88 lines
2.4 KiB
Rust
88 lines
2.4 KiB
Rust
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//! works just like rand::thread_rng but with a rng that is **not** cryptographically secure
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//!
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//! TODO: currently uses Xoshiro256Plus. do some benchmarks
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pub use rand;
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use rand::{Error, Rng, RngCore, SeedableRng};
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use rand_xoshiro::Xoshiro256Plus;
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use std::{cell::UnsafeCell, rc::Rc};
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#[derive(Clone, Debug)]
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pub struct ThreadFastRng {
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// Rc is explicitly !Send and !Sync
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rng: Rc<UnsafeCell<Xoshiro256Plus>>,
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}
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thread_local! {
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pub static THREAD_FAST_RNG: Rc<UnsafeCell<Xoshiro256Plus>> = {
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// use a cryptographically secure rng for the seed
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let mut crypto_rng = rand::thread_rng();
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let seed = crypto_rng.gen();
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// use a fast rng for things that aren't cryptography
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let rng = Xoshiro256Plus::seed_from_u64(seed);
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Rc::new(UnsafeCell::new(rng))
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};
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}
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pub fn thread_fast_rng() -> ThreadFastRng {
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let rng = THREAD_FAST_RNG.with(|t| t.clone());
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ThreadFastRng { rng }
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}
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impl Default for ThreadFastRng {
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fn default() -> Self {
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thread_fast_rng()
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}
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}
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impl RngCore for ThreadFastRng {
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#[inline(always)]
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fn next_u32(&mut self) -> u32 {
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// SAFETY: We must make sure to stop using `rng` before anyone else
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// creates another mutable reference
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let rng = unsafe { &mut *self.rng.get() };
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rng.next_u32()
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}
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#[inline(always)]
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fn next_u64(&mut self) -> u64 {
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// SAFETY: We must make sure to stop using `rng` before anyone else
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// creates another mutable reference
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let rng = unsafe { &mut *self.rng.get() };
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rng.next_u64()
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}
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fn fill_bytes(&mut self, dest: &mut [u8]) {
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// SAFETY: We must make sure to stop using `rng` before anyone else
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// creates another mutable reference
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let rng = unsafe { &mut *self.rng.get() };
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rng.fill_bytes(dest)
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}
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fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
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// SAFETY: We must make sure to stop using `rng` before anyone else
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// creates another mutable reference
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let rng = unsafe { &mut *self.rng.get() };
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rng.try_fill_bytes(dest)
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn test_thread_fast_rng() {
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let mut r = thread_fast_rng();
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r.gen::<i32>();
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assert_eq!(r.gen_range(0..1), 0);
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}
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#[test]
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fn test_thread_fast_rng_struct() {
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let mut r = ThreadFastRng::default();
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r.gen::<i32>();
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assert_eq!(r.gen_range(0..1), 0);
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}
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}
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