Documentation

Overview

    Package rand implements pseudo-random number generators.

    Random numbers are generated by a Source. Top-level functions, such as Float64 and Int, use a default shared Source that produces a deterministic sequence of values each time a program is run. Use the Seed function to initialize the default Source if different behavior is required for each run. The default Source, a LockedSource, is safe for concurrent use by multiple goroutines, but Sources created by NewSource are not. However, Sources are small and it is reasonable to have a separate Source for each goroutine, seeded differently, to avoid locking.

    For random numbers suitable for security-sensitive work, see the crypto/rand package.

    Example
    Output:
    
    Magic 8-Ball says: Most likely
    
    Example (Rand)

      This example shows the use of each of the methods on a *Rand. The use of the global functions is the same, without the receiver.

      Output:
      
      Float32     0.030719291          0.47512934           0.031019364
      Float64     0.6906635660087743   0.9898818576905045   0.2683634639782333
      ExpFloat64  1.24979080914592     0.3451975160045876   0.5456817760595064
      NormFloat64 0.879221333732727    -0.01508980368383761 -1.962250558270421
      Int31       2043816560           1870670250           1334960143
      Int63       7860766611810691572  1466711535823962239  3836585920276818709
      Uint32      2051241581           751073909            1353986074
      Uint64      10802154207635843641 14398820303406316826 11052107950969057042
      Intn(10)    3                    0                    1
      Int31n(10)  3                    8                    1
      Int63n(10)  4                    6                    0
      Uint64n(10) 2                    9                    4
      Perm        [1 3 4 0 2]          [2 4 0 3 1]          [3 2 0 4 1]
      

      Index

      Examples

      Constants

      This section is empty.

      Variables

      This section is empty.

      Functions

      func ExpFloat64

      func ExpFloat64() float64

        ExpFloat64 returns an exponentially distributed float64 in the range (0, +math.MaxFloat64] with an exponential distribution whose rate parameter (lambda) is 1 and whose mean is 1/lambda (1) from the default Source. To produce a distribution with a different rate parameter, callers can adjust the output using:

        sample = ExpFloat64() / desiredRateParameter
        

        func Float32

        func Float32() float32

          Float32 returns, as a float32, a pseudo-random number in [0.0,1.0) from the default Source.

          func Float64

          func Float64() float64

            Float64 returns, as a float64, a pseudo-random number in [0.0,1.0) from the default Source.

            func Int

            func Int() int

              Int returns a non-negative pseudo-random int from the default Source.

              func Int31

              func Int31() int32

                Int31 returns a non-negative pseudo-random 31-bit integer as an int32 from the default Source.

                func Int31n

                func Int31n(n int32) int32

                  Int31n returns, as an int32, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

                  func Int63

                  func Int63() int64

                    Int63 returns a non-negative pseudo-random 63-bit integer as an int64 from the default Source.

                    func Int63n

                    func Int63n(n int64) int64

                      Int63n returns, as an int64, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

                      func Intn

                      func Intn(n int) int

                        Intn returns, as an int, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

                        func NormFloat64

                        func NormFloat64() float64

                          NormFloat64 returns a normally distributed float64 in the range [-math.MaxFloat64, +math.MaxFloat64] with standard normal distribution (mean = 0, stddev = 1) from the default Source. To produce a different normal distribution, callers can adjust the output using:

                          sample = NormFloat64() * desiredStdDev + desiredMean
                          

                          func Perm

                          func Perm(n int) []int

                            Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n) from the default Source.

                            func Read

                            func Read(p []byte) (n int, err error)

                              Read generates len(p) random bytes from the default Source and writes them into p. It always returns len(p) and a nil error. Read, unlike the Rand.Read method, is safe for concurrent use.

                              func Seed

                              func Seed(seed uint64)

                                Seed uses the provided seed value to initialize the default Source to a deterministic state. If Seed is not called, the generator behaves as if seeded by Seed(1). Seed, unlike the Rand.Seed method, is safe for concurrent use.

                                func Shuffle

                                func Shuffle(n int, swap func(i, j int))

                                  Shuffle pseudo-randomizes the order of elements using the default Source. n is the number of elements. Shuffle panics if n < 0. swap swaps the elements with indexes i and j.

                                  Example
                                  Output:
                                  
                                  [ink corners of from mouth runs the my]
                                  
                                  Example (SlicesInUnison)
                                  Output:
                                  
                                  D: 4
                                  A: 1
                                  E: 5
                                  B: 2
                                  C: 3
                                  

                                  func Uint32

                                  func Uint32() uint32

                                    Uint32 returns a pseudo-random 32-bit value as a uint32 from the default Source.

                                    func Uint64

                                    func Uint64() uint64

                                      Uint64 returns a pseudo-random 64-bit value as a uint64 from the default Source.

                                      Types

                                      type LockedSource

                                      type LockedSource struct {
                                      	// contains filtered or unexported fields
                                      }

                                        LockedSource is an implementation of Source that is concurrency-safe. It is just a standard Source with its operations protected by a sync.Mutex.

                                        func (*LockedSource) Read

                                        func (s *LockedSource) Read(p []byte, readVal *uint64, readPos *int8) (n int, err error)

                                          Read implements Read for a LockedSource.

                                          func (*LockedSource) Seed

                                          func (s *LockedSource) Seed(seed uint64)

                                          func (*LockedSource) Uint64

                                          func (s *LockedSource) Uint64() (n uint64)

                                          type PCGSource

                                          type PCGSource struct {
                                          	// contains filtered or unexported fields
                                          }

                                            PCGSource is an implementation of a 64-bit permuted congruential generator as defined in

                                            PCG: A Family of Simple Fast Space-Efficient Statistically Good
                                            Algorithms for Random Number Generation
                                            Melissa E. O’Neill, Harvey Mudd College
                                            http://www.pcg-random.org/pdf/toms-oneill-pcg-family-v1.02.pdf
                                            

                                            The generator here is the congruential generator PCG XSL RR 128/64 (LCG) as found in the software available at http://www.pcg-random.org/. It has period 2^128 with 128 bits of state, producing 64-bit values. Is state is represented by two uint64 words.

                                            func (*PCGSource) MarshalBinary

                                            func (pcg *PCGSource) MarshalBinary() ([]byte, error)

                                              MarshalBinary returns the binary representation of the current state of the generator.

                                              func (*PCGSource) Seed

                                              func (pcg *PCGSource) Seed(seed uint64)

                                                Seed uses the provided seed value to initialize the generator to a deterministic state.

                                                func (*PCGSource) Uint64

                                                func (pcg *PCGSource) Uint64() uint64

                                                  Uint64 returns a pseudo-random 64-bit unsigned integer as a uint64.

                                                  func (*PCGSource) UnmarshalBinary

                                                  func (pcg *PCGSource) UnmarshalBinary(data []byte) error

                                                    UnmarshalBinary sets the state of the generator to the state represented in data.

                                                    type Rand

                                                    type Rand struct {
                                                    	// contains filtered or unexported fields
                                                    }

                                                      A Rand is a source of random numbers.

                                                      func New

                                                      func New(src Source) *Rand

                                                        New returns a new Rand that uses random values from src to generate other random values.

                                                        func (*Rand) ExpFloat64

                                                        func (r *Rand) ExpFloat64() float64

                                                          ExpFloat64 returns an exponentially distributed float64 in the range (0, +math.MaxFloat64] with an exponential distribution whose rate parameter (lambda) is 1 and whose mean is 1/lambda (1). To produce a distribution with a different rate parameter, callers can adjust the output using:

                                                          sample = ExpFloat64() / desiredRateParameter
                                                          

                                                          func (*Rand) Float32

                                                          func (r *Rand) Float32() float32

                                                            Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).

                                                            func (*Rand) Float64

                                                            func (r *Rand) Float64() float64

                                                              Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).

                                                              func (*Rand) Int

                                                              func (r *Rand) Int() int

                                                                Int returns a non-negative pseudo-random int.

                                                                func (*Rand) Int31

                                                                func (r *Rand) Int31() int32

                                                                  Int31 returns a non-negative pseudo-random 31-bit integer as an int32.

                                                                  func (*Rand) Int31n

                                                                  func (r *Rand) Int31n(n int32) int32

                                                                    Int31n returns, as an int32, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

                                                                    func (*Rand) Int63

                                                                    func (r *Rand) Int63() int64

                                                                      Int63 returns a non-negative pseudo-random 63-bit integer as an int64.

                                                                      func (*Rand) Int63n

                                                                      func (r *Rand) Int63n(n int64) int64

                                                                        Int63n returns, as an int64, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

                                                                        func (*Rand) Intn

                                                                        func (r *Rand) Intn(n int) int

                                                                          Intn returns, as an int, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

                                                                          func (*Rand) NormFloat64

                                                                          func (r *Rand) NormFloat64() float64

                                                                            NormFloat64 returns a normally distributed float64 in the range [-math.MaxFloat64, +math.MaxFloat64] with standard normal distribution (mean = 0, stddev = 1). To produce a different normal distribution, callers can adjust the output using:

                                                                            sample = NormFloat64() * desiredStdDev + desiredMean
                                                                            

                                                                            func (*Rand) Perm

                                                                            func (r *Rand) Perm(n int) []int

                                                                              Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).

                                                                              func (*Rand) Read

                                                                              func (r *Rand) Read(p []byte) (n int, err error)

                                                                                Read generates len(p) random bytes and writes them into p. It always returns len(p) and a nil error. Read should not be called concurrently with any other Rand method.

                                                                                func (*Rand) Seed

                                                                                func (r *Rand) Seed(seed uint64)

                                                                                  Seed uses the provided seed value to initialize the generator to a deterministic state. Seed should not be called concurrently with any other Rand method.

                                                                                  func (*Rand) Shuffle

                                                                                  func (r *Rand) Shuffle(n int, swap func(i, j int))

                                                                                    Shuffle pseudo-randomizes the order of elements. n is the number of elements. Shuffle panics if n < 0. swap swaps the elements with indexes i and j.

                                                                                    func (*Rand) Uint32

                                                                                    func (r *Rand) Uint32() uint32

                                                                                      Uint32 returns a pseudo-random 32-bit value as a uint32.

                                                                                      func (*Rand) Uint64

                                                                                      func (r *Rand) Uint64() uint64

                                                                                        Uint64 returns a pseudo-random 64-bit integer as a uint64.

                                                                                        func (*Rand) Uint64n

                                                                                        func (r *Rand) Uint64n(n uint64) uint64

                                                                                          Uint64n returns, as a uint64, a pseudo-random number in [0,n). It is guaranteed more uniform than taking a Source value mod n for any n that is not a power of 2.

                                                                                          type Source

                                                                                          type Source interface {
                                                                                          	Uint64() uint64
                                                                                          	Seed(seed uint64)
                                                                                          }

                                                                                            A Source represents a source of uniformly-distributed pseudo-random int64 values in the range [0, 1<<64).

                                                                                            func NewSource

                                                                                            func NewSource(seed uint64) Source

                                                                                              NewSource returns a new pseudo-random Source seeded with the given value.

                                                                                              type Zipf

                                                                                              type Zipf struct {
                                                                                              	// contains filtered or unexported fields
                                                                                              }

                                                                                                A Zipf generates Zipf distributed variates.

                                                                                                func NewZipf

                                                                                                func NewZipf(r *Rand, s float64, v float64, imax uint64) *Zipf

                                                                                                  NewZipf returns a Zipf variate generator. The generator generates values k ∈ [0, imax] such that P(k) is proportional to (v + k) ** (-s). Requirements: s > 1 and v >= 1.

                                                                                                  func (*Zipf) Uint64

                                                                                                  func (z *Zipf) Uint64() uint64

                                                                                                    Uint64 returns a value drawn from the Zipf distribution described by the Zipf object.