github.com/xushiwei/go@v0.0.0-20130601165731-2b9d83f45bc9/src/pkg/math/rand/rand.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package rand implements pseudo-random number generators.
     6  package rand
     7  
     8  import "sync"
     9  
    10  // A Source represents a source of uniformly-distributed
    11  // pseudo-random int64 values in the range [0, 1<<63).
    12  type Source interface {
    13  	Int63() int64
    14  	Seed(seed int64)
    15  }
    16  
    17  // NewSource returns a new pseudo-random Source seeded with the given value.
    18  func NewSource(seed int64) Source {
    19  	var rng rngSource
    20  	rng.Seed(seed)
    21  	return &rng
    22  }
    23  
    24  // A Rand is a source of random numbers.
    25  type Rand struct {
    26  	src Source
    27  }
    28  
    29  // New returns a new Rand that uses random values from src
    30  // to generate other random values.
    31  func New(src Source) *Rand { return &Rand{src} }
    32  
    33  // Seed uses the provided seed value to initialize the generator to a deterministic state.
    34  func (r *Rand) Seed(seed int64) { r.src.Seed(seed) }
    35  
    36  // Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
    37  func (r *Rand) Int63() int64 { return r.src.Int63() }
    38  
    39  // Uint32 returns a pseudo-random 32-bit value as a uint32.
    40  func (r *Rand) Uint32() uint32 { return uint32(r.Int63() >> 31) }
    41  
    42  // Int31 returns a non-negative pseudo-random 31-bit integer as an int32.
    43  func (r *Rand) Int31() int32 { return int32(r.Int63() >> 32) }
    44  
    45  // Int returns a non-negative pseudo-random int.
    46  func (r *Rand) Int() int {
    47  	u := uint(r.Int63())
    48  	return int(u << 1 >> 1) // clear sign bit if int == int32
    49  }
    50  
    51  // Int63n returns, as an int64, a non-negative pseudo-random number in [0,n).
    52  // It panics if n <= 0.
    53  func (r *Rand) Int63n(n int64) int64 {
    54  	if n <= 0 {
    55  		panic("invalid argument to Int63n")
    56  	}
    57  	max := int64((1 << 63) - 1 - (1<<63)%uint64(n))
    58  	v := r.Int63()
    59  	for v > max {
    60  		v = r.Int63()
    61  	}
    62  	return v % n
    63  }
    64  
    65  // Int31n returns, as an int32, a non-negative pseudo-random number in [0,n).
    66  // It panics if n <= 0.
    67  func (r *Rand) Int31n(n int32) int32 {
    68  	if n <= 0 {
    69  		panic("invalid argument to Int31n")
    70  	}
    71  	max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
    72  	v := r.Int31()
    73  	for v > max {
    74  		v = r.Int31()
    75  	}
    76  	return v % n
    77  }
    78  
    79  // Intn returns, as an int, a non-negative pseudo-random number in [0,n).
    80  // It panics if n <= 0.
    81  func (r *Rand) Intn(n int) int {
    82  	if n <= 0 {
    83  		panic("invalid argument to Intn")
    84  	}
    85  	if n <= 1<<31-1 {
    86  		return int(r.Int31n(int32(n)))
    87  	}
    88  	return int(r.Int63n(int64(n)))
    89  }
    90  
    91  // Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).
    92  func (r *Rand) Float64() float64 { return float64(r.Int63()) / (1 << 63) }
    93  
    94  // Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).
    95  func (r *Rand) Float32() float32 { return float32(r.Float64()) }
    96  
    97  // Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).
    98  func (r *Rand) Perm(n int) []int {
    99  	m := make([]int, n)
   100  	for i := 0; i < n; i++ {
   101  		m[i] = i
   102  	}
   103  	for i := 0; i < n; i++ {
   104  		j := r.Intn(i + 1)
   105  		m[i], m[j] = m[j], m[i]
   106  	}
   107  	return m
   108  }
   109  
   110  /*
   111   * Top-level convenience functions
   112   */
   113  
   114  var globalRand = New(&lockedSource{src: NewSource(1)})
   115  
   116  // Seed uses the provided seed value to initialize the generator to a
   117  // deterministic state. If Seed is not called, the generator behaves as
   118  // if seeded by Seed(1).
   119  func Seed(seed int64) { globalRand.Seed(seed) }
   120  
   121  // Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
   122  func Int63() int64 { return globalRand.Int63() }
   123  
   124  // Uint32 returns a pseudo-random 32-bit value as a uint32.
   125  func Uint32() uint32 { return globalRand.Uint32() }
   126  
   127  // Int31 returns a non-negative pseudo-random 31-bit integer as an int32.
   128  func Int31() int32 { return globalRand.Int31() }
   129  
   130  // Int returns a non-negative pseudo-random int.
   131  func Int() int { return globalRand.Int() }
   132  
   133  // Int63n returns, as an int64, a non-negative pseudo-random number in [0,n).
   134  // It panics if n <= 0.
   135  func Int63n(n int64) int64 { return globalRand.Int63n(n) }
   136  
   137  // Int31n returns, as an int32, a non-negative pseudo-random number in [0,n).
   138  // It panics if n <= 0.
   139  func Int31n(n int32) int32 { return globalRand.Int31n(n) }
   140  
   141  // Intn returns, as an int, a non-negative pseudo-random number in [0,n).
   142  // It panics if n <= 0.
   143  func Intn(n int) int { return globalRand.Intn(n) }
   144  
   145  // Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).
   146  func Float64() float64 { return globalRand.Float64() }
   147  
   148  // Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).
   149  func Float32() float32 { return globalRand.Float32() }
   150  
   151  // Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).
   152  func Perm(n int) []int { return globalRand.Perm(n) }
   153  
   154  // NormFloat64 returns a normally distributed float64 in the range
   155  // [-math.MaxFloat64, +math.MaxFloat64] with
   156  // standard normal distribution (mean = 0, stddev = 1).
   157  // To produce a different normal distribution, callers can
   158  // adjust the output using:
   159  //
   160  //  sample = NormFloat64() * desiredStdDev + desiredMean
   161  //
   162  func NormFloat64() float64 { return globalRand.NormFloat64() }
   163  
   164  // ExpFloat64 returns an exponentially distributed float64 in the range
   165  // (0, +math.MaxFloat64] with an exponential distribution whose rate parameter
   166  // (lambda) is 1 and whose mean is 1/lambda (1).
   167  // To produce a distribution with a different rate parameter,
   168  // callers can adjust the output using:
   169  //
   170  //  sample = ExpFloat64() / desiredRateParameter
   171  //
   172  func ExpFloat64() float64 { return globalRand.ExpFloat64() }
   173  
   174  type lockedSource struct {
   175  	lk  sync.Mutex
   176  	src Source
   177  }
   178  
   179  func (r *lockedSource) Int63() (n int64) {
   180  	r.lk.Lock()
   181  	n = r.src.Int63()
   182  	r.lk.Unlock()
   183  	return
   184  }
   185  
   186  func (r *lockedSource) Seed(seed int64) {
   187  	r.lk.Lock()
   188  	r.src.Seed(seed)
   189  	r.lk.Unlock()
   190  }