rand

package standard library
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Published: Apr 22, 2024 License: BSD-3-Clause Imports: 5 Imported by: 268

Documentation

Overview

Package rand implements pseudo-random number generators suitable for tasks such as simulation, but it should not be used for security-sensitive work.

Random numbers are generated by a Source, usually wrapped in a Rand. Both types should be used by a single goroutine at a time: sharing among multiple goroutines requires some kind of synchronization.

Top-level functions, such as Float64 and Int, are safe for concurrent use by multiple goroutines.

This package's outputs might be easily predictable regardless of how it's seeded. For random numbers suitable for security-sensitive work, see the crypto/rand package.

Example
answers := []string{
	"It is certain",
	"It is decidedly so",
	"Without a doubt",
	"Yes definitely",
	"You may rely on it",
	"As I see it yes",
	"Most likely",
	"Outlook good",
	"Yes",
	"Signs point to yes",
	"Reply hazy try again",
	"Ask again later",
	"Better not tell you now",
	"Cannot predict now",
	"Concentrate and ask again",
	"Don't count on it",
	"My reply is no",
	"My sources say no",
	"Outlook not so good",
	"Very doubtful",
}
fmt.Println("Magic 8-Ball says:", answers[rand.IntN(len(answers))])
Output:

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.

// Create and seed the generator.
// Typically a non-fixed seed should be used, such as Uint64(), Uint64().
// Using a fixed seed will produce the same output on every run.
r := rand.New(rand.NewPCG(1, 2))

// The tabwriter here helps us generate aligned output.
w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
defer w.Flush()
show := func(name string, v1, v2, v3 any) {
	fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3)
}

// Float32 and Float64 values are in [0, 1).
show("Float32", r.Float32(), r.Float32(), r.Float32())
show("Float64", r.Float64(), r.Float64(), r.Float64())

// ExpFloat64 values have an average of 1 but decay exponentially.
show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64())

// NormFloat64 values have an average of 0 and a standard deviation of 1.
show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64())

// Int32, Int64, and Uint32 generate values of the given width.
// The Int method (not shown) is like either Int32 or Int64
// depending on the size of 'int'.
show("Int32", r.Int32(), r.Int32(), r.Int32())
show("Int64", r.Int64(), r.Int64(), r.Int64())
show("Uint32", r.Uint32(), r.Uint32(), r.Uint32())

// IntN, Int32N, and Int64N limit their output to be < n.
// They do so more carefully than using r.Int()%n.
show("IntN(10)", r.IntN(10), r.IntN(10), r.IntN(10))
show("Int32N(10)", r.Int32N(10), r.Int32N(10), r.Int32N(10))
show("Int64N(10)", r.Int64N(10), r.Int64N(10), r.Int64N(10))

// Perm generates a random permutation of the numbers [0, n).
show("Perm", r.Perm(5), r.Perm(5), r.Perm(5))
Output:

Float32     0.95955694          0.8076733            0.8135684
Float64     0.4297927436037299  0.797802349388613    0.3883664855410056
ExpFloat64  0.43463410545541104 0.5513632046504593   0.7426404617374481
NormFloat64 -0.9303318111676635 -0.04750789419852852 0.22248301107582735
Int32       2020777787          260808523            851126509
Int64       5231057920893523323 4257872588489500903  158397175702351138
Uint32      314478343           1418758728           208955345
IntN(10)    6                   2                    0
Int32N(10)  3                   7                    7
Int64N(10)  8                   9                    4
Perm        [0 3 1 4 2]         [4 1 2 0 3]          [4 3 2 0 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 the half-open interval [0.0,1.0) from the default Source.

func Float64

func Float64() float64

Float64 returns, as a float64, a pseudo-random number in the half-open interval [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 Int32

func Int32() int32

Int32 returns a non-negative pseudo-random 31-bit integer as an int32 from the default Source.

func Int32N

func Int32N(n int32) int32

Int32N returns, as an int32, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

func Int64

func Int64() int64

Int64 returns a non-negative pseudo-random 63-bit integer as an int64 from the default Source.

func Int64N

func Int64N(n int64) int64

Int64N returns, as an int64, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

func IntN

func IntN(n int) int

IntN returns, as an int, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

Example
fmt.Println(rand.IntN(100))
fmt.Println(rand.IntN(100))
fmt.Println(rand.IntN(100))
Output:

func N

func N[Int intType](n Int) Int

N returns a pseudo-random number in the half-open interval [0,n) from the default Source. The type parameter Int can be any integer type. It panics if n <= 0.

Example
// Print an int64 in the half-open interval [0, 100).
fmt.Println(rand.N(int64(100)))

// Sleep for a random duration between 0 and 100 milliseconds.
time.Sleep(rand.N(100 * time.Millisecond))
Output:

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 in the half-open interval [0,n) from the default Source.

Example
for _, value := range rand.Perm(3) {
	fmt.Println(value)
}
Output:

1
2
0

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
words := strings.Fields("ink runs from the corners of my mouth")
rand.Shuffle(len(words), func(i, j int) {
	words[i], words[j] = words[j], words[i]
})
fmt.Println(words)
Output:

Example (SlicesInUnison)
numbers := []byte("12345")
letters := []byte("ABCDE")
// Shuffle numbers, swapping corresponding entries in letters at the same time.
rand.Shuffle(len(numbers), func(i, j int) {
	numbers[i], numbers[j] = numbers[j], numbers[i]
	letters[i], letters[j] = letters[j], letters[i]
})
for i := range numbers {
	fmt.Printf("%c: %c\n", letters[i], numbers[i])
}
Output:

func Uint32

func Uint32() uint32

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

func Uint32N

func Uint32N(n uint32) uint32

Uint32N returns, as a uint32, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

func Uint64

func Uint64() uint64

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

func Uint64N

func Uint64N(n uint64) uint64

Uint64N returns, as a uint64, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

func UintN

func UintN(n uint) uint

UintN returns, as a uint, a pseudo-random number in the half-open interval [0,n) from the default Source. It panics if n <= 0.

Types

type ChaCha8

type ChaCha8 struct {
	// contains filtered or unexported fields
}

A ChaCha8 is a ChaCha8-based cryptographically strong random number generator.

func NewChaCha8

func NewChaCha8(seed [32]byte) *ChaCha8

NewChaCha8 returns a new ChaCha8 seeded with the given seed.

func (*ChaCha8) MarshalBinary

func (c *ChaCha8) MarshalBinary() ([]byte, error)

MarshalBinary implements the encoding.BinaryMarshaler interface.

func (*ChaCha8) Seed

func (c *ChaCha8) Seed(seed [32]byte)

Seed resets the ChaCha8 to behave the same way as NewChaCha8(seed).

func (*ChaCha8) Uint64

func (c *ChaCha8) Uint64() uint64

Uint64 returns a uniformly distributed random uint64 value.

func (*ChaCha8) UnmarshalBinary

func (c *ChaCha8) UnmarshalBinary(data []byte) error

UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.

type PCG

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

A PCG is a PCG generator with 128 bits of internal state. A zero PCG is equivalent to NewPCG(0, 0).

func NewPCG

func NewPCG(seed1, seed2 uint64) *PCG

NewPCG returns a new PCG seeded with the given values.

func (*PCG) MarshalBinary

func (p *PCG) MarshalBinary() ([]byte, error)

MarshalBinary implements the encoding.BinaryMarshaler interface.

func (*PCG) Seed

func (p *PCG) Seed(seed1, seed2 uint64)

Seed resets the PCG to behave the same way as NewPCG(seed1, seed2).

func (*PCG) Uint64

func (p *PCG) Uint64() uint64

Uint64 return a uniformly-distributed random uint64 value.

func (*PCG) UnmarshalBinary

func (p *PCG) UnmarshalBinary(data []byte) error

UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.

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 the half-open interval [0.0,1.0).

func (*Rand) Float64

func (r *Rand) Float64() float64

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

func (*Rand) Int

func (r *Rand) Int() int

Int returns a non-negative pseudo-random int.

func (*Rand) Int32

func (r *Rand) Int32() int32

Int32 returns a non-negative pseudo-random 31-bit integer as an int32.

func (*Rand) Int32N

func (r *Rand) Int32N(n int32) int32

Int32N returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n <= 0.

func (*Rand) Int64

func (r *Rand) Int64() int64

Int64 returns a non-negative pseudo-random 63-bit integer as an int64.

func (*Rand) Int64N

func (r *Rand) Int64N(n int64) int64

Int64N returns, as an int64, a non-negative pseudo-random number in the half-open interval [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 the half-open interval [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 through +math.MaxFloat64 inclusive, 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 in the half-open interval [0,n).

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) Uint32N

func (r *Rand) Uint32N(n uint32) uint32

Uint32N returns, as a uint32, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n == 0.

func (*Rand) Uint64

func (r *Rand) Uint64() uint64

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

func (*Rand) Uint64N

func (r *Rand) Uint64N(n uint64) uint64

Uint64N returns, as a uint64, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n == 0.

func (*Rand) UintN

func (r *Rand) UintN(n uint) uint

UintN returns, as a uint, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n == 0.

type Source

type Source interface {
	Uint64() uint64
}

A Source is a source of uniformly-distributed pseudo-random uint64 values in the range [0, 1<<64).

A Source is not safe for concurrent use by multiple goroutines.

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.

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