Data Structures
struct	Randomizer
	Structure to encapsulate the pseudo random number generators. More...

struct	SavedRandomSeeds
	Stores the state of all random number generators. More...

Functions
static constexpr uint32_t	ScaleToLimit (uint32_t value, uint32_t limit)
	Scale a uint32_t number to be within the range [0,limit). More...

void	SaveRandomSeeds (SavedRandomSeeds *storage)
	Saves the current seeds. More...

void	RestoreRandomSeeds (const SavedRandomSeeds &storage)
	Restores previously saved seeds. More...

void	SetRandomSeed (uint32_t seed)
	(Re)set the state of the random number generators. More...

uint32_t	Random ([[maybe_unused]] const std::source_location location=std::source_location::current())

uint32_t	RandomRange (uint32_t limit, const std::source_location location=std::source_location::current())
	Pick a random number between 0 and limit - 1, inclusive. More...

uint32_t	InteractiveRandom ()

uint32_t	InteractiveRandomRange (uint32_t limit)

bool	Chance16I (const uint32_t a, const uint32_t b, const uint32_t r)
	Checks if a given randomize-number is below a given probability. More...

bool	Chance16 (const uint32_t a, const uint32_t b, const std::source_location location=std::source_location::current())
	Flips a coin with given probability. More...

bool	Chance16R (const uint32_t a, const uint32_t b, uint32_t &r, const std::source_location location=std::source_location::current())
	Flips a coin with a given probability and saves the randomize-number in a variable. More...

void	RandomBytesWithFallback (std::span< uint8_t > buf)
	Fill the given buffer with random bytes. More...

Variables
Randomizer	_random
	Random used in the game state calculations.

Randomizer	_interactive_random
	Random used everywhere else, where it does not (directly) influence the game state.

Detailed Description

Pseudo random number generator.

Definition in file random_func.hpp.

Function Documentation

◆ Chance16()

bool Chance16	(	const uint32_t	a,
		const uint32_t	b,
		const std::source_location	location = `std::source_location::current()`
	)

inline

Flips a coin with given probability.

This function returns true with (a/b) probability.

See also: Chance16I()

Parameters

a	The nominator of the fraction
b	The denominator of the fraction

Returns: True with (a/b) probability

Definition at line 134 of file random_func.hpp.

References Chance16I().

Referenced by Disaster_Helicopter_Init(), DisasterTick_Submarine(), FindSubsidyCargoDestination(), IsRoadAllowedHere(), SetupFarmFieldFence(), and TownActionBribe().

◆ Chance16I()

bool Chance16I	(	const uint32_t	a,
		const uint32_t	b,
		const uint32_t	r
	)

inline

Checks if a given randomize-number is below a given probability.

This function is used to check if the given probability by the fraction of (a/b) is greater than low 16 bits of the given randomize-number r.

Do not use this function twice on the same random 16 bits as it will yield the same result. One can use a random number for two calls to Chance16I, where one call sends the low 16 bits and the other the high 16 bits.

Parameters

a	The numerator of the fraction
b	The denominator of the fraction, must of course not be null
r	The given randomize-number

Returns: True if the probability given by r is less or equal to (a/b)

Definition at line 118 of file random_func.hpp.

Referenced by Chance16().

◆ Chance16R()

bool Chance16R	(	const uint32_t	a,
		const uint32_t	b,
		uint32_t &	r,
		const std::source_location	location = `std::source_location::current()`
	)

inline

Flips a coin with a given probability and saves the randomize-number in a variable.

This function uses the same parameters as Chance16. The third parameter must be a variable the randomize-number from Random() is saved in.

The low 16 bits of r will already be used and can therefore not be passed to Chance16I. One can only send the high 16 bits to Chance16I.

See also: Chance16I()

Parameters

a	The numerator of the fraction
b	The denominator of the fraction
r	The variable to save the randomize-number from Random()

Returns: True in (a/b) percent

Definition at line 154 of file random_func.hpp.

Referenced by AmbientSoundEffectCallback(), HandleCrashedAircraft(), and HandleCrashedTrain().

◆ RandomBytesWithFallback()

void RandomBytesWithFallback ( std::span< uint8_t > buf )

Fill the given buffer with random bytes.

This function will attempt to use a cryptographically-strong random generator, but will fall back to a weaker random generator if none is available.

In the end, the buffer will always be filled with some form of random bytes when this function returns.

Parameters

buf	The buffer to fill with random bytes.

Definition at line 95 of file random_func.cpp.

References Debug.

Referenced by X25519SecretKey::CreateRandom(), X25519Nonce::CreateRandom(), GenerateUid(), and X25519AuthenticationHandler::SendResponse().

◆ RandomRange()

uint32_t RandomRange	(	uint32_t	limit,
		const std::source_location	location = `std::source_location::current()`
	)

inline

Pick a random number between 0 and limit - 1, inclusive.

That means 0 can be returned and limit - 1 can be returned, but limit can not be returned.

Parameters

limit Limit for the range to be picked from.

Returns: A random number in [0,limit).

Definition at line 88 of file random_func.hpp.

References ScaleToLimit().

Referenced by Vehicle::Crash(), FindSubsidyIndustryCargoRoute(), FindSubsidyPassengerRoute(), Town::GetRandom(), Industry::GetRandom(), CYapfFollowShipT< Types >::GetRandomTrackdir(), FlowStat::GetVia(), FlowStat::GetViaWithRestricted(), GrowTownWithBridge(), RandomDiagDir(), RandomHeight(), IndustryBuildData::SetupTargetCount(), StationCargoList::Truncate(), and IndustryBuildData::TryBuildNewIndustry().

◆ RestoreRandomSeeds()

void RestoreRandomSeeds ( const SavedRandomSeeds & storage )

inline

Restores previously saved seeds.

Parameters

storage Storage where SaveRandomSeeds() stored th seeds

Definition at line 65 of file random_func.hpp.

References _interactive_random, and _random.

Referenced by CmdAutoreplaceVehicle().

◆ SaveRandomSeeds()

void SaveRandomSeeds ( SavedRandomSeeds * storage )

inline

Saves the current seeds.

Parameters

storage Storage for saving

Definition at line 55 of file random_func.hpp.

References _interactive_random, and _random.

Referenced by CmdAutoreplaceVehicle(), and StartupOneEngine().

◆ ScaleToLimit()

static constexpr uint32_t ScaleToLimit	(	uint32_t	value,
		uint32_t	limit
	)

staticconstexpr

Scale a uint32_t number to be within the range [0,limit).

Parameters

value	The value to scale.
limit	The limit to scale to.

Returns: The scaled value.

Definition at line 19 of file random_func.hpp.

Referenced by Randomizer::Next(), and RandomRange().

◆ SetRandomSeed()

void SetRandomSeed ( uint32_t seed )

(Re)set the state of the random number generators.

Parameters

seed	the new state

Definition at line 66 of file random_func.cpp.

References _interactive_random, _random, and Randomizer::SetSeed().

Referenced by StartupOneEngine().

Data Structures

Functions

Variables

Detailed Description

Function Documentation

◆ Chance16()

◆ Chance16I()

◆ Chance16R()

◆ RandomBytesWithFallback()

◆ RandomRange()

◆ RestoreRandomSeeds()

◆ SaveRandomSeeds()

◆ ScaleToLimit()

◆ SetRandomSeed()