Struct Rng 

pub struct Rng { /* private fields */ }

XorShift64 PRNG — deterministic per seed.

Implementations

impl Rng

pub fn new(seed: u64) -> Self

Construct from a 64-bit seed.

Applies one round of SplitMix64 mixing to decorrelate low-entropy seeds (Issue 296). Without this, small seeds like 0, 1, 2, 42 keep the XorShift64 state small enough that the first next() has zero upper 24 bits, so uniform() returns exactly 0.0 — which sits on the left boundary of any inverse-CDF sampler and deterministically selects the first token with nonzero mass. SplitMix64 is the standard remedy for XorShift “small seed” weakness: it diffuses any input (including 0) into a well-distributed 64-bit state in O(1).

Cost: ~3 mul/shift per Rng::new. Negligible — new() is called once per inference/training session, not in hot loops.

pub fn next(&mut self) -> u64

pub fn uniform(&mut self) -> f32

Uniform [0, 1) — 24 bits of entropy (full f32 mantissa precision).

Note: returns a value in the half-open interval [0, 1). The exact bound 0.0 is reachable in principle (24 zero bits) but, after the SplitMix64 seed mixing in Rng::new, is no longer the deterministic first draw for small seeds. Samplers that require a strictly positive variate should still redraw on r == 0.0 as a defensive belt — see Issue 296.

pub fn normal(&mut self) -> f32

Standard normal via Box-Muller transform.