Struct Prng 

pub struct Prng { /* private fields */ }

A small, deterministic pseudo-random generator that lives inside game state.

The whole reproducible position is a single u64 (Prng::position), so the generator is Copy, serializes with the state it lives in (O(1) snapshot and resume), and a Reversible game’s undo record can restore its position exactly. Everything is integer-only with a fixed algorithm, so a seed reproduces the same stream on every platform. Do not rely on the concrete algorithm (currently PCG XSH-RR 64/32, single stream): it is an implementation detail of this newtype and may change.

This is not cryptographically secure and must not be used for security.

Implementations

impl Prng

pub const fn new(seed: u64) -> Self

Creates a generator seeded from seed.

Equal seeds produce identical streams; different seeds are extremely likely to diverge immediately.

pub const fn position(&self) -> u64

Returns the generator’s current position in its stream.

Capture this before a move and pass it to Prng::set_position to rewind, which is how a make/unmake (Reversible) undo record restores the random stream.

pub const fn set_position(&mut self, position: u64)

Restores a position previously read from Prng::position.

pub const fn next_u32(&mut self) -> u32

Returns the next 32-bit value and advances the stream by one step.

pub const fn next_u64(&mut self) -> u64

Returns the next 64-bit value (two steps of the stream).

pub const fn below(&mut self, bound: u64) -> u64

Returns a uniformly distributed value in 0..bound.

Uses rejection sampling to avoid modulo bias, so a single call consumes a variable number of steps. That is why a pre-move Prng::position must be snapshotted rather than reconstructed by counting draws.

Panics

Panics if bound is zero.

pub const fn range(&mut self, low: u64, high: u64) -> u64

Returns a uniformly distributed value in low..high.

Panics

Panics if low >= high.

pub fn choose<'a, T>(&mut self, items: &'a [T]) -> Option<&'a T>

Returns a reference to a uniformly chosen element, or None if empty.

pub const fn shuffle<T>(&mut self, items: &mut [T])

Shuffles items in place with an unbiased Fisher-Yates shuffle.

Trait Implementations

impl Clone for Prng

fn clone(&self) -> Prng

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Prng

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Prng

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Hash for Prng

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Prng

fn eq(&self, other: &Prng) -> 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 Serialize for Prng

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for Prng

impl Eq for Prng

impl StructuralPartialEq for Prng