golang rand 代码
文件路径：/src/math/rand/rand.go
/ 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 unsuitable for
/ security-sensitive work.
/
/ 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 is safe for concurrent use by multiple goroutines, but
/ Sources created by NewSource are not.
/
/ 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 "sync"
/ A Source represents a source of uniformly-distributed
/ pseudo-random int64 values in the range [0, 1<<63).
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.
func NewSource(seed int64) Source {
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) {
if lk, ok := r.src.(*lockedSource); ok {
return lk.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
*/
var globalRand = New(&lockedSource{src: NewSource(1).(*rngSource)})
/ Type assert that globalRand's source is a lockedSource whose src is a *rngSource.
var _ *rngSource = globalRand.src.(*lockedSource).src
/ 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 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.
func Seed(seed int64) { globalRand.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.
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
src *rngSource
}
func (r *lockedSource) Int63() (n int64) {
r.lk.Lock()
n = r.src.Int63()
r.lk.Unlock()
return
}
func (r *lockedSource) Uint64() (n uint64) {
r.lk.Lock()
n = r.src.Uint64()
r.lk.Unlock()
return
}
func (r *lockedSource) Seed(seed int64) {
r.lk.Lock()
r.src.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.src.Seed(seed)
*readPos = 0
r.lk.Unlock()
}
/ 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.src, readVal, readPos)
r.lk.Unlock()
return
}