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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 ¶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.
package main import ( "fmt" "math/rand/v2" "os" "text/tabwriter" ) func main() { // 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]This section is empty.
This section is empty.
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() / desiredRateParameterFloat32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0) from the default Source.
Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0) from the default Source.
Int32 returns a non-negative pseudo-random 31-bit integer as an int32 from the default Source.
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.
Int64 returns a non-negative pseudo-random 63-bit integer as an int64 from the default Source.
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.
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 ¶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 ¶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 + desiredMeanPerm 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 ¶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 ¶Uint returns a pseudo-random uint from the default Source.
Uint32 returns a pseudo-random 32-bit value as a uint32 from the default Source.
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.
Uint64 returns a pseudo-random 64-bit value as a uint64 from the default Source.
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.
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.
A ChaCha8 is a ChaCha8-based cryptographically strong random number generator.
NewChaCha8 returns a new ChaCha8 seeded with the given seed.
AppendBinary implements the encoding.BinaryAppender interface.
MarshalBinary implements the encoding.BinaryMarshaler interface.
Read reads exactly len(p) bytes into p. It always returns len(p) and a nil error.
If calls to Read and Uint64 are interleaved, the order in which bits are returned by the two is undefined, and Read may return bits generated before the last call to Uint64.
UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
A PCG is a PCG generator with 128 bits of internal state. A zero PCG is equivalent to NewPCG(0, 0).
AppendBinary implements the encoding.BinaryAppender interface.
MarshalBinary implements the encoding.BinaryMarshaler interface.
UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
A Rand is a source of random numbers.
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() / desiredRateParameterFloat32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0).
Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0).
Int32N returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n <= 0.
Int64N returns, as an int64, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n <= 0.
IntN returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n <= 0.
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 + desiredMeanPerm returns, as a slice of n ints, a pseudo-random permutation of the integers in the half-open interval [0,n).
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.
Uint32N returns, as a uint32, a non-negative pseudo-random number in the half-open interval [0,n). It panics if n == 0.
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.
A Zipf generates Zipf distributed variates.
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