Struct rand::rngs::SmallRng

[+] Show declaration

pub struct SmallRng(_);

[−] Expand description

An RNG recommended when small state, cheap initialization and good performance are required. 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 for StdRng.

Reproducibility of output from this generator is however not required, thus future library versions may use a different internal generator with different output. Further, this generator may not be portable and can produce different output depending on the architecture. If you require reproducible output, use a named RNG. Refer to The Book.

The current algorithm is Pcg64Mcg on 64-bit platforms with Rust version 1.26 and later, or Pcg32 otherwise. Both are found in the rand_pcg crate.

Examples

Initializing SmallRng with a random seed can be done using FromEntropy:

use rand::FromEntropy;
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())
    .take(10)
    .collect();

Trait Implementations

impl Clone for SmallRng[+]

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fn clone(&self) -> SmallRng[−]

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)[−]

Performs copy-assignment from source.

impl Debug for SmallRng[+]

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fn fmt(&self, f: &mut Formatter) -> Result[−]

Formats the value using the given formatter.

impl RngCore for SmallRng[+]

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fn next_u32(&mut self) -> u32[−]

Return the next random u32.

fn next_u64(&mut self) -> u64[−]

Return the next random u64.

fn fill_bytes(&mut self, dest: &mut [u8])[−]

Fill dest with random data.

fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>[−]

Fill dest entirely with random data.

impl SeedableRng for SmallRng[+]

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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).

fn from_seed(seed: Self::Seed) -> Self[−]

Create a new PRNG using the given seed.

fn from_rng<R: RngCore>(rng: R) -> Result<Self, Error>[−]

Create a new PRNG seeded from another Rng.

fn seed_from_u64(state: u64) -> Self[−]

Create a new PRNG using a u64 seed.