dasmig::core::rng Class Reference

The core random engine: xoshiro256** (Blackman and Vigna 2018). More...

#include <rng.hpp>

Public Types
using	result_type = std::uint64_t
	Type of the values produced.

Public Member Functions
constexpr	rng (std::uint64_t seed) noexcept
	Construct from a seed.
constexpr rng &	seed (std::uint64_t seed) noexcept
	Reset the engine to the start of the sequence for a seed.
rng &	unseed ()
	Reseed from std::random_device.
constexpr std::uint64_t	seed () const noexcept
	The seed this engine was last seeded with.
constexpr result_type	operator() () noexcept
	Advance and return the next value.
constexpr std::uint64_t	child_seed (std::string_view label) const noexcept
	Derive the child seed for a label.
constexpr std::uint64_t	child_seed (std::uint64_t index) const noexcept
	Derive the child seed for an index.
constexpr rng	split (std::string_view label) const noexcept
	A child engine for a label, independent of this engine's state.
constexpr rng	split (std::uint64_t index) const noexcept
	A child engine for an index, independent of this engine's state.

Static Public Member Functions
static rng	from_entropy ()
	Construct with a seed taken from std::random_device.
static std::uint64_t	entropy_seed ()
	A 64-bit seed from std::random_device.
static constexpr std::uint64_t	child_seed_of (std::uint64_t seed, std::uint64_t index) noexcept
	child_seed(index) for a seed, without building an engine.
static constexpr result_type	min () noexcept
	Smallest value produced.
static constexpr result_type	max () noexcept
	Largest value produced.

Friends
constexpr bool	operator== (const rng &, const rng &) noexcept=default
	Engines are equal when their seed and position are equal.

Detailed Description

The core random engine: xoshiro256** (Blackman and Vigna 2018).

Satisfies std::uniform_random_bit_generator, but use the core's own distributions with it: the std:: distributions give different results on different standard libraries.

An engine remembers the seed it was built from. split() derives a child engine from that seed and a label, not from the current state, so the streams a generator hands to its parts do not shift when another part draws more or fewer numbers.

dasmig::core::rng r{42};
auto height = r.split("height");   // same stream for seed 42, always
auto weight = r.split("weight");   // independent of height's draws

Definition at line 107 of file rng.hpp.

Member Typedef Documentation

result_type

using dasmig::core::rng::result_type = std::uint64_t

Type of the values produced.

Definition at line 110 of file rng.hpp.

Constructor & Destructor Documentation

rng()

constexpr dasmig::core::rng::rng ( std::uint64_t  seed )

inlineexplicitconstexprnoexcept

Construct from a seed.

Parameters

seed	Seed; every value, including 0, is a valid seed.

Definition at line 114 of file rng.hpp.

Member Function Documentation

child_seed() [1/2]

constexpr std::uint64_t dasmig::core::rng::child_seed ( std::string_view  label ) const

inlineconstexprnoexcept

Derive the child seed for a label.

splitmix64_mix(seed ^ splitmix64_mix(fnv1a64(label))).

Parameters

label

UTF-8 label naming the child stream.

Returns

The child seed.

Definition at line 177 of file rng.hpp.

child_seed() [2/2]

constexpr std::uint64_t dasmig::core::rng::child_seed ( std::uint64_t  index ) const

inlineconstexprnoexcept

Derive the child seed for an index.

splitmix64_mix(seed ^ splitmix64_mix(index ^ 0x6a09e667f3bcc909)); the constant keeps index streams apart from label streams.

Parameters

index

Index of the child stream (for example a family member).

Returns

The child seed.

Definition at line 190 of file rng.hpp.

child_seed_of()

static constexpr std::uint64_t dasmig::core::rng::child_seed_of ( std::uint64_t  seed, std::uint64_t  index  )

inlinestaticconstexprnoexcept

child_seed(index) for a seed, without building an engine.

Building an engine expands the seed into 256 bits of state; callers that only need the derived seed (item_seed()) skip that.

Parameters

seed	Parent seed.
index	Index of the child stream.

Returns

The same value as rng{seed}.child_seed(index).

Definition at line 204 of file rng.hpp.

entropy_seed()

static std::uint64_t dasmig::core::rng::entropy_seed ( )

inlinestatic

A 64-bit seed from std::random_device.

Returns

An unpredictable seed.

Definition at line 126 of file rng.hpp.

from_entropy()

static rng dasmig::core::rng::from_entropy ( )

inlinestatic

Construct with a seed taken from std::random_device.

For the instance engines of non-seeded calls only; anything that must replay takes a seed explicitly.

Returns

An engine with an unpredictable seed.

Definition at line 122 of file rng.hpp.

max()

static constexpr result_type dasmig::core::rng::max ( )

inlinestaticconstexprnoexcept

Largest value produced.

Returns

2^64 - 1.

Definition at line 232 of file rng.hpp.

min()

static constexpr result_type dasmig::core::rng::min ( )

inlinestaticconstexprnoexcept

Smallest value produced.

Returns

0.

Definition at line 228 of file rng.hpp.

operator()()

constexpr result_type dasmig::core::rng::operator() ( )

inlineconstexprnoexcept

Advance and return the next value.

Returns

A uniformly distributed 64-bit value.

Definition at line 158 of file rng.hpp.

seed() [1/2]

constexpr std::uint64_t dasmig::core::rng::seed ( ) const

inlineconstexprnoexcept

The seed this engine was last seeded with.

Returns

The seed; constructing an engine from it replays the sequence.

Definition at line 154 of file rng.hpp.

seed() [2/2]

constexpr rng & dasmig::core::rng::seed ( std::uint64_t  seed )

inlineconstexprnoexcept

Reset the engine to the start of the sequence for a seed.

Parameters

seed	The new seed.

Returns

*this.

Definition at line 137 of file rng.hpp.

split() [1/2]

constexpr rng dasmig::core::rng::split ( std::string_view  label ) const

inlineconstexprnoexcept

A child engine for a label, independent of this engine's state.

Parameters

label

UTF-8 label naming the child stream.

Returns

An engine seeded with child_seed(label).

Definition at line 213 of file rng.hpp.

split() [2/2]

constexpr rng dasmig::core::rng::split ( std::uint64_t  index ) const

inlineconstexprnoexcept

A child engine for an index, independent of this engine's state.

Parameters

index

Index of the child stream.

Returns

An engine seeded with child_seed(index).

Definition at line 221 of file rng.hpp.

unseed()

rng & dasmig::core::rng::unseed ( )

inline

Reseed from std::random_device.

Returns

*this.

Definition at line 150 of file rng.hpp.

---

The documentation for this class was generated from the following file:

• dasmig/core/rng.hpp