Struct scuttlebutt::UniformIntegersUnderBound

pub struct UniformIntegersUnderBound { /* private fields */ }

Sample u32s uniformly from [0, bound).

Implementations

impl UniformIntegersUnderBound

pub fn new(bound: u32) -> Self

Create the distribution.

Performance

This function performs very well as long as the bound, $b$ is such that $t(b)$ is small, where:

t(b) = (2^{32} - b + 1) \mod b

In particular, the probability that a random vector of $N$ elements is accepted is:

\left(1 - \frac{t(b)}{2^{32}}\right)^N

Thus, if $t(b)$ is quite small, then it is efficient for us to reject $N$ elements at a time, as opposed to rejecting individual elements.

Repeated Invocations

It is inefficient to repeatedly call new with a fresh bound. However, an alternative algorithm has not yet been implemented.

Timing Side-Channel

bound should be a public value, since it may be leaked in the timing of sampling.

Panics

Panics if bound is 0.

pub fn bound(&self) -> u32

The exclusive bound of the integers produced by this generator.

pub fn sample(&self, rng: &mut AesRng) -> [U32x8; 4]

Produce Aes128EncryptOnly::BLOCK_COUNT_HINT * 4 uniformly distributed u32s (under the given bound).

pub fn sample_20(&self, rng: &mut AesRng) -> [U32x8; 3]

Produce 20 uniformly distributed u32s under the given bound.

Random numbers are returned in out[0][..], out[1][..], and the even-indexed entries of out[2] (i.e. out[2][0], out[2][2], out[2][4], out[2][6]).

Alternatives

Consider using Self::sample instead. It may be faster on some platforms.

Trait Implementations

impl Clone for UniformIntegersUnderBound

fn clone(&self) -> UniformIntegersUnderBound

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for UniformIntegersUnderBound

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

Formats the value using the given formatter.

impl Copy for UniformIntegersUnderBound