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// Package fastrand implements fast pesudorandom number generator
// that should scale well on multi-CPU systems.
//
// Use crypto/rand instead of this package for generating
// cryptographically secure random numbers.
package fastrand
import (
"sync"
"time"
)
// Uint32 returns pseudorandom uint32.
//
// It is safe calling this function from concurrent goroutines.
func Uint32() uint32 {
v := rngPool.Get()
if v == nil {
v = &RNG{}
}
r := v.(*RNG)
x := r.Uint32()
rngPool.Put(r)
return x
}
var rngPool sync.Pool
// Uint32n returns pseudorandom uint32 in the range [0..maxN).
//
// It is safe calling this function from concurrent goroutines.
func Uint32n(maxN uint32) uint32 {
x := Uint32()
// See http://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
return uint32((uint64(x) * uint64(maxN)) >> 32)
}
// RNG is a pseudorandom number generator.
//
// It is unsafe to call RNG methods from concurrent goroutines.
type RNG struct {
x uint32
}
// Uint32 returns pseudorandom uint32.
//
// It is unsafe to call this method from concurrent goroutines.
func (r *RNG) Uint32() uint32 {
for r.x == 0 {
r.x = getRandomUint32()
}
// See https://en.wikipedia.org/wiki/Xorshift
x := r.x
x ^= x << 13
x ^= x >> 17
x ^= x << 5
r.x = x
return x
}
// Uint32n returns pseudorandom uint32 in the range [0..maxN).
//
// It is unsafe to call this method from concurrent goroutines.
func (r *RNG) Uint32n(maxN uint32) uint32 {
x := r.Uint32()
// See http://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
return uint32((uint64(x) * uint64(maxN)) >> 32)
}
// Seed sets the r state to n.
func (r *RNG) Seed(n uint32) {
r.x = n
}
func getRandomUint32() uint32 {
x := time.Now().UnixNano()
return uint32((x >> 32) ^ x)
}
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