gmx::ThreeFry2x64Fast< internalCounterBits > Class Template Reference

#include <gromacs/random/threefry.h>

Inheritance diagram for gmx::ThreeFry2x64Fast< internalCounterBits >:

Collaboration diagram for gmx::ThreeFry2x64Fast< internalCounterBits >:

Description

template<unsigned int internalCounterBits = 64>
class gmx::ThreeFry2x64Fast< internalCounterBits >

ThreeFry2x64 random engine with 13 iteractions.

Template Parameters

internalCounterBits,default

64.

This class provides relatively high quality random numbers that only fail one BigCrush test, and it is a bit faster than the 20-round version. It works with two 64-bit values each for keys and counters, and is most efficient when we only need a few random values before restarting the counters with new values.

Public Types
typedef uint64_t	result_type
	Integer type for output.
typedef std::array < result_type, 2 >	counter_type
	Use array for counter & key states so it is allocated on the stack.

Public Member Functions
	ThreeFry2x64Fast (uint64_t key0=0, RandomDomain domain=RandomDomain::Other)
	Construct ThreeFry random engine with 2x64 key values, 13 rounds. More...
	ThreeFry2x64Fast (uint64_t key0, uint64_t key1)
	Construct ThreeFry random engine from 2x64-bit unsigned integers, 13 rounds. More...
void	seed (uint64_t key0=0, RandomDomain domain=RandomDomain::Other)
	Seed 2x64 random engine with two 64-bit key values. More...
void	seed (uint64_t key0, uint64_t key1)
	Seed random engine from 2x64-bit unsigned integers. More...
void	restart (uint64_t ctr0=0, uint64_t ctr1=0)
	Restart 2x64 random engine counter from 2 64-bit values. More...
result_type	operator() ()
	Generate the next random number. More...
void	discard (uint64_t n)
	Skip next n random numbers. More...
bool	operator== (const ThreeFry2x64General< rounds, internalCounterBits > &x) const
	Return true if two ThreeFry2x64 engines are identical. More...
bool	operator!= (const ThreeFry2x64General< rounds, internalCounterBits > &x) const
	Return true of two ThreeFry2x64 engines are not identical. More...

Static Public Member Functions
static constexpr result_type	min ()
	Smallest value that can be returned from random engine.
static constexpr result_type	max ()
	Largest value that can be returned from random engine.

Constructor & Destructor Documentation

template<unsigned int internalCounterBits = 64>

gmx::ThreeFry2x64Fast< internalCounterBits >::ThreeFry2x64Fast ( uint64_t  key0 = 0, RandomDomain  domain = RandomDomain::Other  )

inline

Construct ThreeFry random engine with 2x64 key values, 13 rounds.

Parameters

key0	Random seed in the form of a 64-bit unsigned value.
domain	Random domain. This is used to guarantee that different applications of a random engine inside the code get different streams of random numbers, without requiring the user to provide lots of random seeds. Pick a value from the RandomDomain class, or RandomDomain::Other if it is not important. In the latter case you might want to use gmx::DefaultRandomEngine instead.

Note

The random domain is really another 64-bit seed value.

Exceptions

InternalError

if the high bits needed to encode the number of counter bits are nonzero.

template<unsigned int internalCounterBits = 64>

gmx::ThreeFry2x64Fast< internalCounterBits >::ThreeFry2x64Fast ( uint64_t  key0, uint64_t  key1  )

inline

Construct ThreeFry random engine from 2x64-bit unsigned integers, 13 rounds.

This constructor assigns the raw 128 bit key data from unsigned integers. It is meant for the case when you want full control over the key, for instance to compare with reference values of the ThreeFry function during testing.

Parameters

key0	First word of key/random seed.
key1	Second word of key/random seed.

Exceptions

InternalError

if the high bits needed to encode the number of counter bits are nonzero. To test arbitrary values, use 0 internal counter bits.

Member Function Documentation

void gmx::ThreeFry2x64General< rounds, internalCounterBits >::discard ( uint64_t  n )

inlineinherited

Skip next n random numbers.

Moves the internal random stream for the give key/counter value n positions forward. The count is based on the number of random values returned, such that skipping 5 values gives exactly the same result as drawing 5 values that are ignored.

Parameters

n	Number of values to jump forward.

Exceptions

InternalError

if the internal counter space is exhausted.

bool gmx::ThreeFry2x64General< rounds, internalCounterBits >::operator!= ( const ThreeFry2x64General< rounds, internalCounterBits > &  x ) const

inlineinherited

Return true of two ThreeFry2x64 engines are not identical.

Parameters

x	Instance to compare with.

This routine should return true if the two engines will generate different random streams when drawing.

result_type gmx::ThreeFry2x64General< rounds, internalCounterBits >::operator() ( )

inlineinherited

Generate the next random number.

This will return the next stored 64-bit value if one is available, and otherwise generate a new block, update the internal counters, and return the first value while storing the others.

Exceptions

InternalError

if the internal counter space is exhausted.

bool gmx::ThreeFry2x64General< rounds, internalCounterBits >::operator== ( const ThreeFry2x64General< rounds, internalCounterBits > &  x ) const

inlineinherited

Return true if two ThreeFry2x64 engines are identical.

Parameters

x	Instance to compare with.

This routine should return true if the two engines will generate identical random streams when drawing.

void gmx::ThreeFry2x64General< rounds, internalCounterBits >::restart ( uint64_t  ctr0 = 0, uint64_t  ctr1 = 0  )

inlineinherited

Restart 2x64 random engine counter from 2 64-bit values.

Parameters

ctr0	First word of new counter, in the form of 64-bit unsigned values.
ctr1	Second word of new counter

Restarting the engine with a new counter is extremely fast with ThreeFry64, and basically just consists of storing the counter value, so you should use this liberally in your innermost loops to restart the engine with e.g. the current step and atom index as counter values.

Exceptions

InternalError

if any of the highest bits that are reserved for the internal part of the counter are set. The number of reserved bits is to the last template parameter to the class.

void gmx::ThreeFry2x64General< rounds, internalCounterBits >::seed ( uint64_t  key0 = 0, RandomDomain  domain = RandomDomain::Other  )

inlineinherited

Seed 2x64 random engine with two 64-bit key values.

Parameters

key0	First word of random seed, in the form of 64-bit unsigned values.
domain	Random domain. This is used to guarantee that different applications of a random engine inside the code get different streams of random numbers, without requiring the user to provide lots of random seeds. Pick a value from the RandomDomain class, or RandomDomain::Other if it is not important. In the latter case you might want to use gmx::DefaultRandomEngine instead.

Note

The random domain is really another 64-bit seed value.

Re-initialized the seed similar to the counter constructor. Same rules apply: The highest few bits of the last word are reserved to encode the number of internal counter bits, but to save the user the trouble of making sure these are zero when using e.g. a random device, we just ignore them.

void gmx::ThreeFry2x64General< rounds, internalCounterBits >::seed ( uint64_t  key0, uint64_t  key1  )

inlineinherited

Seed random engine from 2x64-bit unsigned integers.

This assigns the raw 128 bit key data from unsigned integers. It is meant for the case when you want full control over the key, for instance to compare with reference values of the ThreeFry function during testing.

Parameters

key0	First word of key/random seed.
key1	Second word of key/random seed.

Exceptions

InternalError

if the high bits needed to encode the number of counter bits are nonzero. To test arbitrary values, use 0 internal counter bits.

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

• src/gromacs/random/threefry.h