd.org/getentropy.2
-/// [7]: http://netbsd.gw.com/cgi-bin/man-cgi?random+4+NetBSD-current
-/// [8]: https://leaf.dragonflybsd.org/cgi/web-man?command=random&section=4
-/// [9]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
-/// [10]: https://docs.oracle.com/cd/E86824_01/html/E54777/random-7d.html
-/// [11]: https://fuchsia.googlesource.com/zircon/+/HEAD/docs/syscalls/cprng_draw.md
-/// [12]: https://github.com/redox-os/randd/blob/master/src/main.rs
-/// [13]: https://github.com/NuxiNL/cloudabi/blob/v0.20/cloudabi.txt#L1826
-/// [14]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
-/// [15]: https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
-/// [16]: #support-for-webassembly-and-amsjs
-
-
-#[derive(Clone)]
-pub struct OsRng(imp::OsRng);
-
-impl fmt::Debug for OsRng {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.0.fmt(f)
-    }
-}
-
-impl OsRng {
-    /// Create a new `OsRng`.
-    pub fn new() -> Result<OsRng, Error> {
-        imp::OsRng::new().map(OsRng)
-    }
-}
-
-impl CryptoRng for OsRng {}
-
-impl RngCore for OsRng {
-    fn next_u32(&mut self) -> u32 {
-        impls::next_u32_via_fill(self)
-    }
-
-    fn next_u64(&mut self) -> u64 {
-        impls::next_u64_via_fill(self)
-    }
-
-    fn fill_bytes(&mut self, dest: &mut [u8]) {
-        use std::{time, thread};
-
-        // We cannot return Err(..), so we try to handle before panicking.
-        const MAX_RETRY_PERIOD: u32 = 10; // max 10s
-        const WAIT_DUR_MS: u32 = 100; // retry every 100ms
-        let wait_dur = time::Duration::from_millis(WAIT_DUR_MS as u64);
-        const RETRY_LIMIT: u32 = (MAX_RETRY_PERIOD * 1000) / WAIT_DUR_MS;
-        const TRANSIENT_RETRIES: u32 = 8;
-        let mut err_count = 0;
-        let mut error_logged = false;
-
-        // Maybe block until the OS RNG is initialized
-        let mut read = 0;
-        if let Ok(n) = self.0.test_initialized(dest, true) { read = n };
-        let dest = &mut dest[read..];
-
-        loop {
-            if let Err(e) = self.try_fill_bytes(dest) {
-                if err_count >= RETRY_LIMIT {
-                    error!("OsRng failed too many times; last error: {}", e);
-                    panic!("OsRng failed too many times; last error: {}", e);
-                }
-
-                if e.kind.should_wait() {
-                    if !error_logged {
-                        warn!("OsRng failed; waiting up to {}s and retrying. Error: {}",
-                                MAX_RETRY_PERIOD, e);
-                        error_logged = true;
-                    }
-                    err_count += 1;
-                    thread::sleep(wait_dur);
-                    continue;
-                } else if e.kind.should_retry() {
-                    if !error_logged {
-                        warn!("OsRng failed; retrying up to {} times. Error: {}",
-                                TRANSIENT_RETRIES, e);
-                        error_logged = true;
-                    }
-                    err_count += (RETRY_LIMIT + TRANSIENT_RETRIES - 1)
-                            / TRANSIENT_RETRIES;    // round up
-                    continue;
-                } else {
-                    error!("OsRng failed: {}", e);
-                    panic!("OsRng fatal error: {}", e);
-                }
-            }
-
-            break;
-        }
-    }
-
-    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-        // Some systems do not support reading 0 random bytes.
-        // (And why waste a system call?)
-        if dest.len() == 0 { return Ok(()); }
-
-        let read = self.0.test_initialized(dest, false)?;
-        let dest = &mut dest[read..];
-
-        let max = self.0.max_chunk_size();
-        if dest.len() <= max {
-            trace!("OsRng: reading {} bytes via {}",
-                   dest.len(), self.0.method_str());
-        } else {
-            trace!("OsRng: reading {} bytes via {} in {} chunks of {} bytes",
-                   dest.len(), self.0.method_str(), (dest.len() + max) / max, max);
-        }
-        for slice in dest.chunks_mut(max) {
-            self.0.fill_chunk(slice)?;
-        }
-        Ok(())
-    }
-}
-
-trait OsRngImpl where Self: Sized {
-    // Create a new `OsRng` platform interface.
-    fn new() -> Result<Self, Error>;
-
-    // Fill a chunk with random bytes.
-    fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error>;
-
-    // Test whether the OS RNG is initialized. This method may not be possible
-    // to support cheaply (or at all) on all operating systems.
-    //
-    // If `blocking` is set, this will cause the OS the block execution until
-    // its RNG is initialized.
-    //
-    // Random values that are read while this are stored in `dest`, the amount
-    // of read bytes is returned.
-    fn test_initialized(&mut self, _dest: &mut [u8], _blocking: bool)
-        -> Result<usize, Error> { Ok(0) }
-
-    // Maximum chunk size supported.
-    fn max_chunk_size(&self) -> usize { ::core::usize::MAX }
-
-    // Name of the OS interface (used for logging).
-    fn method_str(&self) -> &'static str;
-}
-
-
-
-
-// Helper functions to read from a random device such as `/dev/urandom`.
-//
-// All instances use a single internal file handle, to prevent possible
-// exhaustion of file descriptors.
-#[cfg(any(target_os = "linux", target_os = "android",
-          target_os = "netbsd", target_os = "dragonfly",
-          target_os = "solaris", target_os = "redox",
-          target_os = "haiku", target_os = "emscripten"))]
-mod random_device {
-    use {Error, ErrorKind};
-    use std::fs::File;
-    use std::io;
-    use std::io::Read;
-    use std::sync::{Once, Mutex, ONCE_INIT};
-
-    // TODO: remove outer Option when `Mutex::new(None)` is a constant expression
-    static mut READ_RNG_FILE: Option<Mutex<Option<File>>> = None;
-    static READ_RNG_ONCE: Once = ONCE_INIT;
-
-    #[allow(unused)]
-    pub fn open<F>(path: &'static str, open_fn: F) -> Result<(), Error>
-        where F: Fn(&'static str) -> Result<File, io::Error>
-    {
-        READ_RNG_ONCE.call_once(|| {
-            unsafe { READ_RNG_FILE = Some(Mutex::new(None)) }
-        });
-
-        // We try opening the file outside the `call_once` fn because we cannot
-        // clone the error, thus we must retry on failure.
-
-        let mutex = unsafe { READ_RNG_FILE.as_ref().unwrap() };
-        let mut guard = mutex.lock().unwrap();
-        if (*guard).is_none() {
-            info!("OsRng: opening random device {}", path);
-            let file = open_fn(path).map_err(map_err)?;
-            *guard = Some(file);
-        };
-        Ok(())
-    }
-
-    pub fn read(dest: &mut [u8]) -> Result<(), Error> {
-        // We expect this function only to be used after `random_device::open`
-        // was succesful. Therefore we can assume that our memory was set with a
-        // valid object.
-        let mutex = unsafe { READ_RNG_FILE.as_ref().unwrap() };
-        let mut guard = mutex.lock().unwrap();
-        let file = (*guard).as_mut().unwrap();
-
-        // Use `std::io::read_exact`, which retries on `ErrorKind::Interrupted`.
-        file.read_exact(dest).map_err(|err| {
-            Error::with_cause(ErrorKind::Unavailable,
-                              "error reading random device", err)
-        })
-
-    }
-
-    pub fn map_err(err: io::Error) -> Error {
-        match err.kind() {
-            io::ErrorKind::Interrupted =>
-                    Error::new(ErrorKind::Transient, "interrupted"),
-            io::ErrorKind::WouldBlock =>
-                    Error::with_cause(ErrorKind::NotReady,
-                    "OS RNG not yet seeded", err),
-            _ => Error::with_cause(ErrorKind::Unavailable,
-                    "error while opening random device", err)
-        }
-    }
-}
-
-
-#[cfg(any(target_os = "linux", target_os = "android"))]
-mod imp {
-    extern crate libc;
-
-    use {Error, ErrorKind};
-    use super::random_device;
-    use super::OsRngImpl;
-
-    use std::io;
-    use std::io::Read;
-    use std::fs::{File, OpenOptions};
-    use std::os::unix::fs::OpenOptionsExt;
-    use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
-    use std::sync::{Once, ONCE_INIT};
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng {
-        method: OsRngMethod,
-        initialized: bool,
-    }
-
-    #[derive(Clone, Debug)]
-    enum OsRngMethod {
-        GetRandom,
-        RandomDevice,
-    }
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            if is_getrandom_available() {
-                return Ok(OsRng { method: OsRngMethod::GetRandom,
-                                  initialized: false });
-            }
-            random_device::open("/dev/urandom", &|p| File::open(p))?;
-            Ok(OsRng { method: OsRngMethod::RandomDevice, initialized: false })
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            match self.method {
-                OsRngMethod::GetRandom => getrandom_try_fill(dest, false),
-                OsRngMethod::RandomDevice => random_device::read(dest),
-            }
-        }
-
-        fn test_initialized(&mut self, dest: &mut [u8], blocking: bool)
-            -> Result<usize, Error>
-        {
-            static OS_RNG_INITIALIZED: AtomicBool = ATOMIC_BOOL_INIT;
-            if !self.initialized {
-                self.initialized = OS_RNG_INITIALIZED.load(Ordering::Relaxed);
-            }
-            if self.initialized { return Ok(0); }
-
-            let result = match self.method {
-                OsRngMethod::GetRandom => {
-                    getrandom_try_fill(dest, blocking)?;
-                    Ok(dest.len())
-                }
-                OsRngMethod::RandomDevice => {
-                    info!("OsRng: testing random device /dev/random");
-                    let mut file = OpenOptions::new()
-                        .read(true)
-                        .custom_flags(if blocking { 0 } else { libc::O_NONBLOCK })
-                        .open("/dev/random")
-                        .map_err(random_device::map_err)?;
-                    file.read(&mut dest[..1]).map_err(random_device::map_err)?;
-                    Ok(1)
-                }
-            };
-            OS_RNG_INITIALIZED.store(true, Ordering::Relaxed);
-            self.initialized = true;
-            result
-        }
-
-        fn method_str(&self) -> &'static str {
-            match self.method {
-                OsRngMethod::GetRandom => "getrandom",
-                OsRngMethod::RandomDevice => "/dev/urandom",
-            }
-        }
-    }
-
-    #[cfg(target_arch = "x86_64")]
-    const NR_GETRANDOM: libc::c_long = 318;
-    #[cfg(target_arch = "x86")]
-    const NR_GETRANDOM: libc::c_long = 355;
-    #[cfg(target_arch = "arm")]
-    const NR_GETRANDOM: libc::c_long = 384;
-    #[cfg(target_arch = "aarch64")]
-    const NR_GETRANDOM: libc::c_long = 278;
-     #[cfg(target_arch = "s390x")]
-    const NR_GETRANDOM: libc::c_long = 349;
-    #[cfg(target_arch = "powerpc")]
-    const NR_GETRANDOM: libc::c_long = 359;
-    #[cfg(target_arch = "powerpc64")]
-    const NR_GETRANDOM: libc::c_long = 359;
-    #[cfg(target_arch = "mips")] // old ABI
-    const NR_GETRANDOM: libc::c_long = 4353;
-    #[cfg(target_arch = "mips64")]
-    const NR_GETRANDOM: libc::c_long = 5313;
-    #[cfg(target_arch = "sparc")]
-    const NR_GETRANDOM: libc::c_long = 347;
-    #[cfg(target_arch = "sparc64")]
-    const NR_GETRANDOM: libc::c_long = 347;
-    #[cfg(not(any(target_arch = "x86_64", target_arch = "x86",
-                  target_arch = "arm", target_arch = "aarch64",
-                  target_arch = "s390x", target_arch = "powerpc",
-                  target_arch = "powerpc64", target_arch = "mips",
-                  target_arch = "mips64", target_arch = "sparc",
-                  target_arch = "sparc64")))]
-    const NR_GETRANDOM: libc::c_long = 0;
-
-    fn getrandom(buf: &mut [u8], blocking: bool) -> libc::c_long {
-        const GRND_NONBLOCK: libc::c_uint = 0x0001;
-
-        if NR_GETRANDOM == 0 { return -1 };
-
-        unsafe {
-            libc::syscall(NR_GETRANDOM, buf.as_mut_ptr(), buf.len(),
-                          if blocking { 0 } else { GRND_NONBLOCK })
-        }
-    }
-
-    fn getrandom_try_fill(dest: &mut [u8], blocking: bool) -> Result<(), Error> {
-        let mut read = 0;
-        while read < dest.len() {
-            let result = getrandom(&mut dest[read..], blocking);
-            if result == -1 {
-                let err = io::Error::last_os_error();
-                let kind = err.kind();
-                if kind == io::ErrorKind::Interrupted {
-                    continue;
-                } else if kind == io::ErrorKind::WouldBlock {
-                    return Err(Error::with_cause(
-                        ErrorKind::NotReady,
-                        "getrandom not ready",
-                        err,
-                    ));
-                } else {
-                    return Err(Error::with_cause(
-                        ErrorKind::Unavailable,
-                        "unexpected getrandom error",
-                        err,
-                    ));
-                }
-            } else {
-                read += result as usize;
-            }
-        }
-        Ok(())
-    }
-
-    fn is_getrandom_available() -> bool {
-        static CHECKER: Once = ONCE_INIT;
-        static AVAILABLE: AtomicBool = ATOMIC_BOOL_INIT;
-
-        if NR_GETRANDOM == 0 { return false };
-
-        CHECKER.call_once(|| {
-            debug!("OsRng: testing getrandom");
-            let mut buf: [u8; 0] = [];
-            let result = getrandom(&mut buf, false);
-            let available = if result == -1 {
-                let err = io::Error::last_os_error().raw_os_error();
-                err != Some(libc::ENOSYS)
-            } else {
-                true
-            };
-            AVAILABLE.store(available, Ordering::Relaxed);
-            info!("OsRng: using {}", if available { "getrandom" } else { "/dev/urandom" });
-        });
-
-        AVAILABLE.load(Ordering::Relaxed)
-    }
-}
-
-
-#[cfg(target_os = "netbsd")]
-mod imp {
-    use Error;
-    use super::random_device;
-    use super::OsRngImpl;
-
-    use std::fs::File;
-    use std::io::Read;
-    use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng { initialized: bool }
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            random_device::open("/dev/urandom", &|p| File::open(p))?;
-            Ok(OsRng { initialized: false })
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            random_device::read(dest)
-        }
-
-        // Read a single byte from `/dev/random` to determine if the OS RNG is
-        // already seeded. NetBSD always blocks if not yet ready.
-        fn test_initialized(&mut self, dest: &mut [u8], _blocking: bool)
-            -> Result<usize, Error>
-        {
-            static OS_RNG_INITIALIZED: AtomicBool = ATOMIC_BOOL_INIT;
-            if !self.initialized {
-                self.initialized = OS_RNG_INITIALIZED.load(Ordering::Relaxed);
-            }
-            if self.initialized { return Ok(0); }
-
-            info!("OsRng: testing random device /dev/random");
-            let mut file =
-                File::open("/dev/random").map_err(random_device::map_err)?;
-            file.read(&mut dest[..1]).map_err(random_device::map_err)?;
-
-            OS_RNG_INITIALIZED.store(true, Ordering::Relaxed);
-            self.initialized = true;
-            Ok(1)
-        }
-
-        fn method_str(&self) -> &'static str { "/dev/urandom" }
-    }
-}
-
-
-#[cfg(any(target_os = "dragonfly",
-          target_os = "haiku",
-          target_os = "emscripten"))]
-mod imp {
-    use Error;
-    use super::random_device;
-    use super::OsRngImpl;
-    use std::fs::File;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng();
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            random_device::open("/dev/random", &|p| File::open(p))?;
-            Ok(OsRng())
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            random_device::read(dest)
-        }
-
-        #[cfg(target_os = "emscripten")]
-        fn max_chunk_size(&self) -> usize {
-            // `Crypto.getRandomValues` documents `dest` should be at most 65536
-            // bytes. `crypto.randomBytes` documents: "To minimize threadpool
-            // task length variation, partition large randomBytes requests when
-            // doing so as part of fulfilling a client request.
-            65536
-        }
-
-        fn method_str(&self) -> &'static str { "/dev/random" }
-    }
-}
-
-
-// Read from `/dev/random`, with chunks of limited size (1040 bytes).
-// `/dev/random` uses the Hash_DRBG with SHA512 algorithm from NIST SP 800-90A.
-// `/dev/urandom` uses the FIPS 186-2 algorithm, which is considered less
-// secure. We choose to read from `/dev/random`.
-//
-// Since Solaris 11.3 the `getrandom` syscall is available. To make sure we can
-// compile on both Solaris and on OpenSolaris derivatives, that do not have the
-// function, we do a direct syscall instead of calling a library function.
-//
-// We have no way to differentiate between Solaris, illumos, SmartOS, etc.
-#[cfg(target_os = "solaris")]
-mod imp {
-    extern crate libc;
-
-    use {Error, ErrorKind};
-    use super::random_device;
-    use super::OsRngImpl;
-
-    use std::io;
-    use std::io::Read;
-    use std::fs::{File, OpenOptions};
-    use std::os::unix::fs::OpenOptionsExt;
-    use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng {
-        method: OsRngMethod,
-        initialized: bool,
-    }
-
-    #[derive(Clone, Debug)]
-    enum OsRngMethod {
-        GetRandom,
-        RandomDevice,
-    }
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            if is_getrandom_available() {
-                return Ok(OsRng { method: OsRngMethod::GetRandom,
-                                  initialized: false });
-            }
-            let open = |p| OpenOptions::new()
-                .read(true)
-                .custom_flags(libc::O_NONBLOCK)
-                .open(p);
-            random_device::open("/dev/random", &open)?;
-            Ok(OsRng { method: OsRngMethod::RandomDevice, initialized: false })
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            match self.method {
-                OsRngMethod::GetRandom => getrandom_try_fill(dest, false),
-                OsRngMethod::RandomDevice => random_device::read(dest),
-            }
-        }
-
-        fn test_initialized(&mut self, dest: &mut [u8], blocking: bool)
-            -> Result<usize, Error>
-        {
-            static OS_RNG_INITIALIZED: AtomicBool = ATOMIC_BOOL_INIT;
-            if !self.initialized {
-                self.initialized = OS_RNG_INITIALIZED.load(Ordering::Relaxed);
-            }
-            if self.initialized { return Ok(0); }
-
-            let chunk_len = ::core::cmp::min(1024, dest.len());
-            let dest = &mut dest[..chunk_len];
-
-            match self.method {
-                OsRngMethod::GetRandom => getrandom_try_fill(dest, blocking)?,
-                OsRngMethod::RandomDevice => {
-                    if blocking {
-                        info!("OsRng: testing random device /dev/random");
-                        // We already have a non-blocking handle, but now need a
-                        // blocking one. Not much choice except opening it twice
-                        let mut file = File::open("/dev/random")
-                            .map_err(random_device::map_err)?;
-                        file.read(dest).map_err(random_device::map_err)?;
-                    } else {
-                        self.fill_chunk(dest)?;
-                    }
-                }
-            };
-            OS_RNG_INITIALIZED.store(true, Ordering::Relaxed);
-            self.initialized = true;
-            Ok(chunk_len)
-        }
-
-        fn max_chunk_size(&self) -> usize {
-            // The documentation says 1024 is the maximum for getrandom, but
-            // 1040 for /dev/random.
-            1024
-        }
-
-        fn method_str(&self) -> &'static str {
-            match self.method {
-                OsRngMethod::GetRandom => "getrandom",
-                OsRngMethod::RandomDevice => "/dev/random",
-            }
-        }
-    }
-
-    fn getrandom(buf: &mut [u8], blocking: bool) -> libc::c_long {
-        extern "C" {
-            fn syscall(number: libc::c_long, ...) -> libc::c_long;
-        }
-
-        const SYS_GETRANDOM: libc::c_long = 143;
-        const GRND_NONBLOCK: libc::c_uint = 0x0001;
-        const GRND_RANDOM: libc::c_uint = 0x0002;
-
-        unsafe {
-            syscall(SYS_GETRANDOM, buf.as_mut_ptr(), buf.len(),
-                    if blocking { 0 } else { GRND_NONBLOCK } | GRND_RANDOM)
-        }
-    }
-
-    fn getrandom_try_fill(dest: &mut [u8], blocking: bool) -> Result<(), Error> {
-        let result = getrandom(dest, blocking);
-        if result == -1 || result == 0 {
-            let err = io::Error::last_os_error();
-            let kind = err.kind();
-            if kind == io::ErrorKind::WouldBlock {
-                return Err(Error::with_cause(
-                    ErrorKind::NotReady,
-                    "getrandom not ready",
-                    err,
-                ));
-            } else {
-                return Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "unexpected getrandom error",
-                    err,
-                ));
-            }
-        } else if result != dest.len() as i64 {
-            return Err(Error::new(ErrorKind::Unavailable,
-                                  "unexpected getrandom error"));
-        }
-        Ok(())
-    }
-
-    fn is_getrandom_available() -> bool {
-        use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
-        use std::sync::{Once, ONCE_INIT};
-
-        static CHECKER: Once = ONCE_INIT;
-        static AVAILABLE: AtomicBool = ATOMIC_BOOL_INIT;
-
-        CHECKER.call_once(|| {
-            debug!("OsRng: testing getrandom");
-            let mut buf: [u8; 0] = [];
-            let result = getrandom(&mut buf, false);
-            let available = if result == -1 {
-                let err = io::Error::last_os_error().raw_os_error();
-                err != Some(libc::ENOSYS)
-            } else {
-                true
-            };
-            AVAILABLE.store(available, Ordering::Relaxed);
-            info!("OsRng: using {}", if available { "getrandom" } else { "/dev/random" });
-        });
-
-        AVAILABLE.load(Ordering::Relaxed)
-    }
-}
-
-
-#[cfg(target_os = "cloudabi")]
-mod imp {
-    extern crate cloudabi;
-
-    use std::io;
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let errno = unsafe { cloudabi::random_get(dest) };
-            if errno == cloudabi::errno::SUCCESS {
-                Ok(())
-            } else {
-                // Cloudlibc provides its own `strerror` implementation so we
-                // can use `from_raw_os_error` here.
-                Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "random_get() system call failed",
-                    io::Error::from_raw_os_error(errno as i32),
-                ))
-            }
-        }
-
-        fn method_str(&self) -> &'static str { "cloudabi::random_get" }
-    }
-}
-
-
-#[cfg(any(target_os = "macos", target_os = "ios"))]
-mod imp {
-    extern crate libc;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    use std::io;
-    use self::libc::{c_int, size_t};
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    enum SecRandom {}
-
-    #[allow(non_upper_case_globals)]
-    const kSecRandomDefault: *const SecRandom = 0 as *const SecRandom;
-
-    #[link(name = "Security", kind = "framework")]
-    extern {
-        fn SecRandomCopyBytes(rnd: *const SecRandom,
-                              count: size_t, bytes: *mut u8) -> c_int;
-    }
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let ret = unsafe {
-                SecRandomCopyBytes(kSecRandomDefault,
-                                   dest.len() as size_t,
-                                   dest.as_mut_ptr())
-            };
-            if ret == -1 {
-                Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "couldn't generate random bytes",
-                    io::Error::last_os_error()))
-            } else {
-                Ok(())
-            }
-        }
-
-        fn method_str(&self) -> &'static str { "SecRandomCopyBytes" }
-    }
-}
-
-
-#[cfg(target_os = "freebsd")]
-mod imp {
-    extern crate libc;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    use std::ptr;
-    use std::io;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let mib = [libc::CTL_KERN, libc::KERN_ARND];
-            let mut len = dest.len();
-            let ret = unsafe {
-                libc::sysctl(mib.as_ptr(), mib.len() as libc::c_uint,
-                             dest.as_mut_ptr() as *mut _, &mut len,
-                             ptr::null(), 0)
-            };
-            if ret == -1 || len != dest.len() {
-                return Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "kern.arandom sysctl failed",
-                    io::Error::last_os_error()));
-            }
-            Ok(())
-        }
-
-        fn max_chunk_size(&self) -> usize { 256 }
-
-        fn method_str(&self) -> &'static str { "kern.arandom" }
-    }
-}
-
-
-#[cfg(any(target_os = "openbsd", target_os = "bitrig"))]
-mod imp {
-    extern crate libc;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    use std::io;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let ret = unsafe {
-                libc::getentropy(dest.as_mut_ptr() as *mut libc::c_void, dest.len())
-            };
-            if ret == -1 {
-                return Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "getentropy failed",
-                    io::Error::last_os_error()));
-            }
-            Ok(())
-        }
-
-        fn max_chunk_size(&self) -> usize { 256 }
-
-        fn method_str(&self) -> &'static str { "getentropy" }
-    }
-}
-
-
-#[cfg(target_os = "redox")]
-mod imp {
-    use Error;
-    use super::random_device;
-    use super::OsRngImpl;
-    use std::fs::File;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng();
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            random_device::open("rand:", &|p| File::open(p))?;
-            Ok(OsRng())
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            random_device::read(dest)
-        }
-
-        fn method_str(&self) -> &'static str { "'rand:'" }
-    }
-}
-
-
-#[cfg(target_os = "fuchsia")]
-mod imp {
-    extern crate fuchsia_zircon;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let mut read = 0;
-            while read < dest.len() {
-                match fuchsia_zircon::cprng_draw(&mut dest[read..]) {
-                    Ok(actual) => read += actual,
-                    Err(e) => {
-                        return Err(Error::with_cause(
-                            ErrorKind::Unavailable,
-                            "cprng_draw failed",
-                            e.into_io_error()));
-                    }
-                };
-            }
-            Ok(())
-        }
-
-        fn max_chunk_size(&self) -> usize {
-            fuchsia_zircon::sys::ZX_CPRNG_DRAW_MAX_LEN
-        }
-
-        fn method_str(&self) -> &'static str { "cprng_draw" }
-    }
-}
-
-
-#[cfg(windows)]
-mod imp {
-    extern crate winapi;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    use std::io;
-
-    use self::winapi::shared::minwindef::ULONG;
-    use self::winapi::um::ntsecapi::RtlGenRandom;
-    use self::winapi::um::winnt::PVOID;
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng;
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> { Ok(OsRng) }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            let ret = unsafe {
-                RtlGenRandom(dest.as_mut_ptr() as PVOID, dest.len() as ULONG)
-            };
-            if ret == 0 {
-                return Err(Error::with_cause(
-                    ErrorKind::Unavailable,
-                    "couldn't generate random bytes",
-                    io::Error::last_os_error()));
-            }
-            Ok(())
-        }
-
-        fn max_chunk_size(&self) -> usize { <ULONG>::max_value() as usize }
-
-        fn method_str(&self) -> &'static str { "RtlGenRandom" }
-    }
-}
-
-
-#[cfg(all(target_arch = "wasm32",
-          not(target_os = "emscripten"),
-          feature = "stdweb"))]
-mod imp {
-    use std::mem;
-    use stdweb::unstable::TryInto;
-    use stdweb::web::error::Error as WebError;
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    #[derive(Clone, Debug)]
-    enum OsRngMethod {
-        Browser,
-        Node
-    }
-
-    #[derive(Clone, Debug)]
-    pub struct OsRng(OsRngMethod);
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            let result = js! {
-                try {
-                    if (
-                        typeof self === "object" &&
-                        typeof self.crypto === "object" &&
-                        typeof self.crypto.getRandomValues === "function"
-                    ) {
-                        return { success: true, ty: 1 };
-                    }
-
-                    if (typeof require("crypto").randomBytes === "function") {
-                        return { success: true, ty: 2 };
-                    }
-
-                    return { success: false, error: new Error("not supported") };
-                } catch(err) {
-                    return { success: false, error: err };
-                }
-            };
-
-            if js!{ return @{ result.as_ref() }.success } == true {
-                let ty = js!{ return @{ result }.ty };
-
-                if ty == 1 { Ok(OsRng(OsRngMethod::Browser)) }
-                else if ty == 2 { Ok(OsRng(OsRngMethod::Node)) }
-                else { unreachable!() }
-            } else {
-                let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
-                Err(Error::with_cause(ErrorKind::Unavailable, "WASM Error", err))
-            }
-        }
-
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            assert_eq!(mem::size_of::<usize>(), 4);
-
-            let len = dest.len() as u32;
-            let ptr = dest.as_mut_ptr() as i32;
-
-            let result = match self.0 {
-                OsRngMethod::Browser => js! {
-                    try {
-                        let array = new Uint8Array(@{ len });
-                        self.crypto.getRandomValues(array);
-                        HEAPU8.set(array, @{ ptr });
-
-                        return { success: true };
-                    } catch(err) {
-                        return { success: false, error: err };
-                    }
-                },
-                OsRngMethod::Node => js! {
-                    try {
-                        let bytes = require("crypto").randomBytes(@{ len });
-                        HEAPU8.set(new Uint8Array(bytes), @{ ptr });
-
-                        return { success: true };
-                    } catch(err) {
-                        return { success: false, error: err };
-                    }
-                }
-            };
-
-            if js!{ return @{ result.as_ref() }.success } == true {
-                Ok(())
-            } else {
-                let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
-                Err(Error::with_cause(ErrorKind::Unexpected, "WASM Error", err))
-            }
-        }
-
-        fn max_chunk_size(&self) -> usize { 65536 }
-
-        fn method_str(&self) -> &'static str {
-            match self.0 {
-                OsRngMethod::Browser => "Crypto.getRandomValues",
-                OsRngMethod::Node => "crypto.randomBytes",
-            }
-        }
-    }
-}
-
-#[cfg(all(target_arch = "wasm32",
-          not(target_os = "emscripten"),
-          not(feature = "stdweb"),
-          feature = "wasm-bindgen"))]
-mod imp {
-    use __wbg_shims::*;
-
-    use {Error, ErrorKind};
-    use super::OsRngImpl;
-
-    #[derive(Clone, Debug)]
-    pub enum OsRng {
-        Node(NodeCrypto),
-        Browser(BrowserCrypto),
-    }
-
-    impl OsRngImpl for OsRng {
-        fn new() -> Result<OsRng, Error> {
-            // First up we need to detect if we're running in node.js or a
-            // browser. To do this we get ahold of the `this` object (in a bit
-            // of a roundabout fashion).
-            //
-            // Once we have `this` we look at its `self` property, which is
-            // only defined on the web (either a main window or web worker).
-            let this = Function::new("return this").call(&JsValue::undefined());
-            assert!(this != JsValue::undefined());
-            let this = This::from(this);
-            let is_browser = this.self_() != JsValue::undefined();
-
-            if !is_browser {
-                return Ok(OsRng::Node(node_require("crypto")))
-            }
-
-            // If `self` is defined then we're in a browser somehow (main window
-            // or web worker). Here we want to try to use
-            // `crypto.getRandomValues`, but if `crypto` isn't defined we assume
-            // we're in an older web browser and the OS RNG isn't available.
-            let crypto = this.crypto();
-            if crypto.is_undefined() {
-                let msg = "self.crypto is undefined";
-                return Err(Error::new(ErrorKind::Unavailable, msg))
-            }
-
-            // Test if `crypto.getRandomValues` is undefined as well
-            let crypto: BrowserCrypto = crypto.into();
-            if crypto.get_random_values_fn().is_undefined() {
-                let msg = "crypto.getRandomValues is undefined";
-                return Err(Error::new(ErrorKind::Unavailable, msg))
-            }
-
-            // Ok! `self.crypto.getRandomValues` is a defined value, so let's
-            // assume we can do browser crypto.
-            Ok(OsRng::Browser(crypto))
-        }
-
-        fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
-            match *self {
-                OsRng::Node(ref n) => n.random_fill_sync(dest),
-                OsRng::Browser(ref n) => n.get_random_values(dest),
-            }
-            Ok(())
-        }
-
-        fn max_chunk_size(&self) -> usize {
-            match *self {
-                OsRng::Node(_) => usize::max_value(),
-                OsRng::Browser(_) => {
-                    // see https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues
-                    //
-                    // where it says:
-                    //
-                    // > A QuotaExceededError DOMException is thrown if the
-                    // > requested length is greater than 65536 bytes.
-                    65536
-                }
-            }
-        }
-
-        fn method_str(&self) -> &'static str {
-            match *self {
-                OsRng::Node(_) => "crypto.randomFillSync",
-                OsRng::Browser(_) => "crypto.getRandomValues",
-            }
-        }
-    }
-}
-
-
-#[cfg(test)]
-mod test {
-    use RngCore;
-    use super::OsRng;
-
-    #[test]
-    fn test_os_rng() {
-        let mut r = OsRng::new().unwrap();
-
-        r.next_u32();
-        r.next_u64();
-
-        let mut v1 = [0u8; 1000];
-        r.fill_bytes(&mut v1);
-
-        let mut v2 = [0u8; 1000];
-        r.fill_bytes(&mut v2);
-
-        let mut n_diff_bits = 0;
-        for i in 0..v1.len() {
-            n_diff_bits += (v1[i] ^ v2[i]).count_ones();
-        }
-
-        // Check at least 1 bit per byte differs. p(failure) < 1e-1000 with random input.
-        assert!(n_diff_bits >= v1.len() as u32);
-    }
-
-    #[test]
-    fn test_os_rng_empty() {
-        let mut r = OsRng::new().unwrap();
-
-        let mut empty = [0u8; 0];
-        r.fill_bytes(&mut empty);
-    }
-
-    #[test]
-    fn test_os_rng_huge() {
-        let mut r = OsRng::new().unwrap();
-
-        let mut huge = [0u8; 100_000];
-        r.fill_bytes(&mut huge);
-    }
-
-    #[cfg(not(any(target_arch = "wasm32", target_arch = "asmjs")))]
-    #[test]
-    fn test_os_rng_tasks() {
-        use std::sync::mpsc::channel;
-        use std::thread;
-
-        let mut txs = vec!();
-        for _ in 0..20 {
-            let (tx, rx) = channel();
-            txs.push(tx);
-
-            thread::spawn(move|| {
-                // wait until all the tasks are ready to go.
-                rx.recv().unwrap();
-
-                // deschedule to attempt to interleave things as much
-                // as possible (XXX: is this a good test?)
-                let mut r = OsRng::new().unwrap();
-                thread::yield_now();
-                let mut v = [0u8; 1000];
-
-                for _ in 0..100 {
-                    r.next_u32();
-                    thread::yield_now();
-                    r.next_u64();
-                    thread::yield_now();
-                    r.fill_bytes(&mut v);
-                    thread::yield_now();
-                }
-            });
-        }
-
-        // start all the tasks
-        for tx in txs.iter() {
-            tx.send(()).unwrap();
-        }
-    }
-}
diff --git a/rand/src/rngs/small.rs b/rand/src/rngs/small.rs
index e74a83e..b652c8c 100644
--- a/rand/src/rngs/small.rs
+++ b/rand/src/rngs/small.rs
@@ -10,9 +10,9 @@
 
 use {RngCore, SeedableRng, Error};
 
-#[cfg(all(rust_1_26, target_pointer_width = "64"))]
+#[cfg(all(all(rustc_1_26, not(target_os = "emscripten")), target_pointer_width = "64"))]
 type Rng = ::rand_pcg::Pcg64Mcg;
-#[cfg(not(all(rust_1_26, target_pointer_width = "64")))]
+#[cfg(not(all(all(rustc_1_26, not(target_os = "emscripten")), target_pointer_width = "64")))]
 type Rng = ::rand_pcg::Pcg32;
 
 /// An RNG recommended when small state, cheap initialization and good
diff --git a/rand/src/rngs/thread.rs b/rand/src/rngs/thread.rs
index ff772e3..7977d85 100644
--- a/rand/src/rngs/thread.rs
+++ b/rand/src/rngs/thread.rs
@@ -87,10 +87,11 @@ thread_local!(
     }
 );
 
-/// Retrieve the lazily-initialized thread-local random number
-/// generator, seeded by the system. Intended to be used in method
-/// chaining style, e.g. `thread_rng().gen::<i32>()`, or cached locally, e.g.
-/// `let mut rng = thread_rng();`.
+/// Retrieve the lazily-initialized thread-local random number generator,
+/// seeded by the system. Intended to be used in method chaining style,
+/// e.g. `thread_rng().gen::<i32>()`, or cached locally, e.g.
+/// `let mut rng = thread_rng();`.  Invoked by the `Default` trait, making
+/// `ThreadRng::default()` equivelent.
 ///
 /// For more information see [`ThreadRng`].
 ///
@@ -99,6 +100,12 @@ pub fn thread_rng() -> ThreadRng {
     ThreadRng { rng: THREAD_RNG_KEY.with(|t| t.get()) }
 }
 
+impl Default for ThreadRng {
+    fn default() -> ThreadRng {
+        ::prelude::thread_rng()
+    }
+}
+
 impl RngCore for ThreadRng {
     #[inline(always)]
     fn next_u32(&mut self) -> u32 {
@@ -125,7 +132,6 @@ impl CryptoRng for ThreadRng {}
 #[cfg(test)]
 mod test {
     #[test]
-    #[cfg(not(feature="stdweb"))]
     fn test_thread_rng() {
         use Rng;
         let mut r = ::thread_rng();