# Struct rand_pcg::Lcg128CmDxsm64

source · [−]`pub struct Lcg128CmDxsm64 { /* private fields */ }`

## Expand description

A PCG random number generator (CM DXSM 128/64 (LCG) variant).

Permuted Congruential Generator with 128-bit state, internal Linear Congruential Generator, and 64-bit output via “double xorshift multiply” output function.

This is a 128-bit LCG with explicitly chosen stream with the PCG-DXSM
output function. This corresponds to `pcg_engines::cm_setseq_dxsm_128_64`

from pcg_cpp and `PCG64DXSM`

from NumPy.

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 while two generators with different stream parameter may be closely correlated, this is mitigated by the DXSM output function.

## Implementations

source### impl Lcg128CmDxsm64

### impl Lcg128CmDxsm64

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

#### 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.

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

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

Construct an instance compatible with PCG seed and stream.

Note that the highest bit of the `stream`

parameter is discarded
to simplify upholding internal invariants.

Note that while two generators with different stream parameter may be closely correlated, this is mitigated by the DXSM output function.

PCG specifies the following default values for both parameters:

`state = 0xcafef00dd15ea5e5`

`stream = 0xa02bdbf7bb3c0a7ac28fa16a64abf96`

## Trait Implementations

source### impl Clone for Lcg128CmDxsm64

### impl Clone for Lcg128CmDxsm64

source#### fn clone(&self) -> Lcg128CmDxsm64

#### fn clone(&self) -> Lcg128CmDxsm64

1.0.0 · source#### fn clone_from(&mut self, source: &Self)

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

`source`

. Read moresource### impl Debug for Lcg128CmDxsm64

### impl Debug for Lcg128CmDxsm64

source### impl PartialEq<Lcg128CmDxsm64> for Lcg128CmDxsm64

### impl PartialEq<Lcg128CmDxsm64> for Lcg128CmDxsm64

source#### fn eq(&self, other: &Lcg128CmDxsm64) -> bool

#### fn eq(&self, other: &Lcg128CmDxsm64) -> bool

source### impl RngCore for Lcg128CmDxsm64

### impl RngCore for Lcg128CmDxsm64

source#### fn fill_bytes(&mut self, dest: &mut [u8])

#### fn fill_bytes(&mut self, dest: &mut [u8])

`dest`

with random data. Read moresource### impl SeedableRng for Lcg128CmDxsm64

### impl SeedableRng for Lcg128CmDxsm64

source#### fn from_seed(seed: Self::Seed) -> Self

#### fn from_seed(seed: Self::Seed) -> Self

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]

#### type Seed = [u8; 32]

`u8`

arrays (we recommend `[u8; N]`

for some `N`

). Read moresource#### fn seed_from_u64(state: u64) -> Self

#### fn seed_from_u64(state: u64) -> Self

`u64`

seed. Read moresource#### fn from_rng<R>(rng: R) -> Result<Self, Error>where

R: RngCore,

#### fn from_rng<R>(rng: R) -> Result<Self, Error>where

R: RngCore,

`Rng`

. Read more