Struct SmallRng 

pub struct SmallRng(Xoshiro256PlusPlus);

A small-state, fast, non-crypto, non-portable PRNG

This is the “standard small” RNG, a generator with the following properties:

• Non-portable: any future library version may replace the algorithm and results may be platform-dependent. (For a small portable generator, use the rand_pcg or rand_xoshiro crate.)
• Non-cryptographic: output is easy to predict (insecure)
• Quality: statistically good quality
• Fast: the RNG is fast for both bulk generation and single values, with consistent cost of method calls
• Fast initialization
• Small state: little memory usage (current state size is 16-32 bytes depending on platform)

The current algorithm is Xoshiro256PlusPlus on 64-bit platforms and Xoshiro128PlusPlus on 32-bit platforms. Both are also implemented by the rand_xoshiro crate.

Seeding (construction)

This generator implements the SeedableRng trait. All methods are suitable for seeding, but note that, even with a fixed seed, output is not portable. Some suggestions:

1. To automatically seed with a unique seed, use SeedableRng::from_rng:

   use rand::SeedableRng;
   use rand::rngs::SmallRng;
   let rng = SmallRng::from_rng(&mut rand::rng());

   or SeedableRng::from_os_rng:

   let rng = SmallRng::from_os_rng();

2. To use a deterministic integral seed, use seed_from_u64. This uses a hash function internally to yield a (typically) good seed from any input.

   let rng = SmallRng::seed_from_u64(1);

3. To seed deterministically from text or other input, use rand_seeder.

See also Seeding RNGs in the book.

Generation

The generators implements RngCore and thus also Rng. See also the Random Values chapter in the book.

Tuple Fields

0: Xoshiro256PlusPlus

Trait Implementations

impl Clone for SmallRng

fn clone(&self) -> SmallRng

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SmallRng

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for SmallRng

fn eq(&self, other: &SmallRng) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl RngCore for SmallRng

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.

impl SeedableRng for SmallRng

type Seed = [u8; 32]

Seed type, which is restricted to types mutably-dereferenceable 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 seed_from_u64(state: u64) -> Self

Create a new PRNG using a u64 seed.

fn from_rng(rng: &mut impl RngCore) -> Self

Create a new PRNG seeded from an infallible Rng.

fn try_from_rng<R>(rng: &mut R) -> Result<Self, <R as TryRngCore>::Error>

where R: TryRngCore,

Create a new PRNG seeded from a potentially fallible Rng.

fn from_os_rng() -> Self

Creates a new instance of the RNG seeded via getrandom.

fn try_from_os_rng() -> Result<Self, Error>

Creates a new instance of the RNG seeded via getrandom without unwrapping potential getrandom errors.

impl Eq for SmallRng

impl StructuralPartialEq for SmallRng