feat: Enable using thread_rng for faster WyHash initialisation

Cargo.toml

@@ -23,10 +23,12 @@ serde1 = ["dep:serde"]
 wyhash = []
 randomised_wyhash = ["wyhash", "dep:getrandom"]
 fully_randomised_wyhash = ["randomised_wyhash"]
+threadrng_wyhash = ["dep:rand", "randomised_wyhash"]
 v4_2 = []
 
 [dependencies]
 getrandom = { version = "0.2", optional = true }
+rand = { version = "0.8", optional = true }
 rand_core = { version = "0.6", default-features = false, optional = true }
 serde = { version = "1.0", features = ["derive"], optional = true }
 

README.md

@@ -37,6 +37,7 @@ The crate will always export `WyRand` and will do so when set as `default-featur
 - **`wyhash`** - Enables `WyHash`, a fast & portable hashing algorithm. Based on the final v4 C implementation.
 - **`randomised_wyhash`** - Enables `RandomisedWyHashBuilder`, a means to source a randomised state for `WyHash` for use in collections like `HashMap`/`HashSet`. Enables `wyhash` feature if it is not already enabled.
 - **`fully_randomised_wyhash`** - Randomises not just the seed for `RandomisedWyHashBuilder`, but also the secret. Incurs a performance hit every time `WyHash` is initialised but it is more secure as a result. Enables `randomised_wyhash` if not already enabled.
+- **`threadrng_wyhash`** - Enables sourcing entropy from `rand`'s `thread_rng()` method. Much quicker than `getrandom` and best used without the `fully_randomised_wyhash` flag as the overhead of calculating new secrets dwarfs any gains in entropy sourcing. Enables `randomised_wyhash` if not already enabled. Requires `std` environments.
 - **`v4_2`** - Switches the PRNG/Hashing algorithms to use the final v4.2 implementation.
 
 ## Building for WASM/Web

src/hasher/builder.rs

@@ -46,8 +46,17 @@ impl RandomWyHashState {
 
         let mut state = [0; SIZE];
 
-        getrandom::getrandom(&mut state)
-            .expect("Failed to source entropy for WyHash randomised state");
+        #[cfg(not(feature = "threadrng_wyhash"))]
+        {
+            getrandom::getrandom(&mut state)
+                .expect("Failed to source entropy for WyHash randomised state");
+        }
+        #[cfg(feature = "threadrng_wyhash")]
+        {
+            use rand::RngCore;
+
+            rand::thread_rng().fill_bytes(&mut state);
+        }
 
         Self { state }
     }

src/lib.rs

@@ -8,9 +8,9 @@
 mod constants;
 #[cfg(feature = "wyhash")]
 mod hasher;
-mod rand;
+mod wyrand;
 mod utils;
 
 #[cfg(feature = "wyhash")]
 pub use hasher::*;
-pub use rand::WyRand;
+pub use wyrand::WyRand;