Struct StdRng

pub struct StdRng(/* private fields */);

A strong, fast (amortized), non-portable RNG

This is the “standard” 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 portable version, use the rand_chacha crate directly.)
• CSPRNG: statistically good quality of randomness and unpredictable
• Fast (amortized): the RNG is fast for bulk generation, but the cost of method calls is not consistent due to usage of an output buffer.

The current algorithm used is the ChaCha block cipher with 12 rounds. Please see this relevant rand issue for the discussion. This may change as new evidence of cipher security and performance becomes available.

Seeding (construction)

This generator implements the SeedableRng trait. Any method may be used, but note that seed_from_u64 is not suitable for usage where security is important. Also note that, even with a fixed seed, output is not portable.

Using a fresh seed direct from the OS is the most secure option:

let rng = StdRng::from_os_rng();

Seeding via rand::rng() may be faster:

let rng = StdRng::from_rng(&mut rand::rng());

Any SeedableRng method may be used, but note that seed_from_u64 is not suitable where security is required. 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.

Trait Implementations

impl Clone for StdRng

fn clone(&self) -> StdRng

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for StdRng

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

Formats the value using the given formatter.

impl PartialEq for StdRng

fn eq(&self, other: &StdRng) -> 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 StdRng

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, dst: &mut [u8])

Fill dest with random data.

impl SeedableRng for StdRng

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 CryptoRng for StdRng

impl Eq for StdRng

impl StructuralPartialEq for StdRng