Struct rand_core::block::BlockRng

pub struct BlockRng<R> where
    R: BlockRngCore + ?Sized,  {
    pub core: R,
    // some fields omitted
}

A wrapper type implementing [RngCore] for some type implementing [BlockRngCore] with u32 array buffer; i.e. this can be used to implement a full RNG from just a generate function.

The core field may be accessed directly but the results buffer may not. PRNG implementations can simply use a type alias (pub type MyRng = BlockRng<MyRngCore>;) but might prefer to use a wrapper type (pub struct MyRng(BlockRng<MyRngCore>);); the latter must re-implement RngCore but hides the implementation details and allows extra functionality to be defined on the RNG (e.g. impl MyRng { fn set_stream(...){...} }).

BlockRng has heavily optimized implementations of the [RngCore] methods reading values from the results buffer, as well as calling [BlockRngCore::generate] directly on the output array when fill_bytes / try_fill_bytes is called on a large array. These methods also handle the bookkeeping of when to generate a new batch of values.

No whole generated u32 values are thown away and all values are consumed in-order. next_u32 simply takes the next available u32 value. next_u64 is implemented by combining two u32 values, least significant first. fill_bytes and try_fill_bytes consume a whole number of u32 values, converting each u32 to a byte slice in little-endian order. If the requested byte length is not a multiple of 4, some bytes will be discarded.

See also [BlockRng64] which uses u64 array buffers. Currently there is no direct support for other buffer types.

For easy initialization BlockRng also implements [SeedableRng].

Fields

core: R

The core part of the RNG, implementing the generate function.

Methods

impl<R> BlockRng<R> where
    R: BlockRngCore, 

pub fn new(core: R) -> BlockRng<R>

Create a new BlockRng from an existing RNG implementing BlockRngCore. Results will be generated on first use.

pub fn index(&self) -> usize

Get the index into the result buffer.

If this is equal to or larger than the size of the result buffer then the buffer is "empty" and generate() must be called to produce new results.

pub fn reset(&mut self)

Reset the number of available results. This will force a new set of results to be generated on next use.

pub fn generate_and_set(&mut self, index: usize)

Generate a new set of results immediately, setting the index to the given value.

Trait Implementations

impl<R> Debug for BlockRng<R> where
    R: BlockRngCore + Debug, 

fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.

impl<R> CryptoRng for BlockRng<R> where
    R: BlockRngCore + CryptoRng, 

impl<R> Clone for BlockRng<R> where
    R: BlockRngCore + Clone + ?Sized,
    <R as BlockRngCore>::Results: Clone, 

fn clone(&self) -> BlockRng<R>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<R> RngCore for BlockRng<R> where
    R: BlockRngCore<Item = u32>,
    <R as BlockRngCore>::Results: AsRef<[u32]>,
    <R as BlockRngCore>::Results: AsMut<[u32]>, 

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<R> SeedableRng for BlockRng<R> where
    R: BlockRngCore + SeedableRng, 

type Seed = <R 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: <BlockRng<R> as SeedableRng>::Seed) -> BlockRng<R>

Create a new PRNG using the given seed.

fn seed_from_u64(seed: u64) -> BlockRng<R>

Create a new PRNG using a u64 seed.

fn from_rng<S>(rng: S) -> Result<BlockRng<R>, Error> where
    S: RngCore, 

Create a new PRNG seeded from another Rng.