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