[][src]Struct rand::rngs::SmallRng

pub struct SmallRng(_);

A small-state, fast non-crypto PRNG

SmallRng may be a good choice when a PRNG with small state, cheap initialization, good statistical quality and good performance are required. It is not a good choice when security against prediction or reproducibility are important.

This PRNG is feature-gated: to use, you must enable the crate feature small_rng.

The algorithm is deterministic but should not be considered reproducible due to dependence on platform and possible replacement in future library versions. For a reproducible generator, use a named PRNG from an external crate, e.g. rand_pcg or rand_chacha. Refer also to The Book.

The PRNG algorithm in SmallRng is chosen to be efficient on the current platform, without consideration for cryptography or security. The size of its state is much smaller than StdRng. The current algorithm is Pcg64Mcg on 64-bit platforms and Pcg32 on 32-bit platforms. Both are implemented by the rand_pcg crate.


Initializing SmallRng with a random seed can be done using SeedableRng::from_entropy:

use rand::{Rng, SeedableRng};
use rand::rngs::SmallRng;

// Create small, cheap to initialize and fast RNG with a random seed.
// The randomness is supplied by the operating system.
let mut small_rng = SmallRng::from_entropy();

When initializing a lot of SmallRng's, using thread_rng can be more efficient:

use std::iter;
use rand::{SeedableRng, thread_rng};
use rand::rngs::SmallRng;

// Create a big, expensive to initialize and slower, but unpredictable RNG.
// This is cached and done only once per thread.
let mut thread_rng = thread_rng();
// Create small, cheap to initialize and fast RNGs with random seeds.
// One can generally assume this won't fail.
let rngs: Vec<SmallRng> = iter::repeat(())
    .map(|()| SmallRng::from_rng(&mut thread_rng).unwrap())

Trait Implementations

impl Clone for SmallRng[src]

impl Debug for SmallRng[src]

impl SeedableRng for SmallRng[src]

type Seed = <Pcg64Mcg as SeedableRng>::Seed

Seed type, which is restricted to types mutably-dereferencable as u8 arrays (we recommend [u8; N] for some N). Read more

impl RngCore for SmallRng[src]

Auto Trait Implementations

impl Unpin for SmallRng

impl Sync for SmallRng

impl Send for SmallRng

impl UnwindSafe for SmallRng

impl RefUnwindSafe for SmallRng

Blanket Implementations

impl<R> Rng for R where
    R: RngCore + ?Sized

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T> From<T> for T[src]

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> FromCast<T> for T

impl<T, U> Cast<U> for T where
    U: FromCast<T>, 

impl<T> FromBits<T> for T

impl<T, U> IntoBits<U> for T where
    U: FromBits<T>, 

impl<V, T> VZip<V> for T where
    V: MultiLane<T>,