Struct Lcg128Xsl64

pub struct Lcg128Xsl64 { /* private fields */ }

A PCG random number generator (XSL RR 128/64 (LCG) variant).

Permuted Congruential Generator with 128-bit state, internal Linear Congruential Generator, and 64-bit output via “xorshift low (bits), random rotation” output function.

This is a 128-bit LCG with explicitly chosen stream with the PCG-XSL-RR output function. This combination is the standard pcg64.

Despite the name, this implementation uses 32 bytes (256 bit) space comprising 128 bits of state and 128 bits stream selector. These are both set by SeedableRng, using a 256-bit seed.

Note that two generators with different stream parameters may be closely correlated.

Implementations

impl Lcg128Xsl64

pub fn advance(&mut self, delta: u128)

Multi-step advance functions (jump-ahead, jump-back)

The method used here is based on Brown, “Random Number Generation with Arbitrary Stride,”, Transactions of the American Nuclear Society (Nov. 1994). The algorithm is very similar to fast exponentiation.

Even though delta is an unsigned integer, we can pass a signed integer to go backwards, it just goes “the long way round”.

Using this function is equivalent to calling next_64() delta number of times.

pub fn new(state: u128, stream: u128) -> Self

Construct an instance compatible with PCG seed and stream.

Note that two generators with different stream parameters may be closely correlated.

PCG specifies the following default values for both parameters:

• state = 0xcafef00dd15ea5e5
• stream = 0xa02bdbf7bb3c0a7ac28fa16a64abf96

Trait Implementations

impl Clone for Lcg128Xsl64

fn clone(&self) -> Lcg128Xsl64

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Lcg128Xsl64

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

Formats the value using the given formatter.

impl PartialEq for Lcg128Xsl64

fn eq(&self, other: &Lcg128Xsl64) -> 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 Lcg128Xsl64

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 Lcg128Xsl64

We use a single 255-bit seed to initialise the state and select a stream. One seed bit (lowest bit of seed[8]) is ignored.

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<R>(rng: R) -> Result<Self, Error>

where R: RngCore,

Create a new PRNG seeded from another Rng.

impl Eq for Lcg128Xsl64

impl StructuralPartialEq for Lcg128Xsl64