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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.

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)

}

// NewSource returns a new pseudo-random Source seeded with the given value.

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

}

// New returns a new Rand that uses random values from src

// to generate other random values.

func New(src Source) *Rand { return &Rand{src} }

// Seed uses the provided seed value to initialize the generator to a deterministic state.

func (r *Rand) Seed(seed int64) { r.src.Seed(seed) }

// 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) }

// 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 [0,n).

func (r *Rand) Int63n(n int64) int64 {

        if n <= 0 {

                return 0

        }

        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 [0,n).

func (r *Rand) Int31n(n int32) int32 {

        if n <= 0 {

                return 0

        }

        max := int32((1 << 31) - 1 - (1<<31)%uint32(n))

        v := r.Int31()

        for v > max {

                v = r.Int31()

        }

        return v % n

}

// Intn returns, as an int, a non-negative pseudo-random number in [0,n).

func (r *Rand) Intn(n int) int {

        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 [0.0,1.0).

func (r *Rand) Float64() float64 { return float64(r.Int63()) / (1 << 63) }

// Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).

func (r *Rand) Float32() float32 { return float32(r.Float64()) }

// Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).

func (r *Rand) Perm(n int) []int {

        m := make([]int, n)

        for i := 0; i < n; i++ {

                m[i] = i

        }

        for i := 0; i < n; i++ {

                j := r.Intn(i + 1)

                m[i], m[j] = m[j], m[i]

        }

        return m

}

/*

 * Top-level convenience functions

 */

var globalRand = New(&lockedSource{src: NewSource(1)})

// Seed uses the provided seed value to initialize the generator to a

// deterministic state. If Seed is not called, the generator behaves as

// if seeded by Seed(1).

func Seed(seed int64) { globalRand.Seed(seed) }

// Int63 returns a non-negative pseudo-random 63-bit integer as an int64.

func Int63() int64 { return globalRand.Int63() }

// Uint32 returns a pseudo-random 32-bit value as a uint32.

func Uint32() uint32 { return globalRand.Uint32() }

// Int31 returns a non-negative pseudo-random 31-bit integer as an int32.

func Int31() int32 { return globalRand.Int31() }

// Int returns a non-negative pseudo-random int.

func Int() int { return globalRand.Int() }

// Int63n returns, as an int64, a non-negative pseudo-random number in [0,n).

func Int63n(n int64) int64 { return globalRand.Int63n(n) }

// Int31n returns, as an int32, a non-negative pseudo-random number in [0,n).

func Int31n(n int32) int32 { return globalRand.Int31n(n) }

// Intn returns, as an int, a non-negative pseudo-random number in [0,n).

func Intn(n int) int { return globalRand.Intn(n) }

// Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).

func Float64() float64 { return globalRand.Float64() }

// Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).

func Float32() float32 { return globalRand.Float32() }

// Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).

func Perm(n int) []int { return globalRand.Perm(n) }

// NormFloat64 returns a normally distributed float64 in the range

// [-math.MaxFloat64, +math.MaxFloat64] 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 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).

// 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 Source

}

func (r *lockedSource) Int63() (n int64) {

        r.lk.Lock()

        n = r.src.Int63()

        r.lk.Unlock()

        return

}

func (r *lockedSource) Seed(seed int64) {

        r.lk.Lock()

        r.src.Seed(seed)

        r.lk.Unlock()

}