Use Hc128 on Emscripten

This is considered an ugly hack, but easier than making the new ChaChaRng
compatible with Emscripten. Potentially support for Emscripten will be dropped
in the future, if it doesn't get support for u128.

Author: dhardy

Cargo.toml

@@ -55,7 +55,6 @@ members = [
 
 [dependencies]
 rand_core = { path = "rand_core", version = "0.4" }
-rand_chacha = { path = "rand_chacha", version = "0.2" }
 rand_pcg = { path = "rand_pcg", version = "0.1", optional = true }
 # Do not depend on 'getrandom_package' directly; use the 'getrandom' feature!
 getrandom_package = { version = "0.1.1", package = "getrandom", optional = true }
@@ -72,6 +71,13 @@ features = ["into_bits"]
 # Used for fork protection (reseeding.rs)
 libc = { version = "0.2.22", default-features = false }
 
+# Emscripten does not support 128-bit integers, which are used by ChaCha code.
+# We work around this by using a different RNG.
+[target.'cfg(not(target_os = "emscripten"))'.dependencies]
+rand_chacha = { path = "rand_chacha", version = "0.2" }
+[target.'cfg(target_os = "emscripten")'.dependencies]
+rand_hc = { path = "rand_hc", version = "0.1" }
+
 [dev-dependencies]
 rand_pcg = { path = "rand_pcg", version = "0.1" }
 # Only for benches:

src/distributions/integer.rs

@@ -11,7 +11,8 @@
 use {Rng};
 use distributions::{Distribution, Standard};
 #[cfg(rustc_1_28)]
-use core::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU128, NonZeroUsize};
+use core::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroUsize};
+#[cfg(not(target_os = "emscripten"))] use core::num::NonZeroU128;
 #[cfg(feature="simd_support")]
 use packed_simd::*;
 #[cfg(all(target_arch = "x86", feature="nightly"))]

src/lib.rs

@@ -62,7 +62,8 @@
 extern crate getrandom_package as getrandom;
 
 extern crate rand_core;
-extern crate rand_chacha;
+#[cfg(not(target_os = "emscripten"))] extern crate rand_chacha;
+#[cfg(target_os = "emscripten")] extern crate rand_hc;
 #[cfg(feature="small_rng")] extern crate rand_pcg;
 
 #[cfg(feature = "log")] #[macro_use] extern crate log;

src/rngs/adapter/reseeding.rs

@@ -324,14 +324,14 @@ mod fork {
 #[cfg(test)]
 mod test {
     use {Rng, SeedableRng};
-    use rand_chacha::ChaCha8Core;
+    use rngs::std::Core;
     use rngs::mock::StepRng;
     use super::ReseedingRng;
 
     #[test]
     fn test_reseeding() {
         let mut zero = StepRng::new(0, 0);
-        let rng = ChaCha8Core::from_rng(&mut zero).unwrap();
+        let rng = Core::from_rng(&mut zero).unwrap();
         let thresh = 1; // reseed every time the buffer is exhausted
         let mut reseeding = ReseedingRng::new(rng, thresh, zero);
 
@@ -351,7 +351,7 @@ mod test {
     #[test]
     fn test_clone_reseeding() {
         let mut zero = StepRng::new(0, 0);
-        let rng = ChaCha8Core::from_rng(&mut zero).unwrap();
+        let rng = Core::from_rng(&mut zero).unwrap();
         let mut rng1 = ReseedingRng::new(rng, 32*4, zero);
 
         let first: u32 = rng1.gen();

src/rngs/std.rs

@@ -9,7 +9,11 @@
 //! The standard RNG
 
 use {RngCore, CryptoRng, Error, SeedableRng};
-use rand_chacha::ChaCha20Rng;
+
+#[cfg(target_os = "emscripten")] pub(crate) use rand_hc::Hc128Core as Core;
+#[cfg(not(target_os = "emscripten"))] pub(crate) use rand_chacha::ChaCha20Core as Core;
+#[cfg(target_os = "emscripten")] use rand_hc::Hc128Rng as Rng;
+#[cfg(not(target_os = "emscripten"))] use rand_chacha::ChaCha20Rng as Rng;
 
 /// The standard RNG. The PRNG algorithm in `StdRng` is chosen to be efficient
 /// on the current platform, to be statistically strong and unpredictable
@@ -27,7 +31,7 @@ use rand_chacha::ChaCha20Rng;
 ///
 /// [rand_chacha]: https://crates.io/crates/rand_chacha
 #[derive(Clone, Debug)]
-pub struct StdRng(ChaCha20Rng);
+pub struct StdRng(Rng);
 
 impl RngCore for StdRng {
     #[inline(always)]
@@ -50,14 +54,14 @@ impl RngCore for StdRng {
 }
 
 impl SeedableRng for StdRng {
-    type Seed = <ChaCha20Rng as SeedableRng>::Seed;
+    type Seed = <Rng as SeedableRng>::Seed;
 
     fn from_seed(seed: Self::Seed) -> Self {
-        StdRng(ChaCha20Rng::from_seed(seed))
+        StdRng(Rng::from_seed(seed))
     }
 
     fn from_rng<R: RngCore>(rng: R) -> Result<Self, Error> {
-        ChaCha20Rng::from_rng(rng).map(StdRng)
+        Rng::from_rng(rng).map(StdRng)
     }
 }
 

src/rngs/thread.rs

@@ -13,7 +13,7 @@ use std::cell::UnsafeCell;
 use {RngCore, CryptoRng, SeedableRng, Error};
 use rngs::adapter::ReseedingRng;
 use rngs::OsRng;
-use rand_chacha::ChaCha20Core;
+use super::std::Core;
 
 // Rationale for using `UnsafeCell` in `ThreadRng`:
 //
@@ -58,12 +58,12 @@ const THREAD_RNG_RESEED_THRESHOLD: u64 = 1024 * 64;
 #[derive(Copy, Clone, Debug)]
 pub struct ThreadRng {
     // use of raw pointer implies type is neither Send nor Sync
-    rng: *mut ReseedingRng<ChaCha20Core, OsRng>,
+    rng: *mut ReseedingRng<Core, OsRng>,
 }
 
 thread_local!(
-    static THREAD_RNG_KEY: UnsafeCell<ReseedingRng<ChaCha20Core, OsRng>> = {
-        let r = ChaCha20Core::from_rng(OsRng).unwrap_or_else(|err|
+    static THREAD_RNG_KEY: UnsafeCell<ReseedingRng<Core, OsRng>> = {
+        let r = Core::from_rng(OsRng).unwrap_or_else(|err|
                 panic!("could not initialize thread_rng: {}", err));
         let rng = ReseedingRng::new(r,
                                     THREAD_RNG_RESEED_THRESHOLD,