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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-16 19:25:22 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-16 19:25:22 +0000
commitf6ad4dcef54c5ce997a4bad5a6d86de229015700 (patch)
tree7cfa4e31ace5c2bd95c72b154d15af494b2bcbef /src/math/rand/rand.go
parentInitial commit. (diff)
downloadgolang-1.22-f6ad4dcef54c5ce997a4bad5a6d86de229015700.tar.xz
golang-1.22-f6ad4dcef54c5ce997a4bad5a6d86de229015700.zip
Adding upstream version 1.22.1.upstream/1.22.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/math/rand/rand.go')
-rw-r--r--src/math/rand/rand.go547
1 files changed, 547 insertions, 0 deletions
diff --git a/src/math/rand/rand.go b/src/math/rand/rand.go
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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// 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.
+package rand
+
+import (
+ "internal/godebug"
+ "sync"
+ "sync/atomic"
+ _ "unsafe" // for go:linkname
+)
+
+// A Source represents a source of uniformly-distributed
+// pseudo-random int64 values in the range [0, 1<<63).
+//
+// A Source is not safe for concurrent use by multiple goroutines.
+type Source interface {
+ Int63() int64
+ Seed(seed int64)
+}
+
+// A Source64 is a [Source] that can also generate
+// uniformly-distributed pseudo-random uint64 values in
+// the range [0, 1<<64) directly.
+// If a [Rand] r's underlying [Source] s implements Source64,
+// then r.Uint64 returns the result of one call to s.Uint64
+// instead of making two calls to s.Int63.
+type Source64 interface {
+ Source
+ Uint64() uint64
+}
+
+// NewSource returns a new pseudo-random [Source] seeded with the given value.
+// Unlike the default [Source] used by top-level functions, this source is not
+// safe for concurrent use by multiple goroutines.
+// The returned [Source] implements [Source64].
+func NewSource(seed int64) Source {
+ return newSource(seed)
+}
+
+func newSource(seed int64) *rngSource {
+ var rng rngSource
+ rng.Seed(seed)
+ return &rng
+}
+
+// A Rand is a source of random numbers.
+type Rand struct {
+ src Source
+ s64 Source64 // non-nil if src is source64
+
+ // readVal contains remainder of 63-bit integer used for bytes
+ // generation during most recent Read call.
+ // It is saved so next Read call can start where the previous
+ // one finished.
+ readVal int64
+ // readPos indicates the number of low-order bytes of readVal
+ // that are still valid.
+ readPos int8
+}
+
+// New returns a new [Rand] that uses random values from src
+// to generate other random values.
+func New(src Source) *Rand {
+ s64, _ := src.(Source64)
+ return &Rand{src: src, s64: s64}
+}
+
+// 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 (r *Rand) Seed(seed int64) {
+ if lk, ok := r.src.(*lockedSource); ok {
+ lk.seedPos(seed, &r.readPos)
+ return
+ }
+
+ r.src.Seed(seed)
+ r.readPos = 0
+}
+
+// Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
+func (r *Rand) Int63() int64 { return r.src.Int63() }
+
+// Uint32 returns a pseudo-random 32-bit value as a uint32.
+func (r *Rand) Uint32() uint32 { return uint32(r.Int63() >> 31) }
+
+// Uint64 returns a pseudo-random 64-bit value as a uint64.
+func (r *Rand) Uint64() uint64 {
+ if r.s64 != nil {
+ return r.s64.Uint64()
+ }
+ return uint64(r.Int63())>>31 | uint64(r.Int63())<<32
+}
+
+// Int31 returns a non-negative pseudo-random 31-bit integer as an int32.
+func (r *Rand) Int31() int32 { return int32(r.Int63() >> 32) }
+
+// Int returns a non-negative pseudo-random int.
+func (r *Rand) Int() int {
+ u := uint(r.Int63())
+ return int(u << 1 >> 1) // clear sign bit if int == int32
+}
+
+// Int63n returns, as an int64, a non-negative pseudo-random number in the half-open interval [0,n).
+// It panics if n <= 0.
+func (r *Rand) Int63n(n int64) int64 {
+ if n <= 0 {
+ panic("invalid argument to Int63n")
+ }
+ if n&(n-1) == 0 { // n is power of two, can mask
+ return r.Int63() & (n - 1)
+ }
+ max := int64((1 << 63) - 1 - (1<<63)%uint64(n))
+ v := r.Int63()
+ for v > max {
+ v = r.Int63()
+ }
+ return v % n
+}
+
+// Int31n returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n).
+// It panics if n <= 0.
+func (r *Rand) Int31n(n int32) int32 {
+ if n <= 0 {
+ panic("invalid argument to Int31n")
+ }
+ if n&(n-1) == 0 { // n is power of two, can mask
+ return r.Int31() & (n - 1)
+ }
+ max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
+ v := r.Int31()
+ for v > max {
+ v = r.Int31()
+ }
+ return v % n
+}
+
+// int31n returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n).
+// n must be > 0, but int31n does not check this; the caller must ensure it.
+// int31n exists because Int31n is inefficient, but Go 1 compatibility
+// requires that the stream of values produced by math/rand remain unchanged.
+// int31n can thus only be used internally, by newly introduced APIs.
+//
+// For implementation details, see:
+// https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
+// https://lemire.me/blog/2016/06/30/fast-random-shuffling
+func (r *Rand) int31n(n int32) int32 {
+ v := r.Uint32()
+ prod := uint64(v) * uint64(n)
+ low := uint32(prod)
+ if low < uint32(n) {
+ thresh := uint32(-n) % uint32(n)
+ for low < thresh {
+ v = r.Uint32()
+ prod = uint64(v) * uint64(n)
+ low = uint32(prod)
+ }
+ }
+ return int32(prod >> 32)
+}
+
+// Intn returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n).
+// It panics if n <= 0.
+func (r *Rand) Intn(n int) int {
+ if n <= 0 {
+ panic("invalid argument to Intn")
+ }
+ if n <= 1<<31-1 {
+ return int(r.Int31n(int32(n)))
+ }
+ return int(r.Int63n(int64(n)))
+}
+
+// Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0).
+func (r *Rand) Float64() float64 {
+ // A clearer, simpler implementation would be:
+ // return float64(r.Int63n(1<<53)) / (1<<53)
+ // However, Go 1 shipped with
+ // return float64(r.Int63()) / (1 << 63)
+ // and we want to preserve that value stream.
+ //
+ // There is one bug in the value stream: r.Int63() may be so close
+ // to 1<<63 that the division rounds up to 1.0, and we've guaranteed
+ // that the result is always less than 1.0.
+ //
+ // We tried to fix this by mapping 1.0 back to 0.0, but since float64
+ // values near 0 are much denser than near 1, mapping 1 to 0 caused
+ // a theoretically significant overshoot in the probability of returning 0.
+ // Instead of that, if we round up to 1, just try again.
+ // Getting 1 only happens 1/2⁵³ of the time, so most clients
+ // will not observe it anyway.
+again:
+ f := float64(r.Int63()) / (1 << 63)
+ if f == 1 {
+ goto again // resample; this branch is taken O(never)
+ }
+ return f
+}
+
+// Float32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0).
+func (r *Rand) Float32() float32 {
+ // Same rationale as in Float64: we want to preserve the Go 1 value
+ // stream except we want to fix it not to return 1.0
+ // This only happens 1/2²⁴ of the time (plus the 1/2⁵³ of the time in Float64).
+again:
+ f := float32(r.Float64())
+ if f == 1 {
+ goto again // resample; this branch is taken O(very rarely)
+ }
+ return f
+}
+
+// Perm returns, as a slice of n ints, a pseudo-random permutation of the integers
+// in the half-open interval [0,n).
+func (r *Rand) Perm(n int) []int {
+ m := make([]int, n)
+ // In the following loop, the iteration when i=0 always swaps m[0] with m[0].
+ // A change to remove this useless iteration is to assign 1 to i in the init
+ // statement. But Perm also effects r. Making this change will affect
+ // the final state of r. So this change can't be made for compatibility
+ // reasons for Go 1.
+ for i := 0; i < n; i++ {
+ j := r.Intn(i + 1)
+ m[i] = m[j]
+ m[j] = i
+ }
+ return m
+}
+
+// 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 (r *Rand) Shuffle(n int, swap func(i, j int)) {
+ if n < 0 {
+ panic("invalid argument to Shuffle")
+ }
+
+ // Fisher-Yates shuffle: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
+ // Shuffle really ought not be called with n that doesn't fit in 32 bits.
+ // Not only will it take a very long time, but with 2³¹! possible permutations,
+ // there's no way that any PRNG can have a big enough internal state to
+ // generate even a minuscule percentage of the possible permutations.
+ // Nevertheless, the right API signature accepts an int n, so handle it as best we can.
+ i := n - 1
+ for ; i > 1<<31-1-1; i-- {
+ j := int(r.Int63n(int64(i + 1)))
+ swap(i, j)
+ }
+ for ; i > 0; i-- {
+ j := int(r.int31n(int32(i + 1)))
+ swap(i, j)
+ }
+}
+
+// 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 (r *Rand) Read(p []byte) (n int, err error) {
+ switch src := r.src.(type) {
+ case *lockedSource:
+ return src.read(p, &r.readVal, &r.readPos)
+ case *runtimeSource:
+ return src.read(p, &r.readVal, &r.readPos)
+ }
+ return read(p, r.src, &r.readVal, &r.readPos)
+}
+
+func read(p []byte, src Source, readVal *int64, readPos *int8) (n int, err error) {
+ pos := *readPos
+ val := *readVal
+ rng, _ := src.(*rngSource)
+ for n = 0; n < len(p); n++ {
+ if pos == 0 {
+ if rng != nil {
+ val = rng.Int63()
+ } else {
+ val = src.Int63()
+ }
+ pos = 7
+ }
+ p[n] = byte(val)
+ val >>= 8
+ pos--
+ }
+ *readPos = pos
+ *readVal = val
+ return
+}
+
+/*
+ * Top-level convenience functions
+ */
+
+// globalRandGenerator is the source of random numbers for the top-level
+// convenience functions. When possible it uses the runtime fastrand64
+// function to avoid locking. This is not possible if the user called Seed,
+// either explicitly or implicitly via GODEBUG=randautoseed=0.
+var globalRandGenerator atomic.Pointer[Rand]
+
+var randautoseed = godebug.New("randautoseed")
+
+// globalRand returns the generator to use for the top-level convenience
+// functions.
+func globalRand() *Rand {
+ if r := globalRandGenerator.Load(); r != nil {
+ return r
+ }
+
+ // This is the first call. Initialize based on GODEBUG.
+ var r *Rand
+ if randautoseed.Value() == "0" {
+ randautoseed.IncNonDefault()
+ r = New(new(lockedSource))
+ r.Seed(1)
+ } else {
+ r = &Rand{
+ src: &runtimeSource{},
+ s64: &runtimeSource{},
+ }
+ }
+
+ if !globalRandGenerator.CompareAndSwap(nil, r) {
+ // Two different goroutines called some top-level
+ // function at the same time. While the results in
+ // that case are unpredictable, if we just use r here,
+ // and we are using a seed, we will most likely return
+ // the same value for both calls. That doesn't seem ideal.
+ // Just use the first one to get in.
+ return globalRandGenerator.Load()
+ }
+
+ return r
+}
+
+//go:linkname runtime_rand runtime.rand
+func runtime_rand() uint64
+
+// runtimeSource is an implementation of Source64 that uses the runtime
+// fastrand functions.
+type runtimeSource struct {
+ // The mutex is used to avoid race conditions in Read.
+ mu sync.Mutex
+}
+
+func (*runtimeSource) Int63() int64 {
+ return int64(runtime_rand() & rngMask)
+}
+
+func (*runtimeSource) Seed(int64) {
+ panic("internal error: call to runtimeSource.Seed")
+}
+
+func (*runtimeSource) Uint64() uint64 {
+ return runtime_rand()
+}
+
+func (fs *runtimeSource) read(p []byte, readVal *int64, readPos *int8) (n int, err error) {
+ fs.mu.Lock()
+ n, err = read(p, fs, readVal, readPos)
+ fs.mu.Unlock()
+ return
+}
+
+// Seed uses the provided seed value to initialize the default Source to a
+// deterministic state. Seed values that have the same remainder when
+// divided by 2³¹-1 generate the same pseudo-random sequence.
+// Seed, unlike the [Rand.Seed] method, is safe for concurrent use.
+//
+// If Seed is not called, the generator is seeded randomly at program startup.
+//
+// Prior to Go 1.20, the generator was seeded like Seed(1) at program startup.
+// To force the old behavior, call Seed(1) at program startup.
+// Alternately, set GODEBUG=randautoseed=0 in the environment
+// before making any calls to functions in this package.
+//
+// Deprecated: As of Go 1.20 there is no reason to call Seed with
+// a random value. Programs that call Seed with a known value to get
+// a specific sequence of results should use New(NewSource(seed)) to
+// obtain a local random generator.
+func Seed(seed int64) {
+ orig := globalRandGenerator.Load()
+
+ // If we are already using a lockedSource, we can just re-seed it.
+ if orig != nil {
+ if _, ok := orig.src.(*lockedSource); ok {
+ orig.Seed(seed)
+ return
+ }
+ }
+
+ // Otherwise either
+ // 1) orig == nil, which is the normal case when Seed is the first
+ // top-level function to be called, or
+ // 2) orig is already a runtimeSource, in which case we need to change
+ // to a lockedSource.
+ // Either way we do the same thing.
+
+ r := New(new(lockedSource))
+ r.Seed(seed)
+
+ if !globalRandGenerator.CompareAndSwap(orig, r) {
+ // Something changed underfoot. Retry to be safe.
+ Seed(seed)
+ }
+}
+
+// Int63 returns a non-negative pseudo-random 63-bit integer as an int64
+// from the default [Source].
+func Int63() int64 { return globalRand().Int63() }
+
+// Uint32 returns a pseudo-random 32-bit value as a uint32
+// from the default [Source].
+func Uint32() uint32 { return globalRand().Uint32() }
+
+// Uint64 returns a pseudo-random 64-bit value as a uint64
+// from the default [Source].
+func Uint64() uint64 { return globalRand().Uint64() }
+
+// Int31 returns a non-negative pseudo-random 31-bit integer as an int32
+// from the default [Source].
+func Int31() int32 { return globalRand().Int31() }
+
+// Int returns a non-negative pseudo-random int from the default [Source].
+func Int() int { return globalRand().Int() }
+
+// Int63n returns, as an int64, a non-negative pseudo-random number in the half-open interval [0,n)
+// from the default [Source].
+// It panics if n <= 0.
+func Int63n(n int64) int64 { return globalRand().Int63n(n) }
+
+// Int31n returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n)
+// from the default [Source].
+// It panics if n <= 0.
+func Int31n(n int32) int32 { return globalRand().Int31n(n) }
+
+// Intn returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n)
+// from the default [Source].
+// It panics if n <= 0.
+func Intn(n int) int { return globalRand().Intn(n) }
+
+// Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0)
+// from the default [Source].
+func Float64() float64 { return globalRand().Float64() }
+
+// Float32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0)
+// from the default [Source].
+func Float32() float32 { return globalRand().Float32() }
+
+// 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].
+func Perm(n int) []int { return globalRand().Perm(n) }
+
+// 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.
+func Shuffle(n int, swap func(i, j int)) { globalRand().Shuffle(n, swap) }
+
+// 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.
+//
+// Deprecated: For almost all use cases, [crypto/rand.Read] is more appropriate.
+func Read(p []byte) (n int, err error) { return globalRand().Read(p) }
+
+// 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 NormFloat64() float64 { return globalRand().NormFloat64() }
+
+// 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 ExpFloat64() float64 { return globalRand().ExpFloat64() }
+
+type lockedSource struct {
+ lk sync.Mutex
+ s *rngSource
+}
+
+func (r *lockedSource) Int63() (n int64) {
+ r.lk.Lock()
+ n = r.s.Int63()
+ r.lk.Unlock()
+ return
+}
+
+func (r *lockedSource) Uint64() (n uint64) {
+ r.lk.Lock()
+ n = r.s.Uint64()
+ r.lk.Unlock()
+ return
+}
+
+func (r *lockedSource) Seed(seed int64) {
+ r.lk.Lock()
+ r.seed(seed)
+ r.lk.Unlock()
+}
+
+// seedPos implements Seed for a lockedSource without a race condition.
+func (r *lockedSource) seedPos(seed int64, readPos *int8) {
+ r.lk.Lock()
+ r.seed(seed)
+ *readPos = 0
+ r.lk.Unlock()
+}
+
+// seed seeds the underlying source.
+// The caller must have locked r.lk.
+func (r *lockedSource) seed(seed int64) {
+ if r.s == nil {
+ r.s = newSource(seed)
+ } else {
+ r.s.Seed(seed)
+ }
+}
+
+// read implements Read for a lockedSource without a race condition.
+func (r *lockedSource) read(p []byte, readVal *int64, readPos *int8) (n int, err error) {
+ r.lk.Lock()
+ n, err = read(p, r.s, readVal, readPos)
+ r.lk.Unlock()
+ return
+}